Influence of solvent evaporation on ultimate tensile strength of contemporary dental adhesives

Abstract

The aim of this study was to evaluate the influence of solvent evaporation on the ultimate tensile strength (UTS) of commercial adhesives. Two 1-step (OptiBond All-In-One and G-Premio Bond) and two 2-step (Clearfil SE Protect, OptiBond XTR) adhesives were selected. Two bottles of each adhesive were opened and stored at 37?°C in a dry oven with silica gel shielded from light for 2?weeks (“Desiccated”). Two unopened bottles were stored at room temperature (“Original”). After 2?weeks, the adhesives were used to fill an hour-glass shaped, metallic matrix mold and light-cured. Samples were weighed, and then immersed in a 37?°C water bath for 1?h or 7?days. The UTS of each sample was then measured at a cross-head speed of 1?mm/min (n?=?10). The UTS for the Clearfil SE Protect was higher in the “Original” than “Desiccated” samples (p?<?0.05). For the OptiBond XTR, no significant difference was found between the ‘Original’ and ‘Desiccated’ samples (p?>?0.05). Neither of the two “Original” 1-step samples could be hardened, even after light-curing, yet the ‘Desiccated’ OptiBond All-In-One samples obtained high UTS values. Both OptiBond All-In-One and Clearfil SE Protect had an increase in weight after the 7-day immersion in water. In conclusion, residual solvent reduces the mechanical strength of the adhesive. The hydrophilicity of the adhesive resin might also affect its mechanical strength.