不同部位牙体缺损对根管治疗后离体下颌磨牙折裂特点的影响

目的探讨不同部位牙体缺损对根管治疗后离体下颌磨牙折裂特点的影响,为临床选择修复方法提供理论依据。方法收集冠根完整的离体下颌磨牙55颗,分层随机抽样法分为对照组和实验组,实验组按照分类设计制备牙体缺损,全部牙齿完成根管治疗后用树脂恢复牙冠形态,环氧树脂包埋,沿牙体长轴方向施压至牙冠折裂,记录折裂载荷值及折裂模式,并进行统计学分析。结果各组的折裂载荷随牙体轴壁缺损数量的增多而下降,经单因素方差分析,各组试件折裂载荷的差异有统计学意义（F=21.14,P〈0.001）。缺损两轴壁时,近中-牙合面-远中洞形组出现可修复性折裂的比例最高。各组折裂模式的差异有统计学意义（P=0.024）。结论牙体缺损轴壁数对折裂载荷和折裂模式均产生影响,缺损轴壁数越多,折裂载荷越低,折裂后可再修复的比例越高,舌侧牙体折裂风险较颊侧牙体高。

Influence of different coronal defects location on fracture characteristics of endodontically treated mandibular molars in vitro

Objective Compare the fracture characteristics of mandibular molars in vitro with different coronal delects location, to find out whether distribution of remaining tooth structure has influence on the prognosis of root canal lherapy. Methods Fifty-five human mandibular first and second molars, extracted for periodontal disease, were selected. Strati- fied randomization was chosen to set up 5 experimental groups and I control group. Cavity access and artificial coronal de- fects were made in I -5 experimental groups according to the criteria of classifieation, then finished root-canal therapy routinely. After the defect crowns were reconstructed, all teeth were apically embedded in E-51 epoxy resin. A pressure head was used to spread load along the axial on every tooth. Fracture and fracture mode were then recorded and analyzed by SPSS. Results Means of fracture loads reduced as the missing axial walls increased. Fracture loads presented statistically significant difference （P 〈0. 001 ） among 6 groups. When two axial walls remained, the teeth with MOD （mesial-oechtsal-distal） defect showed the most restorable fracture. There was statistically significant difference among fracture modes of all 6 groups （ P = 0. 024 ）. Conclusion The number of defect axial walls displays an influence on both fracture load and fraeture mode. The less remaining axial walls exist, the smaller fracture load required and less unrestorable fracture occurs. Lingual wall posses a higher fracture risk.