Force distribution of the temporomandibular joint and temporal bone surface subjected to the head-chincup force.

The present study is an in vitro study of chincup therapy. The purpose of the study was to investigate the localization and distribution of stress induced by the head-chincup appliance. Thin single and three-dimensional strain gauges were affixed on a young dry human skull capped by the head-chincup appliance. Three kilograms of force was then applied in the direction of the condyle. In a slight opening (5 mm at the incisor position), compressive force was observed to be constant at the anterior part of mandibular neck and tensile force at the posterior part. The joint cavity showed both tensile and compressive forces, whereas its posterior site showed only compressive force. Stress distribution at the lateral surface of the temporal bone indicated that long-term use of the chincup appliance affects the craniofacial structures. The longitudinal laminagraph records of a clinical case were also presented to support the current biomechanical findings.