- 學位論文
牙冠磨損及牙根幾何形狀對垂直牙根斷裂之影響
Effects of Attrited Crown and Root Canal Geometry on the Vertical Root Fracture of Tooth
摘要
摘 要 垂直牙根斷裂多發生在根管治療之後的牙齒，然而有些研究報告發現垂直牙根斷裂也有發生在沒有接受根管治療的牙齒上，且大都在後牙區而且牙冠有嚴重磨損。本研究目的在使用有限元素法來分析牙冠磨損及牙根和牙髓腔形狀對垂直牙根斷裂機轉之影響。本研究中針對門齒及前臼齒進行有限元素分析，首先比較牙週膜韌帶的影響，接著比較完整和磨損牙齒的應力分布，最後再比較不同牙根和牙髓腔形狀對應力分布的影響。當牙週膜韌帶的楊氏係數越高會使牙本質上的應力提高，牙週膜韌帶的楊氏係數越低則會降低牙本質上的應力。緻密骨的情形剛好相反。比較完整牙齒及磨損牙齒在牙本質上的應力分布可以發現到無太大差異，但是在牙髓腔上方的應力分布差異卻會造成不同的斷裂型態，磨損牙齒易斷在牙根，反之完整牙齒易斷在牙冠上。當改變牙根和牙髓腔形狀時，牙齒在牙尖端處會有明顯的應力集中現象，這跟文獻中發現到垂直牙根斷裂易發生在近心徑和遠心徑較短的扁平牙根的情形是一致的。
並列摘要
Abstract Vertical root fracture (VRF) usually occurs in endodontically treated teeth. However, there are reports found VRF in non-endodontically treated teeth and almost all in posterior teeth with severe crown attrition. The purpose of this study was to investigate the effects of attrited crown and root canal geometry on the VRF of tooth by finite element analysis. Finite element models of an incisor tooth and a premolar tooth were created. At first, different material properties of the periodontal ligament (PDL) were simulated. Secondly, intact and attrited teeth were simulated. At last, different types of root and canal geometries were simulated. Resutls showed that the absence of a PDL was detrimental to the surrounding bone, because the stress remains concentrated at the bone crest and cervical third of the root. A PDL with a lower elastic modulus, on the other hand, helps to alleviate the stress magnitude throughout the surrounding bone crest. The stress distributions of the intact and attrited crown tooth were similar. However, the stress distribution at the root canal was different and it can lead to different fracture types. Attrited crown can lead to root fracture. On the other hand, intact crown can lead to crown fracture. When the tress distribution of the apical region was compared for different root canal geometries, results corresponded well with previous clinical observations that there is a higher tendency to fracture for tooth with thin and flat root canal of smaller mesio and distal diameters.