Stress distribution in metal-ceramic crowns with a facial porcelain margin

The use of metal-ceramic restorations with porcelain butt-joint facial margins has increased in the past several years. Although these crowns exhibit improved esthetics compared with metal-ceramic crowns which display a metal gingival collar or metal knife-edge margin, the effectiveness of this design in resisting intra-oral forces is not known. The objective of this study was to analyze the stress distribution induced by simulated intra-oral loads on crowns with variable coping configurations. The copings, with a thickness of either 0.1 or 0.3 mm, were modeled with a facial termination of metal at three locations: at the gingival floor, 0.9 mm above the gingival floor, and 4.2 mm above the gingival floor. The coping and crown dimensions were based on a prepared maxillary central incisor with a facial shoulder and a lingual chamfer. Both Ni-Cr and Au-Pd alloy copings were employed in the crown models. Finite element stress and analyses were performed on crowns which were subjected to several loading conditions. A cement film thickness of 0.030 mm was assumed. For all cases, the stresses which developed in porcelain and cement near the facial and lingual margins due to a vertical load of 200 N were predominantly compressive in nature. For the crowns with Ni-Cr copings, the tensile stress in porcelain ranged from 11.0 MPa (for crowns with a facial metal thickness of 0.3 mm) to 12.5 MPa (for a metal thickness of 0.1 mm). The corresponding stresses for crowns with Au-Pd alloy copings were 8.3 MPa and 8.6 MPa, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of incompatibility stress on the fit of metal-ceramic crowns

The interactive effect of coping thickness and a positive thermal contraction mismatch between metal and porcelain on the fit of metal-ceramic crowns has not yet been experimentally determined. Previous studies have suggested that marginal distortion may be due to contraction differences, although finite element analyses indicate that these distortion effects should be negligible. The marginal gap between metal-ceramic crowns and prepared dies was determined under conditions designed to exaggerate distortion effects. These included the use of thin metal copings (0.1 and 0.2 mm), a chamfer preparation, an alloy with relatively poor creep resistance, and a large thermal contraction mismatch between the alloy and porcelain layers. Gap changes which resulted during porcelain firing cycles were relatively small, but larger marginal discrepancies developed in crowns prepared with a compatible porcelain during grinding and abrasive blasting procedures. This study conclusively demonstrates that incompatibility stress induced by a positive contraction mismatch is not a primary cause of marginal or generalized distortion of metal-ceramic crowns and suggests that external grinding and internal abrasive blasting of crowns are more likely causes of this effect.     

Effect of metal design on marginal distortion of metal-ceramic crowns

An analysis of residual stress and marginal distortion due to thermal contraction mismatch between metal and ceramic is presented for metal-ceramic crowns. Using dilatometric data, finite element stress analyses were performed on pre-molar crowns designed with chamfer-knife edge, chamfer with collar, shoulder with collar, and shoulder-bevel with collar geometries and a maxillary central incisor crown with a chamfer-knife edge geometry. Calculations were made using combinations of a Ni-Cr alloy or a Au-Pd alloy with each of three porcelain products. Calculated marginal distortions due to crown design and metal-porcelain thermal contraction incompatibility were found to be well below experimental values found in the literature. For the cases studied, the calculated marginal distortions due to metal-porcelain thermal contraction mismatch depend primarily on the metal-porcelain combination and are insensitive to the coping design. However, this study excluded copings which have been extensively ground to thicknesses of 0.1 mm or less, and such copings may be more susceptible to localized or generalized distortion.     

A comparison of the porcelain fracture resistance of screw-retained and cement-retained implant-supported metal-ceramic crowns

STATEMENT OF PROBLEM: The presence of a screw opening on the occlusal surface of implant-supported metal-ceramic crowns may decrease the porcelain fracture resistance and shorten the longevity of the crown. PURPOSE: The purpose of this study was to compare the porcelain fracture resistance between screw-retained and cement-retained implant-supported metal-ceramic crowns and to assess whether narrowing the occlusal table or offsetting the screw-access opening affects fracture resistance. MATERIAL AND METHODS: Forty standardized maxillary premolar metal copings were fabricated with a Pd-Ga alloy (Protocol) on an implant abutment. Copings were divided into 4 groups (n=10): Group 1 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening placed in the center of the occlusal surface; Group 2 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening positioned 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group 3 (Cement-retained; occlusal surface buccolingual width=5 mm), copings were not altered; and Group 4 (Cement-retained; occlusal surface buccolingual width=4 mm), copings designed to have a reduced occlusal surface width. All castings were finished with aluminum oxide stones and airborne-particle abraded. Two layers of opaque and dentin porcelain were applied, respectively, on all specimens, which were then glazed. The crown specimens were positioned in a custom testing apparatus and vertically loaded on the middle of the occlusal surface with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. Mean values of load at fracture (Kgf) were calculated in each group and compared with a 1-way analysis of variance and Tukey's Studentized test (alpha=.05). RESULTS: Mean values of loads required to fracture the crowns were as follow: Group 1: 95.01+/-46.6 Kgf; Group 2: 108.61+/-57.9 Kgf; Group 3: 390.94+/-151.3 Kgf; Group 4: 380.04+/-211.8 Kgf. Groups 1 and 2 required a significantly lower force to fracture the crowns compared with Groups 3 and 4 (P=.0001). Comparing Group 1 with 2 (P=.9) and Groups 3 with 4 (P=.6), no significant differences were noted. CONCLUSIONS: Screw-retained implant-supported metal-ceramic crowns demonstrated a significantly lower porcelain fracture resistance than cement-retained crowns. Placing the screw access opening 1 mm offset from the center of the occlusal surface did not result in lower fracture resistance. Cement-retained crowns with 4- or 5-mm buccolingual width of the occlusal surface showed similar porcelain fracture resistance.     

Finite element analysis studies of a metal-ceramic crown on a first premolar tooth

PURPOSE: This study examined the stresses developed during loading in a first premolar metal-ceramic crown made of different metal cores, and used them to anticipate the locations and form of the most likely failure modes. The maximum principal stresses in the porcelain are indicators of fracture, and the von Mises stresses in the metal core are indicators of the location of yielding. MATERIALS AND METHODS: Two-dimensional axisymmetric models with different core metals were analyzed using finite element analyses. An axial load of 600 N was applied vertically downward, over a circular area around the crown's fissure. RESULTS: The peak maximum principal tensile stress in the porcelain existed on the surface of the crown, partially outside the cusp, with the greatest peak in the gold-porcelain system (15.8 MPa). An inverse relationship between the peak maximum principal tensile stress of each system and the elastic modulus of each core material was found. According to evaluation of the critical flaw size for each system, even a crack completely through the thickness of the porcelain was not critical. The maximum von Mises stress existed in the metal coping, on the radial edge at the axial/occlusal line angle, with the highest maximum in the nickel-chromium system (143.9 MPa). There existed a proportional relationship between the maximum von Mises stress in each metal and their respective elastic moduli. All maximums were well below the yield strength of the metal alloys used. CONCLUSION: A greater understanding of the influence of an axial load on the resulting stresses has been achieved, showing that the phenomena of fracture and yielding are unlikely for the crown experiencing this axial load.     

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.     

Influence of finish line design on marginal adaptation of electroformed metal-ceramic crowns

STATEMENT OF PROBLEM: Gold electroformed metal-ceramic restorations have been promoted as alternatives to conventional metal-ceramic restorations. However, little is known about the relationship between tooth preparation design and marginal adaptation for this type of crown. PURPOSE: This study evaluated the influence of 3 different finish line designs on the marginal adaptation of electroformed metal copings and metal-ceramic crowns. MATERIAL AND METHODS: Three steel dies were prepared for maxillary central incisor crowns with 3 finish line designs: shoulder, rounded shoulder, and deep chamfer preparations. Eight standardized electroformed metal-ceramic crowns were fabricated for each group. Marginal discrepancies were measured at 60 points for each specimen along the circumferential margin at 4 sites (labial, mesial, lingual, and distal surfaces, with 15 points for each site) before and after firing procedures using a laser microscope. Data among the 3 different groups were statistically analyzed using the Kruskal-Wallis test and the Mann-Whitney U test with the Bonferroni correction. Marginal discrepancies between prefiring and postfiring procedures were evaluated using the Wilcoxon signed-ranks test (alpha = .05). RESULTS: Significant differences in the marginal discrepancies of electroformed metal copings without porcelain and metal-ceramic crowns were found among all groups. The lowest range of median marginal discrepancy values (P < .05) at 4 sites, both before and after firing, occurred with the deep chamfer preparation (17.64-21.78 microm and 23.96-25.72 microm, respectively). The highest range values were observed in the shoulder preparation (38.13-49.89 microm and 73.87-89.44 microm, respectively). In all situations, the marginal discrepancies of the postfiring procedures were significantly greater (P = .02 or less) than those of the prefiring procedures. CONCLUSION: Within the limitations of this study, the marginal adaptation of electroformed metal copings or metal-ceramic crowns is affected by finish line design and sequentially diminished by porcelain firing procedures.     

A mechanical study on new ceramic crowns and bridges for clinical use

By the recent development of new ceramics, i.e. castable glass ceramics and high strength porcelain, the clinical use of all-ceramic bridges as well as all-ceramic crowns have been expected. The purpose of this study was to evaluate the mechanical properties of new ceramics and to analyze the stress distributions in new ceramic crowns and bridges. The Young's modulus, flexural strength and diametral tensile strength of four types of new ceramics (DICOR, BIORAM-C, OPTEC, and HI-CERAM) were measured, and the fracture loads of new ceramic anterior crowns and bridges on the metal abutments were evaluated. Three dimensional finite element analyses of new ceramic anterior crowns and bridges were also carried out to investigate the effects of various mechanical factors; locations of loading point, types of ceramics, thickness of crowns, luting materials, core materials, and designs of fixed joints. In each experiment, the loading forces were applied at 45 degree to the tooth axis. The results were summarized as follow; 1) DICOR showed the highest flexural strength. HI-CERAM hard core porcelain showed the highest Young's modulus and tensile strength. 2) HI-CERAM crowns showed the highest fracture load among the new ceramic crowns. DICOR bridges were significantly stronger than BIORAM-C bridges. The stress analyses of the experimental cases indicated that the fractures of crowns and bridges occurred by the concentration of tensile stresses. 3) By the load at the incisal edge, the highest tensile stresses were caused in the crown. In the crown with 0.5 mm thickness at axial wall, high tensile stresses were observed at more wide regions of palatal side than in the crown with 0.75 mm or 1 mm thickness. However, in the case with an enamel layer remained on the surface of the abutment tooth, the stresses were reduced in spite of the crown thickness. When the abutment tooth was restored with a metal post and core, the stresses of the crown decreased in comparison with the natural abutment tooth. 4) In case of bridges, high tensile stresses concentrated at the fixed joints under any loading point. The stresses tended to rise slightly according to the increase of the Young's modulus of bridges. The aluminous core material which had high Young's modulus was effective for the reduction of the stresses at the surface of the bridge. Those tensile stresses were reduced remarkably by increasing the thickness of the fixed joints toward the labial and vertical side.(ABSTRACT TRUNCATED AT 400 WORDS)     

肩台瓷在金瓷冠中的临床应用及与其他修复方法的比较

目的 分析肩台瓷金瓷冠修复的临床效果。方法 根据统一标准对92个肩台瓷金瓷冠、36个金沉积烤瓷冠及50个普通金瓷冠的一年后修复效果进行复查，对比评价复查结果。结果 三组间，在颜色、边缘适合性及牙龈健康情况方面无差别，外形方面差异无统计学意义。肩台瓷金瓷冠和金沉积烤瓷冠之间边缘变色方面无差异；牙龈灰线方面差异无统计学意义。肩台瓷金瓷冠或金沉积烤瓷冠与普通金瓷冠之间边缘变色和牙龈灰线方面有显著统计学差异。结论 应用肩台瓷可以提高金瓷冠的美观效果，达到较好的边缘适合性和边缘形态。     

Customization of milled zirconia copings for all-ceramic crowns: a clinical report

Generically milled zirconia copings for all-ceramic crowns may not provide optimal thickness and form for the coping or the porcelain veneer. This article describes the customization of milled zirconia copings to provide even and controlled porcelain thickness with the aim of decreasing cohesive porcelain fracture and other failures. A full-contour waxing and cut back in conjunction with a dual-scan technique was used to ensure adequate coping thickness, adequate, even porcelain thickness, and butt joints at the porcelain-to-coping junctions.     

Influence of incisal length of ceramic and loading orientation on stress distribution in ceramic crowns

For ceramic crowns, the recommended depth of tooth reduction from the incisal edge of anterior teeth is 1.5 mm to 2.0 mm. Although some prosthodontists have suggested that incisal heights of ceramic which exceed 2 mm are associated with dangerously high intra-oral stresses, this theory has not been verified. The objective of this study was to test the hypothesis that the stress distribution in ceramic crowns designed for a prepared maxillary central incisor which are subjected to applied loading is relatively insensitive to the incisal length of ceramic. Finite element stress analyses were performed on three crown designs loaded with a horizontal or vertical force of 200 N along the lingual surface near the incisal edge. Ceramic crowns for maxillary central incisors were modeled with incisal lengths of 1.0 mm (Case I), 1.9 mm (Case II), and 4.0 mm (Case III). Zinc phosphate cement with a film thickness of 30 micron was included for each case. Plane-stress finite element analyses indicated that tensile and compressive stresses which were induced in cement and ceramic due to a vertically applied load of 200 N were comparable in magnitude for all three cases within the gingival third of the crowns. For Cases I, II, and III, tensile stresses at the facial region were 6.7, 5.4, and 6.5 MPa, respectively, in cement and 46.2, 48.6, and 49.2 MPa, respectively, in the ceramic. The results of this study tend to support the hypothesis that the amount of tooth reduction (1 to 4 mm) in an incisogingival direction does not significantly influence the stress distribution in the crown or cement layer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Complete and partial contour zirconia designs for crowns and fixed dental prostheses: a clinical report

Since the introduction of milled zirconia copings for ceramic crowns, a variety of techniques have been introduced to reduce the incidence of chipping or fracturing of the porcelain veneer. These include methods of improving the interface between the coping and the veneer, reducing thermal incompatibility between the two, and optimizing the coping design to minimize tensile loading on the porcelain. Another method of reducing porcelain chipping and fracture is to limit or eliminate the porcelain coverage of zirconia copings and frameworks. Even though patients often demand tooth colored or nonmetallic restorations, they tend to be less concerned with the optimal esthetics of their posterior teeth. This article describes 4 representative clinical situations where efforts were made to minimize or eliminate porcelain coverage on posterior zirconia crowns and a fixed dental prosthesis, while still achieving acceptable, but not optimal, esthetics.     

Influence of core thickness on a restored crown of a first premolar using finite element analysis

PURPOSE: This study examined the influence of ceramic coping thickness on the maximum stresses that arise in a first premolar all-ceramic crown. MATERIALS AND METHODS: Axisymmetric finite element models with different In-Ceram Alumina coping thicknesses (0.3, 0.6, and 0.9 mm) were examined. Models with and without resin lute were constructed. To all models, an identical axial load of 600 N was applied vertically downward, over an area around the crown's fissure. RESULTS: The resulting peak tensile maximum principal stresses in each part of the crown existed below the fracture strengths of the respective materials making up the crown. This was true for all variations of core thickness, with and without resin lute. The peak tensile stresses in the coping, porcelain, and dentin decreased for an increase in core thickness. This was most evident in the porcelain and coping. CONCLUSION: The thickness of the ceramic core has a significant influence on the resulting stresses in the coping, porcelain, and dentin of this axially loaded crown.     

Residual Thermal Stress Simulation in Three‐Dimensional Molar Crown Systems: A Finite Element Analysis

Purpose: To simulate coefficient of thermal expansion (CTE)‐generated stress fields in monolithic metal and ceramic crowns, and CTE mismatch stresses between metal, alumina, or zirconia cores and veneer layered crowns when cooled from high temperature processing. Materials and Methods: A 3D computer‐aided design model of a mandibular first molar crown was generated. Tooth preparation comprised reduction of proximal walls by 1.5 mm and of occlusal surfaces by 2.0 mm. Crown systems were monolithic (all‐porcelain, alumina, metal, or zirconia) or subdivided into a core (metallic, zirconia, or alumina) and a porcelain veneer layer. The model was thermally loaded from 900°C to 25°C. A finite element mesh of three nodes per edge and a first/last node interval ratio of 1 was used, resulting in approximately 60,000 elements for both solids. Regions and values of maximum principal stress at the core and veneer layers were determined through 3D graphs and software output. Results: The metal‐porcelain and zirconia‐porcelain systems showed compressive fields within the veneer cusp bulk, whereas alumina‐porcelain presented tensile fields. At the core/veneer interface, compressive fields were observed for the metal‐porcelain system, slightly tensile for the zirconia‐porcelain, and higher tensile stress magnitudes for the alumina‐porcelain. Increasingly compressive stresses were observed for the metal, alumina, zirconia, and all‐porcelain monolithic systems. Conclusions: Variations in residual thermal stress levels were observed between bilayered and single‐material systems due to the interaction between crown configuration and material properties.     

Marginal adaptation and microleakage of Procera AllCeram crowns with four cements

PURPOSE: This study investigated the effect of different cements on microleakage and marginal adaptation of porcelain crowns. MATERIALS AND METHODS: Eighty extracted molars were divided into two groups. Teeth in one group were prepared to receive Procera AllCeram crowns, whereas the other group was prepared to receive metal-ceramic crowns. Copings were made following standard techniques, and groups were divided for cementation with zinc phosphate, glass-ionomer, resin-modified glassionomer, or resin cement. Specimens were subjected to thermocycling prior to microleakage testing, then sectioned. Microleakage was scored using a five-point scale; marginal adaptation was assessed with a traveling microscope. RESULTS: A significant association was found between cement type and degree of microleakage. With zinc phosphate, 76% of Procera AllCeram and 90% of metal-ceramic copings exhibited extensive microleakage. With glass-ionomer, 49% of Procera AllCeram and 66% of metal-ceramic copings had 0 microleakage scores; with resin-modified glass-ionomer, 10% of Procera AllCeram and 84% of metal-ceramic copings had 0 microleakage scores. With resin cement, 34% of Procera AllCeram and 96% of metal-ceramic copings exhibited 0 microleakage. Procera AllCeram copings had a significantly larger mean marginal gap (54 microm) compared to metal ceramic (29 microm). CONCLUSION: In both types of crowns, the use of resin cement resulted in the highest percentage of 0 microleakage scores, whereas the zinc phosphate cement resulted in the highest percentage of extensive microleakage.     

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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。     

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。     

Tensile stress in glass-ceramic crowns: effect of flaws and cement voids.

The objective of this study was to analyze the relative effect of loading site, occlusal thickness, ceramic flaws, elastic modulus of the cement, and voids in the cement layer on tensile stress that develops in molar glass-ceramic crowns under applied loads. Finite-element stress analyses were performed. Resin cement with a thickness of 0.05 mm was used. A central conical flaw (0.05 mm [diameter] x 0.05 mm) and a circular grooved flaw located under the cusp tips were included in all flaw cases. A void space confined within the occlusal region of the cement layer was also included in selected cases. For a ceramic thickness of 0.5 mm and a vertical distributed load applied at a distance of 1.3 mm from the vertical axis, the maximum tensile stresses were 100 MPa for a crown with flaws and a void, 87 MPa for a crown with no flaws and a void, and 75 MPa for a crown with flaws and no void. For a 1.5-mm-thick crown with flaws and a void, the tensile stress decreased to 22 MPa. When the load of 600 N was concentrated at the central point of the occlusal region, the peak tensile stress in a crown with flaws and no void was increased to 325 MPa. For the conditions analyzed in this study a large void in a flawed occlusal region of a thin molar crown (0.5 mm) is proposed as a mechanism of crown failure.     

氧化锆和纯钛基底冠材料及饰瓷烧结对种植全冠适合性的影响

目的 研究氧化锆和纯钛基底冠材料及饰瓷烧结对种植全冠内部和边缘适合性的影响。方法 制作计算机辅助设计/计算机辅助制作（CAD/CAM）氧化锆烤瓷种植全冠（A组）和纯钛烤瓷种植全冠（B组）各8个（n=8）。分别用硅橡胶轻体复制饰瓷烧结前基底冠和饰瓷烧结后全冠的内部和边缘间隙,采用Micro-CT扫描硅橡胶,建立三维图像,测量冠边缘垂直间隙（MG）、冠边缘水平间隙（HMD）和冠内部轴面中点间隙（AW）。采用SPSS 17.0软件对测量结果进行统计学分析。结果 饰瓷烧结前,A组基底冠MG、HMD和AW均大于B组（P<0.05）。饰瓷烧结后,A组全冠MG小于B组（P<0.05）,两组的HMD和AW均无统计学差异（P>0.05）。饰瓷烧结使A组MG减小（P<0.05）,使B组MG、HMD和AW均增大（P<0.05）,而A组HMD和AW烧结前和烧结后的差异无统计学意义（P>0.05）。结论 氧化锆烤瓷种植全冠边缘适合性优于纯钛烤瓷种植全冠;饰瓷烧结对氧化锆和纯钛烤瓷种植全冠适合性均会产生影响。     

气孔缺陷对磨牙双层全瓷冠力学性能影响的有限元研究

目的研究饰瓷气孔缺陷对磨牙二硅酸锂（LDG）及氧化锆（Y-TZP）双层全瓷冠力学性能的影响。 方法制作上颌第一磨牙LDG双层全瓷冠,使用显微CT扫描并三维重建分析饰瓷内气孔缺陷的尺寸及分布。分别构建上颌第一磨牙LDG及Y-TZP双层全瓷冠三维有限元模型,根据CT数据于饰瓷内添加气孔缺陷并进行加载;A组为对颌牙以200 N加载于牙冠模拟牙尖交错位时的垂直向受力;B组为以200 N与牙长轴呈45°加载于牙冠近、远中舌尖颊斜面,模拟侧方受力;C组为压头垂直位移1 mm加载于牙冠中央窝,模拟体外实验中的加载;计算最大主应力并分析气孔缺陷对其数值的影响。 结果LDG与Y-TZP在各载荷条件下的应力分布近似;垂直向加载时牙尖接触区应力集中,最大应力分别为51.683、50.084 MPa,存在气孔时,应力集中于牙尖接触应力区的气孔缺陷,最大应力上升至290.72、285.92 MPa;45°斜向加载时拉应力集中于核瓷颈部,气孔缺陷无应力集中,最大应力不变;体外加载时中央窝、沟及加载点应力集中,最大应力为107.3、125.41 MPa,存在气孔时,应力集中于拉应力区的气孔缺陷,最大应力上升至359.93、322.39 MPa。 结论饰瓷气孔缺陷对双层全瓷冠应力分布的影响与受载方式有关,位于拉应力集中区的气孔缺陷是导致冠失效的因素。