Effects of Particle Abrasion Media and Pressure on Flexural Strength and Bond Strength of Zirconia

Influence of different airborne-particle abrasion pressures, cleaning methods, and artificial aging on zirconia ceramic bonding

STATEMENT OF PROBLEM

Airborne-particle abrasion (APA) with alumina combined with a primer or luting resin containing a phosphate monomer has been well established for resin bonding to zirconia. However, a standardized method for bonding to zirconia is unavailable, as some factors including the optimal pressure of airborne-particle abrasion, the cleaning method, and the luting resin system are still unclear because of the limited available data.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of different airborne-particle abrasion pressures and different cleaning methods of zirconia on the tensile bond strength (TBS) of 2 luting resins system containing methylacryloyloxydecyl-dihydrogenphosphate (MDP) either in the primer or in the luting resin.

MATERIAL AND METHODS

A total of 128 disk specimens were milled from zirconia blocks and divided into groups according to the pressure of airborne-particle abrasion of either 0.1 MPa or 0.25 MPa (n=64). The specimens were then divided into 2 subgroups and were either cleaned in an ultrasonic device in isopropanol or with oil-free air stream (n=32). The subgroups were further divided according to the luting resin (n=16) and the bonding surfaces were perpendicularly luted to the acrylic resin tubes filled with a composite resin (Clearfil F II) with either an MDP-containing primer and a luting resin or with a self-adhesive MDP-containing luting resin. Each of the 8 groups was further divided into 2 subgroups (n=8) with either 3-days water storage at 37 °C or 150-days water storage with additional thermal cycling (37 500 thermal cycles between 5 °C and 55 °C) for artificial aging. The TBS was evaluated with a universal testing machine. All specimens underwent failure mode analysis. Statistical analysis was performed with 4-way ANOVA and, if required, with 3-way ANOVA (α=.05).

RESULTS

The mean ±standard deviations ranged from 57.0 ±11.1 MPa to 61.5 ±7.1 MPa after 3 days and from 32.3 ±11.7 MPa to 61.0 ±12.4 MPa after 150 days. The pressure of airborne-particle abrasion and the cleaning method had no significant effect on the TBS (P>.05), whereas the luting resin and artificial aging significantly influenced the TBS (P<.05).

CONCLUSIONS

Irrespective of the pressure of airborne-particle abrasion and the cleaning method, the use of an MDP-containing luting resin for bonding to zirconia was found to be more advantageous compared with an MDP-containing primer and luting resin because of higher bond strength and no significant decrease after artificial aging.

Effect of Surface Treatment with Zirconium Dioxide Slurry on the Bond Strength of Resin Cement to Ultratranslucent Zirconia

This laboratory study aimed to evaluate the effects of zirconium dioxide (ZrO2) slurry surface treatment on the bond strength of ultratranslucent zirconia to resin cement using different ceramic primers. The surface morphology was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the interface was evaluated by SEM. Additionally, the phase composition was analyzed by X-ray diffraction (XRD). Specimens of zirconia (n=120) were obtained and divided into two groups according to the surface treatment: (1) airborne particle abrasion with 50-μm aluminum oxide (n=60) and (2) ZrO2 slurry (n=60). The 60 specimens were then further divided into three groups (n=20) according to the ceramic primer application: no primer (NP), Monobond N (MB), and Clearfil ceramic primer (CP). Four resin cement cylinders were built on each ceramic specimen. Half of the specimens (n=10) were subjected to a microshear bond strength (μSBS) test after 24 hours of storage in distilled water, and the other half (n=10) were subjected to a μSBS test after thermocycling. Additional specimens were prepared for SEM, AFM, and XRD analyses. According to the Kruskal-Wallis and Student-Newman-Keuls post hoc tests, the μSBS values were significantly higher for MB and CP than for NP (p<0.05), and there were no significant differences in μSBS for both surface treatments associated with MB and CP after 24 hours of storage (p>0.05). Thermocycling significantly decreased the μSBS values for all specimens, especially for the NP groups and ZrO2 slurry treatment groups, and gaps at the interface were observed by SEM. SEM and AFM analyses showed agglomerate-type irregularities on the ceramic surface for ZrO2 slurry treatment. XRD spectra showed that ZrO2 slurry did not cause phase transformation. It was concluded that ZrO2 slurry promoted irregularities on the ultratranslucent zirconia surface, not causing phase transformation; moreover, the values of μSBS were comparable to those of airborne particle abrasion with aluminum oxide. However, neither surface treatment nor ceramic primer prevented the degradation of the interface.

Effect of printing layer orientation and polishing on the fatigue strength of 3D-printed dental zirconia

OBJECTIVE

The aim of the study was to evaluate the influence of surface polishing and printing layer orientation on the fatigue behaviour of 3 mol% yttria-stabilized zirconia (3Y-TZP) by stereolithography (SLA) in comparison with subtractive manufacturing.

MATERIALS AND METHODS

60 experimental zirconia bar-shaped specimens were 3D-printed (P) via SLA, and 30 specimens were milled (M) from commercial zirconia block (Lava™ Frame, 3 M ESPE AG). All specimens had the same dimensions (1 mm × 1 mm x 12 mm) after sintering. The 3D-printed specimens were randomly divided according to printing orientations: parallel or perpendicular to the tensile surface in the fatigue test. The specimens were subsequently submitted to two surface finishing protocols (n = 15/gr): unpolished or polished. Their phase compositions were analysed by X-ray diffraction. The fatigue behaviour was evaluated by a stepwise approach.

RESULTS

The milled and both 3D-printed groups showed similar phase compositions for the as-sintered condition. Considerable amounts of rhombohedral phase were detected after polishing. Milled unpolished samples presented significantly higher fatigue strength than 3D-printed unpolished samples. Polishing did not improve the fatigue strength for milled zirconia but was advantageous for the 3D-printed specimens. 3D-printed specimens with parallel printing-layer orientation were significantly stronger than specimens with perpendicular layers regardless of surface finishing.

CONCLUSION

The manufacturing techniques had a significant influence on the fatigue strength of 3Y-TZP, but not on the phase compositions of the surface. The polishing protocol showed different effects on 3Y-TZP fatigue strength and induced phase transition of the 3Y-TZP from Tetragonal to Rhombohedral. The best fatigue strength was achieved through milling using an unpolished surface and SLA-printed layers that were parallel to the tensile surface, followed by polishing.

The Effect of Restoration Thickness on the Fracture Resistance of 5 mol% Yttria-Containing Zirconia Crowns

BACKGROUND

To determine what thickness of 5 mol% yttria zirconia (5Y-Z) translucent crowns cemented with different cements and surface treatments would have equivalent fracture resistance as 3 mol% yttria (3Y-Z) crowns.

METHODS

The study included 0.8 mm, 1.0 mm, and 1.2 mm thickness 5Y-Z (Katana UTML) crowns and 0.5 and 1.0 mm thickness 3Y-Z (Katana HT) crowns as controls. The 5Y-Z crowns were divided among three treatment subgroups (n = 10/subgroup): (1) cemented using RMGIC (Rely X Luting Cement), (2) alumina particle-abraded then luted with the same cement, (3) alumina particle-abraded and cemented using a resin cement (Panavia SA Cement Universal). The 3Y-Z controls were alumina particle-abraded then cemented with RMGIC. The specimens were then loaded in compression at 30° until failure.

RESULTS

All 5Y-Z crowns (regardless of thickness or surface treatment) had a similar to or higher fracture force than the 0.5 mm 3Y-Z crowns. Only the 1.2 mm 5Y-Z crowns with resin cement showed significantly similar fracture force to the 1 mm 3Y-Z crowns.

CONCLUSION

In order to achieve a similar fracture resistance to 0.5 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns may be as thin as 0.8 mm. To achieve a similar fracture resistance to 1.0 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns must be 1.2 mm and bonded with resin cement.