| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 94 === A mechanical force applied to a tooth is transmitted to the root surrounding tissues of the periodontium and initiates remodeling activities that allow for movement of the tooth through alveolar bone. The periodontal ligament (PDL) , in normal thickness from 0.15mm to 0.38mm, is a unique structure situated between the hard tissues of the alveolar bone and cementum. The PDL contains a large number of highly specialized fibroblasts that are believed to involve the normal maintenance, repair and regeneration of the ligament, the cementum and alveolar bone. PDL fibroblasts have been shown to possess the phenotypes of osteoblasts and to undergo osteoblast differentiation in response to various stimuli. The research results in the responses of PDL cells to mechanical strain varied due to different experiment models, different strain patterns and different strain levels. We hypothesize that the differentiation stage of PDL cells determines the gene expression of osteogenic markers (alkaline phosphatase, osteocalcin), transcription factor for osteoblastic differentiation (Cbfa-1/Runx2), extracellular matrix proteins (COL-I, COL-III) and proinflammatory gene (COX-2) when PDL cells responding to mechanical strain in vitro. In this study, the human PDL cells were cultured in standard medium or mineralizing medium with osteogenic factors, such as L-ascorbic acid 2-phosphate (0.05mM), sodium β- glycerophosphate (10 mM) and dexamethasone (10 -7 M). We examined the influences of culture periods (7 , 14, 21 days), addition of osteogenic supplements and the effects of different magnitudes of cyclic tensional force (3% v.s. 10% elongation, 0.1Hz, 6 cycles/
min ) for 24 hours on the responses of PDL cells.
Our results demonstrated that the osteogenic supplements of mineralizing medium induced the extracellular matrix mineralization and enhanced the expression of osteoblastic phenotype in PDL cell culture, which increased in a time-dependent manner. The mRNA expression of ALP、OC、Cbfa-1 of PDL cells cultured with standard medium was up regulated by 3% cyclic tensional force, but down regulated by 10% cyclic tensional force. However, the mRNA expression of ALP、OC、Cbfa-1 in PDL cells cultured with mineralizing medium decreased by both levels of cyclic tensional force, and this regulation was dependent on the magnitude of the force. The mRNA expression of COL-1 and COX-2 was increased by both levels of mechanical stimulation. The mRNA expression of COL-III was up regulated by 3% cyclic tensional force,
but down regulated by 10% tensional force.
These results suggest that PDL cells when cultured with different culture medium receiving different mechanical loads, have the ability to induce a variety of biological responses including altering ECM protein synthesis.
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