AUTOCORRELATION OF ACOUSTIC-SIGNALS FROM THE TEMPOROMANDIBULAR-JOINT

Although there have been many investigations of TMJ sounds in the time and frequency domains, no previous reports have been found of; invest igations of the autocorrelation spectra of these sounds. In the presen t study, TMJ sounds were digitized at 1.7 kHz and 300 ms samples conta ining either clicks (single short duration sounds), crepitus (long dur ation continuous sounds) or creaks (a series of two or more clicks) we re selected. These samples were compared with sounds of known origin: tooth impact sounds, frictional sounds elicited by scratching the head , and bruxing sounds resulting from stick-slip friction as teeth were slid against one another under high pressure. There were clear qualita tive and quantitative differences between the autocorrelation spectra of the three types of TMJ sounds. Clicks were similar to tooth impact contact sounds, creaks were similar to the bruxing sounds, and crepitu s was similar to the scratching sounds. The repetition rate of creaks was 16 Hz (s.d. 9 Hz), this being similar to the resonance of the mand ible about the condylar axis. It is suggested that the creaks are due to stick-slip friction in the lower joint compartment of the TMJ.