The Effect Of Enhanced Masticatory Pressure On The Expression Of Integrin β3mRNA Of Rat Residual Ridge

Residual ridge resorption is the important factors affecting function and retention in the process of restoration. It is the main reason for failure of denture. All patients wearing the unsuitable denture will accelerate residual ridge resorption. It results in a vicious circle, affecting the life quality of the patients, and increasing the difficulty of treatment.IntegrinαVβ3 is an extracellular matrix (ECM) receptor at cell surface that mediate cell adhesion to ECM. By far, there have been a lot of reports about the role of integrinαVβ3 in angiogenesis and bone remodeling during various pathological or physiological course. The high level expression of integrinαVβ3 in the osteoclast cell surface plays an essential role not only in osteoclast precursors differentiation, migration, and fusion, but also in osteoclast signaling event, cytoskeletal organization and the formation of actin loop and the sealing zone. Numbers of studies in vivo or in vitro suggest that osteoclastic bone resorption can be inhibited through inference with the functions of integinαVβ3.The purposes of this study were not only to detect the effect of enhanced masticatory pressure on the expression of integrinβ3mRNA of rat residual ridge by in situ hybridization and to discuss the role of integrinαVβ3 in the residual ridge resorption, but also to discuss the relevance of denture, masticatory pressure and alveolar bone remodeling with a series of researches and the impact of masticatory pressure on alveolar bone remodeling.50 healthy ten-week male Wistar rats were allotted at random into two groups——experiment group and control group. The left and right maxilla first molars were extracted, and then took impression in a custom impression tray after 2 weeks. The denture bases were made of the self-cured acrylic resin. The height of the denture base of the experiment group was about 0.8mm over occlusal plane, but equal to occlusal plane for the control one. 50 rats were perfused and sacrificed on 3rd day, 7th day, 14th day, 28th day and 56th day. All the buccolingual sections in the first molar region were processed with TRAP staining and integrinβ3 mRNA in situ hybridization staining. Observing the histological changes of tissue, and the results were analyzed by the Computer Image Analyzing System and treated by statistics test.This study found that when residual ridge suffered too much pressure in experimental group, alveolar bone appeared a large number of osteoclasts and bone resorption lacunae. With the increasing of the observation time, alveolar bone resorption results in the space between base and the tissue is larger, masticatory pressure decreased and alveolar bone resorption activity slowed. TRAP staining results showed that: for the experimental group, the number of TRAP staining positive osteoclast was fewer on the 3rd day. On 7th day, TRAP staining positive osteoclast cells increased significantly. This phenomenon was most obvious in the bone surface, and increased while the number of experiment days increased. On the 14th day, there were a lot of TRAP staining positive osteoclasts in the junction between mucosa and alveolar bone. Bone resorption lacunae were obvious. TRAP staining positive osteoclasts and the number of TRAP staining positive particles reached the peak on the 14th day. The number of TRAP staining positive osteoclasts substantial reduced on the 28th day, and basically returned to normal levels on the 56th day. It showed that osteoclast activity was closely related with masticatory pressure loading on the alveolar ridge. Integrinβ3 mRNA in situ hybridization showed that: on the 3rd day, compared with the control group integrinβ3 mRNA staining intensity increased slightly. On the 7th day, integrinβ3 mRNA expression increased significantly and staining intensity markedly strengthened, and at 14 day integrinβ3 mRNA expression and staining intensity remained the same, but the number of osteoblast increased slightly. On the 28th day,β3 mRNA expression of integrin decreased, and on the 56th day, compared with the control group, integrinβ3 mRNA expression was no significant difference which meaned the osteoclastic bone resorption activity slowed to stop. Integrinβ3 mRNA expression and the amount of staining intensity and bone resorption process were consistent, and integrinβ3 mRNA expression and the amount of staining intensity and were related with the stress.So we speculated that while rats eating, masticatory pressure was larger than normal bite force which made a micro-alveolar bone tissue injury as a trauma. Integrin was stimulated by stress and transmitted stress to the actin, and then transmitted it to entire cytoskeleton. It induced rearrangement of the cytoskeleton, osteoclast polarization, actin ring and podosome formation and resulted the alveolar bone resorption. Because the space between the base and the tissue was larger after alveolar bone resorption, so the masticatory pressure which was transmitted to alveolar ridge reduced in the later observation period, and osteoclast differentiation and activation was inhibited through a series of signal transduction. Therefore, on 28th and 56th day, osteoclast reduced and integrinβ3 mRNA decreased, staining intensity reduced on alveolar surface.To sum up, we can presume that too much pressure can cause residual ridge resorption. The change of the number of TRAP-positive osteoclast and TRAP staining particles and integrinβ3 mRNA content reflect the pressure caused by the biological response comprehensive response. Excessive pressure changes the expression of integrinβ3 mRNA in the alveolar bone. Therefore integrinβ3 mRNA plays an important role in the residual ridge resorption.