Effect of occlusal thickness design on the fracture resistance of endocrowns restored with lithium disilicate ceramic and zirconia

目的 探讨二硅酸锂陶瓷和氧化锆制作的下颌第一磨牙髓腔固位冠的面厚度设计对抗折性能的影响。方法 根据修复设计（冠部材料及厚度）的不同,将24个下颌第一磨牙树脂仿真牙随机分成4组,每组6个。二硅酸锂2 mm组：采用二硅酸锂陶瓷制作修复体,面厚度2 mm,固位体长4 mm;二硅酸锂4 mm组：采用二硅酸锂陶瓷制作修复体,面厚度4 mm,固位体长2 mm;氧化锆2 mm组：采用氧化锆制作修复体,面厚度2 mm,固位体长4 mm;氧化锆4 mm组：采用氧化锆制作修复体,面厚度4 mm,固位体长2 mm。使用树脂水门汀粘接系统（RelyX Ultimate Clicker）粘接后,冷热循环10 000次。将万能试验机与牙长轴呈135°,位移速度0.5 mm·min^-1,在颊尖加载,测定抗折力及折裂方式,并用SPSS 15.0软件进行方差分析和多重比较。结果 二硅酸锂2 mm组、二硅酸锂4 mm组、氧化锆2 mm组、氧化锆4 mm组的抗折力分别为（890.54±83.41）、（2 320.87±728.57）、（2 258.05±557.66）和（3 847.70±495.99）N。氧化锆4 mm组的抗折力最高,二硅酸锂2 mm组的抗折力最低。结论 磨牙髓腔固位冠使用氧化锆较二硅酸锂陶瓷有更高的抗折力,增加修复体面厚度可提高抗折力,但基牙折裂风险也增加。     

有限元方法模拟不同全瓷冠破坏过程初探

目的 用有限元方法模拟不同材料和形态的基底冠全瓷冠破坏过程,分析材料和形态对全瓷冠破坏机制的影响.方法 分别建立均匀厚度、不均匀厚度、带颈环3种基底冠形态的氧化铝和氧化锆全瓷冠模型,用BFPA'2D有限元分析软件模拟加载后全瓷冠的破坏过程.结果 6种模型均由拉应力引发破坏,裂纹始于牙尖顶的饰瓷表面,并沿基底冠与饰瓷的界面扩展.在本项研究加载条件下,仅饰瓷破坏,无基底瓷破坏,加载压强5 MPa时氧化锆模型破坏,加载6 MPa时氧化铝模型破坏.加载开始时有颈环模型呈现颈环处最小主应力集中,不均匀厚度基底冠模型呈现颈部最大主应力集中.结论 氧化锫模型的基底瓷与饰瓷界面存在更大的应力.不均匀厚度基底冠设计未增加全瓷冠破坏的风险,有颈环基底冠模型的颈部是拉应力集中的薄弱环节.     

不同厚度饰瓷与基底瓷双层结构全瓷桥残余应力的有限元分析

目的:建立不同厚度饰瓷与基底瓷双层结构的后牙三单位全瓷桥有限元模型,分析饰瓷与基底瓷厚度对全瓷桥残余应力的分布及其影响。方法:使用WIELAND ZENOTEC Scan对上颌后牙三单位固定桥基牙标准模型进行三维光学扫描,在上述模型基础上通过WIELAND ZENOTEC Cad;Geomagic;CATIA构建三组不同厚度饰瓷与基底瓷双层结构后牙三单位全瓷桥实体模型,将模型导入ABAQUS6.10有限元软件,分析修复体从575℃降至室温25℃过程中残余应力的形成及分布。结果:全瓷修复体残余应力主要分布在饰瓷与基底瓷结合界面处,其中冠边缘、连接体处修饰瓷分布较薄的部位界面处残余应力较为集中,而在修饰瓷较厚的部位残余应力分布较为均匀。随着温度的降低,饰瓷与基底瓷结合界面的残余应力逐渐增大。随着饰瓷与基底瓷热膨胀系数之差逐渐增大和饰瓷厚度的增加,结合界面的残余应力也逐渐增大。结论:双层结构全瓷桥三维有限元模型的建立使得修复体残余应力分析得以实现。修饰瓷较薄和热膨胀系数差较大时残余应力分布较大,在进行全瓷桥修复时除饰瓷与基底瓷热膨胀系数匹配外,要保证饰瓷一定的厚度。     

不同桩核材料对四种牙科底层瓷颜色的影响

目的 探讨3种桩核材料对4种牙科底层瓷颜色的影响,以期为修复医师正确选择适宜的修复材料提供参考.方法 制作A2色热压铸二硅酸锂玻璃陶瓷(Empress Ⅱ,A组)、Z2色瓷沉积氧化锆陶瓷(B组)、氧化锆陶瓷(Cercon base color,C组)、氧化锆陶瓷(Cereon base,D组)底层瓷试件各5个,A组试件厚度为0.80 mm,B～D组试件厚度为0.50 mm.采用色差计测量4组底层瓷试件在金铂合金、镍铬合金和复合树脂背景上的色度值,并计算每种底层瓷在不同背景间的色差值(△Eab*).结果 B、C和D组试件在不同背景间的色差均值分别为(0.14±0.08)、(0.90±0.20)和(0.99±0.09),不易为人眼所辨别(△Eab*<1.5),而A组试件在不同背景间的色差均值为(2.83±0.70),能够为人眼所辨别(△Eab*>1.5).结论 玻璃陶瓷易受背景颜色的影响,宜在与牙齿颜色相近的桩核条件下使用;氧化锆的遮色能力强,适用于基牙严重变色或染色以及各类非牙色桩核等情况.     

CAD／CAM制作的整体硅酸锂全瓷冠与饰面瓷一氧化锆全瓷冠的比较研究：模拟疲劳试验下的破坏模式与可靠性

目的：本研究的目的在于评估CAD／cAM制作的整体硅酸锂全瓷冠与手工饰瓷的氧化锆全瓷冠的体外疲劳表现和可靠性。材料和方法：利用CAD设计并采用快速成型技术制作下颌磨牙进行全冠预备后的基牙模型,通过CAD／CAM系统分别完成全解剖式的19颗硅酸锂全瓷冠（IPS e.maxCAD）和21颗手工饰瓷的氧化锆全瓷冠（IPS e.max ZirCAD／Ceram）。用树脂粘结材料将上述全瓷冠粘结于前期储存在水中的拟牙本质复合树脂模型上。在模拟口腔运动的疲劳试验中,用半径318mm的碳钨压头从全瓷冠的远颊尖加力并缓慢向舌侧滑动07mm．用三种不同的步进应力方法测试,直到试件发生破坏。当试件出现大块崩瓷或冠折裂时视为失败。如果承受高负载（〉900N）时试件仍未出现失败．则测试方法改变为应力比r呈阶梯式变化的疲劳试验。计算应力水平概率曲线及可靠性。结果：手工饰瓷的氧化锆全冠加载200N负荷完成10万次循环时出现崩瓷,其可靠性〈0．01（0．03～000,双侧90％的可信区间）。在整个步进应力（18万循环,900N）模拟1：3腔运动疲劳试验中未发生CAD／CAM制作的整体硅酸锂全瓷冠的失败,在应力比r的疲劳试验（100万循环．100～1000N）中整体硅酸锂全瓷冠也未见失败。1100～1200N负载可能是阈值范围．硅酸锂全瓷冠出现破坏或折裂。结论：基于目前的疲劳试验结果．CAD／CAM制作的全解剖式硅酸锂全瓷冠具有较高的抗疲劳特性．而手工饰瓷的氧化锆全瓷冠在较低负载的循环试验过程中易出现崩瓷。     

不同全瓷材料和厚度的种植牙冠应力分布有限元分析

目的通过有限元方法比较不同全瓷材料和厚度在种植牙冠修复的应力分布情况,为临床冠部修复材料的选择和设计提供参考。方法建立下颌第一磨牙种植牙冠修复有限元模型,并进行6种冠厚度和4种不同冠修复材料,即树脂基陶瓷(Lava Ultimate和Vita Enamic)、二硅酸锂玻璃陶瓷(IPS e.max CAD)和氧化锆陶瓷(Cercon)进行组合。在下颌第一磨牙面加载600 N,使用有限元软件ANSYS 10.0分析应力分布。结果冠部应力分析显示,4 mm?Cercon组156.05 MPa最高,1 mm?Lava Ultimate组18.85 MPa最低。树脂水门汀应力分析显示,4 mm?Lava Ultimate组62.52 MPa最高,1 mm?IPS e.max CAD组16.74 MPa最低。使用成品基台时,Lava Ultimate组在冠修复体、树脂水门汀中的应力集中较相同冠厚度的个性化基台高。结论随着冠厚度增加,冠修复体和树脂水门汀中的最大主应力集中呈现上升趋势;树脂基陶瓷使用个性化基台更有利于减少应力集中。     

影响髓腔固位冠边缘密合性及机械强度的材料与牙体预备因素

髓腔固位冠是一种全冠和超嵌体的改良型,兼具粘接固位和髓腔机械固位。边缘密合性和机械强度是口腔修复体最常见的评价标准,笔者就近年来髓腔固位冠边缘密合性和机械强度的国内外研究进行综述。研究结果表明:各类临床常用的修复材料如玻璃陶瓷、氧化锆陶瓷及树脂基陶瓷制作的髓腔固位冠基本都具有临床可接受的边缘密合性;氧化锆是临床常用的陶瓷材料,但有不可再修复的根折风险;与氧化锆陶瓷材料相比,树脂基陶瓷、玻璃陶瓷如二硅酸锂陶瓷制作的髓腔固位冠较少出现不可再修复的缺陷,但其强度不及氧化锆。同时,牙体预备方式如髓腔固位冠类型、髓腔固位深度、髓腔洞形轴壁外展度以及[牙合]面厚度均对髓腔固位冠的机械强度存在影响。釉锆作为一种新型氧化锆材料,与传统氧化锆有相似的弹性模量(210 GPa),但美观性更佳,且与髓腔固位冠一样适合于咬合空间不足的短冠患者。如何进行改良以降低氧化锆制作髓腔固位冠修复失败后的根折风险需要进一步的研究。     

三种牙科全瓷底层材料饰瓷后相对透明率的对比测定

目的饰瓷及上釉后Vita In-Ceram 渗透氧化铝陶瓷、氧化锆陶瓷和Ivoclar Vivodent Empress Ⅱ铸瓷材料相对透明率的对比测定.方法在标准黑白背景下,采用接触式色彩色差计测定饰瓷后3种全瓷系统底层材料试样的表面光反射率并计算Yb/Yw的比值.结果饰瓷后,3种核瓷材料的相对透明率均有所下降.其相对透明率的范围从Empress Ⅱ的0.8880到氧化锆渗透陶瓷的1.00,其中以EmpressⅡ最为透明.结论 3种全瓷系统底层材料饰瓷后的相对透明率组间存在统计学显著差异.按照相对透明率数值高低的顺序排列为:Vita Alpha 饰瓷＞EmpressⅡ饰瓷(0.8 mm)＞In-Ceram氧化铝核瓷＞In-Ceram氧化锆核瓷.     

陶瓷厚度与基牙底色对4种常用CAD/CAM瓷修复体颜色的影响

目的 研究4种不同厚度和半透明度CAD/CAM陶瓷在不同基牙底色上的遮色效果，为临床的陶瓷材料选择提供参考。方法 4种CAD/CAM陶瓷分别是：IPS e.max CAD（硅酸锂玻璃）, VITA SUPRINITYPC（氧化锆增强玻璃）, VITABLOCS MarkⅡ（长石基玻璃）和Vita Enamic（聚合物渗透陶瓷），制作成不同厚度(1 mm、1.5 mm、2 mm)的瓷块试样，在7种基牙底色(A1、A2、ND7色调复合树脂、白色(White)、黑色(Black)、钴铬合金(CC)、贵金属合金(PMA)下使用分光光度计检测Lab值，同一种瓷块2 mm厚度在A2色上的表现作为对照组，横向比较各种瓷块在不同基牙底色上的色差值以及半透明度。结果 ΔL、Δa、Δb值随着陶瓷厚度的增加逐渐减小，且在4种陶瓷间存在明显差异；半透明性参数均值按半透明度递减顺序依次为长石基玻璃>硅酸锂玻璃>氧化锆增强玻璃>聚合物渗透陶瓷；其中半透明度越大，其陶瓷的遮色效果反而越差；当厚度达到2 mm时，4种陶瓷在各种基牙底色下的ΔE（临床可接受颜色阈值）均<3.7;4种陶瓷中ΔE与厚...     

不同基底冠材料对上颌中切牙全瓷冠受载应力分布的影响

目的：研究上中切牙不同基底冠材料全瓷冠受载时的应力分布特点。方法：运用逆向工程软件构建上颌中切牙全瓷冠（双层冠结构）的三维有限元数值模型,选择氧化锆全瓷冠、氧化铝全瓷冠为实验组,贵金属烤瓷冠为对照组,施以不同部位静态载荷模拟加载,分析其应力分布趋势的异同。结果：应力分布云图显示,不同基底冠材料的全瓷冠应力分布趋势相同,载荷区和全冠颈缘为应力集中区,其中应力极值点位于载荷点。不同基底冠材料全瓷冠的应力值不同,随着材料弹性模量的增加,基底冠的等效应力极值相应增加,而饰面瓷则适当减小;基底冠弹性模量的增加也会使得基底冠与预备体界面、基底冠与饰面瓷界面以及邻面颈缘的张应力显著提高,饰面瓷的张应力则稍有下降。结论：高弹性模量基底冠可降低上中切牙全瓷冠饰面瓷的折裂风险。     

Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design

STATEMENT OF PROBLEM: Indirect composite or ceramic fixed partial dentures (FPDs) have become an alternative to conventional metal-ceramic adhesive fixed partial dentures (AFPDs). Little information about the adequate restorative material and tooth preparation design for inlay-anchored AFPDs is available to the clinician. PURPOSE: The purposes of this simulation study were: (1) to use 2-dimensional finite element modeling to simulate stresses at the surface and interface of 3-unit posterior AFPDs made with 6 different restorative materials, and (2) to investigate the influence of 3 different abutment preparation configurations on the stress distribution within the tooth/restoration complex. MATERIAL AND METHODS: A mesio-distal cross-section of a 3-unit AFPD was digitized and used to create 2-dimensional models of the periodontal membrane, supporting bone, different restorative materials (gold, alumina, zirconia, glass-ceramic, composite, and fiber-reinforced composite), and different abutment preparation configurations (interproximal slots vs. 2-surface [MO, DO] vs. 3-surface [MOD]). A simulated 50-N vertical occlusal load was applied to the standardized pontic element. The principal stress within the restorative materials, stresses at the tooth/restoration interface, and surface tangential stresses at the level of the pontic were calculated in MPa from the postprocessing files and compared to each other. RESULTS: All materials and tooth preparation design exhibited a similar stress pattern, with a definite compressive area at the occlusal side of the pontic, a tensile zone at the gingival portion of the pontic, and tensile stress peaks in the abutment/pontic connection areas. Among isotropic materials, standard non-reinforced composites exhibited better stress transfer and reduced tensile stresses at the adhesive interface than ceramics and gold. Optimized placement of the glass fibers within the composite resulted in similar stress distribution when tested in 2-surface abutment preparation configuration. There was no detectable influence of preparation design on the behavior of the pontic area. Among all 3 preparation designs, only the DO design exhibited almost pure compression at the interface. CONCLUSION: Within the limitations of this simulation experiment, the composite materials tested demonstrated a resilient component that favored stress transfer within the tooth/restoration complex. Their clinical use, however, may be contraindicated due to insufficient strength and fracture toughness. The addition of extremely tough fibers to composites represents the most promising combination. Clinical trials are required to ensure that veneering composite can survive under clinical conditions.     

Finite element analysis of fixed partial denture replacement

The purpose of this study was to investigate, by means of the finite element method the mechanical behaviour of three designs of fixed partial denture (FPD) for the replacement of the maxillary first premolar in shortened dental arch therapy. Two-dimensional, linear, static finite element analyses were carried out to investigate the biomechanics of the FPDs and their supporting structures under different scenarios of occlusal loading. Displacement and stress distribution for each design of FPD were examined, with particular attention being paid to the stress variations along the retainer-abutment--and the periodontal ligament-bone interfaces. The results indicated that displacement and maximum principal stresses in the fixed-fixed, three-unit FPD were substantially less than those in the two-unit cantilever FPDs. Of the two cantilever FPDs investigated, the distal cantilever design was found to suffer less displacement and stresses than the mesial cantilever design under similar conditions of loading. The highest values for maximum principal stress in the cantilever FPDs were found within the connector between the pontic and the retainer, and within the periodontal ligament and adjacent bone on the aspect of the retainer away from the pontic.     

ALL-CERAMIC AND PORCELAIN-FUSED-TO-METAL FIXED PARTIAL DENTURES: A COMPARATIVE STUDY BY 2D FINITE ELEMENT ANALYSES

All-ceramic fixed partial dentures (FPDs) have an esthetic approach for oral rehabilitation. However, metal-ceramic FPDs are best indicated in the posterior area where the follow-up studies found a lower failure rate. This 2D finite element study compared the stress distribution on 3-unit all-ceramic and metal-ceramic FPDs and identified the areas of major risk of failure. Three FPD models were designed: (1) metal-ceramic FPD; (2) All-ceramic FPD with the veneering porcelain on the occlusal and cervical surface of the abutment tooth; (3) All-ceramic FPD with the veneering porcelain only on the occlusal surface. A 100 N load was applied in an area of 0.5 mm² on the working cusps, following these simulations: (1) on the abutment teeth and the pontic; (2) only on the abutment teeth; and (3) only on the pontic. Relative to the maximum stress values found for the physiological load, all-ceramic FPD with only occlusal veneering porcelain produced the lowest stress value (220 MPa), followed by all-ceramic FPD with cervical veneering porcelain (322 MPa) and metal-ceramic FPD (387 MPa). The stress distribution of the load applied on the abutments was significantly better compared to the other two load simulations. The highest principal stress values were low and limited in a small area for the three types of models under this load. When the load was applied on the pontic, the highest stress values appeared on the connector areas between the abutments and pontic. In conclusion, the best stress values and distribution were found for the all-ceramic FPD with the veneering porcelain only on the occlusal surface. However, in under clinical conditions, fatigue conditions and restoration defects must be considered.     

下颌固定义齿基牙齿槽骨降低时不同受载的三维有限元分析

目的 研究下颌后牙固定义齿在齿槽骨降低后受载的三维有限元应力分布情况。方法在建立的下颌固定义齿三维有限元模型的基础上，选取桥体、两侧基牙的咬合面施加不同方向的载荷，利用MARC有限元分析软件计算并绘制各种载荷下的应力分布图像。结果 固定义齿受垂直载荷时基牙的牙周支持组织的应力分布集中在根尖部位，以压应力为主。斜向载荷使基牙支持组织的应力增加且分布不均匀，颈部的应力增加较多。齿槽骨的降低使固定义齿基牙支持组织的应力增加，但分布规律不变。结论 齿槽骨的降低使固定义齿基牙支持组织的应力增加，此类修复体的设计应特别注意基牙牙周组织的健康。     

桩核冠修复材料对牙体应力的影响

目的：通过不同的桩核冠材料修复牙的牙体应力分析，为临床选择修复材料提供生物力学依据。方法：建立上中切牙桩核修复的三维有限元模型，分别分析金合金桩核-镍铬全冠、金合金桩核-金合金全冠、金合金桩核-陶瓷全冠和镍铬桩核-镍铬全冠、镍铬桩核-金合金全冠、镍铬桩核-陶瓷全冠6种情况下牙体应力的情况。结果：镍铬合金桩核组牙体内最大Von Mises应力为113.70MPa，金合金桩核组为74.03MPa，较前者降低了34.89％。结论：桩核材料对牙体应力分布和应力峰值的影响明显，而冠材料对牙体应力的影响不大。用弹性模量较低的桩核材料进行修复有助于降低牙体折裂的可能性。     

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge

IntroductionFailures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPD.ObjectivesThe purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD.MethodsA structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD.ResultsResults obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic, forming a U-shape substructure that extended into the connectors linking the teeth and the pontic. FE analyses of the optimized design indicated stress reduction in both the veneering composite and at the interface between the veneer and the FRC substructure.SignificanceThe optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.     

Three-dimensional finite element modelling of all-ceramic restorations based on micro-CT

ObjectivesTo describe and apply a method of modelling dental crowns and three-unit fixed partial dentures (FPD) for finite element analyses (FEA) from 3D images obtained using a micro-CT scanner.MethodsA crown and a three-unit fixed partial denture (FPD) made of a ceramic framework (Y-TZP) and veneered with porcelain (VM9) were scanned using an X-ray micro-CT scanner with a pixel size of 6.97 μm. Slice images from both structures were generated at each 0.034 mm and processed by an interactive image control system (Mimics). Different masks of abutments, framework and veneer were extracted using thresholding and region growing tools based on X-ray image brightness and contrast. 3D objects of each model were incorporated into non-manifold assembly and meshed simultaneously. Volume meshes were exported to the FEA software (ABAQUS), and the load-generated stress distribution was analyzed.ResultsFEA models showed great shape resemblance with the structures. The use of non-manifold assembly ensured matching surfaces and coinciding nodes between different structural parts. For the crown model, tensile stresses were concentrated in the internal surface of the core, near to the applied load. For the FPD model, the highest tensile stresses were located in the framework, on the cervical area of connectors and pontic.ConclusionsValid 3D models of dental crown and FPD can be generated by combining micro-CT scanning and Mimics software, emphasizing its importance as design tool in dental research.Clinical significanceThe 3D FEA method described in this work is an important tool to predict the stress distribution, assisting on structural design of dental restorations.     

Biomechanical interactions in tooth-implant-supported fixed partial dentures with variations in the number of splinted teeth and connector type: a finite element analysis.

OBJECTIVE: The aim of this study was to investigate the biomechanical interactions in tooth-implant-supported fixed partial dentures (FPDs) under several loading conditions with different numbers of splinted teeth and connector types (rigid and non-rigid) by adopting the three-dimensional (3D) non-linear finite element (FE) approach. MATERIAL AND METHODS: A 3D FE FPD model was constructed containing one Frialit-2 implant in the mandibular second-molar region splinted to the first and second premolars. Frictional contact elements were used to simulate realistic interface conditions within the implant system and the non-rigid connector function. The main effects for each level of the three investigated factors (loading condition, number of splinted teeth and connector type) in terms of the stress values and dissimilar mobility of the natural teeth and implant were computed for all models. RESULTS: The results indicated that load condition was the main factor affecting the stress developed in the implant, bone and prosthesis when comparing the type of connector and the number of splinted teeth. The stress values were significantly reduced in centric or lateral contact situations once the occlusal forces on the pontic were decreased. However, the prosthesis stress for the non-rigid connections was increased more than 3.4-fold relative to the rigid connections. Moreover, the average tooth-to-implant displacement ratios (R(TID)) with a non-rigid connection were obviously larger than those for rigid connections under axial loading forces. Adding an extra tooth to support a three-unit tooth-implant FPD only exploited its function when the prosthesis withstood lateral occlusal forces. CONCLUSIONS: The load condition is the main factor affecting stress distribution in different components (bone, prosthesis and implant) of tooth-implant-supported FPDs. Minimizing the occlusal loading force on the pontic area through selective grinding procedures could reduce the stress values obviously. A non-rigid connector may more efficiently compensate for the dissimilar mobility between the implant and natural teeth under axial loading forces but with the risk of increasing unfavorable stresses in the prosthesis.     

Three-dimensional finite element analysis of posterior fiber-reinforced composite fixed partial denture Part 2: influence of fiber reinforcement on mesial and distal connectors

The aim of this study was to evaluate the influence of connectors under two different loading conditions on displacement and stress distribution generated in isotropic hybrid composite fixed partial denture (C-FPD) and partially anisotropic fiber-reinforced hybrid composite fixed partial denture (FRC-FPD). To this end, two three-dimensional finite element (FE) models of three-unit FPD from mandibular second premolar to mandibular second molar - intended to replace the mandibular first molar - were developed. The two loading conditions employed were a vertical load of 629 N (applied to eight points on the occlusal surface) and a lateral load of 250 N (applied to three points of the pontic). The results suggested that the reinforcing fibers in FRC framework significantly improved the rigidity of the connectors against any twisting and bending moments induced by loading. Consequently, maximum principal stress and displacement generated in the connectors of FRC-FPD were significantly reduced because stresses generated by vertical and lateral loading were transferred to the reinforcing fibers.     

Finite element analysis of fiber-reinforced fixed partial dentures

Two-dimensional finite element models were created for a three-unit posterior fixed partial denture. An experimental resin-impregnated glass fiber was used as the fiber-reinforced composite (FRC) for the framework. The FRC was evaluated using varying combinations of position and thickness, alongside with two types of veneering composite. A load of 50 N simulating bite force was applied at the pontic in a vertical direction. Tensile stress was examined using a finite element analysis program. Model without FRC showed tensile stress concentrations within the veneering composite on the cervical side of the pontic--from the connector area to the bottom of the pontic. Model with FRC at the top of the pontic had almost the same stress distribution as the model without FRC. Models with 0.4-0.8 mm thick FRC positioned at the bottom of the pontic showed maximum tensile stresses reduced by 4-19% within the veneering composite.