It has been suggested that stabilization appliances and mandibular anterior repositioning appliances work by decompressing the temporomandibular joint. To indirectly test this assumption, tomograms of right temporomandibular joints of seven subjects were taken during comfortable closure and maximum clenching in maximum intercuspation and on the two types of occlusal appliances. Outlines of the condyle and the temporal fossa were automatically determined by an edge detection protocol. Upon comfortable closure, the anterior joint space dimension was reduced with stabilization appliances and mandibular anterior repositioning appliances. Upon maximum clenching, the minimum joint space dimension on stabilization appliances was equivalent to that seen in maximum intercuspation, while that on mandibular anterior repositioning appliances was substantially less (P .05). Findings do not indicate that these appliances induce an increase in joint space during clenching.