PRINCIPLES OF FUNCTIONAL APPLIANCES

PRINCIPLES OF
FUNCTIONAL APPLIANCES
www.indiandentalacademy.com

CONTENTS
• Introduction
• Anatomical considerations in the use of
functional appliances
• Muscle physiology
• Hormones & growth
• Growth of the craniofacial skeleton
• Growth, development & theories
• Cephalometric diagnosis

• Functional analysis
• Principles and mode of action of functional
appliances
• Skeletal changes and muscular adaptations
• Timing of treatment
• Treat now or wait
• The future: using bio-MECHANICS to
becoming BIO-mechanics
• Conclusion
• Bibliography

INTRODUCTION
Functional appliances have been in use
for over half a century. These appliances
are an invaluable tool for the practicing
orthodontist.
However, these appliances and their use
have been mired in controversy all these
years.

There have been periods where extreme
enthusiasm was experienced from the
proponents of these appliances followed
by a period of extreme criticism from
others.
This is largely because of the fact that the
understanding of the principles,
applications and limitations of these
appliances was not completely
understood. Moreover, our understanding
of growth and craniofacial biology has
also been limited.www.indiandentalacademy.com

ANATOMICAL CONSIDERATIONS
• Retrodiscal pad- the “metabolic pump”

PRE NATAL DEVELOPMENT
OF THE TMJ

POST NATAL
DEVELOPMENT OF THE TMJ
• In the newborn the articular surface of TMJ is
relatively flat to allow complete freedom during
suckling
• As the deciduous incisors erupt there is an
appearance of small ridge that represents the first
sign of articular eminence
• In a mature adult joint, contours are fully
developed as adaptive changes to functional
demand

BUCCINATOR MECHANISM

MUSCLE PHYSIOLOGY
• A muscle belly consists of large number of
fasciculi
• Each fasciculus consists of large number of
muscle fibers.
• A single muscle fiber contains numerous
myofibrils
• The portion of a myofibril, in between any
two successive Z lines is called sarcomere.

MUSCLE PHYSIOLOGY
• Isometric contraction occurs when a muscle
is simply resisting an external force without
any actual shortening.
• In an isotonic contraction, such as flexing
the biceps, there is an actual shortening
• The greatest strength of contraction is
elicited when the muscle approximates its
resting length.

MYOTATIC REFLEX

CLASP-KNIFE REFLEX

HORMONES AND GROWTH
GROWTH HORMONE
• Stimulation Of Cartilage And Bone Growth
• Act through IGF I and IGF II, also called
somatomedins
• After adolescence, secretion decreases to
about 25 per cent of the adolescent level in
very old age.

HORMONES AND GROWTH
TESTOSTERONE
• Increases the total quantity of bone matrix
• Causes the epiphyses of the long bones to
unite with the shafts of the bones
• ESTROGEN
• Cause increased osteoblastic activity
• Early uniting of the epiphyses with the
shafts of the long bones

PUBERTY
• It is the transitional period between the
juvenile stage and adulthood, during which
the secondary sexual characteristics appear
• This period is particularly important in
dental and orthodontic treatment
• There is a great deal of individual variation,
but puberty and the adolescent growth spurt
occur on the average nearly 2 years earlier
in girls than in boys

GROWTH OF THE
CRANIOFACIAL SKELETON
• Morphogenesis works constantly toward a
state of composite, architectonic balance
among all of the separate growing parts
• The potential for relapse exists when the
functional, developmental, or
biomechanical aspects of growth among
key parts are clinically altered to a
physiologically imbalanced state

Regional control of development
Replacing the archaic notion of master
growth control centers of yesteryear, is the
understanding that tissues within each local
area contain an array of cell types carrying
out the specific developmental requirements
of that area

The mandibular condyle: A
secondary cartilage

The new image of the condyle
• Historically, it has been the condyle that has been
given all the glory
• With regard to the growth and adaptive
requirements for the mandible, it is not just the
condyle, however, that participates as the key
component. The whole ramus is directly involved
• Mandibular orthopedics must modify growth
signals targeted at both the ramus and condyle to
be maximally effective

The Architectonics Of Growth
Control: A Summary
• Growth is a differential process of
progressive maturation
• There are two principal categories of
growth movement, displacement and
remodeling. This is one of the most
fundamental concepts of growth

The Architectonics Of Growth
Control: A Summary
• When the muscles of facial expression
contract (function), the mechanical
effect is an upward and backward
retrusive force exerted on the maxilla.
Yet everyone knows that the maxilla
grows forward and downward. Does
this not contradict the functional matrix
principle?
• First, the important distinction betweenwww.indiandentalacademy.com

PATTERN, VARIABILITY, AND
TIMING
In a general sense, PATTERN reflects
proportionality
VARIABILITY: Everyone is not alike in the
way that they grow as in everything else
TIMING: The biologic clocks of different
individuals are set differently

Facial Growth in Adults
• The growth process is one that declines to a
basal level after the attainment of sexual
maturity
• Vertical changes in adult life are more
prominent than anteroposterior changes,
where as width changes are least evident,
and so the alterations observed in the adult
facial skeleton seem to be a continuation of
the pattern seen during maturation

GROWTH, DEVELOPMENT &
THEORIES
• Biomechanical forces
Wolff’s law of bone transformation, introduced in
the late 1800s, quickly became a leading and most
useful working concept
• Sutural theory
Dimensions of a bone are governed by intrinsic
genetic programming residing within that bone’s
own bone-producing cells of the periosteum,
sutures, and bone-related cartilages

• Cartilaginous theory
Cartilaginous nasal septum has features and
occupies a strategic position that might
answer the question of what “motor” causes
the displacement of the midface inferiorly
as it grows in size
The major question was about “where do
heredity and the genes act - at sutures,
within the cartilages of the cranial base,
midface, and mandible; or at all three
areas ?

Functional matrix theory
• The growth of the bone is compensatory
and adaptive to that of its surrounding tissue
• Growth enlargements of muscles are a
significant factor
• Placed emphasis on the potential of
modification of craniofacial growth and
form using the principals of orthodontics
and dentofacial orthopedics.

van Limborgh’s epigenetic theory

Servosystem theory

Genetic theory: A contemporary view
• Initially, the genetic theory was focused on
the mechanisms by which the traits are
transmitted
• The second focus was on the mechanisms
of gene action during development
• Understanding of the Homeobox genes and
other regulatory factors is fundamental to an
understanding of the mechanisms of
craniofacial development.

Equilibrium theory revisited

Equilibrium theory revisited
• An imbalance of force between tongue on
one side and lip or cheeks on the other
normally is present
• Forces produced by active metabolism in
the periodontal membrane stabilize the teeth
against reasonable imbalances in tongue
and lip forces
• In the short term, function adapts to changes
in form
• In the long term form adapts to function

Bioelectric signals
(The ‘Piezo’ Effect)

Other Factors
• Neurotropic Factors
Transport of neurosecretory material along
nerve tracts or by an axoplasmic streaming
within the neuron
• Signalling processes
A first-messenger (tension factor) acting on
the cell’s outer sensory membrane receptors
can activate a second messenger

CEPHALOMETRIC DIAGNOSIS
• Saddle angle (N-S-
Ar)
• Articular angle ( S-
Ar-Go)

Gonial angle (Ar-Go-Me)

• A-P face height: • Cranial base length

• S-N-A • S-N-B

Mutual relationship of the rotation jaw
bases

Linear measurement of the jaw bases
• N-Se: Man Base 20:21
• Ascending ramus: Man Base 5:7
• Max Base: Man Base 2:3

Morphology of the
mandible

Analysis of dentoalveolar relationships

FUNCTIONAL ANALYSIS
Evaluation of the path of closure from
postural rest to occlusion in the sagittal
plane

FUNCTIONAL ANALYSIS
Evaluation of the path of closure from
postural rest to habitual occlusion in the
vertical plane

FUNCTIONAL ANALYSIS
• Evaluation of the path of closure from
postural rest to habitual occlusion in the
transverse plane

Examination Of The
Temporomandibular Joint and
condylar Movement
The simplified clinical examination of the
TMJ area consists of three steps
• Ausculation
• Palpation
• Functional analysis

Evaluation of the swallowing
function
The first and most obvious step in functional
assessment is to study the deglutitional
cycle
• Somatic or visceral swallowing pattern
• Complex or simple tongue thrust

Examination of the tongue
• Function
• Posture
• Size
• Shape

Respiration
• Mouth breathing can be considered an
etiologic factor or at least a predisposing
causes for some malocclusion symptoms
• It is impoartant to assess whether the nasal
breathing is due to an obstructive cause or
habitual mouth breathing

Visual Treatment Objective
Diagnostic Test (FR – VTO)
• The patient is instructed to close the teeth in
habitual occlusion
• The patient is then asked to posture the
mandible forward into a correct sagittal
relationship
• If this clinical exercise makes the facial
balance look better, the functional appliance
will probably be beneficial

PRINCIPLES AND MODE OF ACTION
OF FUNCTIONAL APPLIANCES
• Respiratory function: An important
physiologic base for functional appliance
therapy
• A primary objective of functional
appliances is to take advantage of natural
forces and transmit them to selected areas to
produce the desired change.

FORCES
• The duration of force in most functional
appliance treatment is interrupted
• The direction of force for the movement of
teeth should be consistent
• The magnitude of force is small in
functional appliance therapy

• Applied force may be compressive or
tensile. Depending on the type applied, two
treatment principles can be differentiated:
force application and force elimination
• In force application, compressive stress and
strain act on the structures involved,
resulting in a primary alteration in form
with a secondary adaptation in function
• In force elimination, abnormal and
restrictive environmental influences are
eliminated, allowing optimal development

The success of functional appliance therapy
depends on the neuromuscular response.
The pure screening appliances are primarily
designed to not so much change the form of
the dental arches as eliminate abnormal
perioral muscle functional effects on the
developing dentoalveolar area.

Classification of functional
appliances
• Group I – Transmit muscle force directly to
the teeth
• Group II - All reposition the mandible
downward and forward
• Group III - Major operating area is in the
vestibule
Also been classified as ‘Myotonic’ and
‘Myodynamic’

ACTIVATOR
• In 1880, Kingsley introduced the term and
concept of “jumping the bite”
• Over 100 years later the possibility of
achieving a permanent forward positioning
of the mandible is still controversial in
some circles
• A second postulate of Kingsley jumping of
the bite should be performed without
proclination of the lower incisors

• Viggo Andresen (1930) did not develop an
appliance based on Robin’s monobloc
(1902) but based on Farrars concepts
• Andresen teamed up with Haupl, who
explained the working of the appliance on
Roux’s “shaking of the bones”

• As to whether the activator promotes
mandibular growth, the answer is qualified
by the term individual optimum.
• The activator cannot create a large mandible
from a small one, but it can help the patient
achieve the optimal size consistent with
morphogenetic pattern.
• Haupl considered this the goal of activator
treatment.

Efficacy Of The Activator
• According to Andresen and Haupl, the activator
induces musculoskeletal adaptation by introducing
a new pattern of mandibular closure .
• The construction bite does not open the mandible
beyond postural rest position
• If the mandible opens beyond the 4mm limit, the
appliance does not work in the manner Andresen
and Haupl suggest but instead works by stretching
the soft tissues or relying on the viscoelastic
properties of the muscles

Classification of Views
• Andresen-Haupl concept: Myotatic reflex
activity and isometric contractions induce
musculoskeletal adaptation
• Herren, Woodside: The viscoelastic
properties of muscle and the stretching of
the soft tissues are decisive for activator
action
• Between the two extremes a number of
authors support a higher construction bite
without the extreme extension advocated by
Woodside

Mode Of Action Of The Activator
(on the basis of the Servosystem theory)
• Postural Hyperpropulsor: LPM activity
while wearing the appliance
• Class II Elastics: Mediated primarily
through the retrodiscal pad
• Herren (L.S.U.) Activator: Through the
LPM when the appliance is removed

Increased contractile activity of LPM
Intensification of the repetitive activity of the Retrodiscal
pad
Increase in growth-stimulating factors
Enhancement of local mediators.
Reduction in factors having negative feedback effects on cell
multiplication rate
Change in condylar trabecular orientation
Additional growth of condylar cartilage
Additional subperiosteal ossification of the posterior border of
the mandible.
Supplementary lengthening of the mandible.
MODE OF ACTION OF
FUNCTIONAL APPLIANCES

Rigid v/s Elastic activators
• The rigid activator does not permit muscle
shortening, and therefore contractions that
arise are isometric in nature
• The elastic activators bring about isotonic
muscle contractions. But due to increased
wear, may show greater efficiency

Vertical and sagittal effects
• Woodside believes that a small vertical
opening restricts only horizontal midfacial
development, whereas a wide vertical
opening achieves the restriction by
downward displacement of the midface
area.
• Therefore depending on the construction
bite you can produce the desired changes.

The Bionator
• According to Balters, the equilibrium
between the tongue and circumoral muscle
is responsible for the shape of the dental
arches and intercuspation
• The tongue (as the center of reflex activity
in the oral cavity) was most important
factor in treatment
• He took only secondary consideration of the
neuromuscular envelope

• Balters designed his appliance to take
advantage of tongue posture
• Forward posturing of the mandible enlarged
the oral space, bringing the dorsum of the
tongue into contact with the soft palate, and
helped accomplish lip closure, the appliance
was designed to help patients learn normal
functional patterns.
• The principle of treatment with the bionator
is not to activate the muscles but to
modulate muscle activity

• The transpalatal bar provides a sensory
stimulus for the tongue
• The tongue is actually subjected to
continuous exercise in reseating the
bionator
• Also the labial bow wire produces a
negative pressure, with the wire supporting
lip closure

• Myotatic reflex activity with isotonic
muscle contraction is stimulated
• However, worn day and night so the
Bionator’s action is faster than that of the
classic Activator

The Functional Regulator
• The treatment with this appliance is not primarily
directed toward the teeth or the skeletal tissues
themselves but rather to the functional disorders
• The primary aim of treatment is to identify a
faulty postural performance of the orofacial
musculature and to correct it by a functional
therapy.
• A training effect on the orofacial musculature can
be achieved only if the appliance to be used for
this purpose acts as a trainer

• The pressure exerted by any appliance, even
if produced by muscular forces, is and
remains an application of pressure and has
nothing to do with a “functional stimulus”
• In attempting to develop a concept for
realizing orofacial orthopedics, it should be
considered that the term orthopedics derives
from Greek and literally means “proper
education.”

• It is important to understand that certain
concepts of growth as emphasized by
Frankel
• He emphasized the impact of the “space –
problem” in the physiology of the orofacial
complex
• In Frankel’s view, neuromuscular forces are
classified as epigenetic control factors
which is in contrast to van Limborgh’s
analytical concept

• The reestablishment of adequate space
conditions of the oral functioning space is
primary aim of a functional treatment
• However, we must not only correct the
existing structural aberrations but also the
functional performances of the muscles
forming the circumoral capsule
• E.g. Buccal shields form an “ought to be
matrix” and carry our “forced gymnastics”

• The buccal shields and lip pads hold the buccal
and labial musculature away from the teeth and
investing tissues, eliminating and possible
restrictive influence from this functional matrix.
• Buccal shield act in three ways:
1. Stimulating midpalatal suture growth
2. Increasing bone apposition on the external
subperiosteal layer of the maxilla
3. Influence on the eruptive path of the
succedaneous teeth

• The main purpose of the lip pads is to
prevent a hyperactive mentalis muscle from
raising the lower lip.
• This inhibitory action is necessary in order
to achieve a training effect on the lip
muscles which are destined to bring about
the physiological seal of the oral cavity.
• Certainly, the full training effect of the lip
pads can only be established when
concomitant lip seal exercises are
performed.

• According to Frankel the mandible should
not be postured forward forcefully or
mechanically
• The forward posturing should be
“proprioceptive” and carried out by
muscles.
• Accordingly he developed the lingual pads
• Also the advancement should not be more
than 2-3mm

Clark’s Twin Block
• Wolff’s law - The internal and external
structures of bone is modified by functional
demands
• In the dentition the force of occlusion of the
teeth is the most natural functional
mechanism that can be used to influence the
structure of the supporting bone.

• Occlusal forces transmitted through the
dentition provide constant
proprioceptive stimuli to influence the
growth rate and trabecular structure of
the supporting bone.
• The proprioceptive sensory feed back
mechanism controls muscular activity
and provides a functional stimulus or
deterrent to the full expression of
maxillary and mandibular bone growth

• The unfavorable cuspal contacts of distal
occlusion are obstructions to normal
forward mandibular translation in function
and as such do not encourage the mandible
to achieve its optimal genetic growth
potential.
• Twin blocks are simple bite – blocks that
effectively modify the occlusal inclined
plane

SKELETAL ADAPTATIONS
• Condylar growth amount during treatment: 1 to 3
mm
• Fossa displacement, growth and adaptation: 3 to 5
mm
• Elimination of functional retrusion: 0.5 to 1.5 mm.
• More favorable growth direction: Trabecular
orientations 0.5 to 1.5 mm.
• With holding of downward and forward maxillary
growth: 1 to 1.5 mm.
• Differential upward and forward eruption of lower
buccal segments: 1.5 to 2.5
• Headgear effect: 0.5 to 0.0 mm.

MUSCULAR ADAPTATION
• Within the central nervous system
• At the muscle/bone interface –The
myofibroblast
• Within muscle tissue
1. Geometric rearrangement of fibers
2. Changes in Sarcomere number.
3. Changes in Sarcomere length.
4. Changes in muscle physiology

The Pterygoid Response
• Within a few days of the fitting of twin
block appliances, the position of muscle
balance is altered so greatly that the patient
experiences pain when retracting the
mandible
• Due to the formation of a “tension zone”
distal to the condyle

TIMING OF TREATMENT
• Growth modulation is possible only in
patients who are growing actively
• Girls before boys?
• Severe cases should begin earlier than mild
cases
• Retention must continue until active growth
is essentially complete
• If a patient grows slowly during treatment,
more likely to retract the maxilla

• Where prominent upper incisors are
vulnerable to trauma - early treatment is
indicted after eruption of permanent
incisors.
• Class III malocclusion also responds to
early intervention
• Abnormal perioral musculature must be
eliminated at the earliest.

TREAT NOW OR WAIT
• Ideally, treatment would be provided when
it is most effective and most efficient.
• The question is whether early treatment,
which is more often than not followed by a
second phase of treatment, provides
superior results to conventional treatment
started in the permanent dentition
• Proffit carried out a study at UNC for the
answer

• Not only did early treatment fail to provide any
advantage in final treatment outcome or
simplification of subsequent procedures, but also
it took longer.
• It was no more effective and somewhat less
efficient.
• However, there are many reasons for
recommending early treatment for some including
children with psychological distress, those who
are particularly accident – prone, and those whose
skeletal maturity is well ahead of their dental
development

Applying bio MECHANICS
v/s
becoming BIO mechanics

CONCLUSION
Functional appliances are not a panacea for
all skeletal deformities during the growth
period. You cannot use any appliance at any
time for any patient. These are truly a
“thinking” clinician’s tools. Moreover, we
must keep ourselves abreast with any
developments in appliances and craniofacial
biology to ensure maximum effectiveness
and efficiency.

CONCLUSION
Though it has not been covered in this
seminar, a proper design and construction
of the appliance is of paramount
importance. With these thought in mind, I
think that we can maximize the benefits to
our patients, which is the ultimate goal of
orthodontic therapy.

BIBLIOGRAPHY
• Williams P L. Gray’s Anatomy. Edinburgh: Churchill
Livingstone; 1995.
• Sachdeva R C L. Orthodontics for the next millenium.
Dallas: Ormco; 1997.
• Sperber G H. Craniofacial Embryology. Bristol: John
Wright and sons Ltd.; 1976.
• Duggal R. Maxillofacial Growth Regulation by Twin
Block Appliance: An update. New Delhi: AIIMS ; 2002.
• Graber T M. Orthodontics Principles and Practice.
Philadelphia: WB Saunders Co.; 2001.
• Chaudhari S K. Concise Medical Physiology. Calcutta:
New Central Book Agency; 1993.

• Graber T M, Neumann B. Removable Orthodontic
Appliances. Philadelphia: WB Saunders Co.; 1984.
• Guyton A C. Text book of Medical Physiology.
Philadelphia: WB Saunders Co.; 1991.
• Dixon A D, Hoyte D A N, Ronning O. Fundamentals of
Craniofacial growth. Boca Raton: CRC Press; 1997.
• Carlson D S, McNamara J A Jr., Ribbens K A.
Developmental Aspects of Temporomandibular Joint
Disorders : Monograph Number 16 Craniofacial Growth
Series. Ann Arbor: The University of Michigan ; 1984.
• Proffit W R . Contemporary Orthodontics. St. Louis : C V
Mosby Company; 2000.
• Enlow D H, Hans MG. Essentials of Facial Growth.
Philadelphia: W B Saunders Co., 1996.
• McNamara J A Jr. Growth Modification : What Works,
What Doesn’t, and Why : Monograph Number 35:
Craniofacial Growth Series. Ann Arbor: The University of
Michigan; 1984.

• Carlson D S, McNamara J A Jr. Muscle Adaptation in the
Craniofacial Region : Monograph Number 8 Craniofacial
Growth Series. Ann Arbor: The University of Michigan;
1978.
• McNamara J A Jr, Ribbens K A, Howe R P. Clinical
Alterations of the Growing Face Monograph Number 14
Craniofacial Growth Series. Ann Arbor: The University of
Michigan; 1983.
• Frankel R, Frankel C. Orofacial Orthopedics with the
Functional Regulator. Basel: Karger; 1989.
• Clark W J. Twin Block Functional Therapy. London:
Mosby Wolfe; 1995.
• Graber T M, Vanarsdall R L. Orthodontics Current
Principles and Techniques. St. Louis: Mosby; 2000.
• Carlson D S. Biological rationale of early treatment of
dentofacial deformities. Am J Orthod Dentofac Orthop
2002; 121 : 554 – 558.
• Proffit W R, Tulloch J F C. Preadolescent class II
problems : treat now or wait 2002; 121 : 560 – 562.www.indiandentalacademy.com

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