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

Abstract

Purpose: This study was designed to evaluate three veneering materials for an allceramic 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.Interest in all-ceramic restorations has evolved primarily in response to the esthetic limitations of metal-ceramic restorations. To achieve optimum esthetics, strong all-ceramic cores are veneered with a ceramic material, which is built in successive layers, giving the final restoration individual optical characteristics that can barely be distinguished from the surrounding natural dentition. Successful performance and reliability of these restorations may be limited by mechanical integrity and adhesion of the veneering porcelain to the ceramic substrate. The mechanical properties of the core and veneering porcelains should match to achieve a durable bond.2 The Cohesive Plateau theory states that the strength of a bonded interface should equal the cohesive strength of the substrate with which it is formed. 3 In addition, studies testing the porcelain-to-metal bond strength suggest that shear bond strength (SBS) equal to the shear strength of the veneering porcelain provided an adequate bond. In a study by Kelly et al 5 on the failure behavior of In-Ceram fixed partial dentures, it was reported that failure occurred in the connectors, none from contact damage, with approximately 70% to 78% originating from the cor...

Confocal Raman microscopy and SEM/EDS investigations of the interface between the zirconia core and veneering ceramic: the influence of a liner and regeneration firing

“…Thus, the success of the entire prosthesis depends largely on the physical properties of the metal substructure [26]. Probable factors affecting the interface of zirconia-based restorations include weak infiltration glass [9]. With zirconia core and veneering feldspathic ceramic, an interdiffusion process between the main oxides [zirconium (Zr) and silicon (Si)] has been suggested previously by Aboushelib et al in 2006 [7], Tholey et al in 2009 [19].…”

“…With viscoelastic effect, the residual stress may explain the delaminations encountered in clinical practice [18]. Similarly, well-known factors, such as the surface finish of the core or wetting properties, can affect mechanical retention [6,7,9]. Impurity content, grain size, density and temperature lead to the destabilization of the tetragonal to the monoclinic phase of the zirconia core [19] during the transformation of its crystals during various manufacturing methods [11,19].…”

“…Combining the strength of ceramic cores and the superior aesthetics of a weaker veneer ceramic can result in a reliable and more biocompatible restoration [7]. Which its built-in successive layers, the final restoration gives individual optical characteristics that are barely distinguishable from the surrounding natural dentition [8][9][10].…”

“…Like many authors, he has highlighted the importance of three factors: cooling rate, the thermal expansion coefficient (CTE) [5,6,9,16,17] and thickness of the ceramic. With viscoelastic effect, the residual stress may explain the delaminations encountered in clinical practice [18].…”

Y-TZP zirconia regeneration firing: Microstructural and crystallographic changes after grinding

“…Often during clinical and laboratorial procedures, zirconia frameworks require processing to achieve a better adjustment 8,9) . This is commonly done by means of chemical and/or mechanical manipulations including milling, sandblasting and/or grinding procedures that may induce stresses that promote t→m transformation [10][11][12][13] . Adjustments of zirconia abutments using high or low speed grinding require further studies due to the divergent results in literature 14) .…”