摘要
目的:分析根管器械在弯曲、扭转载荷下的应力分布。方法:将根管器械刃部假设截面为圆的金属细锥杆,利用材料力学及断裂力学的原理与方法,分别计算根管器械在弯、扭载荷下的应力分布,分析应力与根管弯曲角度、根管弯曲半径、器械直径、器械横截面极惯性距、金属弹性模量等参数的确切关系;探讨器械屈服、断裂失效的准则。结果:弯曲载荷下,根管器械横截面上任一点的弯曲正应力σ的计算公式为:σ=Ey/ρ(E为金属材料的弹性模量;ρ为根管与器械在该点的弯曲半径;y为该点到中性轴的距离)。扭转载荷下,横截面某点的切应力与扭距成正比,与到截面中心的距离也成正比,与横截面的极惯性距成反比。根管器械断裂的原因主要有2个:一是扭转超过极限扭距,器械顺着扭转的方向发生塑性扭转直至断裂,圆杆的极限扭距与其半径的3次方成正比;二是器械在循环载荷下发生疲劳损伤,最后突然断裂。疲劳损伤不仅来自弯曲循环载荷,同样来自扭转循环载荷;对于根管器械,低周疲劳损伤的危害及临床意义要大于高周疲劳。结论:根管器械在弯曲、扭转载荷下的力学分析结果对根管器械的优化设计具有重要的参考价值。
AIM： To analyze the stress distribution of endodontic instruments subjected to bending and torsional loads. METHODS ： The endodontic instrument was assumed as a metal conical bar. The normal stress of bending loads and the shear stress of torsional loads were calculated with the knowledge of mechanics. The relations between stress and such parameters as angle and radius of canal curvature, radius of instrument, polar moment of inertia, and metal elastic modulus were analyzed. The criteria for yielding and fracture of the instrument were discussed. RE- SULTS ： If the endodontic instrument is subjected to the bending loads, the normal stress at every cross section can be described by equation：σ= Ey/p（ E is elastic modulus, p is radius of canal curvature,y is the distance to neutral axis）. If the instrument is subjected to torsional loads, the shear stress at every cross section is proportional to the torque and the radical distance from the barg axis, and is inverse proportional to the polar moment of inertia of the cross section. There are two causes leading fractures of the endodontic instruments. Firstly as the value of the toque increases beyond the limited toque, the instrument will twist with no increase in toque and will fracture soon. The value of limited toque is proportional to 3 squares of the fileg radius. Secondly the instrument is subjected to cyclic loads which cause fatigue failure. Not only bending loads, but also torsional loads could be the cyclic loads . The low - cycle fatigue is more harmful than high - cycle fatigue for endodontic instruments. CONCLUSION ： The stress distribution of endodontic instruments subjected to bending and torsional loads is critical important for optimum design of endodonticl instruments.
出处
《牙体牙髓牙周病学杂志》
CAS
2008年第10期568-572,580,共6页
Chinese Journal of Conservative Dentistry
关键词
根管预备
根管器械
疲劳断裂
弯曲根管
root canal preparation
endodontic instrument
fatigue failure
curved root canal
