Objective To study the regularity of the passive tensile of the masticatory muscles and ligaments by Twin-Block appliance under various bite reconstruction, and to provide some biomechanical references for the clinical use and improvement of Twin-Block appliance.Methods "Temporomandibular joint, mandible and Twin-Block appliance" model was set up by the three dimensional finite element method, and the related masticatory muscles and ligaments were added on it. Seven experimental groups were designed according to the clinical and research, the occlusal inclined plate' angles of Twin-Block appliance were 40°, 45°, 50°, 55°, 60°, 65° and 70°. The passive tensile in the masticatory muscles and ligaments were analyzed by the computer.Results Under various experimental groups, the passive tensile in the anterior deep masseter (AM), the posterior deep masseter (PM) , the anterior temporalis (AT), the posterior temporalis (PI), the stylomandibular ligament and sphenomandibular ligament improved with the increased slant angles of occlusal guide. The maximum value of the passive tensile was 82.57 N, the minimum value was 0.07 N.Conclusion 1) In various experimental groups, AT, AM, PM, PT, stylomandibular ligament and sphenomandibular ligament are subject to passive tension force in the process of Twin-Block appliance guiding the mandibular forward and play the important role on the remodeling of the mandible. 2) All groups of occlusal inclined plate's angle are in physiologically tolerable range and can be used in clinic.
