microshear bond strength of composite resins to enamel and porcelain substrates utilizing unfi lled versus fi lled resins

background: failures such as marginal discoloration and composite chipping are still the problems of tooth-colored restorations on the substrate of enamel and porcelain, which some of these problems are consequently as a result of failures in the bonding layer. using fi lled resin has been recently introduced to increase the bond strength of this layer. the aim of this study was to compare the microshear bond strength (μ-sbs) of composite resins to enamel incubated in periods of 24 h and 9 months and porcelain with unfi lled resin and fl owable composites (fi lled resin). materials and methods: in this in vitro study, two groups of 75 enamel samples with different storage times (24 h and 9 months) and a group of 75 porcelain samples were used. they were divided into 5 experimental groups of 15 samples in each. composite cylinders in tygon tubes were bonded on the surface of acid-etched enamel and pretreated porcelain. wave, wave mv, wave hv, grandiofl ow and margin bond were used as bonding agents. the μ-sbs was measured at the speed of 1.0 mm/min. the bond strengths were analyzed with one-way analysis of variance (anova) test followed by tukey test. p < 0.05 was selected as the level of statistical signifi cance in this study. results: the results showed that for enamel (24 h), the μ-sbs of the wave mv and wave hv groups were signifi cantly lower than the margin bond group. tukey test indicated the absence of a signifi cant difference between the μ-sbs of the wave group and the margin bond group. however, the μ-sbs of the grandiofl ow group was signifi cantly higher than the one for the margin bond as a bonding agent. in enamel (9 months), there was a signifi cant difference between the grandiofl ow and margin bond groups. regarding bonding to the porcelain the one-way anova test did not show a signifi cant difference among the groups. conclusion: this study revealed that fl owable composites (fi lled resins) can be used instead of unfi lled resins in bonding composite resins to enamel and porcelain substrates. key words: composite resins, dental enamel, dental porcelain, shear strength