Photoelastic evaluation of the standard bionator appliance

A study was undertaken to demonstrate the forces in the craniofacial complex generated by the activation of the standard bionator appliance. A three-dimensional skull replica of an orthodontic patient with a Class II Division 1 malocclusion in the mixed dentition was fabricated using a urethane based photoelastic material to simulate bone. Four muscles of mastication were simulated on the photoelastic model. Various anatomical areas of the skull were viewed in a circular polariscope and recorded photographically before and after inserting the bionator. The downward and forward repositioning of the lower jaw by the bionator appliance caused various stresses on the craniofacial complex. The photoelastic stresses visualized in this investigation would most likely cause: an increase in the gonial angle; downward repositioning of the midface; and a posterior displacement and expansion of the maxilla.