摘要
目的 分析椭圆形根管牙根两种预备形态下,根管壁微裂纹对牙根受力的影响.方法 选择椭圆形根管的前磨牙 20 颗,器械扩大预备根管、制造微裂纹并染色,切片后显微镜下观察牙本质微裂纹的产生及分布.据此构建两种预备形态下预制裂纹的牙根模型,评估受力时微裂纹处及牙根的应力分布.结果 椭圆形根管牙根的微裂纹总是出现在颊舌侧,由根管壁向牙根表面扩展,与有限元分析所展示的应力集中在根管壁颊舌侧的规律一致.微裂纹使根管壁的应力集中点向裂纹尖端处转移,且在尖端极小区域内出现近 5 倍的应力剧增,使微裂纹极易沿尖端方向扩展,尤其在牙体长轴方向.结论 微裂纹的存在不改变椭圆形根管牙根颊舌侧应力集中的特点,但微裂纹的产生使其尖端极小区域内出现剧增的应力集中,这可能是微裂纹迅速扩展为牙根纵裂的机制,临床操作需提高警惕.
Abstract
Objective To analyze the stress distributions of two root canal preparation shapes of oval root canals with micro-crack.Methods Twenty single-canal mandibular premolars with oval canals were expanded to create micro-cracks.Roots were sectioned after staining.The generation and distribution of dentin micro-cracks were observed under microscope.Then a finite element(FE)model of sectioned enlarged oval canal roots with micro-cracks was established.The stress distribution of micro-crack and root were analyzed under lateral loading.Results Cracks always appeared in the buccolingual sides of oval canal roots and extended from the intracanal wall to the root surface.This was consistent with the stress concentration on the buccolingual side of the root canal wall shown by FE analysis.When micro-cracks occurred,stresses were transferred to the crack tip and the peak values increased sharply nearly 5 times.This made the cracks propagate easily along this direction,especially in the long axis direction of the tooth.Conclusions The presence of micro-cracks does not change the general stress concentration on root with two preparation morphologies of oval canals.However,the micro-crack causes an extreme stress concentration in the crack tip.This may be the mechanism of rapid propagation of microcracks into vertical root fracture,and dentists need to pay high attention.
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