Evaluation of shear bond strength between zirconia core and ceramic veneers fabricated by pressing and layering techniques: In vitro study

A comparative evaluation of shear bond strength between feldspathic porcelain and lithium di silicate ceramic layered to a zirconia core- An in vitro study

Background

The bond strength between the zirconia core and ceramic veneer is the weakest component in the layered structure. Delamination of veneering ceramic is reported as one of the most frequent problems associated with Veneered Zirconia restorations. The aim of this study is to compare the shear bond strength of lithium di silicate porcelain to that of feldspathic porcelain on a zirconia Substrate.

Material and Methods

Two groups (group A and B) of zirconia blocks with each group having 20 samples were fabricated according to Schmitz Schulmeyer method. Group A (n =20 ) samples were veneered with feldspathic veneering porcelain and Group B (n=20) samples were veneered with heat pressed lithium disilicate ceramic. The fabricated samples were then evaluated for shear bond strength in Universal Testing Machine. The values were then statistically analyzed using independent sample t-test.

Results

Results of the current study showed that mean shear bond strength of feldspathic porcelain 11.40±1.29 MPa is comparatively lower than the mean shear bond strength of the lithium disilicate group 18.81±1.76 MPa. The statistical analysis indicated that (p value<0.01) there is a statistically significant difference in the shear bond strength between the two groups.

Conclusions

The heat pressed lithium disilicate veneering materials has a better shear bond strength compared to feldspathic veneering ceramic material when layered to a zirconia core and it can be used as a viable alternative material to feldspathic porcelain layering material in bilayered zirconia restorations. Key words:Zirconia, bilayered ceramics, lithium disilicate , shear bond strength, ceramic chipping.

Does veneering technique affect the bond strength of bilayer Y-TZP? A systematic review and meta-analysis

STATEMENT OF PROBLEM

Reasons for failures of bilayer yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations include the core-veneer interface bond strength. The influence of the veneering method on the bond strength of veneered Y-TZP is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the effect of the veneering method on the bond strength of bilayer Y-TZP.

MATERIAL AND METHODS

This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Searches were performed on PubMed/MEDLINE, Web of Science (Core Collection), and Scopus for in vitro studies evaluating the effect of the veneering technique on the bond strength of bilayer Y-TZP. Statistical analyses were performed with random-effect models (α=.05).

RESULTS

From 619 identified studies, 140 were selected for full-text analysis and 16 were included. Manual searching yielded no additional articles. The meta-analyses comprised 15 studies, and 1 study was included only in the descriptive analysis. Meta-analyses compared the hand-layered method (control) with pressed, fused, and cemented veneering methods. The fused and cemented techniques were analyzed by using subgroups assessing the veneering ceramic type (predominantly glass-ceramics and particle-filled glass-ceramics). Similar bond strength results (P=.540) were found for pressed and hand-layered veneered Y-TZP specimens. Fused veneers achieved higher bond strength values (P<.001) than the hand-layered veneers on Y-TZP frameworks, irrespective of the veneering ceramic type (predominantly glass-ceramics: P=.002; particle-filled glass-ceramics: P<.001). Global and subgroup analyses indicated that lower core-veneer bond strength values (P<.001) were found for cemented in relation to hand-layered veneers.

CONCLUSIONS

Core-veneer interfacial adhesion was equivalent for pressed and hand-layered veneering techniques. Improved bond strength, regardless of the veneer ceramic material type, was achieved by the fused veneering method, which seems to be a promising choice for the veneering of Y-TZP. In contrast, the cemented method may be unsuitable for veneering Y-TZP structures because of its lower bond strength than the hand-layered veneering technique.

Shear Bond Strength of Porcelain to a Base-Metal Compared to Zirconia Core

STATEMENT OF PROBLEM

Recent clinical results for Zirconia all-ceramic restorations have revealed that the fracture rate 6-15% of the Zirconia framework is so low and the core of Zirconia has high stability. However, chipping-off fractures of porcelain are the most common reason for failures of Zirconia in the fixed partial dentures.

OBJECTIVES

The purpose of this study was to compare the shear bond strength (SBS) of porcelain in the porcelain fused to metal and all-ceramic crowns with Zirconia core.

MATERIALS AND METHODS

Two groups were selected: porcelain fused to metal (PFM) and porcelain fused to Zirconia (PFZ) (n = 30).In the PFM group, a wax model (10 × 10 × 10mm)was used to cast metal base (Ni_Cr alloy). In the PFZ group, an acrylic cubic model (10 × 10 × 10mm) was made as Zirconia model for scanning.15 cubic Zirconia samples were milled by CAD-CAM. The procedure of porcelain veneering was conducted by the conventional layering technique up to 2 mm thickness (2.5 × 2.5 × 2 mm). All specimens were stored in water for 48 hrs. Thermal cycling was conducted for 20000 cycles between 55°C and 5ºC alternatively for 30s.All samples were mounted in acrylic resin and the SBS test was performed, using a universal testing machine. The analysis of data was performed at a significance level of 0.05 using Kolmogorov-Smirnov and Mann-Whitney U-test.

RESULTS

Mean of SBS in PFM and PFZ was 24.57 and 20.88, respectively. The results of Mann-Whitney test showed that there was no statistically significant difference between the two groups of porcelain fused to metal and Zirconia in item shear bond strength (p = 0.455).

CONCLUSIONS

There was no significant difference between the two groups of PFM and PFZ in the item SBS.