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Biologic basis of Functional appliances www.indiandentalacademy.com


INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com

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• INTRODUCTION • SERVOSYSTEM THEORY OF FACIAL GROWTH • ACTION OF FUNCTIONAL APPLIANCES • ESTIMATION OF CONDYLAR GROWTH DIRECTION • STUDIES ON FUNCTIONAL APPLIANCES

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INTRODUCTION • • • •

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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


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

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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

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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 www.indiandentalacademy.com


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

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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 www.indiandentalacademy.com


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) www.indiandentalacademy.com

­ 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 www.indiandentalacademy.com


SERVOSYSTEM THEORY OF FACIAL GROWTH

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• 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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


Cybernetics

Transfer of Information

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

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Input

Input

Process

Cybernetic System Transfer Function

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Output

Output


Physiological cybernetic systems

Open loop

Closed loop

Regulator

Servosystem

Comparator

Feedback

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Peripheral Central Positive Negative


Open Loop Output has no affect on the input

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Closed Loop Relationship maintained between input and output

Input

Comparator

Feedback Loop

Transfer function

Output

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

Comparator

Regulation of input www.indiandentalacademy.com

Transfer function


Servosystem Type of Closed Loop

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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 www.indiandentalacademy.com

Performance Analyzing Elements

Performance


GROWTH OF THE FACE ACCORDING TO THE SERVOSYSTEM THEORY www.indiandentalacademy.com


Types of Cartilage Primary

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Types of Cartilage Secondary

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


Factors influencing Primary Growth Cartilage

Secondary Cartilage

Hormones

Yes

Yes

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 www.indiandentalacademy.com Strasburg, France


Role of Lateral Pterygoid and Retrodiscal Pad •Blood Supply

•Bio-mechanic

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Relationship Between Lateral Pterygoid, Retrodiscal Pad and Condyle

MENISCUS

LPM RDP

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Stutzmann and Petrovic

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


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.

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The Face as a Servosystem

Input – Maxillary dental arch

Output – Adjustment of the position of mandibular dental arch www.indiandentalacademy.com


Growth of the maxilla

Growth in Length

Growth in Width

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Growth in Length:

Traction Septo足 Premaxillary ligament

Induction

Growth of Nasal Septum

Biomechanical

Labio narinary Muscles Release of STH Somatomedin

Thrust

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 www.indiandentalacademy.com

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

www.indiandentalacademy.com 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)

Hormones

Growth at condyle (Controlled System)

OCCLUSION Output

Periodontium, Teeth Musculature Joint

Actuating signal

Actuator (Motor Cortex) Brain (sensory engram)

(Comparator)

Deviation Signal www.indiandentalacademy.com

Mastication (Performance)


Growth at the Posterior Border of the Ramus

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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 www.indiandentalacademy.com


constantly changing reference input upper dental arch

lower arch controlled variable www.indiandentalacademy.com


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 www.indiandentalacademy.com


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

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Attractor

Cusp to fossa relation

Repeller

Cusp to cusp relation

Disturbances

Abnormal tooth position Occlusal interferences Arthritis Muscle Inflammation Periodontitis, Pulpitis www.indiandentalacademy.com


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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 www.indiandentalacademy.com


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

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Discontinuities

Stable

Unstable

Catastrophe Theory www.indiandentalacademy.com

Stable


Bifurcation

Small fluctuatations Different types of occlusal relationships. www.indiandentalacademy.com


Most often in patients between 8足10 yrs old

Mixed dentition therapy is thus strongly supported biologically.

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Importance of Discontinuities

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

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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

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Periodic increase in the thickness

Increases in LPM and RDP activity

Increase in the rate and amount of condylar cartilage growth

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• 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. www.indiandentalacademy.com


Height of Bifurcation

OR

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The Sensory Engram

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

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Optimality of Function

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

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

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Action of Functional Appliances

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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 www.indiandentalacademy.com


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.

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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. www.indiandentalacademy.com


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


Chondroblasts lost

Increased multiplication of prechondroblasts

(hypertrophy, surgically removed)

Local control prechondroblasts

over

multiplication

of

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


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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. www.indiandentalacademy.com


Reduced negative feedback signal reaching prechondroblasts Increased growth at the condyle

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Cytoplasmic junctions between skeletoblasts reduce.

Transmission of inhibitory factors reduce.

Increased mitotic rate and rate of differentiation into prechondroblasts.

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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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


Action of first group

while appliance is worn

Action of second

while appliance is not worn

group

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


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

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

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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

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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. www.indiandentalacademy.com


Drawbacks Lot of importance on condyle: Fracture?

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


Occurrence of Class II end on relation is seen often?

Action of reverse pull headgear on maxilla (primary cartilage)

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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

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• 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 www.indiandentalacademy.com


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

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• 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 www.indiandentalacademy.com


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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 www.indiandentalacademy.com


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Formation of Additional Trabeculae

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

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

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

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


CYBERNETIC MODEL OF THE CONTROL MECHANISMS OF THE CONDYLAR CARTILAGE GROWTH RATE

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Effects of STH and Testosterone

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

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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. www.indiandentalacademy.com


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

www.indiandentalacademy.com 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

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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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


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

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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 www.indiandentalacademy.com


STUDIES ON FUNCTIONAL APPLIANCES

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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

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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)

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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 www.indiandentalacademy.com


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

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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

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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

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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

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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

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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 www.indiandentalacademy.com


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

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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

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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

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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.

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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

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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

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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.

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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 www.indiandentalacademy.com


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 www.indiandentalacademy.com


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

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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)

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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.

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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

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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

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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.

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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 www.indiandentalacademy.com Graber and Neumann


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