Influence of Bite Raising on the Temporomandibular Joint in SAMP8

Objectives: In recent years, the incidence of DegenerativeTemporomandibular Joint Disease (DJD) has been increasing in the elderly. DJD is regressive changes of the mandibular condyle. Senescence-Accelerated Mouse P8 (SAMP8) has approximately 11 months life-span which is half of an ordinary mouse and develops DJD at high frequency. We have previously reported that a decrease in the vertical occlusion may promote a deformation in the mandibular condyle, causing more serious DJD in SAMP8. The purpose of this study was to investigate morphological changes of the mandibular condyle by bite raising in SAMP8. Methods: Thirty male SAMP8 aged 2 months were divided into 2 groups. SAMP 8 both in the treated and untreated groups were raised until 8 months. In the treated group, the bite of bilateral maxillary molars were raised with light-activated resin at the age of 2 months. All mice were sacrificed, and the surface of the mandibular condyle was observed under the substantial microscope and evaluated degenerative morphological changes such as fissure, erosion and others according to the classification described by Chen. The data were analyzed by student's Welch's t-test. Results: The surface of the mandibular condyle in the bite raising group showed minor degenerative changes than the untreated group at 8 months old. Conclusions: The present results suggested that bite raising reduces DJD inSAMP8. It is considered important to reduce mechanical stress to prevent DJD.