effects of mandibular canine intrusion obtained using

I

“EFFECTS OF MANDIBULAR CANINE INTRUSION OBTAINED

USING CANTILEVER VS BONE ANCHORAGE: A COMPARATIVE

FINITE ELEMENT STUDY”

By

DR. AFSHAN SAMAN WAREMANI

Dissertation Submitted to

Rajiv Gandhi University of Health Sciences, Bengaluru, Karnataka

In partial fulfillment of the requirements for the degree of

MASTER OF DENTAL SURGERY

IN

ORTHODONTICS AND DENTOFACIAL ORTHOPAEDICS

Under the guidance of

DR. NAUSHEER AHMED M.D.S.

Associate Professor

Department of Orthodontics and Dentofacial Orthopaedics

Government Dental College and Research Institute

Bengaluru - 560002

Karnataka, India

(2016-2019)

Scanned by CamScanner

LIST OF ABBREVIATIONS USED

VII

(In alphabetical order)

Sl.No Abbreviation

Full Form

1. CT Computed Tomography

2. FEM Finite Element Method

3. fig Figure

4. gm Gram

5. mm Millimeter

6. µmm Micro millimeter

7. MBT McLaughlin, Bennet, Trevesi preadjusted

edgewise bracket system

8. MPa Mega Pascal

9. N Newton

10. PDL Periodontal Ligament

11. i.e. That is

12. 3 D Three Dimensional

13. TMA Titanium Molybdenum alloy

14. SS Stainless Steel

15. TAD Temporary Anchorage Device

16. TiAlVn Titanium aluminium vanadium alloy

17. AD Anno domini

LIST OF TABLES

VIII

SL.NO PARTICULARS PAGE NO

1. Material properties of the members 48

2. Amount of force on the x-axis produced with the toe-ins

tested 48

3. Amount of intrusion of crest node and root node

Displacement along y axis 48

4. Labial/lingual movements of crest and root node

Displacement along z axis 48

5. Stresses in canine periodontium 49

6. Alveolar bone stress around canine 49

LIST OF GRAPHS

Sl.No PARTICULARS PAGE NO


Displacement along y axis

46


Displacement along y axis

46

3. Stresses in canine periodontium 47

4. Alveolar bone stresses around canine 47

LIST OF PHOTOGRAPHS

IX

SL.NO PARTICULARS PAGE NO. 1. CT Model of the mandibular arch

Fig

77

2(a) Model of the bone from canine to the second molar 77

2(b) Mesh form of the teeth 78

2(c) Teeth with 1.5mm offset of the canine 78

3(a) Canine tooth and its periodontium 79

3(b) Periodontium of the dentition 79

3(c) alveolar bone with sockets 80

4(a) Teeth with bracket and wire 80

4(b) With 4 different toe-in bends of cantilever i.e 0,4,6,8

degrees (Zero from left side).Assembly with

Cantilever arrangement

81

4(c) model in ansys software 81

5(a) mini-implant model with 1.2 mm diameter and 6mm

length

82

5(b) model with elastic chain placed from mini-implants

to canine

82

5(c) model with mini-implant 82

6(a) (Vector plot for beam element)Analysis Results for 0

degree :

83

6(b) (Vector plot for beam element)Analysis Results for 4

degree

83

6(c) (Vector plot for beam element)Analysis Results for 6

degree

84

6(d) (Vector plot for beam element)Analysis Results for 8

degree

84

6(e) (Vector plot for beam element)Analysis Results for

mini-implant

84

7(a) displacement along Y and Z axis (model with 0º toe-

in)

85

7(b) displacement along Y and Z axis (model with 4º toe-

in)

85

7(c) displacement along Y and Z axis (model with 6º toe-

in)

86

7(d) displacement along Y and Z axis (model with 8º toe-

in)

86

7(e) displacement along Y and Z axis (model with mini-

implant

87

8(a) stress in the Canine peridontium (0º toe-in)

87

8(b) stress in the Canine peridontium (4º toe-in) 88

8(c) stress in the Canine peridontium (6º toe-in)

88

LIST OF PHOTOGRAPHS

X

8(d) stress in the Canine peridontium (8º toe-in)

89

8(e) stress in the Canine peridontium (mini-implant) 89

9(a) stress in the alveolar bone (0º toe-in) 90

9(b) stress in the alveolar bone (4º toe-in) 90

9(c) stress in the alveolar bone (6º toe-in) 91

9(d) stress in the alveolar bone (8º toe-in) 91

9(e) stress in the alveolar bone (mini-implant) 92

10(a) effects on the molar (0º toe-in) 92

10(b) effects on the molar (4º toe-in) 93

10(c) effects on the molar (6º toe-in) 93

10(d) effects on the molar (8º toe-in) 94

10(e) effects on the molar (mini-implant) 94

11(a) stress changes in posterior segment (0º toe-in) 95

11(b) stress changes in posterior segment (4º toe-in) 95

11(c) stress changes in posterior segment (6º toe-in) 96

11(d) stress changes in posterior segment (8º toe-in) 96

11(e) stress changes in posterior segment (mini-implant) 97

ABSTRACT

XV

Title: Effects of Mandibular Canine Intrusion Obtained Using Cantilever versus Bone

Anchorage: A Comparative Finite Element Study

Background and objectives: This study was conducted to assess and compare the

effects of mandibular canine intrusion obtained, by using cantilever having different

compensatory toe-in bends and with mini-implants using 3D finite element method

Materials and Method: 3D models of the mandibular right quadrant were created

using FEM. Brackets and molar tubes were modelled with 0.022 x 0.028-in slots and

0o of tip and torque with a base wire of 0.021 x 0.025-inch. In the first model

mandibular canine intrusion was produced using a cantilever loop (17x25 inch TMA)

and having different compensatory toe-in bends (0º, 4º, 6º and 8º). In another model

intrusion was done using two mini-implants placed buccally, on either side of canine

in the interdental bone. Force was applied using an elastic chain. The amount of pure

intrusion and associated labial tipping of canine that occurred in both the models was

assessed and compared using FEM analysis.

Results: Pure intrusion of the canine was produced by both the 6º toe-in as well as the

mini-implant, but the amount of intrusion with the 6º toe-in was higher. The labial

tipping of the canine was also reduced in these two models. The highest amount of

periodontal ligament stress was observed around the canine root with a 0º toe-in bend.

In the posterior segment, the molar displayed a slight tendency for extrusion and distal

crown tipping

Conclusion: The intrusion mechanics using cantilever, simulated in this study may

achieve pure mandibular canine intrusion with minimal labial tipping when a

compensatory toe-in of 6º is incorporated into the cantilever. The molar displayed

slight extrusion and distal tipping

Key words: arch wire; bracket; cantilever; intrusion; FEM; mini-implant

INTRODUCTION

1

EFFECTS OF MANDIBULAR CANINE INTRUSION OBTAINED

USING CANTILEVER VS BONE ANCHORAGE: A

COMPARATIVE FINITE ELEMENT STUDY

INTRODUCTION:

A deep overbite is a malocclusion, which is commonly encountered in an orthodontic

practice. Severe deep bites (overbite >5 mm) are found in nearly 20% of children and

13% of adults, representing about 95.2% of vertical occlusal problems. A deep bite

malocclusion overlies a variety of hidden skeletal or dental discrepancies.

Accordingly, a deep bite should not be approached as a disease entity, and should be

seen as a clinical manifestation of an underlying skeletal or dental discrepancy.1

Deep bite can be divided as dentoalveolar in nature or skeletal due to growth of the

jaws.2 A skeletal deep bite could result from a discrepancy in the vertical position of

the maxilla, the mandible, or their cant. Excessive maxillary and mandibular alveolar

heights have been reported in deep bite cases. At the most basic level of analysis, the

skeletal and dental components that appear to be consequential in affecting overbite

change are (1) maxillary skeletal displacement, (2) mandibular skeletal displacement,

(3) maxillary dental change, and (4) mandibular dental change.3

Few studies, which have dealt with the components of skeletal deep bite, showed that

the gonial angle was the highest shared skeletal factor in deep bite malocclusion.

Ceylan and Eroz studied some components of deep overbite and one of the significant

findings was that the gonial angle was the smallest in the deep bite group, also the

INTRODUCTION

2

study showed that the vertical component of mandibular growth has a more

remarkable effect than the rotational component and that the mandibular skeletal

changes were twice as important as the mandibular dental changes and about 2.5 times

as important as the maxillary changes in inducing overbite changes.1

Regarding dental deep bite, a deep curve of Spee and an increased buccal root torque

of the maxillary incisors were proven to be correlated with deep bite malocclusions.

The over-erupted maxillary and mandibular anterior alveolar basal heights and the

under-eruption of the maxillary and mandibular posterior segments were also shown

to have positive correlations with deep bite malocclusions.1The exaggerated curve of

Spee has been shown repeatedly, to have a main role in developing dental deep bites.

This finding reflects the importance of the mandibular dentoalveolar factor in deep

bite malocclusions, emphasizing the need for extruding the mandibular buccal

segment and intruding the mandibular incisors in most deep bite mechanotherapies.

Andrews, found that the curve of Spee in subjects with good occlusion ranged from

flat to mild, noting that the best static intercuspation occurred when the occlusal plane

was relatively flat. He proposed that flattening the occlusal plane should be a

treatment goal in orthodontics.4

Correction of deep bite is often a challenging step in orthodontic treatment. Deep bite

cases that are untreated can cause increased anterior crowding, maxillary dental

flaring, periodontal problems, and temporomandibular joint problems and can

interfere with lateral and anterior mandibular movements. Deep bite can be treated

orthodontically by intrusion or flaring of the incisors, extrusion or passive eruption of

the buccal segments, or a combination of these. Although, extrusion of the posterior

dentition is an effective method of bite opening in growing patients, it is not indicated

INTRODUCTION

3

in patients with normal incisor display or normal or long lower facial height, its

stability is questionable in non-growing patients with average to low mandibular plane

angles. Intrusion of the maxillary incisors is undertaken in patients with excessive

incisor and gingival display and a large interlabial gap. Considering these facts,

mandibular incisor intrusion is the most suitable deepbite treatment for adults with

normal incisor and gingival display and a normal or high mandibular plane angle. 5

Intrusion refers to the apical movement of the geometric center of the root (centroid)

in respect to the occlusal plane or a plane based on the long axis of the tooth. Labial

tipping of an incisor around its centroid produces pseudo-intrusion as it influences the

vertical incisal edge position.7Although this pseudo-intrusion gives clinical impression

of deep overbite correction, it should not be confused with the genuine intrusion.

Recently, several researchers have focused on the effect of aging on anterior tooth

display and on how treatment mechanics change the perception of age. Sarver,

Ackerman and Zachrisson drew attention to the importance of lower incisor intrusion

in deep bite patients with reduced upper incisor display to preserving a youthful

appearance. Lower incisor intrusion can be accomplished using different arches, such

as a reverse Spee arch, a three-piece intrusion arch, or a utility arch. Even though

intrusion can be achieved successfully with all of these appliances, incisor

proclination during intrusion and unwanted distal tipping on posterior anchorage teeth

are inevitable.9

Although continuous arches provide rapid correction through both incisor proclination

and majorly posterior extrusion, the extrusion of posterior teeth is not always stable,

especially in adult patients. Intrusion using segmental arches not only provides

INTRODUCTION

4

accurate prediction of forces or moments but also predominantly produces incisor

intrusion with molar extrusion to a lesser degree thus minimizing counteracting side

effects. The use of temporary anchorage devices for lower incisor intrusion have been

described in a few case reports, and the effects were limited to the mandibular anterior

area.9,10

Approximately 50% of patients with deep bite have anatomically extruded mandibular

canines. Because simultaneous orthodontic intrusion of the 6 anterior teeth can cause

undesirable effects in the posterior anchorage segment, segmented intrusion of the

mandibular canines should be considered when levelling the curve of Spee.11

A few reports have described the methods for individual intrusion of the canines. A

technique described by Ricketts et al involved using the utility arch after complete

incisor intrusion as a stabilization arch and gently tying an elastic band from the

canine bracket to a step-down bypass segment in the utility arch.6 In another study

reported by Marcotte, suggested the use of a cantilever from the auxiliary tube of the

first molar to the canine bracket slot. Burstone, in a study, also described a method for

individual intrusion of the canines that included a slight compensatory toe-in bend to

deliver a lingual force for controlling the tendency of buccal crown tipping of the

canine.11

Since Creekmore and Eklund initially performed maxillary incisor intrusion using a

vitallium screw inserted just below the anterior nasal spine, many clinicians have tried

to intrude the incisors with absolute anchorage. Recently, implant-anchored

orthodontics has led to the development of new orthodontic treatment strategies.

These implants provide stationary anchorage for various tooth movements and even

make it possible to move a tooth in more than a direction which was impossible with

INTRODUCTION

5

traditional orthodontic methods. Miniscrew anchorage is especially useful for tooth

intrusion, because it can apply a low, continuous force of a set magnitude without

causing reciprocal movements of other teeth.14

In conventional mechanics, cuspids are traditionally intruded by means of arch wires

with second order bends or bypass bends associated with elastics and using the

neighboring teeth for anchorage. In these cases, the extrusive component of the

anchorage units cannot be avoided. Another alternative is the use of segmented arch

wires relying on posterior teeth for anchorage. When one wishes to intrude a cuspid

tooth while keeping its axial inclination, the buccal insertion of two mini-implants is

recommended, one on the mesial and one on the distal region of the tooth targeted to

be intruded.15

In this case, mini-implants emerge as an excellent alternative as they provide efficient

anchorage, requiring no tooth support and with no esthetic compromise. Additionally,

patient cooperation is less required. Mini-implants have been used in the orthodontic

office with increasing frequency in cases where an inadequate number of dental units

stand in the way of an effective anchorage, or even only to simplify orthodontic

mechanics and make it more predictable.15

Mini-implant anchorage is especially

useful for tooth intrusion, because it can apply a low, continuous force of a set

magnitude without causing reciprocal movements of other teeth.14

Finite element method was first developed in 1956 in the aircraft industry. This

method has since been in widespread use not only in aerospace engineering, but also

in civil engineering. The finite element method is an extremely effective technique for

INTRODUCTION

6

the treatment of problems of plane stress and plane strain. The first three dimensional

FEM study in dentistry appeared in 1974, where J.W.Farah and R.G.Craig did finite

element stress analysis in a restored first molar.16

Finite element analysis has been

applied to the description of form changes in biological structures (morphometrics),

like area of growth and development. Finite element method is also useful for the

study of structures with inherent material homogeneity and potentially complicated

shapes such as dental implants. The mechanical behaviour of the orthodontic wires

and different design of brackets and its contact problem can be well modelled and

simulated by the finite element method. Advantages are that extensive instrumentation

is not required, complex larger problems can be split into smaller problems,

FEM enables the evaluation of biomechanical effects such as stress and strain on

human body parts that are difficult to access without causing harm to subjects,11

it is a

completely non-invasive procedure, three dimensional models can be generated,

actual physical properties can be simulated and external environment can be simulated

and the operator can repeat the study as many times as possible.16

In orthodontics, finite element method has been used to clarify the stress distribution

causing root resorption, to evaluate the risk of adverse events during technical

procedures, and to verify and devise new mechanics. Orthodontic treatment requires

adequate management of the mechanics and attention to biology in order to achieve

efficient tooth movement. Recently, finite element analysis has provided a visual

image of the effects of an orthodontic force on the tooth and its supporting structures.

It also serves as a useful tool to simulate different loading systems and evaluate the

initial effects in the dentoalveolar structures to better understand biomechanics.17

INTRODUCTION

7

A finite element model is constructed by dividing solid objects into several elements

that are connected at a common nodal point. Each element is assigned appropriate

material properties corresponding to the properties of the object being modelled. The

first step is to subdivide the complex object geometry into a suitable set of smaller

‘elements’ of ‘finite’ dimensions. When combined with the ‘mesh’ model of the

investigated structures, each element can adopt a specific geometric shape (i.e.

triangle, square, tetrahedron, etc.) with a specific internal strain function. Using these

functions and the actual geometry of the element, the equilibrium equations between

the external forces acting on the element and the displacement occuring at each node

can be determined.18

Uncontrolled canine intrusion in the treatment of deep bite may lead to buccal crown

tipping and thus to increased mandibular intercanine width, and it could also increase

the chances of orthodontic treatment relapse.19

Buccal crown tipping control is

important because excessive buccal tipping of the canine may increase the risk of

gingival recession or bone resorption, especially in patients with a history of

periodontal disease and bone loss.33

The proclination of these teeth could also lead to

abfraction lesions because the canines receive additional loads when mandibular

lateral excursions are performed.41

Therefore, there is still a need to improve the

clinical approach for intruding the mandibular canines while adequately levelling the

curve of Spee.11

The purpose of this study was to use the finite element method to simulate and

compare the effects of intrusion of mandibular canine obtained using segmented

mechanics with a cantilever having different compensatory bucco-lingual activations

(toe-in bends) and with bone anchorage using mini-implants.

OBJECTIVES

8

OBJECTIVES

The objectives of this finite element study are:

1. To simulate the segmented intrusion of mandibular canine with a cantilever

and to evaluate the effects produced by different compensatory bucco-lingual

activations (toe-in bends) on the canine and the posterior teeth.

2. To simulate the intrusion of mandibular canine with mini-implant and evaluate

the effects on canine and the posterior teeth.

3. To compare the results and effects produced by cantilever and mini implant on

the mandibular canine and the posterior anchor teeth.

REVIEW OF LITERATURE

9

REVIEW OF LITERATURE:

A study was conducted to explore the different components of deep bite

malocclusion and determine their actual contributions in its development. Dental

and skeletal measurements were made on lateral cephalometric radiographs of 124

patients and analysed. Results showed that a deep bite malocclusion is multi-

factorial having definite dental and skeletal components. The gonial angle was

found to be the highest contributing skeletal factor confirming the importance of

the growth and angulation of the ramus. Among dental components a deep curve

of Spee was the highest contributing factor, confirming the importance of

intruding the mandibular incisors in deep bite mechanotherapy. The study

concluded that a thorough analysis of all deep bite components reduces the

clinician's bias toward predetermined mechanics in treating deep bite patients and

allows for better individualized treatment planning and mechanotherapy 1

A longitudinal study was conducted to analyse the multidimensional nature of

overbite changes that occur during adolescence. The study used cephalograms of

181 untreated children (102 males, 79 females) taken at ages 10 and 15. Four

major components like maxillary vertical displacement, mandibular vertical

displacement, upper incisor vertical change within the bone and lower incisor

vertical change within the bone were measured. The results showed that although

the average overbite changes between 10 and 15 years were minimal (0.2 mm),

variation ranged from 2.4mm of bite opening to 5.6 mm of bite deepening. Despite

the large discrepancy between maxillary and mandibular skeletal displacement,

overbite remains relatively stable, supporting the notion of vertical dentoalveolar


10

compensatory mechanisms. The multivariate model suggests that mandibular

changes, specifically vertical growth and rotation, are more important than

maxillary changes in determining overbite changes. Also important clinical

approaches can be developed in the treatment of developing open/deep bites. 3

A study was conducted determine the curve of Spee by examining its development

longitudinally in a sample of untreated subjects with normal occlusion from the

deciduous dentition to adulthood. Sixteen male and 17 female subjects were

selected and the maximum depth of the curve of Spee was measured. The depth of

the curve of Spee was measured on their study models at 7 time points from ages 4

(deciduous dentition) to 26 (adult dentition) years. The result showed that the

occlusal plane in the deciduous dentition is relatively flat and the largest increase

in the maximum depth of the curve of Spee results specifically from, the eruption

of the mandibular permanent first molars and incisors relative to the deciduous

second molars. During the mixed dentition stage, the curve decreases slightly and

then remains relatively stable into early adulthood. The study concluded that there

are no significant differences in maximum depth of the curve of Spee between the

right and left sides of the mandibular arch or the sexes 4

A retrospective longitudinal study was done to investigate the long-term stability

of deep overbite correction with mandibular incisor intrusion with utility arches in

adult patients. Pre-treatment (T1), post-treatment(T2) , and 5-years post-retention

(T3) lateral cephalograms of 31 patients (range, 24.1-30.9 years) with Class II

Division 1 malocclusion and deep bite, treated by maxillary first premolar


11

extraction and mandibular incisor intrusion, were traced and measured. The

treatment protocol included intrusion of the mandibular incisors to correct the

deep bite and extraction of the maxillary first premolars to correct the overjet. In

the maxillary arch, after alignment and retraction of canines, the upper incisors

were retracted by 0.017 x 0.025-in beta titanium alloy archwires with mushroom

loops. In the mandibular arch, utility arches (0.016 × 0.022 inch) Blue Elgiloy

wires, activated to exert 40 g of force, were used for incisor intrusion. The mean

active treatment time was 2.7 years. Significant decreases in overjet and overbite,

significant retroclination and retraction of the maxillary incisors, and significant

increases in protrusion, proclination, and intrusion of the mandibular incisors were

observed at T2. At T3, there were statistically significant but clinically

unimportant increases in overjet, overbite and extrusion of the mandibular

incisors. With mandibular intrusion utility arches, 2.6 mm of true incisor intrusion

was obtained. The study concluded that deep bite treatment with mandibular

incisor intrusion with utility arches was effective and appeared to be stable in non-

growing patients.5

A study was conducted to measure the amount of true incisor intrusion attained

during orthodontic treatment. Abstracts were selected and from these, original

articles were retrieved, and their references were hand searched for missing

articles. The results showed that twenty-eight articles met the initial inclusion

criteria, but 24 were rejected because they did not quantify true incisor intrusion or

factor out normal growth impact when required. The remaining 4 articles showed

that true incisor intrusion is attainable but with large variability depending on the

appliance used. The mean estimates of intrusion and 95% CI were 1.46 mm (1.05-


12

1.86 mm) for the maxillary incisors and 1.90 mm (1.22-2.57 mm) for the

mandibular incisors. The study concluded that true incisor intrusion is achievable

in both arches, but the clinical significance of the magnitude of true intrusion as

the sole treatment option is questionable for patients with severe deep bite. In non-

growing patients, the segmented arch technique can produce 1.5 mm of incisor

intrusion in the maxillary arch and 1.9 mm in the mandibular arch. 7

A study was conducted to compare the dento-facial effects of mandibular incisor

intrusion using mini-implants with those of a conventional incisor intrusion

mechanic, the utility arch. Twenty-six deep-bite patients were divided into two

groups. In group 1 the mandibular incisors were intruded using a 0.16 x 0.22–inch

stainless-steel segmental wire connected to two mini-implants. In the second

group, mandibular incisor intrusion was performed using a conventional utility

arch. Lateral cephalometric radiographs were taken at pre-treatment and at the end

of intrusion. Thirty landmarks were identified to measure 23 linear and 20 angular

measurements and compared. The results showed that the duration of intrusion

was 5 months for group 1 and 4 months for group 2. The study concluded that

pure upper incisor intrusion could be achieved using a segmental arch to the

incisors when it is supported by two mini-implants that are placed between the

lateral and canine teeth. Also the incisor intrusion that was achieved using TAD

supported segmented archwire was no different than the movement achieved by

the conventional intrusion utility arch. 9

A study was conducted to compare the efficacy of overbite correction achieved by

conventional continuous arch wire technique and the segmented arch technique as


13

recommended by Burstone. The sample consisted of 50 adult patients having low

angle, deep bite malocclusions and were at least 18 years old. Twenty-five patients

were treated with a continuous arch wire (CAW) technique with a pre-torqued and

pre-angulated bracket system. The other group were treated with the segmented

arch technique. An intrusive force of 10 to 15gms per tooth was used. Results

showed that the treatment period of the Burstone group was 4 months longer than

that of the continuous arch wire group. Incisor intrusion with little extrusive

movement in the molar area, however, is found with the segmented arch technique

as recommended by Burstone. This study concluded that the arch leveling

technique, according to Burstone, can produce genuine intrusion of the incisors

with little vertical effect in the molar area in adult patients 10

A finite element study was conducted to evaluate the effects of mandibular canine

intrusion produced using cantilever loop with different toe in bends and the

subsequent effects on the posterior teeth. A finite element study of the right

quadrant of the mandibular dental arch together with periodontal structures was

modelled using Solidworks software. All bony, dental, and periodontal ligament

structures from the second molar to the canine along with brackets and molar

tubes were graphically represented and modelled. A 0.021 x 0.025-in stainless

steel base wire and a 0.017 x 0.025-inch titanium-molybdenum alloy cantilever

was also modelled. Discretization and boundary conditions of all anatomic

structures tested were determined with Hypermesh software and compensatory

toe-in bends of 0, 4, 6 and 8 degrees were simulated with Abaqus software. The

results showed that there was a tendency for buccal crown tipping of the

mandibular canine when a passive 0 degree toe-in was simulated. The amount of


14

this buccal tipping tendency decreased as the amount of compensatory toe-in

increased. When a compensatory toe-in of 6 degree was simulated, the buccal

crown tipping tendency was completely eliminated. The stress produced in the

PDL of the posterior teeth used as dental anchorage was minimal and the anchor

molar showed a tendency for distal crown tipping and extrusion. This study

proved the need of incorporating compensatory toe-ins to prevent undesired buccal

or lingual crown tipping of the mandibular canines during intrusion with a

cantilever. 11

A study was done to describe the One-couple orthodontic appliance systems. One-

couple systems are capable of applying well-defined forces and couples to effect

controlled tooth movement during treatment and consist of two sites of

attachment: one in which the appliance is inserted into a bracket or tube where

both a couple and force is generated, and one at which the appliance is placed as a

point contact where only a force is produced. Appliances with long interbracket

spans between two points of attachment have low load deflection rates and deliver

relatively constant forces and moments as the teeth move toward their desired

locations. Moreover, in two-tooth systems where the appliance is engaged in the

bracket of only one tooth and tied as a point contact to the other tooth, the force

system created is statically determinate which means that the forces and moments

that the wire will apply to the teeth are easy to discern clinically. This makes tooth

movements more predictable. A couple is created only at the tooth in which the

wire is engaged but forces exist at both attachment sites acting in opposite

directions because the appliance is in static equilibrium. By applying tile basic

laws of equilibrium, one-couple appliances can be designed and adapted to


15

perform numerous functions like canine extrusion, midline movement, anterior

intrusion, and anterior extrusion. The large range of activation of these wires

means that tooth movement will proceed even without frequent monitoring and

appliance adjustment. The actions of such appliances are highly predictable and

any unwanted side effects can be localized and easily monitored during treatment.

The simplicity and flexibility afforded by one-couple orthodontic appliance

systems make them an attractive choice in clinical situations where maximal

control of tooth movement is desired. 12

A case report illustrates the successful treatment of over-erupted mandibular

incisors and excessive mandibular curve of Spee with the indirect use of

miniscrew anchorage and segmented wires. A 22 year old female patient

diagnosed with a severe Class II Division 1 malocclusion, deep overbite and

excessive curve of Spee was treated. After initial levelling and aligning,

Miniscrews (length, 9 mm; diameter, 1.5 mm) were placed into the buccal alveolar

bone at the mandibular premolar extraction sites to achieve en-masse intrusion of

the mandibular anterior teeth. A 0.016-in × 0.022-in utility archwire was installed

and ligated to the mandibular miniscrews and intrusive force of 50mg was applied

to the anterior segment to be retracted. A cephalometric evaluation immediately

after the intrusion procedure detected intrusion of 5.0 mm without molar

extrusion. This report concluded that the indirect use of miniscrews is an efficient

method for intruding over-erupted mandibular incisors.14


16

An FEM study was done to determine the most desirable force system and loading

conditions required to achieve effective molar protraction from an interdental

miniscrew with minimal side-effects. The variation of force delivery was

simulated through changes in the height of a miniscrew, length of a molar

extension arm, and incorporation of a lingual force. CBCT data from a 27-year-old

male patient with missing mandibular right first molar, brackets, molar tubes,

mini-screws and protraction appliances were modelled with finite element

software. A total of 80 loading conditions were simulated by altering the extension

arm length (2–10 mm), miniscrew height (0–8 mm), and magnitude of protraction

force from the lingual side (0–1.5 N). Results showed that in this specific FE

model of mandibular molar protraction, a long extension arm (8–10 mm) was

necessary to eliminate mesial tipping when a protraction force was applied. The

most ideal force system in the model appeared to be the longest extension arm (10

mm) and the addition a lingual force half or equal magnitude of the labial force

(0.5–1 N). The height of the miniscrew was not critical to achieve translation

during mandibular molar protraction; although, a more occlusal position of a

miniscrew may help reduce mesial tipping with a long extension arm 17

A study was conducted to examine the success rates and find factors affecting the

clinical success of screw implants used as orthodontic anchorage. Eighty-seven

patients (35 male, 52 female; mean age, 15.5 years) with a total of 227 screw

implants of 4 types were examined. Results showed that the overall success rate

was 91.6%, with a mean period of force application of 15 months. Therefore, it

was concluded that screw implants can be used for orthodontic anchorage

predictably and consistently in routine orthodontic practice. Mobility at the


17

mandibular implant sites, and inflammation were the factors associated with screw

implant failure in this study. The study concluded that to minimize failure,

clinicians should attempt to reduce inflammation around the screw implants,

especially for screws placed on the right side in the mandible. 20

An FEM study was conducted to specify the required toe (º) of the vertical

segment of a cantilever from the distal aspect to achieve pure intrusion of a

mandibular canine with a segmented arch in lingual orthodontics. The geometrical

model of a mandibular canine tooth was developed and the mathematical equation

was devised to evaluate º (positive value: toe-in, negative value: toe-out) based on

certain input parameters. To determine this numerical study by finite element

analysis (FEA), total eight different positions of point of force application (Pf) on

bracket top (occlusal) surface were considered based on different values of input

parameters In FEA, the results were displayed in the form of instantaneous

movement of a mandibular canine due compression and tension of PDL. From the

distribution pattern, it was clear that the equivalent stress was concentrated at apex

which leads to maximum bone remodelling in that region. Hence, it signifies the

intrusive nature of mandibular canine movement. Thus, the values of the required

vertical segment toe of a cantilever from the distal aspect of a mandibular canine

were verified with FEA. The range of an intrusive force within the biological limit

of a mandibular canine was found to be 20–30 g. The study anticipated that the

pure intrusion of a mandibular canine with a segmented arch in Lingual

orthodontics will be achieved quiet efficiently and rapidly. 21


18

A study was done to provide equivalent E and v pairs suitable for finite element

modeling of a tooth, periodontal ligament, and bone complex by using a reported

crown load-displacement relationship as the criterion. In any finite element

analysis, 2 mechanical parameters of the PDL are needed: Young’s modulus (E)

and Poisson’s ratio (v). Previous studies have reported quite different values of E

and v. Especially, E values were reported in a large range, from 0.01 to 1,750

MPa. CBCT images of a selected maxillary central incisor with the 2 neighbouring

teeth were used to create a finite element model. The PDL was created

surrounding the roots by dilating the roots with 1 voxel (0.25 mm). The PDL,

teeth, and bone were assembled to create a virtual tooth, PDL, and bone complex

called the solid model. The solid model was then imported into software (version

12.1; ANSYS, Canonsburg, Pa) for meshing and analysis=-+ for v = 0.35, E =0.71

MPa for = 5 0.4, and E = 0.47 MPa for v = 0.45 can be used for finite element

modelling of the tooth, PDL, and bone complex. 22

A three-dimensional finite element study was designed to investigate the stress

levels induced in the periodontal tissue by orthodontic forces. A three-dimensional

model of the lower first premolar was constructed on the basis of average

anatomic morphology and consisted of 240 iso parametric elements. Principal

stresses were determined at the root, alveolar bone, and periodontal ligament

(PDL). In all loading cases for the bucco-lingually directed forces, three principal

stresses in the PDL were very similar. At the surface of the root and the alveolar

bone, large bending stresses acting almost parallel to the root were observed.

During tipping movement, stresses non-uniformly varied with a large difference

from the cervix to the apex of the root. On the other hand, in case of translatory


19

movement, the stresses induced were either tensile or compressive at all occluso-

gingival levels with some difference of stress from the cervix to the apex. It was

inferred that the pattern and magnitude of stresses in the periodontium from a

given magnitude of force were markedly different, depending on the centre of

rotation of the tooth. 23

A study was developed to directly and accurately measure orthodontic tooth

movement in a group of human volunteers. A 3D computer model of a maxillary

incisor tooth was simulated, which was subjected to an orthodontic load. An

apparatus of laser was used to sample tooth movement every 0·01 seconds over a

1-minute cycle for 10 healthy volunteers, whilst a constant 0·39 N load was

applied. This process was repeated on eight separate occasions and the most

consistent five readings were taken for each subject. The data gleaned by this

method were used to validate the 3D FEM model. This was formed of 15,000

four-noded tetrahedral elements. Tooth displacements ranged from 0·012 to 0·133

mm. An elastic modulus of 1 N/mm2 and Poisson’s Ratio of 0·45 was derived for

the PDL. Strain analysis, using the model, suggested that a maximum PDL strain

of 4·77×10-3 was recorded at the alveolar crest, while the largest apical strain

recorded was 1·55 ×10-3. The maximum recorded strain in the surrounding

alveolar bone was 35 times less than for the PDL. This FEM model validated that,

the PDL is the main mediator of orthodontic tooth movement 24

A study was undertaken to investigate the stress components (S1 and S3) that

appear in the periodontal membrane, when subjected to transverse and vertical

loads equal to 1 N and to quantify the alteration in stress that occurred as alveolar


20

bone height was reduced by 1, 2.5, 5, 6.5, and 8 mm, respectively. Six three‐

dimensional (3D) finite element models (FEM) of a human maxillary central

incisor were designed with different alveolar bone height. When, there is absence

of alveolar bone loss, a tipping force of 1 N produced stresses, which reached

0.072 N/mm2 at the cervical margin, up to 0.0395 N/mm2 at the apex and up to

0.026 N/mm2 sub‐apically. When, 8 mm of alveolar bone loss is present, the

findings were −0.288, 0.472, and 0.722 N/mm2, respectively. Without bone loss,

an intruding force of the same magnitude produced stresses of −0.0043, −0.0263,

and 0.115 N/mm2, respectively, for the same areas and sampling points. In the

presence of 8 mm of alveolar bone loss the findings were −0.019, −0.043, and

0.185 N/mm2 for intrusive movement. The study showed that alveolar bone loss

caused increased stress production under the same load compared with healthy

bone support. Tipping movements resulted in an increased level of stress at the

cervical margin of the periodontal membrane in all sampling points and at all

stages of alveolar bone loss. The study concluded that the increased stress

components were found to be at the sub‐apical and apical levels for intrusive

movement. 25

A 3-dimensional finite element study was undertaken to determine the types of

orthodontic forces that cause high stress at the root apex. A three dimensional

model of a maxillary central incisor, its periodontal ligament (PDL), and alveolar

bone was constructed on the based on the average anatomic morphology. The

maxillary central incisor was chosen, as it is more prone to apical root resorption.

The material properties and 5 different load systems (tipping, intrusion, extrusion,

bodily movement, and rotational force) were tested. The analysis showed that


21

purely intrusive, extrusive, and rotational forces had stresses concentrated at the

apex of the root. The principle stress from a tipping force was located at the

alveolar crest. For bodily movement, the stress was distributed throughout the

PDL; however, it was concentrated more at the alveolar crest. The study

concluded that, intrusive, extrusive, and rotational forces produced more stresses

at the apex and bodily movement and tipping, produced forces concentrated at the

alveolar crest and not at the apex. 26

A study was undertaken to analyse the distribution of the stress on dental and

periodontal structures when a simple tipping dental movement or torque

movement is produced. A tri-dimensional computer model based on the finite

element technique was used for this purpose. The model of a lower canine was

constructed based on the average anatomical morphology and 396 isoparametric

elements were considered. The three principal stresses (maximum, minimum and

intermediate) and Von Misses stress were determined at the root, alveolar bone

and periodontal ligament (PDL). In loading cases for the bucco-lingually directed

forces, the three principal stresses were very similar in the PDL. The study

concluded that the dental apex and alveolar crest zones are the areas that suffer the

greatest stress when these types of movements are produced 27

A study was done to examine the relationship between intrusion with low forces

(25 gm) using utility arches in the bioprogressive technique of upper and lower

incisor teeth and root shortening. Thirty-eight cases were selected and by means of

a modified computer program, the lateral cephalograms (T, and T,) for each

patient were digitized. For each patient intrusion was measured as the length from


22

the incisal edge of the upper incisor to the palatal plane of the maxilla and from

the incisal edge of the lower incisor to a line from gonion to the lowermost point

of the inner border of the symphysis. For the measurements from the intraoral

radiographs, all incisors were measured along tooth’s longitudinal axis for total

tooth length, crown length, and root length. Root shortening was found to average

1.64 mm for maxillary incisors and 0.61 mm for mandibular incisors subjected to

intrusive force. No relationship was found between the amount of root shortening

and of intrusion achieved. A prolonged treatment time was significantly correlated

to root shortening. This study concluded that control of treatment time is of

importance especially when intrusion in the maxilla is performed. 28

A study was done to analyze the changes of biomechanical characteristics of

micro-implant-bone interface by establishing a 3D finite element model of stress

variation of micro-implant anchorage-assisted intrusion of orthodontic teeth molar.

ANSYS software was used for modelling. Pure titanium micro-implants were

implanted into the alveolar bone, leaving 3 mm outside the alveolar bone. Von-

Mises stress and displacement (mean displacement and peak displacement) under

the five tilt angles of 30°, 45°, 60°, 75°, and 90° were calculated by applying 200 g

of horizontal force. Under the 200 g of horizontal force, the Von-Mises stresses

and the mean displacements decreased with the increase of the special tilt angles.

Under the 200 g of horizontal force, all peak displacements of different tilt angles

were relatively small. The study concluded that, the micro-implants can maintain

certain stability under a horizontal force of 200 g 29


23

A study was done to investigate the 3D position of the center of resistance of 4

mandibular anterior teeth, 6 mandibular anterior teeth, and the complete

mandibular dentition by using 3D finite-element analysis for establishing actual

clinical treatment plans by observing the initial displacement pattern of the teeth

groups subjected to horizontal and vertical forces. After the alveolar bone was

formed along the curvature of the cemento-enamel junction (CEJ) at a distance of

1 mm below the CEJ,16 a 3D finite-element model of the 14 teeth of the complete

mandibular dentition, periodontal ligament, and alveolar bone was created

ensuring left-right symmetry. A 200-g retraction force was applied to the 4

mandibular anterior teeth group, 6 mandibular anterior teeth group, and complete

mandibular dentition group. The forces were applied 0 mm, 5 mm, 10 mm, 15

mm, and 20 mm apically from the center of the incisal edge of the mandibular

central incisors to the lingual direction. The results of this study showed that the

position of the center of resistance of the 4 mandibular anterior teeth group was

13.0 mm apical and 6.0 mm posterior to the incisal edge of the mandibular central

incisors. The position of the center of resistance of the 6 mandibular anterior teeth

group was 13.5 mm. apical and 8.5 mm posterior to the incisal edge of the

mandibular central incisors. The position of the center of resistance of the

complete mandibular dentition group was 13.5 mm apical and 25.0 mm posterior

to the incisal edge of the mandibular central incisors. The study suggests that

miniscrews be placed distal to the lateral incisor in the 4 mandibular anterior teeth

and distal to the canine in the 6 mandibular anterior teeth 30

A study was done to compare 4 strategies for image-based model generation of the

PDL on the finite element simulation results and, thereby, to assess the sensitivity


24

of simulation results to modeling assumptions during segmentation and meshing.

Two methods(1 and 3) were based on approximating early on the geometry of the

PDL (by using prescribed thicknesses), whereas methods 2 and 4 were entirely

image based. Mapped meshes of 8-noded hexahedral elements with 3 elements

across the thickness of the PDL were generated to create 3 models with different

prescribed constant thicknesses 0.1 mm (model 1a), 0.2 mm (model 1b), and 0.3

mm (model 1c). The locations of the 2 most significant stress maxima and the 4

most significant stress minima correspond to the 4 modelling strategies. This

shows that, qualitatively, the stress distribution in the PDL is remarkably

insensitive to the modelling and reconstruction techniques for low orthodontic

forces. The predicted values of tooth intrusion were not significantly affected by

the PDL’s thickness. The study inferred that if tooth intrusion is to be used to

determine the material properties of the PDL, then a robust and accurate

reconstruction of the PDL is a prerequisite. 31

The purpose of this FEM study was to investigate the relationship between

moment to force (M/F) ratios and the center of rotation by use of the finite element

method (FEM). A 3D finite element model of the upper right central incisor was

made comprising the tooth, PDL, and alveolar bone and consisted of 1184 nodes

and 908 solid elements. A 100-g lingual force was applied at the midpoint of the

labial surface of crown, 5.25 mm from the incisal edge. The relationship between

the M/F ratio at a crown point and where the tooth moved was determined. The

center of resistance was located at 0.24 the root length apical to the alveolar crest.

Results showed the M/F ratios at the midpoint of the crown were - 9.53 for root

movement, - 8.39 for translation, and - 6.52 for crown tipping. The study showed


25

that very small difference in the M/F ratios produces clinically significant changes

in the centers of rotation, showing that the center of rotation is very sensitive to the

M/F ratio difference, particularly as movement approaches translation 32

A series of orthodontic procedures were performed on adult patients in an attempt

to intrude elongated teeth with varying degrees of periodontal damage for the

purpose of studying the results clinically and radiographically, thus evaluating the

influence of treatment on the periodontal status. Sample comprised of 30 patients,

five men and 25 women, aged 22 to 56 years. In 24 patients migration of incisors

had been noted in relation to progressing periodontal disease. Four different types

of appliance were used for correction of the overbite by intrusion. One patient was

treated by use of an edgewise appliance with a J hook for intrusion, adapted for

100 gm per side. Four patients were treated by use of 0.016 x 0.016-inch edgewise

utility arches, three patients had intrusion adjustments bent into a loop of a 0.017 x

0.025inch stainless steel wire. All other patients were treated with a base arch

intrusive mechanism. The study showed that the utility arch and the base arch

seemed to result in both the largest intrusion and the largest gain in bony support.

33

A study was done to show a new radiographic method developed for measuring

changes in root length. With this method, orthodontic intrusion was investigated as

a potential cause of apical root resorption of maxillary incisors. The study had an

experimental and a control group each consisting of 17 patients. The experimental

subjects had a treatment plan that called for 2.0 to 4.0 mm of overbite correction.

The appliance consisted of a 0.017 x 0.025-inch TMA intrusion arch from the


26

maxillary tube of the maxillary right first molar to the maxillary left first molar. A

lateral cephalometric and periapical radiograph were taken before and after the

intrusion phase to measure changes in position of the central incisor and root

resorption. Intrusion was carried out for a mean duration of 4.6 months. The

average amount of intrusion was 1.9 ram, and the mean rate of intrusion was 0.41

mm per month. The control group had a mean resorption of 0.2 mm after an

interval of 4.3 months. In this study, the method used for intrusion was found to be

effective in reducing overbite, while causing only a small amount of root

resorption 34

A study was done to evaluate the clinical usefulness of miniscrews as orthodontic

anchorage. Seventy-five patients consisting of 116 titanium screws of 2 types, and

38 miniplates were retrospectively examined. Each patient was given a

questionnaire that included a visual analog scale to indicate discomfort after

implantation. The results showed that miniscrews had a high success rate of

approximately 90%—the same as miniplates and large titanium screws, and they

provided sufficient anchorage immediately after placement surgery for any

orthodontic tooth movement. In addition, miniscrews placed without a

mucoperiosteal incision or flap surgery significantly reduced the patient’s pain and

discomfort after implantation. The study concluded that miniscrews have suitable

characteristics as orthodontic anchorage.35

A study was done to investigate the effects of incisor intrusion obtained with the

aid of miniscrews. Miniscrews are used as a stable anchorage unit in orthodontics.

They have small dimensions and can be placed in interdental areas where


27

traditional implants cannot be inserted. Eleven patients (three males and eight

females; mean age: 19.79 ± 4.79 years; mean overbite: 5.9 ± 0.9 mm) with a deep

bite of at least 4 mm, excessive gingival display on smiling and normal vertical

dimensions were treated. Two miniscrews 1.2 mm in diameter and 6 mm in length,

were placed distal to the maxillary lateral incisors and forces applied for intrusion.

The upper incisor intrusion was achieved in 4.55 ± 2.64 months. The mean rate of

intrusion was 0.42 mm/month. The mean overbite pre-treatment was 5.54 ± 1.38

mm. The mean intrusion of the upper anterior segment was 1.92 ± 1.19 mm (CR-

PP distance) and the mean change in overbite 2.25 ± 1.73 mm. the study

concluded that true intrusion of upper incisors can be achieved using miniscrew

anchorage. 36

A study was done to analyze the stress distribution patterns in a conical self-

drilling type of miniscrew implant system and the surrounding osseous structures,

with no ossseointegration, for 2 implant materials—Ti6Al4Vn alloy and implant-

grade stainless steel—under horizontal and torsional loading. A numeric approach

was used to investigate how the load transfer at the bone-screw interface changes

for miniscrew implants made of different materials and for different directions of

loading. Results showed that the maximum stresses occurred in the cortical bone

surrounding the neck of the implant at 6 and 8.5 MPa for horizontal and with

stress values for the stainless steel model considerably greater than those for the

titanium alloy model. The values obtained for stainless steel were 19.6 and 17.2

MPa; those for titanium alloy were 11.7 and 8.3 MPa. The results demonstrated

that a conical type of miniscrew implant with a length of 10 mm and a diameter of

2.0 mm composed of either stainless steel or titanium alloy can safely resist the


28

high levels of orthodontic force. Implant-grade stainless steel and Ti6Al4Vn alloys

are suitable materials for miniscrew implants 37

A study was done to compare and evaluate the extrusive forces and torquing

moments on the posterior dentition generated during anterior intrusion with

different intrusion techniques in the maxillary and mandibular dental arch. Seven

wire specimens were used for each of the following intrusive arches: Utility arch

0.016× 0.016” Blue Elgiloy, Utility arch 0.017× 0.025” TMA, and Burstone

Intrusion arch 0.017 ×0.025” TMA. Simulated intrusion from 0.0–3.0 mm was

performed on the Orthodontic Measurement and Simulation System (OMSS). The

forces and moments were recorded in all three planes of space at 0.1 mm

increments and the values at 3.0 mm for all wires were used for all statistical

evaluations. The results showed that at 3 mm vertical displacement of the incisors,

the Utility intrusion archwires recorded mean extrusive forces in the range of

1.59–2.10 Newton. The Utility 0.016× 0.016-inch Blue Elgiloy exerted higher

force than the Utility 0.017×0.025-inch TMA. The recorded magnitudes for the

Burstone 0.017×0.025-inch TMA intrusive arches were 1.30–1.56 Newton. The

study concluded that the upper Burstone 0.017×0.025-inch TMA intrusion arch

exerted the lowest forces ⁄ moments on posterior teeth. The highest forces were

generated by the 0.016×0.016-inch Blue Elgiloy utility arch and the highest

moments by the lower 0.017×0.025-inch TMA utility arch.38

A study was done to investigate the roles of bone quality, loading conditions,

screw effects, and implanted depth on the biomechanics of an orthodontic mini-

screw system by using finite element analysis. A 3-dimensional bone block model


29

integrated with a mini-screw was constructed with a computer-aided design

program to simulate a mini-screw implanted in bone as an orthodontic anchorage

unit. The analysis showed that both stress and displacement increased with

decreasing cortex thickness, as cancellous bone density played a minor role in the

mechanical response. The study concluded that a wider screw provided superior

mechanical advantages. The exposed length of the miniscrew was the real factor

affecting mechanical performance. Both bone stress and screw displacement

decreased with increasing screw diameter and cortex thickness, and decreasing

exposed length of the screw, force magnitude, and oblique loading direction. 39

A finite element study was done to evaluate the influence of placement angle and

direction of force on the stability of miniscrews. Three-dimensional finite element

models were created to represent screw placement angles of 30, 60, 90, 120, and

150 degrees. Bone models were also created using FEM and simplified to

dimensions of 20 mm in length and width, and 15 mm in height for evaluation.

The screws were modelled as a titanium alloy miniscrew with an elastic modulus

of 110 gigapascals (GPa) and Poisson’s ratio of 0.34. The screws were inserted to

a depth of 8 mm up to the collar of the miniscrew. The contact between the bone

and the screw was defined as a frictional interface with a coefficient of friction of

0.37. The interface between the miniscrew and the bone elements was fixed and

the traction force was fixed at 2 N, which is the approximate orthodontic force

applied to a miniscrew. Von Mises stresses were evaluated for miniscrew

insertions into bone model at 30, 60, and 90 degree angles. The finite element

analysis showed cortical bone stress in both 0 and 30 degree direction of force was

greatest for screws placed at 120 and 60 degree angles and least for 90 degree


30

angle. Trabecular bone stresses were 35 and 35.1 MPa for 60 and 120 degree

angles, respectively at 0 degree direction of force, and 33.4 and 34 MPa for 60 and

120 degree angles, respectively at 30 degree direction of force. The trabecular

bone stress for 90 degree angle was 5.6 MPa at both directions of force. The study

concluded that insertion of miniscrews at angles less than or greater than 90

degrees to the alveolar process bone might decrease the anchorage stability of the

miniscrew.40

A study was done to determine risk indicators for the aetiology of abfractions

(cervical wedge-shaped defects) on teeth using dental and medical variables

obtained in a population based sample. Medical history, dental, and socio-

demographic parameters of 2707 representatively selected subjects 20–59 years of

age with more than four natural teeth were checked for associations with the

occurrence of abfractions. The estimated prevalence of developing abfractions

generally increased with age. The following independent variables were associated

with the occurrence of abfractions: buccal recession of the gingiva, occlusal wear

facets, tilted teeth, inlays, toothbrushing behaviour. The first premolars had the

highest estimated risk for developing abfractions, followed by the second

premolars maxillary and mandibular canines. The results of this analysis indicated

that abfractions are associated with occlusal factors, like occlusal wear, inlay

restorations, altered tooth position and tooth brushing behaviour. This study

delivers further evidence for a multifactorial aetiology of abfractions. 41

A clinical study was undertaken to analyze adult skeleto-dental changes induced

by a reverse curve mushroom archwire. Lateral cephalograms from before


31

treatment and immediately after bite opening were evaluated from 8 female adult

patients with a mean overbite of 3.9 mm. 6 linear and 5 angular measurements

were selected for cephalometric analysis. Alignment was performed by using

progressively larger cross-section round mushroom archwires placed on lingual

brackets. After completing alignment, a reverse curve mushroom arch was

engaged into the occlusal slot of the lingual bracket and tied back at the first

molar. The results showed that there was highly significant reduction in overbite

with a resulting post-intrusion overbite of 2.0 mm. Some lower incisor

proclination was seen, which was not of significance. The inclination of the

occlusal plane was increased by 1.68 and the lower anterior face height was not

significantly increased. The study inferred that the use of a reverse curve

mushroom archwire is capable of intruding the lower incisors with minimal side

effects on the posterior teeth.42

A study was conducted to investigate whether levelling the curve of spee, using

two orthodontic treatment techniques, produces stable results on a long-term basis.

All patients had Class II malocclusion with an overbite of 50% or greater, a

mandibular plane angle less than 32°, and a curve of spee 2 mm. The records used

consisted of dental casts taken at T1, after orthodontic therapy (T2), and at

postretention (T3). All subjects in both the groups were treated with fully

preadjusted fixed orthodontic appliances with 0.018-in slots. The curves of Spee

were measured on the left and right sides of each set of mandibular models. The

results showed that both techniques produced highly significant reductions in the

curve of spee (T1 to T2). Statistically significant, but clinically insignificant,

postretention relapse of the curve of spee occurred (T2 to T3). For both


32

techniques, a statistically significant difference was seen in the incidence of the

relapse of the curve of spee between patients who were completely levelled post-

treatment and those who were not. The study did not find a correlation between

pre-treatment curve of spee and relapse in any of the other occlusal traits studied 43

A study was done to determine the reactions in the pulp and dentine following

experimental orthodontic tooth movement performed under controlled conditions.

The material consisted of seventy clinically intact premolars from children 10 to

13 years of age. Thirty-five of the teeth were extracted without treatment and

served as control. The remaining thirty-five received fixed orthodontic appliances

which initiated continuously acting intrusive forces. The intrusive force was

recorded, at the start of the experiment and immediately before extraction of the

teeth. The force applied varied from 35 to 250 grams for the different teeth, and

the experiments lasted from 4 to 35 days. The appliance consisted of a spring

which was attached to the molars and activated against the first premolar. The use

of such appliances resulted in intrusion of the teeth, but since the spring was

engaged on one side of the tooth only, a certain tipping movement would also

occur. All the teeth went through the same histologic procedure. The results

showed that alterations in the normal histologic structure of the pulp and dentine

were noted both in the untreated control material and in the experimental material.

The pulp alterations in the experimental material were always most pronounced in

the coronal portion, gradually decreasing toward the apical region. Forces above

150 to 200 gm invariably resulted in stasis in the pulp vessels, as judged by the

presence of brown pigment from deteriorating erythrocytes. The width of the pre-

dentine zone was often reduced in those teeth in the experimental series which


33

showed severe vacuolization of the odontoblast layer. Teeth which had completed

apex exhibited more severe changes than teeth with open apices, and the

magnitude of the force was also important. The resorption observed in dentine was

related to the magnitude of the force and the duration of the experiment 44

A study was done to elucidate relationships between the dental roots and

surrounding tissues in order to prevent complications after placement of a

miniscrew. Cross sections of human jaws were analyzed in 20 mandible and 20

maxilla. Resin blocks were prepared and cut serially at 1 mm intervals from the

cervical line to the root apex and images of each section then were obtained at a

resolution, the interroot distance, buccolingual bone width, cortical bone

thickness, mucosal thickness were measured. The results showed that the interroot

distance increased from anterior to posterior teeth and from the cervical line to the

root apex in both the maxilla and the mandible. The study concluded that the

safest zone for placement of a miniscrew is between second premolar and first

molar, from 6 to 8 mm above the cervical line in the maxilla, and between first and

second molars, less than 5 mm from the cervical line in the mandible. In the

maxillary, the regions for which a miniscrew of 8 mm is recommended are a

buccal installation between central incisor and canine (from 9 mm above cervical

line), between first and second premolars (from 3 mm above cervical line), and

between second premolar and first molar (from 3 mm to 4 mm above cervical

line). In the mandible, the regions for which a miniscrew of 8 mm is recommended

are between canine and first premolar (from 9 mm below cervical line), between

first and second premolars (from 5 mm to 8 mm below cervical line), and between

first and second molars (from 2 mm to 3 mm below cervical line).45


34

A study was conducted to compare the skeletal and dental effects of 2 intrusion

systems involving mini-implants and the Connecticut intrusion arch in patients

with deepbites. Forty-five patients (26 women, 19 men) fulfilling the criteria were

selected and divided into 3 groups with 15 subjects in each group. The

Connecticut intrusion arch group, comprising 6 men and 9 women, had intrusion

with Connecticut intrusion arches; the implant group, comprising 6 men and 9

women, had intrusion with a mini-implant system. The initial intrusive force of the

Connecticut intrusion arches was 60 g, and it was checked and reactivated

monthly after controlling the intrusive force. In the implant group, 0.018 × 0.025-

in brackets were placed on the patients’ 4 maxillary incisors.. Aligning and

levelling were not performed. A passive 0.016-in round segmental archwire was

placed to maintain the initial position of the 4 maxillary incisors. Two self-drilling

mini-implants were inserted into the alveolar bone and intrusion force was

delivered by nickel-titanium coil springs. Results showed that the mean amounts

of genuine intrusion were 2.20 mm (0.31 mm per month) in the Connecticut

intrusion arch group and 2.47 mm (0.34 mm per month) in the implant group.

Both systems led to protrusion and intrusion of the maxillary incisors, and

protrusion and extrusion of the mandibular incisors. Although movement of the

maxillary molars led to loss of sagittal and vertical anchorage during intrusion of

the incisors in the Connecticut intrusion arch group, these anchorages were

conserved in the implant group. The overall success rate was 90%. 46

A study was done to determine whether the size of the maxillary buccal segment

influences the amount of steepening, extrusion, or narrowing of the buccal


35

segments, or the rate of intrusion that occurs with maxillary incisor intrusion. 40

patients included in the sample were between 9 and 14 years of age needing

maxillary central and lateral incisor intrusion of at least 2 mm. Patients in the long

buccal-segment group had maxillary buccal segments that included the canines,

both premolars, and the first molars. In the short buccal-segment group, the buccal

segments consisted of only the maxillary first molars. Patient records were taken

at the beginning and end of maxillary incisor intrusion. Results showed that both

groups had about the same amounts of incisor intrusion. In the long buccal-

segment group, a small decrease in maxillary arch width was observed; in the

short segment group, a small increase was found. In both groups, the buccal

segment steepened in the short buccal-segment group almost 14° more than in the

long buccal-segment group. Both groups had small amounts of extrusion of the

buccal segments. The axial inclination of the anterior segment changed (proclined)

more in the long buccal segment group. There was no difference in rate of

intrusion between the long and short segment groups 47

A study was done to examine the effect that varying the position of an occlusal

load would have on the stress contour in the cervical region of a lower second

premolar using a two-dimensional plane strain finite element model. A two-

dimensional finite element model was generated of a lower second permanent

premolar. The outline of the tooth, amelodentinal junction and pulp were

represented. The periodontal ligament was assumed to be 0.3 mm wide, and the

dimensions of the surrounding compact and cancellous bone were derived from

standard texts. The model was loaded using seven different loading positions. The

first six loads used a single 500 N load distributed at various points radially around


36

the crown. The maximum principal or first principal stress in the buccal and

lingual enamel in the cervical region was sampled along two horizontal planes.

The first plane A-A was 1.1 mm above the amelo-cemental junction while the

second plane B-B was 2.2 mm above the amelo-cemental junction. This study

showed that varying the position of the occlusal load produced marked variations

in the stresses found in the cervical enamel. Loads applied to the inner buccal and

lingual cuspal inclines, that mimic the loading produced during lateral excursions

of the mandible, produced the highest stresses and these were of the correct order

of magnitude to initiate enamel failure 48

MATERIAL AND METHOD

37

MATERIAL AND METHOD

The Finite Element Method (FEM) is a precisely constructed three dimensional

mathematical method that is majorly used in engineering studies. It helps solve large

numbers of equations based on the shape of complex geometric objects and their

physical properties to calculate structural stress, and also has the advantage of being

applicable to any solid of irregular geometry that contains heterogeneous material

properties. The finite element analysis provides the orthodontist with quantitative data

that can yield an improved understanding of the reactions and interactions of

individual tissues and helps evaluate different loading conditions in order to optimize

the biomechanics delivered.

It involves the graphical simulation of a structure in a computer to form a mesh which

explains the geometry of the designated structure. This mesh is further divided into a

number of finite elements by a process of discretization or subdivision. The elements

are further connected at intersections called nodes. Thus a complex structure is formed

by discretization and formation of elements, which can be arranged in two or three

dimensions.

Steps involved in the finite element model preparation:

1. Construction of the geometric model of the structure

2. Conversion of geometric model into finite element model

3. Material properties and data representation

4. Loading the configuration

CONSTRUCTION OF THE MODEL

A geometric model of the mandibular segment from the right second permanent molar

to the right permanent canine was created through CT scan and converted to three

MATERIAL AND METHOD

38

dimensional step file format through reverse engineering technique (fig.2a, 2b). All

teeth (elastic modulus 20 GPa; poisson’s ratio 0.3) were modified until the proper

crown-to-root ratio was obtained. The posterior teeth from the second molar to the

first premolar were levelled, and the canine with its surrounding alveolar bone (elastic

modulus 345 MPa; poisson’s ratio 0.3) was extruded by 1.5 mm. Further, it was

converted into finite element format through a meshing software ANSYS (fig.2c).

Two 3- dimensional solid models were constructed and periodontal ligament (elastic

modulus 0.71 MPa; poisson’s ratio of 0.4) modified with 0.20-mm linear thickness

uniformly. After all bony, dental, and PDL structures were graphically represented,

brackets and molar tubes were modelled with 0.022 × 0.028-in slots and 0º of tip and

torque. The brackets were placed on the facial axis of the tooth. The first molar

auxiliary tube had a 0.018 × 0.025-in slot. A 0.021 × 0.025-in base wire was also

modelled to passively fill the second molar tube, the first molar main tube, and the

premolar bracket slots to simulate the posterior anchorage segment. This passive fit of

the base wire into the posterior appliances was achieved because of the pre-levelling

and alignment. All brackets and tubes, and the base wire were assumed to be

composed of stainless steel (elastic modulus of 200 GPa; poisson’s ratio 0.3) In the

first model (fig. 4a, 4c) a cantilever with a cross-section of 0.017 × 0.025 inch and the

properties of titanium-molybdenum alloy (elastic modulus 69 GPa; poisson’s ratio 0.3

) was simulated. The posterior end of the cantilever was fitted inside the first molar

auxiliary tube, and a helix 3 mm in diameter was constructed mesially to be flush to

the tube. The horizontal segment extends mesially to the area corresponding to the

interproximal contact point between the first premolar and the canine. At this point, a

90º bend was modelled occlusally, comprising a vertical segment that ended at the

level of the uppermost portion of the canine bracket. Finally, another 90º bend was

MATERIAL AND METHOD

39

made to generate the final segment of the cantilever, which was in contact with the

upper part of the canine bracket. Another model constructed had two self-drilling

mini-screws of dimension 6 mm in length and 1.6 mm in diameter (Ti6 Al4,113.8 GPa

elastic modulus , poissons coefficient 0.3) inserted buccally at 90º angulation 40

, in the

interdental area ,one at the mesial aspect of the mandibular canine i.e. between the

canine and lateral incisor and the other at the distal aspect of mandibular canine i.e.

between the canine and the first premolar (fig. 5b, 5c). In this model, the mandibular

right segment from the canine to the 2nd

molar will be modelled with metal bracket

0.022 x 0.028 inch slot. A straight 0.019” x 0.025” stainless steel archwire will be

fashioned and placed alongside the canine’s buccal surface immediately below the

bracket to prevent undesirable lingual root torque. Intrusive force to the tooth will be

applied using an elastic chain from the mini-screws to the canine bracket.

Model 1(a) - model having a cantilever loop with a toe in of 0º for intrusion of canine

Model 1(b) - model having a cantilever loop with a toe in of 4º for intrusion of canine

Model 1(c) - model having a cantilever loop with a toe in of 6º for intrusion of canine

Model 1(d) - model having a cantilever loop with a toe in of 8º for intrusion of canine

Model 2 – model with two mini-screws placed buccally and mesial and distal to the

canine for intrusion of canine

CONVERSION OF GEOMETRIC MODEL TO A FINITE ELEMENT MODEL

After the geometric model construction, discretization was done to transfer the model

into a number of finite elements (smaller bodies or units with pentahedron,

MATERIAL AND METHOD

40

hexahedron or rectangular structures) and nodes which are the intersecting points

between two or more elements. Nodes are the points at which the degrees of freedom

are defined, which in turn determine the number of ways a node is allowed to move.

This procedure is carried out towards making the model more suitable for numerical

evaluation and implementation on digital computers. The boundary conditions of the

anatomic structures tested were performed using ANSYS software to create a finite

element model. Version (14.0)

MATERIAL PROPERTIES AND DATA REPRESENTATION:

In this study the periodontal ligament, alveolar bone, teeth, brackets, molar tubes, arch

wire, miniscrew, and cantilever were modelled. The arch wire, bracket, buccal tubes

are considered to be made of stainless steel and these structures were modelled as

being homogenous and isotropic. Also the cantilever was considered to be made up of

titanium molybdenum alloy and the implant was considered to be made of titanium

alloy. The properties of the anatomic structures and the materials used in this study

were based on the elastic modulus and poissons ratio. The PDL had hybrid meshes

with pentahedron and hexahedron elements, which provided more accurate

estimations of the stresses on these structures. The diversity of the mesh was

important because the PDL was being evaluated for stress in this study. The other

materials had pentahedron elements, and each element had 6 degrees of freedom, thus

they could move and rotate in any direction within the space. Eventually, each

pentahedron element had 6 nodes, and each hexahedron element had 8 nodes. The

interactions present between the brackets and wires were determined using beam

elements. The remaining contacts between the elements of different objects were

MATERIAL AND METHOD

41

made by rigid contact interactions, in which phases from the different materials

remain without relative displacement between them. Three reference axes (X,Y,Z)

having the mandibular canine as the reference point were used for cantilever

activation:

(1) X -axis for the mesio-distal aspect

(2) Y-axis for the occluso-gingival direction, and

(3) Z-axis for the bucco-lingual aspect

EXPERIMENTAL CONDITIONS (METHODOLOGY)

In the first constructed model a cantilever was used for intrusion of the canine (fig.

4a,4c). It was placed from the molar tube extending till the canine bracket and pre-

activated with a 35º tip-back. This offset applied a force of 0.02 N on the Y-axis

(mesio-distally) and 0.37 N (occluso-gingivally) on the Z-axis of the canine. This was

achieved by prescribing a displacement vector at the bottom of the cantilever, which

was in contact with the canine bracket. After achieving this position, the cantilever

was caught by a rigid link. Thus, all of the energy accumulated at the offset was

transmitted to the bracket and then to the tooth.

The following compensatory toe-in bends were simulated in this experiment: 0º, 4º,

6º, 8º each applying a force of 0.01 N, 0.052 N, 0.082 N, 0.12 N, on the X-axis

(bucco-lingually) respectively (fig. 4b). The activation of each simulated

compensatory toe-in was equivalent to the magnitude of the force in the x-axis

inferred from the visualization correspondent to the force that each toe-in produced.

Therefore, the force variation was only in the x-axis. Also the resultant counter-effect

produced by the cantilever with different toe-in’s, on the anchor molar causing its

MATERIAL AND METHOD

42

movement along the Y-axis (mesio-distally) and along Z-axis (occluso-gingivally)

was determined.

In the second model (fig.5a, 5c) two mini-screws were placed at angulation of 90º

buccally in the interdental bone on both the mesial and the distal sides of the canine,

and an intrusive force of 0.147 N was applied onto the tooth using an elastic chain

extending from the mini-screws to the canine bracket. A straight 0.019” x 0.025”

stainless steel archwire was fashioned and placed alongside the canine’s buccal

surface immediately below the bracket to prevent undesirable lingual root torque.

In the first model, the amount of pure intrusion of canine was measured by the

movement of the tooth along the Z-axis, and the amount of buccal crown tipping that

occurs due to different compensatory toe-in bends of cantilever was measured along

the X-axis. Also the counter-effect on the posterior anchorage system and stress

changes in the alveolar bone and periodontal ligament surrounding the canine and the

molar tooth were assessed. In the second model canine intrusion was achieved using

two mini-screws placed on either side of the target tooth with an elastic chain from the

miniscrews to the tooth. The effects of this intrusion on the surrounding alveolar bone

and periodontal ligament were measured. The results obtained from these two models

were evaluated and compared using the three dimensional finite element analysis

using ANSYS software.

RESULTS

43

RESULTS

The values of pure intrusion produced by two finite element models were obtained. In

the first model (fig 4a,4b) intrusive forces were applied by a cantilever with different

toe-in bends (fig 4c) and in the other model, force was applied using mini-implants

(fig 5b). The result of the analysis is called ‘post processing’. Stresses and the

displacements are calculated and represented in coloured bands, different colours

representing different stress levels and different values for maxillary molar

displacements.

Red colour area of the spectrum indicates maximum principal stress, followed by

orange, yellow, green and blue representing the reducing levels of stress. White colour

of the spectrum represents the least level of stress.

Two nodes, the tip of the buccal cusp (crest node- no. 128046), and the apex of the

root (root node- no. 129160) were selected for evaluating the movement of the canine

along the Y-axis indicating intrusion and the Z-axis indicating tipping of the tooth in

the labial or lingual direction.

When intrusive forces were applied by the different toe-in bends of the cantilever and

with the mini- implant, the amount of displacement of the crest and root nodes of the

mandibular canine model that occurs along the Y-axis was measured and tabulated in

table 3. The displacement of the canine along the Y-axis due to 0º, 4º, 6º and 8º toe-in

bend of cantilever is represented in the fig 7(a), 7(b), 7(c) and 7(d) respectively. The

displacement of canine due to forces applied by the mini-implant is represented in fig

7(e).

RESULTS

44

In the first model with 0º toe-in bend of cantilever, the amount of crown movement as

depicted by the blue dots was 0.949μmm apically , and the root movement as depicted

by the red dots was 0.184μmm apically (table-3, fig 7a), the 4º toe-in bend showed

3.056μmm apical movement of crown and 2.456μmm apical root movement ( table-3,

fig 7b), the 6º toe-in showed crown movement of 5.486μmm apically and root

movement of 5.027μmm towards apex (table-3, fig 7c), the 8º toe-in showed apical

crown movement of 7.31μmm and apical root movement of 7.37μmm (table-3,fig 7d).

In the second model the amount of crown and root displacement along the y axis

produced as a result of forces from the mini-implant were 1.9μmm and 1.6μmm

towards apex respectively (table-3, fig 7e). The amount of intrusion obtained by the 8º

toe-in bend of the cantilever was found to be the highest among all models and the

least value was produced by the cantilever with 0º toe-in bend (graph-1).

The amount of labial/lingual tipping of the canine was evaluated by the movement of

the crest node and the root node along the Z- axis and represented in the table 4. The

figures 6(a), 6(b), 6(c), 6(d), 6(e), illustrate the movement of the crest and root node.

The amount of labial displacement of the crest node that occurred with the 0º toe-in of

the cantilever was 3.71μmm while the root node moved lingually by 3.21μmm (table-

4, fig 6a), 4º toe-in bend produced 3.59μmm labial displacement of the crest node and

the root node moved lingually by 1.59μmm (table-4, fig 6b), 6º toe-in bend produced

0.67μmm labial movement of crest node and 0.65μmm movement of root node

lingually (table-4, fig 6c). The opposite effect was seen with the 8º toe-in bend of

cantilever which produced a lingual displacement of both the crest node and the root

node by 3.01μmm and 2.4μmm respectively (table-4, fig 6d). The amount of labial

displacement of crest node produced by the forces from mini implant was 0.048μmm

RESULTS

45

while the root node moved lingually by 0.036μmm (table-4, fig 6a). The results

showed that in the mini-implant model least amount of tipping of the canine tooth

occurred on application of intrusive forces, whereas the maximum amount of labial

tipping of canine was seen with the model having a cantilever with 0º toe in bend

(graph-2).

The counteracting effects on the molar produced by the cantilever were illustrated in

the figures 10(a), 10(b), 10(c), 10(d). The molar tooth in all the models showed slight

extrusion and distal tipping of the crest node which represented the tip of the mesio-

buccal cusp. The implant model however did not display any significant molar

counter-effects (fig 10e).

The periodontal stresses around the root of the canine produced by the intrusive forces

applied from the cantilever and the mini-implant were illustrated by the figures 8(a),

8(b), 8(c), 8(d), and 8(e) respectively. The red areas showed maximum stress

distribution whereas the blue areas showed minimum stress distribution. The

maximum stresses were evaluated and tabulated in table 5.

The 0º toe-in cantilever model displayed maximum stress (0.0024 MPa, fig. 8a , table-

5) in the periodontium of the canine followed by the cantilever model with 6º, 8º and

4º of toe-in the the decreasing order (table 5). The least amount of stress was seen in

the mini-implant model (0.000340 MPa, fig. 8 e, table-5, graph-3).

The stresses occurring in the alveolar bone around the canine were also evaluated and

tabulated in table 6. The maximum stress values were obtained in the implant model

(0.0039MPa, fig. 9e, table 6), followed by the 6º, 8º, 4º toe-in cantilever models (fig.

9b, 9c, 9d, table-6 ) while the least amount of alveolar bone stress was seen with the

cantilever with 0º toe in bend (0.0016MPa, fig. 9a, table-6, graph-4).

RESULTS

46

GRAPH 1: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE

DISPLACEMENT ALONG Y AXIS

GRAPH 2: LABIAL/LINGUAL TIPPING OF CREST AND ROOT NODE

(DISPLACEMENT ALONG Z AXIS

RESULTS

47

GRAPH 3: PERIODONTAL STRESSES AROUND CANINE

GRAPH 4: ALVEOLAR BONE STRESSES AROUND CANINE

RESULTS

48

TABLE 1: MATERIAL PROPERTIES OF THE MEMBERS:

Member Elastic Modulus Poison’s ratio

Tooth 20GPa 0.3

Periodontal Ligament 0.71Mpa 0.4

Bone 345Mpa 0.3

Stainless steel Wire 200Gpa 0.3

Titanium –Molibdium alloy 69Gpa 0.3

Implant 110Gpa 0.33

TABLE 2: AMOUNT OF FORCE ON THE X-AXIS PRODUCED WITH THE

TOE-INS TESTED

Toe in Force in the y axis (N)

0º 0.01

4º 0.052

6º 0.082

8º 0.12

TABLE 3: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE

DISPLACEMENT ALONG Y AXIS (µmm)

0 degree 4 degree 6 degree 8 degree Implant

Crest node -0.949µmm -3.056µmm -5.486µmm -7.31µmm -1.9µmm

Root node -0.184µmm -2.456µmm -5.027µmm -7.37µmm -1.6µmm

RESULTS

49

TABLE 4 : LABIAL/LINGUAL MOVEMENTS OF CREST AND ROOT NODE

DISPLACEMENT ALONG Z AXIS

0 degree 4 degree 6 degree 8 degree Implant

Crest node 3.71µmm 3.59µmm 0.675µmm -3.01µmm 0.0485µmm

Root node -3.219µmm -1.59µmm -0.65µmm -2.4µmm -0.0365µmm

TABLE 5: STRESSES IN CANINE PERIODONTIUM

0º toe-in 4º toe-in 6º toe-in 8º toe-in Mini-

implant

Stress 0.002443 0.00194 0.002361 0.002069 0.00034

( MPa)

TABLE 6: ALVEOLAR BONE STRESS AROUND CANINE

0º toe-in 4º toe-in 6º toe-in 8º toe-in Mini-

implant

Stress 0.001603 0.002215 0.003581 0.003192 0.003994

( MPa)

RESULTS

50

NODE NUMBERS

CREST : 128046

ROOT : 129160

Number of elements

Number of nodes

Model 1

790774

172545

With Implant

817659

177001

NODAL SOLUTIONS

1. 0º toe-in cantilever model


RESULTS

51



5. Mini-implant model

DISCUSSION

52

DISCUSSION

A deep bite is a complex orthodontic problem that is a common feature of many

malocclusions. It consists of a variety of skeletal and dental factors. A decrease in

vertical skeletal growth, axial inclinations of the upper and lower anterior teeth,

vertical positions of the anterior and posterior teeth, and loss of periodontal support

are among the factors that contribute to the development of deepening of the bite.

Correction of a deep bite is an important part of orthodontic treatment due to the

potential deleterious effects on the temporomandibular joint, the periodontal health

and facial aesthetics.9

A deep overbite is typically corrected by intrusion of the anterior teeth or extrusion of

the posterior teeth.14

In patients with an excessive gingival display and a normal

vertical dimension, incisor intrusion is the treatment of choice.9 A study by burstone

concluded that it is much easier to intrude lower incisors because of their smaller root

mass and the common presence of a curve of Spee in the lower arch. 8

Deep bite is often corrected using continuous or segmented arches. Melsen et al.

(1989) indicated that the segmented arch technique is the treatment of choice for

patients with elongated incisors or periodontal bone loss.5 A study done by Varlik et al

concluded that deep bite treatment with mandibular incisor intrusion with utility

arches was effective and appeared to be stable in non-growing patients.33

Weiland et

al showed that segmented arch mechanics can produce genuine intrusion of the

incisors with little vertical effect in the molar area in adult patients.10

However, during anterior intrusion with the segmented or the continuous technique,

the posterior teeth are subjected to a vertical force, which tends to extrude them and a

DISCUSSION

53

moment or torque, which in the upper arch will steepen the occlusal plane and in the

lower arch flatten it. According to principles of static equilibrium, the magnitudes of

the posterior extrusive and anterior intrusive forces are equal. If intrusive forces are

kept low, occlusal forces tend to negate the eruptive tendency of the posterior teeth.38

Most of the deep bite cases have anatomically extruded mandibular canines, and the

treatment plan often involves the intrusion of the incisors and the canines. As

simultaneous orthodontic intrusion of the 6 anterior teeth can cause undesirable effects

in the posterior anchorage segment, segmented intrusion of the mandibular canines

should be considered when levelling the curve of Spee. 8,11

Intrusion is defined as the apical movement of the geometric center of the root

(centroid) in respect to the occlusal plane or a plane based on the long axis of the

tooth. Labial tipping of an incisor around its centroid produces pseudo-intrusion,

Conventional intrusion mechanics frequently cause labial tipping of incisors, a

situation which does not always give favourable treatment outcomes.8

Orthodontic appliances such as the cantilever, spring, etc. deliver relatively constant

forces owing to the large inter-bracket distance between two points of attachment. In a

two-tooth system, if an appliance is engaged in the bracket slots of both the teeth, it

generates a force and a couple at both the brackets resulting in a two couple statically

indeterminate system 13

But, if an appliance is engaged in the bracket slot of one tooth

and tied as a point of contact on the bracket of another tooth, then this force system is

called as a one-couple system because a couple acts only at the bracket slot where an

appliance is engaged. One couple system is statically determinate as equal and

DISCUSSION

54

opposite forces act at both the attachment sites (engaged and tied) to maintain the

static equilibrium of an appliance.12

In this study a cantilever was fabricated with 0.017×0.025 inch TMA wire and one

end was inserted into the molar auxiliary tube and the other end was placed over the

canine bracket to create a one couple statistically indeterminate system (fig. 4a). The

one-couple system produces the reactive force as well as the couple on the molar tube

which try to displace the molar tooth. This can be minimized by engaging an archwire

from second molar tube to first molar tube and extending further through brackets

slots of first and second premolars to generate posterior teeth anchorage segment.

Thus, posterior teeth will act as a one complete anchorage unit, making the effects of

couple and reactive force significantly lower than the effect of force on the canine. A

study done by Kojima and Fukui showed that the addition of the second molar to the

anchorage unit decreases the reactive forces on the posterior anchorage system and

also increases the amount of anterior intrusion.50

Hence in our study the posterior

segment was consolidated with 0.019x 0.025inch stainless steel wire from the

premolars to the second molar teeth.

Many studies have been done to intrude the mandibular canine individually but are

often faced with the problems of unwanted labial tipping of the concerned tooth.

One technique was described by Ricketts et al and involved using the utility arch after

complete incisor intrusion as a stabilization arch and gently tying an elastic band from

the canine bracket to a segment in the utility arch which had a step down.6 Another

technique was reported by Marcotte, and burstone 8 who suggested the use of a

cantilever from the auxiliary tube of the first molar to the canine bracket slot.

DISCUSSION

55

However, these techniques do not include a method for controlling the buccolingual

inclination.8,11

Hence in our study a cantilever loop was used to intrude the mandibular

canine. The cantilever was tested with 0,4,6,8 degree toe-in bends which were

incorporated to determine its effectiveness of each toe-in bend in controlling

unwanted labial tipping of the mandibular canine on application of intrusive forces

(fig. 4b).

Creekmore and Eklund initially performed maxillary incisor intrusion using a

vitallium screw inserted just below the anterior nasal spine, and since then many

clinicians have tried to intrude the incisors with absolute anchorage.14

The

development of mini-implants in the past years has enabled efficient anchorage,

requiring no tooth support and with no esthetic compromise whatsoever. Additionally,

no patient cooperation is required.15

Miniscrews have a high success rate of

approximately 90%, which is the same as miniplates and large titanium screws, and

they provided sufficient anchorage immediately after placement surgery for any

orthodontic tooth movement.14

Many studies have been done to intrude the incisors and canines using mini implants.

A study done by Telma martin et al showed that pure cuspid intrusion can be achieved

by the use of elastic forces applied from two mini implants placed on either sides of

the labial surface of canine root. The unwanted buccal tipping was prevented by the

placement of a rigid 0.019x0.025 inch stainless steel wire on the labial surface of the

crown just below the bracket.15

A study done by esen aydogdu et al concluded that

pure incisor intrusion could be achieved using a segmental arch to the incisors when it

is supported by two mini-implants that are placed between the lateral and canine teeth.

DISCUSSION

56

Also the incisor intrusion that was achieved using TAD supported segmented archwire

was no different than the movement achieved by the conventional intrusion utility

arch.9 A study by Ishihara et al showed that the indirect use of miniscrews is an

efficient method for intruding over-erupted mandibular incisors.14

Omur Polat-Ozsoy et al conducted a study which investigated the effects of incisor

intrusion obtained with the aid of miniscrews and showed that mini screw mechanics

produce pure intrusion of the incisors.36

A study by Singh S, Mogra S showed that

Implant-grade stainless steel and Ti6Al4Vn alloys are suitable materials for miniscrew

implants.37

Letizia Perillo conducted a finite element study to evaluate the influence of

placement angle and direction of force on the stability of miniscrews and found that a

mini screw placed at 90 degree angulation to the alveolar bone surface provided good

anchorage.40

A study by Kyung-Seok Hua et al showed that in the mandible, the

regions for which a miniscrew of 8 mm is recommended are between canine and first

premolar (from 8 mm below cervical line), between first and second premolars (from

5 mm to 8 mm below cervical line), and between first and second molars.45

In this FEM study mandibular canine intrusion was attempted using two mini implants

composed of titanium and with a diameter of 1.5mm and length 6mm. The implants

were placed on either side of the mandibular canine labial surface at a distance of

8mm from the alveolar crest and angulated at 90 degrees. To control any undesirable

effect a straight 0.019 x 0.025inch stainless steel archwire could be fashioned and

placed alongside the cuspid’s buccal surface immediately below the bracket.15

(fig.5b,

5c)

DISCUSSION

57

The phenomenon of tooth movement in response to an applied load was first reported

nearly 2000 years ago (Celsus, 1st century AD). Although teeth are moved routinely

in orthodontic practice, it is still the case that there is much to learn about the exact

ongoing changes in the biomechanical loading of tissues and the precise mechanism of

tissue response following force application. To better understand the biomechanics of

tooth movement, a variety of methods have been used like theoretical mathematical

techniques, photo-elastic systems and laser holographic interferometry. However,

such techniques have the disadvantage of only examining surface stress, whilst having

the added problem of usually being supported by poor validation systems, as judged

by current standards. In the last decade the application of the finite element method

(FEM) has revolutionized dental biomechanical research.24

The finite element method (FEM) is a highly precise technique used to analyse

structural stress. Used in engineering field for years, this method uses the computer to

solve large numbers of equations to calculate stress on the basis of the physical

properties of structures being analyzed. FEM has plenty of advantages over other

methods (such as the photoelastic method), highlighted by the ability to include

heterogeneity of tooth material. The irregularity of the tooth contour can also be

formed in the model design and it has a relative ease with which loads can be applied

at different directions and magnitudes for a more complete analysis.

Finite element analysis has been used in dentistry to investigate a wide range of

topics, such as the structure of teeth, biomaterials and restorations, dental implants and

root canals. 24

FE analysis has provided a visual image of the effects of an orthodontic

force on the tooth and its supporting structures. Furthermore, it serves as a useful tool

DISCUSSION

58

to simulate different loading systems and evaluate the initial effects in the

dentoalveolar structures to better understand biomechanics.

14

The object to be studied is graphically simulated in a computer in the form of a mesh,

which defines the geometry of the body being studied. This mesh is divided, by a

process known as discretization, into a number of sub-units termed elements. These

are connected at a finite number of points called nodes, which are, in turn, defined by

their global co-ordinates. The constituent elements are prescribed the appropriate

material properties of the structure they represent. 24

By using this, the function and the actual geometry of the element, the equilibrium

equations between the external forces acting on the element and the displacements

occurring on its nodes can be determined. The information required for the software

used in the computer is as follows.

1. Co-ordinates of the nodal points

2. The number of nodes present for each element

3. Young’s modulus and poisson’s ratio of the material modelled by different

elements: Young's modulus (MPa), also known as the tensile modulus, is a quantity

used to characterize materials and also determines the stiffness of an elastic material.

Young’s modulus is also called the elastic modulus or modulus ofelasticity, because

Young's modulus is the most commonly used elastic modulus. When an object is

stretched, Poisson’s ratio is the ratio of the contraction or transverse strain

(perpendicular to the applied load), to the extension or axial strain (in the direction of

the applied load). When a sample material is compressed in 1 direction, it tends to

expand in the other 2 directions perpendicular to the direction of compression. This

DISCUSSION

59

phenomenon is called the Poisson effect. Poisson's ratio is a measure of the Poisson

effect.18

4. The boundary conditions: A boundary condition is the application of force and

constraint.

5. The forces applied on the structure.

In structural analysis, boundary conditions are applied to those regions of the model

where the displacements and/or rotations are known. Such regions may be constrained

to remain fixed (have zero displacement and/or rotation) during the simulation or may

have specified, non-zero displacements and/or rotations. 18

In the present study two finite element models of the right mandibular quadrant were

created with teeth present from the canine to the second molar. The brackets, molar

tubes and wires were modelled along with the periodontal ligament and the alveolar

bone. A study by Hohman kober et al showed that for intrusive tooth movements a

robust construction of PDL is important.31

The PDL plays a major role in orthodontic

tooth movement, and its thickness and viscoelasticity varies along the root surface.

Clinically, these variations may have an influence over the intensity of the biologic

events that take place during orthodontic tooth movement. 11, 34

In our study, the PDL

was modelled with 0.20-mm uniform linear thickness and elasticity was maintained

the same along the roots of all teeth.

In the first model a cantilever made up of 0.017x 0.025 inch TMA wire placed from

the auxiliary tube to the canine was used for intrusion of the canine. The cantilever

was tested with four different toe-in bends i.e. 0,4,6,8 degrees each applying a force of

0.10N, 0.052N, 0.082N and 0.12N respectively (table-2).

11 These bends were

DISCUSSION

60

incorporated to assess the amount of labial tipping that occurred while intruding the

canine tooth.

In the second model two mini implants were placed in the interdental area on either

sides of the canine root at a level of 8 mm from the alveolar crest (fig. 5b, 5c).55

Intrusive force of 0.12N was applied to the canine using an elastomeric chain from the

mini-implants. The amount of intrusion along with the labial tipping that occurred in

both the models was evaluated and compared using the finite element analysis.

A few studies have been done to determine true intrusion of the canine. Caballero et al

in an FEA study used a cantilever loop with different toe in bends to intrude the

mandibular canine and showed that the 6 degree toe in bend produced pure intrusion

of the canine tooth with negligible labial tipping. The study also showed that the

amount of tipping decreased with an increase in the toe-in bend. The anchor molar

displayed tendency for extrusion and distal tipping.11

A study by Telma martin et al

used mini implants along with an elastic force to intrude a canine tooth and showed

favourable results,15

an FEA study done by Thote et al showed that pure intrusion of

mandibular canine in lingual orthodontics occurred with an optimal force of 20-

30gm.21

In our study the movement of the crest (tip of buccal cusp, node no. 12806) and the

root nodes (tip of apex of root, node no. 129160) were used to determine the amount

of intrusion and labial tipping. The amount of intrusion obtained by different toe in

bends of the cantilever was assessed. The intrusion produced by 8º toe-in bend of the

cantilever was found to be the highest among all models and the least value was

produced by the cantilever with 0º toe-in bend (table-3, graph-1). The amount of pure

intrusion increased with increase in the degree of toe-in bend, and the amount of labial

DISCUSSION

61

tipping of the canine decreased with increase in toe in upto 6 degree, but the 8 degree

toe in bend produced lingual tipping of the tooth. Both the implant model and the 6

degree toe-in model showed almost pure intrusion with least amount of labial tipping,

although the intrusion values produced by the 6 degree toe in of cantilever model were

higher. The maximum tipping was present in the cantilever with a zero degree toe- in

bend, indicating that incorporating a toe-in reduces the tendency of labial tipping of

the concerned tooth (table-4, graph-2). This is in accordance with the study by

caballero.11

In the posterior segment, the anchor molar showed tendency for extrusion and distal

tipping in all the cantilever models (fig. 10a, 10b, 10c, 10d) whereas, this was

negligible in the implant model (fig.10e) inferring that the implant model produces

intrusion of the canine with negligible effect on the posterior anchorage.

A few studies have been done to evaluate the amount of stress that occurs in the

periodontium during tooth movement. A study by jones Hickam et al showed that the

maximum strains recorded in the surrounding alveolar bone were 35 times less than

for the PDL. This FEM model validated that, the PDL is the main mediator of

orthodontic tooth movement.24

Puente et al, studied the stress difference between tipping and torque movements on a

computer model of a mandibular canine and inferred that, the dental apex and bone

crest zones are the areas that suffer the greatest stress when forces are directed bucco-

lingually. It was concluded that, a tri dimensional model is useful to investigate the

biomechanics of tooth movement, keeping in mind that it is more valid as a qualitative

study 21

. A study done by David J. Rudolph et al showed that intrusive, extrusive, and

rotational forces produce more stress at the apex. Bodily movement and tipping

DISCUSSION

62

forces concentrate forces at the alveolar crest, not at the apex.26

Geramy (2002)

reported the stress produced in the periodontal membrane by orthodontic loads in the

presence of varying loss of alveolar bone and concluded that, bone loss caused

increased stress under the same load compared with healthy bone support. Tipping

caused increased stress in the cervical margin of the periodontal membrane and in

case of intrusive movements, at the apical and subapical levels.25

Tanne et al (1987),

in a 3D FEM study, reported a cervical margin stress of 0.012 N/mm2 when, a

lingually directed tipping force of 1N was applied to the centre of a mandibular

premolar model.23

In the present study the periodontium and the alveolar bone around the canine tooth

and posterior segment was studied for stress changes. Among the models the

maximum periodontal stress was seen with the model having the cantilever with 0º toe

in bend followed by the 6º, 8º and 4º toe-in cantilever models and the least was seen

with the implant model (table-5, graph-3, fig 8a,8b,8c,8d,8e). The cantilever with a 0º

toe in bend produced labial tipping of the crest node as well as the lingual tipping of

the root node thereby producing more stress around the periodontium due to

uncontrolled tipping. The alveolar bone showed maximum stress around the mini

implants placed in the bone (table-6, graph-4). In the posterior segment negligible

stresses were noted in the periodontium as well as the alveolar bone.

The simulations of this finite element study showed that a significant amount of labial

crown tipping occurs when intrusive forces are applied to a canine tooth without any

labio-lingual control. In such cases, the control of tipping movements of a tooth is

extremely important as it can lead to a variety of unwanted problems. Increased

DISCUSSION

63

tipping of the tooth can lead to an increased risk of gingival recession, periodontal

problems, alveolar bone loss and also abfractions of the tooth. Also, uncontrolled

canine intrusion may lead to buccal crown tipping and may contribute to an increased

mandibular intercanine width, which eventually could increase the chances of

orthodontic treatment relapse.19

A study by bernhardt et al evaluated the multifactorial

causes that lead to abfractions and concluded that gingival recessions are associated

with the genesis of abfractions and must be seen as co-factors.41

More recently

cervical tooth loss has been linked with cuspal flexure. It has been suggested that

occlusal loads cause the tooth to flex, particularly during lateral excursion. As the

tooth flexes, tensile and shear stresses are generated in the cervical region of the tooth

that cause disruption of the bonds between the hydroxyapatite crystals, leading to

crack formation and eventual loss of enamel and the underlying dentine. 48

This

increased risk can be explained as a result of increased proclination of the tooth which

leads to alteration of force vectors that act on the teeth during masticatory and lateral

excursive movements. The above factors reinforce the importance of the results of

this study.

In the present FEM study, a cantilever loop with different toe-in bends and mini-

implants with an elastic force module were tested for their efficacy in producing pure

intrusion of mandibular canine tooth. The results showed that the amount of labial

tipping tendency of the tooth decreased when a toe-in bend was added to the

cantilever. The 6º toe-in bend of cantilever was sufficient to produce almost pure

intrusion of canine with very less amount of tipping tendency. This is in accordance

with the results seen with the study by caballero. The forces applied from the mini-

implants also produced pure intrusion of the canine with negligible tipping, but the

DISCUSSION

64

amount of intrusion produced was less compared to the cantilever model. Although

the forces applied from different toe in bends had major influence on the canine tooth

but the posterior teeth were not much affected. The posterior segment was

consolidated and served as a rigid anchorage system in cantilever models and hence

only a slight tendency for extrusion and distal tipping was noted in the molar 11

.The

molar had negligible counter-effects in the mini-implant model as the main forces

were applied only from the mini-implant, while the rest of the posterior segment

served as an anchorage unit. The periodontal stresses were observed to be

concentrated majorly around the canine periodontium and alveolar bone. Maximum

amount of stress was noted in the model with 0º toe-in bend, and the least periodontal

stress was seen in mini implant model (graph-3). Although the stresses seen with the

6º toe in model were slightly on the higher side, it produced good amount of pure

intrusion with almost negligible labio-lingual tipping making it the appliance of

choice when true intrusion of a canine is desired.

In the present FEM study, idealized tooth models were used to simulate the conditions

and the results obtained from this study were based on a one time simulated tooth

movement. In day to day practice when dealing with patients having different tooth

morphologies, differences in periodontal health, alveolar bone conditions and

biological reactions the resultant effects may vary. The results obtained in this study

may serve as a future reference guide for further customization of different

compensatory bends with cantilever and also influence the mechanics with mini-

implants. Further clinical studies over a period of time are needed to confirm the

results of this study.

CONCLUSION

65

CONCLUSION

This study was conducted to assess the effects of mandibular canine intrusion by using

a cantilever with different compensatory toe-in bends and with mini-implants using 3-

dimensional finite element method.

The following conclusions can be made within the limits of this study.

As assessed by finite element analysis

1. This FEM study showed that among all the models, the cantilever model with

a 6º toe-in produced a good amount of intrusion with minimal labial tipping.

2. The present FEM study proved that, incorporation of compensatory toe-in

bends in a cantilever is necessary to prevent undesirable labial or lingual

crown tipping, of the mandibular canines on application of intrusive forces.

3. Intrusion of the mandibular canine with less labial tipping can also be achieved

using two mini-implants. The labial tipping is reduced with the use of a 0.019x

0.025inch stainless steel wire placed just below the bracket of the tooth

4. In the posterior anchorage segment, the first molar displayed a tendency for

extrusion and distal crown tipping in all the cantilever models whereas the

effects were negligible in the mini-implant model

5. Most of the registered periodontal stresses were around the canine root. The

stress was the highest with a cantilever that was devoid of any compensatory

toe in bend.

6. Further clinical studies are needed to validate the results of this study over a

period of time to determine the long term effects and stability.

SUMMARY

66

SUMMARY

A finite element analysis was conducted to study the effects of mandibular canine

intrusion produced by segmented arch technique, using a cantilever versus mini-

implants. A geometric model of the mandibular base and teeth from canine to second

molar of the right quadrant was created through CT scan and converted to a three

dimensional step file format through reverse engineering technique. Further, it was

converted into finite element format through the meshing software, ANSYS. Three

dimensional geometry of periodontal ligament (PDL), alveolar bone, bracket, molar

tubes, arch wire, cantilever and mini-implants were separately constructed using the

modelling and meshing softwares. All brackets were sited on the facial-axis points.

The posterior teeth from the second molar to the first premolar were levelled, and the

canine with its surrounding alveolar bone (elastic modulus 345 MPa; poisson’s ratio 0.3)

was extruded by 1.5 mm. Two 3- dimensional solid models were constructed and

periodontal ligament (elastic modulus 0.71 MPa; poisson’s ratio of 0.4) modified with

0.20-mm linear thickness uniformly.

A finite element analysis was done using two 3-dimensional solid models, one having

a cantilever with different compensatory toe-in bends placed from molar auxiliary

tube and tied to the canine bracket and other having two mini-implants placed on

either side of the canine tooth interdentally on the labial side. Based on these 3-

dimensional solid models, a finite-element mesh was created to make a node-to-node

connection between the tooth, PDL, and alveolar bone. The amount of pure intrusion

of the canine produced by both the cantilever with different toe-in bends and with

mini-implant was assessed.

SUMMARY

67

The undesirable labial/lingual tipping and effects on the posterior anchorage that

occurred as a result of intrusion were evaluated. The periodontal and alveolar bone

stresses occurring in all the models were also assessed. In the mini implant model, an

elastic chain was used to apply intrusive forces on the canine from the mini-implants.

Also a 0.019×0.02inch stainless steel rigid wire was fabricated and placed alongside

the buccal surface of the canine tooth to prevent tipping.

CONCLUSION:

Two nodes, the tip of the buccal cusp (crest node- no. 128046), and the apex of the

root (root node- no. 129160) were selected for evaluating the movement of the canine

along the Y-axis indicating intrusion and the Z-axis indicating tipping of the tooth in

the labial or lingual direction.

In the first model with 0º toe-in bend of cantilever, the amount of crown movement

was 0.9μmm apically, and the root movement was 0.18μmm apically, the 4º toe-in

bend showed 3.0μmm apical movement of crown and 2.4μmm apical root movement,

the 6º toe-in showed crown movement of 5.4μmm apically and root movement of

5.0μmm, the 8º toe-in showed apical crown movement of 7.3μmm and apical root

movement of 7.37μmm. In the second model the amount of crown and root

displacement along the y axis produced as a result of forces from the mini-implant

were 1.9μmm and 1.6μmm towards apex respectively.

The amount of labial displacement of the crest node that occurred with the 0º toe-in of

the cantilever was 3.7μmm while the root node moved lingually by 3.2μmm, 4º toe-in

bend produced 3.59μmm labial displacement of the crest node and the root node

moved lingually by 1.5μmm, 6º toe-in bend produced 0.6μmm labial movement of

SUMMARY

68

crest node and 0.65μmm movement of root node lingually. The opposite effect was

seen with the 8º toe-in bend of cantilever which produced a lingual displacement of

both the crest node and the root node by 3.01μmm and 2.4μmm respectively. The

amount of labial displacement of crest node produced by the forces from mini implant

was 0.048μmm while the root node moved lingually by 0.03μmm.

This study showed that the amount of intrusion obtained by the 8º toe-in bend of the

cantilever was found to be the highest followed closely by the 6º, 4º and mini-implant.

The least value was produced by the cantilever with 0º toe-in bend. Also, it was noted

that a 0º toe-in bend produced the highest amount of labial tipping of the canine tooth.

As the toe-in bend increased from 0º to 6º, the amount of labial tipping of the canine

decreased whereas with an 8º toe-in bend the tooth tipped lingually. The molar

displayed a slight tendency for extrusion and distal tipping in all the cantilever models

but these counter-effects were negligible in the mini-implant model. The periodontal

stress was seen to be the maximum with 0º toe-in cantilever model and least with mini

implant.

This FEM study concluded that when pure intrusion of a canine is desired, the use of a

cantilever with a 6º toe-in proved to be the appliance of choice as it produced a good

amount of intrusion with minimal tipping. As this study, was a one-time FEM study,

further clinical studies are needed to evaluate the effects on a long term basis and also

to determine the stability of these mechanics.

Key words: FEM; arch wire; brackets; buccal tube; cantilever; mini-implants.

SUMMARY

69

LIMITATIONS OF THE STUDY:

1. In this study the results were tabulated on the basis of a one-time finite element

study. The stability of intrusion produced must be determined. Also, the effects

of these appliances on the tooth and alveolar bone needs to be evaluated with

long term clinical studies

2. Idealised models were used in this FEM study, the effects may differ when

used on individuals with various tooth morphologies. The presence of

periodontal diseases and bone loss may also influence the intrusion mechanics.

3. In FEM analysis, certain assumptions are made to simulate the physical

environment which can result in errors of stress or displacements.

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70

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CONSENT FORM

77

CONSENT FORM

DEPARTMENT OF ORTHODONTICS AND DENTOFACIAL

ORTHOPAEDICS

GOVERNMENT DENTAL COLLEGE AND REASEARCH INSTITUTE

BANGALORE

This is an in-silico study (finite element analysis) and hence no consent form is

required.

PROFORMA PROTOTYPE

78

TABLE 1: MATERIAL PROPERTIES OF THE MEMBERS:

Member Elastic modulus Poissons ratio

Tooth

Periodontal ligament

Bone

Stainless steel wire

Titanium molybdenum alloy

Implant

TABLE 2: AMOUNT OF FORCE ON THE X-AXIS PRODUCED WITH THE

TOE-INS TESTED

Toe-in Force in the Y-axis (N)

0º

4º

6º

8º

TABLE 3: AMOUNT OF INTRUSION OF CREST NODE AND ROOT NODE

DISPLACEMENT ALONG Y AXIS

0 degree 4 degree 6 degree 8 degree Mini-

implant

Crest node

Root node

TABLE 4: LABIAL/LINGUAL MOVEMENTS OF CREST AND ROOT NODE

DISPLACEMENT ALONG Z AXIS


implant

Crest node

Root node

PROFORMA PROTOTYPE

79

TABLE 5: STRESSES IN CANINE PERIODONTIUM:


implant

Stress

(MPa)

TABLE 6: ALVEOLAR BONE STRESS AROUND CANINE:


implant

Stress

(MPa)

ANNEXURE/PHOTOS/IMAGES

77

FIGURES:

FIG 1 : CT MODEL OF THE MANDIBULAR ARCH

FIG 2a: CUT MODEL OF THE BONE FROM CANINE TO THE SECOND MOLAR


78

FIG 2b: MESH FORM OF THE TEETH

FIG (2c): TEETH WITH 1.5MM OFFSET OF THE CANINE


79

FIG 3a: CANINE TOOTH AND ITS PERIODONTIUM

FIG 3b: PERIODONTIUM OF THE DENTITION


80

FIG 3c: ALVEOLAR BONE WITH SOCKETS

FIG 4a: TEETH WITH BRACKET AND WIRE


81

FIG 4b:WITH 4 DIFFERENT TOE-IN BENDS OF CANTILEVER i.e 0,4,6,8

DEGREES (ZERO FROM LEFT SIDE) ASSEMBLY WITH CANTILEVER

ARRANGEMENT

FIG 4c: MODEL IN ANSYS SOFTWARE


82

FIG 5a: MINI-IMPLANT MODEL WITH 1.2 MM DIAMETER AND 6MM LENGTH

FIG 5b: MODEL WITH ELASTIC CHAIN PLACED FROM MINI-IMPLANTS TO

CANINE

FIG 5c: MODEL WITH MINI-IMPLANT


83

Boundary Conditions :

Both the ends of the bone structure is constrained in all the directions.

FIG 6a: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 0

DEGREE :

FIG 6b: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 4

DEGREE


84

FIG 6c: (VECTOR PLOT FOR BEAM ELEMENT )ANALYSIS RESULTS FOR 6

DEGREE

FIG 6d: (VECTOR PLOT FOR BEAM ELEMENT)ANALYSIS RESULTS FOR 8

DEGREE

FIG 6e: (VECTOR PLOT FOR BEAM ELEMENT ) ANALYSIS RESULTS FOR MINI-

IMPLANT )


85

FIG 7a: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 0º TOE-IN)

FIG 7b: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 4º TOE-IN)


86

FIG 7c: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 6º TOE-IN)

FIG 7d: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH 8º TOE-IN)


87

FIG 7e: DISPLACEMENT ALONG Y AND Z AXIS (MODEL WITH MINI-IMPLANTS)

FIG 8a: STRESS IN THE CANINE PERIDONTIUM (0º TOE-IN)


88

FIG 8b: STRESS IN THE CANINE PERIDONTIUM (4º TOE-IN)

FIG 8c: STRESS IN THE CANINE PERIDONTIUM (6º TOE-IN)


89

FIG 8d: STRESS IN THE CANINE PERIDONTIUM (8º TOE-IN)

FIG 8e: STRESS IN THE CANINE PERIDONTIUM (MINI-IMPLANT)


90

FIG 9a: STRESS IN THE ALVEOLAR BONE (0º TOE-IN)

FIG 9b: STRESS IN THE ALVEOLAR BONE (4º TOE-IN)


91

FIG 9c: STRESS IN THE ALVEOLAR BONE (6º TOE-IN)

FIG 9d: STRESS IN THE ALVEOLAR BONE (8º TOE-IN)


92

FIG 9e: STRESS IN THE ALVEOLAR BONE (MINI-IMPLANT)

FIG 10a: EFFECTS ON THE MOLAR (0º TOE-IN)


93

FIG 10b: EFFECTS ON THE MOLAR (4º TOE-IN)

FIG 10c: EFFECTS ON THE MOLAR (6º TOE-IN)


94

FIG 10d: EFFECTS ON THE MOLAR (8º TOE-IN)

FIG 10e: EFFECTS ON THE MOLAR (MINI-IMPLANT)


95

FIG 11a: STRESS CHANGES IN POSTERIOR SEGMENT (0º TOE-IN)

FIG 11b: STRESS CHANGES IN POSTERIOR SEGMENT (4º TOE-IN)


96

FIG 11c: STRESS CHANGES IN POSTERIOR SEGMENT (6º TOE-IN)

FIG 11d: STRESS CHANGES IN POSTERIOR SEGMENT (8º TOE-IN)


97

FIG. 11e: STRESS CHANGES IN POSTERIOR SEGMENT (MINI-IMPLANT)

effects of mandibular canine intrusion obtained using

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