ETIOLOGY OF TMJ


      - Most TM disorders are idiopathic, that is, of unknown origin, some TMD complaints have been associated with serious organic diseases.

       
    Single Versus Multifactorial Etiologies
     - factors including external trauma, intubation during general anesthesia, difficult dental extractions, and orthodontic procedures were evaluated in 195 TMD cases and 50 non-TMD controls.

      
    >  PREDISPOSING FACTORS

        1. Anatomic Conditions
     These factors mainly involved developmental abnormalities of the jaws. Most reports recognized abnormal maxillomandibular relations, dental or skeletal malocclusions, malalignment of the mandible, and improper position of   the head and the spinal column.

        2. Morphologic Malocclusions
      - Certain skeletal and dental malocclusions have been suggested as causing     neuromuscular disturbances  in the masticatory system,  including TMJ disorders. The aberrant functions may be  either a direct result  of the  morphologic malocclusion of and indirect result  of functional occlusal  interferences. Potential causes have been categorized into vertical,  horizontal, and lateral  discrepancies.

       Angle class , especially division 2, have been considered particularly vulnerable to TMD.    Morphologic malocclusion, class and class occlusions, frontal open bite, and cross bite if  correlated  with functional  malocclusion, may predispose to dysfunction bite, if correlated with functional malocclusion, may   predispose to dysfunction.  abnotmal overbite and overjet were associated with condylar DIF.   Excessive overjet was associated with DIF of the disk, patricularly displacement.
         * DIF-deviation in fom

    A.  Functional Malocclusion and Occlusal Disharmonies

    B.  Malalignment of the mandible

      The dysfunction derives from a developmental problem concomitant with a dental  malocclusion. According to this theoretical cause, and unstable occlusion resulting from either premanture tooth contacts of parafunctional oral habits causes malaignment of the mandible. Usually posterior  displacement of the mandible results in compression of the mandible.  

    Undue stress is placed on  muscles, ligaments, and bones. Pain, impairment  of the blood supply, and degeneration of the  joint follow.

    Based on this malaignment, TMD and malocclusion  have been considered synonymous.  
    Condylar displacement originating from occlusal changes was endorsed as the probable cause of TMD, vertigo, tinnitus, and associated auditory symptoms.  
    Significance : A conclusion that condylar displacement caused by altered occlusion leads to TMD symptomatology must be regarded  cautiously.

    C.  Improper position of the Head and spinal Column

       Because the TMJ are anatomically close to the spine, it is logical to argue that the complex  of TMJsymptoms includes head, neck and shoulder problems. There is unsubstantiated opinio  that subjects presenting with forward   head posture and protracted shoulders are prone to  TMD.     
     
    D.  Pathophysiologic Conditions

                     TMJ pathology may derive from various sources.

          E.  Joint Disorders
         1) INTERNAL DERANGEMENT.
     
     Internal derangement of the TM joint is defined as an abnormal relation of the
    mandibular condyle, fossa, and articular eminence. Joint noise or a history of joint sounds is the key   symptom of this disorder. The most common disk displacement was anteromedial,  but posterior displacement also  occurred. Perforations were found in advanced stages.  
     
    Advanced disk displacement characterized Cases of steoarthritis. Three models have been proposed a causing disk isplacement: hyperextension of the mandible, condylardisplacement caused by trauma, and chronic muscular  hypertonicity. Hyperextension of the mandible may result from  minor of majo events.

    Sudden yawning of prolonged mouth opening are potential minor causes.
    An acceleration-deceleration force comparable to the force of whiplash could
    hyperextend the  mandible and induce displacement. A mechanism has been proposed for disk displacement  resulting  from whiplash.  incisal clenching has been suggested as a major etiologic factor in anterior disk displacement.


       2) OSTEOARTHRITIS.
       
    The etiology of TMJ arthritis is unknown.  A strong argument has been made that prior internal derangement leads to TMJ osteoarthritis. Osteoarthritis may create insidious skeletal  changes, simultaneous intrusion of the teeth, realignment on the ipsilatera side.  

     3)  AVASCULAR NECROSIS.
       
    Occlusal changes, caused by the decreased vertical dimension, may include contralateral anterior open bite with ipsilateral premanture contact of the molars. Ultimately, these hanges produce facial deformity and lateral shift of the mandible towards the affected joint   on mouth opening. Potential triggers may include trauma, iatrogmanipulation, ystemic inflammatory  ilness, of administration of exogenous steroids

         4)  REGRESSIVE REMODELING.
     
    There is loss of convexity or flattening of the contour of surfaces. remodeling is charactosseous  remodeling and resorption with eventual decrease in   condylar size. The process is slow developing, insidious, and without hypertrophic changes.  Loss of vertical dimension is probably   accomplished by osteoporosis.  

       5)  RHEUMATOID ARTHRITIS.
      
    Rheumatoid arthritis is an example of an inflammatory synovitis of unknown etiology.
      Inflammation develops mainly within the synovial membranes of the joints.  As in osteoarthritis, the major TMD symptoms are  masticatory muscle tenderness and joint crepitation.
      A chief difference is that rheumatoid arthritis is a symmetric synovitis affecting joints bilaterally.  Usually joints of the hands and feet are affected first. The cervical spine may become involved  late in the course of the disease.  Patients may suffer from lateral neck pain as inflammation develops at the  C1-C2 articulation. Orofacial pain may be referred from the neck.

      
     F.  Muscle Disorders

     1) HYPERACTIVITY.
      
    Hyperactivity of the jaw muscles has long been considered a primary etiologic factor in  TMD. Theoretically, excessive emotional  stress promotes the hyperactivity.

       2)  MYOSPASM
      
    Many patients with TMD present with widespread tenderness of the muscles to palpation.
     
        3)  FATIGUE.
      
     
    Fatigue may be a significant factor in causing muscle pain. Levels of tension may build in  the musculature, leading to chronic fatigue and, potentially, to dysfunction.
     
      4)  TRIGGER POINTS.
       
    A trigger point is a tender area in a firm band of muscle tissue. They populate the muscles of  the head, neck, shoulders, and lower  back. Trigger points are thought are thought to be activated  by acute or chronic muscular  overload, fatigue, or trauma.
       5)  TENDER POINTS.
            
    Usually trigger points of MPD are unilateral.

    G. Cervical spinal Disorders
      
    Cervical spinal disorders may lead to complaints often associated with TMD. Pain may be felt   along  the side of the head from  disorders of the C2 to C3 vertebrae.  A possible mechanism  whereby pathology of the cervical  spine could lead to pain in the trigeminal system would include   the input by way of the upper cervical nerve roots. Cervical spine  disorders may, in fact, in fact, result in bizarre symptoms. These disorders may involve pain of the head, sinuses, face, ear, and  throat. Sensory disturbances of the pharynx, vertigo, tinnitus, diminished hearing, sweating, flushing, lacrimation, and salivation are possible Hymptoms.   
     H.  Headache
      
    In two different groups of 80 patients, the frequency of recurrent headache correlated with the  frequency of masticatory muscle pain and TMJ pain on palpation. There is considerable evidence  that  headache may arise from myofacial trigger points of masticatory, neck, and back muscles.     
     
     I.  Neoplastic Disease
      Malignant disease may disguise as TMD. A review of the literature found 42 cases of malignancy  hat mimicked TMD.

      J.  Uncommon Causes

       1) NEURALGIAS.
       
    Neuralgias, including trigeminal, glosspharyngeal, or atypical(vascular)neuralgias, contribute little  to TMD symptoms. significance:No firm relation has been established between TMD and  neuralgias.  
          
     2) VASCULAR DISORDERS.
       
    Reports of TMD-like pain from cardiac origin are rare. Simultaneous presence of jaw    and vascular pain explained by overlap of cervical nerve C-spinal nerve T with the    trigeminal  nerve. Significance: Vascular disorders, exclusive of headache,    generallycontribute little to TMD symptoms.

     3)   RESPIRATORY DISORDERS.
       
    Hyperventilation, or overbreathing, has been documented as a cause of orofacial     pain.
       Light-headedness, dizziness, and shortness of breath were described as classic     symptoms  of  hyperventilation.
     4)  CONNECTIVE TISSUE DISORDERS.
         
    Few patients with TMD symptoms have connective tissue disease.
         


      
       >  PRECIPITATING FACTORS
          1. Trauma
     
    Trauma as a potential precipitating factor in TMD has created  much  inspeculation.   Precipitating trauma was identified as the major factor in causing TMD pain.  Trauma may cause  specific disturbances of the TMJ area. Direct injury to the joint  has been proposed as a cause of TMJ osteoarthritis. Sudden changes in the vertical dimension,  caused by disk derangement, have been suggested as capable of altering the occlusion.

          2.  Whiplash
     
    Whiplash may produce disturbances at specific anatomic sites of the head, TMJ, and cervical musculature.

          3.   Dental Treatment
     
     Patients often ask if a particular dental treatment causes adverse effects or improves a  preexisting TMD condition. Loss of teeth, orthodontics, prosthetic treatment, or root canal  therapy are the most frequently asked about procedures.

             A.  Loss of Teeth
     
    The overclosure causes the mandible to be malaligned, resulting in joint disturbances.  This  malalignment alters the position of the condyle in the fossa, which tends to "overload" the joint. Unilateral tooth loss was common on the side opposite the dysfunction but was identified with  the same side in another study.

             B.  Extraction of Teeth
       
    Overmanipulation of the mandible during the extraction of molars has been considered a   factor  in producing TMD problems.
       Although the loss of tooth support or overmanipulation of the mandible might be   detrimental  to health of the TMJs and surrounding soft tissues.

             C.  Restoration of the Occlusion
        
    If occlusal support is necessary to avoid TMD, then restoration of the occlusion should     reduce or eliminate symptoms.
        If dysfunction is present, restoration should help lessen the severity.

        
          D.  Orthodontics
        
    Numerous anecdotal remarks have been made about orthodontics and TMD.     Evaluations of  condyle position and vertical overlap of anterior teeth were made in    patients who had the  premolars extracted for orthodontic purposes and in patients    without  xtractions.  Although  some authors argue that orthodontic treatment    superimposed on preexisting subclinic symptoms  may lead to a full blown TMD    condition.            
      
    E.  Root Canal Therapy
        
    Tooth pain may be eliminated by root canal therapy.
         It is generally agreed that prolonged mandibular hyperextension may elicit new or     agpreexisting  TMD symptoms. Significance: Although prolonged hyperextension during     root canal therapy may be considered significant as an etiologic factor.

    >  PERPETUATING FACTORS

         1.   Bruxism

        Support for the concept that bruxing contributes to dysfunction appears widespread.     Complaints about the masticatory muscles  have received the most attention. TMD    symptoms have been reported among adult bruxers. Positive associations have    been found  betweenbruxing and TMD symptoms in children.     

     
    2.  Other Oral Behavioral Patterns
       
    A few incidental remarks have been made about chronic chewing of gum and TMD   symptoms.
       Jutting of the mandible forward of prolonged lip biting induced pain in the anterior   temporalis muscle.  Interesting associations have been found between oral habits,   muscular changes, facial pain, and different kinds of headache.
       Reclassification of groups into subjects with TMJ pain, TMJ and muscle pain, or no  facial pain showed That nocturnal bruxism was more frequent in the combined  TMJ and  muscle pain  subjects than in other subjects.

        3.  Emotional Factors
        
    Emotional factors have been suggested as being involved in the genesis of TMD pain.    Patients with headache, facial pain, or abdominal pain were less accurate in   remembering their  pain than patients with cervical and low back pain. Individuals who   had histories of  emotional stress or home conflicts, who were less active, and  who   relied on medication were most inaccurate in remembering their  pain. significance:   Many   factors besides pain quality and quantity influence the  discomfort and suffering   associated with recurrent pain.

    *  This articles from p 87-118 " THE TEMPROMANDIBULAR JOINT AND
     RELATED OROFACIAL DIRORDERS " by Francis M. Bush & M.Franklin Dolwick

     

     

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