Bond Strength,Microhardness, and Core/Veneer Interface Quality of an All‐Ceramic System

Purpose: This study was designed to evaluate three veneering materials for an all‐ceramic alumina system in terms of bond strength, microhardness, and core/veneer interface quality. Materials and Methods: Fifteen In‐Ceram cores were constructed for this study, forming three groups of five specimens each divided by the veneering ceramic disc fired on the occlusal surface of the alumina core: Vitadur N, Vitadur Alpha, or VM7. The specimens underwent shear bond and microhardness testing. Gross examination of debonded discs by SEM and EDAX analysis was conducted. Data for shear bond strength (SBS) and microhardness were presented as means and standard deviation (SD) values. One‐way ANOVA and Duncan's post hoc test were used for pairwise comparison between the means when ANOVA test was significant. Results: VM7 showed the highest shear bond value and lowest microhardness values of the three tested veneering materials. No statistically significant difference was evident between the SBSs of Vitadur N and Vitadur Alpha to the alumina cores. Vitadur Alpha showed statistically the highest mean VHN, followed by Vitadur N, while VM7 showed statistically the lowest mean values of VHN. Conclusions: In‐Ceram core/Vitadur N disc debondings appeared to be interfacial by complete delaminations, leaving a shiny visible and quite distinct area, whereas there appeared to be perfect adhesion between the core and VM7 veneering material. VM7 appeared to possess ultra‐fine texture with intimate contact to the core, forming what seemed like a transition zone where the ceramic and core appeared to blend for a distance. VM7's finer particle size has improved the core/veneer bond strength and decreased micohardness values. This new veneering material will probably enhance the performance and esthetics of the In‐Ceram system.     

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.     

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

Effect of Veneering Techniques on Color and Translucency of Y‐TZP

Purpose: This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria‐stabilized tetragonal zirconia polycrystalline (Y‐TZP) all‐ceramic restorations. Materials and Methods: Thirty disc specimens (10‐mm diameter, 0.50 ± 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10‐mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat‐pressing IPS e.max ZirPress fluorapatite glass‐ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low‐fusing nano‐fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (τ) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (ΔE) were calculated using color difference formula. One‐way analysis of variance (ANOVA) combined with a Tukey multiple‐range test were used to analyze the data (α= 0.05). Results: As to ZP, ZPC, and ZC groups, the value of a* increased (?1.35 ± 0.07, ?0.64 ± 0.06, ?0.36 ± 0.05, respectively) (p < 0.05); b* decreased (27.01 ± 0.07, 25.48 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 ± 0.08, 25.49 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 ± 0.48, 1.64 ± 0.03, respectively), and lowest in ZPC group (82.14 ± 0.18, 1.47 ± 0.01, respectively) (p < 0.05). Conclusions: Y‐TZP all‐ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.     

Influence of Veneering Materials on the Marginal Fit and Fracture Resistance of an Alumina Core System

Purpose: This study was undertaken to assess the influence of three‐veneering materials on the marginal fit, fracture resistance, and failure pattern of In‐Ceram alumina crowns. Materials and Methods: Forty In‐Ceram cores were constructed and divided into four groups of ten each. Ten alumina cores were left unveneered, forming the first group for core testing, while the other 30 copings were divided into three groups depending on the veneering material used. The vertical marginal gaps of the alumina copings were measured before and after veneer placement at 16 sites using an optical microscope. The specimens were then loaded to fracture at a crosshead speed of 1 mm/min. Fractured specimens were examined, and the fracture patterns of the crowns were recorded. Selected specimens were examined using scanning electron microscope. Data were presented as means and standard deviation values. One‐way ANOVA was used to compare between mean gap areas and fracture resistance of the three materials. Duncan's post hoc test was used for pairwise comparison between the means when ANOVA test was significant. Results: Vitadur‐N‐veneered crowns showed statistically the highest mean vertical gaps, while no significant difference was evident between the marginal fits of Vitadur‐α‐ and VM7‐veneered crowns. Regarding the strength, a statistically significant decrease in fracture resistance of the cores was evident after veneering with Vitadur‐N; however, no significant change in mean fracture resistance value of Vitadur‐α‐ and VM7‐veneered crowns was evident compared to the alumina cores. VM7‐veneered crowns showed the highest fracture resistance values. Conclusions: Vitadur‐N‐veneered crowns showed the highest mean vertical gaps and the lowest mean fracture resistance values of the tested groups, while VM7‐veneered crowns combined the highest fracture resistance values and clinically acceptable margins. The best interface quality and finest ceramic texture were evident in case of VM7 material.     

Flexural strength and internal defects of some dental porcelains

The flexural strength, number (n), size, and form of pores in seven different dental porcelains were examined. The flexural strength was approximately 100 MPa for the core materials for metal bonding, 116 MPa for traditional alumina porcelains (NBK 1000, Vitadur N), 150 MPa for two new high-alumina porcelains (Vita Hi Ceram, Cerestore), and 240 MPa for a castable glass (Dicor). The mean pore diameter was approximately 10 microns in all porcelains except Dicor, but with a large and varying range. Dicor showed a mean pore size of 1 micron. The pore density varied from 36.5/mm2 in one of the porcelains for metal bonding to 4367/mm2 in Cerestore. The mean cross-sectional area occupied by pores was below 10% for most porcelains except Vitadur N and Cerestore, showing 17.5% and 32.5%, respectively. No correlation was found between flexural strength and frequency or cross-sectional area of pores of the various products.     

The Effect of Multiple Firings on Microtensile Bond Strength of Core‐Veneer Zirconia‐Based All‐Ceramic Restorations

Purpose: Differences in core and veneer coefficients of thermal expansion, firing shrinkage, and speed of increasing and decreasing the temperature may generate stress in veneered all‐ceramic restorations. Given the necessity of performing multiple firing cycles to achieve improved contour, color, and esthetics, the purpose of this study was to determine the effect of multiple firing cycles on the microtensile bond strength (MTBS) of zirconia core to the porcelain veneer in zirconia‐based all‐ceramic restorations. Materials and Methods: Thirty blocks (12 × 12 × 4 mm³) of semi‐sintered zirconia were machined and sintered according to manufacturer's instruction. Specimens were placed in three groups based on the number of firing cycles (4, 6, 8) for the veneering process. After veneering, the specimens were sectioned into microbars with 8 mm length and 1 mm cross‐section. Twenty sound microbars in each group were stressed to failure in a microtensile tester machine at 1 mm/min. Fractured specimens were surveyed under a scanning electron microscope and classified as cohesive in core, cohesive in veneer, and mixed. MTBS data were analyzed using one‐way ANOVA and Tukey test (p < 0.05). Results: The mean MTBS (MPa) after 4, 6, and 8 firing cycles were 30.33 ± 2.13, 27.43 ± 1.79, and 25.06 ± 1.76, respectively. There was a statistically significant difference between the bond strengths of each of the three groups (p < 0.001). Conclusion: Increase in firing cycles decreased MTBS. Most of the failures (90–95%) in all three groups were cohesive in the veneering porcelain and did not change as the number of firing cycles increased.     

Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE

The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia.

MATERIALS AND METHODS

Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (α≤.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (α≤.05).

RESULTS

The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups.

CONCLUSION

The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.     

GI-Ⅱ型着色玻璃渗透后渗透陶瓷的性能测试

目的 :探讨用GIⅡ型着色渗透玻璃渗透后的渗透陶瓷底层材料的热膨胀性能、机械力学性能和密度 ,为材料性能的改进和临床应用奠定基础。方法 :选用GIⅡ型着色渗透玻璃的IG2色玻璃料及GIⅡ型氧化铝粉体 ,制作氧化铝基体及渗透陶瓷样本 ,在TMA2940型热分析仪上绘制样本的热膨胀曲线 ,计算热膨胀系数 ;三点弯曲法测定渗透陶瓷材料的挠曲强度和弹性模量 ,显微压痕法测量断裂韧性和维氏硬度 ;重量体积法测定其密度。结果 :渗透陶瓷的热膨胀系数为 7.620×10(6)℃(-1)（2 5～ 5 0 0℃ ） ,略高于Vitaduralpha饰面瓷的热膨胀系数。材料的三点挠曲强度、弹性模量、维氏硬度、显微断裂韧性和密度分别为 389.6MPa、92GPa、9.409GPa、3.2425MNm3/2和3.662g/cm3 。结论 :用GIⅡ型着色渗透玻璃渗透后的渗透陶瓷底层材料 ,其热膨胀性能与Vitaduralpha饰面瓷匹配 ,机械强度也达到了临床应用的要求。     

不同表面处理方法对氧化锆基底材料与饰面瓷结合强度的影响

目的 比较不同表面处理方法对氧化锆基底与饰面瓷之间的结合强度及结合界面微观结构的影响。方法 将WIELAND氧化锆瓷块胚体烧结制成10 mm×5 mm×5 mm大小试件33个。将试件随机分为3组,每组11个。喷砂组在烧结前进行喷砂处理;处理剂组先喷砂处理,再烧结结合衬底瓷;对照组不做处理。3组基底瓷材料采用粉浆涂塑法烧结5 mm×5 mm×5 mm大小的饰面瓷。每组随机抽取1个基底瓷及双层瓷试件,采用扫描电镜、能谱分析方法,研究氧化锆底瓷与饰面瓷之间的结合情况。其余试件则通过电子拉伸机测试结合界面的剪切强度,并用SPSS 17.0软件对实验数据进行统计学分析。结果 喷砂组、处理剂组、对照组试件的剪切强度分别为（18.06±0.59）、（21.04±1.23）、（13.80±1.54） MPa,各组间差异均有统计学意义（P<0.01）。结论 氧化锆胚体烧结前喷砂处理能提高氧化锆基底冠与饰面瓷的结合强度,结合衬底瓷的应用能提高氧化锆基底冠与饰面瓷的结合强度。     

硅藻土基底瓷与饰面瓷厚度比对抗弯强度的影响

目的:探讨不同基底瓷与饰面瓷厚度比对硅藻土基全瓷材料结合强度的影响。方法:硅藻土基底瓷尺寸为16 mm×5. 4 mm×1 mm,随机分为4组,表面堆塑不同厚度的IPS e.max饰面瓷,分别为不烧结（A组）、0.6 mm（B组）、0.8 mm（C组）和1.0 mm（D组）,测定不同分组的抗弯强度并观察陶瓷试件的断裂模式,扫描电镜观察断面显微形貌。采用SPSS 17.0软件包对数据进行单因素方差分析。结果:随着饰面瓷厚度的增加,抗弯强度也随之增强,其中C组抗弯强度最大,达到（277.24±15.47） MPa。结论:基底瓷与饰面瓷厚度比可显著影响硅藻土基底瓷与饰面瓷的抗弯强度。     

The effect of surface treatment of the interfacial surface on fatigue-related microtensile bond strength of milled zirconia to veneering porcelain

Purpose: The success of zirconia‐reinforced all‐ceramic crowns depends on the formation of a stable bond between the zirconia core and the veneering porcelain. The purpose of this study was to test the effects of liner application and airborne particle abrasion of a postsintered Y‐TZP core on the bond strength between the zirconia core and veneering porcelain with or without cyclic loading. Materials and Methods: Kavo Everest® Y‐TZP blank disks were sintered and divided into three treatment groups: airborne particle abrasion, IPS e.max® Ceram Zirliner application, or no surface treatment. The disks were then veneered with IPS e.max® ZirPress veneering porcelain. Half the veneered disks from each group were cyclically loaded. This created six experimental groups: three surface treatment groups cyclically loaded and three not loaded. The disks were then sectioned into microbars for microtensile bond strength (MTBS) testing (40 specimens per group). Specimens were luted to a fixture mount and loaded to failure using a universal testing machine (MTS Insight). The maximum force was measured and bond strength computed. Data were analyzed with a two‐way ANOVA and Tukey's HSD test (α= 0.05). Results: Airborne particle abrasion significantly decreased MTBS values (p= 0.043), and ZirLiner application did not have a significant effect on MTBS values compared to control. Cyclic loading did not have a significant effect on MTBS values. The predominant failure mode in all groups was mixed. Conclusions: Airborne particle abrasion of the interfacial surface of the Everest® Y‐TZP core significantly decreased the MTBS to ZirPress veneering porcelain when compared to no interfacial surface treatment. Application of ZirLiner to the interfacial surface of the Everest® Y‐TZP core did not significantly increase or decrease the MTBS to ZirPress veneering porcelain, compared to the other surface treatments. Cyclic loading did not affect bond strengths in any of the groups, regardless of surface treatment. Neither cyclic loading nor surface treatment affected the failure mode of the specimens.     

Interface bond and compatibility between GI-II glass/alumina composite and Vitadur alpha veneering porcelain]

OBJECTIVE: Multiple layer techniques were commonly employed in fabricating all-ceramic restorations. Bond and compatibility between layers were vitally important for the clinical success of the restorations. The purposes of this study were to investigate the bond of the interface between the GI-II glass/alumina composite and Vitadur alpha veneering porcelain, and to study the thermal compatibility between them. METHODS: Prepared a bar shaped specimen of GI-II glass/alumina composite 25 mm x 5 mm x 1 mm in size, with bottom surface pre-notched. The upper surface was veneered with Vitadur alpha veneering porcelain (0.2 mm opaque dentin and 0.6 mm dentin porcelain), then fractured and the fracture surface were examined under scanning electron microscope (SEM) and electron microprobe analyzer (EMPA) with electron beam of 10 micrometer in diameter; ten all-ceramic single crowns for an upper right central incisor were fabricated and the temperatures of thermal shock resistance were tested. RESULTS: SEM observation showed tight bond between the composite and the porcelain; The results of EMPA showed that penetration of Na, Al elements from glass/alumina into veneering porcelain and Si, K, Ca elements from veneering porcelain into glass/alumina occurred after sintering baking; The temperature of thermal shock resistance for anterior crowns in this study was 158 +/- 10.3 degrees C, cracks were mainly distributed in veneering porcelain with thicker layer. CONCLUSIONS: Chemical bond exists between the GI-II glass/alumina composite and Vitadur alpha veneering porcelain, and there is good thermal compatibility between them.     

Effect of Preparation Taper,Height and Marginal Design Under Varying Occlusal Loading Conditions on Cement Lute Stress: A Three Dimensional Finite Element Analysis

The functional surfaces of the porcelain fused to metal fixed partial dentures are often abraded to adjust occlusion, such restorations are often found to fail in service. This study was therefore conducted to study the effect of surface abrasion on flexural strength of glazed porcelain fused to metal samples. It was also the aim of this study to find the effect of re-glazing on flexural strength of abraded samples. A total of ninety glazed porcelain fused to metal bar samples of the dimension 15 mm × 2 mm × 1.5 mm were fabricated. These samples were then divided into three groups (30 samples each) according to the surface treatments: group A-glazed (control); group B-abraded and group C-abraded and then re-glazed (self-glazed). Flexural strength was measured by using three point bend test on universal testing machine (texture analyser) with a cross-head speed of 0.6 mm/min. Peak force at the time of failure for all the samples was recorded. Statistical analysis found that mean flexural strength was highest for group A-80.65 ± 12.81 MPa; as compared to group B-74.18 ± 10.74 MPa and group C-77.85 ± 9.39 MPa. Student’s t test indicated that the difference in the flexural strength between groups A and B was significant while it was non-significant between groups B and C and also between groups A and C. The ‘f’ test indicated that the difference between the groups was non-significant. This study therefore showed that there is a marked decrease in the flexural strength of the porcelain fused to metal restorations after occlusal abrasion. The study also found that reglazing of these restorations may not restore their flexural strength significantly.     

Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography.

OBJECTIVES: The aim of this study was to test the hypothesis that the flexural strengths and critical flaw sizes of dental ceramic specimens will be affected by the testing environment and stressing rate even though their fracture toughness values will remain the same. METHODS: Ceramic specimens were prepared from an aluminous porcelain (Vitadur Alpha; VITA Zahnfabrik, Bad S?ckingen, Germany) and an alumina-zirconia-glass composite (In-Ceram Zirconia; VITA Zahnfabrik). Three hundred uniaxial flexure specimens (150 of each material) were fabricated to dimensions of 25 mmx4 mmx1.2 mm according to the ISO 6872 standard. Each group of 30 specimens was fractured in water using one of four different target stressing rates ranging on a logarithmic scale from 0.1 to 100 MPa/s for Vitadur Alpha and from 0.01 to 10 MPa/s for In-Ceram Zirconia. The fifth group was tested in inert environment (oil) with a target stressing rate of 100 MPa/s for Vitadur Alpha and 1000 MPa/s for In-Ceram Zirconia. The effects of stressing rate and environment on flexural strength, critical flaw size, and fracture toughness were analyzed statistically by Kruskal-Wallis one-way ANOVA on ranks followed by post hoc comparisons using Dunn's test (alpha=0.05). In addition, 20 Vitadur Alpha specimens were fabricated with controlled flaws to simplify fractography. Half of these specimens were fracture tested in water and half in oil at a target stressing rate of 100 MPa/s, and the results were compared using Mann-Whitney rank sum tests (alpha=0.05). A logarithmic regression model was used to determine the fatigue parameters for each material. RESULTS: For each ceramic composition, specimens tested in oil had significantly higher strength (P0.05). Specimens tested at faster stressing rates had significantly higher strength (P0.05). Regarding critical flaw size, stressing rate had a significant effect for In-Ceram Zirconia specimens (P0.05). Fatigue parameters, n and lnB, were 38.4 and -12.7 for Vitadur Alpha and were 13.1 and 10.4 for In-Ceram Zirconia. SIGNIFICANCE: Moisture assisted subcritical crack growth had a more deleterious effect on In-Ceram Zirconia core ceramic than on Vitadur Alpha porcelain. Fracture surface analysis identified fracture surface features that can potentially mislead investigators into misidentifying the critical flaw.     

Effect of airborne-particle abrasion and mechanico-thermal cycling on the flexural strength of glass ceramic fused to gold or cobalt-chromium alloy

Purpose: To evaluate the effect of airborne‐particle abrasion and mechanico‐thermal cycling on the flexural strength of a ceramic fused to cobalt–chromium alloy or gold alloy. Materials and Methods: Metallic bars (n = 120) were made (25 mm × 3 mm × 0.5 mm): 60 with gold alloy and 60 with Co–Cr. At the central area of the bars (8 mm × 3 mm), a layer of opaque ceramic and then two layers of glass ceramic (Vita VM13, Vita Zahnfabrick) were fired onto it (thickness: 1 mm). Ten specimens from each alloy group were randomly allocated to a surface treatment [(tungsten bur or air‐particle abrasion (APA) with Al₂O₃ at 10 mm or 20 mm away)] and mechanico‐thermal cycling (no cycling or mechanically loaded 20,000 cycles; 10 N distilled water at 37°C and then thermocycled 3000 cycles; 5°C to 55°C, dwell time 30 seconds) combination. Those specimens that did not undergo mechanico‐thermal cycling were stored in water (37°C) for 24 hours. Bond strength was measured using a three‐point bend test, according to ISO 9693. After the flexural strength test, failure types were noted. The data were analyzed using three factor‐ANOVA and Tukey's test (α= 0.05). Results: There were no significant differences between the flexural bond strength of gold and Co–Cr groups (42.64 ± 8.25 and 43.39 ± 10.89 MPa, respectively). APA 10 and 20 mm away surface treatment (45.86 ± 9.31 and 46.38 ± 8.89 MPa, respectively) had similar mean flexural strength values, and both had significantly higher bond strength than tungsten bur treatment (36.81 ± 7.60 MPa). Mechanico‐thermal cycling decreased the mean flexural strength values significantly for all six alloy‐surface treatment combinations tested when compared to the control groups. The failure type was adhesive in the metal/ceramic interface for specimens surface treated only with the tungsten bur, and mixed for specimens surface treated with APA 10 and 20 mm. Conclusions: Considering the levels adopted in this study, the alloy did not affect the bond strength; APA with Al₂O₃ at 10 and 20 mm improved the flexural bond strength between ceramics and alloys used, and the mechanico‐thermal cycling of metal‐ceramic specimens resulted in a decrease of bond strength.     

Effect of Surface Treatment on Shear Bond Strength of Zirconia to Human Dentin

Purpose: The effect of surface treatment using tribochemical silica coating/silane coupling on the shear bond strengths of (1) a glass‐infiltrated, zirconia‐reinforced alumina (In‐Ceram Zirconia) and (2) a yttria‐stabilized zirconia ceramic (YZ Zirconia) to human dentin was studied. Materials and Methods: Twelve specimens of each ceramic were randomly assigned to one of three surface treatments: (1) no surface treatment (control group); (2) a chairside tribochemical silica coating/silane coupling system (CoJet group); and (3) a laboratory tribochemical silica coating/silane coupling system (Rocatac group). The mode of failure of each specimen was determined under magnification. Results: The shear bond strengths (mean ± SD) of In‐Ceram Zirconia of the control, CoJet and Rocatec groups were 5.7 ± 4.3 MPa, 11.4 ± 5.4 MPa, and 6.5 ± 4.8 MPa, respectively. The corresponding figures for YZ Zirconia were 8.2 ± 5.4 MPa, 9.8 ± 5.4 MPa, and 7.8 ± 4.7 MPa. Two‐way ANOVA revealed significant differences in bond strength due to the difference in surface treatment (p= 0.02), but the bond strengths between the two ceramics were not significantly different (p= 0.56). Post hoc tests showed that In‐Ceram Zirconia treated with CoJet had significantly higher shear bond strengths than those untreated (p < 0.05) or treated with Rocatec (p < 0.05). Surface treatment did not affect the shear bond strength of YZ Zirconia significantly (p > 0.05). Conclusion: The bonding of In‐Ceram Zirconia can be improved by the chairside surface treatment system.     

Biaxial flexural strength of the bilayered disk composed of ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) and veneering porcelain

Objective

Herein we investigated the flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks using different veneering porcelains.

Shear bond strength of veneering porcelain to zirconia and metal cores

STATEMENT OF PROBLEM

Zirconia-based restorations have the common technical complication of delamination, or porcelain chipping, from the zirconia core. Thus the shear bond strength between the zirconia core and the veneering porcelain requires investigation in order to facilitate the material''s clinical use.

PURPOSE

The purpose of this study was to evaluate the bonding strength of the porcelain veneer to the zirconia core and to other various metal alloys (high noble metal alloy and base metal alloy).

MATERIAL AND METHODS

15 rectangular (4×4×9mm) specimens each of zirconia (Cercon), base metal alloy (Tillite), high noble metal alloy (Degudent H) were fabricated for the shear bond strength test. The veneering porcelain recommended by the manufacturer for each type of material was fired to the core in thickness of 3mm. After firing, the specimens were embedded in the PTFE mold, placed on a mounting jig, and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.5mm/min until fracture. The average shear strength (MPa) was analyzed with the one-way ANOVA and the Tukey''s test (α= .05). The fractured specimens were examined using SEM and EDX to determine the failure pattern.

RESULTS

The mean shear strength (± SD) in MPa was 25.43 (± 3.12) in the zirconia group, 35.87 (± 4.23) in the base metal group, 38.00 (± 5.23) in the high noble metal group. The ANOVA showed a significant difference among groups, and the Tukey''s test presented a significant difference between the zirconia group and the metal group. Microscopic examination showed that the failure primarily occurred near the interface with the residual veneering porcelain remaining on the core.

CONCLUSION

There was a significant difference between the metal ceramic and zirconia ceramic group in shear bond strength. There was no significant difference between the base metal alloy and the high noble metal alloy.     

To Evaluate the Effect of Various Surface Treatments on the Shear Bond Strength of Three Different Intraoral Ceramic Repair Systems: An In Vitro Study

Fractures of metal-ceramic restoration pose an esthetic and functional dilemma both for patient and the dentist. Intraoral repair systems eliminate the remake and removal of restoration. Many intraoral repair materials and surface treatments are available to repair intraorally fractured metal-ceramic restoration. Bond strength data of various materials and specific technique used for repair are necessary for predicting the success of a given repair system. This study evaluated the shear bond strength of three different intraoral repair systems for metal-ceramic restorations applied on exposed metal and porcelain surface. One hundred and twenty metal discs (20 mm in diameter × 0.7 mm thick) were fabricated with nickel–chromium alloy (Mealloy, Dentsply, USA). Feldspathic porcelain (Duceram, Degudent, Germany) were applied over one test surface of the discs in the thickness of 1.8 mm followed by conventional firing. The defect, which simulates clinical failures were created in 1/4th area of the metal-ceramic discs. The metal-ceramic discs samples were divided into ceramic substrate (Group I, n = 60) and metal substrate (Group II, n = 60), according to the defect location. Then, samples of ceramic substrate (Group I) and metal substrate (Group II) were subdivided into A, B according to the surface treatments (A; roughening with diamond bur and B; abraded with 50 μ Al₂O₃) and repaired with one of the intraoral repair systems tested (a. Ceramic repair system, Ivoclar Vivadent; b. Clearfil repair system, Kurary, c; Porcelain repair system, 3 M ESPE). All the repaired samples were stored in distilled water at 37 °C for 24 h. After thermocycling at 6–60° C, all the samples were stored at 37 °C for additional 7 days. Shear bond strength of all the samples were calculated by using Universal testing machine. The mean shear bond strength values for the group I (A/B) were as follows: Ceramic repair system (9.47 ± 1.41/14.03 ± 2.54 MPa), Clearfil repair system (14.03 ± 2.32/14.64 ± 2.28 MPa), and Porcelain repair system (14.41 ± 3.96/14.86 ± 3.10 MPa). The mean shear bond strength values for the group II (A/B) were as follows: Ceramic repair system (9.42 ± 1.44/18.61 ± 2.60 MPa), Clearfil repair system (14.44 ± 3.23/14.98 ± 2.73 MPa), and Porcelain repair system (11.86 ± 2.24/13.24 ± 2.72 MPa). Air abrasion with 50 μm aluminum oxide particles is the preferred surface treatment. Porcelain repair system showed the highest shear bond with air abrasion for ceramic substrate and for metal substrate Ceramic repair system showed the highest bond strength with air abrasion as a surface treatment. This study suggest that the three repair systems tested are adequate for intraoral chairside repair of metal-ceramic restoration when air abrasion is used for surface treatment of the substrate (Ceramic repair system, Ivoclar Vivadent, Germany; Clearfil repair system, Kurary, Japan; Porcelain repair system, 3M ESPE, Germany).