Abstract: Objective To study the occurrence time and the characteristics of the joint vibration from TMJs in both of the patients with anterior disc displacement with reduction(ADDR)and controls， thus to provide the basis for quantitative clinical diagnosis. Methods The joint vibration pictures from TMJ were recorded bilaterally from 24 patients with ADDR and 24 healthy controls by electrovibratography. The total integral of the vibration energy（TI）， the ratio of the integral between frequencies above 300 Hz and below 300 Hz (ratio of >300 Hz/<300 Hz)， peak frequency（FP）， median frequency（MF）， peak amplitude（PA）and distance to centric occlusion position（D）were calculated. Data were analyzed with MannKendall nonparametric test to assess the joint vibration characteristics. Results The values of total integral (P<0.001)， integral<300 Hz(P<0.001)， integral>300 Hz(P<0.001)， peak amplitude(P<0.001) and peak frequency (P=0.002)were significantly higher than those of the control group. The vibration analysis showed that the sensitivity， specificity and accuracy of the disc displacement with reduction were respectively 87.5%， 79.5% and 83.3%. The joint vibration of the ADDR subjects occurred mostly at the beginning of the opening phase and the end of the opening phase， while in normal subjects， the vibration often occurred at the end of the opening phase and the beginning of the closing phase. Conclusion The joint vibration of the ADDR subjects shows higher energy and frequency， which can be used as auxiliary examination. JVA can provide a fast， noninvasive， and repeatable method to record the status of TMJ. Further studies are needed to identify the characteristic waveforms of different subgroups of TMD and to evaluate the possibility of diagnostic value.

Key words: temporomandibular joint disorders, joint vibration, joint sound, mandibular movement