Fiber system degradation, and periostin and connective tissue growth factor level reduction, in the periodontal ligament of teeth in the absence of masticatory load.
The periodontal ligament (PDL), which is interposed between the alveolar bone and roots, supports teeth against mechanical stress. Periostin and connective tissue growth factor (CTGF) might play essential roles in maintaining PDL fiber integrity under mechanical stress. However, this relationship has not been studied at the protein and gene levels. Therefore, the aim of this study was to assess the PDL fiber system without masticatory load to determine the structural changes in the PDL in the absence of mechanical stress. The study included 45 Wistar male rats (12 wk of age) whose upper-right first molars were relieved from occlusion for 24 h, 72 h, 7 d or 21 d. The PDL was examined histologically, and changes in the gene and protein levels of periostin and CTGF were investigated. The PDL space width was reduced significantly. Histologically, an initial reduction in the fiber number and thinning of PDL fibers were observed, followed by disarrangement of the PDL fibers and their attachments to the alveolar bone; finally, the PDL fibers lost their meshwork structure. Real-time RT-PCR results revealed sharp down-regulation of the periostin and CTGF mRNA levels at 24 and 72 h, respectively, which continued throughout the experiment. Immunohistochemical analysis revealed that periostin localized to both the cellular elements and the extracellular matrix, whereas CTGF localized only to the cellular elements. Periostin and CTGF immunoreactivities became very weak without masticatory load. In the absence of mechanical stress, the PDL fiber system undergoes degradation concomitantly with a reduction in the periostin and CTGF levels in the PDL.