Effect of surface treatment on flexural strength of zirconia bars

https://doi.org/10.1016/S0022-3913(10)60100-XGet rights and content

Statement of problem

Clinical and laboratory processing techniques induce damage to the surface of zirconia frameworks, which significantly lessens their strength.

Purpose

The purpose of this study was to investigate the influence of 3 surface restoration methods on the flexural strength of zirconia bars.

Material and methods

Bar-shaped specimens were polished and received 1 of 2 surface treatments (n=20): airborne-particle abrasion with 110-μm aluminum oxide particles at a pressure of 0.2 MPa, or grinding with a diamond point under water cooling and a load of 2 N using an air turbine. Polished specimens served as the control (n=20). The induced surface damage was restored using one of the following restoration methods: polishing of the specimens using an aluminum oxide polishing point (2-μm grit) coated with 0.5-μm diamond polishing paste, application of a thin coat of glazing porcelain according to the manufacturer's instructions, or application of a phosphate ester monomer (MDP) containing an adhesive resin. The specimens were subjected to a 4-point flexural strength test and then examined using a scanning electron microscope (SEM). Two-way ANOVA and the Bonferroni post hoc test were used to analyze the data (α=.05).

Results

There was a significant interaction between the type of surface damage and the restoration method (P<.001). For the ground specimens, all restoration methods resulted in a statistically significant regain in strength, with the polishing procedure being the most effective (1027 MPa). For airborne-particle-abraded specimens, application of the bonding agent was the only effective restoration method. SEM analysis of the fractured surfaces of specimens indicated that application of the bonding agent resulted in sealing of the surface damage produced by airborne-particle abrasion, while polishing was successful in removing the grinding lines produced by the diamond point.

Conclusions

Within the limitations of this in vitro study, restoration of surface damage improved the flexural strength of zirconia specimens.

Section snippets

Material and methods

Bar-shaped specimens (25 × 3 × 1 mm) were produced by cutting and sintering CAD/CAM zirconia milling blocks (Procera Zirconia; Nobel Biocare AB, Göteborg, Sweden). The bars were polished in a customized rotating metallographic polishing device (EcoMet; Buehler Ltd, Lake Bluff, Ill) and divided into 3 groups. One selected surface of each specimen received one of the following surface treatments, which simulated the surface damage that could be introduced during common clinical and laboratory

Results

Compared to the mean (SD) flexural strength of polished zirconia specimens, 1200 (136) MPa, both types of induced surface damage resulted in a significant reduction in the flexural strength of almost 50%. There was a significant interaction between the type of surface damage and the restoration method (P<.001). For the ground specimens, all restoration methods resulted in a significant (P<.001) regain in strength; the polishing procedure was the most effective, resulting in a mean (SD) flexural

Discussion

According to the findings of this study, surface damage to zirconia specimens can be repaired by using the proper method of surface restoration, resulting in a partial or complete regain of lost strength. Thus, the proposed hypothesis was accepted. Despite the fact that fracture strength tests do not reproduce intraoral loading conditions, they offer a standardized environment in which the variables under investigation can be well controlled. The selected test was easily conducted and offers

Conclusions

Within the limitations of this study, a regain in lost strength of zirconia was possible using the 3 suggested surface restoration methods. For airborne-particle-abraded zirconia, resin bonding was most effective, while polishing with diamond points achieved the best results for ground zirconia.

Acknowledgments

The authors thank the research enhancement program (Alex Rep) of Alexandria University, Alexandria, Egypt, and the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry (SRF for ROCS, SEM), for supporting this study.

References (31)

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Support for this study was provided by the research enhancement program (Alex Rep) of Alexandria University, and the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry (SRF for ROCS, SEM), grant number 20091001-9-4.

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