Photoelastic Analysis of Stress Distribution of Surgically Assisted Rapid Maxillary Expansion With and Without Separation of the Pterygomaxillary Suture

Purpose: The aim of this study was to evaluate in vitro the mechanical effect over teeth and bone structures of surgically assisted rapid maxillary expansion (SARME) in photoelastic analogs by observing stress produced during Hyrax-type and Haas-type appliances activation. Materials and Methods: Two photoelastic analogs were fabricated by use of birefringent materials to simulate an adult skull that contained teeth, bone, and maxillary sinus. Hyrax-type and Haas-type appliances were applied to the anchor teeth and incrementally activated. SARME was simulated by subsequent cuts of the lateral maxillary wall and midpalatine suture and separation of the pterygomaxillary junction. After each osteotomy, the appliances were activated. Resulting stress patterns were recorded photographically in the field of a plane polariscope. Results: Before any osteotomy, the activation of the appliances distributed stress through the anchoring teeth to the zygomaticomaxillary walls, concentrating at the zygomaticomaxillary and zygomaticofrontal sutures and at the midline of the maxilla. After midpalatal and maxillary wall osteotomies, a marked reduction of the stress at the zygomaticomaxillary walls was observed. With successive activations, the stresses increased in intensity at the molars, maxillary tuberosity, and pterygoid plates. After pterygomaxillary separation, the stress intensity at the molar area, maxillary tuberosity, and pterygoid plates decreased considerably. With successive activations, stress increased in intensity around the molars and maxillary tuberosity. There were no differences between stresses produced by the 2 appliances. Conclusions: In this biomechanical model, sectioning of all maxillary articulations, including separation of the pterygomaxillary junction, caused a decrease in stress over anchorage teeth. These data cannot be completely extrapolated to the clinical situation but indicate that electing to perform the SARME technique should be based on periodontal health and amount of expansion necessary for each case. (C) 2011 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 69:1771-1775, 2011