We attempted to determine the effect of universal adhesive application time on dentin bond performance in different etching modes based on shear bond strength (SBS) tests and surface free energy (SFE) measurements. The five universal adhesives used were Adhese Universal (AU), Clearfil Universal Bond Quick (CQ), G-Premio Bond (GP), Scotchbond Universal (SU), and Tokuyama Universal Bond (TU). Bovine dentin specimens were divided into four groups of 10 for each adhesive. SBS and SFE were determined after applying the following surface treatments: 1) self-etch (SE) mode with immediate air blowing after adhesive application (IA treatment), 2) SE mode with prolonged application time (PA treatment), 3) etch-and-rinse (ER) mode with IA treatment, and 4) ER mode with PA treatment. Bonded specimens were subjected to SBS testing. The SFE of adhesive-treated dentin surfaces was measured after rinsing with acetone and water. Three-way analysis of variance revealed that dentin SBS values (p,0.001) were significantly influenced by the factors of adhesive type and application duration, but the factor of pre-etching was not significant(p=0.985). The manufacturer's instructions require longer application times for AU and SU, which showed significantly lower SBS values in IA than in PA treatment in both etching modes. However, the difference in the other adhesives was not significant between the IA and PA treatments in either etching mode. The total SFE (cS) was dependent on the adhesive and etching mode. The cS value of the initial group (SiC paper ground group) at baseline was 69.5 (mNm1) and that of the pre-etching group at baseline was 30.6 (mNm1). For all the adhesives, cS in SE mode showed significantly higher values than in ER mode, regardless of the application time. In SE mode, almost all universal adhesives tested showed lower cS values in PA treatment than in IA treatment. For ER mode, all the adhesives showed significantly higher cS values than those of the preetching baseline, regardless of the application time. Most adhesives did not show any significant differences in cS values between IA and PA treatments, regardless of etching mode.
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