上颌第一磨牙分体桩核冠的三维有限元分析

目的：应用三维有限元分析不同直径和长度的分体桩核冠修复磨牙后牙根及核桩的应力分布规律,比较分体桩的直径和长度对修复磨牙的影响。方法：应用螺旋CT扫描及医学影像传输与转录技术,建立不同直径和长度的分体桩核冠的上颌第一磨牙三维有限元模型,比较不同载荷下各桩核冠修复磨牙后牙根及核桩的应力分布规律。结果：减少核桩的长度,可以降低牙根及核桩的应力峰值;牙根的应力随着核桩直径的增加而增加,而核桩的应力随其直径的增加而减少。结论：适当减少核桩的长度和直径有利于提高修复体的成功率。     

不同设计桩核的后牙残根核桩冠修复体的三维有限元应力分析

目的采用三维有限元法比较不同长度和数目桩核、不同材料桩核对后牙残根桩核冠修复体牙本质应力大小及其分布的影响,探讨后牙残根桩核冠修复时合理的桩核设计及选材。方法采用CT扫描、Mimics软件及Abaqus软件建立上颌第一磨牙桩核冠的三维有限元模型。根据桩长度和数目的不同、桩核材料的不同,将上颌第一磨牙桩核冠的三维有限元模型分为相应的实验组。在模型咬合面上选取3个载荷点,分别施加80 N的载荷,计算各实验组中牙本质上的Von mises应力、最大主应力、剪切应力的应力峰值及分布方式。结果在桩长度和数目不同时,随着桩长度和数目的增加,牙本质上各项应力峰值呈现不规律变化。在不同桩核材料时,随着桩核材料弹性模量的增加,牙本质上的Von mises应力、最大主应力、剪切应力峰值均减小。结论在本实验研究条件下,不同桩长度和数目、不同桩核材料对后牙残根桩核冠修复体牙本质上的应力峰值和应力分布均有影响。     

桩核冠修复下颌中切牙不同长度残根的光弹应力分析

目的：探讨残根长度对桩核冠修复后应力分布的影响。方法：建立不同长度残根的三维光弹模型,对其进行常规桩核冠修复,运用光弹应力分析法分析残根长度对桩核冠修复后应力分布的影响。结果：正常长度残根应力峰值与天然牙无明显区别（P〉0.05）,根缩短1/6的残根应力峰值略大于天然牙,但小于天然牙的2倍,根缩短2/6的残根应力峰值略大于天然牙的2倍,根缩短3/6的残根应力峰值远大于天然牙的2倍。结论：正常长度残根,根缩短1/6的残根可用桩核冠修复,根缩短2/6的残根应慎用桩核冠修复,根缩短3/6的残根不宜用桩核冠修复。     

两种方式修复下颌中切牙不同长度残根的光弹应力分析

目的:探讨残根长度对桩核单冠及桩核联冠修复后应力分布的影响。方法:建立不同长度残根的三维光弹模型,对其进行常规桩核单冠及桩核联冠修复,运用光弹应力分析法分析修复后应力分布的影响。结果:正常长度残根应力峰值与天然牙无明显区别(P>0.05),缩短1/6残根应力峰值小于天然牙2倍,缩短2/6残根应力峰值单冠修复略大于天然牙的2倍,联冠修复小于对照组2倍,缩短3/6残根应力峰值单冠修复远大于天然牙的2倍,联冠修复略大于对照组2倍。结论:正常长度残根,缩短1/6残根可用桩核单冠或者联冠修复,缩短2/6残根应慎用桩核单冠修复,可用桩核联冠。缩短3/6残根不能用桩核单冠修复,应慎用桩核联冠修复。     

不同长度铸造分体桩核修复重度缺损上颌磨牙三维有限元分析

目的通过三维有限元法分析不同长度铸造分体桩核修复重度缺损上颌第一磨牙后牙体组织应力分布。方法以右上颌第一磨牙为标本,通过CT扫描获得图像信息,采用Mimics三维建模软件、FreeForm视觉设计系统,建立五种不同长度铸造分体桩修复重度缺损上颌第一磨牙的三维有限元模型,利用Ansys有限元软件比较加载后牙体组织的Von Mises应力、最大拉应力分布和变化。结果随着铸造分体桩中颊根桩长度增加,上颌磨牙牙体组织Von Mises应力峰值减小,但拉应力峰值却增大;随着铸造分体桩中腭根桩长度增加,上颌磨牙牙体组织Von Mises应力峰值和拉应力峰值均减小。结论铸造分体桩修复重度缺损上颌第一磨牙时,根桩长度影响牙体组织应力分布。     

桩核的种类和设计以及相关力学研究

不同材料和不同设计的桩核将导致不同的应力分布,从而影响桩核的修复效果。本文就桩核修复过程中所用的金属铸造桩、复合树脂桩、纤维桩、瓷桩以及桩核的不同形态、长度和直径所导致的不同应力分布作一综述,以便为临床不同情况的桩核修复提供一定的理论指导。     

三种桩材桩核修复上颌中切牙光弹模型的建立

目的:为分析不同弹性模量桩对根管壁应力分布的影响,建立上颌中切牙桩核修复的光弹模型.方法:以环氧树脂模拟上颌中切牙牙根部、牙槽骨;室温硫化硅橡胶模拟牙周膜;复合树脂制作核,建立桩为成品纤维桩、铸造钛合金、铸造镍铬合金的上颌中切牙桩核修复光弹模型.结果:建立了表面光洁、透明度高,几何尺寸接近实际情况,牙根、牙槽骨、牙周膜弹性模量比接近于1.37:1:0.0003的光弹模型.结论:该模型可以用于分析不同弹性模量桩对根管壁应力分布影响的光弹性实验.     

不同形状和直径纤维桩核修复下颌第二前磨牙的应力分析

目的:研究不同形状和直径纤维桩核修复下颌第二前磨牙的应力分布.方法:分别在直径为根径的1/2、1/3、1/4和形状为柱形、锥形、梯形的玻璃纤维增强树脂桩核修复下颌第二前磨牙的三维有限元模型上,以垂直和斜向(45°)2种方式加载200N,应用Nastran软件进行三维有限元应力分析.结果:不论纤维桩核为何种形态,当其直径增大时,桩核及基牙的应力分布无明显变化;锥形桩和梯形桩在承受斜向加载时牙根最大应力峰值较垂直加载时牙根应力峰值的增幅最小.结论:纤维增强树脂桩核修复时锥形桩和梯形桩是较理想的设计.     

上前牙桩核冠修复后牙体抗力及应力分布的影响因素

桩核冠在上前牙残根残冠修复中占据重要的位置,桩核冠的设计与牙体抗力及应力分布有着密切关系。本文将从桩核材料,桩的长度、直径及形态,牙本质肩领和粘接剂等方面探讨上前牙桩核冠修复后牙体抗力及应力分布的影响因素。     

不同牙槽骨高度下桩核修复后牙本质应力分析

目的应用有限元方法观察不同牙槽骨高度下桩核修复后牙本质内的应力分布情况。方法建立上颌中切牙桩核修复的三维有限元模型,并按照牙槽骨高度降低1/4、1/3和1/2建立修改模型,对模型斜向加载,计算牙体各部位最大应力。结果随着牙槽骨高度的降低,牙本质内部最大应力明显增高,牙体与桩交界部位的最大应力变化呈相同趋势,且愈靠近牙根表面应力值愈高,在4个模型中最大应力都位于牙根上1/3,在牙齿唇侧颈部有明显的应力集中。结论牙槽骨高度的变化显著影响桩核修复后牙齿内的应力变化,两者间呈反比例关系。     

单根锉根管预备系统的研究进展

随着根管预备器械的不断发展创新,镍钛根管预备系统被越来越多地应用到临床治疗中。相比于普通不锈钢K锉,它具有一定优势。而普通旋转镍钛根管预备系统在使用过程中也存在需要更换器械、操作较为繁琐、耗时、易造成器械折断等不足。为了解决这些难题,一种全新的根管预备系统——单根锉根管预备系统应运而生,它摒弃了现有的镍钛系统中多根逐步扩大的根管锉的组合使用,在大多数病例中,仅使用一根扩大锉就能完成根管预备。关于这一新技术国内外都有很多研究报道,本文旨在就这一全新的"单根锉根管预备系统"的研究进展进行综述。     

Stress analysis of endodontically treated anterior teeth restored with different types of post material

Finite element analysis was performed to evaluate stress distribution in maxillary central incisors treated endodontically and restored with a post and an all-ceramic crown. Tensile stress at tooth root was analyzed using two-dimensional finite element models with different post diameters and lengths. One post length was 1/3 of the root (short), while the other was 2/3 of the root (long); one post diameter was 1/3 of the root (narrow), while the other was 2/3 of the root (wide). The following combinations were used for posts and cores: gold alloy cast post and core, commercial stainless steel post and resin core, and fiber post and resin core. Results showed that the fiber post produced less stress on the root dentin around the post tip than did the metal posts. This finding thus suggested that to reduce the stresses that cause root fracture, a long, thin fiber post should be used.     

Effect of core materials on stress distribution of posts.

Severely damaged endodontically treated teeth require the use of a post and core for the retention of the restoration. The choice of material for a post and core and their stress-producing characteristics must be considered by the clinician. Two-dimensional photoelastic analysis of birefringent models was used to investigate the influence of different core materials on the stress distribution of nonthreaded cylindrical posts. Cast posts and cores and prefabricated posts with amalgam and composite resin cores were compared with posts without cores at installation and under two loading conditions. The findings indicate a significant difference between posts with and without cores. It appears that the stiffer core materials can shift the load from the apex to the coronal region.     

Stress analysis of endodontically treated teeth restored with post-retained crowns: A finite element analysis study

BackgroundThe authors conducted a study to analyze the stress concentration areas in a tooth restored with a post-retained crown under various conditions.Materials and MethodsThe authors constructed a three-dimensional finite element model describing a maxillary second premolar restored with an all-ceramic crown supported by a titanium post and a resin-based composite core. They applied static vertical and horizontal loads of 100 newton to the cusp tip of the crown and recorded Von Mises and tensile stress values. The variables investigated were the presence of the post, coronal and apical post extensions, post diameter, post shape, and post and core material.ResultsThe study results showed that horizontal loading generated higher levels of stress than did vertical loading. The greatest stress levels were concentrated at the cervical region and at the post-dentin interface in all models. Under both loads, a higher modulus of elasticity of the post material and a wider post diameter were associated with increased stress values at the post-dentin interface. Reduction of the post extension above the level of bone was associated with increased dentinal stresses near the apex of the post.ConclusionsAlthough endodontic posts provide retention for coronal restorations, they result in dentinal stress values higher than those of crowns without posts. Posts that had a similar modulus of elasticity to dentin and smaller diameters were associated with better stress distribution. Resting coronal restorations on sound dental tissues affected stress distribution more than did the core material or the length of the coronal post extension.Clinical ImplicationsMany factors influence the distribution of stress within dentin and, consequently, the fracture resistance of teeth restored with post-retained crowns. Clinicians need to keep these factors in mind when performing endodontic procedures that involve placement of post-retained crowns to ensure optimal success.     

Three-dimensional finite element analysis of stress distribution in composite resin cores with fiber posts of varying diameters

Using three-dimensional finite element analysis (3D-FEA), stress distributions in the remaining radicular tooth structure were investigated under the condition of varying diameters of fiber post for fiber post-reinforced composite resin cores (fiber post and core) in maxillary central incisors. Four 3D-FEA models were constructed: (1) fiber post (?1.2, ?1.4, and ?1.6 mm) and composite resin core; and (2) gold-cast post and core. Maximum stresses in the tooth structure for fiber post and core were higher than that for gold-cast post and core. In the former models, stresses in the tooth structure as well as in the composite resin were slightly reduced with increase in fiber post diameter. These results thus suggested that to reduce stress in the remaining radicular tooth with a large coronal defect, it is recommended to accompany a composite resin core with a fiber post of a large diameter.     

Stress distribution surrounding endodontic posts

This study compared the stress distribution during insertion and function of three prefabricated endodontic posts with different designs using the criteria of post length and diameter. Test blocks of photoelastic material were prepared with simulated endodontic canals. Three posts for each design, diameter, and depth were cemented. Each specimen was examined and photographed without load, with 135 Newton (N) compressive force, and with 90 N and/or 135 N oblique force applied at 26 degrees by use of a circular polariscope. Para-Post and Para-Post Plus posts produced similar, evenly distributed patterns of stress using the criteria of diameter, depth, and load. Flexi-Post posts produced asymmetric stress patterns with concentration of stress at each thread. During compressive loading and after cementation alone, Flexi-Post posts displayed significantly higher shoulder stresses and substantially greater stresses along the coronal surface of the post's length than Para-Post and Para-Post Plus posts. Apical stresses were similar for Flexi-Post, Para-Post, and Para-Post Plus posts during compressive loading.     

桩核冠受力时的应力分析

目的：用三维有限元法对桩核冠进行应力分析,研究不同材质的冠对分析结果的影响。方法：采用测量法建模,根据标准的桩核冠制作要求,应用美国I-DEAS有限元分析软件分别建立三套上中切牙的三维有限元模型．其中A组包括铸造金属桩核、制备后的牙体组织、牙周组织;B组包括金属烤瓷冠、铸造金属桩核、制备后的牙体组织、牙周组织;C组包括树脂冠、铸造金属桩核、制备后的牙体组织、牙周组织。在同等条件下以上中切牙的平均糟力分别给予加载,并对计算结果进行综合分析。结果：（1）从牙本质的应力大小来看,A组中牙本质最大应力值比B组中牙本质最大应力值增大了1倍以上（最大主应力、最小主应力和最大剪切应力A组分别是B组的236．35％、228．83％和218．05％）,而B组与C组的牙本质最大应力值相差极小;（2）从牙本质的应力分布位置来看,A组与B组的牙本质最大应力分布位置相差甚远（A组主要集中在牙颈部唇舌侧肩台部的牙本质上．B组主要集中于牙槽嵴顶附近及铸造桩核尾端相对应的唇舌侧的牙本质上）,而B组与C组的牙本质最大应力分布几乎在同一位置。结论：用三维有限元法对桩核冠进行应力分析时,不同材质的冠对分析结果无明显影响。     

Influence of Ferrule,Post System,and Length on Stress Distribution of Weakened Root-filled Teeth

Introduction

The aim of this study was to evaluate the influence of a ferrule, post system, and length on the stress distribution of weakened root-filled teeth.

Methods

The investigation was conducted by using 3-dimensional (3D) finite element analysis. A sound tooth and 8 3D models of a weakened root-filled central incisor were generated using computer-aided design/computer-aided manufacturing software. The models were created without a ferrule and with a 2.0-mm ferrule, restored with a relined glass fiber post or a cast post and core (Cpc), and 12.0- and 7.0-mm post lengths. Each 3D model was imported using ∗.STEP files to the finite element software for mesh generation. The models were subjected to 100-N oblique loading at the palatal surface, and the results were evaluated by von Mises criterion and maximum principal stress distribution.

Results

Finite element analysis showed that the Cpc models showed elevated stress levels in the root canal regardless of the presence of a ferrule. Relined glass fiber post models showed homogeneous stress distribution to the dentin external surface similar to the sound tooth model. Without a ferrule, Cpc with a 7- or 12-mm length promoted high levels of tensile stress inside the root canal.

Conclusions

Ferrule presence promoted more satisfactory stress distribution to the roots. Post length influenced the stress distribution only for the models restored with a cast post and core. High levels of tensile stress inside the root canals were verified with a cast post and core, which should be avoided to rehabilitate weakened roots, mainly in the absence of a ferrule.     

Effect of diameter and length on stress distribution of the alveolar crest around immediate loading implants

Background: Many clinical observations have shown that immediate loading is indicated when the stabilization of the bone/implant is optimal and when the estimated loads are not excessively high. Nonetheless, more experimental studies are needed to consider the immediate loading protocol as a safe procedure. Mechanical analysis using the finite element (FE) method analysis has been employed by many authors to understand the biomechanical behavior around dental implants. Purpose: This study was to evaluate the effect of the diameter and length on the stress and strain distribution of the crestal bone around implants under immediate loading. Materials and Methods: By an ad hoc automatic mesh generator, high‐quality FE models of complete range mandible was constructed from computer tomography, with three Straumann (Straumann Institute, Waldenburg, Switzerland) implants of various sizes embedded in the anterior zone. The implant diameter ranged from 3.3 to 4.8 mm, and length ranged from 6 to 14 mm, resulting in seven designs. The implant–bone interface was simulated by nonlinear frictional contact algorithm. For each design, vertical and oblique loadings of 150 N were applied, respectively, to each implant, and stresses and strains in the surrounding cortical bone were evaluated. Results: The biomechanics analysis provided results that the oblique loading would induce significantly higher interfacial stresses and strains than the vertical loading, while the intergroup stress difference significant levels was evaluated using t‐tests method and the level of significance (.05) that was accepted for significance. Under both loadings, the maximal values were recorded in the 3.3 (diameter) × 10 (length) mm implant configuration, whose mean and peak values were both higher than that of others with significant statistical differences. The second maximal one is 4.1 × 6 mm configuration, and the minimal stresses were recorded in 4.8 × 10 mm configuration, whose strains were also near to lowest. Conclusions: Increasing the diameter and length of the implant decreased the stress and strain on the alveolar crest, and the stress and strain values notably increased under buccolingual loading as compared with vertical loading, but diameter had a more significant effect than length to relieve the crestal stress and strain concentration.