An Analysis of the Sounds Produced by the Mandibular Joint

¹ Queen's University of Belfast

The phonoarthrogram, (P.A.G.), a method of recording the sounds emitted by movement of the mandibular joint, is described, together with an apparatus to indicate the degree of mouth opening.

An analysis of the unilateral sound records of 10 normal and 10 abnormal subjects who were known cases of temporomandibular arthrosis was made, irrespective of all other factors. No significant difference in the maximum sounds emitted between types was found.

The significant differences found between phases in this analysis were due mainly to the near-silence of the neutral phase. P.A.G. records were probably symmetrical, as comparable halves of the opening and closing phases were not significantly different. But halves of the closing phase were significantly different and the halves of the opening phase not significantly different, so there were some indications of asymmetry.

An analysis of the simultaneous bilateral sound records of 24 normal and 24 abnormal subjects with equal sex representation was made, irrespective of all other factors. This showed that no significant difference existed between repeated records on the same individuals or between sides, except in normal females during the closing phase. There were also no significant differences between affected and unaffected sides in abnormals.

An examination of individual P.A.G. means from both the unilateral and the bilateral records showed that there was a tendency for high readings to occur in skeletal class 3 subjects. The mean P.A.G. in skeletal class 1 subjects proved to be significantly lower than the mean P.A.G. in subjects allocated to skeletal class 2 or 3.

In general, this investigation shows that crepitus alone cannot be taken as a diagnostic sign of temporomandibular arthrosis.