Effect of thermal and mechanical cycles on shear bond strength of zirconia core to porcelain veneer under different surface treatments

Shear Bond Strength of Colored and Sandblasted Zirconia to Ceramic Veneers Fabricated by the Pressing and Layering Techniques: An In Vitro Study

Introduction

Porcelain-veneered zirconia (PVZ) restorations are increasingly used due to their optimal esthetics and high strength. However, chipping of porcelain limits the application of PVZ restorations. The aim of this study was to assess the shear bond strength (SBS) of colored and sandblasted zirconia to ceramic veneers fabricated by the pressing and layering techniques.

Materials and Methods

Sixty cubic zirconia specimens (10 × 10 × 2 mm) were assigned to three groups according to their surface treatment: (I) control, (II) sandblasting with 50 μm alumina particles (S), and (III) coloring (C). Each group was subsequently divided into two subgroups according to the porcelain-veneering technique: (I) layering (L) and (II) pressing (P). The specimens underwent 10,000 thermal cycles between 5 and 55°C, and their biaxial SBS was measured in an electromechanical universal test machine (0.5 mm/min with 2.5 kN load cell). The failure mode was also assessed under a stereomicroscope. Three samples were randomly selected from each subgroup (n = 18) for examination of zirconia-phase transformation by X-ray diffraction (XRD). Two-way and one-way ANOVA followed by the post hoc Tukey test were used to analyze statistical differences among the groups and subgroups (α = 0.05).

Results

The sandblasted zirconia with press porcelain (SP) subgroup showed the highest (24.40 ± 8.16 MPa) and the colored zirconia with press porcelain (CP) subgroup showed the lowest (13.76 ±3.62 MPa) SBS. All failures were cohesive. Rate of phase transformation in layered porcelain was significantly lower than that in pressed porcelain (P < 0.01).

Conclusion

The sandblasted group showed the highest and the colored group showed the lowest SBS; the layered group showed higher SBS than the pressed group.

On the behaviour of zirconia-based dental materials: A review

Zirconia-based dental materials are extensively used in clinical practice due to their tooth-like appearance, biofunctionality, biocompatibility, and affordability. However, premature clinical failures of veneering porcelains raise a concern about their integrity. Extensive studies have been performed over a decade to resolve this issue, but it is challenging to reference all information effectively. A single source identifying the significance of potential parameters on material performance has not previously been available. An evidence-based meta-narrative review technique was used to review the characteristic parameters that can affect the overall behaviour of zirconia-based materials. Keywords were chosen to assess manuscripts based on scientific coherence with this paper's research objective. Online keyword searches were carried out on ScienceDirect, PubMed, and SAGE databases for relevant published manuscripts from year 1985-2020.261 out of 3170 identified manuscripts were included. A total of 10 parameters were identified and classified into the material, manufacturing, and geometric aspects. The effect of every parameter was reviewed on the performance of the material. A discrepancy in findings was observed and is attributed to the fact that there is no standard methodology. This review acts as a single source that summarizes various parameters' contribution to zirconia-based dental materials' performance. This review facilitates manufacturing improvements by accounting for every parameter's effect on overall performance.

Effects of dimensions of laser-milled grid-like microslits on shear bond strength between porcelain or indirect composite resin and zirconia

PURPOSE

Zirconia cores and frameworks are widely used in restorative dentistry. Although these structures are veneered with porcelain for esthetic reasons, the use of indirect composite resins (ICRs) is expected to increase in the future. The purpose of this study was to investigate the effects of microslits of different dimensions formed by Nd:YVO 4 laser machining on the bond strength between two types of zirconia (3 mol% yttria-partially stabilized zirconia (Y-TZP) and ceria-partially stabilized zirconia/alumina nanocomposite (Ce-TZP/A)) and porcelain or an ICR.

METHODS

The zirconia disks were assigned as follows: 1) blasted with alumina particles (AB) and 2-4) surface machined with gridded microslits with a width, pitch, and depth of 50, 75, or 100 µm (MS50, MS75, and MS100, respectively). After the bonding of the veneering materials to the disks, half of the specimens veneered with the ICR were subjected to thermocycling (4-60°C, 20000 cycles). All the specimens were subsequently shear tested (n = 10/group).

RESULTS

There was no significant difference between the groups of the disks bonded to porcelain. On the other hand, for the disks bonded to the ICR, the bond strengths of the MS groups after thermocycling were statistically higher than that of the AB group. However, there was no significant difference in the bond strengths of the disks with different microslits.

CONCLUSIONS

Within the study limitations, it can be concluded that, for porcelain, the design of the mechanical retentive structure must be modified. However, for the investigated ICR, a simple gridded pattern can improve the bond strength with zirconia.