Influence of solvent type in experimental dentin primer on the marginal adaptation of Class V restorations

Objectives The purpose of this in vitro investigation was to evaluate the influence of the solvent type in two experimental dentin primers (ExP) on the handling sensitivity by determining the marginal adaptation of mixed Class V restorations. Methods Standardized cavities were prepared in 32 extracted human molars and randomly assigned to four test groups (n = 8). After etching, a three-step adhesive was applied using two ExP which only differed in the type of solvent (acetone/water = ExP-A versus ethanol/water = ExP-E). For ExP-A, the drying procedure (blot-drying versus 2 s air drying) prior to primer application was varied, whereas evaporation time (2–3 s versus 10 s) after primer application was varied for ExP-E. An adhesive was added prior to application of the filling material. Specimens were thermocycled (TC: 2500 cycles; 5–55 °C). The length of gap-free margin (LoGfM) was assessed by SEM using replica technique. Data were subjected to non-parametric statistics (p = 0.05) as well as the Levene test (p = 0.05). Results Blot-drying significantly increased the LoGfM after TC for ExP-A in dentin (p < 0.05) but decreased LoGfM in enamel (p < 0.05). Short evaporation (2–3 s) of solvent reduced LoGfM when using ExP-E and led to a significant increase in variances (p < 0.05). Conclusions The use of three-step adhesives with ethanol/water-based solvent is recommended due to a lower technique sensitivity versus acetone/water-based systems. Also when using modern ethanol/water-based three-step adhesives, evaporation of primer solvent remains a critical step regarding the marginal quality of the restorations and consequently has to be carried out thoroughly.