A molecular study of the masseter muscle in subjects with a unilateral posterior crossbite

AIM: It has been shown that subjects with a unilateral posterior crossbite (UPC) exhibit different mandibular kinematics during mastication when chewing on the affected side, resulting in an increased frequency of reverse chewing cycles. Integrins are a family of cell surface membrane proteins that mediate the interaction of cells with each other; these proteins also link the extracellular matrix (ECM) to the cytoskeletal actin and provide a bidirectional signalling between the ECM and the cytoplasm. The aim to this work was to analyze, by immunohistochemical techniques, biopsies of human masseter muscles of surgical patients with severe Class III malocclusions with a UPC. MATERIALS AND METHOD: Biopsies were obtained, under general anaesthesia, from the superficial and anterior portion of both masseters of patients undergoing orthognathic surgery. In the immunohistochemical analysis, the expression of the major integrin specific in the muscular tissue: α7B, ß1D, α7A and ß1A were studied. With specific software, the pixel intensity of 100 fibres was analysed for each reaction and a mean and standard deviation for single fibres were obtained. RESULTS: The amount of integrins appeared significantly lower, in the right masseter, than that detected in left counterpart; furthermore, α7A and ß1A isoforms, compared with α7B and ß1D isoforms, respectively, were significantly predominant in both masseters. CONCLUSION: Based on the results, it is possible to hypothesize that the decreased masseter activity on the crossbite side can be strongly related to integrin behaviour. The data provides the first suggestion that integrins in masseter muscle play a key role in regulating muscular activity, allowing the optimization of the contractile forces of this muscle.