Objective To compare the vibration parameters in reducible anterior disc displacement and symptomless youth, and explore the clinical diagnostic value of frequency spectrogram of temporomandibular joint（TMJ） sounds. Methods 21 youth with anterior disc displacement were included as experimental group, and 26 symptomless youth were included as control group. The joint vibrations during rhythmic maximal open-close jaw movement of all subjects were recorded. The sensitivity and specificity of total integral in diagnosis of reducible anterior disc displacement were calculated. Results All TMJ vibration parameters, include total integral, integral＜300 Hz, integral＞300 Hz, ＞300/＜300 Hz radio, peak amplitude, peak frequency and median frequency, were significantly higher in experimental group than that in control group（P＜0.05）. Along with the increasing of disc displacement degree, the TMJ vibration parameters were increasing, and total integral significantly increased（P＜0.05）. The total integral demonstrated a high sensitivity and specificity in diagnosis of anterior disc displacement with reduction（0.86 and 0.85, respectively）. Conclusion The TMJ vibration parameters are significantly higher in youth with reducible anterior disc displacement than that in symptomless youth. Different pathological stages of disc displacement show different TMJ sounds.
