Osteonecrosis of the jaw (ONJ) is an adverse outcome associated to bisphosphonate treatment. However, it is not known whether the ONJ lesion originates in the bone, or whether it may initiate in the oral mucosa. The aim of our study was to evaluate the pattern of basal lamina of oral mucosa after bisphosphonate administration and to analyze the structural damage of the mucosa in ONJ patients, and in subjects treated with bisphosphonates without osteonecrosis. By immunohistochemistry, we evaluated changes in basement membrane by expression of signalling proteins, laminin, and type IV collagen. All tested proteins were almost absent in basal lamina and mucosa of subjects treated with bisphosphonates without osteonecrosis, whereas in mucosa of patients with ONJ, they showed a clearly detectable pattern of the same proteins, specifically in basal lamina, but less in comparison to control samples. Moreover, in pathological mucosa, the clearly detectable staining pattern for VEGF indicated a massive neoangiogenesis. Bisphosphonates induce changes in expression of proteins also in oral mucosa. The increase of these proteins in basal lamina, and the neo-angiogenesis, concomitant with formation of the lesion, could indicate a compensative behaviour in the remodelling of the gingival mucosa in order to restore the epithelial architecture.

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