UPPER INCISORS POSITION CHANGES AFTER ORTHODONTIC TREATMENT IN CLASS I, II AND III MALOCCLUSIONS

by

KONSTANTINOS BAKOS

CHUNG HOW KAU, COMMITTEE CHAIR KYOUNGA CECILIA CHEON

AMJAD JAVED CHRISTOS VLACHOS

A THESIS

Submitted to the graduate faculty of The University of Alabama at Birmingham, in partial fulfillment of the requirements for the degree of

Masters of Science in Dentistry

BIRMINGHAM, ALABAMA

2015

ii

UPPER INCISORS POSITION CHANGES AFTER ORTHODONTIC TREATMENT IN CLASS I, II AND III MALOCCLUSIONS

KONSTANTINOS BAKOS

DEPARTMENT OF ORTHODONTICS

ABSTRACT

Objective: The purpose of this study was to evaluate the maxillary central incisor

position changes after orthodontic treatment in Class I, II and III malocclusions.

Material and Methods: This retrospective cohort study evaluated nighty non extraction

orthodontic Class I, II and III cases which were collected randomly from the Orthodontic

clinic at the University of Alabama at Birmingham and the Institutional Review Board of

the University of Alabama at Birmingham approved the study. All the chosen cases were

treated with fixed appliances and according to the standards of American Board of

Orthodontics. All the lateral cephalo-metric radiographs were taken using the

Orthopantomograph OP100, Instrumentarium Corp.Imaging Division machine(Finland)

and traced digitally using the Dolphin Management and Imaging Software,

Version05.05.5070.221436(US &Canada). In order to evaluate the maxillary incisor

position changes ,the U1-PP(°), U1-SNº, U1-NAº, U1-NA(mm), U1 perpendicular to FH

mm(U1-FH) and U1-Oc° cephalometric measurements were carried out based on the

post-treatment lateral cephalometric measurements. In order to determine if there is a

statistically significant difference in Maxillary central incisor positions among class I, II

and III malocclusions , equivalence tests for post-treatment cephalometric measurements

were performed using a range of ± 2 either degrees or millimeters

Results: The maxillary incisors position does show a significant difference from the

normal value among the Class I, II and III. Class III malocclusion presented a greater

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proclination of maxillary incisor teeth compared to Class I and Class II malocclusions.

Class I has a tendency to be more positive of the normal and Class II to be more negative

than the normal. The maxillary incisors changes, seem to not fall within the range of ±2

mm according with the equivalent tests for post-treatment cephalometric measurements

compared to the respective normal value. The final position of the maxillary incisors after

orthodontic treatment depends mainly on the initial position of these teeth and the

discrepancy of jaws.

Conclusion: There is a significant difference in the positioning of the maxillary incisors

among the class I, II and III malocclusions. The post-treatment measurements such as

U1-FHmm, U1-NA mm and U1-SN° and U1-NA° present a significance difference

among Class I, II and III malocclusions. In In the class II, the maxillary teeth showed to

be more upright than Class I and III malocclusions after orthodontic treatment. The U1-

PP° showed no significant difference among the malocclusions. In this study, the U1-PP°

was the same for r the Class I and III.

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ACKNOWLEDGEMENTS I would like to thank the entire UAB Department of Orthodontics for its support the last

three years. I would particularly like to thank Prof. Chung H. Kau for his outstanding

dedication and guidance. His help extended well beyond what would be expected from a

thesis advisor and I accredit a large part of where I am today to his support. Dr. Kau and

Dr. Vlachos thank you for selecting me to be one of your residents and giving me the

chance to pursue my dream of being an orthodontist; I am forever grateful. I would also

like to thank Dr. Cheon for their advice and input.

Furthermore, I would like to thank my family. I owe tremendous gratitude to my parents

for their always-present support. I cannot thank my wife, Peni enough for her unyielding

encouragement. Last but not the least I would like to thank my son Ilias for being the best

thing ever happen to my life.

“I am indebted to my parents for living, but to my teachers for living well”.

Alexander the Great

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TABLE OF CONTENTS Page

ABSTRACT ........................................................................................................................ ii ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES ............................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii CHAPTER

I. LITERATURE REVIEW ...........................................................................................1 Introduction………………………………………………………………………..1 Traditional methods for the evaluation of Maxillary central incisor position….…1 Upper incisor position-history of different analysis…………………………….. The use of radiographs…………………………………………………………….2

Growth of Soft Tissue Facial Profile .......................................................................6 Dental and skeletal changes .....................................................................................7 Class II and III correctors and Upper incisor position changes ...............................9 Upper Incisor and Soft Tissue changes in extraction and non extraction orthodontic treatment .............................................................................................11 Expected and Actual Torque of Upper incisors .....................................................12 Purpose of Study ....................................................................................................17

2. MATERIALS AND METODS...............................................................................18

Sample Size ............................................................................................................19 Data Collection ......................................................................................................19 Statistical Analysis .................................................................................................20

3. RESULTS ...............................................................................................................24

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4. DISCUSSION ..........................................................................................................30 LIST OF REFERENCES ...................................................................................................36 APPENDICES A INSTITUTIONAL REVIEW BOARD APPROVAL ....................................41

vii

LIST OF TABLES

Tables Page 1 Cephalometric Landmarks .....................................................................................21 2 Reference Planes ....................................................................................................21 3 Measurements used in Cephalometric Analysis ....................................................22

4 Sample size needed per group ................................................................................23

5 Comparison of mean difference between pre- and post-treatment cephalometric measurements by occlusion class ...........................................................................26

6 Comparison of mean difference between post-treatment cephalometric

measurements with respective normal value by occlusion class ...........................27 7 Equivalence tests for post-treatment cephalometric measurement compared to the

respective normal value .........................................................................................28 8 Inter-observer reliability test……………………………………………………..30

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LIST OF FIGURES

Tables Page 1 Mean difference between post-treatment and normal cephalometric measurements

by occlusion class ..................................................................................................29

1

CHAPTER 1

LITERATURE REVIEW

Orthodontists are increasingly using the position of the upper central incisor as a

reference landmark to support the dentition. The position of this tooth not only has a

significance in supporting the upper lip, it also has an importance to the dentition on

smiling, Ramos1. Often, orthodontists use normative values (mainly cephalometric

readings) in trying to position these teeth. However, once the plan is established, the

biomechanical principles of tooth movement may or may not bring an ideal final

treatment position.

Due to the importance of the maxillary incisors in esthetics, several methods have been

used in Orthodontics for the evaluation of their position, such as: a) cephalometric

measurements, b) tooth inclination protractor on the casts or intra-orally and c) three-

dimensional(3D) methods including angular measurements on 3D cast models.

Traditionally, lateral cephalograms were used to measure the inclination of the incisors.

This technique provided the crown-root inclination relative to a horizontal reference

plane (palatal, occlusal, or mandibular, Sella- Nasion). However, the mistakes in

registering the landmarks to assess the inclination of each tooth, or using the occlusal

plane as the reference, and the ionizing beam radiation are among the shortcomings of

this technique. In dental cast-based methods, some of these drawbacks have been

obviated. Andrews tried to determine the tooth crown inclination, considering the facial

axis of the clinical crown and the occlusal plane that passes through the anterior and

2

posterior teeth. However, his technique was both time-consuming and relatively difficult.

The TIP device was first introduced for the measurement of the inclination of incisors on

a dental cast2. Previous studies have demonstrated that the TIP is a simple, inexpensive,

and reliable tool for the assessment of tooth inclination. However, it has some inherent

deficiencies regarding the validity of the measurements, especially in the case of an

inordinate occlusal plane (eg, deep curve of Spee, severe curve of Wilson, canted

occlusal plane) . On the other hand, considering the popularity of CBCT because of its

lower costs and radiation doses, it is now possible to accurately assess the crown and root

3 dimensionally.3

The development of cephalometry (1931) is credited to Broadbent 4 whose article “A new

X-Ray Technique and Its Application to Orthodontia“ broadened the horizons in the

orthodontic research field and further aided the popularity in orthodontic diagnosis and

treatment planning. In 1938,Allan Brodie was the first to evaluate orthodontic results

using cephalometric analysis5. The publication of Down’s analysis in 1952 expanded the

use of cephalometric analysis to clinical practice. Downs used the Frankfort Horizontal

Plane, established in Frankfort, Germany (1882) as a horizontal reference plane6. The

Frankfort horizontal plane was thought to be a representative of the natural head position

in his research and mimicked past orientations of dry skull. Further research performed

by Bagga7 about the inclination of the horizontal plane to the sella-nasion and porion-

orbitale, found that the FHP was more closely related to true horizontal (average mean -

1.15) compared to Sella–Nasion which it’s average mean was 7.33 degrees. However,

some of the disadvantages of FH compared to Sella-Nasion are 1) the difficulty in

locating both landmarks and especially Anatomic Porion 2) both Orbitale and Porion are

3

bilateral structures and 3) the FH is not in sagittal plane and it is influenced significantly

by head’s position changes in cephalostat. The constructed FH is an alternative method

for the orientation of FH and it is a line drawn 6 to 7 degrees below the Sella–Nasion

Proffit 20008.In this study both horizontal planes FH and Sella-Nasion plane were used.

which leads to an in-accurate evaluation of vertical dimension of face. Ellis and

McNamara(1988)9 showed that the variation of SN-FH angle, in untreated Class I

occlusion with well balanced faces was less correlated when the FH plane was used.

When the measurements were made using the SN-MP angle the SNA, SNB showed a

significant correlation with SN-FH angle ranging from 0.63 to 0,67 and for the SN-MP

angle was 0.43. According to this study the FH plane is more accurate than the SN-MP

angle. However, it should be mentioned that the Sella does not affect the ANB angle

which shows the anterio-posterior skeletal relationship of maxilla and mandible. At this

point, it should be emphasized that Riedel10 was the first to introduce the Sella- Nasion

plane in cephalometrics and used it as a reference plane. Riedel also formed the SNA and

SNB angles, drawing lines from SN plane to Point A and B, located on maxilla and

mandible respectively. Jacobson (1975)11 showed that the ANB angle is influenced both

by the length of cranial base and the rotational effect of jaws. Clockwise rotation of the

jaws increases the ANB angle while the counterclockwise rotational effect decreases it.

Jacobson observed that the ANB angle is not a reliable diagnostic measurement in cases

where the SN-MP angle is less than 27 degrees and greater than 37 degrees. He also

introduced the Wits Appraisal which is a linear measurement and not a cephalometric

analysis itself and it can be used as an additional cephalometric measurement to ANB

angle, for the evaluation of jaw relationship. Furthermore, Wits analysis is affected by the

4

functional occlusal plane and the vertical alveolar dimension. Steiner’s analysis as regard

the upper incisor position included both angular and linear measurements. Steiner 12

showed that the inclination of upper incisors ideally should form 24 degrees with the

NA line and the most labial surface of them be 4mm in front of it. However, there is no

reference in the literature how Steiner derived his mean values from .McNamara 9,

introduced the Nasion-Perpendicular to relate the upper incisor to the maxilla. Its

advantage is that it is not affected by the position of maxilla in cases of maxillo-

mandibular anomalies. On the other hand,when the maxilla moves forward both the U1-

NA°and U1-NAmm are decreased and vise versa. The more protrusive the maxilla the

smaller is the U1-NA angular value. These changes happen , even when the upper

incisors remain at the same position within the maxilla. By tilting the maxilla, both

measurements are affected. In this study , Steiner and both McNamara and the Fastlicht

Tetragon cephalometric analyses were used for the upper incisor position to the cranial

base and to the maxilla respectively. With regard to the position of lower incisor to the

MP plane(GO-ME) , the IMPA used in this study is a reliable cephalometric

measurement because it is not affected by the vertical changes in position of the

mandible. The IMPA is one of the Tweed Triangle 13angular cephalometric

measurements and its mean value is 90 degrees. Tweed observed that the concept of

uprighting the mandibular incisor position was related both with facial balance and

occlusion stability. On the other hand, the L1-Apo line can be influenced by both maxilla

and mandible. By moving the maxilla forward this angle decreases whereas when moving

the mandible to the same direction the angle increases. Therefore, the L1-APO can only

be used to describe the lower face profile and not to relate the lower incisors to

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mandibular symphysis 11 . The interincisal angle U1-L1 has been used from the

orthodontists as an indicator of upper and lower incisors. Kowalski et 14evaluated the

distribution of the U1/L1 in a sample of 1104 subject,474 males and 620 females. The

sample also was divided in 2 different chronological groups, one was 6-8 and the second

18-26 old year. They found that the overall mean value of U1-L1 for the intermediate

group 8-16 year old ,it was129° which differs from Steiner’s ideal of 131°and Down’s of

135.4°. However, the U1-L1 is affected not only by both the position of upper maxillary

and mandibular incisors but also by the relationship of jaws. In 2000, Fastlicht15

introduced the tetragon analysis which is based on two geometric elements: the first

element is the “Tetragon”, a polygon that represents the maxilla-dento-mandibular

complex, made up of-the palatal plane, the mandibular plane and the long axes of the

maxillary and mandibular central incisors. The second element is the “Trigon”, a triangle

situated above the Tetragon and formed by one plane that is intrinsic to the Tetragon - the

palate plane and two extrinsic planes , the pterygo-orbital(Pt-Or) and the pterygo-palatal

plane (Pt-PNS).All the four angles of the tetragon always add up to 360°. In an ideal

Caucasian skeletal and dental class I patient the four angles are as follows: a) the angle

formed between the Palatal plane to the axes of the maxillary central incisor is 110° b)

the angle between maxillary and mandibular central incisors is 130° c) the intersection of

the mandibular incisor axis and the mandibular plane is 90° and d) the intersection of the

mandibular plane and the palatal plane is 30°. The tetragon not only can help the

orthodontist to if any of the above angles is modified either by growth or by orthodontic

treatment but also to help him in his decision for planning the orthodontic treatment

when protraction, retraction and impaction of the premaxilla should be performed.

6

Bhasin16 after a cephalometric evaluation of pretreatment and postreatment outcome

using the tetragon analysis ,found that the post-treatment reduction of upper incisor –

palatal plane angle to be reduced significantly in skeletal class I patients, followed by

class II and least for class III patients. One reason for this, is that in skeletal class III

cases the upper incisors were proclined in 60% of the cases whereas the incisors were

retracted in others. The post-treatment value of U1-PP angle for skeletal class I and III

were above the norm because the norms of Fastlicht’s tetragon are based on Caucasian

population and the incisors in Indian population are more proclined than the Caucasian

population. According to McLaughlin17 , in a class I malocclusion the upper incisor to

Palatal plane angle depends on the skeletal vertical divergency of the patient with a 117°

and 108° in low and high angle patients respectively. In a class II and Class III patient

that angle should be 100° and 120° respectively.

Growth of Soft Tissue Facial Profile

Several angles have been introduced to evaluate facial soft tissues. One of them, is the

NLA angle, first introduced by McNamara 18 in 1984. The NLA could be affected by

nose, lip thickness and the dento -skeletal tissues under the lip and the position of Jaws.

Patients with maxillary prognathism or true dento-alveolar protrusion of the maxillary

teeth usually present an acute Nasiolabial angle and vise versa. However, the Nasiolabial

angle can also be affected by the vertical dimension. In a patient with both retrusive

Maxilla and Mandible with a steep mandibular plane, the NLA can be within normal

limits. Furthemore, growth of soft tissues is a significant determinant of the Nasiolabial

angle. Nanda et19 , showed that in both sexes there is a slight decrease in the NLA

7

between 7 and 18 years old, with the most acute NLA angle for boys at 9 years old and

for girls at 7 years old respectively. Both girls and boys showed the most obtuse NLA

angle around 16 years old. The difference between boys and girls at the age of 9 years

becomes smaller due to decrease in growth velocity in girls and with no difference at 16

years old. This can be explained ,because girls grow quickly at 9 yeas old while boys are

still growing slowly. The velocity curves for both girls and boys usually intersect around

the age of 12. These data were in agreement with Andersen et al20 who also showed that

the upper lip length is longer in boys than in the girls whereas the opposite is true for the

lower lip. Andersen’s study20concluded that girls show a higher gum-line than boys and

they should be treated with caution in cases when upper incisors need to be intruded

because no spontaneous correction can be expected with age. However, it seems that the

age at which orthodontic treatment is commence would be a more important factor about

the anticipated soft tissues changes happening with the age.

Dental and Skeletal changes

For someone to determine and visualize the position of the upper incisor before and after

treatment, one should first observe how these teeth can be compensated in different

skeletofacial patterns in untreated subjects. Bibby21, having observed that different

incisor relationships exist in similar facial types and vise versa, studied both the incisor

and skeletal compensatory mechanism in 268 cases. He used SN plane as a reference

plane to examine if there is any skeletal or dental accommodation. He found that Point A

showed similar position between Class I and II while it was significant different in Class

III. The point B showed similar relationship with cranial base in Class I and III and

8

different in Class II. From the above, Bibby concluded that there is no compensatory

mechanism for the Antero-Posterior jaws discrepancy. However, this study showed that

there is a compensative mechanism for the incisors. The upper and lower incisors were

investigated relative to the Maxillary and Mandibular Plane respectively. In Class II

cases, the upper incisors were retroclined while in Class III they were proclined. The

lower incisors showed a similar proclination both in Class I and II and an upright or

retroclined position in Class III relative to Class I and Class II. As result in Class III both

upper and lower incisors participate in compensation whereas in Class II the

compensation is mainly due to upper incisors.

Variability in tooth morphology can play a significant role in appliance design and the

final results of orthodontic treatment. Grant22 and Bryant23 evaluated the crown –root

shape of the maxillary central incisors in Class I, Class II division 1, Class II division 2

and Class III. In both studies, the crown-root shape of the permanent maxillary central

incisors were similar in Class I, Class II division 1and Class III. However, in Class II

division 2 the crown-root shape was characterized by a short root, long crown, reduced

labio-palatal thickness and an axial bending of incisors. All these characteristics ,might

lead to a deepening of the bite and a limitation in the expression of palatal root torque in a

Class II division 2. In addition, to the proclination of Maxillary incisors in Class II

division 2, the A point tends to move backward (0.25 mm) and downward(0.6 mm) due

to dento-alveolar remodeling. However, according to Kazim et24 ,Bicakci25

andAbdwani26 this backward and downward movement of Point A does not significantly

affect the SNA which contradicts BeGole’s27 findings of reduced SNA by 1.6 degrees.

In 1960,Andrews28 studied the shape, angulation and inclination of crowns in 120 non

9

orthodontic models and then established the Six keys to normal occlusion. The absence

of any or more of the six keys results in a occlusion less than normal. He also provided

the average mean of each tooth’s angulation and inclination for the design of the

Straight Wire Appliance reducing the need for bending to a certain point. Andrews also

said that the degree of crown angulation both in upper and lower incisors ,affects the

posterior segments’ relationship, the arch dental length and the anterior esthetics.

Andrews, also emphasized the wagon wheel effect where tip was lost as torque was

added and he decided to add additional tip to the anterior brackets. With regard to arch

length changes based both on the unchanged anterio-posterior position of upper incisors

and attribution of torque,O’Higgins et al29 and Sangfcharearn et30 found that if all the

maxillary incisors are torqued by 5 degrees then the space gain would be 1mm. This

finding can be explained by the molar occlusion change happening of 0,46 mm per side

which means 0.92 mm increase in total arch length. O’Higgins also showed that as the

incisor angulation is increased, the molar relationship tends towards a Class III molars

relationship while a decrease of it will result in a Class II tendency. The findings of this

study were attributed to torque and not tipping.

Class II and III correctors and Upper incisor position changes

The position of upper incisors after orthodontic treatment is closely related to the type of

biomechanics used during treatment. There is a variety of orthodontic philosophies and

appliances for a Class II orthodontic treatment. Among these are Class II elastics,

headgear and functional appliances such as Twin Block , Herbst etc. In the literature, the

10

dento-skeletal effect of Twin Block is mostly on the mandible and lower teeth with a

decrease in overjet attributed to skeletal changes by 54% and dental changes by 46% of

which the upper incisor contribution appears to be only 9% or 0.5 mm of total 2.7 mm

overjet correction Bacceti et31. In another study Siara-Olds32 showed that there is no

significant long term changes in the lower incisor proclination among Twin Block,

MARA, Herbst and Cross Bow. It is well know that Class II elastics have mainly a dento-

alveolar effect which is associated with lingual retroclination and extrusion of upper

incisors and an increase of IMPA and intrusion of the mandibular incisors and a

clockwise rotation effect on the mandible steepening the occlusal plane. Janson 33, Nelson

34showed that both Herbst appliance and Begg technique with Class II elastics have

skeletal and dental effects in the treatment of Class II. However, the overjet reduction

with Begg method was mostly dental due to maxillary retroclination while the Herbst

had a skeletal overjet reduction of 51% (headgear effect)compared to Begg of 4% .

Miller et al35 compared the incisor inclination changes between Forcus and X-Bow and

found that both of them produce the same amount of proclination of incisor with the

difference that the lower inclination is affected by the treatment length whereas the upper

incisor inclination by the age at start of treatment.LeComu36 has shown the dento-

alveolar effect of Class II elastics with no skeletal contribution. This finding is not in

agreement with Janson33 who showed although the Class II elastics have mainly a

dentoalveolar effect of (72%)have also a skeletal effect of 19%. This study33 also

showed that class II are effective in correcting Class II maloclussion and their effects are

similar in long term to fixed appliances such as Herbst, Headgear and Forsus. The

extrusion of upper incisor can be beneficial when the upper incisor display is inadequate

11

but can be detrimental in gummy smile cases. Class III elastics have both a

counterclockwise effect on the mandible while retracts the lower incisors and proclines

the upper incisors. Class III elastics can be used as an alternative orthodontic treatment

method when the extraction or surgical options are not acceptable to a patient.

Upper Incisors and Soft Tissue changes in extraction and non-extraction orthodontic

treatment

Incisor angulation plays an important role both in obtaining a normal occlusion and

presenting a facial balance of surrounding soft tissues. Changes in arch length can be

influenced not only by inadequate angulation of incisors but also by extractions of teeth

for orthodontic purposes. There has been a continuous debate between extraction and

non-extraction orthodontic treatment, mainly due to the emphasis placed on esthetics.

The majority of laypersons prefer full facial profiles and orthodontists have been started

treating according to the soft tissue paradigm. Konstantonis37, in a sample of 215

borderline cases based on lower crowding, had four first premolars extracted in 66

patients(30.6%). By comparing these 2 groups, in this study found that the extraction

group showed a significant a greater retraction of the lips and a more obtuse nasiolabial

angle (+5.34 degrees) while the incisor display changes between the 2 groups was

insignificant. In cases with class II camouflage treatment, Seden38showed, that the greater

the overjet to begin with, the greater the upper incisor retraction and greater the reduction

of ANB which is in agreement with Tadic39. Seden’s 38 study did not show any significant

nasolabial angle changes and he mentioned the effect of upper incisor retraction to the

12

retrusion of lower lip. The inadequate inclination of the upper incisors could produce a

poor occlusion with remaining extraction spaces in cases of Class II camouflage

treatment. Bishara 40based on the Iowa Growth study, after the comparison of 2 groups

with and without extractions, concluded that the four first premolars’ extraction group is

characterized by straight profiles and upright upper incisors with no detrimental effects

on the facial profile. This finding is similar with Zierhut et al41 who attributed the soft

tissue flattening to both mandibular and nasal growth changes and not to the teeth

extracted. Ong42, in his study included 3 different groups of extraction pattern based on

the overjet presented: four first premolars with a moderate overjet, upper first and lower

second premolars with the largest mean overjet and the four second premolars group in a

class I molar relationship with the same overjet with the four first premolars. The data

from his study were the following: 1) The amount of Overjet and the class of

malocclusion are considered to be important factors for the extraction pattern needed

2)the greater incisor retraction was observed in 4/4 (4.2 mm), 4/5(3.7mm) and

5/5(2.3mm). Cephalometric pre and post-treatment tracings were superimposed and

showed that the mean incisor retraction for 4/4 was 2.5mm ,4/5 was 1.6 mm. However in

the literature there are a variety of published mean incisal changes for different extraction

patterns. Furthermore, growth and treatment response varies individually and the decision

for a particular extraction pattern should be based on pretreatment characteristics and

biomechanics used.

Expected and Actual Torque of Upper incisors

13

The development of fixed appliances started in the late 1929 by Dr.Angle who

introduced the E-arch appliance followed by the Pin and tube appliance and Ribbon arch.

However, the above fixed appliances had a poor control of root placement. The

Edgwewise was the first fixed appliance, which allowed both tip and torque control of

teeth. In 1972,Andrews studied 120 normal occlusions using as reference plane the

“Andrews plane” and innovated the Straight Wire Appliance(SWA). In SWA each

bracket slot is designed to align with all adjacent slots when the teeth are perfectly

positioned. The “wagon wheel effect”, made Andrews to add additional tip in the anterior

teeth. However, due to heavy forces used at that period and the additional tip

incorporated into the brackets, the ‘roller coaster“ effect was seen in many cases. In 1993,

the MBT system changed the anterior tip of SWA and used the original research values.

The result of this change was that the upper front teeth had 10 degree less distal root tip

and the lower 12 degrees less compared with the original SWA. The changes made to

overcome some disadvantages of SWA such as loss of anchorage and bite deepening.

Today, there have been not only a large variety of pre-adjusted brackets with different

torque values for the same teeth, but also customized brackets for each patient.

The expression of torque is influenced by a variety of factors such as: 1)crown-root

morphology, labial enamel surface(LES) morphology, bracket placement technique,

bracket/wire play, excess composite on the pad of bracket’s base and the ligation mode

used to retain the archwire in the bracket slot. In the literature there is a variety in the

crown root angulation ranging from 156° to 194.8° according to Knosel43 and Bryant et

al 23,, by using lateral caphalograms such as U1-NA angle, studied the interaction

between incisor crown–root morphology and third order angulation in Class II division 2

14

cases. They found that the torque values of the brackets for the incisors should be

different between Class I and Class II division 2; based on the crown root angulation

which differ significantly from the normal values in class II division 2 case. Richmond 44

used, a tooth inclination protractor(TIP)based on occlusal plane and the cephalometric

angles U1-PP and IMPA to determine if any relationship existed between them in class I,

II and III. He found that the TIP method consistently underestimated the lateral

cephalometric measurements of maxillary incisor angulation by 10.46 degrees and

overestimated the lower incisors ones by 2.57 degrees. The TIP according with

Richmond is a reliable method and there is a close relationship between the maxillary and

mandibular incisors inclination on cast and with their cephalometric angulations .

However, the measurements of facio-lingual inclination and mesio-distal angulation

based on the model cast are not considered to be reliable method for obtaining the above

measurements because are based just on the crown and not on the crown –root

angulation. This variation between the long axis of the crown and the long axis of the

root would result in different root positions with constant crown positions. Hongsheng

45using CBCT, studied the facio-lingual inclination and mesio-distal angulation of 76

patients with “near normal” occlusion instead of the normal occlusion that Andrews used

in his sample of 120 non-orthodontic models. Hongsheng45 showed that the facio-lingual

angulation of upper central incisors and lower central and lateral incisors are similar with

those that Andrews found, while Hongsheng’s measurements was higher than Andrews

for the rest of upper teeth. Another important factor affecting the torque’s expression is

the LA point (midpoint of a crown) on which the bracket is placed. Over the years,

different bracket placement protocols have been recommended for the straight-wire

15

system. The FA point used by Andrews for placement of brackets was based on his belief

that the facial surface is more consistent with La point instead of using millimetric

measurements. This finding is not in agreement with Bryant17and Germane47 found a

standard deviation at La Point of maxillary central incisors of +/- 3.02 and +/-2.9 mm

respectively.

Germane46 also found that if the facio-lingual contour and wire size remain the same but

the vertical placement of a bracket differs from 4 to 5 and from 5 to 6 mm then the torque

expression is quite different from 24 to 22 and from 22 to 18.6 in Andrews prescription.

Miethke47 using the La point, studied the torque changes related to change in vertical

bracket positioning and found that 1 mm away from the LA point, alters the torque of

upper central, upper lateral and canine by 2.5, 4 and 3 degrees respectively if no play

existed between wire and bracket. The deviation of LA point led some researchers to

recommend a variety of bracket positioning charts based on incisal or occlusal edge of

teeth. According to McLaughlin, positioning the brackets using the incisal edge would

reduce the placement errors by 50-60% as well as the need to reposition brackets.

Armstrong 48,compared two methods of bracket positioning on cast models, using the FA

point and the distance from the incisal edge(ME). Armstrong 48 found that for the ME

method the correct bracket placement was more incisal than for the CC method and that

ME seems to be more accurate for the upper and lower teeth and less accurate for the

upper first premolars. Overall, Armostrong49 concluded that in both methods there is a

need for wire bending for acceptable orthodontic treatment results. Another factor, which

play important role on the expression of torque, is the bracket slot size used. There are 2

bracket slot systems incorporated in orthodontic treatment; the 0.18 and 0.22 inch-slot.

16

Detterline49 compared the two bracket slot system based on the ABO Objective Grading

System and found that although there is a statistically but not a clinically significant

difference in treatment time (4 months) and ABO–OGS score (2.7) in favor of 0,018 slot.

The amount of torque expressed from the bracket is the difference of the torque built into

the bracket slot and the degree of wire play engaged in the slot.Capeloza50shows that in

the literature there is a variety of wire play values in 0.22 slot with a 0.019x0.025

archwire such as: Dellinge shows a 9.63 , Creekmore 10.5 and Mclaughin 10 degrees.

Gioka et51 shows that there is a similar torque loss of 14 degrees between the

0.016x0.0.22 and 0.19x0.025 archwires in the 0.018 and 0.22 slots respectively. By

increasing the archwire size to 0.017x0.25 in a 0.018 bracket slot the torque play

decreases to a 6 degrees. Gioka et50 also showed that there is a significant difference

between the theoretical and the actual torque loss of 5% to 10% which is about 1 to 1.5

degrees of torque loss due to dimensional inaccuracy and torque inconsistency of

bracket’s slot. Taloumis52 showed that the steel ligatures provide a better control of

torque loss since the elastomeric materials show a rapid force decay of 53%-68% within

24 hours in vivo, because they are affected both from the intraoral temperature and

moisture. In conclusion, even with the use of customized braces and wires, orthodontists

should have always in his mind that a wire bending is the rule and no the exception for a

functional and esthetic orthodontic treatment result.

17

The purpose of this study was to determine if the upper incisor position changed

significantly after orthodontic treatment in Class I,II and III both dental and skeletal

malocclusions.

Purpose of Study

18

CHAPTER 2 MATERIALS AND METHODS Subject Selection Subjects that finished non-extraction orthodontic treatment to a high standard were

automatically included into the study. Each of these subjects had to meet the following

criteria:

1) All non-extraction cases should be finished in a Class I molar and cuspid relationship.

2) Normal cusp to fossa/cusp to embrasure position of teeth at completion of treatment.

3) Normal Overjet(1-2 mm) and Overbite (1-2 mm), where the mandibular canines and

incisors contact the lingual surfaces of the maxillary canines and incisors with a normal

inter-incisal angle.

4) Good quality of cephalometric radiographs before and after orthodontic treatment.

Once these criteria were met, the patients were reorganized into initial treatment

malocclusion and the pre-treatment cephalometric measurements such as the ANB angle

,Wits appraisal ,the mandibular angle and the FMA(MP-FH) angle to identify cases based

on the inclusion criteria:

1) Class I malocclusion should present an ANB from 0-2°, Wits from -1-0,

2) Class II malocclusion should present an ANB >2° and Wits > 1 and

3) Class III malocclusion should present an ANB <0 ° and a Wits <-1.Because the ANB

is influenced by the mandibular plane, the latter should be within a range of 27°-37°,

4) No significant dento-facial deformity (-3≥ ANB≤+5).

19

Approval for this study was given by UAB Institutional Review Board and the committee

assigned the ethics protocol number E140214011.

Sample Size

The sample size calculation was performed by using the non-inferiority test based on the

standard deviation for U1-SN(°) and U1-NA(mm).Table 2 as these showed the highest

variability. From these values, it was deemed that at least 30 individuals were needed in

each group and was based on the ability to have a non-inferiority value of 2 both

millimetric and degrees for U1-NA and 4 degrees for U1-NA and 4 degrees for SN °.

Data Collection

An initial search using the Dolphin management and Imaging Software system data base

provided a report of all patients who presented with a Class I, II and III malocclusion.

Almost 1500 patients were registered to be in the system having malocclusions at that

time. Each of these patients were further searched to meet necessary criteria and included

into the study.

All the lateral cephalograms were taken using the Orthopantomograph OP100,

Instrumentarium Corp. Imaging Division machine (Finland) and traced digitally using the

Dolphin Management and Imaging Software, Version 05.05.5070.221436(US &Canada).

After a careful search, 90 consecutive orthodontic cases were found based on the

inclusion criteria and evaluated at the time of debond.

20

Parameters measured

The parameters analyzed in the study were categorized into skeletal and dental groups.

A) Skeletal

In order to evaluate the skeletal relationships of the jaws with the cranial base the

1) SNA and 2) SNB angles were recorded, while both the 1) ANB angle and 2)

Wits analysis were used to evaluate the relationship of jaws to each other.

(B) Dental

In order to evaluate the maxillary and mandibular incisor positions, the 1) U1-PP(°), 2)

U1-SNº, 3) U1-NAº, 4) U1-NA(mm), 5) U1 perpendicular to FH mm, and 6) U1-L1(°)

cephalometric measurements were carried out based on the post-treatment lateral

cephalometric measurements. A summary of the cephalometric landmarks and planes can

be found in Table 1.

Statistical Analysis

For the purpose of this study, all the pre-treatment and post-treatment lateral

cephalograms, were traced by an orthodontic resident (K.B). The same lateral

cephalograms were traced by one senior orthodontist (CHK). The inter-observer

reliability was performed to determine any random and systematic error in tracing .The

intra-observer reliability was determined using the intra-class correlation coefficient

statistic analysis, table 8.

In order to calculate the maxillary incisor position changes based on our post-treatment

cephalometric measurements ANOVA test was used. In order to determine if there is a

statistically significant difference for the post- treatment position of maxillary incisors

21

among the Class I, II and III the range of +/- 2 degrees or millimetric of difference was

used and an ANOVA test was performed. A difference beyond that range should be

considered as a significant difference for the post-treatment position of maxillary incisors

position among the Class I, II and III malocclusions. The intra-rater and inter-rater

reliability were close to 1 for most of cephalometric measurements, Table 8.

Table 1

Cephalometric Landmarks

Landmarks Abbreviation Definition

A point A Deepest point of the curve of the maxilla between

Anterior spine and the dental alveolus

Point B B Deepest point between the most superior point on the

Alveolar bone overlying the mandibular incisors

and Pogonion.

Anterior Nasal Spine ANS The tip of the anterior nasal spine

Nasion N The most anterior point on the frontonasal suture in the

midsagittal plane

Orbitale Or The lowest point on the inferior rim of orbit

Posterior Nasal Spine PNS The tip of the posterior nasal spine

Sella S Center of the pituitary fossa of the sphenoid bone

Table 2

Reference Planes Abbreviation Definition

Frankfort Horizontal Plane FH The line connecting Po and OR

Nasion Perpendicular Plane NP A vertical reference plane created by drawing a line Perpendicular to FH through Nasion

22

Palate Plane PP The line connecting ANS and PNS

Mandibular plane MP Defined as a line connecting Gonion and Gnathion

Sella –Nasion SN The line forming the anterior cranial base

Nasion-A line NA Defined as a line connecting Nasion and A point.

Occlusal plane OC The line drawn through the region of the overlapping cusps of the first premolars and first molars.

Table 3

Measurements used in Cephalometric Analysis

Measurement Abbreviation Definition

SNA(°) SNA The angle from Sella -Nasion –A point.

SNB(°) SNB The angle from Sella –Nasion-B point.

ANB(°) ANB The antero-posterior discrepancy of the maxillary to the mandibular apical bases.

GoGn-SN (°) MP The angle formed between the GoGn and SN plane.

Go-Me-FH(°) FMA The angle formed between the Go-Me and FH plane.

AO-BO(mm) Wits The antero-posterior spatial relationship of the jaws relative to the occlusal plane.

U1-SN(°) U1-SN Angular relationship of the maxillary central incisor

to the anterior cranial base.

U1-NA(mm) U1-NA 1 Millimetric relationship of the maxillary central incisor to the NA line.

U1-NA(°) U1-NA 2 Angular relationship of the maxillary central incisor to

the NA line.

U1-FH(mm) U1-FH The distance from a vertical line drawn through point A and parallel to N-Pa, to the facial surface of the maxillary incisor.

U1-PP(°) U1-PP Angular relationship of the maxillary central incisor to

the PP.

U1-Ocl.Plane(°) U1-Oc Angular relationship of the maxillary central incisor to the occlusal plane

For the calculation of sample size, multiple tests for both the angular and millimetric

distances were performed for the U1-SN and U1-NA respectively. The total sample size

23

required for this study is 90 cases of which 30 was Class I, Class II and Class III

respectively. Table 4 provides the results of the analysis:

Table 4.

Sample size needed per group

U1-SN U1-NA

Difference values(° or mm)

2 94 23

3 42 11

4 24 6

24

CHAPTER 3

RESULTS

Our sample consisted of 90 patients with 30 patients in each Class I, Class II and Class III

malocclusion. All the orthodontic cases treated with upper and lower pre-adjusted

edgewise appliances (0.022’’ x 0.028 ‘’ slot) with MBT prescription. A 19x25 SS were

used as final archwire for all the treated orthodontic cases. All patients presented a mild

to moderate crowding of the teeth with the greatest amount of crowding presented in

Class I malocclusions. All the patients in Class II and III orthodontic cases were treated

with class II and III inter-maxillary elastics respectively while in some Class II cases a

ForsusTM (3M Unitek Corporation,Monrovia,CA) was used for that purpose due to poor

compliance reasons.

A comparison of mean difference between pre-treatment (T1) and post-treatment (T2)

measurements was performed in order to observe if there is a difference in the movement

during treatment by malocclusion classification. Negative values indicated a backward

movement and positive values indicated forward movement of the maxillary incisors

respectively. The null hypothesis is rejected when the p-value is <0.05.

A comparison of mean difference between the post-treatment measurement and normal

value by occlusion class was performed in order to show if there is a difference in how

far the measurements are from the normal value by occlusion class. The results of this

comparison are presented in Table 6 and Figure 1. According to p-value, the post-

treatment values of ANB, Wits appraisal, U1-NA mm, U1-FH mm, IMPA and U1-L1°

show a statistically significance among the Class I, II and III when are compared to the

normal value. However, the U1-SN°, U1-PP° do not show a significant difference from

25

the normal value, with the Class III to present the most positive values for the maxillary

incisors, followed by Class I and Class II malocclusion. From the above could someone

observe that there is a significant amount of dento-alveolar compensation for the

maxillary incisors not only in treated Class II and III but also in Class I malocclusions?

On the other hand, the ANB ° changes happened with orthodontic treatment in Class I, II

and III are statistically significant with the greater changes happened in class III

malocclusion.

In order to determine if there is a significant difference in the post-treatment position of

maxillary incisors among Class I, II and III we used a range for the maxillary incisor

position changes. Table 7 shows, whether the post-treatment measurement falls within

2mm/degrees of the normal value. If the p-value is significant, then the mean value is not

within 2mm/degrees of the normal value.

In Table 7, we see that very few cephalometric measurements were not statistically

different within 2 units of the normal value. In both the class I and II malocclusions the

measurements which fall within the range of 2± are the Wits and L1-APO whereas in the

class II malocclusion the U1-Na mm is the only one. In the class III the only

measurement within the 2± range, is the L1-Apo mm. From looking over the results,

Class III has a tendency to show more positive U1-SN°, U1-NA°, U1-NA mm and U1-

FH mm of the normal, followed by Class I and Class II respectively. Although, the U1-

PP ° is not within the 2± range, it seems to have almost the same mean difference

between Class I and III, but with a high variability in the range of movement of the

maxillary incisors position. The only cephalometric measurement that falls within the

range of ±2 for all three malocclusions is the L1-Apo mm. However, the L1-MP°

26

presents the most negative mean difference within the range of ±2 in the Class III

malocclusion showing the greatest dento-alveolar compensation of the lower central

incisors happened both due to continuous growth of the mandible and the effect of Class

III inter-maxillary elastics. On the other hand , L1-MP ° in the class II malocclusion

shows a positive mean difference within the range of ±2 , showing the proclination of the

lower incisors by using Class II elastics for the correction of the Class II malocclusions.

The results of the analysis suggest that, the direction of movement during treatment is

similar between Class I and III but not in the class II and the post-treatment position of

the maxillary incisors depends on malocclusion.

Table 5. Comparison of mean difference between pre- and post-treatment cephalometric measurements by occlusion class Class I Class II Class III

Normal Mean difference from pre-treatment value

Mean difference from pre-treatment value

Mean difference from pre-treatment value p-value*

ANB(°) 1.6 -0.22±1.05 -1.34±1.30 -0.25±1.96 0.0057 Wits Appraisal(mm) -1 0.55±2.04 -2.03±2.47 0.30±2.19 <0.0001 SN-GOGN(°) 33 -1.05±4.05 -0.41±6.98 0.70±3.52 0.4077 FMA(MP-FH)(°) 25 0.45±5.19 0.29±3.44 0.17±5.52 0.9748 U1-SN(°) 102.3 7.55±6.65 5.61±9.78 6.50±8.62 0.1652 U1-NA(°) 22.8 6.74±6.90 6.50±8.62 4.17±6.86 0.3457 U1-NA (mm) 4.3 1.03±1.52 1.15±2.41 1.24±3.55 0.9527 U1-(per to FH)mm 3.2 0.20±2.19 0.15±2.12 3.55±0.77 0.5424 U1-PP(°) 110 5.94±7.75 6.55±7.72 0.92±21.87 0.2441 U1-Oc.Pl(°) 57.6 -5.56±5.80 -7.52±6.60 -3.48±7.79 0.0750 L1-APO(mm) 2.7 0.89±1.78 2.15±1.33 -0.82±2.53 <0.0001 IMPA(L1-MP) 95 2.49±8.58 2.95±5.21 -3.43±7.27 0.0011 U1-L1 (°) 130 -5.97±14.45 -9.19±10.03 -1.00±11.29 0.0344 * P-value based on analysis of variance

27

Table 6. Comparison of mean difference between post-treatment cephalometric measurements with respective normal value by occlusion class Class I Class II Class III

Normal

Mean difference from

normal Mean difference from

normal Mean difference from

normal p-value* ANB(°) 1.6 -0.35±1.10 2.04±1.67 -3.00±1.73 <0.0001 Wits Appraisal(mm) - 1 0.47±1.91 1.10±2.21 -2.86±-2.86 <0.0001 SN-GOGN(°) 33 -1.09±6.73 0.90±7.36 -1.54±6.13 0.3341 FMA(MP-FH)(°) 25 -1.24±4.66 -0.69±4.57 -3.28±6.07 0.1271 U1-SN(°) 102.3 8.45±8.55 3.68±3.68 10.73±7.84 0.0021 U1-NA(°) 22.8 6.87±7.03 1.97±5.64 8.98±5.73 0.0001 U1-NA (mm) 4.3 1.49±1.77 -0.84±1.60 2.80±2.73 <0.0001 U1-(per to FH)mm 3.2 2.85±1.92 1.54±1.68 4.27±2.48 <0.0001 U1-PP(°) 110 6.45±5.89 4.66±5.51 6.42±20.72 0.8368 U1-Oc.Pl(°) 57.6 -0.92±5.54 -1.70±3.72 -2.08±5.17 0.6444 (L1-APO)(mm) 2.7 -0.05±2.02 0.40±2.08 -0.29±2.71 0.5018 IMPA(L1-MP) 95 -1.85±7.43 2.65±7.65 -11.06±8.60 <0.0001 U1-L1 (°) 130 -5.83±9.12 -8.58±7.73 1.57±8.82 <0.0001 * P-value based on analysis of variance

28

Table 7. Equivalence tests for post-treatment cehpalometric measurement compared to the respective normal value Class I Class II Class III

Mean diff from

normal (90% CI)

Equivalence(

p-value

Equivalent Y/N

Mean diff from

normal (90% CI)

Equivalence

p-value

Equivalent Y/N

Mean diff

from normal (90%

CI)

Equivalence

p-value

Equivalent Y/N

ANB(°)

-0.35 (-0.69-[0.01])

<0.0001 Yes 2.04 (1.52-2.56)

0.5473 No -3.00 (-3.53-[-

2.46])

0.9982 No

Wits Appraisal(mm)

0.47 (-0.24-1.19)

<0.0001 Yes 1.10 (0.42-1.79)

0.0171 Yes -2.86 (-3.50-[-

2.23])

0.9862 No

SN-GOGN(°)

-1.09 (-3.18-0.99)

0.2331 No 0.90 (-1.39-3.18)

0.2100 No -1.54 (-3.45-0.46)

0.3432 No

FMA(MP-FH)(°)

-1.24 (-2.98-0.50)

0.1886 No -0.69 (-2.11-0.72)

0.0641 No -3.28 (-5.17-[-

1.40])

0.8718 No

U1-SN(°)

8.45 (5.80-11.10)

0.9999 No 3.68 (1.69-5.66)

0.9189 No 10.73 (8.30-13.17)

1.0000 No

U1-NA(°)

6.87 (4.69-9.05)

0.9997 No 1.97 (0.22-3.72)

0.4872 No 8.98 (7.20-10.75)

1.0000 No

U1-NA (mm)

1.49 (0.94-2.04)

0.0641 No -0.84 (-1.33-[-

0.34])

0.0002 Yes 2.80 (1.96-3.65)

0.9408 No

U1-(per to FH)mm

2.85 (2.26-3.45)

0.9894 No 1.54 (1.01-2.06)

0.0712 No 4.27 (3.50-5.04)

1.0000 No

U1-PP(°)

6.45 (3.24-9.66)

0.9959 No 4.66 (2.95 -6.37)

0.9934 No 6.42 (-0.003-12.85)

0.8741 No

U1-Oc.Pl(°)

-0.92 (-2.64-0.80)

0.1464 No -1.70 (-2.86-[0.54])

0.3292 No -2.08 (-3.68-[-

0.48])

0.5321 No

L1 Protrusion(L1-APO)(mm)

-0.05 (-0.80-0.70)

<0.0001 Yes 0.40 (-0.25-1.04)

0.0001 Yes -0.29 (-1.13-0.55)

0.0008 Yes

IMPA(L1-MP)

-1.85 (-4.16-0.45)

0.4573 No 2.65 (0.28-5.02)

0.6775 No -11.06 (-13.73-[-8.40])

1.0000 No

Interincisal Angle U1-L1 (°)

-5.83 (-8.66-[-

3.00])

0.9856 No -8.58 (-10.98-[-

6.18])

1.0000 No 1.57 (-1.16-4.31)

0.3964 No

* P-value based on equivalence t-test using (-2,2) as the test range † Comparisons that are equivalent note that the 90% confidence interval of the mean difference from normal falls between -2 and 2 (degrees or mm)

29

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

Mea

n di

ffere

nce

(mm

or

degr

ees)

Mean difference between post-treatment and normal cephalometric

measurements by occlusion class

Class I

Class II

Class III

Figure 1

30

Table 8. Intra-and inter-rater reliability for measurements stratified by initial and final measurements

Intra-rater Inter-rater

Initial Final Initial Final

ANB(°) 0.952 0.787 0.974 0.701 FMA(MP-FH)(°) 0.994 0.907 0.994 0.808 IMPA(L1-MP) 1.000 1.000 1.000 0.997 Interincisal Angle U1-L1 (°) 1.000 0.999 0.623 0.984 L1 Protrusion(L1-APO)(mm) 0.993 0.994 0.993 0.991 Lower Lip to E-Plane(mm) 1.000 1.000 1.000 0.991 Nasolabial Angle 1.000 1.000 1.000 1.000 SN-GOGN(°) 0.000 0.984 0.000 0.986 SNA 0.992 0.987 0.992 0.988 SNB 0.991 0.995 0.989 0.993 Soft tissue convexity 1.000 0.996 0.999 1.000 U1-(per to FH)mm 0.990 0.940 0.881 0.740 U1-NA (mm) 0.941 0.980 0.949 0.953 U1-NA(°) 0.990 0.999 0.799 0.987 U1-SN(°) 0.999 0.998 0.844 0.921 Upper Lip to E-Plane(mm) 1.000 1.000 1.000 0.964 Wits Appraisal(mm) 0.990 0.996 0.995 0.995

* Based on Shrout-Fleiss reliability, where 1 denotes excellent reliability and 0 denotes no reliability

31

CHAPTER 4 DISCUSSION

To date, few studies of significant sample size have been published on the use of

maxillary incisors position as a reference point in diagnosis and orthodontic treatment.

Therefore, the goal of this retrospective cohort study was to evaluate the post-treatment

values of maxillary incisors and determine if there is any significant difference in their

final position among Class I, II and III malocclusions.

According to the inclusion criteria of this study, nighty subjects were collected from the

UAB orthodontic clinic at the University of Alabama at Birmingham. All the above

orthodontic cases were treated with fixed appliances and according to the standards of

American Boards. All the cases were treated using with MBT bracket prescription and

the final archwire size was a 19x25 SS .In this study, they have been used the following

cephalometric analyses: Downs, Steiner, McNamara and Fastlicht Tetragon. All the

lateral cephalometric radiographs were taken using the Orthoceph0c100D x-ray machine

(Finland) and traced digitally using the Dolphin management Version

05.05.5070.221436(US &Canada).

By using a range of Sn-Go between 26° and 38° and with an ANB° between -2° and 6°

,we consider our sample to represent an average orthodontic treatment complexity for an

orthodontist. In this study the average post-treatment values of U1-PP° was 116° in both

Class I and III whereas this angle was 114° for Class II. In comparison to McLaughlin’s

study, regarding the U1-PP normal value after the orthodontic treatment, in this study

32

there is an additional difference of 14° in the Class II(114° instead of 100°) and 4 ° less in

the Class III (116° instead of 120°) .In this study, the average post-treatment value of

U1-PP in the Class I is 116°, (similar with the Class III malocclusion in this study) is in

agreement to McLaughlin’s17 study in which the average post-treatment value of U1-PP°

is between 108°-117° . At this point we need to mention that all of the orthodontic cases

in this study presented a moderate amount crowding with the greatest amount of

crowding presented in Class I malocclusions.. In the literature, the maxillary incisors

position is important because of their effect on space within the dental arches. In extreme

cases, incisor protrusion can produce an ideal alignment of the teeth instead of sever

crowding of teeth, at the expense of lip competence. From the above we can assume that

both the angulation and inclination of the maxillary incisors just after the alignment and

before the correction of it , should be greater in comparison to their pre-treatment values.

Further comparing our findings with literature, Bhasin16 found that the post-treatment

reduction of U1-PP angle to be reduced significantly in skeletal class II patients followed

by class I and least for class III patients. Our data, in Class I and III show that U1-SN °,

U1-NA°, U1-NA mm and U1-OC° angles have a similar both movement direction, but in

class II although the U1-Na° is slightly increase the U1-FH is reduced with a movement

in a negative direction. On the other hand, in Class III, the U1-PP° angle seems to have a

greater positive movement in a forward direction which is in agreement with Bashin 16

study which showed that in skeletal class III cases the upper incisors were proclined in

60% of the cases .

In table 7, we observe that the only equivalent cephalometric measurement among the

three malocclusions within the range of ± 2, is the L1-APO whereas both IMPA° and

33

U1-L1 ° are not. More specifically, it seems that the IMPA ° plays a more important role

in the correction of Class III malocclusions compared to class II malocclusions which is

in not in agreement with Bibby 21. The U1-L1 seems to be decreased more in class II

compared to Class I malocclusion whereas it shows a slightly increase in the Class III

malocclusions..

In this study, both millimetric and angular cephalometric measurements were used to

determine the maxillary incisors position changes relative to the anteroposterior

position of this tooth in facial complex . Further comparing the U1-NA mm and U1-FH

mm , it seems to be a greater inclination of the maxillary incisors for the Class I and

Class III compared to a lesser value of U1-FH mm and a negative inclination changes

of U1-NA mm in Class II malocclusions33,34. By looking at U1-NA mm (Table 6) we

can see that the malocclusion with the greater post-treatment proclination of upper

incisors is the Class III which also presents the most negative change in ANB .The

negative ANB post-treatment changes in Class III malocclusion might not be only

caused of the jaws relationship each other but also because the backward movement of

point A due to proclination of the upper central incisors. The last phenomenon is in

agreement with BeGole 22 who showed that the SNA° was reduced by 1.6 ° due to

proclination of maxillary teeth. On the other hand, the proclination of maxillary incisors

accompanied by backward movement of incisor root apex caused posterior movement of

point A but this does not significantly affect the SNA°.19 20 21 The inclination changes of

U1-NA mm in Class II, seem to be within the range of -2 and 2 mm according with

the equivalent tests for post-treatment cephalometric measurements compared to the

respective normal value whereas is not for maxillary incisors angulation as the U1-NA°

34

shows . Figure1, shows that both U1-FH and U1-NA mm post-treatment values compared

to U1-SN° and U1-NA° seem to be less influenced after orthodontic treatment. From the

above we can assume that the class II and Class III inter-maxillary elastics influence

more the inclination and less the angulation of the upper maxillary teeth during the

orthodontic treatment. In literature is also mentioned that using Class II elastics in a long-

term period has a side effect to upright the maxillary incisors.

By comparing the post-treatment changes in ANB the smallest amount of changes was in

Class III followed by Class I and Class II respectively. On the other hand, by relating the

post-treatment changes happened in the inter-incisal angle we observe that both in Class I

and Class II there is a tendency for decreasing this angle whereas for Class III this angle

tends to be increased . From the above we can conclude that the greater the skeletal

discrepancy initially in both Class I and II , the lesser the inter-incisal angle would be

after treatment ,whereas in Class III there seems that the inter-incisal angle have a

tendency for increasing mainly due to the dento-alveolar compensation of lower incisors

.12 From the above, the ideal inter-incisal angle of 131° according to Steiner or Down’s

of 135.4° seems to be not a realistic goal for every orthodontic case since it depends on

the skeletal discrepancy of jaws.14

Statistical analysis yield high standard deviations for most measurements and variables

investigated. This is due in part to the different orthodontic treatment methods used for

the correction of malocclusion in class I, II and III, but also the small range ±2 used in

the equivalent test. Although in this study the final archwire size for all the selected cases

was 0.019 x 0.025 SS, it is not only unknown the bracket placement method used in our

sample but also the duration of wearing the inter-maxillary elastics for the correction of

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Class II and III which both of them could influence the final position of maxillary central

incisors .48,49,52.

Future studies could attempt to have a more uniform sample with regard to the amount of

crowding presented among Class I, II and III malocclusions. It seems that the final

position of maxillary incisors was not only influenced by both their pre-treatment

position and the jaw discrepancy but also by their variability of crowding among the

malocclusions. From the above, we could compare more precisely the final position of

maxillary teeth among the three malocclusions. By relating the data presented in this

study, it may be possible to meet this goal.

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CONCLUSIONS

There is a significant difference in the positioning of the maxillary incisors among the

class I, II and III malocclusions. The post-treatment measurements such as U1-FHmm,

U1-NA mm and U1-SN° and U1-NA° present a significance difference among Class I, II

and III malocclusions. In In the class II, the maxillary teeth showed to be more upright

than Class I and III malocclusions after orthodontic treatment.

The U1-PP° showed no significant difference among the malocclusions. In this study, the

U1-PP° was the same for the Class I and III.

The U1-L1° presented a significant difference among the 3 malocclusions with the

greatest amount of reduction in Class II, followed by Class I malocclusion. On the other

hand, this angle was increased in Class III malocclusions. From the above we can

conclude that the greater the skeletal discrepancy initially in Class II, the lesser the inter-

incisal angle would be after treatment. Whereas, in Class III it seems that the inter-

incisal angle has a tendency to increase due to the dento-alveolar compensation of

Maxillary and mandibular incisors(U1-Namm and L1-MP°) .

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APPENDIX A

INSTITUTIONAL REVIEW BOARD APPROVAL

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