occlusion and tmd

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OCCLUSION AND TMDDR. BAHJAT ABU HAMDAN CONULTANT PROSTHODONTIST.

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Introduction. Epidemiologic studies of TMDs. Development of functional disturbances in the

masticatory system. 1.Normal function. 2. Events. 3. Physiologic tolerance 4.TMD symptoms. Etiologic considerations of TMD. occlusal conditions 1. static. 2. dynamic. Effects of acute changes in the occlusion and

TMD.

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Introduction.

TMD have place in the practice of dentistry

Because: 1.It represents a significant problem

in the general population. 2.It is related to structures that are

treated by the dentist. 3. The occlusion represent one of the

contributing factors leading to TMD.

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Introduction.

Before starting treatment of TMD by the dentist, a comprehensive understanding of the occlusal problems that affect TMD is basic.

However somes dentists feel that the occlusion of the teeth is the primary cause of TMD symptoms.

But some believe that occlusion has little or no role in TMD, if this true, dentist role in the treatment of TMD is negligible.

In this lecture, the mechanism, how the occlusion contribute as cause of TMD, will be discussed.

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Epidemiologic Studies of TMDs

Okson has examined numerous epidemiologic studies which interested in the examination of the prevalence of TMDs in given population.

These studies suggest that signs and symptoms of TMDs are quite common in the population.

41% of these population reported at least one symptom associated with TMD.

56% showed at least one clinical sign.

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Based on that half of the patients seen in the dental office do not appear suffering from TMD.

It was reported that only 10% of the total group had symptoms that were severe enough to seek treatment.

These kind of findings are more readily accepted as factual.

Most of TMD symptoms are reported in patients 20-40 years of age.

These studies reveal that prevalence of functional disorders in the masticatory system is high.

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It is documented that occlusal contact influence function of the masticatory system.

If this relation is correct it makes the study of occlusion an important part of dentistry.

Okson reviewed 57 epidemiologic studies that attempted to examine the RS between occlusion and signs and symptoms associated with TMD in a variety of population.

The question is whether the occlusion is the main cause of TMDs. Or the occlusion has nothing with TMD.

Apparently neither of these conclusion is true.

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Confusion and controversy concerning the RS between occlusion and TMD continues.

In the 37 that did find RS between occlusion and TMD. the clinician may ask;

What was the significant occlusal relationship that was found to be related to TMD symptom ??

Variety of occlusal conditions were reported but these conditions are also found in normal population.

which means that these occlusal conditions do not always lead to TMD.

To appreciate the role of occlusion in TMD one must better understand the many factors that can influence function of this extremely complex system.

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Development of Functional Disturbances in The Masticatory System No single cause accounts for all sign and symptoms

in the masticatory system. 1.When there is one therapy for treating a disorder

thus treatment is quite effective. 2.On the other hand if multiple therapies suggested

for the same disorder. The clinician can assume that none of the suggested therapies will always be effective. These findings lead to

Either the disorder has multiple causes or; The disorder is not a single problem but represents

an umbrella term under which multiple disorders are grouped.

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Development of Functional Disturbances in The Masticatory System

In TMD case, both of these explanations are true, its multifactorial and a variety of disorders.

The following formula simplify how TMD symptoms develop.

NORMAL FUNCTION + EVENT PHYSIOLOGIC TOLERANCE OR TMD SYMPTOMS

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To explain this formula each factor will be discussed aside.

Normal function; functions of the mastictory system are basic to life, these tasks are carried out by the complex NM system.

The brain stem regulate muscle action by way of muscle engram that appropriately according to sensory input received from peripheral structure.

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Events could be local or systemic.

Local Events. Local event could be may represent any change in

sensory or proprioception input such as crown, filling , traumatic injection or traumatic occlusion due to parafunction (bruxing or gnashing ).

Deep pain input where masticatory system and associated structure become sites of pain which alter normal muscle function, by way of central excitatory effects.

It is a pain of unknown cause (idiopathic pain). Clinician should be able to recognize this type of pain.

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Systemic Events. Any change at the CNS level will

affect the whole body including the masticatory system.

So that any dental treatment or occlusal modification will never cure the case.

One of the most common types of systemic alterations is an increased level of emotional stress.

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Physiologic Tolerance. Reaction to an event is different between

individuals. This variation reflects the individuals physiologic tolerance.

This tolerance is influenced by local and systemic factors.

Local Factor. Reaction of masticatory system to local factors is

influenced in part by its orthopedic stability. When there is orthopedic stability, masticatory

system Is best able to tolerate local and systemic events.

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Poor orthopedic stability make the function of the masticatory prone to be disrupted by insignificant event.

This is one way in which occlusal condition may affect symptoms associated with TMD.

Orthopedic instability may result from conditions that are related to the occlusion, TMJ or both.

Lack of occlusal stability may be associated with genetic , developmental or iatrogenic causes.

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Systemic Factors. Multiple systemic factors are likely to

influence the physiologic tolerance. Pateint character, genetic, gender, diet,

disease and physical conditions. Systemic factors influence pain modulation

system and individual and response to an event.

Descending inhibitory system does not effectively modulate nociceptive input. So that becomes more vulnerable.

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Symptoms of TMDs

Physiologic tolerance exceeded which leads to certain break down and pathologic changes.

Each component of the masticatory sys. Has a specific structural tolerance.

The element of the masticatory sys. With lowest tolerance will be affected first.

Breakdown site varies from individual to individual. If the masticatory sys.is considered as links of chain.

so that a chain is as strong as its weakest link. when it is stretched the weakest link breaks first.

Causing the separation of the rest of chain.

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Symptoms of TMDs

Due to an event, signs and symptoms will appear on the weakest link.

The particular sites of breakdown are; mucles, TMJ, tooth pulp and hard tissue, and tooth supportive structures.

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Etiologic Considerations of TMDs

Causes of TMD are complex and multifactorial. Numerous factors can contribute to TMD. 1. Predisposing factors.Those that increase the risk of TMD. 2 Initiating factors.Are those that cause the onset of TMD. 3 Perpetuating factors.Those which affect healing and enhance the progression of

TMD.One factor or combination of several factors may serve all

these roles.Successful management of TMD is dependent upon

identifying and controlling these factors.

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A review of the scientific literature reveals five major factors associated with TMD.

Occlusal condition. Trauma. Emotional stress. Deep pain input. Parafunctional activities. Importance of these factors vary greatly from

pt to pt. Occlusion may be not the most important

cause of TMD.

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Figure 4 : Risk factors associated with TMD

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Occlusal condition Occlusion was considered to be the most

contributing factor in TMD. Recently many researchers argue that occlusal

factors play little or no role in TMD. It should be remembered that the role of occlusion

in TMD does not reflect the importance of occlusion in dentistry.

However occlusion is the foundation of dentistry, its stability is basic for successful masticatory function.

Role of occlusion as a cause of TMD is not the same in all pateint.

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Occlusal condition. When evaluating the RS between

occlusion and TMD, the occlusal conditions should be considered both -Statically.

-Dynamically. Most occlusal studies have assessed the

static RS of the teeth so that findings were not impressive regarding any single factor being consistently associated with a TMD.

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Occlusal Condition. Pullinger, Seligman and Gornbien

investigated the interaction of 11 occlusal factors, they considered them in randomly collected but strictly defined diagnostic group with asymptomatic control.

Four occlusal features, however, noticed in TMD pts. And were rare in normal subjects.

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Occlusal Condition 1. Skeletal anterior open bite. 2. Retruded contact position (RCP) and (ICP) slide of

more than 2-3 mm. 3.Overjet greater than 4mm. 4. 5 or more missing posterior teeth. These signs have limited diagnostic utility because

they are rare in Pts as in healthy subjects. Thus they concluded that occlusion can not be

considered the most important factor in the definition of TMD.

These studies evaluate the static RS can provide only limited insight into the role of occlusion and TMD.

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Skeletal Anterior Open Bite

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Overjet more than 4mm

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DYNAMIC FUNCTIONAL RELATIONSHIPS BETWEEN OCCLUSION AND TMDs.

Considering the dynamic functional RS between the mandible and the cranium, these occlusal conditions can affect some TMDs in at least 2 ways.

1. How the occlusal condition affect the orthopedic stability of the mandible as it loads against the cranium.

2.How acute changes in the occlusal condition can influence mandibular function thus leading to TMD symptoms.

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Contact with all teeth should be of even magnitude and simultaneousForces on individual teeth are minimized with this arrangementCondyles should be in their most anterosuperior position in the fossa (MS position or CR position)Therefore ideally, ICP is coincident with CR (MS)This is called orthopedic stability

Muscle activity and mandibular movement with bilateral molar and premolar contacts

Okeson Fig. 5-8

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DYNAMIC FUNCTIONAl RS BETWEEN OCCLUSION AND TMDs.

Effects of Occlusal Factors on Orthopedic Stability.

Orthopedic stability exist when the stable ICP ( MI) of the teeth is in harmony with the Musculoskeletal Stability of the condyles in the fossae. If this condition exist functional forces can be applied to the teeth and joints without tissue injury.

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DYNAMIC FUNCTIONAl RS BETWEEN OCCLUSION AND TMDs

When orthopedic instability exist and the teeth are not in occlusion,the condyles are maintaned in the MS position by the elevator muscles. In this condition when the teeth are brought into contact only one tooth may contact.

This represents a very instable occlusal position but condyles remain in a stable position.

The individual now has 2 choices; Maintain the stable joint position and only

occlude on one tooth. Bring the teeth into more stable occlusal

position, which may compromise joint stability.

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The condyle seats in CR simultaneous with the teeth occluding in MI. No slide occur

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Centric Relation A condylar positionSuperior and AnteriorThinnest portion of the articular disc is interposed between the condyle and temporal boneDescribes the most stable position of the condyleSuperior and anterior position of the mandible with the disc properly interposedThe position is reproducible, but not easily achievable

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Maximum Itercuspation

► An occlusal position

► If CR and MI do not coincide, the patient will have a “slide”

► Most patients have some degree of a slide into maximum intercuspation (approximately 1-2 mm)

► MI is simultaneous contact

► Forces concentrated on long axis

► Posterior contacts should dominate

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Because occlusal stability is basic to function (chweing, swallowing and speaking) the priority is to achieve occlusal stability and the mandible is shifted to a position that maximize the occlusal contact.( the ICP ).

When this occurs, this shift can force one or both condyles from its MS, resulting in orthopedic instability.

That means when the teeth are in a stable position for loading, the condyles are not ( or vice versa).

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When orthopedic instability exists; merely bring the teeth into occlusion

may not create problems because loading force are minimal loading forces are minimal.

problems arise when such an orthopedic instability conditions is loaded by the elevator muscles or by the extrinsic forces (trauma).

ICP is the most stable position so no problem with the teeth.

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Only 15% of the population have no CR to MI discrepancyAfter the first contact in CR (usually on 2 or more posterior teeth), the patient continues to close, and the teeth come together more completely (MI). The condyles must move out of their most ideal position when the teeth come fully together

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If loading occurs when a joint is not in a stable RS with the disc and fossa, unusual movement can occur in an attempt to gain stability.

This movement although small is often translatory shift between disc and condyle.

Movement such as this can lead to strain to the discal ligaments and eventually elongation of the discal ligaments and thinning of the disc.

These changes can lead to a group of intracapsular disorders.

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Ideal: orthopedic stability Musculoskeletal S + ICP (MI)Orthopedic Instab. stab.ICP+ M Instab.Orthopedic Instab. Instab. ICP+ MSTwo factors are decisive in the development of the intracapsular

disorders; 1.The degree of orthopedic instability. 1-2mm orthopedic instability is not significant to create

problem. Discrepancy between the MS position of the condyles and the

ICP of teeth becomes greater, the risk of intracapsular disorders increases.

2. Increased loading amount, therefore bruxing patients with orthopedic instability represent a higher risk for developing problem than non bruxers with the same orthopedic instability.

Forceful unilateral chewing can provide the mechanics that lead to sudden intracapsular disorders.

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A more significant static occlusal RS may not lead to develop the disorder.

The dynamic functional aspects of occlusion as it relates to the joint position is likely to provide more important information regarding the relative risk of developing TMDs.

The term dental malocclusion refers to the specific relationship of the teeth to each other, but it does not necessarily reflect any risk factor for the development of functional disturbances in the masicatory system.

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So that the study of the occlusal RS on the cast does not provide any information concerning the risk factor for TMD.

0nly observing the occlusal RS with respect to the stable joint position can the clinician appreciate the degree of orthopedic instability present.

Orthopedic instability is the critical factor that needs to be considered when accessing relative risk factors to TMD.

Discrepancy of 1-3mm is in the limit of physiologic tolerance.

Shift of greater than 3mm present more significant risk factor.

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Effects of Acute Changes in The Occlusal Conditions and TMD

Functional activities achieved with minimum damage to the different elements of the masticatory system.

Occlusal contact patterns will influence the precise functional activities.

Parafuntional muscle activities appear to be controlled by entirely different mechanism, this includes bruxism and clenching, and various oral habits.

The concept that certain tooth contacts cause parafunctional activities, have, for the most, been disproved

Occlusal contact does not influence nocturnal bruxism.

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Specific occlusal contact patterns can influence specific muscle groups.

Heavy contact on a tooth cause nociceptive reflex to shut down the muscle that pull across the joint (temp. mass. Medial pteryg.).

This tooth contact can create painful muscle symptoms.

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Williamson and Lunquist. studying the effect of various occlusal contact patterns on the temporal and masseter muscles , they reported;

1. Bilateral contact in laterotrusive movement all four muscles remained active, elimination of the meditrusive contacts only the working side muscles remain active. ( WS and non WS)

2. If a group function guidance exists, both mass. and temp. muscles are active during laterotrusive. If the canines make contact (canine guidance) only the temporal muscle on the ipsilateral side is active.

3. This study points out the merit of canine guidance over group function.

4. It confirms that occlusal relation can increase muscle activity .

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In a protrusive movement, the maxillary left lateral incisor can potentially come in contact with

the mandibular left lateral incisor and mandibular canine

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canine guidance; the gold standard

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canine guidance (ideal

group function (secondary choice

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Does occlusal contact cause bruxism. Rugh et al placed a high crown in 10 subjects and

observed its effects on nocturnal bruxism. They found that this high occlusal contacts do not

increase bruxing activity, and no muscle activity due to nocturnal activity. Once the crown is accommodated bruxism is back.

Its clear that these two studies are different, 1st study evaluate the occlusal contact on conscious and controlled mandibular movement.

The 2nd study assesses the effects on subconscious and uncontrolled, involuntary muscle activities (nocturnal bruxism ).

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So that functional activities is greatly influenced by peripheral input (co-contraction) and parafunctional activity is predominantly influenced by CNS input (excitatory).

Based on that, treatment of bruxism could not be through occlusal modification.

If a pt. reports early morning muscle tightness and pain bruxism should be suspected, the treatment of choice is likely to be occlusal appliance that will alter CNS induced activity.

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Pain due to alteration in the occlusion ( filling or crown ), based on the history of the case the treatment of choice is occlusal adjustment.

Disturbances in the occlusal condition can lead to increased muscle tonus ( co-contraction) and symptoms.

Pbs with bringing the teeth into occlusion are answered by the muscles, however once the teeth are in occlusion problems with loading the masticatory structures are answered in the joints.

These RSs are in fact, how dentistry relates to TMD. So that if any of these conditions exists, dental therapy is likely indicated.

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