Microhardness and flexural strength after chemical aging of chlorhexidine delivery systems based on acrylic resin

Objectives: To evaluate the effect of chlorhexidine incorporation on the microhardness and flexural strength of three reline acrylic resins, after a 28-day chemical aging process. Methods: Forty-eight specimens were fabricated according to the several possible combinations of acrylic reline resin and concentrations of incorporated chlorhexidine (Kooliner 0% vs. 2.5%; Ufi Gel Hard 0% vs. 5%; and Probase Cold 0% vs. 5%), to set 6 experimental groups (n=8). After a 4-week chemical aging process (pH fluctuation in artificial saliva, with cycles of 6 hours at pH=3 and 18 hours at pH=7), the Knoop microhardness (98.12 mN, 30 seconds) and flexural strength (1 kN, 5 mm/min) of all specimens were evaluated. Data were submitted to non-parametric statistical tests, according to Kruskal-Wallis and Mann-Whitney (α=0.05). Results: Chlorhexidine incorporation did not significantly affect the microhardness of the three tested resins (Kooliner p=0.798; Ufi Gel Hard p=0.798; and Probase Cold p=0.195). Although chlorhexidine incorporation did not influence the flexural strength of Kooliner (p=0.959) and Ufi Gel Hard (p=0.645), the incorporation of 5% chlorhexidine in Probase Cold led to a statistically lower flexural strength than that obtained without incorporation (p=0.021). Conclusion: After chemical aging, the microhardness of chlorhexidine-incorporated acrylic resins is not affected. However, the incorporation of 5% chlorhexidine into Probase Cold negatively affects its flexural strength. (Rev Port Estomatol Med Dent Cir Maxilofac. 2019;60(3):104-110) c 2019 Sociedade Portuguesa de Estomatologia e Medicina Dentaria.