Morphological and molecular changes in denture-supporting tissues under persistent mechanical stress in rats

The purpose of this study was to determine the effects of mechanical compression on the palatal mucosa using an experimental palatal base. The palatal base was either pressed onto (stress group) or not pressed onto (fit group) rat palatal mucosa. Blood flow was measured and the animals were sacrificed 6-72 h later for analysis. The expression of heat shock protein 70 (HSP70), vascular endothelial growth factor (VEGF) and proliferation cell nuclear antigen (PCNA) was characterized by immunohistochemical staining. For morphometric analysis, connective tissues were divided into bone side and epithelial side tissues. The ratio of PCNA-positive cells (PCNA score) was calculated, and the expressions of mRNA encoding HSP70 and VEGF was evaluated. Whereas blood flow in the stress group showed ischaemia, none was found in the fit group. Proliferation cell nuclear antigen scores on the bone side were higher than on the epithelial side in the stress group (P < 0.05). Heat shock protein 70- and VEGF-positive cells were observed under compression conditions, particularly in the periosteum. In the stress group, the expressions of mRNA encoding HSP70 and VEGF were highest at 12 h (P < 0.05). These results suggest that mechanical compression of the palatal plate induces ischaemia, and that cells in the underlying denture-supporting tissue, which includes the periosteum, synthesize HSP70 and VEGF to maintain homeostasis under these conditions.