Mode of Action of Functional Appliances / orthodontic courses by Indian dental academy

MODE OF ACTION OF FUNCTIONAL APPLIANCES INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

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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: Hotzwww.indiandentalacademy.co

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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.” - Moss (1972)


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

- rate-limiting effect of growth of the midface on the growth of the mandible



Activator: Initial appliance: passive Loose appliance:Biting into the appliance

effected the extrinsic force; worn only at night

Andresen and Haupl: altering skeletal relationship depending on

the direction and amount of jaw growth incorporated in appliance ( Norwegian system)


Activator: Activator: Andresen and Haupl Sagittal positioning of the mandible Elimination of abnormal musculature Musculoskeletal adaptation by inducing a

new pattern of mandibular closure

Condylar adaptation: growth in upward and backward direction to maintain integrity of TMJ structures



Activator: Stimulation of myotactic reflex activity,

causing isometric muscle contractions Loose fit of appliance with low vertical

dimension Muscle force transmitted onto teeth: uses

kinetic energy Increased activity of elevator and

protractor muscles with relaxing and stretching of retractors


Activator:Other views: Muscle contraction: superior head of

lateral pterygoid muscle - Petrovic (rat studies), McNamara

(primate studies) - variations in the mode and direction

of dislocation of mandible Condylar unloading: Lysle Johnston


Activator: Viscoelastic activity:Herren(1953), Woodside(1973),

Harvold(1974 Viscoelastic reaction: - emptying of vessels - Pressing out of interstitial fluid - Stretching of fibres - Elastic deformation of bone - Bioplastic adaptation


Activator: Herren: anterior crossbite relationship Woodside: 10- 15 mm. Beyond postural

rest vertical dimension

Opening of 4-6 mm: Eschler(1952) no overcompensation

Transitional type of activator action Uses isometric and isotonic contractions


Activator: Head posture during sleep:Changes of head posture alter the

magnitude and direction of force Change in mandibular position varies

force vectors acting on mandible and different muscle groups

Plane of sleep( light or deep), intraoral air pressure, dream cycle, state of mind also affects activator response during sleep


Activator: Skeletal effects: - movement of condle in forward and

downward position due to the appliance - adaptation to the new position through

condylar growth; growth in more backward and upward direction

- adaptation to new position through fossa remodeling

- more posterior orientation of trabaculaewww.indiandentalacademy.co

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Activator: Dental effects: - forward displacement of lower

anterior segment (Bjork,1969) - bodily displacement of incisors

(Jacobsson, 1967) - labial tipping of lower incisors

(Richardson,1982) - lingual tipping (Moss, 1962)


Activator: Types of force employed in activator

therapy: - sagittal: mandible downward and forward-

muscle force to condyle and slight reciprocal force to maxilla

- vertical: teeth and alveolar processes are either loaded or relieved of normal forces ; high construction bite inhibits growth, direction and inclination of maxillary base

- transverse: incorporation of screws and springs; midline correction


Bionator: Balters (1943) Equilibrium between tongue and

circumoral muscles infleunces shape of dental arches and intercuspation

Tongue is the center of reflex activity in the oral cavity



Bionator: Position of the tongue: posterior displacement: class II low anterior displacement: class III narrow arches and crowding: low

outward pressure open bite: hyperactivity and forward

posturewww.indiandentalacademy.co

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Bionator: Forward posturing of mandible: - enlargement of oral space - dorsum of tongue contacting soft

palate - accomplish lip closure


Bionator:Effects: Modulation of muscle activity of tongue elimination of abnormal influences of

perioral musculature Stimulation of myotactic muscle activity

and isotonic muscle contractions


Bionator:Effects: No vertical component except for guiding

eruption of teeth No viscoelastic response Prevention of deleterious parafunctional

activity at night : relaxation of lateral pterygoid ( used for TMJ problems)


Frankel function regulator:Frankel philosophy: Potential restraining influence of the

active muscle and tissue mass of the buccinator mechanism and the orbicularis oris complex

Artificial matrix allowing the muscles to exercise and adapt




Frankel function regulator: Exercise device: stimulates normal function,

eliminating the lip trap, hyperactive mentalis, aberrant orbicularis oris and buccinator

Negative pressure of the muscles during deglutition is prevented

Bodily buccal movement of posterior teeth Oral gymnastics: lip seal exercises


Frankel function regulator: Periosteal pull of buccal shields and lip

pads increases bone activity Stimulation of mid palatal suture

growth lesser extent increasing bone apposition on the external subperiosteal layer of maxilla

( Stutzmann et al 1983, Graber et al 1991)



Frankel function regulator:Dental effects: Appliance anchored to maxillary arch;

allows more downward and outward movement of upper teeth

Lower posterior teeth are allowed to erupt upward and forward; sagittal and vertical correction


Twin block: Clark ,1977 Modification of occlusal inclined planes by

means of acrylic inclined planes on bite blocks

Guide mandible downward and forward Favorable proprioceptive contacts of inclined

planes Adaptation of the muscles of mastication Vertical and transverse control



Twin block:Mode of action: McNamara(1980) Rapid neuromuscular response Gradual dentoalveolar response Pterygoid response: pain while

retracting the mandible


Twin block: Proliferation of connective tissue and

blood vessels in the retrodiscal area Johnston( 1976) unloading of the

condyle Discomfort on removal of appliance

due to compression in the tension zone behind the condyle


Functional appliances and extraoral force: Class II div 1 with excessive vertical

growth Unloading of the condyle by forward

posture of mandible Retardation of horizontal and vertical

maxillary growth by headgear Margolis ACCO(1976); Jacobsson splint

(1967); Stockli and Teuscher activator-headgear combination


Fixed functional appliances: Herbst, 1909- Scharnier Mandible was kept forward

continuously, eliminating the need for patient compliance

Herbst and Schwartz, 1934 Pancherz, 1979



Fixed functional appliances:Sagittal changes: Restraint of maxillary growth: headgear like

effect Stimulation of mandibular growth: - remodeling on lower border of

mandible(Pancherz and Ruf,1997) - modification of TMJ fossa( Paulsen,1997;

Buschang,1998) - ultimate condylar position in fossa is

unaffectedwww.indiandentalacademy.co

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Fixed functional appliances:Sagittal changes: Proclination of lower incisors Posterior movement of upper

molars: headgear like effect


Fixed functional appliances:Vertical changes: Eruption of lower molars; intrusion of

lower incisors: reduction of overbite Proclination of lower incisors

contributing to overbite reduction



Fixed functional appliances:Long term changes: Class I relationship is maintained with stable

cuspal interdigitation Causes of relapse: - too early treatment - mixed dentition treatment - persistent abnormal musculature - unstable post treatment occlusion - insufficient length of appliance wear and

retention www.indiandentalacademy.co

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Fixed functional appliances:Soft tissue changes: Reduction of soft tissue convexity,

excluding the nose Increase in soft tissue convexity, including

the nose, because of normal nasal growth Retrusion of upper and lower lips in

relation to esthetic line due to normal chin and nose growth


Fixed functional appliances:Jasper jumper: James Jasper, 1987 Effects:- functional effect similar to Herbst

appliance- dentoalveolar changes



Fixed functional appliances: Repositioning effect: Farrar effect: reciprocal clicking Recapturing of the disc Repositioning of condyle Maintaining the repositioning effect Orthodontic occlusal correction in

the desired positionwww.indiandentalacademy.co

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Mode of action:Condylar growth: Forward positioning of mandible Increased activity of LPM Intensification of repetitive activity

of retrodiscal pad


Mode of action:Mode of action: Condylar growth:- increase in growth stimulating factors:

1. enhancement of local mediators2. Reduction of local regulators- change in condylar trabacular orientation- additional growth of condylar cartilage- additional subperiosteal ossification of

posterior border of mandible- lengthening of mandible


Mode of action: Increased activity of LPM Retrodiscal pad- mediator of response1. Blood circulating effect: - increase in blood and lymph flow, - increase in nutritive and growth

stimulating factor supply ( STH-somatomedin, testosterone and

estrogen in low doses, insulin, prostaglandin F2, mitogenic peptides)

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Mode of action: - decrease in locally produced

catabolites and other negative feedback factors

( prechondroblast’s multiplication restraining signal, cAMP, prostaglandin E2, somatostatin-like substance)

- iterative actionwww.indiandentalacademy.co

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Mode of action: 2. Biomechanic effect: - Accentuated concavity at the posterior border of

mandibular ramus due to increase in condylar growth and more posterior directed growth

- piezoelectric effect: increase in negative charges along posterior border, causing increased periosteal bone formation and vice versa

- supplementary lengthening of mandible



Herren and LSU activator: Bite opened well beyond postural rest position Forward positioning of mandible leads to

reduced increase in length of LPM Sensory engram formed for new position of

mandible Functioning of mandible in more forward

position when appliance is not worn Increased activity of retrodiscal pad with

acceleration of condylar growthwww.indiandentalacademy.co

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Growth restriction of glenoid fossa:normal growth of glenoid fossa is in

posterior and inferior directionAnterior slope of articular eminence

undergoes bone deposition on posterior slope and resorption on anterior slope

Anterior relocation of glenoid fossa in orthopedic treatment

Reciprocal forces from viscoelastic tissue between condyle and fossa


Growth relativity hypothesis:Voudoris, Kuftinec AJODO March 2002 Mandibular advancement Fibrocartilagenous lining in glenoid fossa

induces bone formation locally Stretch of nonmuscular viscoelastic

tissues New bone formation some distance from

the actual retrodiscal attachments in the fossa




Growth relativity hypothesis: Fibrocartilage caps the condyle in 3

dimensions: posterior, anterior and 2 collateral along with fibrous capsule and synovial fluid

Advancement: engorgement of blood vessels, influx of nutrients and biodynamic factors

Reseating of condyle in fossa: expulsion of these factors

Resulting metabolic pump-like action



Growth relativity hypothesis: Disoccluding appliances cause low intra-

articular subatmospheric pressures within TMJ in open position ( Nitzan, 1994)

Shift of synovial fluid perfusion on a posteriorly displaced direction

Negative pressures are below capillary perfusion pressure

Greater flow of blood to the regionwww.indiandentalacademy.co

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Growth relativity hypothesis:

Bone architecture is influenced by the neuromusculature and the contiguous nonmuscular, viscoelastic tissues anchored to the glenoid fossa and the altered dynamics of the fluids enveloping bone


Displacement+ viscosity+ referred force

Three growth stimuli:1. Anterior orthopedic displacement2. Posterior viscoelastic tissues between

condyle and fossa3. Transduction of forces over the

fibrocartilage cap of the condylar head, increases radiating endochondral bone formation beneath condylar fibrocartilage and periosteal bone formation in the fossa




Condylar light bulb analogy: Condyle acts like a light bulb on a

dimmer switch Lights up during advancement,

dimming back to near normal levels during retention

Growth potential diminishes with age while remodeling potential last long into adulthood




Clinical implications: Prevention of condylar compression

by using Herbst with thin posterior bite blocks

Rapid maxillary expander to reduce occlusal interferences and functional shifts due to the anterior positioned mandible


Studies on functional appliances:

Activator: 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


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Histologic study: - growth of bony trabaculae formed in parallel and posteriorly oriented condylar cartilage



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 www.indiandentalacademy.co

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Activator: - lengthening of mandible measured from

posterior edge of condylar cartilage to mental foramen is greater in case of opening of angle

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)




Activator: Resection of lateral pterygoid muscle: decrease in condylar growth rate and

lengthening of mandible ( Petrovic, Stutzmann 1972, 1974); opening of

Stutzmann angle Effect of postural hyperpropulsor: greater the sagittal advancement, greater the

condylar cartilage growth rate and mandibular lengthening, opening of angle; decreases with time



Activator: Growth rotation and alveolar bone

turnover of mandible: high alveolar turnover rate with

anterior growth rotation than posterior rotation


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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



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: Woodside 1985: EMG activity in LPM

by Frankel functional regulator and activator

- both appliances generated similar amounts of LPM activity after initial appliance insertion




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



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



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




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


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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 www.indiandentalacademy.co

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Taken from the AJO-DO 1982 Oct (288-298): - McNamara, Hinton and Hoffman

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.



- a proliferative chondrogenic response accompanied by deposition of new bony trabeculae at the bone-cartilage interface, though greatly reduced in magnitude as compared to juvenile monkeys



Taken from the AJO-DO 1987 Mar (213-224): - DeVincenzo, Huffer, and Winn

- 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


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-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.




Bionator: Taken from the AJO-DO 1990 Feb (113-120):

Mandibular response to orthodontic treatment with the Bionator appliance - Mamandras and Allen

- 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 growth-prediction parameters



Bionator: - both the total mandibular length and the

horizontal mandibular dimensions in the large-advancement group was greater than that in the small-advancement group. Only the vertical mandibular dimension remained slightly, but not significantly, reduced when compared with the small-advancement group

- more distal posttreatment condylar position in the large-advancement group as compared with the small-advancement group



Frankel appliance: Taken from the AJO-DO 1989 Oct (333-

341): - Falck and Fränkel Clinical relevance of step-by-step

mandibular advancement in the treatment of mandibular retrusion using the Fränkel appliance

120 pts: 60 with end on relationship, 60 with step wise advancement



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)



Taken from the AJO-DO 1982 Jul (10-22): Arch width development in Class II patients treated with Fränkel appliance - McDougall, McNamara, and Dierkes

60 treated with FR 1 and 2 and 47 untreated cases

changes in lingual, buccal, and alveolar arch widths were compared.



expansion of the maxillary and mandibular dental arches and their supporting structure occurs routinely with a functional regulator (FR-1 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



Taken from the AJO-DO 1990 Aug (134-144): Comparison of Herbst and Frankel appliances - McNamara, Howe, and Dischinger

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



- 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.

- Greater dentoalveolar treatment effects were noted in the group wearing the tooth-borne functional appliance than in those wearing the tissue-borne appliance.


Proffit, Tulloch AJODO,June 2002 Optimal timing of treatment for Class II

malocclusion - can jaw growth really be modified, by

how much, with what predictability, in which patients?

- do different appliances produce different effects?

- would early intervention make later treatment simpler and with better treatment results?


Proffit, Tulloch AJODO,June 2002

Methods: Children with overjet> 7mm, in mixed

dentition, at least 1 yr before peak height velocity, excluding children with extreme vertical disproportions

2 phases: 1. - Treatment with either a combination

headgear or functional appliance - Control with no treatment until permanent

dentition2. All children were treated with fixed appliances


Proffit, Tulloch AJODO,June 2002Methods: Boys- 57.8%, girls- 42.2% Mean age- 9.4 yrs Mean overjet- 8.4 mm, 91%

bilateral class II 175 children, 166 completed phase

1, 143 started and completed phase 2


Proffit, Tulloch AJODO,June 2002

Results: Small mean reduction in jaw relationship with

early treatment Mechanism of change: - headgear group: restriction in fwd movement

of maxilla - functional appliance: increase in mandibular

length and increase in chin projection 75% of early treatment pts had highly

favourable changes as compared to 25% of untreated pts


Proffit, Tulloch AJODO,June 2002Second phase: Clinician centered outcome:

change in skeletal jaw relationship or alignment and occlusion of teeth

Patient or parent oriented outcome: duration of treatment or need for extractions or other surgical procedures


Proffit, Tulloch AJODO,June 2002 2 early treatment groups : reduction in

ANB angle in phase 1, no sustained advantage in phase 2

No difference in patients with convex profiles

No difference in quality of occlusion Early treatment did not reduce the

percentage of children needing extractions in phase 2 or eventual orthognathic surgery


Proffit, Tulloch AJODO,June 2002Treatment time: length of time in phase 2, and time spent wearing fixed appliances Early treatment had very little

effect in reducing the time of fixed treatment


Proffit, Tulloch AJODO,June 2002Discussion: Early treatment produced an initial

differential growth change Not effective in correcting later

skeletal and dental class II malocclusion

No advantage in final treatment outcome or simplification of later treatment procedures


Proffit, Tulloch AJODO,June 2002Early treatment: Psychological distress Accident prone children Skeletal maturity is ahead of dental

development Children with vertical and class II

problems

Conclusion: no clear advantage for early treatment


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Mode of Action of Functional Appliances / orthodontic courses by Indian dental academy