A comparative photoelastic analysis of force distribution over teeth and maxilla between a hyrax-type and a custom-made device in surgically assisted rapid maxillary expansion

Abstract

The aim of this study was evaluate the mechanical effect over teeth and bone structures of surgically assisted rapid maxillary expansion (SARME) in photoelastic skull analogs by comparing stress produced during Hyrax activation and a custom-made hyrax appliance. Two photoelastic analogs were fabricated by use of birefringent materials to simulate an adult skull that contained teeth, bone and maxillary sinus. A hyrax appliance was cemented to the first premolars and first molars. A custom made hyrax device with bands cemented to the first premolars and first molars were united to the cuspid, bicuspid first and second molars by means of a passively adapted 0.22″ rectangular orthodontic wire and brackets. SARME was simulated by subsequent cuts of the lateral maxillary wall, midpalatine suture and separation of the pterygomaxillary junction. After each osteotomy, the appliances were incrementally activated. Resulting stress patterns were recorded photographically in the field of a plane polariscope. Before osteotomies, the activation of the appliances distributed stress through the anchoring teeth and alveolar bone. Stress concentrated at the maxillary tuberosity and pterygoid plates and around the central incisors for both appliances. The custom-made appliance showed a wider distribution of force between the alveolar bone. Following simulation of the osteotomies, there was a marked decrease in stress intensity. In conclusion the use of a splint produces a better distribution of stress around teeth, which means less force applied over each teeth when compared to the hyrax-type appliance. Separation of the pterygomaxillary junction caused a decrease in stress over anchorage teeth.