Veneered Zirconia-Based Restorations Fracture Resistance Analysis

Interface adhesion on layered zirconia: Effects of the veneering ceramic material and veneering technique

PURPOSE

To evaluate the effect of different veneering ceramics and veneering techniques on the bond strength to zirconia.

MATERIALS AND METHODS

3Y-TZP zirconia blocks were sliced into 60 slabs, polished, and sintered. Each slab received one ceramic cylinder (Ø = 3.4 mm, 5 mm-high), according to the veneering ceramic type (feldspathic-FEL or lithium disilicate-based-LD) and the veneering technique (file-splitting with resin-based luting agent-RC, file-splitting with fusion ceramic-FC, or heat-pressing-HT), which resulted in six groups: FEL-RC, FEL-FC, FEL-HT, LD-RC, LD-FC, LD-HT. After preparation, the samples were immersed in distilled water for 24 h before the shear bond strength (SBS) test. The failure modes were classified as adhesive, predominantly adhesive, or cohesive. Representative failure mode images were taken in a Scanning Electron Microscope. The SBS data were analyzed by two-way ANOVA and Tukey's test.

RESULTS

Both type of veneering ceramic and technique affected the bond strength. FC led to the highest SBS values. RC and HP provided similar results when compared within each veneering ceramic. Lithium disilicate achieved lower bond strength than feldspathic ceramic when the heat-pressing technique was applied. The most frequent failure modes were predominantly adhesive and adhesive for FEL and LD, respectively.

CONCLUSION

File-splitting with fusion ceramic provided the highest adhesion to zirconia when feldspathic or lithium disilicate-based ceramics were used. The heat-pressing technique for veneering with lithium disilicate significantly decreased the bond strength when compared to the feldspathic ceramic.

Four-point flexural strength and microtensile bond strength of digitally and conventionally veneered zirconia

This study intended to evaluate the effect of digital veneering on four-point flexural strength (FS) and microtensile bond strength (μTBS) of veneered zirconia. Two different zirconia blocks, a lithium disilicate and a feldspathic ceramic block, and two different layering ceramics were used. IPS e.max Zir CAD (ZC) and Vita In-Ceram YZ (YZ) with yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were used as substructures. IPS e.max CAD (LD), Vita Mark II (VMII), IPS e.max Ceram (EC) and Vita VM9 (VM9) were used for veneering. Resin cement and fusion ceramic were placed between veneer and zirconia substructure for digital veneering. A total of one hundred and fifty specimens in five groups (n = 30) were prepared for FS and tested in universal machine at 1.0 mm/min. One hundred specimens in five groups (n = 20) were obtained for the μTBS and tested at 1.0 mm/min. Statistical analysis was made by one way ANOVA and Tukey HSD. Conventional veneering showed statistically significant FS. ZC veneered with EC had the highest mean FS and the lowest was obtained in groups veneered through resin cement. YZ layered with VM9 had the highest mean μTBS. ZC veneered through fusion ceramic and YZ veneered through resin cement showed significantly lower and similar μTBS.

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.

Surface Roughness of Monolithic and Layered Zirconia Restorations at Different Stages of Finishing and Polishing: An In Vitro Study

PURPOSE

To evaluate surface roughness and topography of different zirconia-based restorations at various steps of finishing and polishing.

MATERIALS AND METHODS

Seventy-five zirconia discs were fabricated and divided into 3 layered and 2 monolithic groups: layered conventional (VM9; Vita), layered pressed (PM9; Vita), layered digital (TriLuxe Forte; Vita), opaque monolithic (Ceramill Zi; Amann Girrbach), and translucent monolithic (Zolid FX; Amann Girrbach). Surface roughness testing (Ra, Rz) and scanning electron microscopy were performed at the glazed, unglazed, finished, polished, super-polished, and super-polished with diamond paste steps. One-way ANOVA and Tukey tests were used for statistical analysis.

RESULTS

There were significant differences in all groups among the different steps (p < 0.001, F = 77.67 for layered conventional; p < 0.001, F = 133.90 for layered pressed; p < 0.001, F = 47.94 for layered digital; p < 0.001, F = 48.05 for zirconia opaque; p < 0.001, F = 43.91 for zirconia translucent). For the layered groups, glazed stage was significantly different from all other steps (p < 0.001). For the layered conventional and digital groups, polishing using diamond paste was not significantly different from the polished and super-polished steps (p = 0.448, p = 0.153), while for the layered pressed group, polishing using diamond paste was not significantly different from the super polished step (p = 0.815). For monolithic groups, there were no significant differences between the polished and super-polished steps (p = 0.957 for zirconia opaque, p = 1.00 for zirconia translucent). Both the diamond paste and super-polished steps showed no significant differences (p = 0.620, p = 0.550) from the glazed surface in the opaque zirconia group.

CONCLUSIONS

Surface roughness of monolithic and layered zirconia was improved by polishing; however, only opaque zirconia reached the level of surface roughness of the glazed stage. Type of buildup affected the surface roughness of adjusted ceramics, with monolithic zirconia showing lower surface roughness than layered zirconia. Polishing with diamond paste provided no significant improvement in the surface roughness of monolithic or layered zirconia.

Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations

Background. Effects of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations are unclear. The aim of this study was to evaluate the impacts of veneering porcelain thickness and background shade on the shade match of zirconia-based restorations.

Methods. Forty A2 shade veneered zirconia disk specimens (10 mm in diameter) were fabricated, with veneering porcelain thicknesses of 1.6, 1.8, 2.0 and 2.2 mm. Three backgrounds were made of A2 shade composite resin (A2), nickel-chromium alloy (NC) and amalgam (AM). The veneered zirconia specimens were placed on the backgrounds. CIELab values were measured with a spectrophotometer. ΔE values were measured to determine color differences between the specimens and the A2 VITA classical shade (target shade). ΔE values were compared with an acceptability threshold (ΔE=3.7). Repeated measures ANOVA, Bonferroni, and 1-sample t-test were used to analyze data (P<0.05).

Results. Mean ΔE values ranged between 1.9 and 5.0. The veneering porcelain thickness, the background shade and their interaction affected the ΔE (P<0.0001). The minimum veneering porcelain thickness for the shade match was 2 mm for NC and 1.8 mm for AM.

Conclusion. Veneering porcelain thickness and background shade affected the shade match of zirconia-based restorations. With dark-shaded backgrounds, the amount of veneering porcelain thickness needed for the shade match might be beyond acceptable clinical limits. Tooth-shaded backgrounds are esthetically advocated rather than dark-shaded backgrounds in zirconia-based restorations.

Does veneering technique affect the flexural strength or load-to-failure of bilayer Y-TZP? A systematic review and meta-analysis

STATEMENT OF PROBLEM

Causes of failures of bilayer yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations include the processing technique and the properties of the veneer ceramic. The effect of the veneering method on the mechanical behavior of veneered Y-TZP remains unclear.

PURPOSE

The purpose of this systematic review was to assess the effect of the veneering method on the flexural strength and failure load of bilayer Y-TZP.

MATERIAL AND METHODS

This study followed the Preferred Reporting Items for the Systematic Reviews and Meta-Analyses (PRISMA) statement. Searches were performed through August 2017 in PubMed/MEDLINE, Web of Science (Core Collection), Scopus, and Embase, with no year or language limit, targeting in vitro studies evaluating the effect of the veneering technique on the flexural strength and load-to-failure of bilayer Y-TZP immediately or after aging. Statistical analyses were conducted using an appropriate software. Comparisons were drawn with random effect models (α=.05).

RESULTS

From 3242 identified studies, 241 were selected for full-text analysis; from these, 33 studies were included. Manual searching yielded no additional papers. The meta-analysis consisted of 32 studies. Meta-analysis was performed separately for flexural strength and failure load data to compare the hand-layered method (control) with pressed, fused, and cemented veneering techniques. The cemented and fused methods were analyzed using subgroups depending on the veneering material being examined (predominantly glass-ceramics and particle-filled glass-ceramics), and the results were compared with those of the hand-layered method. The pressed group presented flexural strength (7 studies) (P=.150) and failure load (19 studies) (P=.140) values that were similar to those of the hand-layered group. Subgroup analysis revealed that the fused group with particle-filled glass-ceramics (7 studies) produced higher load-to-failure (P=.006) values than the hand-layered group. Subgroup analyses showed a statistical difference that favored the hand-layered over the cemented method, with predominantly glass-ceramic materials (5 studies) (P=.002).

CONCLUSIONS

The fused technique with particle-filled glass-ceramics seems more appropriate for the veneering of Y-TZP, with improved failure load, than the hand-layered method with predominantly glass-ceramic materials. The use of predominantly glass-ceramics for the cemented method is not recommended as failure load was lower than for the hand-layered group. Pressed veneers showed failure load and flexural strength values similar to those of the the hand-layered technique.

Effect of coping thickness and background type on the masking ability of a zirconia ceramic

STATEMENT OF PROBLEM

The masking ability of zirconia ceramics as copings is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of coping thickness and background type on the masking ability of a zirconia ceramic and to determine zirconia coping thickness cut offs for masking the backgrounds investigated.

MATERIAL AND METHODS

Thirty zirconia disks in 3 thickness groups of 0.4, 0.6, and 0.8 mm were placed on 9 backgrounds to measure CIELab color attributes using a spectrophotometer. The backgrounds included A1, A2, and A3.5 shade composite resin, A3 shade zirconia, nickel-chromium alloy, nonprecious gold-colored alloy, amalgam, black, and white. ΔE values were measured to determine color differences between the specimens on the A2 shade composite resin background and the same specimens on the other backgrounds. The color change (ΔE) values were compared with threshold values for acceptability (ΔE=5.5) and perceptibility (ΔE=2.6). Repeated measures ANOVA, the Bonferroni test, and 1-sample t tests were used to analyze data (α=.05).

RESULTS

Mean ΔE values ranged between 1.44 and 7.88. The zirconia coping thickness, the background type, and their interaction affected the CIELab and ΔE values (P<.001).

CONCLUSIONS

To achieve ideal masking, the minimum thickness of a zirconia coping should be 0.4 mm for A1 and A3.5 shade composite resin, A3 shade zirconia, and nonprecious gold-colored alloy, 0.6 mm for amalgam, and 0.8 mm for nickel-chromium alloy.