全瓷冠内部应力分布规律的三维有限元研究

目的 运用有限元法分析全瓷冠的应力分布规律,为临床修复没计提供依据.方法 利用CT断层影像构建右下第一磨牙全瓷冠三维有限元模型.设计5种加载方式:垂直集中载荷600 N、垂直八点分布载荷600 N、垂直偏舌侧载荷600 N、10°偏颊侧载荷600 N、颊侧20°咀嚼载荷225 N,利用ANSYS软件分析各瓷层和界面的应力值大小.结果 5种加载方式下全瓷冠应力分布的相同之处:加载点可引起饰面瓷应力集中,沿载荷方向核瓷内表面拉应力集中.5种加载方式下全瓷冠应力分布的不相同之处:垂直集中载荷作用下,全瓷冠颈部肩台拉应力分布均匀;10°偏颊侧载荷仅使全瓷冠颊舌侧颈部肩台拉应力集中,最大值为32.25 MPa;颊侧20°咀嚼载荷引起全瓷冠颊侧、近中、远中颈部肩台拉应力集中,最大值为11.29 MPa.结论 制作全瓷冠应增加咬合接触面积,减少牙尖斜度,并提高颈部肩台陶瓷的抗拉能力.     

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.     

不同磨损状态下金属烤瓷全冠的三维有限元分析

目的:探讨饰瓷咬合面中央窝区域不同磨损程度下,金属烤瓷全冠饰瓷层应力变化情况。方法:以1∶15标准下颌第一磨牙塑料模型为对象,运用逆向工程和计算机辅助设计技术建立全冠饰瓷中央窝区域与对颌牙尖不同磨损深度的有限元模型,分别设定磨损深度为0.1、0.3、0.5、0.7、1.0 mm。并在全冠磨损面上垂直加载350 N的力,约束于牙槽骨底面。观察不同磨损程度对于全冠饰瓷层Von Mises应力峰值的影响。结果:随着中央窝区域磨损程度加深,咬合面上磨损面积变大,瓷层厚度减小,并且面积增大的幅度明显大于瓷层厚度的变化;饰瓷Von Mises应力峰值随之减小(224 MPa降低至35.5 MPa),但界面处的应力峰值减小幅度较低,并且有形成应力集中区域的趋势。结论:磨损造成的面积增大对于应力峰值的影响较大;适当的磨损面有利于饰瓷应力的合理分布。     

饰瓷对磨牙e.max双层全瓷冠断裂类型的影响

目的：通过抗折破坏实验研究饰瓷对磨牙e.max双层全瓷冠断裂强度和断裂类型的影响,为减少临床双层全瓷修复体崩瓷提供实验依据。方法：制作单层全瓷冠（IPS e.max Press）和双层全瓷冠（IPS e.max Press/Ce-ram）共40个（每组20个）,粘接于树脂代型后进行抗折破坏实验并记录断裂强度值;体视显微镜和扫描电子显微镜下观察断裂类型;能谱分析饰瓷-核瓷界面化学元素构成。结果：单层全瓷冠断裂强度值[（2665.4±759.2）N]与双层全瓷冠[（1431.1±404.3）N]间差异有统计学意义（P=0.000）。饰瓷内部及饰瓷-核瓷界面缺陷催生裂纹造成饰瓷崩裂是双层全瓷冠断裂的主要模式。结论：饰瓷对磨牙e.max双层全瓷冠断裂强度和断裂类型均有影响;饰瓷内部及饰瓷-核瓷界面缺陷是全瓷冠断裂的主要原因,提高饰瓷断裂强度及减少界面缺陷可减少因崩瓷造成的修复体失败。     

不同瓷层厚度对全瓷冠内部应力分布规律影响有限元分析

目的    探讨不同饰瓷和核心瓷牙合面厚度对双层结构氧化锆全瓷冠内部应力分布规律的影响,为临床修复设计提供依据。方法    本研究于2012年3—7月在清华大学计算机教研室进行。利用螺旋CT断层图像,构建上颌第一磨牙氧化锆全瓷冠（核心瓷层和饰瓷层）、黏结剂层、牙体组织、牙根、牙周膜、牙槽骨6部分的三维有限元模型,设计垂直集中载荷600 N的加载方式,观察不同饰瓷牙合面厚度（V）与核心瓷牙合面厚度（C）两因素变化对全瓷冠的最大主应力（S1）分布情况。结果    随着饰瓷厚度增加,饰瓷本身的应力先减小后上升,即饰瓷厚度为0.7 mm时,S1为73.20 MPa;厚度升至0.9 mm时,S1下降至54.56 MPa;厚度升至1.7 mm时,S1则上升至60.16 MPa。而随着核心瓷厚度增加,核心瓷的应力在减小,即核心瓷厚度为0.3 mm时,S1为116.40 MPa;厚度升至1.3 mm时,S1下降至4.17 MPa,其应力峰值下降幅度为96.75%。结论    对全瓷冠的应力分析,得出双层全瓷冠的V和C范围：0.9 mm ≤ V ≤ 1.5 mm,C≥0.5mm。这就要求在全瓷冠临床预备过程中,必须留出至少1.4 mm的空间,即为两者最低限之和。     

下颌第一磨牙全瓷冠三维有限元建模及力学分析

目的：使用一种新方法建立下颌第一磨牙双层全瓷冠的三维有限元模型。方法：以两种不同比例的硫酸钡与自凝塑料混合物来代替陶瓷制作双层全瓷冠,经Micro-CT扫描获取图像,Simpleware软件建模,Geomagic软件光滑处理,Ansys11．0分析软件进行网格划分及分析。实验模拟牙尖交错耠的功能状态进行应力力学计算分析。结果：建立了下颌第一磨牙双层全瓷冠的三维有限元模型,单元数800491,节点数1128058。全瓷冠第一主应力的分布从高到低依次为：载荷相应核瓷组织面（38．12MPa）、饰瓷加载点周围（26．71MPa）、加载侧肩台核瓷内表面（17．98MPa）,其余部分的应力分布均匀且较低。结论：将显影塑料代替双层全瓷冠并用Micro—CT扫描,通过Simple、Geomagic、Ansys软件建模的方法可行,为全瓷冠有限元的分析提供了一种更精确、简便的建模方法。应力分析提示全瓷冠咬合接触点、颈部肩台及核瓷组织面是张应力集区域。     

基于全瓷冠饰瓷厚度及基底厚度连续变化的全瓷冠三维有限元分析

目的:探讨饰瓷面厚度和基底面厚度双变量同时连续变化情况下全瓷冠饰瓷的应力变化情况。方法:以下颌第一磨牙为例,运用逆向工程和计算机辅助设计技术建立包含两参数(饰瓷面厚度和基底面厚度)连续变化的有限元模型,设定饰瓷面厚度变化范围为0.5～3 mm,肩台宽度变化范围为0.1～1 mm,并在全瓷冠远中颊尖垂直加载200 N的力,约束于牙槽骨底面,观察两因素联动变化对全瓷冠饰瓷最大主应力峰值的影响。结果:随着饰瓷面厚度的增加,饰瓷的MPS峰值从32.048 MPa降低到11.036 MPa,下降幅度为65.56%;随着饰瓷厚度的增加饰瓷厚度变化对饰瓷应力峰值的影响在不断减小;基底面厚度变化对饰瓷的应力峰值没有影响。结论:在全瓷冠的设计过程中可以适度增加饰瓷的厚度而减小基底的厚度。     

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目的探讨不同饰瓷和核心瓷牙合面厚度对双层结构氧化锆全瓷冠内部应力分布规律的影响,为临床修复设计提供依据。方法本研究于2012年3—7月在清华大学计算机教研室进行。利用螺旋CT断层图像,构建上颌第一磨牙氧化锆全瓷冠(核心瓷层和饰瓷层)、黏结剂层、牙体组织、牙根、牙周膜、牙槽骨6部分的三维有限元模型,设计垂直集中载荷600 N的加载方式,观察不同饰瓷牙合面厚度(V)与核心瓷牙合面厚度(C)两因素变化对全瓷冠的最大主应力(S1)分布情况。结果随着饰瓷厚度增加,饰瓷本身的应力先减小后上升,即饰瓷厚度为0.7 mm时,S1为73.20 MPa;厚度升至0.9 mm时,S1下降至54.56 MPa;厚度升至1.7 mm时,S1则上升至60.16 MPa。而随着核心瓷厚度增加,核心瓷的应力在减小,即核心瓷厚度为0.3 mm时,S1为116.40 MPa;厚度升至1.3 mm时,S1下降至4.17 MPa,其应力峰值下降幅度为96.75%。结论对全瓷冠的应力分析,得出双层全瓷冠的V和C范围:0.9 mm≤V≤1.5 mm,C≥0.5mm。这就要求在全瓷冠临床预备过程中,必须留出至少1.4 mm的空间,即为两者最低限之和。     

下颌第一磨牙任意两壁缺损不同充填材料全瓷冠修复的三维有限元应力分析

目的:应用三维有限元法对不同充填材料全瓷冠修复两壁缺损下颌第一磨牙应力分析。方法:通过CBCT扫描离体牙,Mincis三维重建,Geomagic优化处理,Ansys布尔运算建立下颌第一磨牙两壁缺损6种模型,分别使用银汞合金充填及复合树脂充填全瓷冠修复,在最大、垂直、斜向及水平4种载荷下,分别比较牙本质Mohr应力分布及牙本质最大Mohr值。结果:下颌第一磨牙牙冠缺损1/2时,不同充填材料全瓷冠修复,同一载荷下6种缺损模型的牙根应力分布无明显区别,银汞合金充填全瓷冠修复的应力集中区较复合树脂充填全瓷冠修复更偏向根方。结论:下颌第一磨牙牙冠缺损1/2时,复合树脂充填全瓷冠修复优于银汞合金充填全瓷冠修复,且缺损位置对修复效果无明显影响。     

前牙全瓷冠饰瓷崩裂断口形貌分析

目的 通过断口形貌观察分析临床失效的前牙全瓷冠,分析疲劳损伤的起源和发展,以期为优化全瓷冠桥修复体的临床设计及修复工艺提供依据.方法 收集临床失效前牙二硅酸锂基瓷冠( IPS EmpressⅡ)3例,玻璃渗透氧化铝瓷冠(In-Ceram)2例,采用体视显微镜和扫描电子显微镜观察断裂面,分析特征形貌.结果 5例全瓷冠主要失效模式均为唇侧饰瓷内聚破坏,裂纹起源于切端咬合接触区,并由切端向龈端扩展,裂纹源附近饰瓷内部见较多气孔缺陷.结论 饰瓷内聚破坏是全瓷修复失效的重要原因;饰瓷内部易出现制作缺陷,成为双层瓷修复体的薄弱环节;改良饰瓷制作及烧结工艺,设计多点咬合接触将有助于减少饰瓷崩瓷.     

Influence of veneer pore defects on fracture behavior of bilayered lithium disilicate glass-ceramic crowns

Objective

To identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure.

Influence of veneer and cyclic loading on failure behavior of lithium disilicate glass-ceramic molar crowns

Objective

This in vitro study was designed to investigate the influence of the veneer and cyclic loading on the failure behavior of lithium disilicate glass-ceramic (LDG) crowns on maxillary first molar.

Methods

Sixty-four LDG crowns were divided into 4 groups (n = 16). Thirty-two monolithic crowns were fabricated from IPS e.max Press (M), and the remaining bilayered crowns using cut-back technique and conventional manual layering technique from IPS e.max Press/Ceram (B). Monolithic or bilayered crowns were subjected to single-load-to-fracture (SLF) testing using a universal testing machine, before (M1 and B1) and after exposure to sliding-contact fatigue (SCF) testing (M2 and B2), consisting of 1,200,000 mechanical cycles (F_max = 98 N). Data were statistically analyzed using two-by-two factorial design ANOVA. Fractographic analysis was performed to determine the fracture modes of the failed specimens.

Results

The mean fracture load values (N ± S.D.) for M1, B1, M2 and B2 were 2686 ± 628 N, 1443 ± 327 N, 2133 ± 578 N and 1464 ± 419 N, respectively. Significant differences were found between the failure loads of all groups (P < 0.001), except between groups B1 and B2. Bulk fracture initiating from the occlusal surface is the primary failure mode of monolithic and veneered LDG crowns. Cracking that initiated from core–veneer interfacial defects and ultimately resulted in bulk fracture is another major failure origin of veneered all-ceramic crowns.

Significance

Veneer application resulted in significantly lower fracture load values compared to monolithic LDG crowns. Cyclic loading is an accelerating factor contributing to fracture for monolithic LDG crowns but not for bilayered ones.     

渗透陶瓷双层结构的双轴抗弯强度及断裂模式研究

目的:考察渗透陶瓷与饰面瓷双层结构的双轴抗弯强度及其可靠性和断裂方式,以帮助了解修复体失败的原因。方法:制作1.6mm×16mm盘状试件40个,MC和MV分别为渗透陶瓷和饰面瓷的单层试件,BV和BC为两者的双层试件,采用球-环法测定以上4组的双轴抗弯强度,其中BV组在加载时饰面瓷承受张应力,BC组加载时渗透陶瓷承受张应力。结果用SPSS13.0软件包行单因素方差分析及Weibull分析,体视显微镜及扫描电镜观察确定试件断裂源及断裂模式。结果:MC组强度最高(P<0.001),BC组强度高于BV组(P<0.001),MV组与BV组双轴抗弯强度无统计学差异(P=0.381)。Weibull模量主要受承受张应力一侧的材料影响,BC组与BV组都未发生明显的界面剥离。结论:加载时,承受张应力的材料决定双层试件的双轴抗弯强度和断裂模式。强度较差的饰面瓷会影响全瓷修复体的强度。     

Stress analysis of metal-free polymer crowns using the three-dimensional finite element method

PURPOSE: The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior metal-free crowns made of new composite materials. MATERIALS AND METHODS: A three-dimensional finite element model representing a mandibular first molar was constructed. Variations of the model had crowns of two types of composite, a glass ceramic, and porcelain fused to metal. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45-degree angle, and horizontally). RESULTS: The stress distributions in both types of composite crown were similar to that of the glass-ceramic crown. In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.9 to 18.3 MPa) concentrated around the loading points. In the masticatory force-stimulation test, the specimens experienced maximum tensile stresses of 20.3 to 26.6 MPa under a horizontal load and 10.9 to 11.0 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of composite and glass-ceramic crowns, and in the cervical area of the metal coping in the porcelain-fused-to-metal crowns. CONCLUSION: It would appear that the strength of occlusal contact points is important to the integrity of posterior metal-free crowns made of new composite materials and that bite forces applied from the horizontal direction are a critical factor determining success and failure.     

显微CT与三维重建技术对双层二硅酸锂玻璃陶瓷内部缺陷探测的可靠性分析

目的通过比较二硅酸锂双层瓷试件剖面影像学形貌与相应显微CT扫描成像和三维重建结果,分析显微CT与三维重建技术用于无损探测二硅酸锂双层瓷材料内部缺陷的可靠性。 方法制作双层二硅酸锂双层瓷矩形试件,进行显微CT扫描;扫描后沿垂直于试件长轴将试件平均切成6段,对每段剖面进行光学显微镜观察并获取5个剖面图像。根据剖面位置确定显微CT扫描断层图像,并将显微镜图像与显微CT图像进行灰度差值匹配比对,分析显微CT对全瓷材料内部缺陷探测的可靠性与精确性。对CT扫描结果进行三维重建,比较二硅酸锂双层瓷试件内部缺陷的二维形貌与三维形貌的差异。 结果显微镜图像与显微CT图像的平均相似度为（83 ± 7.9）%;缺陷的二维剖面形貌与三维形貌存在较大差异。 结论显微CT能够可靠地无损探测二硅酸锂双层瓷材料的内部缺陷结构,但对尺寸接近探测分辨率的孔洞成像较模糊。三维重建分析较二维形貌观察能更全面地反映缺陷的形貌。     

Compatibility of machined Ce-TZP/Al2O3 nanocomposite and a veneering ceramic

OBJECTIVES: Due to its high fracture toughness ceria-stabilized ZrO(2)/Al(2)O(3) nanocomposite (Ce-TZP/A) could be superior to Y-TZP in clinical use. However, the compatibility to veneering ceramics is not yet investigated and therefore subject of this study. METHODS: Fracture strength and crazing resistance of veneered Ce-TZP/A frameworks (Nanozir, Matsushita Electric Works) were investigated in comparison to sintered and hipped Y-TZP (Hint-ELs). Frameworks were machined (HiCut, Hint-ELs), sintered where applicable (hiTherm, Hint-ELs), and veneered in a standardized procedure (Cerabien ZR, Noritake). Fracture strength of the crowns was assessed in a shear test (n=10). Biaxial flexural strength of the core materials was measured according to ISO 6872 (n=10). To assess the thermal compatibility between framework and veneer the coefficient of thermal expansion (CTE) of all materials was determined (n=3) and a crazing test carried out (n=12). RESULTS: Fracture strength was equal for crowns with Ce-TZP/A (866.6+/-132.1N) and sintered Y-TZP (904.5+/-168.2N), while crowns with hipped Y-TZP were significantly stronger (1380.6+/-253.2N) (Student's t-test, p<0.05). These values correlated with the biaxial flexural strength of the three core materials (Ce-TZP/A: 1238.0+/-200.0MPa, sintered Y-TZP: 1181.8+/-232.5MPa and hipped Y-TZP: 1521.8+/-163.8MPa). Failure of both hipped and sintered Y-TZP crowns occurred by chipping of the veneer or total fracture, while the Ce-TZP/A crowns predominantly failed by chipping of the veneer. In the crazing test both sintered and hipped Y-TZP performed slightly better than Ce-TZP/A. CTE's were as follows: Ce-TZP/A: 10.3microm/mK, sintered Y-TZP: 10.7microm/mK, hipped Y-TZP: 10.9microm/mK, and Cerabien ZR: 9.9microm/mK. SIGNIFICANCE: The CTE of the veneering ceramic has to be adjusted to Ce-TZP/A frameworks.     

牙科着色氧化锆陶瓷饰瓷前后的力学性能及断裂模式分析

目的:本研究对牙科氧化锆陶瓷着色及构筑饰面瓷前后的力学性能及断裂模式进行分析.方法:球磨混合一定组分的着色剂(氧化铁及氧化铈)和3Y-TZP(钇稳定氧化锆)粉体制备着色氧化锆陶瓷.根据ISO6872牙科陶瓷标准,制备着色和未着色氧化锆陶瓷的三点弯曲强度样品和构筑饰面瓷后的双层瓷样品,核心瓷与饰面瓷的厚度比为1:1.对所获得样品进行三点弯曲强度、断裂韧性和维氏硬度测试.采用X射线衍射(XRD)分析物相结构,扫描电镜(SEM)观察样品的断裂模式.结果:白色氧化锆陶瓷与着色氧化锆陶瓷的三点弯曲强度分别为1301 MPa和1203:MPa,统计学结果显示二者间没有明显差异,构筑饰面瓷后的三点弯曲强度分别为817 MPa和803 MPa,统计学结果显示二者间没有明显差异,但构筑饰面瓷后比单一材料样品强度降低,二者间有显著差异.在所有的双层瓷样品中,断裂模式的应力位移曲线显示为单峰断裂模式,断裂起始于核心瓷的张应力面中心区域同时发生饰面瓷的破碎和瓷层剥脱.结论:对氧化锆粉体的适当着色并没有明显影响材料的机械性能,着色和未着色氧化锆材料与饰面瓷具有良好的物理匹配性.     

Esthetic modification of cast dental-ceramic restorations

The advantages and disadvantages of conventional opaque substructures (eg, metal ceramic restorations) used for creating esthetic complete crown restorations are reviewed, and the esthetic advantages of veneering a translucent crown (Dicor) are considered. An appropriate aluminous veneering porcelain was identified (Vitadur Veneer). This veneer porcelain was chosen to match the thermal coefficient of expansion of the cast glass-ceramic substructure. A flexural strength study was then completed and it showed no difference in the strength of the veneered and nonveneered translucent cast glass-ceramic specimens. Scanning electron microscopy revealed that the interface between the porcelain veneer and cast glass-ceramic substructure had no visible porosity and resulted in a continuous-appearing structure. Potential coping designs, as well as the clinical applications and ramifications of this modified crown, are discussed.     

The influence of various core designs on stress distribution in the veneered zirconia crown: a finite element analysis study

PURPOSE

The purpose of this study was to evaluate various core designs on stress distribution within zirconia crowns.

MATERIALS AND METHODS

Three-dimensional finite element models, representing mandibular molars, comprising a prepared tooth, cement layer, zirconia core, and veneer porcelain were designed by computer software. The shoulder (1 mm in width) variations in core were incremental increases of 1 mm, 2 mm and 3 mm in proximal and lingual height, and buccal height respectively. To simulate masticatory force, loads of 280 N were applied from three directions (vertical, at a 45° angle, and horizontal). To simulate maximum bite force, a load of 700 N was applied vertically to the crowns. Maximum principal stress (MPS) was determined for each model, loading condition, and position.

RESULTS

In the maximum bite force simulation test, the MPSs on all crowns observed around the shoulder region and loading points. The compressive stresses were located in the shoulder region of the veneer-zirconia interface and at the occlusal region. In the test simulating masticatory force, the MPS was concentrated around the loading points, and the compressive stresses were located at the 3 mm height lingual shoulder region, when the load was applied horizontally. MPS increased in the shoulder region as the shoulder height increased.

CONCLUSION

This study suggested that reinforced shoulder play an essential role in the success of the zirconia restoration, and veneer fracture due to occlusal loading can be prevented by proper core design, such as shoulder.     

The influence of the veneering porcelain and different surface treatments on the biaxial flexural strength of a heat-pressed ceramic

STATEMENT OF PROBLEM: The strength of all-ceramic restorations can be adversely affected by surface defects, leading to restoration failures. Additionally, when a 2-layer all-ceramic restoration is required for esthetic purposes, part of the stronger ceramic core material is replaced by veneering porcelain. PURPOSE: This study evaluated the effect of different surface treatments on the strength of a ceramic core material and veneering porcelain, as well as the influence of veneering porcelain on the strength of a 2-layer ceramic structure. MATERIAL AND METHODS: Fifty heat-pressed ceramic cores and 30 veneering porcelain discs (17 mm diameter x 2 mm) were made. From the ceramic core group, 20 discs were selected and reduced to a thickness of 1 mm and veneered with 1 mm of porcelain. These specimens were divided into 2 groups of 10 each. The remaining 30 ceramic core and the 30 veneering porcelain discs were divided into 2 sets of 3 equal sized groups (n=10). Ceramic core groups were prepared for testing having the following surfaces: airborne-particle abrasion, ground, and overglazed. Veneering porcelain groups were tested: as fired (no additional treatment), ground, and overglazed. Biaxial flexural strength was measured using the ball-on-ring test method. All specimens were loaded to fracture. One and 2-way analysis of variance were used to analyze the data (alpha=.05). RESULTS: The ceramic core discs were significantly (P=.001) stronger than the veneering porcelain discs for the airborne-particle abrasion, as-fired, and ground surface treatments (82 +/- 11 MPa vs 51 +/- 8 MPa and 93 +/- 14 MPa vs 60 +/- 6 MPa, respectively). For the overglazed treatment, there was not a significant difference between the core (115 +/- 1 4 MPa) and the veneer materials (107 +/- 14 MPa). The ground 1-layer core was significantly (P=.015) stronger (93 +/- 14 MPa) than the 2-layer with the core tested in tension (72 +/- 19 MPa). There was no significant difference between 1-layer veneer overglazed (107 +/- 14 MPa) and 2-layer discs when tested with the veneer in tension (105 +/- 16 MPa). CONCLUSION: The overglazed surface treatment significantly improved the strength of the materials tested, as well as the strength of 2-layer discs with the veneer in tension. The veneering porcelain influenced the strength of 2-layer specimens only when tested with the ground ceramic core surface in tension.