Mandibular movement characteristics of an anterior disc displacement with reduction.

Aims: According to the Research Diagnostic Criteria (J Craniomandib Disord 1992;6(4):301-355), an anterior disc displacement with reduction (ADD) is characterized by reciprocal clicking with the opening click occurring at a mouth opening at least 5 mm greater than that of the closing click. The aim of this study was to test whether the 5-mm criterion of the RDC is characteristic for a click due to an ADD.

Methods: From 30 participants with a unilateral ADD, recordings of mandibular movements with 6 degrees of freedom as well as joint sound recordings were made. The participants performed free open movements and loaded closing movements.

Results: In 8 joints (27%), the 5-mm criterion was not fulfilled. For 2 participants, the click while closing occurred with an even larger mouth opening than that while opening. Recordings of the condylar movements showed that the opening clicks occurred over a broad range of the opening movement, whereas all the closing clicks occurred just before the condyle reached its terminal position in the fossa.

Conclusion: The 5-mm criterion of the RDC is not characteristic of all anterior disc displacements with reduction.