直线通路微创开髓洞型对上颌第一前磨牙力学性能影响的有限元分析

目的通过有限元分析探讨直线通路微创开髓洞型对上颌第一前磨牙力学性能的影响。方法收集2018年6月至2020年6月于四川大学华西口腔医院口腔颌面外科就诊患者因正畸或牙周病拔除的上颌第一前磨牙,从中选取牙体完整、根尖孔发育完成的双根管牙20颗,对其显微CT(micro-CT)数据进行三维重建,在三维模型中模拟传统开髓洞型、桁架开髓洞型与直线通路微创开髓洞型的开髓与根管治疗(每组样本量均为20个)。建模完成后进行有限元分析,记录纵向及斜向负载模式下各组模型的牙颈部von Mises等效应力峰值(VM)并观测各组模型的应力分布模式。结果纵向负载模式下,3种开髓洞型牙颈部颊侧和腭侧VM分别为:桁架开髓洞型[(146.0±12.9)和(167.6±15.9)MPa],直线通路微创开髓洞型[(142.6±13.7)和(168.1±17.4)MPa],传统开髓洞型[(188.7±13.4)和(200.9±25.7)MPa]。与传统开髓洞型相比,桁架开髓洞型(t=9.01,P<0.001;t=4.59,P<0.001)和直线通路微创开髓洞型(t=9.64,P<0.001;t=3.76,P=0.004)均可有效降低根管治疗后上颌第一前磨牙颊侧和腭侧牙颈部VM,同时缓解应力在[牙合]面集中力加载区域、牙颈部及牙根的集中。在斜向负载模式下得到了相似的结果。在两种负载模式下,桁架开髓洞型与直线通路微创开髓洞型间颊腭侧牙颈部VM差异均无统计学意义(P>0.05)。结论直线通路微创开髓洞型可以有效保护根管治疗后上颌第一前磨牙的力学性能,具有一定的临床可行性。     

Influence of minimally invasive access cavities on load capacity of root-canal-treated teeth: A systematic review and meta-analysis

This systematic review (PROSPERO-CRD42020147333) aimed to compare the effects of conservative, ultraconservative and truss access cavities with traditional access cavities on the load capacity of root-canal-treated teeth. Online databases were searched until December 2021, and 25 ex vivo studies in which the effects of different access cavities on load capacity of permanent teeth had been investigated were included. Quality assessment was completed using a modified risk of bias tool for in vitro studies adapted from previous studies. Meta-analysis was performed using the maximum-likelihood-based random-effects model with similar groups. Conservative access cavities significantly improved the load capacity of maxillary premolars (p < 0.01 [−1.32, −0.028]) and molars (p < 0.05 [−0.89, −0.02]) compared to traditional access cavities. Additionally, truss access cavities significantly improved the load capacity of mandibular molars with (p < 0.05, [−1.18, −0.02]) mesio-occluso-distal cavity preparations. Higher levels of evidence are needed to determine the long-term implications of minimal preparations for treatment outcomes.     

微创开髓及其牙体的应力分析的研究进展

微创开髓(conservative endodontic access cavity,CEC)是微创根管治疗术的第一步,经CEC治疗后的患牙较大程度保留了牙尖嵴和颈周牙本质等牙体硬组织,对于减少患牙的牙体流失及增强远期疗效具有重要意义。CEC存在多种入路方式及相应的洞型。确定髓腔入路的方法包括X线片定位法、显微CT/锥形束CT定位法以及数字化导板定位法。其中,X线片、显微CT/锥形束CT定位法操作简便,临床较为常用;而较为复杂的根管系统,利用数字化导板可建立更精准的开髓通路,减少牙体硬组织不必要的丧失,但数字化导板定位价格较高,临床上并未得到广泛的应用。CEC的洞型包括微创开髓洞型、超保守微创开髓洞型、"Truss"洞型以及切端洞型。CEC洞型与传统开髓洞型的应力分析目前以万能力学试验机加载离体牙、有限元分析法及临床观察为主,大多数学者的研究显示保留较多牙体组织的CEC可提高牙齿的抗折强度,但二者之间的抗折能力仍存在争议,在达到牙髓治疗目的与最大限度保留牙体结构之间如何达到平衡,仍需进一步的探索。     

不同大小MO洞型复合树脂嵌体修复应力分布的有限元分析

目的 探讨复合树脂嵌体修复后,近中邻（meiso-occlusal,MO）洞型面深度及宽度变化对牙体抗力的影响。方法采用锥形束CT（cone beam computed tomography,CBCT）扫描,结合Mimics、Geomagic Studio逆向工程等软件,建立不同大小邻（II类）MO洞型树脂嵌体修复的三维有限元模型,用ANSYS Workbench软件网格划分并求解分析各模型内部牙体及嵌体在垂直、舌向45°加载下主应力峰值及Von-mises应力分布情况。结果大小不同的MO洞型以复合树脂嵌体修复时,龈壁对应处是嵌体的主要应力所在,洞底部近髓腔处是牙体的主要应力集中区。随着面洞型深度、宽度增加,牙体、修复体的最大应力峰值及Von-mises应力集中区分布范围加大;牙体Von-mises应力受洞型宽度的影响更大,嵌体的Von-mises应力受洞型深度增加影响更大。侧向加载大大增加了牙体和修复体的应力峰值。结论MO洞型以树脂嵌体修复后,洞深、洞宽度加大及侧向加载增加了牙体与嵌体的应力峰值,改变了应力集中区分布范围。     

Clear aligner orthodontic therapy of rotated mandibular round-shaped teeth: A finite element study

Objective:To evaluate, using the finite element method, the orthodontic rotational movement of a lower second premolar obtained with clear aligners, analyzing different staging and attachment configurations.Materials and Methods:A CAD model including a complete lower dental arch (with element 4.5 mesially rotated 30°) and the corresponding periodontal ligaments, attachments, and aligner was designed and imported to finite element software. Starting from the CAD model, six projects were created to simulate the following therapeutic combinations for correcting element 4.5 position: (1) without attachments, (2) single attachment placed on the buccal surface of element 4.5, (3) three attachments placed on the buccal surfaces of teeth 4.4 to 4.6. For each project, both 1.2° and 3° of aligner activation were considered.Results:All the analyzed configurations revealed a clockwise rotation movement of element 4.5 on the horizontal plane. Models with attachments showed a greater tooth displacement pattern than models without attachments. Simulations with attachments and 3° of aligner activation exhibited the best performance concerning tooth movement but registered high stresses in the periodontal ligaments, far from the ideal stress levels able to produce tooth rotational movement.Conclusions:The model with a single attachment and 1.2° of aligner activation was the most efficient, followed by the three attachment model with the same degree of activation. Aligner activation should not exceed 1.2° to achieve better control of movement and reasonable stress in periodontal structures.     

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.     

磨牙全瓷冠断裂类型的力学实验与三维有限元分析研究

通过力学实验和三维有限元研究不同直径半球形压头对全瓷冠断裂强度、断裂类型的影响,以期为临床全瓷冠(牙合)面形态设计提供理论依据.方法分别用直径为4 mm、10 mm的压头对20个下颌第一磨牙全瓷冠(IPS e.maxpress)试件进行力学实验,观察全瓷冠试件的断裂类型.通过改变三维有限元模型3个受力点的位置及受力大小和方向,模拟直径为4 mm、10 mm的压头加载于全瓷冠时的应力分布状态,计算主应力的大小及分布.结果三维有限元分析显示,两种压头加载状态下,全瓷冠第一主应力均随载荷的增加而增加;4 mm直径压头作用下全瓷冠应力集中在(牙合)面中央窝,而10 mm直径压头作用下全瓷冠应力集中于(牙合)面近远中方向窝沟处,呈"一"字形;4mm、10 mm直径压头作用下全瓷冠的抗折载荷分别为600～700 N和2500～2750 N.力学实验显示,4 mm、10 mm直径压头作用下全瓷冠的主要断裂类型分别为Ⅱ型和Ⅴ型,与三维有限元分析结果一致.结论 4 mm直径压头多造成全瓷冠中央窝破坏,10 mm直径压头多造成全瓷冠和牙体模型严重折裂,提示临床工作中应注意减小全瓷修复体对(牙合)牙的牙尖曲率.     

开髓洞型对全冠修复后隐裂牙抗力影响的 三维有限元研究

目的探讨在牙隐裂患牙根管治疗中采用传统开髓洞型和微创开髓洞型对烤瓷全冠修复后牙体抗力的影响。方法制作3种裂纹深度的牙隐裂三维虚拟模型,模拟微创开髓和传统开髓,并完成根管治疗和烤瓷全冠修复。在垂直加载和斜向加载条件下,记录牙体应力的分布情况和数值大小。结果在2种加载条件下,修复前牙齿应力集中于裂纹底部,局部应力集中随着隐裂深度的加深而增大,烤瓷全冠修复后基牙局部应力主要分布在肩台处,局部应力集中得到大幅缓解。不同开髓洞型对隐裂牙应力分布和大小的影响无明显差异。结论根管治疗后烤瓷全冠修复是治疗牙隐裂的有效措施;相比传统开髓洞型,微创开髓洞型并不能改善全冠修复后隐裂牙的应力分布。     

外力方向对防护牙托性能影响的有限元分析

目的: 运用有限元分析评估外力方向对牙托缓冲能力的影响。方法: 采集仿真模型锥形束CT（CBCT）影像资料,利用MIMICS软件建立分析模型。运用ABAQUS软件模拟研究在牙托厚度不同的情况下（分别为0、1.5、3、4.5和6 mm）,经不同方向外力（撞击方向与牙长轴交角分别为30°、60°、90°和120°）撞击后,牙体表面的应力变化情况,进而评价牙托的缓冲能力。结果: 在研究实验条件下,当牙托厚度较薄时（1.5 mm和3 mm）,与其他方向相比,牙托缓冲效率在60°交角时最低,在120°交角时最高。而在牙托厚度增加后（4.5 mm和6 mm）,牙托缓冲效率在90°交角时最低,在30°交角时最高。外力方向不同时,牙托的应力缓冲效率随着牙托厚度的增加而提高。结论: 外力方向对防护牙托的缓冲能力有一定影响,但其易受牙托厚度的影响。     

微创无痛方法拔除下颌复杂阻生智齿的应用研究

目的 与传统拔牙技术相比，探究采用微创无痛方法拔除下颌复杂阻生智齿的临床应用效果。方法 选取2021年3月至2022年9月就诊于东莞市东部中心医院的200例下颌复杂阻生智齿患者，根据拔牙术式不同分为实验组（n=101）和对照组（n=99），实验组采取微创无痛拔牙方法，对照组采用传统拔牙方法。比较两组的临床参数，包括术中出血、拔牙时间、拔牙窝是否完整、术后疼痛及面部肿胀情况、骨愈合时间、术后并发症及患者满意度等。结果 与传统拔牙技术相比，微创无痛拔牙方法的术中出血量少（5.64±1.50 ml）、拔牙时间短（16.55±3.11）、拔牙窝完整率高（94.06%）、断根率更低（5.94%），且术后张口受限、关节疼痛、面部肿胀的症状较轻（P<0.01），创口愈合时间更短、术后并发症发生率低（P<0.01），患者满意度更高（P<0.001）。结论 相比传统拔牙技术，微创拔牙技术具有临床疗效高、术后不良反应少、患者满意度高等显著优势，更适合应用于临床拔除下颌复杂阻生智齿。     

切牙颈部穿髓型缺损唇、舌面入路的有限元分析

目的：应用三维有限元法比较颈部穿髓型缺损的切牙,在唇侧和舌侧不同开髓入路下的牙体受力情况,探讨唇侧入路在抗折力方面是否具有优势。方法：进行锥形束CT(cone-beam CT,CBCT)扫描,采用Mimics、Catia、Ansys软件建立上切牙模型,分别用唇、舌侧2种入路及直接树脂充填、纤维桩树脂修复、纤维桩全瓷冠修复3种不同修复方式,对其施加载荷,比较缺损部位及髓腔根管表面应力分布和最大von Mises值,采用Ansys10.0有限元分析软件对数据进行统计学分析。结果：在实验条件下,直接树脂修复时,唇、舌侧入路无明显区别;纤维桩复合树脂修复时,唇侧入路可以转移牙体应力集中部位,降低缺损处牙体折断几率而增加根折几率;桩冠修复可有效分散缺损处的应力集中,从而降低牙体从缺损处折断的几率。结论：对于颈部穿髓型缺损的切牙,直接树脂充填时,唇、舌侧入路均可采用;纤维桩树脂修复和桩冠修复时,分散了牙体应力的集中,而唇侧入路较舌侧入路更为明显。     

开髓方式与全冠修复对上颌中切牙应力分布影响的三维有限元分析

目的 采用三维有限元分析法分析不同开髓方式及全冠修复对上颌中切牙牙体组织应力分布的影响。方法 采用锥形束CT扫描上颌中切牙构建上颌中切牙三维实体模型,根据开髓方式的不同及是否行全瓷冠修复建立4组实验模型：传统开髓树脂充填（A）组、传统开髓后全瓷冠修复（B）组、微创开髓树脂充填（C）组和微创开髓后全瓷冠修复（D）组。于舌侧切1/3与中1/3交界处施加大小为100 N、与牙体长轴呈45°方向的力,对所建立的牙体组织有限元模型中最大主应力、von Mises应力和改良von Mises应力进行分析。结果 1）应力峰值：A组的最大主应力、von Mises应力和改良von Mises应力的应力峰值均表现为最大,除了D组的von Mises应力峰值略低于C组外,C组的最大主应力及改良von Mises应力的应力峰值均表现为最低,D组的最大主应力及改良von Mises应力的应力峰值均低于A组和B组。2）应力分布：相比于A组,C组牙颈部区域的应力集中程度较低,且应力集中的区域较小;在牙根牙本质处,C组的应力分布与A组相比更为均匀,应力分散至根尖更多区域;冠修复后,B组和D组在牙根区域的应力分布未见明显差异;B组应力分布状态与A组相比未见明显改变;D组相比于C组应力分布状态未见明显改变。结论 从生物力学角度考虑,上颌中切牙开髓尽量采取微创开髓方式;传统开髓后建议行冠修复,微创开髓后冠修复未见明显优势。     

开髓方式与全冠修复对上颌中切牙应力分布影响的三维有限元分析

目的 采用三维有限元分析法分析不同开髓方式及全冠修复对上颌中切牙牙体组织应力分布的影响。方法 采用锥形束CT扫描上颌中切牙构建上颌中切牙三维实体模型,根据开髓方式的不同及是否行全瓷冠修复建立4组实验模型：传统开髓树脂充填（A）组、传统开髓后全瓷冠修复（B）组、微创开髓树脂充填（C）组和微创开髓后全瓷冠修复（D）组。于舌侧切1/3与中1/3交界处施加大小为100 N、与牙体长轴呈45°方向的力,对所建立的牙体组织有限元模型中最大主应力、von Mises应力和改良von Mises应力进行分析。结果 1）应力峰值：A组的最大主应力、von Mises应力和改良von Mises应力的应力峰值均表现为最大,除了D组的von Mises应力峰值略低于C组外,C组的最大主应力及改良von Mises应力的应力峰值均表现为最低,D组的最大主应力及改良von Mises应力的应力峰值均低于A组和B组。2）应力分布：相比于A组,C组牙颈部区域的应力集中程度较低,且应力集中的区域较小;在牙根牙本质处,C组的应力分布与A组相比更为均匀,应力分散至根尖更多区域;冠修复后,B组和D组在牙根区域的应力分布未见明显差异;B组应力分布状态与A组相比未见明显改变;D组相比于C组应力分布状态未见明显改变。结论 从生物力学角度考虑,上颌中切牙开髓尽量采取微创开髓方式;传统开髓后建议行冠修复,微创开髓后冠修复未见明显优势。     

Influence of crown ferrule heights and dowel material selection on the mechanical behavior of root-filled teeth: a finite element analysis

Purpose: This study used the 3D finite element (FE) method to evaluate the mechanical behavior of a maxillary central incisor with three types of dowels with variable heights of the remaining crown structure, namely 0, 1, and 2 mm. Materials and Methods: Based on computed microtomography, nine models of a maxillary central incisor restored with complete ceramic crowns were obtained, with three ferrule heights (0, 1, and 2 mm) and three types of dowels (glass fiber = GFD; nickel‐chromium = NiCr; gold alloy = Au), as follows: GFD0 – restored with GFD with absence (0 mm) of ferrule; GFD1 – similar, with 1 mm ferrule; GFD2 – glass fiber with 2 mm ferrule; NiCr0 – restored with NiCr alloy dowel with absence (0 mm) of ferrule; NiCr1 – similar, with 1 mm ferrule; NiCr2 – similar, with 2 mm ferrule; Au0 – restored with Au alloy dowel with absence (0 mm) of ferrule; Au1 – similar, with 1 mm ferrule; Au2 – similar, with 2 mm ferrule. A 180 N distributed load was applied to the lingual aspect of the tooth, at 45° to the tooth long axis. The surface of the periodontal ligament was fixed in the three axes (x = y = z = 0). The maximum principal stress (σ_max), minimum principal stress (σ_min), equivalent von Mises (σ_vM) stress, and shear stress (σ_shear) were calculated for the remaining crown dentin, root dentin, and dowels using the FE software. Results: The σ_max (MPa) in the crown dentin were: GFD0 = 117; NiCr0 = 30; Au0 = 64; GFD1 = 113; NiCr1 = 102; Au1 = 84; GFD2 = 102; NiCr2 = 260; Au2 = 266. The σ_max (MPa) in the root dentin were: GFD0 = 159; NiCr0 = 151; Au0 = 158; GFD1 = 92; NiCr1 = 60; Au1 = 67; GFD2 = 97; NiCr2 = 87; Au2 = 109. Conclusion: The maximum stress was found for the NiCr dowel, followed by the Au dowel and GFD; teeth without ferrule are more susceptible to the occurrence of fractures in the apical root third.     

镍钛根管锉疲劳应力变化的三维有限元分析

目的 研究弯曲参数对镍钛根管锉的疲劳应力大小和分布的影响,为进一步揭示镍钛锉折断机制提供依据.方法 采用1支切割刃连续清晰完整的30号02锥度新镍钛锉(HER0642,MicroMega,法国),用Solidworks软件建立三维实体模型.设计60.和20.两种弯曲角度、5 mm和2 mm两种弯曲半径,使用ANSYS11.0 WorkBench软件作弯曲加载分析.观察拉压应力和切应力的分布、大小和变化.结果 镍钛锉在60.、2 mm及60.、5 mm弯曲条件下的最大拉压应力值均较大(分别为1274.20、980.48 MPa),最大切应力值亦较大(分别为38.16、42.48 MPa);而在20.、2 mm及20.、5 mm弯曲条件下的最大拉压应力值均较小(分别为533.37、493.56 MPa),最大切应力值也较小(分别为16.81、14.26 MPa).最大拉压应力均集中在弯曲起点附近器械表面的切割刃上,最大切应力集中在弯曲起点附近器械表面的沟槽底;最大拉压应力在锉内部表现为自切割刃表层向下方扩展,并从器械表面向核心方向递减;最大切应力在锉内部表现为自表面沟槽底向切割刃处和核心区扩展.结论 镍钛锉在弯曲条件下,拉压应力集中在弯曲起点附近器械表面的切割刃上,预示该区域疲劳折断的风险较高.     

Effects of washer on the stress distribution of mini-implant: A finite element analysis

Objective:To investigate the biomechanical effects of ‘washer’ designed for improving mini-implant stability.Materials and Methods:Four three-dimensional finite element models of the mini-implant and surrounding bone were constructed with washers in different spike lengths (1.5 mm, 2.0 mm, and 2.5 mm). The force was applied in two directions (45° and 90°). The stress distribution on surrounding bone and the displacement of the mini-implant were analyzed. Plots of tensile stress, compression stress, and displacement were calculated, and maximum values in each category were analyzed.Results:The stress distribution was different between the models with washer and without washer. However, no remarkable differences in stress distribution were observed among the models with washer, regardless of spike length. A significantly greater displacement value was observed in the model without washer compared to the models with washer, but no notable difference in displacement value was found among the models with washer. The plots of the displacement distribution of the models with washer presented notable pattern differences as compared with that of the model without washer.Conclusion:With the use of the washer, a more homogeneous distribution of bone stress and less displacement of the mini-implant can be achieved.     

Influence of connector design and material composition and veneering on the stress distribution of all-ceramic fixed dental prostheses: A finite element study

Objectives

Finite element analysis is a standard method to simulate the stress distribution in all-ceramic dental restorations in order to estimate the loading capacity of the brittle components. The hypothesis of this study was that stresses in the connector area of a veneered FDP are strongly influenced by the framework dimensions and the veneering material.

Methods

Finite element analyzes of bilayered fixed dental prostheses with three different framework-designs and three different veneering materials were conducted, applying the loads onto the veneering as well as directly onto the framework. The outer shape of the veneering ceramic remained constant for all cases.

Results

The maximum first principal stresses in the framework of the fixed dental prostheses (FDP) decreased with smaller framework dimensions when the load was applied on the veneering. By applying the load directly onto the framework of the FDP without veneering a converse tendency was found. The variation of the veneering material lead to the conclusion that stresses in the framework became higher with decreasing Young's modulus of the veneer, while the stresses in the veneer increased at the same time.

Significance

The veneering material plays a significant role for the failure of a FDP and cannot be neglected neither in testing nor in simulation. Thus the loading capacity of dental restorations can only be reasonably evaluated when the whole restoration is taken into account, including framework and veneering.     

Effects of overdenture attachment systems with different working principles on stress transmission: A three-dimensional finite element study

PURPOSEThe aim of the present study was to compare the stress distributions on the dental implants, abutments, and bone caused by different overdenture attachment types under functional chewing forces.MATERIALS AND METHODSThe 3D finite element models of the mandible, dental implants, attachment types, and prostheses were prepared. In accordance with a conventional dental implant supported overdenture design, the dental implants were positioned at the bone level in the canine teeth region bilaterally. A total of eight models using eight different attachment systems were used in this study. All the models were loaded to simulate chewing forces generated during the centric relationship (450 N), lateral movement (400 N), protrusive movement (400 N), and also in the presence of a food mass unilaterally (200 N). Stress outputs were obtained as the maximum principal stress and the equivalent von-Mises stress.RESULTSIn all attachment types, higher stress values were observed in the abutments, dental implants, and bone in the magnet attachments in different loading conditions. The highest stress values were observed among the magnet systems in the components of the Titanmagnetics model in all loading conditions (stresses were 15.4, 17.7, and 33.1 MPa on abutment, dental implant, and bone, respectively). The lowest stress value was observed in the models of Zest and O-Ring attachments.CONCLUSIONThe results of the present study implied that attachment types permitting rotation and tolerating various angles created lower stresses on the bone, dental implants, and abutments.