Wavelet transforms of TM joint vibrations: a feature extraction tool for detecting reducing displaced disks

The objective of this study was to determine if wavelet transforms (WTs) of vibrations recorded from temporomandibular joints (TMJs) with reducing displaced disks could be visually separated from WTs of vibrations recorded from normal TM joints by blinded observers. From a continuous series of 124 diagnosed TMD patients, 28 were confirmed with at least one reducing displaced disk. Vibrations were recorded from each affected joint, together with incisal point movements, using BioPAK (BioResearch, Inc., Milwaukee, WI) during opening, closing, and lateral excursions. Identical recordings were taken from 28 patients who were determined to have normal "nondisplacing, nondisplaced" joints. A 3x7 Biorthogonal Spline Wavelet Transform was used to create three-dimensional time-frequency graphs of the vibration events for each subject. Printed copies of the graphs were then shown sequentially to seven blinded observers who were asked to separate them into two groups without any knowledge of their significance. Each observer was independently able to separate the two groups without committing more than one error. We conclude that the vibrations generated by reducing displaced disks are sufficiently different from the vibrations of normal joints to be separable by visual inspection of their respective wavelet transforms.