中文摘要：

目的：比较K3XF和K3经过预加载疲劳应力后的表面形态和疲劳折断性能。方法：25 mm长、25#/0.06锥度的K3XF和K3各48支,随机分为4组（n=12）,组1不做预加载。组2~组4分别使用60°弯曲角度、3.5mm弯曲半径的模拟金属根管预加载疲劳应力5s、10s、20s。每组随机选取2支锉在SEM下观察表面形态,其余10支锉使用上述模拟根管进行疲劳折断实验。记录疲劳折断时间,计算疲劳折断圈数;测量折断段长度,并对折断断口进行SEM观察。SAS 9.3软件进行双因素的方差分析,显著性水平0.05。结果：SEM见两种根管锉弯曲最大处的切割刃明显磨损、出现大量裂纹、边缘不整齐。K3XF表面缺陷明显少于K3。K3XF预加载疲劳应力20s后的疲劳折断圈数从新锉的（210±59）降低为（156±37）,差异有显著性（P〈0.05）。K3预加载疲劳应力5s、10s、20s后的疲劳折断圈数从新锉的（145±38）分别降低为（110±27）、（101±31）和（62±31）,5s和10s组无显著差异,其余两两之间差异有显著性（P〈0.05）。结论：K3XF对预加载疲劳应力的抵抗性优于K3。

英文摘要：

Objective：To compare the effect of pre-load on surface microstructure and cyclic fatigue resistance of K3 XF and K3.Methods：Forty-eight K3 XF or K3instruments#25/.06 were randomly divided into 4groups（n=12）.The instruments from group 1were not pre-loaded,and the group 2to 4underwent pre-load for 5s,10sand20 sby using a simulated metal root canal with curvature of 60°and radius of 3.5mm,respectively.The surface microstructure of two instruments randomly selected from each group was observed using SEM.Then the remaining 10 instruments were submitted to the cyclic fatigue test using the before mentioned apparatus.The time till fracture was recorded as well as the number of cyclic fatigue（NCF）and the fragment length.The topographic features were analyzed using SEM.The data were analyzed with the Two-Way ANOVA analysis at a significance level of P〈0.05 by using SAS 9.3.Results：SEM observation demonstrated obvious flute abrasion,numerous cracks and irregularities on both of the files.However,this kind of destruction was less on K3 XF than that on K3.Cyclic fatigue resistance of K3 XF significantly decreased from（210±59）to（156±37）after pre-loaded for 20s（P〈0.05）.Cyclic fatigue resistance of K3 decreased from（145±38）to（110±27）,（101±31）and（62±31）after pre-loaded for 5s,10 sand 20s,respectively（P〈0.05）.Significant difference was observed between groups（P〈0.05）except that between 5sand 10 sgroups.Conclusion：K3XF exhibits better resistance against pre-load compared to K3.