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MYOFUNCTIONAL APPLIANCESCONTENTSDEFINITIONHISTORYCLASSIFICATIONMECHANISM OF CRANIO FACIAL GROWTHADVANTAGES AND DISADVANTAGESCRITERIA FOR CASE SELECTIONPRINCIPLES OF MYOFUNCTIONAL APPLIANCEACCORDING TO TOM GRABERS CLASSIFICATION

BITE PLANEINCLINED PLANEORAL SCREEN VESTIBULAR SCREEN

DEFINITIONFunctional or myofunctional appliances are defined as loose fitting or passive appliances, whichharness natural forces of the oro-facial musculature, that are transmitted to the teeth and alveolar bone through the medium of the appliance.

HISTORYTHE PAST

History ..the pastROUX 1883-Reported the influence of natural forces and the functional stimulation on form of tissues.This hypothesis shaking of bone became the background of both general and functional dental orthopedic procedures.HISTORY the past

History traced back to 1879Norman .w. kingsley:- introduced the term jumping the bitefor patients with mandibular retrusion-1880.

HISTORY.The pastHe used a vulcanite palatal plate with an anterior inclined plane, which guided the mandible to a forward position when patient closed on it.

His ideas influenced the development of functional jaw orthopedics

HISTORY.THE PASTPierre robin, -1902- developed the monobloc appliance, used to influence muscular activity by change in spatial relationship of jaws.

Fore runner of all functional appliance.

Designed this appliance for persons with gloosoptosis syndrome :-robbins syndrome11HISTORY..The pastAlfred p.rogersSometimes called father of myofunctinal therapy

Recognized the importance of whole oro facialsystem in the problem of orthodontic treatment.

HISTORY ..The pastViggo andresen-1920-ACTIVATORNot initially well received .Karl haupl:- became enthusiastic, and they together called this the norwegian system.VIGGO ANDRESEN

HISTORY-----THE PASTHAUPL Applied roux concepts to the correction of jaw and dental arch deformities.Explained how functional appliances worked through the activity of orofacial muscles. the principle and their application lead to development of orthodontics in Europe.Crisis in orthodontics-Oppenheim showed potential tissue damaging effect of heavy orthodontic force.

KARL HAUPLFunction is inherent in all cells ,tissues,and organs .it influences the medium in which it works,literally as functional stimulus.the goal of dental orthopedics is to utilize this functional stimulus channeling it as far astissues ,jaws ,condyles and teeth will allow.mot:passive,forces are purely functional and itermittent in nature,he belived cont active force cannot bring about remodelling.clinical aspect -anderson14HISTORY.The pastFirst functional appliance to be widely accepted. universal applianceHISTORY-----------THE PASTschwarz, reitan and other investigators proved that any force applied causes hyalinization changes in bone.

A. MARTIN SCHWARZHISTORY OF DEVELOPMENT OF FUNCTIONAL APPLIANCEROBIN 1902-MONOBLOCANDRESEN 1920-ACTIVATORHERBST 1934-HERBSTBALTERS 1960-BIONATORBIMLER 1964-BIMLERFRANKEL 1967-FRANKELCLARK 1977-TWIN BLOCKAN17CLASSIFICATION 1. StockfishTOM GRABER 2. when functional appliances where still removable

GROUP A GROUP BGROUP CTOOTH SUPPORTEDTOOTH/TISSUE SUPPORTEDTISSUE SUPPORTED 3. WITH THE ADVENT OF FIXED FUNCTIONALS PETER VIGI WITH THE AWARENESS AND ACCEPTENCE OF CONCEPT OF HYBRIDISATIONPROFITT FORCE ANALYSISTYPES OF FORCEPRIMARY FORCE - force applied by functional applianceSECONDARY FORCE - reaction of tissues to primary forceThis causes strain in tissues.Types of forcesForce application and force eliminationchangesFunctional appliance can bring about ORTHOPEDIC CHANGES DENTAL CHANGES MUSCULAR CHANGES1 orthopedic changes Accelerating growth in condylar region. Remodeling of glenoid fossa Restrictive influences and changing direction of growth of jawsDENTAL CHANGESMuscular change:- functional appliance can induce sensory stimulation to trigger a neuromuscular response.Children with neuromuscular disease such as poliomyelities and cerebral palsy cannot be treated successfully with functional appliance therapy.Muscular hypothesis MECHANISM OF CRANIO FACIAL GROWTHAndersen-Haupl

Petrovic and McNamara MECHANISM OF CRANIO FACIAL GROWTH

Viscoelastic hypothesis MECHANISM OF CRANIO FACIAL GROWTHSelmer-oslenHaroldWoodsideHerrenPassive tension caused by stretching of muscles, soft tissues, e.t.c applies a rigid stretch and create a build up of potential energy.Depending on the magnitude and direction, viscoelastic reaction can be divided into1 Emptying of vessels2 Pressing out of interstitial fluid3 Stretching of fibers4 Elastic deformation of bone5 Bioplastic adaptation

Servosystem Theory of Craniofacial Growth

Introduction:

The concept of cybernetics and control theory was put forth by Petrovic (1977, 1982) to describe the craniofacial growth mechanisms and the method of operation of functional and orthopedic appliances. The theory demonstrates a qualitative and quantitative relationship between observationally and experimentally collected findings. It helps in a broader understanding of orthodontic problems as the language of cybernetics is compatible with the rapidly expanding use of computers among clinicians.

Cybernetics is based on the communication of information.

Any cybernetically organized system operates through signals that transmit information (which may be physical, chemical or electromagnetic in nature).Any cybernetic system, when provided an input (or stimulus), processes such an input and produces an output. The output is related to the input by a transfer function:-

This is similar to feeding numbers into a computer, and obtaining the sum or product of the numbers. The calculations performed by the computer, correspond to the TRANSFER FUNCTION

Physiological systems can be of the various types shown below:

Loops:The previous example shows an open loop. The Output does not affect the input.

In a closed loop system, a specific relation is maintained between the input and output.

Closed loops are characterized by a feedback loop and a comparator.

The input is fed into a comparator which analyses the input and judges the degree to which the transfer function needs to be carried out to obtain a certain output.

The output is fed back to the comparator (by a feed back loop) and is analyzed as to its adequacy. If found to be inadequate, the transfer function is carried out once again. The feed back loop can have a positive or enhancing effect or a negative or attenuating effect.

Closed loops can be of two types:-

A Regulator type of closed loop is one which the input is constant. Any disturbance in the input will cause the comparator to initiate a regulatory feedback system, which will restore the input to its normal state. An example of this is the temperature regulation system of the body. Any change in body temperature acts as the input into the comparator (the hypothalamus), which causes an action (pilorection or shivering) which ultimately brings the body temperature back to normal.

Servo-system- In this, the main input is constantly changing with time, and the output is constantly adjusted in accordance with the input.

Various Components of a Servo-System

1) Command- A signal established independent of the servosystem, and is not affected by the output of the system. Hence, as the name suggests, it tells the system what is to be done. 2) Reference Input- The input into the servo-system (which is brought about by the command). The command created a reference input through the action of a reference input element.

So the design of the servo-system so far is

3) Comparator (Peripheral) - The input is fed into the comparator which is the component that analyses the reference input and judges the performance of the system through performance judging elements.

4) Central Comparator- The performance judging elements then transmit a deviation signal to the central comparator which sends a signal to various components the actuator, the coupling system and the controlled system (which will be discussed later). This ultimately brings about an output (also known as the controlled variable).

Therefore, the servo-system is:-

Growth of the Face As Explained by the Servosystem Theory

Background1) Types of Cartilage and influence of growth factors on them.2) Role of the lateral Pterygoid and retrodiscal pad in condylar growth.

Types of Cartilage:

a) Primary Cartilage The zone of growth is comprised of functional chondroblasts, which divide, and synthesize a cartilaginous matrix. Chondroblasts undergo maturation and are later transformed into hypertrophied chondroblasts. Deeper in the cartilaginous matrix, calcium is deposited and endochondral ossification begins.

b) Secondary CartilageThe zone of growth includes skeletoblasts and perchondroblasts cells that divide but do not synthesize a cartilaginous matrix. Once the prechondroblasts mature into chondroblasts, they become surrounded by cartilaginous matrix and do not divide.

Primary cartilages are seen in:-1) Epiphysial cartilages of long bones2) Cartilages of synchondroses of cranial bones3) Nasal septal cartilage4) Lateral cartilaginous masses of ethmoid5) Cartilage between greater wings and body and sphenoid.

Secondary cartilages are seen in:-1) Coronoid cartilage2) Condylar cartilage3) Midpalatal suture cartilage4) Post fracture callus

According to studies carried out by Charlier, Petrovic and Stutzmann on organ cultures, at the Strasbourg Laboratory of Craniofacial Growth Mechanisms, France:-

1) Dividing chondroblasts (in primary cartilage) are more susceptible to general extrinsic factors, especially growth hormone, somatomedin, sex hormones and thyroxinel.The cartilage matrix surrounding the mature chondroblasts isolates them from the effect of local factors. Local Biomechanical factors (like functional appliances) can only modify the direction of growth.

2) In the secondary cartilages, where prechondroblasts ate the dividing cells, general and local extrinsic factors can affect the growth. The amount of growth of these cartilages can be modulated by using orthopedic appliance.

Role of Lateral Pterygoid muscle and retrodiscal pad on condylar growth.

Lateral pterygoid muscle is involved in 2 important aspects:-a. Blood Circulationb. Biomechanic

The blood supply to condylar cartilage is mainly from the lateral pterygoid muscle and the retrodiscal pad. On surgical excision of these 2 structures the growth rate of the condyle is significantly diminished.

Biomechanical effects:-

Contraction of the lateral pterygoid muscle places the condyle in a more anterior position. This causes a stretching of the retrodiscal pad. Repeated contraction causes increases activity of the retrodiscal pad, resulting in an increased blood supply and increases washing away of metabolites, which tend to inhibit growth.

Increase in the blood supply increases the supply of nutritive factors as well as growth factors such as stomatomedin, testosterone, and other hormones.

Rat experiments by Stutzmann and Petrovic have shown that proper function of these two structures is essential for proper mandibular growth.

Growth of the Face

The growth of the maxilla is brought about by the release of hormones (esp. STH-Somatomedin). These hormones have various direct and indirect effects which result in the growth of the maxilla.

Somatomedin induces growth of primary and secondary cartilages (like the nasal cartilage, spheno-occipital synchondrosis, lateral cartilaginous masses of ethmoid, cartilage between the greater wings and body of the sphenoid) which results in an outward and forward growth of the maxilla.

Another important action of somatomedin is the increase in the size of the tongue, which also facilitates the outward and forward growth of the maxillary dental arch.

Once the maxilla increases in length and width, the position of the maxillary dental arch is changed.

THE POSITION OF THE MAXILLARY DENTAL ARCH FORMS THE REFERENCE INPUT OF THE SERVOSYSTEM.

The release of somatomedin represents the COMMAND (command to grow). The hormone itself is the REFERENCE INPUT ELEMENT.

The OCCLUSION between the upper and lower teeth forms the COMPARATOR.

Owing to the forward and outward growth of the maxilla there is an obvious change in the relation of the teeth. What was originally a cusp to fosse relationship becomes a cusp to cusp relationship.

Hence the PERIPHERAL COMPARATOR (occlusion) senses this due to a chance in PERFORMANCE or the efficiency of mastication. Due to improper mastication, there is increased force on the periodontium, teeth, muscles and TMJ, which serve as the PERFORMANCE ANALYSING ELEMENTS.

The performance analyzing elements send signals to the CENTRAL COMPARATOR which is represented by the central nervous system. The CNS is equipped with a SENSORY ENGRAM which is a record of ideal tooth relations, and a record of the ideal muscular posture which can help to attain proper mandibular position. Details on the development and functioning of the sensory engram are given subsequently.

The CNS compares the present muscular position with the ideal muscular position stored in the sensory engram. It then sends a DEVIATION SIGNAL to correct this discrepancy.

The deviation signal is sent to an ACTUATOR which is represented by the motor cortex. The actuator then sends an ACTUATING SIGNAL to the COUPLING SYSTEM of the lateral pterygoid muscle and the retrodiscal pad. The LPM positions the mandible forward and the activity of the retrodiscal pad induces mandibular growth at the condyle (THE CONTROLLED SYSTEM)

The resultant output or CONTROLLED SYSTEM is the forward growth of the mandible which results in an ideal cusp to fossa dental relation.

Growth at the Posterior Border of the Mandible

Once growth occurs at the condyle, the posterior border of the mandible becomes more concave in shape.

This causes a negative piezoelectric effect to develop at the posterior border of the mandible, and bone apposition results. At the same time, the anterior border of the condylar process becomes more convex, causing a subsequent POSITIVE piezoelectric current to develop and a subsequent resorption of bone occurs. This accounts for an increase in length of the mandible.

SOME OTHER TERMS RELATED TO A SERVOSYSTEM

Gain- Gain of a system is the output divided by the input

Gain = OutputInput

If the gain is greater than 1, it indicates amplification caused by the system. If it is less than 1, it indicates and attenuation.

Petrovic suggests that the gain is genetically determined, but can be altered to an extent by hormonal influences.

Attractor- It is the final structural state that the system tries to attain. i.e.:- Maximum interception.

Repeller- All the unstable states that the system tries to avoid.i.e.:- cusp to cusp relation.

Disturbance- Any input, other than the reference input, which tends to have an effect of the output.E.g. - Abnormal tooth positions or occlusal interferences can act as a disturbance to the peripheral comparator.

The Sensory Engram

The CNS serves as a central comparator for the servosystem. The central comparator refers to what is known as the SENSORY ENGRAM.

The sensory engram is a collection of feedback loops, which record the activity of the masticatory muscles corresponding to a particular, habitual mandibular position. In other words, the optimal functional blueprint is recorded as the sensory engram.

As optimal function of the masticatory muscles develops, the CNS develops feedback loops which, in effect, memorize the best muscle function. Once these feedback loops develop, the CNS tends to operate along these pathways.

The sensory engram operates on the principle of OPTIMALITY OF FUNCTION. Any particular muscle action or mandible position that gives the minimum deviation signal is recorded in the sensory engram.

This means that when any new mandibular position is dictated to the patient, unless the new position causes a smaller deviation signal than the ole position, the CNS will tend to make the mandible relapse to its older position, wherein the function was more ideal.

An observation of Jacobs clearly demonstrates this. He observed that chain gang prisoners need to alter the way in which they walk owing to the extra weight they have to carry. Once the chains are removed, they retain the altered walking pattern only for a short while, and later reverted back to a normal gait. So when the restrictions are removed, the optimal muscular pattern is readopted.

Hence, once the sensory engram is established, the CNS has a reference of optimal function, towards which it strives to maintain all bodily functions.

Peripheral comparator, Catastrophe Theory and Bifurcations

The peripheral comparator is an important element in control of the growth of the face (especially the mandible). Its functions can be divided into 2 stages:-1. When inter-cuspal relationships have not yet developed (very young children) Since stable occlusion is not established, the peripheral comparator is not established. Since there is no stable occlusion, the reference engram is unable to develop. Hence even though the other components of the servosystem are operational, they cannot control growth of the mandible in very young children, since the peripheral comparator is not yet developed. Therefore mandibular growth is mainly genetically influenced. This stage lasts foe a different amount of time in different individuals, and can last indefinitely in case of anodontia.

2. The second phase is the development of stable occlusion Sensory engram begins forming Peripheral comparator can control craniofacial growth.

Another characteristic of the peripheral comparator is the existence of DISCONTINUITIES. Between two stable points (intercuspation) there is an area of instability (cusp to cusp relation).

So a stable phase can never be changes to another stable phase without an unstable phase.This forms the basis of the CATASTROPHE THEORY.

When the cuspal relation reaches the cusp to cusp relation, 2 possibilities can result:-

This is known as a bifurcation.

The alteration in the occlusion can result in either of the types of cusp to fossa relations. This brings us to the concept of OPTIMAL OCCLUSION (Class I) which is always desired, and SUBOPTIMAL OCCLUSION (Class II and Class III) which is not optimal, but stable none the less.

So a Class II molar relation will never spontaneously revert to a Class I

As the teeth move into a cusp to cusp relation, there is always a feedback system which rends to bring it back to cusp to fossa relation.

DISCONTIUITIES as seen above are important points in control of cranio-facial growth, and should always be taken into consideration during growth prediction, treatment planning and decision making. As mentioned earlier, a given occlusal pattern can be formed due to any number of causes. But once it is established, it remains relatively stable, as any local changes are minimized by the regulatory process.

Another important aspect of discontinuities is that it explains how a genotype may only partially influence the phenotype. The gene sequence only codes a regulatory pattern. It is around these regulatory patterns that a phenotype is expressed. This means that very small fluctuations taking place around a bifurcation at a crucial time can lead to very different results.

Failure of the Servosystem to Control Growth

The peripheral comparator is the most fragile component of the servosystem. Any problem in the dentition (rampant caries, missing teeth, mutilated dentition) can cause an improper functioning of the servosystem, as the occlusion cannot be established properly.

If there is a discrepancy between the rotation pattern and location of the comparator (if anterior teeth form the comparator in posteriorly rotating mandible, or the posterior teeth form the comparator in the anteriorly rotating mandible) then the servosystem cannot fine tune the growth process of the mandible to the maxilla.

Development of Skeletal Malocclusion According to the Servosystem theory

The development of malocclusion can be explained with the help of the following graph.

For every unit of STH-Somatomedin or testosterone that is released, the amount of maxillary growth is less than that of the mandible.

The line Max. indicates the growth of the maxilla (LPMmax) Growth of the mandible with maximum activity of the LPM(LPMmin) Growth of the mandible with minimum activity of the LPM(LPMnorm) Growth of the mandible with normal activity of the LPM

Under normal circumstances, the hormonal level is around N and a good maxillo-mandibular relation is maintained. As the hormonal level starts increasing towards L2, the maxilla starts to grow, and the mandible grows at an even faster rate. The action of the servosystem at this stage is to reduce the amount of LPM activity, so that less mandibular growth occurs. So, a good maxillo-mandibular relation is maintained.

When hormonal levels reach L2, the LPM is at its minimum activity. This is the maximum restraint on mandibular growth. Beyond L2, the activity of the LPM can no longer control growth of the mandible adequately enough and mandibular growth starts to exceed maxillary growth resulting in prognathism.

The opposite happens when hormone levels fall below L1.

So within levels L1 to L2, a good maxillo mandibular relation is maintained. Outside these levels, malocclusions result.

The relation between the maxilla and mandible between the levels L1 & L2 are maintained by contractile activity of the LPM, as controlled by the servosystem, as well as by a change in the gonial angle.

Action of Functional Appliances based on the Servosystem Theory

As it can be seen from the preceding graph, in a patient with retrognathism, the LPM is at its maximum activity. Hence the mandible cannot be brought forward any more and therefore retrognathism results.

Two types of functional appliances have been recognized according to their mode of action:-1. Appliances like the activator, postural hyperpropulsor, Frankel appliance, Twin block, Bionator etc.2. Appliances like the Herren &LSU activator, Harvold-Woodside activator, Extra oral traction on the mandible, which position the mandible forward and open it beyond the physiologic rest position.

First Group

When appliance is in place, there is increased activity of the LPM and RDP due to the forward positioning of the mandible.

Studies by Oudet et al (1988) and Carlson et al (1990) show that this increases the number of non fatigable fibers in the LPM. This shows that the LPM is, in effect helped to contract more by the functional appliance. Hence, the mandible grows forward by deposition of bone at the condyle. Hence length and even direction of growth is altered.

Also, when the mandible is positioned forward, a cusp to cusp relation results. The peripheral comparator interprets it as a forward movement of the maxilla (as even that will result in a cusp to cusp relation). So, since the reference input has been moved forward, the peripheral comparator sends a deviation signal to the central comparator. Then the central comparator sends the actuating signal to the actuator, and so on, ultimately resulting in growth of the mandible.

Cellular levelIt is important to know the effects at the cellular level, especially to understand the effect of Class II elastics, where, electromyographically no increase in contractile activity of the lateral pterygoid is seen. The action of Class II elastics requires the retrodiscal pad to be present. If RDP is excised, Class II elastics do not induce mandibular growth.

Before discussing how Class II elastics stimulate condylar growth, it is important to understand the microscopic working of the cartilage.

The mitotic cells in the condylar cartilage are of 2 types:-1. Precursor cells pleuripotent, fibroblast like skeletoblasts which differentiates into 2. Prechondroblast faster cell cycle & the main cell of the mitotic component. The prechondroblasts mature into chondroblasts.

It is seen experimentally, that if chondroblasts are lost by resection or hypertrophy and death, there is increased multiplication of prechondroblasts. This indicates that there is a local control over multiplication of prechondroblasts, which originates from the chondroblastic layer. And, the thicker the chondroblastic layer, the more intense is this negative feedback signal. (Stutzmann & Petrovic 1982, 1990)

Class II elastics, (and other functional appliances, but to a lesser extent) cause increase in activity of the RDP and hence increase in the blood and lymph supply to the condylar region. Hence nutrients and growth factors are supplied and metabolites and growth inhibitors are washed away.

In addition, to increasing mitosis, this leads to an earlier start of the hypertrophy of chondroblasts. Hence the previously mentioned negative feedback signal is mitigated and increased growth at the condyle results.

Also, cytoplasmic junctions between skeletoblasts are reduced and hence transmission of inhibitory factors also reduces. Skeletoblast mitotic rate increased and rate of differentiation into prechondroblasts also increases.

The second group of appliances has a slightly different type of action:-The appliances in this group tend to position the mandible forward as well as open it well beyond the physiologic rest position. The mobility of the mandible is also reduced. No increase or even a slight decrease in the activity of the LPM was seen when these appliances were worn. Yet there was in increase in growth.

This can be explained as a 2 step process.

1. The time the appliance is worn, the forward positioning of the mandible caused a reduction in the length of the LPM. At this time a new sensory engram is formed for this position of the mandible. 2. When the appliance is not worn, the mouth functions according to this new sensory engram. So the mandible is functioning in a more anterior position. This increases the activity of the RDP, leading to earlier hypertrophy of chondroblasts and in turn, increased multiplication of prechondroblasts.

Hence actual lengthening of the mandible takes place when appliance is not worn.

Also, the bite can be opened only to a particular limit. If it is opened more than that, no growth is seen.

Clinical Implications

1) According to the principle of optimality of function, a condition which results in maximum efficiency is one that is instilled into the brain. So, all orthodontic treatment must strive to reach the optimal functional situation, or, if this is not possible, the post treatment functional condition should be better than the pretreatment condition.

If this is established, the tendency for relapse is less.

2) A functional appliance should be removed only when growth is completed, or if growth is not completed, it should achieve a good intercuspal relation (the attractor). This ensures a stable result. If the treatment ends with the teeth in poor occlusion (repeller), relapse is more likely to occur.

3) An understanding of how functional appliances affect the servosystem is important to know how long the appliance is to be worn.

The first group of appliances should be worn full time.

The second group of appliances should be worn part time.

4) Proper function of the LPM RDP is essential for growth. This was shown by rat experiments by Petrovic and Stutzmann.

Ideal functioning of LPM-RDP not only increases the amount of growth of the mandible, but also improved the response to functional appliances, as was seen in breast fed versus gavage fed rats.

This is important to know for counseling purposes.

5) The sensory engram in children is poorly developed. Hence younger children respond better to functional appliance therapy than older children, and the results are more stable.

6) Hormonal activity is highest at puberty, during the pubertal growth spurt. Since hormones are very important for growth, one must take full advantage of the increased hormonal activity if any growth modulation is required.

Drawbacks

1) The theory places a lot of importance on the condyle as the growth centre. Hence if the condylar cartilage is lost subsequent to a fracture, growth should seize. But studies done in Scandinavia show that this does not happen.

2) The author places a lot of importance on the role of hormones in controlling growth. In all probability, they do not have such a large role to play.

3) The peripheral comparator, the occlusion, itself, is unstable. Discrepencies in the occlusion can easily be overcome by dentoalveolar changes, rather than by growth of the mandible.

4) According to the theory, an end on relation is a repeller. Still, end on relation of the molars and other teeth are often seen.

5) The theory does not explain the action of the reverse pull headgear.

_________________Servosystem Theory of Craniofacial Growth

Introduction:

The concept of cybernetics and control theory was put forth by Petrovic (1977, 1982) to describe the craniofacial growth mechanisms and the method of operation of functional and orthopedic appliances. The theory demonstrates a qualitative and quantitative relationship between observationally and experimentally collected findings. It helps in a broader understanding of orthodontic problems as the language of cybernetics is compatible with the rapidly expanding use of computers among clinicians.

Cybernetics is based on the communication of information.

Any cybernetically organized system operates through signals that transmit information (which may be physical, chemical or electromagnetic in nature).Any cybernetic system, when provided an input (or stimulus), processes such an input and produces an output. The output is related to the input by a transfer function:-

This is similar to feeding numbers into a computer, and obtaining the sum or product of the numbers. The calculations performed by the computer, correspond to the TRANSFER FUNCTION

Physiological systems can be of the various types shown below:

Loops:The previous example shows an open loop. The Output does not affect the input.

In a closed loop system, a specific relation is maintained between the input and output.

Closed loops are characterized by a feedback loop and a comparator.

The input is fed into a comparator which analyses the input and judges the degree to which the transfer function needs to be carried out to obtain a certain output.

The output is fed back to the comparator (by a feed back loop) and is analyzed as to its adequacy. If found to be inadequate, the transfer function is carried out once again. The feed back loop can have a positive or enhancing effect or a negative or attenuating effect.

Closed loops can be of two types:-

A Regulator type of closed loop is one which the input is constant. Any disturbance in the input will cause the comparator to initiate a regulatory feedback system, which will restore the input to its normal state. An example of this is the temperature regulation system of the body. Any change in body temperature acts as the input into the comparator (the hypothalamus), which causes an action (pilorection or shivering) which ultimately brings the body temperature back to normal.

Servo-system- In this, the main input is constantly changing with time, and the output is constantly adjusted in accordance with the input.

Various Components of a Servo-System

1) Command- A signal established independent of the servosystem, and is not affected by the output of the system. Hence, as the name suggests, it tells the system what is to be done. 2) Reference Input- The input into the servo-system (which is brought about by the command). The command created a reference input through the action of a reference input element.

So the design of the servo-system so far is

3) Comparator (Peripheral) - The input is fed into the comparator which is the component that analyses the reference input and judges the performance of the system through performance judging elements.

4) Central Comparator- The performance judging elements then transmit a deviation signal to the central comparator which sends a signal to various components the actuator, the coupling system and the controlled system (which will be discussed later). This ultimately brings about an output (also known as the controlled variable).

Therefore, the servo-system is:-

Growth of the Face As Explained by the Servosystem Theory

Background1) Types of Cartilage and influence of growth factors on them.2) Role of the lateral Pterygoid and retrodiscal pad in condylar growth.

Types of Cartilage:

a) Primary Cartilage The zone of growth is comprised of functional chondroblasts, which divide, and synthesize a cartilaginous matrix. Chondroblasts undergo maturation and are later transformed into hypertrophied chondroblasts. Deeper in the cartilaginous matrix, calcium is deposited and endochondral ossification begins.

b) Secondary CartilageThe zone of growth includes skeletoblasts and perchondroblasts cells that divide but do not synthesize a cartilaginous matrix. Once the prechondroblasts mature into chondroblasts, they become surrounded by cartilaginous matrix and do not divide.

Primary cartilages are seen in:-1) Epiphysial cartilages of long bones2) Cartilages of synchondroses of cranial bones3) Nasal septal cartilage4) Lateral cartilaginous masses of ethmoid5) Cartilage between greater wings and body and sphenoid.

Secondary cartilages are seen in:-1) Coronoid cartilage2) Condylar cartilage3) Midpalatal suture cartilage4) Post fracture callus

According to studies carried out by Charlier, Petrovic and Stutzmann on organ cultures, at the Strasbourg Laboratory of Craniofacial Growth Mechanisms, France:-

1) Dividing chondroblasts (in primary cartilage) are more susceptible to general extrinsic factors, especially growth hormone, somatomedin, sex hormones and thyroxinel.The cartilage matrix surrounding the mature chondroblasts isolates them from the effect of local factors. Local Biomechanical factors (like functional appliances) can only modify the direction of growth.

2) In the secondary cartilages, where prechondroblasts ate the dividing cells, general and local extrinsic factors can affect the growth. The amount of growth of these cartilages can be modulated by using orthopedic appliance.

Role of Lateral Pterygoid muscle and retrodiscal pad on condylar growth.

Lateral pterygoid muscle is involved in 2 important aspects:-a. Blood Circulationb. Biomechanic

The blood supply to condylar cartilage is mainly from the lateral pterygoid muscle and the retrodiscal pad. On surgical excision of these 2 structures the growth rate of the condyle is significantly diminished.

Biomechanical effects:-

Contraction of the lateral pterygoid muscle places the condyle in a more anterior position. This causes a stretching of the retrodiscal pad. Repeated contraction causes increases activity of the retrodiscal pad, resulting in an increased blood supply and increases washing away of metabolites, which tend to inhibit growth.

Increase in the blood supply increases the supply of nutritive factors as well as growth factors such as stomatomedin, testosterone, and other hormones.

Rat experiments by Stutzmann and Petrovic have shown that proper function of these two structures is essential for proper mandibular growth.

Growth of the Face

The growth of the maxilla is brought about by the release of hormones (esp. STH-Somatomedin). These hormones have various direct and indirect effects which result in the growth of the maxilla.

Somatomedin induces growth of primary and secondary cartilages (like the nasal cartilage, spheno-occipital synchondrosis, lateral cartilaginous masses of ethmoid, cartilage between the greater wings and body of the sphenoid) which results in an outward and forward growth of the maxilla.

Another important action of somatomedin is the increase in the size of the tongue, which also facilitates the outward and forward growth of the maxillary dental arch.

Once the maxilla increases in length and width, the position of the maxillary dental arch is changed.

THE POSITION OF THE MAXILLARY DENTAL ARCH FORMS THE REFERENCE INPUT OF THE SERVOSYSTEM.

The release of somatomedin represents the COMMAND (command to grow). The hormone itself is the REFERENCE INPUT ELEMENT.

The OCCLUSION between the upper and lower teeth forms the COMPARATOR.

Owing to the forward and outward growth of the maxilla there is an obvious change in the relation of the teeth. What was originally a cusp to fosse relationship becomes a cusp to cusp relationship.

Hence the PERIPHERAL COMPARATOR (occlusion) senses this due to a chance in PERFORMANCE or the efficiency of mastication. Due to improper mastication, there is increased force on the periodontium, teeth, muscles and TMJ, which serve as the PERFORMANCE ANALYSING ELEMENTS.

The performance analyzing elements send signals to the CENTRAL COMPARATOR which is represented by the central nervous system. The CNS is equipped with a SENSORY ENGRAM which is a record of ideal tooth relations, and a record of the ideal muscular posture which can help to attain proper mandibular position. Details on the development and functioning of the sensory engram are given subsequently.

The CNS compares the present muscular position with the ideal muscular position stored in the sensory engram. It then sends a DEVIATION SIGNAL to correct this discrepancy.

The deviation signal is sent to an ACTUATOR which is represented by the motor cortex. The actuator then sends an ACTUATING SIGNAL to the COUPLING SYSTEM of the lateral pterygoid muscle and the retrodiscal pad. The LPM positions the mandible forward and the activity of the retrodiscal pad induces mandibular growth at the condyle (THE CONTROLLED SYSTEM)

The resultant output or CONTROLLED SYSTEM is the forward growth of the mandible which results in an ideal cusp to fossa dental relation.

Growth at the Posterior Border of the Mandible

Once growth occurs at the condyle, the posterior border of the mandible becomes more concave in shape.

This causes a negative piezoelectric effect to develop at the posterior border of the mandible, and bone apposition results. At the same time, the anterior border of the condylar process becomes more convex, causing a subsequent POSITIVE piezoelectric current to develop and a subsequent resorption of bone occurs. This accounts for an increase in length of the mandible.

SOME OTHER TERMS RELATED TO A SERVOSYSTEM

Gain- Gain of a system is the output divided by the input

Gain = OutputInput

If the gain is greater than 1, it indicates amplification caused by the system. If it is less than 1, it indicates and attenuation.

Petrovic suggests that the gain is genetically determined, but can be altered to an extent by hormonal influences.

Attractor- It is the final structural state that the system tries to attain. i.e.:- Maximum interception.

Repeller- All the unstable states that the system tries to avoid.i.e.:- cusp to cusp relation.

Disturbance- Any input, other than the reference input, which tends to have an effect of the output.E.g. - Abnormal tooth positions or occlusal interferences can act as a disturbance to the peripheral comparator.

The Sensory Engram

The CNS serves as a central comparator for the servosystem. The central comparator refers to what is known as the SENSORY ENGRAM.

The sensory engram is a collection of feedback loops, which record the activity of the masticatory muscles corresponding to a particular, habitual mandibular position. In other words, the optimal functional blueprint is recorded as the sensory engram.

As optimal function of the masticatory muscles develops, the CNS develops feedback loops which, in effect, memorize the best muscle function. Once these feedback loops develop, the CNS tends to operate along these pathways.

The sensory engram operates on the principle of OPTIMALITY OF FUNCTION. Any particular muscle action or mandible position that gives the minimum deviation signal is recorded in the sensory engram.

This means that when any new mandibular position is dictated to the patient, unless the new position causes a smaller deviation signal than the ole position, the CNS will tend to make the mandible relapse to its older position, wherein the function was more ideal.

An observation of Jacobs clearly demonstrates this. He observed that chain gang prisoners need to alter the way in which they walk owing to the extra weight they have to carry. Once the chains are removed, they retain the altered walking pattern only for a short while, and later reverted back to a normal gait. So when the restrictions are removed, the optimal muscular pattern is readopted.

Hence, once the sensory engram is established, the CNS has a reference of optimal function, towards which it strives to maintain all bodily functions.

Peripheral comparator, Catastrophe Theory and Bifurcations

The peripheral comparator is an important element in control of the growth of the face (especially the mandible). Its functions can be divided into 2 stages:-1. When inter-cuspal relationships have not yet developed (very young children) Since stable occlusion is not established, the peripheral comparator is not established. Since there is no stable occlusion, the reference engram is unable to develop. Hence even though the other components of the servosystem are operational, they cannot control growth of the mandible in very young children, since the peripheral comparator is not yet developed. Therefore mandibular growth is mainly genetically influenced. This stage lasts foe a different amount of time in different individuals, and can last indefinitely in case of anodontia.

2. The second phase is the development of stable occlusion Sensory engram begins forming Peripheral comparator can control craniofacial growth.

Another characteristic of the peripheral comparator is the existence of DISCONTINUITIES. Between two stable points (intercuspation) there is an area of instability (cusp to cusp relation).

So a stable phase can never be changes to another stable phase without an unstable phase.This forms the basis of the CATASTROPHE THEORY.

When the cuspal relation reaches the cusp to cusp relation, 2 possibilities can result:-

This is known as a bifurcation.

The alteration in the occlusion can result in either of the types of cusp to fossa relations. This brings us to the concept of OPTIMAL OCCLUSION (Class I) which is always desired, and SUBOPTIMAL OCCLUSION (Class II and Class III) which is not optimal, but stable none the less.

So a Class II molar relation will never spontaneously revert to a Class I

As the teeth move into a cusp to cusp relation, there is always a feedback system which rends to bring it back to cusp to fossa relation.

DISCONTIUITIES as seen above are important points in control of cranio-facial growth, and should always be taken into consideration during growth prediction, treatment planning and decision making. As mentioned earlier, a given occlusal pattern can be formed due to any number of causes. But once it is established, it remains relatively stable, as any local changes are minimized by the regulatory process.

Another important aspect of discontinuities is that it explains how a genotype may only partially influence the phenotype. The gene sequence only codes a regulatory pattern. It is around these regulatory patterns that a phenotype is expressed. This means that very small fluctuations taking place around a bifurcation at a crucial time can lead to very different results.

Failure of the Servosystem to Control Growth

The peripheral comparator is the most fragile component of the servosystem. Any problem in the dentition (rampant caries, missing teeth, mutilated dentition) can cause an improper functioning of the servosystem, as the occlusion cannot be established properly.

If there is a discrepancy between the rotation pattern and location of the comparator (if anterior teeth form the comparator in posteriorly rotating mandible, or the posterior teeth form the comparator in the anteriorly rotating mandible) then the servosystem cannot fine tune the growth process of the mandible to the maxilla.

Development of Skeletal Malocclusion According to the Servosystem theory

The development of malocclusion can be explained with the help of the following graph.

For every unit of STH-Somatomedin or testosterone that is released, the amount of maxillary growth is less than that of the mandible.

The line Max. indicates the growth of the maxilla (LPMmax) Growth of the mandible with maximum activity of the LPM(LPMmin) Growth of the mandible with minimum activity of the LPM(LPMnorm) Growth of the mandible with normal activity of the LPM

Under normal circumstances, the hormonal level is around N and a good maxillo-mandibular relation is maintained. As the hormonal level starts increasing towards L2, the maxilla starts to grow, and the mandible grows at an even faster rate. The action of the servosystem at this stage is to reduce the amount of LPM activity, so that less mandibular growth occurs. So, a good maxillo-mandibular relation is maintained.

When hormonal levels reach L2, the LPM is at its minimum activity. This is the maximum restraint on mandibular growth. Beyond L2, the activity of the LPM can no longer control growth of the mandible adequately enough and mandibular growth starts to exceed maxillary growth resulting in prognathism.

The opposite happens when hormone levels fall below L1.

So within levels L1 to L2, a good maxillo mandibular relation is maintained. Outside these levels, malocclusions result.

The relation between the maxilla and mandible between the levels L1 & L2 are maintained by contractile activity of the LPM, as controlled by the servosystem, as well as by a change in the gonial angle.

Action of Functional Appliances based on the Servosystem Theory

As it can be seen from the preceding graph, in a patient with retrognathism, the LPM is at its maximum activity. Hence the mandible cannot be brought forward any more and therefore retrognathism results.

Two types of functional appliances have been recognized according to their mode of action:-1. Appliances like the activator, postural hyperpropulsor, Frankel appliance, Twin block, Bionator etc.2. Appliances like the Herren &LSU activator, Harvold-Woodside activator, Extra oral traction on the mandible, which position the mandible forward and open it beyond the physiologic rest position.

First Group

When appliance is in place, there is increased activity of the LPM and RDP due to the forward positioning of the mandible.

Studies by Oudet et al (1988) and Carlson et al (1990) show that this increases the number of non fatigable fibers in the LPM. This shows that the LPM is, in effect helped to contract more by the functional appliance. Hence, the mandible grows forward by deposition of bone at the condyle. Hence length and even direction of growth is altered.

Also, when the mandible is positioned forward, a cusp to cusp relation results. The peripheral comparator interprets it as a forward movement of the maxilla (as even that will result in a cusp to cusp relation). So, since the reference input has been moved forward, the peripheral comparator sends a deviation signal to the central comparator. Then the central comparator sends the actuating signal to the actuator, and so on, ultimately resulting in growth of the mandible.

Cellular levelIt is important to know the effects at the cellular level, especially to understand the effect of Class II elastics, where, electromyographically no increase in contractile activity of the lateral pterygoid is seen. The action of Class II elastics requires the retrodiscal pad to be present. If RDP is excised, Class II elastics do not induce mandibular growth.

Before discussing how Class II elastics stimulate condylar growth, it is important to understand the microscopic working of the cartilage.

The mitotic cells in the condylar cartilage are of 2 types:-1. Precursor cells pleuripotent, fibroblast like skeletoblasts which differentiates into 2. Prechondroblast faster cell cycle & the main cell of the mitotic component. The prechondroblasts mature into chondroblasts.

It is seen experimentally, that if chondroblasts are lost by resection or hypertrophy and death, there is increased multiplication of prechondroblasts. This indicates that there is a local control over multiplication of prechondroblasts, which originates from the chondroblastic layer. And, the thicker the chondroblastic layer, the more intense is this negative feedback signal. (Stutzmann & Petrovic 1982, 1990)

Class II elastics, (and other functional appliances, but to a lesser extent) cause increase in activity of the RDP and hence increase in the blood and lymph supply to the condylar region. Hence nutrients and growth factors are supplied and metabolites and growth inhibitors are washed away.

In addition, to increasing mitosis, this leads to an earlier start of the hypertrophy of chondroblasts. Hence the previously mentioned negative feedback signal is mitigated and increased growth at the condyle results.

Also, cytoplasmic junctions between skeletoblasts are reduced and hence transmission of inhibitory factors also reduces. Skeletoblast mitotic rate increased and rate of differentiation into prechondroblasts also increases.

The second group of appliances has a slightly different type of action:-The appliances in this group tend to position the mandible forward as well as open it well beyond the physiologic rest position. The mobility of the mandible is also reduced. No increase or even a slight decrease in the activity of the LPM was seen when these appliances were worn. Yet there was in increase in growth.

This can be explained as a 2 step process.

1. The time the appliance is worn, the forward positioning of the mandible caused a reduction in the length of the LPM. At this time a new sensory engram is formed for this position of the mandible. 2. When the appliance is not worn, the mouth functions according to this new sensory engram. So the mandible is functioning in a more anterior position. This increases the activity of the RDP, leading to earlier hypertrophy of chondroblasts and in turn, increased multiplication of prechondroblasts.

Hence actual lengthening of the mandible takes place when appliance is not worn.

Also, the bite can be opened only to a particular limit. If it is opened more than that, no growth is seen.

Clinical Implications

1) According to the principle of optimality of function, a condition which results in maximum efficiency is one that is instilled into the brain. So, all orthodontic treatment must strive to reach the optimal functional situation, or, if this is not possible, the post treatment functional condition should be better than the pretreatment condition.

If this is established, the tendency for relapse is less.

2) A functional appliance should be removed only when growth is completed, or if growth is not completed, it should achieve a good intercuspal relation (the attractor). This ensures a stable result. If the treatment ends with the teeth in poor occlusion (repeller), relapse is more likely to occur.

3) An understanding of how functional appliances affect the servosystem is important to know how long the appliance is to be worn.

The first group of appliances should be worn full time.

The second group of appliances should be worn part time.

4) Proper function of the LPM RDP is essential for growth. This was shown by rat experiments by Petrovic and Stutzmann.

Ideal functioning of LPM-RDP not only increases the amount of growth of the mandible, but also improved the response to functional appliances, as was seen in breast fed versus gavage fed rats.

This is important to know for counseling purposes.

5) The sensory engram in children is poorly developed. Hence younger children respond better to functional appliance therapy than older children, and the results are more stable.

6) Hormonal activity is highest at puberty, during the pubertal growth spurt. Since hormones are very important for growth, one must take full advantage of the increased hormonal activity if any growth modulation is required.

Drawbacks

1) The theory places a lot of importance on the condyle as the growth centre. Hence if the condylar cartilage is lost subsequent to a fracture, growth should seize. But studies done in Scandinavia show that this does not happen.

2) The author places a lot of importance on the role of hormones in controlling growth. In all probability, they do not have such a large role to play.

3) The peripheral comparator, the occlusion, itself, is unstable. Discrepencies in the occlusion can easily be overcome by dentoalveolar changes, rather than by growth of the mandible.

4) According to the theory, an end on relation is a repeller. Still, end on relation of the molars and other teeth are often seen.

5) The theory does not explain the action of the reverse pull headgear.

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49MODUS OPERANDI OF FUNCTIONAL APPLIANCEADVANTAGES AND DISADVANTAGESADVANTAGESHelps in elimination of abnormal muscle function aiding in normal development.Less chair side time with less frequent adjustments.Treatment can be started as early as mixed dentition period, avoid psychological disturbance associated with malocclusion

Worn during night, patient acceptance is good.Do not interfere with oral hygiene maintenance.

LIMITATIONS patients whose growth has ceased (adults)Cannot bring about individual tooth movement.Un cooperative patientFixed appliance therapy may be required at the termination of treatment.May require prefunctinal orthodontic treatment for correction of minor local irregularities.Severe crowdingMoth breathersCriteria for case selectionWell aligned lower/upper arch.Class I, mild class II skeletal pattern.Forward posture of mandible will give a satisfactory soft tissue profile.Person undergoing active treatment(8-12yrs)PRINCIPLE OF FUNTIONAL APPLIANCEGrowth utilizationCorrect diagnosisIdeal and responsive type of malocclusionConstruction biteEruptive bite platformLinguo facial screeningForce delivery/eliminationPatient cooperationPatience

APPLIANCESORAL SCREEN/ VESTIBULAR SCREEN - Introduction1912 Newell Introduced vestibular screen.Before world war II it was used frequently in England.Recently, it is widely advocated by Kraus, Hotz, Nord and Fingeroth.Simple appliance in early interceptive treatment of dental arch deformities.

According to KrausVestibular screen Appliances that extent into the vestibule in contact with alveolar process, but did not contact tooth at all.

Oral screen Appliance with primary objective of controlling tongue function.

PRINCIPLEForce application as well as elimination.Anterior segment influenced directly by appliance -through muscle pressure.Posterior segment influenced by keeping away of cheek muscle allowing tongue posture and function to expand posterior areas.

Oral screenprinciple $ indicationINDICATION:- 1. Intercept habits:- Mouth breathing [when airways are open] thumb sucking tongue thrusting lip and cheek biting

2, Mild disto occlusion with premaxillary protrusion.

3, Perform muscle exercise-hypotonic lip and cheek.

4, Correct openbite in deciduous and mixed dentition.

Oral screen ..construction1 - CastsWorking casts that reproduce the depths of sulcus is made.2- Construction biteSagittal relationship normal-Casts are sealed in occlusion using plaster.Disto-occlusion case it is taken by moving mandible forward by 1-3 mm and bite opened by 2mm.After wax construction bite, it is transferred on the models and articulated on a straight line articulator.63construction3 Extension - Into the sulcus to the point where mucosal tissue reflects outwards. Care not to impinge on frenum and muscle attachment. Posteriorly - up to distal margin of last erupted molar.

4 , Models covered with 2-3mm wax over labial surface of tooth and alveolar process.

Case of proclined teeth that is to retract, wax is removed from incisal 1/3rd of tooth

constructionEnsure that screen contacts maxillary incisors only and stands away 3mm on each side from buccal segment.Open bite case no need expansion appliance allowed to rest on tissue.

Appliance fabricated using either self cure or heat cure .Appliance smoothened using sand paper and polished.MANAGEMENT -Patient should be asked to wear the appliance at night and 2-3 hours during day time.Instructed to maintain lip seal.First few days certain areas of inflammation seen that should be trimmed .Best time for treatment is 3 - 4 years of age. Duration 3-6 months MODIFICATION OF ORAL SCREENHOTZ MODIFICATION - Oral screen with a Metal ring projecting between lips .The ring used to carry out various exercise.

MODIFICATION OF ORAL SCREENVESTIBULAR SCREEN WITH BREATHING HOLES:- Fingeroth and Kraus.Mouth breathers

3 small holes at the inter incisal angle .Holes can be gradually reduced as the patient become accustomed to the appliance, which will stimulate nasal breathing. Convert mouth breather into nasal breather.

COMBINED VESTIBULAR SCREEN AND TONGUE CRIB:-

KRAUS A crib of wire or acrylic can be placed in the area of open bite and attached to screen by a wire that extends around the last molar tooth or passed through inter occlusal space in the region of canine and first premolar.In both cases it should not touch teeth even in occlusion.Such appliance should be worn for 12-14 hours.

Appliance worn at night and 1-2 hours

BITE PLANESBITE PLANEThesearesimplefunctionalappliancesthat bringaboutminor correctionsofthe anteroposteriorrelationshipofthejaws.

Theycanbe:-Anterior or PosteriorInclined or flat

ANTERIOR BITE PLANEThickened platform of acrylic palatal to upper incisors on which the lower incisor occlude leaving the posterior tooth out of occlusion.DESIGNCaninetocanine

consists of Adams clasps on the molars retaining the appliance. A labial bow is incorporated to counter any forward component of force on the upper anteriors.

73INDICATION Class I deep bite with low facial height

Class II div II

CONTRAINDICATION High facial height Skeletal deep bite

Severely protruded/ retruded lower anteriors

CONSTRUCTION AND ADJUSTMENTCorrection of height - Bite plane should be high enough, so that posteriors are separated by 2-3 mm

Horizontal adjustment Surface of bite plane should be parallel to occlusal plane and horizontal. The posterior limit of bite plane should extent just sufficiently to engage lower incisorAdjustment of bite plane during treatment Appliance should be worn full time, If bite opening requires again bite is increased . Before the upper incisors can be retracted to reduce the overjet acrylic is trimmed from lingual surface but should be careful that lower incisors maintain contact with it until overjet is almost corrected. These teeth will otherwise reerupt again.

POSTERIORBITEPLANE Indications:Togiveocclusalclearanceforthecorrectionof thecross biteofeithertheanteriororposteriorteeth.Fordiagnosisofocclusalprematurities

CONSTRUCTION: covertheocclusalsurfaceofposteriorteeth, extendinganteriorlyfromfirstpremolartothelast erupted toothposteriorly. The thickness should be kept as minimum as possible. It is constructed as an extension of the acrylic base while acrylising the base plate, similar to that of the other bite planes

CLINICALMANAGEMENT Whentheapplianceisdelivered,careistakentosee thatthebiteplaneshouldcontactthebuccaland lingualcuspsoftheposteriorteethoftheopposingarchuniformlyonboththesides.Thebiteplaneshouldbesufficientlythicktorelievetheocclusalinterference.

Ifananteriorcrossbiteisbeingcorrected,the biteplaneneedsonlytobesufficientlythickto disengageocclusiononanteriorteeth.Oncethecrossbiteiscorrected,themolar cappingshouldbereducedorremovedINCLINED PLANE/CATALANS APPLIANCE Loweranteriorinclinedplane.IntroducedbyCatalan more than 150years ago Thisappliance guideseruptingtoothintonormal position.All inclined planes have characteristic of opening the bite by allowing posterior teeth to erupt.So inclined plane is contraindicated unless there is appreciable amount of overbite.

INDICATION-Where anterior cross bite(single tooth or a segment of upper arch) is developing with a good degree of overbite and there is sufficient space for the erupting teeth.

DESIGN Fabricated using self cure acrylic, designed to have a 45 angulation, which forces teeth in crossbite to more labial position

MANAGEMENT OF APPLIANCE Must be worn continuously, If appliance is removed during eating the tooth will be forced back towards original malposition.

Correction will occur within 6 weeks.

After correction advise patient to wear appliance during sleep to guard against the tendency to move mandible forward .DISADVANTAGES1- Speech problem during therapy.2- Anterior open bite if used for more than 6 weeks.3-May need frequent recementation.

Thank you !