The Strengthening Mechanism of Resin Cements on Porcelain Surfaces

Quantifying the Strength of a Resin-coated Dental Ceramic

Resin luting all-ceramic restorations increases clinical performance; however, the strengthening mechanisms are not fully understood. The authors have previously proposed the existence of a resin-ceramic hybrid layer, and the hypothesis tested was that ceramic strength enhancement was conferred by the characteristics of the resin-ceramic hybrid layer. Dentin porcelain discs were polished with a P4000-grade abrasive paper, and half were centrally indented at 9.8 N. Further discs were alumina-air-abraded. Groups of 30 specimens were coated with resin cement thicknesses varying from 0 to 250 ± 20 μm before bi-axial flexure testing. Following investigation of residual stresses by annealing, regression analysis enabled us to calculate the magnitude of ’actual’ strengthening for a theoretical ’zero’ thickness of resin cement on each surface texture. Accounting for resin bulk strengthening, resin cement coating significantly increased the mean strength that was attributed to a resin-ceramic hybrid layer sensitive to surface texture.

Light-activation of resin cement through ceramic: relationship between irradiance intensity and bond strength to dentin

This study investigated the relationship between the irradiance transmitted through ceramic and the bond strength of a resin cement to dentin. After application of an adhesive system, elastomer molds with cylindrical orifices (1.2 mm in diameter) were placed onto bovine dentin surfaces and filled with a photoactivated luting agent (Enforce; Dentsply Caulk). Light-activation was performed through a 0.6-mm-thick ceramic disc using different intensities: 250, 400, 550, 700, or 850 mW/cm(2). Control specimens were irradiated without ceramic (1050 mW/cm(2)). The radiant exposure was kept at 30 J/cm(2). Light spectral distribution was analyzed with a spectrometer. Microshear test was conducted and modes of failure were classified under SEM. Bond strength data were analyzed with ANOVA and Student-Newman-Keuls' test (alpha < or = 0.05), and failure scores with the Kruskal-Wallis test (alpha < or = 0.05). A linear regression model assessed the relationship between irradiance and bond strength. Groups light-cured at 250 and 400 mW/cm(2) presented lower bond strengths than groups activated at 850 and 1050 mW/cm(2). The linear regression showed that a decrease in light irradiance predicts a decrease in bond strength (r(2) = 0.955; p = 0.004). A predominance of mixed failures was observed. No significant alteration in the spectral wavelengths was observed. Despite the constant energy dose, the bond strength was dependent upon the irradiance level.

Recent advances in materials for all-ceramic restorations

The past 3 years of research on materials for all-ceramic veneers, inlays, onlays, single-unit crowns, and multi-unit restorations are reviewed in this article. The primary changes in the field were the proliferation of zirconia-based frameworks and computer-aided fabrication of prostheses, and a trend toward more clinically relevant in vitro test methods. This article includes an overview of ceramic fabrication methods, suggestions for critical assessment of material property data, and a summary of clinical longevity for prostheses constructed of various materials.

Resin strengthening of dental ceramics—The impact of surface texture and silane

OBJECTIVES

To examine the effect of porcelain surface texture achieved utilising three clinically relevant surface preparation methods prior to silane and unfilled resin application on the flexure strength of a low fusing feldspathic porcelain.

MATERIALS AND METHODS

Five hundred and forty dentine disc-shaped specimens (15.0mm diameter and 0.9mm thickness) were condensed, fired and allocated to 18 groups. Six groups were stored as-fired, six were alumina abraded and six were acid-etched. Samples were coated with silane, unfilled resin or both prior to bi-axial flexure testing. Group means were compared utilising a three factor design general linear model and post hoc all paired Tukey tests at P<0.05. Weibull analysis was employed to examine the reliability of the strength data. Profilometry was used to characterise the surface texture of the specimen surfaces.

RESULTS

Alumina abraded and acid-etched specimens had significantly lower flexure strengths than the as-fired specimens. A significant difference between the degree of strengthening observed following unfilled resin application on the three surface texture investigated was observed (P<0.001). Silane application prior to resin coating resulted in no further significant increases in the mean bi-axial flexure strengths of the three surface textures. The as-fired surfaces had a low frequency of irregular amplitude defects, alumina abraded surfaces had an increased frequency of regular amplitude defects whilst the acid-etched surface consisted of an increased frequency of irregular amplitude defects.

CONCLUSION

The strengthening mechanism whilst dependent on surface texture was independent of defect severity. No significant strengthening occurred following silane priming suggesting that, for the unfilled resin utilised, the strengthening mechanism was not enhanced by improved resin-ceramic adhesion.

Influence of Light Irradiation Condition on Microshear Bond Strength of Dual-cured Resin Luting Agents

The purpose of this study was to evaluate the microshear bond strength and bond durability between ceramic and two dual-cured resin luting agents irradiated by different light intensities. Ceramic specimens were bonded with two resin bonding systems: Ceramic Primer and Linkmax HV (CP/LMHV) and Monobond S and Variolink IIHV (MBS/VLIIHV), and were either irradiated by 800, 310, 160, 80, and 40 mW/cm2 light or not irradiated. Bond strength was measured after 24-hour water storage at 37 degrees C and after subsequent 10,000 times of thermal cycling. Failure modes were determined by stereomicroscopy. After 24-hour water storage, there were no significant differences among the various irradiation conditions for both MBS/VLIIHV and CP/LMHV. However, regardless of light intensity, MBS/VLIIHV showed higher bond strength than CP/VLIIHV at each thermal cycling, except for no irradiation condition at 10,000 thermal cycles. In conclusion, thermal cycling significantly reduced the bond strength for all groups.