THE WAVE-FORMS OF TEMPOROMANDIBULAR-JOINT SOUND CLICKING AND CREPITATION

The aim of the present study was to determine the sound wave forms whi ch correspond to auscultatory findings of temporomandibular joint (TMJ ) clicking and crepitation. Such knowledge is important when selecting parts of digital recordings for spectral analysis. Electronic digital recordings were made with a sampling rate of 44 100 Hz from 60 subjec ts, including 51 patients referred for suspected rheumatological disea se and nine healthy subjects. Accelerometers with the bandwidth 20-360 0 Hz were used for all subjects and complementary recordings were made from a subgroup of nine subjects using a measurement microphone with the bandwidth 20-20 000 Hz. The clicking sounds could be classified in to different types according to differences in temporal period duratio n (T) as measured on the analogue display. One type of clicking, found in 51% of the patients, had a T of 2-20 ms. Another type, found in 70 % of the subjects, had a T of less than 1 ms, often as low 0.2 ms. Thi s type of clicking was not seen at all in the analogue display if the sampling rate was below 3 000 Hz. The character of the two types of cl icking differed: the short duration sounds had a very high pitch, whil e the pitch of the longer duration sound was lower. Crepitation was fo und in 63% of the subjects and was observed to be composed of a series of short duration sounds, occurring with brief (less than 10 ms) inte rvals. It is concluded that the accelerometer (or microphone) bandwidt h should cover the entire audible range (20-20 000 Hz), and that sampl ing rates must be much higher than 3000 Hz, and preferably greater tha n 10 000 Hz, before the true significance of electronically recorded j oint sounds/vibrations can be determined.