MicroTBS of Sealants on Different Enamel Substrate under Cariogenic Challenge

Objectives: The aim of this in vitro study was to evaluate the microtensile bond strength (µTBS) of resinous sealant materials on different enamel substrate after cariogenic challenge (pH-cycling). Methods: Enamel blocks (5x5 mm) were obtained from impacted human third molars. The buccal surface was polished to obtain flat enamel. The blocks were randomly divided into six groups (n=10), according to the enamel substrate (S - sound, CL - like-caries lesion or ACR - like-caries lesion + remineralization) and sealant materials (F - FluroShield® or H - Helioseal Clear Chroma®): G1-SF; G2-CLF; G3-ACRF; G4-SH; G5-CLH; G6-ACRH. Sealants were placed on enamel surfaces, stored in 100% humidity for 24 hours at 37°C, and then longitudinally sectioned. Hourglasses were obtained with a cross-sectional area of approximately 1 mm². The specimens of each group were subdivided into two groups, which were submitted or not to high cariogenic challenge model (7-day pH cycling – demineralization and remineralization solutions). µTBS testing was performed using a universal testing machine at a crosshead speed of 0.5 mm/min. µTBS data (MPa) were submitted to 3-way ANOVA and Tukey's tests (p≤ 0.05). The fracture patterns were observed by SEM analysis. Results: Regarding substrate, the highest µTBS (MPa) values were found for ACR enamel (26.0±7.6) followed by S and CL lesion (22.0±7.4; 15.5±4.9, respectively). A significant difference for µTBS was observed for interaction (p=0.0001) between material and pH-cycling. F (23.9±7.6) showed the highest µTBS values compared to H (18.3±7.5) when the materials were submitted to pH cycling. Sealant materials showed no difference in µTBS when were or not submitted to pH cycling. Conclusions: µTBS was considerably influenced by different enamel substrate. When caries-like enamel lesions were remineralized they showed the highest µTBS values. The µTBS achieved by Helioseal when submitted to pH-cycling was significantly lower than that developed by FluroShield.