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Influence of solvent evaporation on ultimate tensile strength of contemporary dental adhesives
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 eachadhesive were opened and stored at 37 Ā°C in a dry oven with silica gelshielded from light for 2 weeks (āDesiccatedā). Two unopened bottles were stored at room temperature (āOriginalā). 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 Ā°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 (nā=ā10). The UTS for the Clearfil SE Protect was higher in theāOriginalā than āDesiccatedā samples (pāā0.05). Neither of the two āOriginalā 1-step samples could be hardened, even after light-curing, yet the āDesiccatedā 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