4 Mandibular Mobility Disorders

Woman grabbing her jaw with both hands because of TMJ pain from a mandibular mobility disorder.

1. Muscle Contracture

Muscle contractures are abnormal reductions in the extensibility of the jaw muscles (usually the closers). Contractures can result from a trauma induced scar, a spontaneous slowly developing shortening of the muscles without enlargement, or a muscle hypertrophy condition. The latter two problems should present as a long standing progressive loss of motion.

Related Reading: How to Diagnose Masticatory Muscle Disorders

The injury induced problem of contracture occurs when the patient has an intramuscular and subperiosteal bleeding, which subsequently organizes into a fibrotic or ossification of the muscle tissue. This binds it to the underlying periosteum and is called a myositic-fibrosis. If the jaw closers are involved, the patient should exhibit a relatively normal lateral range of jaw movement with an abnormal opening jaw movement.

Evidence Needed to Diagnose Masticatory Muscle Contractures

  1. A significantly limited jaw opening (<30mm)
  2. An unyielding passive stretch test with a firm end feel
  3. No intracapsular cause of the restriction.

Related Reading: Internal Derangements of the Temporomandibular Joint

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2. Ankylosis (Fibrous or Bony) of the TMJ

Ankylosis involves a severe loss of rotation and translation joint motion. If the ankylosis is bony, then a clear loss of all normal form of the condyle and fossa will exist. If the ankylosis is fibrous, the bony morphology on radiographic evaluation will be normal.

Evidence Needed to Diagnose Ankylosis

  1. A history of trauma or injury to the TMJ
  2. Severely limited mouth opening and lateral or protrusive motions
  3. For bony ankylosis, imaging of the TMJ to see if the condyle anatomy is altered (e.g. loss of joint space and possible fusion or adhesion to the fossa or eminence of the TMJ)
  4. For fibrous ankylosis, the bony morphology on radiographic evaluation will be more normal while with bony ankylosis the morphology is abnormal

Related Reading: Closed Lock Mobilization: TMJ Exercises & Stretches

3. TMJ Hypermobility

Hypermobility occurs in association with a generalized benign joint laxity disorder. Diagnosis is based on data gathered by a physical examination of the flexibility of the patient’s joints (usually fingers, wrists, elbows, and knees).

Evidence Needed to Diagnose Hypermobility

  1. Episodic open locking and clicking of the joint
  2. An interincisal opening of >60 or more millimeters
  3. Benign joint hypermobility syndrome (Beighton score >/=7)

Related Reading: Commonly Used Medications For Temporomandibular Disorders

4. Coronoid Elongation

Coronoid elongation occurs when the coronoid process alters shape to such a degree that it actually bumps into the maxillary zygoma upon attempted opening. There are other extracapsular reasons for a decreased motion of the jaw, such as epithelial scarring from injuries, burns or developmental disturbances (e.g. scleroderma).

The zygoma may actually become malformed following an accident which fractures it and produces a depression of this structure (especially if it is not reset properly). It is always difficult to differentiate a false ankylosis from a fibrous ankylosis since both situations may present with a limited opening and normal appearing tomograms.

Evidence Needed to Diagnose Coronoid Elongation

  1. A radiographically proven elongated coronoid process
  2. Limited opening of jaw due to coronoid process hitting the zygoma during opening

Related Reading: TMJ Manipulation & Mobilization Treatments

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