Surface properties after chemical aging of chlorhexidine delivery systems based on acrylic resin

Objectives: To evaluate the effect of chlorhexidine incorporation on the surface free energy and microtensile bond strength of three reline acrylic resins, after chemical aging. Methods: For each of the studies, six experimental groups were set according to reline resin and chlorhexidine incorporation [Kooliner – 0% vs. 2.5% chlorhexidine; Ufi Gel Hard and Probase Cold – 0% vs. 5% chlorhexidine]. The specimens were submitted to a chemical aging process for 4 weeks (pH fluctuation in artificial saliva, cycles of 6 hours at pH=3 and 18 hours at pH=7). For the first study, 42 specimens were prepared (n=7) and, after chemical aging, the surface free energy was calculated. For the adhesive strength study, 36 denture base resin cubes were prepared and reline resin was applied to them according to the experimental group (n=6). Five sticks (1×1 mm section) were obtained from each specimen and submitted to chemical aging followed by microtensile test (1 kN; 1 mm/min). Data were analyzed with Kruskal-Wallis and Mann-Whitney non-parametric tests (α=0.05). Results: Differences (p<0.05) were observed between resins, both in surface energy and in bond strength. The chlorhexidine incorporation did not affect the surface energy of neither of the resins and also did not affect the bond strength of Kooliner and Ufi Gel Hard (p>0.05). Incorporating 5% chlorhexidine (p=0.004) decreased the Probase Cold bond strength to the denture base resin. Conclusions: After chemical aging, chlorhexidine incorporation only negatively affected the bond strength of Probase Cold.