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Biologic basis of Functional appliances

INDIAN DENTAL ACADEMY Leader in continuing dental education



Major shift in the past 25 years Multisystem environment More than "straight teeth." Changing of the specialty to Dentofacial Orthopedics • Teeth can literally be used as a handle to manipulate facial changes • Age-oriented therapy (i.e., early treatment) • Literature is ambivalent

INTRODUCTION • Hamilton :Orthodontists are an interesting, com­plex egocentric, 'almost' omniscient, quality oriented and stubborn group • ­85 % agree and 7 % disagree­ alter the skeletal pattern of a growing child, • ­74 % : earlier the correction of the skeletal problem, the greater the chances of success and stability • ­25 % : European colleagues were more advanced in growth guidance. • ­67 % : earlier orthodontics • ­72 % : prevent nonspecialist treatment and inroads by pediatric dentists and general practitioners • ­ 71 % : patient compliance

INTRODUCTION • 78 % : simple biteplate ­ maxillary constriction ­ mandibular entrapment • 21 % : mandibular growth could be stimulated beyond its natural potential. • 59 % :condylar heads of the mandible and glenoid fossa could be remodeled • 96% : Maxillary expansion • 85 % : airway problems • 91 % : prolonged thumb or finger sucking and dummy sucking • 69% : tongue thrust and posture • 80% : no causative relationship between functional appliances and TMDs

INTRODUCTION • Correction of malocclusion, primarily by means of controlled movement of the developing and mature dentition into a desirable occlusal relationship • Control and modification of growth of skeletal structures of the craniofacial complex, especially via tooth borne appliances

Historical perspective • Genetic control theory: ­inheritance and immutability of normal and abnormal facial form ­ genotype supplies all information required for phenotypic expression

Historical perspective • Late 1890s: Wolff’s law and Roux hypothesis: changes in functional stress produced changes in internal bone architecture and external shape • Early 1900s: Pierre Robin: monobloc ­ passive positioning device • Modified from bite jumping vulcanite maxillary guide planes designed by Norman Kingsley (1880) • Vorbissplatte: Hotz

Historical perspective • Viggo Andresen : Activator • Lischer’s theory: If abnormal musculature can exacerbate existing malocclusions, can not the same muscles be used to correct these problems? • Andresen: modified Hawley type retainer with lower lingual horse shoe flange Significant sagittal basal bone and neuromuscular improvement

Historical perspective • Initially not accepted in US: ­ facial growth could not be affected ­ tooth position can be altered with appropriate appliances and biomechanics

Theories of growth • Genetic theory • Sutural growth theory: Sicher (1947): growth at the sutures results in growth of cranial vault and downward and forward growth of the midface • Cartilage­ directed growth theory: Scott (1956): synchondroses, nasal septum and mandibular condyle are centers of growth

Theories of growth • Functional matrix hypothesis: Melvin Moss (1960) • Craniofacial skeleton develops initially and grows in direct response to its extrinsic, epigenetic environment • Functional matrix and skeletal unit • “ Bones do not grow, bones are grown.” (1972)

­ Moss

Theories of growth • Servosystem theory of craniofacial growth: Alexandre Petrovic (1970s) • 2 factors: ­ hormonally regulated growth of the midface and anterior cranial base, which provides a constantly changing reference input via the occlusion ­ rate­limiting effect of growth of the midface on the growth of the mandible


• Growth control involves a multitude of factors • Interaction that occurs among them is often highly important • Local and regional extrinsic factors :tissue contacts, muscles, blood supply and nerve signals • General factors :STH, somatomedin, thyroxine, and sex hormones

Petrovic 1977 • Demonstrate qualitative and quantitative relationship between observed and experimental findings. • Broader understanding of orthodontic problems, and action of appliances • Familiarity of orthodontists with cybernetics


Transfer of Information

• Cybernetic systems operate through transfer of information • Physical, Chemical, Electromagnetic




Cybernetic System Transfer Function



Physiological cybernetic systems

Open loop

Closed loop





Peripheral Central Positive Negative

Open Loop Output has no affect on the input

Closed Loop Relationship maintained between input and output



Feedback Loop

Transfer function


Regulation Type of Closed Loop Input is constant Any change of the input will initiate a “regulatory process� Input


Regulation of input

Transfer function

Servosystem Type of Closed Loop

Components of a Servosystem COMMAND

Reference Input Elements

Actuator, Coupling System, Controlled System

COMPARATOR Output (Controlled Variable)

Central Comparator (sensory engram)

Reference Input

Deviation Signal

Performance Analyzing Elements



Types of Cartilage Primary

Types of Cartilage Secondary

Primary Cartilage: Epiphysis, Synchondrosis, Nasal Septum, Ethmoid Sphenoid Secondary Cartilage: Condyle, Coronoid, Mid Palatal Suture, Fracture Callus

Factors influencing Primary Growth Cartilage

Secondary Cartilage




Local Factors

No (Chondroblasts

Yes (Pre足

Orthopaedic appliances

Only Direction

Direction and Amount

surrounded by matrix) chondroblasts not surrounded by matrix)

Charlier, Petrovic, Stutzmann Strasburg, France

Role of Lateral Pterygoid and Retrodiscal Pad •Blood Supply


Relationship Between Lateral Pterygoid, Retrodiscal Pad and Condyle



Stutzmann and Petrovic

Proper function of Lateral Pterygoid and retrodicsal pad: • Excision of Lateral Pterygoid • Reduced function of the Retrodiscal pad (Rat experiments)

Elastic retrodiscal pad and its condylar attachment • Predominant intermediaries between the variations of LPM activity and the growth of the condylar cartilage in rats and humans • Direct, repetitive stimulation ­ same condylar response as if the muscle were intact. • Adequate blood supply and function are essential.

The Face as a Servosystem

Input – Maxillary dental arch

Output – Adjustment of the position of mandibular dental arch

Growth of the maxilla

Growth in Length

Growth in Width

Growth in Length:

Traction Septo足 Premaxillary ligament


Growth of Nasal Septum


Labio narinary Muscles Release of STH Somatomedin


Growth of Pre Maxillary extremity

Anterior shift Of premaxillary bones

Growth of Premaxillo足 Maxillary suture

Protrusion of Upper Incisors Increased size Of Tongue

Thrust Protrusion of Lower Incisors Direct Action

Growth of Maxillo Palatine suture

Growth in Width: Growth of Lateral cartilaginous masses of Ethmoid

Release of STH Somatomedin

Outward growth Of maxillary bones

Growth of cartilage B/w greater wings & body of sphenoid

Increased size Of Tongue

Outward shift of Alveolus and molars Direct effect

Transverse Separation of premaxillae

Growth of inter Pre Maxillary suture

Transverse Seperation of Horizontal Maxilla and Palatine plates

Growth of mid Palatine suture

Outward Appositional Bone growth

The Face as a Servosystem Release of Hormones (Command)

LPM & RDP (Coupling system)

Position of Maxillary Dental arch (Ref Input)


Growth at condyle (Controlled System)


Periodontium, Teeth Musculature Joint

Actuating signal

Actuator (Motor Cortex) Brain (sensory engram)


Deviation Signal

Mastication (Performance)

Growth at the Posterior Border of the Ramus

Variation in direction and magnitude of condylar growth

Changes in the lengthening of the maxilla.

Resection of the nasal septal cartilage Growth hormone Testosterone Orthopedic appliances

constantly changing reference input upper dental arch

lower arch controlled variable

Subperiosteal ossification rate and alveolar bone turnover • increased in anterior growth rotation • decreased in posterior growth rotation parallels the condylar cartilage growth rate greater responsiveness to orthopedic and orthodontic appliances in cases of anterior growth rotation

Other Terms Related to a Servosystem Gain


Output Input

Enhancement (Gain>1)

Attenuatation (Gain <1)

1. Large amounts of TESTOSTERONE 2. Small or large amounts of 2. Small amounts of OESTROGEN TESTOSTERONE 3. Large amounts of 3. Very small amounts of CORTISONE OESTROGEN 1. STH â&#x20AC;&#x201C; Somatomedin


Cusp to fossa relation


Cusp to cusp relation


Abnormal tooth position Occlusal interferences Arthritis Muscle Inflammation Periodontitis, Pulpitis

Peripheral Comparator Before development of Occlusion:­ •Sensory engram not developed •Servosystem does not operate •Genetic influence on mandibular growth •Anodontia After Development of Occlusion:­ •Sensory engram forms •Peripheral comparator controls growth

Failure of Servosystem to Control Growth • Peripheral comparator faulty – Caries, Mutilated dentition. •Discrepancy between rotation pattern (Anterior or Posterior) and location of comparator.




Catastrophe Theory



Small fluctuatations Different types of occlusal relationships.

Most often in patients between 8足10 yrs old

Mixed dentition therapy is thus strongly supported biologically.

Importance of Discontinuities

•Growth prediction , treatment planning , decision making •Stability of occlusion after it is established •Genotype does not directly influence the phenotype

Functional appliances Place the mandible in a forward postural position Increase the condylar cartilage growth rate and amount. Sagittal deviation produced by the functional appliance decreases thro the supplementary forward growth of the mandible Deviation signal simultaneously decreases Supplementary growth rate of the cartilage and the lengthening of the mandible also decreases

Periodic increase in the thickness

Increases in LPM and RDP activity

Increase in the rate and amount of condylar cartilage growth

• Appliance is removed after the growth is completed ­ little or no relapse • Removed before growth ­ no significant relapse is detected if a good intercuspation is achieved during the experimental phase • If a good intercuspation is not achieved ­ comparator of the servosystem imposes an increased or decreased condylar growth rate until a state of intercuspal stability is established • No genetically predetermined final length of the mandible has been detected in these experiments.

Height of Bifurcation


The Sensory Engram

• Collection of feedback loops • Blueprint of ideal muscular function/position • CNS tends to operate along these feedback loops

Optimality of Function

â&#x20AC;˘Minimum deviation signal â&#x20AC;˘CNS always tries to revert back to optimal position

For every unit of Growth hormone released, the amount of growth in the maxilla is less than in the mandible.

Action of Functional Appliances

Functional appliance

Increased contractile activity of the LPM

Intensification of the repetive activity of the retrodiscal pad (bilaminar zone)

Increase in growth­stimulating factors ­Enhancement of local mediators ­Reduction of local regulators (factors having negative feedback effects on cell multiplication rate)

­Change in condylar trabecular orientation ­Additional growth of the condylar cartilage ­Additional subperiosteal ossification of the posterior border of the mandible.

Supplementary lengthening of the mandible

Two Types of Functional Appliances:

) Activator, Postural hyperpropulsor, Frankel appliance, Twin block, Bionator, Class II Elastics(?)

) Herren activator, LSU activator, Harvold足Woodside activator, Extra oral traction on the mandible.

FIRST GROUP: Position mandible Forward

Increased activity of LPM and RDP

Less fatigable fibres in LPM •Oudet et al (1988) •Carlson et al (1990)

LPM “helped to contract more” by Functional appliances.

CELLULAR LEVEL 1. Precursor Skeletoblast â&#x20AC;&#x201C; pleuripotent, fibroblast like. 2. Prechondroblast â&#x20AC;&#x201C; faster cell cycle, matures into Chondroblast

Chondroblasts lost

Increased multiplication of prechondroblasts

(hypertrophy, surgically removed)

Local control prechondroblasts




Originates from chondroblastic layer â&#x20AC;˘Stutzmann and Petrovic (1982, 1990)

Functional appliances (especially Class II elastics)

Increased activity of RDP Increased nutrients and growth factors supplied and inhibitors removed. Increased mitoses and earlier hypertrophy of chondroblasts.

Reduced negative feedback signal reaching prechondroblasts Increased growth at the condyle

Cytoplasmic junctions between skeletoblasts reduce.

Transmission of inhibitory factors reduce.

Increased mitotic rate and rate of differentiation into prechondroblasts.

SECOND GROUP: Position mandible forward , open in beyond rest position. No increase in activity of LPM •Herren (1953) •Auf der Maur (1978)

Yet there was an increase in growth

wo steps:

) While appliance is worn:足 Forward position Reduction of length of LPM New sensory engram

) While appliance is not worn:足 New sensory engram Functioning in anterior position Increased activity of RDP

Action of first group

while appliance is worn

Action of second

while appliance is not worn


CLINICAL IMPLICATIONS 1) Principle of optimality of function :足 Less relapse tendency if post orthodontic treatment muscular activity produces a lower deviation signal.

2) Removal of functional appliance â&#x20AC;&#x201C; when growth is complete.

3) If removed when growth not complete â&#x20AC;&#x201C; Proper intercuspation.

4) Understanding of when, and for how long a particular functional appliance should be worn. First group â&#x20AC;&#x201C; Full time Second group â&#x20AC;&#x201C; Part time

5) Proper functioning of LPM and RDP important for growth 6) Sensory engram poorly developed in younger children.

7) Utilization of high hormonal activity at puberty.

Drawbacks Lot of importance on condyle: Fracture?

Peripheral comparator (occlusion) discrepancies may be overcome by Dentoalveolar changes.

Occurrence of Class II end on relation is seen often?

Action of reverse pull headgear on maxilla (primary cartilage)

ESTIMATION OF CONDYLAR GROWTH DIRECTION ( Stutzmann & Petrovic ) â&#x20AC;˘ Correlation between the growth direction of the condyle and the sagittal distribution of dividing cells in condylar cartilage

• Charlier et al 1968, 1969, Petrovic et al 1975: Distribution of dividing cells in sagittal section of condylar cartilage of juvenile rats • Histologic and radiographic study • Results: Treatment with both postural hyperpropulsor and and growth hormone STH produced increase in growth rate of condylar cartilage as compared to controls

Activator: • Location of increase of dividing cells: ­ more posterior in hyperpropulsor ­ more anterior in STH

• Supplement of dividing cells mainly occurred in the posterior part of the condylar cartilage • Newly formed endochondral bone trabeculae became oriented in a more horizontal direction • Posterior growth rotation of the condyle

lengthening of preexisting endochondral bone trabeculae under the condylar cartilage

growth of bone trabeculae that are formed in parallel and posteriorly oriented to the condylar cartilage

Formation of Additional Trabeculae

• Backward direction ­ the growth direction of the condyle is more posterior • Vice versa

Variation in condylar cartilage dividing cell number, mandibular length, and trabecular足mandibular plane angle

• Administration of growth hormone and treatment by functional appliance • Administration of testosterone • Resection of the lateral pterygoid muscle • Seasonal Variations

Growth rate increases Angle has the tendency to close Growth rate decreases Angle has the tendency to open.


Effects of STH and Testosterone

Lengthening of the mandible is relatively greater than lengthening of the maxilla

Reduced stimulation of the RDP Dividing cells are relocated in a less posterior direction Newly formed endochondral bone trabeculae become vertically oriented Closing of the angle Anterior growth rotation.

STH or testosterone level rises beyond a certain hormonal level "jumping of the bite" in足creased contractile activity of the LP stimulation of the retrodiscal pad dividing cells are relocated in a more posterior direc足tion opening of the angle posterior growth rotation

Effect of the Postural Hyperpropulsor operation of con足frontation of the two dental arches deviation signal increased postural activity of the LPM posterior rotation

greater the alteration created greater the supplementation of the condylar cartilage growth rate and mandibular lengthening greater opening of the angle tends to decrease and may even become undetectable opening of the angle appears only as a transient, remedial occurrence

Posterior growth rotation Expression of a decreased growth level increased activity of the LPM Retrognathism Posterior growth rotation Less effective Anterior growth rotation More effective

GROWTH ROTATION AND ALVEOLAR BONE TURNOVER OF THE MANDIBLE High alveolar bone formation rate Anterior growth rotation Low alveolar bone formation rate Posterior growth rotation Anterior rotation : high responsiveness of the cells to growth足stimulating factors

CONCLUSION • Condylar growth direction presents spontaneous variations as a function of the age of the animal and the time of year; it can be modified by different experimental conditions • Cybernetic model of the mechanisms controlling mandibular growth based on research findings enables a better understanding of the biologic phenomena involved in mandibular growth rotation • Measurement of this parameter in estimating condylar cartilage growth direction may become a valuable element in diagnosis and projection of treatment effectiveness in dentofacial orthopedics


Studies on functional appliances: Activator: • Petrovic and Stutzmann (1977), rat experiment • Administration of growth hormone and treatment by postural hyperpropulsor: ­ increase in condylar cartilage growth rate ­ hyperpropulsor: opening of Stutzmann angle ­ growth hormone: closing of Stutzmann angle

Studies on functional appliances: Activator: ­ lengthening of mandible measured from posterior edge of condylar cartilage to mental foramen is greater in case of opening of angle â&#x20AC;˘ Administration of testosterone: male rats for 3 weeks; stimulation in growth rate of condylar cartilage and lengthening of mandible (Stutzmann 1976, Petrovic, Stutzmann 1977, 1978)

Studies on functional appliances: Activator: â&#x20AC;˘ Resection of lateral pterygoid muscle: decrease in condylar growth rate and lengthening of mandible ( Petrovic, Stutzmann 1972, 1974); opening of Stutzmann angle â&#x20AC;˘ Effect of postural hyperpropulsor: greater the sagittal advancement, greater the condylar cartilage growth rate and mandibular lengthening, opening of angle; decreases with time

Studies on functional appliances: Activator: â&#x20AC;˘ Growth rotation and alveolar bone turnover of mandible: high alveolar turnover rate with anterior growth rotation than posterior rotation

Studies on functional appliances: • Woodside et al 1975: ­ effect of activator treatment applied during the evening and night on mandibular length ­ periods of treatment were not coincident with mandibular growth accelerations (except in 1 case) ­ therefore, treatment with functional appliances should be started coincident with naturally occurring mandibular growth accelerations

Studies on functional appliances: â&#x20AC;˘ Altuna, Woodside 1977, 1985: ­ primate experiments using juvenile and adult animals in which mandible was opened 2, 4, 8, 12 mm. Without sagittal advancement ­ openings greater than 2mm resulted in increased mandibular length due to changes in condylar stress

Studies on functional appliances: â&#x20AC;˘ Woodside 1985: EMG activity in LPM by Frankel functional regulator and activator ­ both appliances generated similar amounts of LPM activity after initial appliance insertion

Studies on functional appliances: • Woodside et al 1987: assessment of remodeling changes in the glenoid fossa using juvenile monkeys ­ Herbst appliance with progressive activations used ­ extensive remodeling and anterior relocation of glenoid fossa seen • Voudoris 1988: same changes • Angelopoulos 1991: changes in glenoid fossa remodeling are stable

Studies on functional appliances: • Sessle et al 1990: longitudinal effect of functional appliances on jaw muscle activity using 6 female monkeys ­ pre appliance and post appliance levels compared with controls ­ Herbst and functional protrusive appliances inserted ­ decreased activity in superior and inferior head of LPM, superficial masseter, anterior digastric; persisted for 6 weeks returning to previous levels after 6 week observation period

Studies on functional appliances: â&#x20AC;˘ McNamara 1972, 1973: cephalometric, electromyographic and histologic study of altered functional position of lower jaw in monkeys ­ increased activity of superficial head of masseter, decreases activity of posterior part of temporal muscle, increased activity of superior head of LPM

Studies on functional appliances: • Elgoyhen, McNamara et al, 1972: advancement of mandible of 6 juvenile monkeys for 5 months ­ significant increase in rate of growth of condyle ­ rate increased with increased time of appliance wear; within 3 months with peak in 2 months; reduction in 4 months

Studies on functional appliances: • McNamara 1973, 1974: vertical dimension was increased by using cast gold inlays opening bite from 2 to 15 mm in incisor region in monkeys ­ contraction of superior head of LPM ­ elongation of elevator muscles ­ gradual change ­ inhibition of normal downward and forward growth of maxilla

Studies on functional appliances: • McNamara, Hinton and Hoffman 1982 • Histologic analysis of temporomandibular joint adaptation to protrusive function in young adult rhesus monkeys (Macaca mulatta) ­ twelve young adult female rhesus monkeys were fitted with functional protrusive appliances for periods ranging from 2 to 24 weeks.

Studies on functional appliances: 足 a proliferative chondrogenic response accompanied by deposition of new bony trabeculae at the bone足cartilage interface, though greatly reduced in magnitude as compared to juvenile monkeys

Studies on functional appliances: • DeVincenzo, Huffer, and Winn 1987 ­ A study in human subjects using a new device designed to mimic the protrusive functional appliances used previously in monkeys ­ maxillary and mandibular posterior biteplates separated by a sharp vertical interface perpendicular to the occlusal plane

Studies on functional appliances: â&#x20AC;˘

­The rate of mandibular length increase in the treatment group over that of controls was comparable to values reported in monkeys. Other skeletal and dentoalveolar changes were likewise similar to those found in monkeys.

Studies on functional appliances: Bionator: • Mandibular response to orthodontic treatment with the Bionator appliance ­ Mamandras and Allen AJO­DO 1990 Feb ­ A group of 20 subjects who underwent successful Bionator treatment was compared with 20 subjects who were treated less successfully with the same appliance. Both groups had similar advancements in their bite registrations, as well as similar treatment times and growth­prediction parameters

Studies on functional appliances: Bionator: ­ both the total mandibular length and the horizontal mandibular dimensions in the large­advancement group was greater than that in the small­advancement group. Only the vertical mandibular dimension remained slightly, but not significantly, reduced when compared with the small­advancement group ­ more distal posttreatment condylar position in the large­ advancement group as compared with the small­ advancement group

Studies on functional appliances: Frankel appliance: • Falck and Fränkel AJO­DO 1989 Oct • Clinical relevance of step­by­step mandibular advancement in the treatment of mandibular retrusion using the Fränkel appliance • 120 pts: 60 with end on relationship, 60 with step wise advancement

Studies on functional appliances: Frankel appliance: ­ better sagittal correction with gr. B ­ opening of mandibular plane angle in gr. A ­ more dentoalveolar changes with gr.A ­ condyle in more anterior position in gr. A ­ gr. A had better restraining effect on maxilla (point A and maxillary molar)

Studies on functional appliances: • Arch width development in Class II patients treated with Fränkel appliance ­ McDougall, McNamara, and Dierkes AJO­DO 1982 Jul • 60 treated with FR 1 and 2 and 47 untreated cases • changes in lingual, buccal, and alveolar arch widths were compared.

Studies on functional appliances: • expansion of the maxillary and mandibular dental arches and their supporting structure occurs routinely with a functional regulator (FR­1 or FR­ 2) • largest expansion in the premolar and molar regions, lesser in the canine region; in the maxilla narrower arches tend to expand more than wider arches

Studies on functional appliances: • Comparison of Herbst and Frankel appliances ­ McNamara, Howe, and Dischinger AJO­DO 1990 Aug • A comparison of the Herbst and Fränkel appliances in the treatment of Class II malocclusion ­ 45 pts with acrylic splint Herbst and 41 pts with FR2 ­ cephs compared with 21 untreated class II pts

Studies on functional appliances: 足 Significant skeletal changes were noted in both treatment groups, with both groups showing an increase in mandibular length and in lower facial height, as compared with controls. 足 Greater dentoalveolar treatment effects were noted in the group wearing the tooth足borne functional appliance than in those wearing the tissue足borne appliance.

References Dentofacial Orthopedics with Functional Appliances Graber, Rakosi, Petrovic

Treatment objectives and case retention: Cybernetic and myometric considerations R.M. Jacobs Am J Orthod, 58:552­564, 1970

Removable orthodontic appliances Graber and Neumann


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