[Expression of type I collagen mRNA in rat molar periodontal ligament under normal bite force]

The main component of the periodontal ligament(PDL) is collagen fiber, especially type I collagen, and collagen plays an important role in PDL. The aim of this study is to observe the expression of rat PDL mRNA under normal bite force and to investigate the molecular mechanisms of these changes in type I collagen mRNA.

40 male Wistar rats were used, and animals were intra-cardiac perfused with a solution of 4% polyformaldehyde under anesthesia. Dissected mandibles were immersed in the same fixation for 6 hours and subsequently decalcified in EDTA. The demineralized specimens were embedded in paraffin and cut into slices with thickness 5 microns. The probe was synthesized and labeled with digoxigenin. Expression of type I collagen mRNA was measured by using in situ hybridization(ISH).

Under the normal bite force, the mRNA expression of type I collagen was very strong on the whole, including the alveolar bone side, the root side and the area between them. Positive signals were located mainly in the cytoplasm and some in the nuclei. But the mRNA expression of type I collagen still had spatial characteristics. The signals in some fibroblasts were apparently stronger than those in other fibroblasts in the apical 1/3 fragment of the roots. The signal of type I collagen mRNA was strong near the root sides. The expression signal on the proximal alveolar walls was strong, however, on the distal alveolar wall, there was no expression.

The expression of type I collagen mRNA is closely related with bite force.