【作者】 关卿；

【导师】 倪龙兴； 顾永春；

【作者基本信息】 第四军医大学 ， 口腔临床医学， 2011， 硕士

【摘要】 根管治疗术(root canal therapy,RCT)是临床治疗牙髓病及根尖周病最有效的方法。根管预备是根管治疗的关键步骤之一,包括根管清理和根管成形。通过对根管的预备,可以形成一个理想的根管形态(连续锥形),从而有利于彻底的根管冲洗和严密的根管充填。然而,使用传统的不锈钢器械预备弯曲根管时,易造成根管拉直、根尖拉开、肘部及台阶形成、根管偏移等不良形态,从而降低根管治疗的成功率。根管器械在弯曲根管中的回复力被认为是产生上述根管不良形态的根本原因。研究表明,除了根管器械刃部的几何形态、金属材料的机械性能,根管的弯曲角度与弯曲半径是影响根管预备效果及器械断裂的关键因素。国内外对此虽有报道,然而其详细的力学机制的尚未阐明。本研究目的是采用光弹法及有限元法,分析弯曲根管预备时根管壁及根管器械刃部的应力分布,探讨根管预备不良形态和器械分离的力学机制,为临床弯曲根管的预备提供实验依据。本课题分为两部分。第一部分弯曲根管预备时根管壁受力的光弹分析实验一环氧树脂弯曲根管光弹模型的制备以树脂块人工根管(Densply,瑞士)为样版,用硅橡胶翻制尺寸为10mm×10mm×30mm的长方体阴模。将20#/.02侧压针(Densply,瑞士)弯制成圆心角为60°,弯曲半径为5mm的弧形弯曲,然后将其固定于硅橡胶阴模中,再将顺丁烯二酸酐、环氧树脂、邻苯二甲酸二丁酯、二甲基苯按30∶100∶5∶0.05的比例混合后灌入硅橡胶阴模,以二次固化工艺固化。最后抽去侧压针,共获得形状一致的环氧树脂弯曲根管模型20个。实验二根管预备时根管壁受力的光弹分析20个弯曲根管光弹树脂模型被随机平分为2组,分别用不锈钢K锉(SS组)和镍钛K锉(NiTi组)按逐步后退法进行根管预备(预备次序为:15#→20#→15#→25#→20#→30#→25#→35#→30#→40#)。每号锉预备完毕将锉保留于根管中,然后将模型置于409-Ⅱ型偏振光弹仪,EOS 350D数码相机(Canon,日本)拍摄光弹云纹照片。光弹数码图像导入图像分析软件Image Pro plus 6.0(Media Cybernetics,美国),测量应力面积(area of stress, AS)。结果发现:15#、20#锉预备时,不论是SS组还是NiTi组,都未产生明显的应力区域;从25#锉开始,SS组AS均值明显大于NiTi组(P < 0.05)。2组相比较,SS组25# AS均值与NiTi组35#的AS均值较为接近(P > 0.05);SS组30#的AS与NiTi组40#的AS均值相等(P > 0.05)。此外,SS组AS在根管弯曲外侧壁要明显大于根管内侧壁(P < 0.05),而在NiTi组, AS在根管弯曲内、外侧壁差异均无统计学意义(P > 0.05)。第二部分弯曲根管预备时根管器械的三维有限元应力分析实验一三种根管锉和四种弯曲根管三维有限元模型的建立根据不锈钢K锉、H锉及Protaper的几何设计参数,运用CAD/CAM软件Pro/Engineer 5.0(PTC,美国)建立25# K锉、25# H锉及Protaper系统的F1锉切割刃的三维有限元模型。弯曲根管建模的几何参数为:弯曲半径2mm和5mm,弯曲角度(Pruett测量法)取30°和45°,共形成4个参数组合。实验二根管锉弯曲、扭转加载下的有限元应力分析分别对3个根管锉有限元模型的金属材料属性进行赋值,定义载荷大小、约束位置(距根尖5mm处)及旋转方向(顺螺纹和逆螺纹)。运行Pro/MECHANICA有限元分析软件对弯曲根管中的根管锉进行应力分析。实验结果表明,K锉和H锉组在顺螺纹和逆螺纹扭转负载下,应力大小无明显差异。在弯曲、扭转负载下,K锉在45°/2mm弯曲根管中应力集中区位于切割刃尖;H锉在30°/5mm和45°/2mm弯曲根管中的应力集中区位于两切削刃的沟槽内,在30°/5mm和45°/2mm弯曲根管中最大应力区位于切削刃尖部;Protaper F1锉在45°/5mm弯曲根管中最大应力区在两切削刃的沟槽内,在30°/2mm、30°/5mm及45°/2mm弯曲根管中最大应力区均在切削刃尖部。综上所述,光弹分析及有限元分析法能有效分析并预测根管不良形态及器械分离的发生部位,可以较为准确、直观地分析根管壁与器械的相互作用力,分析结果,对弯曲根管预备时,器械的正确选择和使用有指导的意义。更多还原

【Abstract】 Root canal therapy (RCT) is currently the most effective treatment for pulp and periapical diseases. Root canal preparation, which includes cleaning and shaping of the root canal systems, is one of the key steps of RCT procedure. The aim of root canal instrumentation is to forming an ideal canal shape (continuous tapering), which is essential for complete root canal irrigation and obturation.The conventional preparation of curved root canals with stainless steel (SS) instruments may produce a series of procedural errors such as: root canal straightening, zipping, elbow and step formation, root canal transportation etc, which may reduce the success rate of the RCT. This can be due to the restoring force developed by the file in the curved canals. Scholars found that, in addition to the root canal geometry, mechanical properties of the files, the angle and radius of the root canal curvatures are important factors that contribute to the separation of the root canal instruments, whereas the detailed mechanism is still unclear.The purpose of this study was to analyze the stress distribution of the root canal wall and endodontic instruments during preparation of the curved root canals by photoelastic and finite element methods. A full understanding the mechanism of development of procedural errors and instrument separation is essential for successful RCT on curved root canals.This investigation included 2 parts:Part 1 Photoelastic stress analysis of root canal preparation of curved canalsExperiment 1 : Preparation of epoxy resin models of curved root canalsSilicone rubber impression of a rectangular block (10mm×10mm×30mm ) was made to copy the shape of a resin simulated root canal (Densply, Swiss). A #20/.02 spreader (Densply, Swiss). was bent into an arc with an central angle of 60 degrees and a radius of 5 mm, then the spreader was fixed in the silicone rubber impression. Maleic anhydride, epoxy resin, dibutyl phthalate, and dimethyl were mixed together with a proportion of 30:100:5:0.05, and poured into the impression. After solidification the spreader was pulled out from the resin block, and a total of 20 epoxy resin models were prepared by above method.Experiment 2: Root canal preparation and photoelastic analysis A total of 20 epoxy resin models of curved canals were divided randomly and equally into 2 groups. One group was prepared with SS K file (SS group) and the other with nickel-titanium K file group (NiTi group), both groups using step-back technique (the sequence of file size was:15 #→20 #→15 #→25 #→20 #→30 #→25 #→35 #→30 #→40 #). Each file was retained in the root canal as preparation was completed, and the model was placed in 409-Ⅱpolarized light instrument to take photoelastic moire photos by a EOS 350D digital camera (Canon, Japan). The digital photographs were then input into software Image Pro plus 6.0 (Media Cybernetics, USA) to measure the area of stress (AS).The results showed that, for 15 # and 20 # files, obvious stress areas were not observed in both groups; after 25# file, however, the AS values of the SS group were significantly (P < 0.05) greater than the NiTi group for the file of same size. A 25# SS file produced similar amount of AS as that of a 35 # NiTi file (P> 0.05), and a 30# SS file had a equal AS value to a 40# NiTi file (P> 0.05). In SS group, AS of the outer wall of canal curvature was significantly larger than that of the inner wall (P < 0.05); whereas in NiTi group, the difference of AS values between the outer and inner canal walls had no statistical significance (P > 0.05).Part 2 Finite element analysis of endodontic instruments during preparation of the curved root canalsExperiment 1: Establishment of finite element models of 3 types of root canal files and 4 types of curved root canals.By using CAD/CAM software Pro/Engineer 5.0 (PTC, USA), three-dimensional finite element models of a 25# K file, a 25 # H file and a Protaper F1 file were created according to their manufacture geometrical parameters. Four mathematical models of curved root canals, which respectively had a radius of 2 mm and 5 mm, and a central angle of 30°and 45°, were also established. Experiment 2 Analysis of the stress distribution of the instruments under the bending and torsion loadsAfter defining the material properties for 3 models of endodontic instruments, and applying the loads and the constraints, Pro / MECHANICA FEA analysis software was used to analyze the stress distribution. The results showed that, the stress distribution pattern under clockwise torque was similar to that under the counter-clockwise torsion. In the curved canal of 45°/2mm, stress concentration of a K file presented at the cutting edge. In root canals of 30°/ 5mm and 45°/ 2mm, the maximum stress of the H file was situated at the bottom of the ?ute, that was closest to the center point of the cross section; and Stress position and reverse the direction had no significant relationship; in F1 Group: In root canals of 30°/2mm,30°/5mm and 45°/2mm,the maximum stress position are at the cutting edge, in addition to (45°/ 5mm) group acting on the cutting edge of the bottom of the ?ute. In conclusion,PSA and FEA could efficiently analyze and predict the locations of the procedural errors and instrument separation,could accurately and vividly analyze the interaction between the file and the root canal wall.The results were valuable for guiding proper use of endodontic instruments during preparing curved root canals.更多还原