The reinforcing effect of anti-caries treatments on acidic challenge resistance of irradiated enamel

Abstract

Aim To investigate the effect of applying the following anticaries treatments on the surface microhardness (SMH) of irradiated enamel after pH-cycling: Nanohydroxyapatite (nano-HA), resin infiltration (RI), combination of nano-HA and RI, or curcumin-loaded mesoporous nano-silica (Cur/MSN). Methodology In this in vitro experimental study, 30 sound molars were mesiodistally sectioned into two halves, yielding 60 enamel samples, and randomly divided into six groups (n = 10). Group 1 was kept as non-irradiated. The samples from the other five groups were subjected to fractionated X-ray radiation for 6 weeks, with a total dose of 60 Gy, delivered in 2 Gy fractions 5 days per week. After irradiation, each group was processed as follows: 2) no treatment; 3) treated with 15% nano-HA; 4) treated with RI; 5) treated with a combination of 15% nano-HA and RI; 6) treated with Cur/MSN (3 mg/ml). The initial SMH (SMH0) was measured after irradiation and the final (SMH1) after anticaries treatments and pH cycling. pH cycling consisted of a 3-hour immersion in a demineralizing solution, followed by 21 hours in a remineralization solution at 37 °C for 5 days. The surface micromorphology of irradiated groups after pH-cycling was assessed. Results Mean [±SD] SMH0 of irradiated enamel was significantly lower than that of the nonirradiated one (330.7 ± 23.6 vs 262.9 ± 28.8; P < 0.001). Irradiated enamels treated with all anti-caries treatments showed a significantly higher SMH1 compared to those of no-treatment (192.2 ± 28.7; all P < 0.01). SMH1 of Ir/nano-HA (302.2 ± 16.4) or Ir/ nano-HA+RI (305.4±22.1) groups were higher than those of Ir/RI (245.5±35.1; P<0.001) and not different from Ir/Cur/MSN group (285.9±16.4; P=0.638 and 0.435 respectively). The increase in SMH1 compared to SMH0 (ΔSMH) was significant only in Ir/nano-HA (39.0; P=0.003) and Ir/nano-HA+RI groups (42.9; P=0.001). Conclusion Treatment with nano-HA and a combination of nano-HA with RI demonstrated significant potential to improve the resistance of the irradiated enamel surface to acidic challenges.