Contributing factors of mandibular deformation during mouth opening

Objectives: A decrease in mandibular arch width during forced opening has b een documented. However, the contributing factors of mandibular deformation s are still unclear. This study investigated the mandibular deformation dur ing mouth opening, and searched for contributing factors related to this ph enomenon. Methods: Sixty-two dental students volunteered for this study. A linear var iable differential transducer (LVDT) was cemented on the mandibular first m olars to record mandibular deformation during mouth opening. Proposed facto rs including geometric factors of the mandible such as lower genial angle, mandibular length, symphyseal width and height were measured from cephalome tric analysis. Densitometric analysis was performed to detect symphyseal ar ea and bone density. Results: The changes in width between the mandibular first molars ranged fr om 20 to 437 mum, which was negatively correlated to the symphyseal width, area, and bone density. Where the lower genial angle had a positive influen ce, the arch width changed during mouth opening. A multifactorial model sho wed a significant correlation between the set of predictor variables (symph yseal area, bone density, and mandibular length) and mandibular deformation . Conclusions: Mandibular arch width narrowed during forced opening. Subjects with smaller symphysis, lower bone density and longer mandible tend to hav e larger arch width changes. (C) 2000 Elsevier Science Ltd. All rights rese rved.