Physiologic Basis & Neural Mechanism Of Functional Appliances (39

Physiologic Basis &
Neural Mechanism Of
Functional Appliances
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Definition


Aims of Functional Appliance
Therapy
• Functional Appliance Therapy aims to improve the

•

functional relationship of dentofacial structure by
eliminating the unfavorable factors and improving
muscle environment enveloping the developing
occlusion.
Through alteration of teeth and supporting
tissues,a new functional behavior pattern or
engram is established that can support a new
position of equilibrium.


• An Increasing recognition of the interrelationship
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of form and function
The realization of the neuromuscular
involvement
Recognition of the importance of airway
Recognition of the role of excessive
epipharyngeal lymphoid tissue on head posture
and accomplishment of dentofacial pattern
• 3M

 Muscles

 Malformation

 Malocclusion


The physiologic basis of
functional Appliances
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Role of Respiration
Role of tongue
Role of Deglutition
Role of Lips
Role of Temporomandibular Joints


Role of Respiration
•

The size and shape of the nasopharyngeal space must be adequate for functional
demands
–

Linder - Aronson Study I 1960
• Mouth breathing was associated with crowding and narrow upper Jaws on patients with long and
narrow faces.

–

Study II 1970
• Adenoidectomies were performed in 81 children with nasal obstruction problems
• A comparison of mouth breathers was made with a equal number of nose breathers of similar gender

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and age
Children with obstructed nasal breathing were characterized by increase in lower and total facial
heights
The greatest difference between the two groups was in the vertical development of face and not in the
anteroposterior jaw relation
The breathing changed from mouth breathing to nose breathing
The breathing pattern remained unchanged


Factors contributing to alteration in the
posture of Mandible
Frequent Respiratory
Infection

Swollen Nasal
Mucosa

Nasal Septum Deviation

Reduced Nasal Breathing

Enlarged Adenoids

Mouth Breathing

Lowered Tongue Position

Extended Head Posture

Lowered Mandibular Posture

Contracted Maxillary Arch

Decrease In Nasal Width

Role of Tongue
• Abnormal Tongue posture and Function
• Primary factor as a consequence of
• Retained infantile deglutitional pattern
• Abnormal oral habits

• Secondary Factor

• Adaptive to the unfavorable morphologic pattern
Functional Appliances are indicated when the role of the
tongue malfunction is primary

Role of Deglutition

• Anterior Lip seal and a posterior oral seal
• Tongue and soft palate
• Creates negative pressure in the oral cavity
• Cheeks are sucked in to the interocclusal space
• Mandible returns to postural rest position
• Constricts the dentoalveolar process
• Prevents eruption of buccal segments

Role Of Lips
• The configuration of the lips should be studied in relaxed position for
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assessing incompetency
If there is slight contact or a small gap between the upper and lower
lips,they are said to be competent
If there is a wide gap , or if the lips are too short ,they can be
considered incompetent. Improvement with orthodontic treatment
and exercise is possible only in early stages
If the lips seems normally developed but the incisors are labially
tipped making closure difficult, Ballard And Tulley call this as
potential lip incompetence


Method Of Operation of
• Theories of Cranio Facial Growth
• Genetic Control Theory

– Genotype supplies all information for phenotype

• Cartilage – Directed growth Theory

– Scott ( Nasal septum ,condyle ,Synchonedroses )

• Functional Matrix Theory
– Melvin Moss
 Periosteal Matrix
 Capsular Matrix

• Servosystem Theory

– Primary Cartilage - General Extrinsic Factor ( STH, Thyroxinel )
– Secondary Cartilage – Local Extrinsic Factors ( Functional Orthopedic
Devices )

Control Of Maxillary Growth
• Growth in length of
upper Jaw

• Growth in width of
upper Jaw


Control Of Mandibular Growth


Servo System Theory
•

Gm - Lengthening of Maxilla

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Gc + - Growth of condylar cartilage
after resection of LPM

•

Gc ++ Growth for minimal activity of
LPM

•

Gc+++ Growth for Maximal activity of
LPM


Morphogenetic Classification Of
Human Facial Development


Causal Interpretation of mode Of Operation
of Functional Appliances
• Functional Appliances
• Increased Contractile activity of LPM
• Intensification of repetitive activity of retrodiscal pad
• Increase in growth stimulating factors
• Enhancement of local mediators
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STH GROWTH HORMONE
TESTOSTERONE
INSULIN
THYROXIN
CALCITONIN
PARATHORMONE
GROWTH PROMOTING PEPTIDES

• Reduction of local regulators
( Factors having negative feed back effects on cell multiplication )
CYCLIC AMP
PROSTAGLANDIN E2
SOMATOSTATIN LIKE SUBSTANCE

• 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


Neural Pathway for reflex and Volitional
control of the Masticator Nucleus

• Proprioceptive fibers arising from Periodontal membrane ,Muscles of Mastication,TMJ
• Ascend Via Trigeminal nerve to the brain stem
• Mesencephalic nucleus
• Descends to the masticator nucleus on the ipsilateral side
• Synapses with the lower motor neuron
• Caries motor impulses to the muscles of mastication via Trigeminal Nerve


Reflex control of Skeletal Muscle contraction
• Stretch of Muscle
• Stimulus for Stretch Reflex
• Stretch reflex elicited
• Contraction of Stretched Muscle
• Muscle stretch receptors muscle spindles proprioceptive nerve endings
• Impulses from muscle spindle
• Synapse with motor neurons
• Supply extrafusal muscle fibers

• Contraction of Stretched Muscle

Neural Control Of Skeletal
Muscle Contraction
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Activation Of Gamma Efferents

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Polar Contraction of Intrafusal Fibres

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Non Contractile Nuclear Bag Tensed

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Initiate spindle discharge in absence of
external discharge

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Acts as a biasing Mechanism


Mechanism of Skeletal Muscle
Contraction

• Functional Significance

– Serves as a mechanism for
upright posture
– Acts in the mandibular
musculature to maintain
Postural rest position of the
mandible in relation to maxilla

Clasp – Knife reflex Or
Autogenic Inhibition

• Functional Significance

– Protects the overload by
preventing damaging
contractions against strong
stretching forces

Role of Lateral Pterygoid Muscle in Growth
Of Condylar Cartilage
• Multiplication of Skeletoblasts in condylar cartilage
• Skeletoblasts differentiate in to prechondroblasts
• Resection of LPM
• Significant slowing of condylar cartilage growth rate
• Skeletobalsts no longer differentiate in to prechondroblasts
• Percentage of skeletoblasts increases to the detriment of the prechodrobalsts
• Prechondroblasts decreases in number
• Skeletoblasts begin differentiating in to Preosteoblasts and Osteoblasts
• The condyle then increases in size through periosteal type of growth

Role of Retrodiscal Pad
•

The retrodiscal pad controls the mandibular growth in two ways
– Vascular Component
• Controls the condylar cartilage growth rate and endochondral ossification rate
• An increase in activity of the retrodiscal pad produces an increase in condylar
cartilage growth ossification
– Biomechanic Component
• Governs both bone apposition and condylar growth direction at posterior border of
the ramus
• An increase in the interactivity of the retrodiscal pad produces an accentuation of
the ramus posterior concavity and a local increase in bone apposition and he
number of negative charges at the ramus posterior concavity surface
• It also produces an accentuation of the ramus anterior convexity and a local
increase in bone resorption and the number of positive charges at the ramus
posterior convex surface


• Interruption of the circulatory dependence on the blood supply originating directly
from LPM and directly through the retrodiscal pad may contribute to the inhibited
differentiation of skeletoblasts

• Surgical excision of the retrodiscal pad and anteriorly displaced articular

disks,destroying intracapsular metabolism pump function of the retrodiscal pad,
dramatically demonstrates the mechanistic Iatrogenic potential of nonphysiologic
surgery

• After surgical resection of the LPM the growth of the condylar cartilage and the
lengthening of the mandible continue but are significantly reduced.


Relationship of Retrodiscal Pad
and Lateral Pterygoid Muscle


Condylar Cartilage - Growth Direction

• Mitosis distribution and

area of concentration a
sagittal section of
condylar cartilage.The
cartilage surface is
divided in to 4 sections

Endochondral Bone Trabeculae in
Mandibular Condyle

• Diagram


Biologic Features of Primary & Secondary
Cartilages

Primary Cartilage

Epiphyseal ,Nasal
Septum,Spheno occipital
Synchondrosis

Secondary Cartilage

Condylar, Coroniod,Angular
cartilages


Intrinsic Regulation of condylar
Cartilage Growth Rate
• The acceleration Maturation of
Chondroblasts

– Growth Stimulating effect of
Thyroxinel

• Chondroblasts Hypertrophy
Prechondroblasts Division
Restraining Signal

– Growth Stimulating effect of


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Physiologic Basis & Neural Mechanism Of Functional Appliances (39

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