Myodynamic Appliances:

The development of the myodynamic appliances is due to ingenuity of H.P. Bimler.

I. Petrovic, McNamara substantiate the Andressen-Haupl concept:

• Myotactic reflex activity and isometric contraction induce musculoskeletal adaptation by introducing a new mandibular closing pattern.

• Muscle function with kinetic energy and intermittent forces.

• Stimuli from the activator and muscle receptors and periodontal mechanoreceptors promote displacement of mandible.

• LPM play the most important role in adaptations.

Myotonic Appliances:

II. Selmer-Olsen, Herren, Harvold and Woodside:

• Viscoelastic properties of the muscles and stretching of soft tissues are decisive for activator action I.e. skeletal adaptation.

• During each application of the force, secondary forces arise in the tissues, introducing a bioelastic process.

• Depending on the magnitude and duration of the applied force, the viscoelastic reaction can be divided into the following stages:- Emptying of vessels - Pressing out of interstitial fluid - Stretching of fibers - Elastic deformation of bone - Bioplastic adaptation

•Skeletal adaptation in the vertical plane alone according to Woodside.

The vertical displacement of the mandible was increased first in order to prevent the loss of appliance during the sleep. The gradual increase in the interocclusal distance during the years apparently was due to clinical experience. Thus, the myodynamic activator of Andresen become the myotonic appliance of Andersen-Haupl-Petrik.

• The effect of muscular pressure is increased by immobilizing the activator.

• The construction bite dislocates the mandible in a vertical and sagittal direction. Additional pressure is obtained by increase of dislocation in either direction.

Functional Regulator of Frankel:

• The Frankle’s approach differ from other methods because he makes the oral vestibule the “operational basis” for his treatment.

• According to Kraus, the physiological development of the motor stereotype in muscular action in the orofacial system is interrupted by the results of a substitute, thumb, or tongue sucking, leading to a functional disturbance in the formation of the skeletal components.

• Frankel is in agreement with Kraus that malocclusion, especially that caused by crowding of the teeth, may result from a disturbance of the tonus as well as of the function of the perioral muscles, and this is the keyproblem for successful treatment.

• Widening of dental arches achieved by Franklel

• The stability of results achieved by FR, therefore, interpreted as connected with a change in the original muscular balance and the establishment of a new balance.

The Functioning Space:

•S.F. Fish – denture study

• Surgical repositioning of mandible

Head Posture and Craniofacial Morphology:

The comprehensive system of associations between the varieties expressing the size, shape and position of the craniofacial components and those expressing the postural relationships of the head and cervical column, clearly indicates a relationship between craniofacial morphology and head posture.

Moss and Young have emphasized that morphology of craniofacial skeletal is determined by surrounding functional matrix.

The treatment with functional appliances was based on a simple concept of influencing muscle activity in this region, learning a lesson from morphological adaptability seen with aberrant muscle patterns and changing head posture.

CONSTRUCTION BITE

The determination of the proper construction bite is critical for a functional appliance to succeed. More failures result from incorrect posturing of the mandible

The Vertical Opening of the Mandible:

The amount of vertical opening of the construction bite is still a subject of some considerable controversy despite long clinical experience.

The vertical opening of the mandible is dependent on three major considerations. (1) the kind of dysgnathic or dysplastic problem (sagittal and vertical relationships, morphogenetic growth pattern); (2) the developmental state, sex, and age of the patient (potential incremental changes); and (the type of functional appliance).

Types of Malocclusion:

The Horizontal Posturing of the Mandible:

There are four possibilities for posturing the mandible in the sagittal or anterioposterior dimension for the functional orthopedic appliance.

1. The original sagittal jaw relationship may be maintained, as in a neutroclusion.

2. The mandible may be postured forward to change the sagittal relationship equally on both sides when the problem is a bilaterally symmetrical Class II condition.

3. The bite is changed on one side but is maintained as much as possible on the other side, as with a unilateral class II, Division I malocclusion, Class II, Division 2 malocclusion, or a Class III malocclusion.

Analysis of the Construction Bite Maneuver:

• Functional retrusion, with the path of closure upward and backward from postural rest to occlusion, sagittal correction compensation will be less.

• It is good treatment planning to allow the mandible to come forward a bit, even in a Class I deep bite malocclusion.

• Class II malocclusion may be a mesial position of the maxilla.

• Class I case with an inverted bite (cross bite) of individual or all incisors.

The Magnitude of Horizontal Correction for Class II, Division 1 malocclusions is another controversial question.

The construction bite is shifted as far as the occlusion allows without the creation of a cross bite condition anteriorly or posteriorly for single teeth or groups of teeth. If large width differences exist between the maxillary and the mandibular arches, the shifting, especially in the permanent dentition, is possible only so far that the canines are opposing each other cusp tip to cusp tip. Further mandibular posturing is not to be until the maxillary arch is expanded to prevent cross bite.

Relapse Potential:

Relapse after shifting the bite sagitally with an functional appliance is extremely rare.

Danger of relapse – after transverse widening of dental arches.

Maxillary Protraction Cases:• Class I, Division I malocclusions that are the result of mandibular underdevelopment. • Prognathic maxilla• Cases that are in between the cepahlometric and the cast analysis. • Excessive labial position of the incisors • The forward position of the maxilla is being treated in mixed dentition.

Fabrication of Construction Bite:

Wax Bite Visualization:

• Mixed dentition – the middle of the upper deciduous canine should fit into the embrasure between lower deciduous canine and the first deciduous molar.

• Permanent dentition – the tip of the buccal cusp of the upper first premolar serves well as a guide point. It should fit precisely into the embrasure between the lower first and second premolars.

The Transverse Posturing of the Mandible:

• The upper and lower midlines are coincident in habitual occlusion and the sagittal relationship is bilaterally symmetrical, there is no need to make any transverse compensations.

• The midlines should line up in the forward posturing in the same relationship as in habitual occlusion.

Midline Considerations:

•The upper and lower midlines do not coincide, a determination must be made as to the fault-maxillary or mandibular.

• The patient is observed in the postural rest to full habitual occlusion. If there is any shift from one side to another, the occlusal interference should be checked.

• Dental midline discrepancies – corrected later with fixed appliances.

• If the teeth in each jaw line up with the respective basal midlines but are not coincident in habitual occlusion with the midline of the other jaw. The clinician must use the jaw midlines to determine the construction bite relationship.

• Cross bite

• Tooth size discrepancy

The Construction Bite Technique:• Patient compliance is essential • Patient motivation compliance • Instant correction • Clinical maneuver

Study Model Analysis:

•The first permanent molar relationship in habitual occlusion is determined.

• The nature of the midline discrepancy, if any, is determined. If the midlines are not coincident, a functional analysis should be made on the patient to determine the path of closure from postural rest to occlusion.

• The symmetry of dental arches is determined.

• Curve of spee

• Crowding and any dental discrepancies are checked and measured.

Functional Analysis:

The functional analysis is performed before taking the construction bite to obtain the following information:

1. The precise registration of the rest position is made. The vertical opening of the construction bite depends on this.

2. The path of closure from postural rest to habitual occlusion is analyzed. Any sagittal or transverse deviations are recorded.

3. Prematurities, point of initial contact, occlusal interferences, and resultant mandibular displacement, if any, are checked. Some of the dysfunctions can be eliminated with the activator, but some require other therapeutic measures.

4. The TMJ is carefully palpated for clicking, crepitus, and so forth, which might be characteristic of a functional abnormality or indicative of the need for some modification of the design of the appliance.

5. The interocclusal clearance or freeway space is checked severaltimes, and the mean amount is recorded.

6. Respiration

Cephalometric Analysis:

The most important information required for planning for the construction bite includes the following:-

1. The direction of growth

2. The differentiation between the position and the size of the jaw bases.

3. The morphological characteristics

4. The axial inclination and the position of maxillary and mandibular incisors.

Anterior Positioning of the Mandible:

The usual intermaxillary relationship for the average Class II problem is that of an end to end incisal relationship. However, it should not exceed 7 mm to 8mm or three quarters of the mesiodistal dimension of the first permanent molar. Anterior positioning of this magnitude is contraindicated in following instances.

1. If there is severe labial tipping of the maxillary incisors.

2. If overjet is too large.

3. If one of the incisor usually the lateral incisor erupted markedly to the lingual.

Opening of the Bite:

There are some guiding principles in maintaining the proper horizontal vertical relationship in determining the height of the bite.

• The mandible must be dislocated from the resting position in at least one direction sagitally or vertically.

• If the magnitude of forward position is great 7 to 8mm, the vertical opening should be minimal.

• If the vertical opening must be extensive, the mandible must not be anteriorly positioned. If the bite opening is more than 6mm, the mandibular protraction must be very slight.

General Rules for Construction Bite:

1. If the forward positioning of the mandible is 7mm to 8mm, the vertical opening must be slight to moderate (2mm-4mm).

2. If the forward positioning is no more than 3mm to 5mm, the vertical opening should be 4mm to 6mm.

3. Lower midline shifts

The construction bite prepared on casts has the following disadvantages:

1. The appliance does not fit.

2. There is asymmetrical biting on the appliance.

3. The patient is not really comfortable and there are more frequent disturbances during sleep.

4. The likelihood of unwanted lower incisor procumbency is greater because the appliance exerts undue stress on these teeth.

Technique for the Low Construction with a Marked Forward Positioning of the Mandible:

• Class II functional retrusion cases.

• The mandible moves mesially to engage the appliance, the elevator muscles of mastication are activated.

• The horizontal “H” activator.

• The indication for anterior posturing of the mandible is not only an original posterior position but also the likelihood of a favorable growth pattern.

Technique for a High Construction Bite with Slight Anterior Mandibular Positioning:

Depending on the magnitude of the interocclusal space, the vertical dimension is opened 4 to 6mm, a maximum of 4mm beyond the postural resting vertical dimension registered. The appliance induces activation of myotactic reflex in the muscles of mastication. The stretch reflex activation with increased vertical dimension may well influence the inclination of maxillary base. This appliance is indicated in vertical growth patterns.

The Class II, Division I malocclusion with a vertical growth direction cannot be significantly improved sagitally by anterior positioning of the mandible. There is danger of dual bite.

The Technique for Construction Bite without Forward Positioning of the Mandible:

Such appliances are primarily used in vertical dimension problems (deep overbite and open bite) and in selected cases of crowding.

• Dentoalveolar overbite problems

• Deep overbite cases caused by supraocclusion of the incisors

• The skeletal deep overbite

• Open bite

Arch Length Deficiency Problem:

The malocclusions with crowding can sometimes be treated with activators. In these cases, low construction bite is used since jaw positioning and growth guidance by selective eruption of teeth are not desired.

Constructing Bite with Opening and Posterior Positioning of the Mandible for Class III Malocclusions:

The construction bite is taken by retruding the lower jaw. The extent of the vertical opening depends on the amount of retrusion that is possible.

• Tooth guidance or functional protrusion Class III malocclusion

• Pseudo Class III malocclusion

• Skeletal Class III malocclusion

CEPHALOMETRIC DIAGNOSIS FOR FUNCTIONAL APPLIANCE

THERAPY

The most functional appliance therapy is instituted in the

mixed or transitional dentition stage (at 8 to 9 years), assessment

criteria are adapted to this age period. However, they can be

used equally well to follow the progress of each patient into the

adult dentition.

Four major areas of emphasis exist in cephalometric diagnostic

assessment for patients treated with functional appliances and

functional appliance-headgear orthopedics:

1. Accomplishment of growth increments and the direction or

vector of growth.

2. Assessment of magnitude of growth change.

3. Inclination and position of the upper and lower incisors.

4. Radiographic cephalometrics. It can differentiate between

skeletal and dentoalveolar malocclusions and provides

information on the combination of factors involved in both

areas.

Angular Measurements:

Code DefinitionMean value

(degrees)

1. N-S-Ar Saddle angle 123 ± 5

2. S-Ar-Go Articular angle 143 ± 6

3. Ar-Go-Me Gonial angle 128 ± 7

4. Sum Sum of saddle, articular, and gonial angles 394

5. Ar-Go-N Go 1, upper gonial angle 52 to 55

6. N-Go-Me Go 2, lower gonial angle 70 to 75

7. S-N-A Anteroposterior position of maxilla 81

8. S-N-B Anteroposterior position of mandible 79

9. A-N-B Difference between S-N-A and S-N-B 2

Code DefinitionMean value

(degrees)

10.S-N-Pr Anteroposterior position of alveolar part of premaxilla prosthion)

84

11. S-N-Id Anteroposterior position of alveolar part of mandible (infradentale)

81

12. Pal-MP Angle between palatal and mandibular planes

25

13. Pal-Occ Upper occlusal plane angle 11

14. MP-Occ Lower occlusal plane angle 14

15. S-N-MP Angle between S-N and the mandibular plane

32

16. Pn-Pal Angle of inclination (/) between a perpendicular line dropped from Se-N at Nc and the palatal plane

85

17. N-S-Gn (Y-axis) Angle between S-N and S-Gn anteriorly

66

Code DefinitionMean value

(degrees)

18. 1-SN Angle between the upper incisor axis and S-N posteriorly

102

19. 1-Pal Angle between the upper incisor axis and palatal plane anteriorly

70 + 5

20. 1-MP Angle between the lower incisor axis and mandibular plane posteriorly

90 + 5

21. ii angle Interincisal angle between the upper and lower central incisor axes posteriorly

135

Code DefinitionMean value

(degrees)

1. S-N (Se-N) Anteroposterior extent of the anterior cranial base

71

2. S-Ar Extent of the lateral cranial base 32 to 35

3. S-Go Posterior face height

4. N-Me Anterior face height

5. Max Base Extent of the maxillary base correlated with Se-N

6. ManBase Extent of the mandibular base correlated with Se-N

7. R asc Extent of the ascending ramus correlated with Se-N

Linear Measurements:

Code DefinitionMean value

(degrees)

8. S’-F Ptp Distance from S’ to the projection of the anterior wall of the pterygopalatine fossa on the palatal plane, an expression for anteroposterior displacement of the maxillary base

9. S-S’ Deflection of the maxillary base 42 to 57

10. 1 to N-Pog

Distance from the incisal edge of the upper incisor to N-Pog

11. 1 to N-Pog

Distance from the incisal edge of the lower incisor to N-Pog

Analysis of Facial SkeletonSaddle angle (N-S-Ar): Large saddle angle usually signifies a posterior condylar position and a

mandible that is posteriorly positioned with respect to cranial base and maxilla.

A non-compensated posterior positioning of the mandible is caused by the large saddle angle is very difficult to influence with functional appliance therapy.

Articular Angle (S-Ar-Go):It can be influenced during orthopedic or orthodontic therapy. It decreases with anterior positioning of the mandible, closing of the bite and mesial migration of posterior segment teeth and increases with posterior relocation of mandible, opening of bite and distal driving of posterior teeth.

9 year old children – horizontal 139.5 degree vertical 142.4 degree

Gonial Angle (Ar-Go-Me):Patient with large gonial angle activator treatment is

contraindicated. 9 year old mixed dentition children – horizontal growth pattern – 125.5o

vertical growth pattern – 133.4o

Anterior and posterior face height: Posterior facial height – horizontal growth pattern – 69.5 mm

vertical growth pattern – 64.1 mm The growth between 9 to 15 years – horizontal – 11.05mm

vertical – 10.8 mm

Anterofacial Height:

Horizontal – 103 mm – Growth increment – 12.18 mm

Vertical – 106.6 mm – Growth increment – 12.18 mm

Anterior Cranial Base Length:

9 year old child – horizontal – 68.8 mm – growth increment – 4.46

vertical – 63.8 mm – growth increment – 3.52

Posterior Cranial Length (S-R):

9 year old children – horizontal – 32.2mm – increment – 9.16

vertical – 30 mm – increment – 4.47 mm

Analysis of Jaw Bases:S-N-A:

Growth directionS-N-A angle (degrees)

9 years 15 years

Average 79.5 81.28

Horizontal 79.73 81.57

Vertical 79.0 80.57

S-N-B:Horizontal (77.2 at 9 years and 80.5 degree a 15 years)Vertical (74.3 degree at 9 years and 75.9 degree at 15 years)

Base Plane Angle:

Horizontal 23.4 degrees at 9 years and 20.5 degrees at 15 years

Vertical 32.9 degrees at 9 years and 30.9 degrees at 15 years.

Inclination Angle:

A large angle expresses an upward and forward inclination

whereas a small angle indicate down and back tipping of the anterior end

of the palatal plane and maxillary base.

Rotation of Jaw Bases:

The baseplane angle and inclination angle are used to evaluate the

rotation or upper and lower jaw bases.

The rotation of the mandible is growth conditioned and depend on the

direction and mutual relations of growth increment in the posterior

condyler and anterior facial skeletal.

If the condylar growth proceeds the greater rate, horizontal rotation results. Bjork differentiated two processes involved in rotation of mandible. Remodeling of mandible in the sympheseal and gonial areas. The Vertical or horizontal rotation of mandible in its neuromuscular

envelop. The mandibular rotation is caused by growth dependent and functional influences.

Linear Measurement of Jaw Bases:

N-Se : ManBase 20:21

Ascending ramus: ManBase 5:7

MaxBase : ManBase 2:3

Extent of Mandibular Base:

3 mm longer Se-N until the twelfth year and 3.5mm after the

twelfth year.

A length of 5mm of less than this average is considered within

normal limits until 7 years, however and a length of 5mm or more is

normal until 15 years.

In horizontal – 9 year – 67.59 mm

15 year – 77.35 mm

Vertical – 9 year – 65.23 mm

15 year – 73.5 mm

Extent of Maxillary Base:

Horizontal – 9 year – 44.56 mm

15 year – 48.6 mm

Vertical – 9 year – 44.00mm

15 years – 47.16 mm

Length of Ascending Ramus:

Horizontal – 9 year – 48.9mm

15 year – 58.67 mm

Vertical – 9 year – 44.47 mm

15 year – 51.7 mm

Analysis of Dentoalveolar Relationships:

Axial Inclination of Incisors:

Upper incisors (U1-Sn):

7 year – 94 to 100 degrees

After eruption of permanent teeth – 102 degrees

Lower incisors (IMPA):

6 – 12 years it increases from 88 to 94

Smaller angle – advantageous for functional appliance treatment.

Position of Incisors:

The average position of maxillary incisor is 2 to 4 mm anterior to

N-Pog line. The lower incisor vary from 2mm posterior to 2 mm anterior

to this line.

CYBERNETIC THEORY

Cybernetics and control theory are in this respect new and

powerful tools. They help clinicians rigorously address the study of

communications, control mechanisms, and organizations in both living

and technologic systems. In other words they provide a language of

combined analysis and a systemic approach to biology and the

biomedical sciences. They make it possible to account for the properties

of normal or abnormal systems as an emergence from the organization

of connectivity relations. Modern orthodontists must become acquainted

with the cybernetic language, because cybernetic thinking is the primary

route to data processing and computerizing for the twenty-first century.

• Formation and renewal of the craniofacial skeleton are many-faceted

phenomena.

• The connections between constituents are complex, although the

constituents themselves are not.

• The complexity results from the organization, the structured whole

that is infinitely more complex than the sum of its constituents.

• The identification and analysis of feedback loops (i.e. regulation

processes) are among the main tasks in the field of craniofacial

growth.

• The research measures simultaneously the spontaneous or

experimentally and therapeutically induced variations of a stimulus

(input) and the variations of one or several responses (output).

• the output is related to the input by a transfer function that

characterizes the system under investigation. The system is thus

described as a function of changes affecting the various parameters.

The control theory is becoming the common language of science

and technology. The definition of concept and terms:

• The command: The command is a signal established independent of

the feedback system under scrutiny. It affects the behaviour of

control system without being affected by the consequences of this

behaviour.

• Reference input elements: This establishes the relationship between

command i.e. growth hormone and the reference input (sagital

position of upper dental arch). They include septal cartilage,

septopremaxillary frenum, labionarinary muscles, and premaxillary

and maxillary bones.

• Reference Input: The reference input is a signal established as a

standard of comparison. Ideally it should be independent of the

feedback.

• The Controller: The controller is located between the deviation signal

and the actuating signal.

• Actuating signal: This corresponds to output signal of controller (the

input signal of the controller system). The activity of LPM and

retrodiscal pad corresponds to the actuating signal.

• Controlled system: The controlled system is part of the control

system between the actuating signal and the directly controlled

variable. An example is the growth of condylar cartilage via

metabolic blood interchange in the retrodiscal pad.

• Controlled variable: This is the output signal of the system. The best

example is the sagittal position of the mandible.

• The Gain: The gain of a system is the output divided by the input.

The gain is greater than 1, amplification is present; if it is less than

one, attenuation is the result.

• Feedback signal: The feedback signal is the function of the

controlled variable that is compared to the reference input.

• The disturbance: Any output other than the reference chosen by the

researcher is considered a disturbance.

• The Attractor: This is the final structurally stable steady state in a

dynamic system. An example is full interdigitation type of occlusal

relationship.

• The repeller: This is the set f all unstable equilibrium states, including

their limit points. An example is the cusp-to-cusp type of occlusal

relationship.

Dia: Maxillary

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Dia: Mandibular

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