不同瓷牙鑲面設計受力時之應力分析—有限元素法

臨床上瓷牙鑲面(porcelain laminate veneer)的使用已日漸普遍。瓷牙鑲面不僅修形保守，同時因陶瓷材料顏色接近琺瑯質，解決傳統治療中最為患者所挑剔的美觀問題。然而，瓷牙鑲面與牙釉質介面的破壞和瓷牙鑲面的破裂是臨床上常見的失敗情形。本研究的目的主要是以有限元素法探討在正常咬合力下，瓷牙鑲面的應力分布情形，並希望找出瓷牙鑲面的最佳設計方式。本實驗使用三維有限元素法分別對不同設計的瓷牙鑲面進行應力分析，首先建立出包含三種不同瓷牙鑲面設計〔羽毛形(feather)、弧形(chamfer)、方形(buttjoint)〕之上顎正中門牙的三維實體模型，以有限元素軟體(ANSYS)進行分析。分別於三種不同設計的模型施予一摹擬咬合力的力量(200 N)，施力的位置分別在上顎正中門牙的：(1) P1為舌側切緣三分之一，(2) P2為舌側中間三分之一，(3) P3為舌側齒頸三分之一，(4) P4為切端，(5) P5為唇側切緣三分之一。以P3至P1的摹擬來做為前突運動的代表過程，P4摹擬病患緊咬的情形，P5則摹擬瓷牙鑲面受到外力撞擊的狀況。結果發現，在摹擬前突運動的過程(P3~P1)中，瓷牙鑲面唇側面及舌側面的張應力逐漸增加，但應力值均未超過一般陶瓷的抗張強度，就瓷牙鑲面的縱切面而言，弧形設計有最大的張應力值，方形次之，羽毛形最小。自切端施力(P4)，瓷牙鑲面之張應力最大值出現在唇側中間三分之一與齒頸部三分之一的交界處，並往牙根方向傳導至瓷牙鑲面邊緣。唇側撞擊(P5)，無論是羽毛形、弧形或是方形設計的瓷牙鑲面皆會產生比瓷牙鑲面強度強的應力。

關鍵字

瓷牙鑲面；三維有限元素法；張應力

並列摘要

In recent years, the porcelain laminate veneer had become more popular application. This kind of treatment has the conservative preparation to the tooth, besides, porcelain has similar color with human enamel and was well acceptable for patients’ esthetic consideration. However, detachment and fracture of the porcelain laminate veneer was still the critical problem that usually affected the success rate of it. The purpose of this study was analysis the stress of porcelain laminate veneer during normal masticatory load (200N) by finite element method (FEM) and experimental strain measurement for validity test. Furthermore, attempt to find the best design of porcelain laminate veneer. In this study, the three-dimensional finite element method was employed to analyze the stress difficult to calculate by traditional clinical observation or experimental approaches. Solid models of the maxillary central incisor with three designs (feather; chamfer and buttjoint) of porcelain laminate veneers was build up and then transferred to the mesh model in FE package(ANSYS) to process the stress analysis. Five different force were applied on: (1)P1:incisal third of palatal surface (2) P2:middle third of palatal surface(3)P3:cervical third of palatal surface (4) P4:incisal edge(5) P5:incisal third of labial surface. During protrusion movement (P3~P1), tensile stress increased, but were not excess the tensile strength (24.8MPa) of porcelain. For cross section view of porcelain laminate veneer, chamfer type has the highest tensile stress, than buttjoint, feather type was the smallest. When loading was applied to incisal edge, the highest tensile stress concentrate at the junction of middle third and cervical third, stress conduct toward the apical direction and concentrate at labial cervical margin. When loading was applied to incisal third of labial surface, three design of porcelain laminate veneer will fracture.