biologic basis of Functional appliance /certified fixed orthodontic courses by Indian dental academy

Biologic basis
of
Functional appliances
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INDIAN DENTAL ACADEMY
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• INTRODUCTION
• SERVOSYSTEM THEORY OF FACIAL
GROWTH
• ACTION OF FUNCTIONAL APPLIANCES
• ESTIMATION OF CONDYLAR GROWTH
DIRECTION
• STUDIES ON FUNCTIONAL APPLIANCES


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

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


• 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


• 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

• 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

SERVOSYSTEM THEORY OF FACIAL
GROWTH


• 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

Cybernetics

Transfer of Information

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


Input

Input

Process

Cybernetic
System
Transfer Function


Output

Output

Physiological cybernetic systems

Open loop

Closed loop

Regulator

Servosystem

Comparator

Feedback


Peripheral
Central
Positive
Negative

Open Loop
Output has no affect on the input


Closed Loop
Relationship maintained between input and output

Input

Comparator

Feedback
Loop

Transfer function

Output


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

Comparator

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

Performance

GROWTH OF THE FACE
ACCORDING TO THE
SERVOSYSTEM THEORY

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

Hormones

Yes

Yes

Local Factors

No (Chondroblasts

Yes (Pre

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

•Bio-mechanic


Relationship Between Lateral Pterygoid,
Retrodiscal Pad and Condyle

MENISCUS

LPM
RDP


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
SeptoPremaxillary
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
PremaxilloMaxillary
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

Transverse
Separation of
premaxillae
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

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

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 – Somatomedin


Attractor

Cusp to fossa relation

Repeller

Cusp to cusp relation

Disturbances

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.


Discontinuities

Stable

Unstable

Catastrophe Theory

Stable

Bifurcation

Small fluctuatations
Different types of occlusal relationships.

Most often in patients between 8-10 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

OR


The Sensory Engram

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


Optimality of Function

•Minimum deviation signal
•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 growth-stimulating 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-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 –
pleuripotent,
fibroblast like.
2. Prechondroblast –
faster cell cycle,
matures into
Chondroblast

Chondroblasts lost

Increased
multiplication of
prechondroblasts

(hypertrophy, surgically removed)

Local
control
prechondroblasts

over

multiplication

of

Originates from chondroblastic layer
•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:Forward position
Reduction of length of LPM
New sensory engram

) While appliance is not worn: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

group


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

2) Removal of functional appliance – when growth
is complete.

3) If removed when growth not complete – Proper
intercuspation.


4) Understanding of when, and for how long a
particular functional appliance should be worn.
First group – Full time
Second group – 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 )
• 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-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.

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


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-creased contractile activity of the LP
stimulation of the retrodiscal pad
dividing cells are relocated in a more posterior direc-tion
opening of the angle

posterior growth rotation

Effect of the Postural Hyperpropulsor
operation of con-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
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
Anterior rotation : high responsiveness of the
cells to growth-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


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


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


• 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


• 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


• 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


• 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.


- 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


• 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


•

-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:
• Mandibular response to orthodontic treatment with the
Bionator appliance - Mamandras and Allen AJO-DO
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
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 largeadvancement group as compared with the smalladvancement group

Frankel appliance:
• Falck and Fränkel AJO-DO 1989 Oct
• 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)


• Arch width development in Class II patients
treated with Fränkel appliance - McDougall,
McNamara, and Dierkes AJO-DO 1982 Jul
• 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 FR2)
• 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


• Comparison of Herbst and Frankel appliances McNamara, Howe, and Dischinger AJO-DO 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


- 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.


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

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

Removable orthodontic appliances
Graber and Neumann

THANK YOU


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