functional appliances

2.  Functional appliances are active or passive appliances which harness natural forces of
the oro-facial musculature that are transmitted to the teeth and the alveolar bone in a
predetermined direction.
 Functional appliances have been in use for over half a century. These appliances are an
invaluable tool for the practising orthodontist
 However these appliances and their use have been mired in controversy all these years
 This is largely because the fact that the understanding of the principles, applications and
limitations of these appliances are not completely understood.

3.  In late 1960’s, Petrovic and co-workers produced the first rigorous
demonstrations that the condylar cartilage’s growth rate and amount can be
modified using appropriate functional and orthopedic appliances.
 Research has shown that the lateral pterygoid muscle (LPM) apparently plays
a regulating role in the control of the condylar cartilage’s growth rate.
 Earlier, Stutzmann et al ( 1976) discovered that the retrodiscal pad apparently
has a mediator role in the efforts of LPM to control condylar growth.

4.  The term CYBERNETICS ( Greek kybernetes means steersman) was coined
by mathematician NORBERT WIENER in 1948 to encompass the entire field
of control and communication theory, whether in the machine or in the
animal.
 Cybernetics is concerned with scientific investigations of systematic
processes of a highly varied nature, including phenomenon such as
regulation, information processing, storage, adoption, self organisation and
strategic behavior.

5.  Petrovic has employed the terminology of cybernetics and control theory to
describe craniofacial growth mechanisms and the method of operation of
functional and orthopaedic appliances.
 Cybernetic theory refines orthodontic concepts by demonstrating the
qualitative and quantitative relationships between observationally and
experimentally collected findings.
 It also provides a conceptual tool for a broader understanding of clinical
orthodontic problems, particularly because the rigorous language of
cybernetics is compatible with the rapidly expanding use of computers among
clinicians

6. What is cybernetics ?

8. A regulator type of closed loop is one in which the inputs is constant. Any disturbance in
the input will cause the comparator to initiate a regulatory feedback system, which will
restore the inputs to its normal state.
Servosystem: In this the main input is constantly changing with time and the output is
constantly adjusted in accordance to the input

9. Craniofacial growth is an extremely complex process. In accounting for scientific
findings its mechanisms and the method of operation of orthopedic and orthodontic
appliances , the following set of approaches is useful:
1. Discoveries may be related by placing the observations next to each other.
2. Diagrams displaying qualitative relationships between observations can be
constructed.
3. Diagrams may be improved by making the relationships illustrated by the model
either continuous or discontinuous (time consuming).

10. 4. Diagrams may be improved by using
matrices in mathematical language.
5. Cybernetics is based on communication
and information theory particularly
on feedback mechanism
6. Catastrophic theory is a topologic
process designed to describe
discontinuities, correspond to sudden
changes in references of control
system

12. Effective operation of
servosystem can take place only
through gradual changes
between the dental arches where
upper dental arch is constantly
changing reference input and
lower arch is the controlled
variable.

13.  Genetic control theory
 Cartilage directed growth theory
 Functional matrix theory
 Servosystem theory

14.  Burdi- 1995
 According to this theory genotype supplies all information required for
phenotypic expression.
 Disagreement exists concerning whether general, regional, and local factors
modify the gene expression and the way in which such modification occurs.

15.  Sutural growth theory: Sicher (1947): growth at the sutures results in
growth of cranial vault and downward and forward growth of the
midface

16.  Scott – 1953
 According to this theory cartilage is the primary factor in craniofacial growth
control ( synchondrosis, nasal septal cartilage, mandibular condyle are growth
centres)

17.  Given by MELVIN MOSS
 This concept of Melvin moss revitalized the studies on growth and development
at a times when the sutural theory and cartilaginous theory were severely
criticized for their inadequacy.
 In the year 1981 MOSS gave the classical statement
 The origin, growth and maintenance of all skeletal tissues and organs are always
secondary, compensatory and mechanically obligatory responses to temporally
and operationally prior events or process that occur in specifically related non-
skeletal tissues, organs or functional spaces (Functional matrices).”
 Relationship between FORM AND FUNCTION

18. FUNCTIONAL CRANIAL COMPONENT
SKELETAL UNIT FUNCTIONAL UNIT
MICROSKELETAL MACROSKELETAL PERIOSTEAL
MATRIX
CAPSULAR
MATRIX
1. Periosteal matrices include muscles and teeth
2. The capsular matrices are conceived of as volumes enclosed and protected by both the neurocranial and
the orofacial capsule.

19.  Periosteal matrix act upon skeletal units in a direct fashion by osseous deposition and
resorption .Their net effect is to alter the form (size and shape)
 Capsular matrix act upon functional cranial components as a whole in a secondary and
indirect manner. The effect of such growth causes translation.
 Cranial growth is a combination of the morphogenetically primary activity of both types of
matrix
 Growth is accomplished by both spatial translation and changes in form

20.  Charlier, Petrovic and Stutzmann.
 They found dissimilarities concerning different growth cartilages:
1. Growth by the cell division of differentiated chondroblasts and cartilages of synchondrosis
of cranial base and nasal septum which stems from the primary cartilage is affected by the
general extrinsic factors like growth hormone, sexual hormone and thyroxinel, In such
cases effect of biomechanical factors is reduced to modulation of direction of growth.
2. Growth from the cell division of prechondroblasts is affected by local extrinsic factors and
hence orthopedic appliances can be used to modulate growth

21. Stutzmann (1976) emphasizes the following :
 Primary cartilages exists in the axial skeleton, skull base, and limbs
 The dividing cells, differentiated chondroblasts , are surrounded by a cartilaginous matrix that
isolates them from local factors able to restrain or simulate cartilaginous growth.
 Secondary cartilages exist in condylar and coronoid processes and sometimes in sutures, the
dividing cells, prechondroblasts , are not surrounded by cartilaginous matrix.

22.  In primary cartilage the chondroblasts divide and synthesize intercellular matrix.
 In secondary cartilage the prechondroblasts are not yet surrounded by cartilagenous
matrix.
 When the secondary prechondroblasts begin synthesizing the cartilagenous matrix, they
usually stop dividing.
 Because of the presence of cartilaginous matrix the primary cartilage is not affected by
local factors .
 Absence of cartilagenous factors causes the secondary cartilage to be affected by local
factors.

23.  In normal condylar catilage of
growing individuals, the
skeletoblasts multiply, some
differentiate into
prechondroblasts.
 The resection of LPM produces a
significant slowing of the condylar
cartilage growth rate.
 The skeletoblasts no longer
differentiate into
prechondroblasts.

24.  Adaptive to both extrinsic and local biomechanical and functional factors
 Condylar cartilage growth is integrated into an organized functional whole that
has form of servosystem and able to modulate lengthening of condyle so that
lower jaw adapts to upper jaw during growth.

25.  Fibrous capsule – fibroblasts and type I collagen
 Zone of growth ( mitotic compartment) – skeletoblasts and prechondroblast
type – II, not surrounded by cartilaginous matrix with type I collagen.
 Zone of maturation – functional and hypertrophied chondroblasts
 Zone of erosion
 Zone of endochondral ossification.

27.  Anatomic, microscopic and histologic studies have shown that the
growth direction of the condyle coincide in general, with the axis of
individual trabeculae, located just inferior to the central part of condylar
cartilage
 Hence, the condylar growth direction can be determined by measuring
the main axis of the endochondral bone trabeculae in the condyle and
the angle it forms with the mandibular plane.

28.  A histologic and radiographic study was made of distribution of dividing cells in
a sagittal section of condylar cartilage of juvenile rats.
 Condylar cartilage divided into 4 equal sections from anterior to posterior and
cells counted
 Each experimental group was subjected to specific orthopedic treatment.
 Results showed that both treatment with the postural hyperpropulsor and with
the growth hormone produced significant increases in growth rate of condylar
cartilage compared to control group ( charlier et al, 1968, petrovic et al 1975)

30.  Condylar growth is not exclusively a result of the lengthening of pre-existing endochondral bone
trabeculae under condylar cartilage but also a result of growth of bone trabeculae ( mesenchymal
cells ) that are formed in parallel and posteriorly oriented in condylar cartilage.
 STUTZMANN ANGLE – angle formed between
main axis of endochondral bone trabeculae in
condyle with mandibular plane as viewed on
lateral ceph
 In anterior growth rotation there is closing of
angle as seen in treatment with growth hormone
 In posterior growth rotation there is opening of
angle as seen in treatment with postural
hyperpropulsor.

32.  Appropriate functional appliances that place the mandible in a forward postural position increase
the condylar cartilage growth rate and amount.
APPLICATION OF SERVOSYSTEM IN CLINICAL
ORTHODONTICS
•No increases in the contractile activity
•Action through the retrodiscal pad
•Alters Intrinsic regulation of the prechondroblasts multiplication
•Enhance the rate of hypertrophy of functional chonroblasts so that the decreased amount of
functional chondroblasts enhance prechondroblast replication

33. When the appliance is worn
Reduced length of the muscle as the
mandible is positioned forward
No stimulating effect on the condylar
cartilage
When the appliance is not worn
The retrodiscal pad is more stimulated
Early onset of hypertrophy of the
prechondroblasts
Growth rate of condylar cartilage is
increased

34. Forces
The forces employed in orthodontic and orthopedic procedures are compressive, tensile,
and shearing.
Mechanical appliances mostly use compressive forces and pressure strain.
Tensile forces causes stress and strain in functional appliance therapy

36.  A force can produce the desired orthodontic effect only if it has a certain duration,
direction and magnitude.
1. The duration of force in most functional appliance treatment is interrupted because
the appliance is usually not worn constantly but only for 12 to 16 hours per day
2. The direction of force for the movement of teeth should be consistent
3. The magnitude of force is small in functional appliance therapy,
If the induced strain is too great, the patient has difficulty wearing the appliance.
Application of heavy forces is not feasible for pure functional appliances.

37. Applied forces maybe compressive or tensile, Depending on the type applied, two
treatment principles can be differentiated :
Force Application and Force elimination
1. Force application – Compressive stress and strain act on the structures involved,
resulting in a primary alteration in form with a secondary adaptation in function.
All active fixed or removable appliances work accordingly to this principle.
2. Force elimination – Abnormal and restrictive environmental influences are
eliminated, allowing optimal development
The lip bumper and frankel buccal shields employ force elimination.

38.  The success of functional appliance therapy depends on the neuromuscular response.
 Functional appliances take advantage of growth and development, including osseous
formation and tooth eruption.
 They are considered biologic because of their force elimination and growth guidance
functions.
 Biologic treatment in its strict sense, works by guiding and controlling natural processes
and forces.
 If a relapse occurs after treatment, it is usually not as severe as one occurring after fixed
appliances.

39.  The stimulus of the stretch reflex is the stretch of the muscle.
 The stretch reflex, when elicited causes contraction of the stretched muscle spindles. The
muscle spindle is located within the muscle itself and consists of a bundle of 2 to 15 thin
intrafusal muscle fibers.
 The long slender ends of the intrafusal fibers are striated and contractile, whereas the central
or nuclear bag region is non contractile.
 The impulses arising form the muscle spindle (nuclear bag) are conducted by the Group IA
sensory nerve fibers. These sensory nerve fibers synapse with the motor neurons called
alpha efferents that supply the extrafusal muscle fibers responsible for the contraction of the
stretched muscle.
 The myotatic, or stretch reflex is therefore a monosynaptic reflex arc.

41.  If we attempt to flex the spastic limb of a patient forcibly, resistance is encountered as soon as
the muscle is stretched throughout the initial part of the bending.
 This resistance is, of course, due to the hyperactive reflex. Contraction of the muscle in
response to stretch (Myotactic, or Stretch reflex).
 If flex is forcibly carried further, a point is reached of which all resistance to additional
flexion seems to melt, and the previously rigid limb collapses readily.
 Because the resistance of the limb resembles that of spring loaded folding knife, blade. This
phenomenon is called the “clasp knife” reaction, that is the muscle first resists then relaxes

43.  Growth relative refers to growth that is relative
to its displaced condyles from actively
relocating fossae.
 John C. Voudouris introduced this concept to
explain the possible effect of functional
appliance on condyle and the resulting growth.
 The main foundation of growth relativity
hypothesis are :
› Displacement of condyle
› Nonmuscular viscoelastic tissue stretch
› Force transduction beneath the fibrocartilage of the
glenoid fossa and condyle add new bone formation

45.  A number of appliances primarily influence the lip, cheek, and tongue muscles.
 They can guide stomatognathic function or work solely by eliminating unwanted muscle
influence to permit undisturbed development of the dentition ( as the vestibular screen ).
 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.
 Unfavourable environmental influences over a long period can cause adaptation of orofacial
structures and create true developmental malocclusions, hence the need for early interceptive
therapy.

46.  The lower lip shield is actually the lower half of a full vestibular shield.
 It is extended into the vestibular sulcus to the labial fold and the distal margin of the last molar.
 The lower shield eliminates the persistent and pernicious hyperactivity of the mentalis muscle, which
forces the lower lip into the overjet space.
 It guides the lower lip into a more forward position and eliminating the lip trap, they enable
dentoalveolar development to follow a normal pattern.
 Only indication for this type of appliance is the elimination of perverted lower lip function in class II
division 1 malocclusions. ( or in class I flush terminal plane situations in which a large overjet has
already trapped the lip and the lower incisors are lingualized and crowded.

49.  According to Andresen and Haupl (1955), the activator is effective in exploiting the
interrelationship between function and changes in internal bone structure.
 The activator induces musculoskeletal adaptation by introducing a new pattern of
mandibular closure
 Appliance loosly fits into the mouth.
 Patient has to move mandible forwards to engage the appliance
 This results in stretching of the elevator muscles of mastication, which starts contracting
thereby setting up a myotactic reflex.

50.  This generates kinetic energy which
causes,
› Prevention of further forward growth of
the maxillary dento – alveolar process.
› Movement of the maxillary dento-alveolar
process distally
› A reciprocal forward force in the mandible.
 In addition to this myotactic reflex, a
condylar adaptation by backward and
upward growth occurs.

51.  The bionator is the prototype of a less bulky appliance
 Its lower portion is narrow, and its upper has only lateral extensions, with a crosspalatal
stabilizing bar.
 The palate is free for proprioceptive contact with the tongue; the buccinator wire loops hold
away potentially deforming muscular action; the appliance may be worn all the time, except
during meals.
 Balters (1960) developed the original appliance during the early 1950s, at the same time that
Bimler (1964) was working with a skeletonized activator.

52.  According to Balters, the equilibrium between the tongue and circumoral muscles is
responsible for the shape of the dental arches and intercuspation.

53.  Balter’s believed that only the role of the tongue was decisive.
 Using lateral wire configurations wires to relieve the forces of the surrounding neuromuscular
structures, he took only secondary Consideration of the neuromuscular envelope.
 The tongue exerts three to four times as much force on the dentition as does the buccal and labial
musculature; these findings would seem to support Balter’s thesis, if resting force and other
factors are not considered.
 The principle of treatment with the bionator is not to activate the muscles but to modulate muscle
activity, thereby enhancing normal development of the inherent growth pattern and eliminating
abnormal and potentially deforming environmental factors. In light of this, the bionator falls
between simpler screening appliances and the activator.

54. Vestibular area of operation
 According to Frankel, the denitition
is influenced by perioral muscle
function.
 Abnormal perioral muscle function
creates a barrier for optimal growth
of the dento-alveolar complex.
 Frankel is designed to hold away
muscles (buccal and labial) from the
dentition, so that the dento-alveolar
structures are free to develop

55. Sagittal correction via tooth borne maxillary anchorage
 It is anchored firmly in the maxillary arch by means of grooves in the molar and canine regions
 The mandible is positioned anteriorly by means of an acrylic pad that contacts the alveolar bone
behind the lower anterior segment.
 This lingual pad acts more at a proprioceptive trigger for postural maintenance of mandible
Differential eruption guidance
 It is free of the mandibular teeth.
 This allows selective eruption of the lower posterior teeth that aids in the correction of the
discrepancy in the vertical dimension and also helps in sagittal correction of class II malocclusion by
allowing upward and forward movement of the mandibular teeth.

56. Minimal maxillary basal effect
 In most class II malocclusions, the maxillary position is close to normal while the mandible is
retruded.
 It has relatively little retrusive sagittal effect on the maxilla in contrast to the marked protrusive
change in mandible.
Periosteal pull by buccal shields and lip pads
 The buccal shields and lip pads are extended to bring about outward periosteal pull.
 This aids in bone formation at apical base.

57.  Twin blocks are simple bite blocks with occlusal inclined
planes.
 First given by William Clark in 1977
 Class II skeletal bymaxillary prognathism
 Vertically directed grower
 Labial tipping of lower incisore
 crowding
 Permanant dentition and active grower.
 Uncrowded dentition with developed arches
 Positive VTO
 If patient is class II div 2 with limited overjet or class
II div 1 with crowded and irregular incisors, align the
upper incisor with a fixed or removable appliance
before starting a twin block.

58.  Active phase -
 6-9 months
 Appliance is used to achieve correction of sagittal jaw position
 Overjet, overbite and sagittal relationship is fully corrected.
 Support Phase –
 4 – 6 months
 Maintains corrected incisor relationship until the buccal relationship is fully
interdigited.
 Retentive phase –
 9 months
 Treatment is followed by retention with upper anterior inclined plane appliance.
 Appliance wear is reduced to night time wear only when the occlusion is fully
established.

59.  Functional appliances are not a remedy 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.
 We must keep ourselves updated with any developments in appliances and
craniofacial biology to ensure maximum effectiveness and efficiency
 A proper design and construction of the appliance is of paramount importance

60.  Dentofacial orthopedics with functional appliance – Thomas M. grabber, Alexandre G.
petrovic
 Proffit W R . Contemporary Orthodontics. St. Louis : C V Mosby Company; 2000.
 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.

61. THANK YOU