Occlusion page 3-DoctorSpiller.com

Occlusion pages 12345

Occlusion 4: The Muscles of Mastication==>>

The Damaged TMJ

Internal joint derangement

If a patient forcefully bruxes (grinds or clenches the teeth), the entire masticatory system is placed under great strain.  The teeth can wear. The periodontium (gums and the bone that supports the teeth) may become inflamed, and in combination with poor hygiene, periodontal disease may result.  The TMJ is always placed under stress during bruxing, even if centric occlusion coincides with centric relation.  See my page on TMJ for a full listing of the problems associated with bruxing.

If there is a substantial discrepancy between centric relation and centric occlusion, bruxing can cause serious long term damage to the TM Joint.  This may include stretching of the ligaments that keep the disc in place causing a progressive anterior displacement of the disk forward of the head of the condyle, perforation of the thin area of the disc, tearing of the disc, or outright fragmentation of the articular disc apparatus into several small pieces which may seriously interfere with opening and closing.

Anterior disc displacement (What causes popping and jaw displacement when opening and closing?)

The lateral pterygoid muscle is attached to the condyle and is responsible for drawing the jaw forward when the right and left joints are equally active.  It is also responsible for shifting the jaw to the right or left when only one of the two joints are active.  For example, contraction of the right lateral pterygoid shifts the lower jaw to the left. During unconscious grinding, the lateral pterygoid muscles are extremely active.

anterior_disc_displacementAs noted above, some of the fibers of the lateral pterygoid muscle are attached separately and directly to the anterior of the articular disc. Over time, constant bruxing can cause the disc ligaments to stretch displacing the meniscus anteriorly.  When this happens, popping noises can be heard when the patient opens the mouth.

The popping is due to the noise the condyle makes if it moves under the anteriorly displaced meniscus.  The popping is also associated with deviations in the lateral (side to side) movement of the jaw so the patient no longer experiences smooth opening and closing jaw movements.  As the condition progresses, the popping and jaw movement deviation may be experienced by the patient as the jaw closes as well.

Whenever the condyle pops under the firm, elastic, rubber-like meniscus, the condyle is displaced downward and the jaw is displaced to the opposite side of the face.  These lateral (side to side) jaw deviations can become quite complex if the disks on both sides are anteriorly displaced or otherwise damaged since the popping and displacement on either side generally happen at different points in the jaw opening movement.

It is likely that pain will NOT be experienced during any of this popping and displacement activity since cartilaginous structures do not have nerve endings.  When pain IS experienced, it is generally due to capsulitis which means inflammation of the synovial capsule.  When pain is not experienced by the patient, the dentist will generally strive only to treat the bruxing habit in order to arrest the progressive nature of this disorder.  If pain is experienced by the patient due to internal joint derangements, the dentist generally combines the bruxing treatment with NSAID’s (non steroidal anti inflammatory drugs).

The classification of joint derangements

Type IA–popping in the TM Joints without pain: very common: said to affect as much as 50% of normal subjects.

  • Type IB–popping in the TM Joints associated with pain.
  • Type II– similar to type IB but patient experiences occasional jaw locking with the inability of the jaw to open or close beyond a certain point.  The lock is caused by the displaced meniscus blocking the path of the condyle during translation.  Both types of lock can generally be reduced by the patient with little difficulty.
    • Closed lock–associated with the inability of the condyle to slide under the displaced meniscus when the patient tries to open the mouth beyond a certain point
    • Open lock– associated with the inability of the condyle to slide back under the meniscus when trying to close the mouth.
  • Type III–a persistent lock, usually on trying to open.  Since the patient cannot open the mouth beyond this point, there is no popping.  This condition (unlike all type I and II derangements) requires aggressive therapy with reduction of the lock under anesthesia and physical therapy.  If no improvement is seen in three weeks, surgery is generally indicated.

Serious derangements of the TM Joints are sometimes treated by totaljoint replacement.  Click the image below to be directed to a page with images of the surgery as well as before and after images of the results.

newjointsthumbOther TM Joint disorders

Torn meniscus

This condition results in free movement of the anterior fragment of the meniscus which usually moves ahead of the condyle during translation due to the action of the lateral pterygoid muscle.  The effect of this is generally more serious displacement of the mandible during opening or closing, as well as a higher probability of locks.  It may also be the cause of the type III persistent locking noted above.  This type of injury also allows the cartilage of both the head of the condyle and the glenoid fossa to come into forceful contact without the shock absorbing benefits of an intact meniscus.

Damage to the cartilaginous coverings of the condyle and glenoid fossa

This can lead to severe bone-to bone contact with consequent wear of the bone in both structures.  This results in grinding noises in the joint (called crepitus) and results in severe arthritis and sometimes even a fusing of the bones (called ankylosis) of the joint.

The temperomandibular joint is like any other major joint in the body.  It is susceptible to any disease that can affect any other joint in the body.  Thus osteoarthritis is often found in the TMJ in older persons, although it is generally symptomless.  This joint can suffer traumatic damage which can lead to joint derangements or painful inflammatory changes in the capsule.  It can also suffer dislocations which can lead to stretched ligaments and a tendency to recurrent dislocation.

Dislocation of the TM Joint

Dislocation of the TMJ involves the displacement of the condyle anterior to the articular eminence.  This generally implies severe stretching of the joint ligaments and is one of the more severe effects of parafunction.  Once the condyle slides anterior to the articular eminence, reduction is quite difficult owing to the spasm in virtually all of the muscles of mastication.  Spasm in the masseter, temporalis and medial pterygoid muscles causes them to apply extreme upward force on the condylar head while spasm in the lateral pterygoid applies massive anterior force.  These forces lock the condyle into its anteriorly displaced position making self reduction nearly impossible.  A health professional may reduce the dislocation by placing his/her thumbs well distal and lateral to the lower second molars on either side (taking extreme care to position the thumbs well out of the way of the occlusion to avoid injury to his or her own fingers) and the remaining fingers under the body of the mandible.  The trick is to press down hard with the thumbs while rotating the body of the mandible up so that the patient’s mandible pivots around the thumbs.

Once a patient dislocates one or both condyles, the ligaments remain stretched out for a long time making further dislocations all too easy. Patients will frequently “test” whether their jaws will dislocate again, and find that it happens without too much effort.  Patients should be cautioned not to try to test their jaw.  The ligaments need about a year or sometimes more to heal before they become reasonably resistant to dislocation, and each time a patient tests out their jaw, the ligaments are further injured and healing is delayed again.  A soft diet and a bruxing appliance are probably the best recommendations.

Occlusion 4: The Muscles of Mastication==>>

Occlusion pages 12345