Nonsurgical Treatment of Anterior Disk Displacement Without Reduction of the Temporomandibular Joint : A Case Report on the Relationship Between Condylar Rotation and Translation  ( The Journal of Craniomandibular Practice :Oct. 1995, Vol.13,No.4 )

Yoshi-Nobu Shoji,D.D.S.,M.D.S.

ABSTRACT: Farrar reported that in chronic anterior disk displacement without reduction (ADDw/oR) of the temporomandibular joint (TMJ), the range of mandibular movement gradually increases and the condylar movement normal-disk is still displaced anteriorly. The relationship between condylar rotation and translation was studied in opening/closing jaw movements before and after joint stabilization splint therapy in a patient with ADDw/oR. Movements were recoded by means of an optoelectronic jaw tracking system (Metropoly, Jaw-3D) consisting of three cameras that register the position of six light-emitting diodes (LEDs) mounted on two target frames separately attached to the upper and lower jaw. A computer produced plots of the condylar paths in the sagittal, frontal, and horizontal plane, as well as the opening angle against the anterior condylar translation. Results indicated some variations in the relationship between condylar rotation and translation during jaw opening movement. In the joint with ADDw/oR an increase in anterior condylar translation was found and the relationship between rotation and translation became more linear after joint stabilization therapy. This study supported a hypothesis of Farrar's that condylar movement in chronic ADDw/oR is similar to that expected in asymptomatic TMJs.

  Farrar1 hypothesized on the characteristics of the condylar movement in the temporomandibular joint (TMJ) closed lock position. As looking becomes more chronic, the range of movement increases and condylar path becomes normal. This is achieved by further anterior displacement and advanced deformation of the disk1,2.
  Westesson3 claimed that increasing mouth opening in patients with anterior disk displacement without reduction (ADDw/oR) should not automatically be regarded as normalizetion of joint function. In spite of numerous studies that focused on the topic of TMJ clicking (I.e.YMJ internal derangement) 1,3-9no objective assessment has been available condylar movement in chronic ADDw/oR.
The aim of this study was to determine whether there were characteristic condylar movements in a subject with chronic ADDw/oR treated with joint stabilization splint therapy. This involved an analysis of the relationship between condylar rotation and translation during opening/closing jaw movement.

Case Report
  A 16-year old female patient (EA) diagnosed with ADD w/o R was asked to participate in this investigation. The medical and dental history was not significant.
  The patient was first seen in March 1991 with a history of left TMJ ADD w/o R of six month's duration. During this time chewing was impaired and there was difficulty in jaw opening. The patient had undergone orthodontic treatment for Angle Class �U division.1 malocclusion for three years. Shortly after completion of orthodontic treatment, clicking began in the left TMJ and progressively worsened. TMJ locking occurred six month prior to initial evaluation. The first series of two recordings was made before joint stabilization splint therapy and the second series was made six weeks after the initial recording. The chief complaints of the patient were difficulty in jaw opening and pain on the left side of the face. 
  A clinical and radiographic examination was performed following the standardized procedure of the Orofacial Pain Clinic at the Westmead Dental Clinical School at the University on Sydney. Occlusal examination disclosed that four bicuspid teeth had been extracted and there was an Angle Class �U division 2 malocclusion with a 5mm overbite and 3mm overjet(Figure 1). Maximum intercisor jaw opening was 18mm. Lateral jaw movements of 5mm to the right and 9mm to the left and a protrusion of 10mm were recorded. Slight jaw deflection to the left was observed with jaw opening and protruding. Auscultation revealed no joint sounds and there was no joint tenderness to posterior or lateral palpation.
  Jaw muscle examination revealed pain in the left lateral pterygoid muscle and palpation tenderness of the body of superficial masseter muscles. The pain of the lateral pterygoid muscle was examined by provocation tests (i,e opening and protruding against resistance). No other jaw muscle were tender to palpation. Slight to moderate attribution tooth wear was evident on the maxillary central incisors and canines,and on the mandibular lateral incisors and canines. Inferior joint space arthography for the left TMJ revealed a well-established AAD w/o R, but there was no evidence of perforation(Figure.2).

Treatment
  Initial management of AAD w/o R involved reversible therapy. Acute AAD w/o R can usually be effectively reduced by manipulation of the mandible10. The affected side (left side) of the mandible was forced downward, forward, and incorporated the patient's voluntary maximal lateral excursive jaw movement to the nonaffected side (right side) Most young patients with a recent history of disk displacement usually respond favorably to manipulation. If however, the disk has been dislocated for several weeks or months, the success rate decreases dramatically11. 
  Manipulation was not successful for the patient EA.
  An upper joint stabilization splint 12 was fitted and the patient was instructed to wear it as possible during the day and especially at night while sleeping. The splint was worn after the initial recording until the second recording, which was made after a period of six weeks. The maximum range of jaw opening increased from 18mm to 35mm, and pain decreased in the left lateral pterygoid and superficial masseter muscles.

Recording Procedure
  Movements were recorded by means of the Jaws-3d tracking system consisting of three cameras that register the position of six light-emitting diodes mounted on two target frames separately attached to the upper and lower jaw (Figure 3)9,13,14. A computer produced plots of the opening angle against the anterior condylar translation.
The subject sat in an upright position in a chair during the recording and was asked to perform a sequence of five consecutive opening and closing movements. All procedures were performed at a rate that was comfortable for the subject in a quiet, relaxed, temperature-controlled atmosphere. 

Results
  Condylar movements showed variations depending on the TMJ condition. TMJs were divided into two types: (1) TMJ pro-joint stabilization splint therapy (TMJ-PRE); and (2) TMJ post-joint stabilization splint therapy (TMJ-POST).

Rotation Versus Translation
  The plot of anterior condylar translation versus the opening angle is represented in Figure 4. IN Figure 4A, the opening movement in the TMJ-PRE began mainly by translation. However, the translatory movement was obviously restricted in the latter half of the movements, as movements were possible for a distance of only 9mm. Figure 4B represents tracings made in the TMJ-POST. Greatly increased translatory movement over the entire range of motion was observed. Thus, the ratio between the opening angle and translation became more linear than that of the TMJ-PRE.

Discussion
  It has been claimed that wide mouth opening is produced by both rotation and translation of the condyle15,16. The translation is accomplished by sliding movement in the superior joint cavity,and the pure opening and closing rotation　occur in the inferior joint cavity15. Merlini and Palla9, using Jaws-3D jaw tracking system,reported a linear relationship between condylar rotation and translation during opening and closing movement in a healthy TMJ. IN the present study on the patient EA,joint stabilization splint therapy resulted in an opening movement produced by a near linear relationship between condylar translation and rotation (Figure 4B) . In the TMJ-PRE, the movement occurred mainly by rotation (Figure 4A).After joint stabilization splint therapy,an increase in anterior vondylar translation was found with almost the same opening angle as the one in the TMJ-PRE(Figure 4A). Consequently, it was similar to the relationship between condylar translation and rotation in the healthy TMJ shown in previous reports9,13.
  Occlusal splints provide the possibility for spatial change in jaw position with even tooth contact and an increase in vertical dimension of occlusion(VDO).
The TMJ capsule is richly innervated and sensory information detected by joint receptors is conveyed mainly along the afferent fibers in the temporal-auriculo nerve to the central nervous system. It has been stated that the TMJ may fulfill several important sensory functions that include the signaling of joint position and pain,and the initiation of reflex movements17. The joint stabilization splint may cause sensorimotor change due to an increase of VDO with even tooth contacts. Therefore, it seems that the joint stabilization splint may have allowed reestablishment of muscle coordination18 and resolution of muscle soreness19.  

  In the present study, the patient EA had a reduction in muscle soreness of the left lateral pterygoid and superficial masseter muscles during joint stabilization splint therapy. It has been proposed that anterior disk displacement could be caused by hyperactivity of the upper head of the lateral pterygoid20. However, Mahan et al21. clamed that dysfunction of the upper head could be a result of prolonged disk displacement, not its cause, since the majority of fibers of the upper head insert into the condylar fovea.    Although opinions regarding the insertion of the upper head are divided12,22-24, synchrony is important for smooth condylwe/diisk movement since the upper head is responsible for stabilizing disk and condyle during jaw closing21,25.
It has been reported that the articular disk is not in a normal position in a number of patients who had a good clinical course using arthrography26 and/or magnetic resonance images (MRI)27. This may suggest that the clinical success of treatment for TMJ internal derangement does not occur as a result of disk repositioning or recapturing28.
The alteration of the relationship between condylay translation and rotation after the joint stabilization splint therapy of ADD w/o R suggests that changes in neuromuscular coordination may have occurred during joint stabilization splint therapy without anatomical reduction27,29 of the articular disk.

Summary
  Although there are a few limitations to this study, the comparison between the condylar movement in the TMJ-PRE and the TMJ-POST of ADD w/o R supported the hypothesis of Farrar1  that condylar movement in chronic ADD w/o R is similar to that expected in asymptomatic TMJs.

Conclusions
  Joint stabilization splint therapy clearly changed the condylar movement in ADD w/o R. Changes were seen in the relationship between condylar rotation and translation.
The recording of the relationship between condylar rotation and translation may have a diagnostic value in patients with disk displacement of the TMJ. Future studies need to include numerous subjects.

Acknowledgments
  The author grateful to Professor Iven Klineberg in the Department of Prosthetic Dentistry at the University of Sydney and Dr. Richard Pertes in the TMJ/Facial Pain Center at the University of Medicine and Dentistry of New Jersey for their helpful support.

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