Does the application of an adhesive layer improve the bond strength of etched and silanized glass-ceramics to resin-based materials? A systematic review and meta-analysis

Statement of problem A consensus on whether to use an adhesive layer on glass-ceramics after etching with hydrofluoric acid and applying a silane-coupling agent is lacking. Purpose The purpose of this systematic review and meta-analysis was to determine whether adhesive layer application after etching and silanization influences the bond strength values of glass-ceramics to resin-based materials. Material and methods PubMed, ISI Web of Science, and Scopus electronic databases were searched to select in vitro studies comparing bond strength values of etched and silanized glass-ceramics bonded with or without an adhesive layer. No publication year or language restriction was applied. Data sets were extracted, and the mean differences were applied by using the Rev Man 5.3 program. The association between bond strength (shear/microshear or tensile/microtensile) and an adhesive layer application on nonaged and aged specimens was analyzed. Results Of 4727 potentially eligible studies, 54 were selected for full-text analysis, and 15 were included for qualitative synthesis; of these, 14 were used in the meta-analysis. A total of 2 meta-analyses were performed with heterogeneity varying from high to moderate among study specimens. For shear/microshear studies, both nonaged (MD, 1.36 [95% CI: -0.18, 2.90], P=.080, I2=79%) and aged (MD, 0.89 [95% CI: -1.04, 2.82], P=.370, I2=80%) specimens presented no statistically significant difference between groups bonded with or without an adhesive layer application. For microtensile studies, both nonaged (MD, -1.49 [95% CI: -2.48, -0.50], P=.003, I2=88%) and aged (MD, -3.87 [95% CI: -5.63, -2.11], P<.001, I2=97%) specimens exhibited higher values without an adhesive application. Conclusions Regardless of the bond strength test used, an adhesive layer application did not improve the bond strength of etched and silanized glass-ceramics to resin-based materials. The influence of this adhesive layer application should be evaluated under clinical conditions.