二級窩洞設計及填補材料對後牙復形之生物力學分析

Abstract

臨床上常可見到填補材料失敗之案例，其中包含填補材料之斷裂、脫落，或是牙齒本身之斷裂等。具有良好之窩洞外型及適當性質的填補材料對於牙科治療之良好預後為相當重要之因素；然而隨著黏著技術的發展及填補材料的演進，對於窩洞修形之要求與傳統銀粉填補方式已有所差異。本研究目的為探討上顎小臼齒之二級窩洞設計與填補材料對於牙齒應力分布之影響，進而透過窩洞設計與填補材料的選擇，改善牙齒應力分布的狀況，以減少牙齒及填補材料之斷裂或是脫離的情形發生。 本研究使用有限元素分析模型及牙齒樣本壓力測試實驗，建構一上顎小臼齒之二級窩洞模型，並以牙齒樣本實驗印證其結果。使用一種牙科陶瓷復形材料及兩種不同彈性係數之牙科複合樹脂復形材料進行牙齒的復形；窩洞設計則分別為具有小凹之設計與無小凹設計，共六種組別。藉由探討牙齒窩洞之應力分布及位移量之差別，比較材料與窩洞設計對於牙齒之生物力學影響。 實驗結果顯示於小臼齒模型中，應力皆往顎側集中，且使用陶瓷復形材料之組別於牙齒窩洞底部邊緣有較低之應力分布。而小凹之窩洞設計雖於統計學上無顯著之影響，其對於陶瓷修復材料之窩洞邊緣中央區域之應力降低效果高於複合樹脂之組別；對於窩洞設計中之小凹大小深度設計，仍需進一步研究及確認。 根據本實驗之結果，在進行後牙二級窩洞之復形時，建議使用高彈性係數之復形材料搭配具有小凹之窩洞設計，以降低窩洞底部邊緣之應力集中情形。而小凹之窩洞設計則會因不同復形材料本身之彈性係數，而有效果顯著上之差異。

Restoration failure is a common problem in dental daily practice. The obvious failure types were restoration fracture, dislodgement, or tooth fracture. A well-designed cavity and proper restoration material are important factors to the prognosis of therestoration. With new adhesive restorations and good adhesive techniques, preparation guidelines for the restorations seems to be less strict. Instead, the properties of the restoration and the cavity design are become more significant. The purpose of this study was to evaluate the biomechanical effects of different cavity designs and restorative materials in human upper premolar model. Furthermore, to improve the stress distribution of the cavity and reduce the possibility of tooth fracture and adhesive failure by cavity design and restorative material selection. In this study, finite element methods and compressive test of tooth model were used. Restorative materials were one dental ceramic material and two composite resins with different elastic modulus. The cavities were designed with coves or without coves. By comparing the displacement and stress distribution of the model, in order to analyze the effects of cavities and the restorative materials. The results showed that a greater stress concentration over palatal cervical area. Tooth with ceramic restoration had lower stress distribution within the cavity margin. Application of two coves to the gingival margin of the cavity could reduce the stress distribution of the cavity margin. For the ceramic restorations, the effect was more obvious than composite restorations. The depth and the width of the coves need to be investigated further. Based on the result of this study, using restoration with high elastic modulus combined cavity designed with coves could reduce the stress distribution over cavity margin when restore class II cavities of posterior teeth. The efficacy of the cove cavity design was affected by the elastic modulus of the restoration.