Effect of Temperature of 1.23% Acidulated Phosphate Fluoride Gel on Enamel Microhardness of Permanent Teeth

Objectives: This study aimed to assess the effect of temperature of 1.23% acidulated phosphate fluoride (APF) gel on enamel microhardness of permanent teeth. Materials and Methods: This in vitro experimental study was conducted on 36 surgically extracted impacted human third molars. The teeth were mounted in acrylic resin and mesiodistally sectioned into buccal and lingual halves by a high-speed cutting saw. The buccal halves of the teeth were polished with silicone carbide abrasive paper and subjected to pH cycling (8 h of immersion in demineralizing agent and 16 h of immersion in remineralizing agent) for 10 days. Their primary enamel microhardness was subsequently measured by a Vickers microhardness tester. The specimens were then randomly assigned to three groups (n = 12) for application of 1.23% APF gel at 4, 25, and 37°C for 4 min. The specimens were then rinsed and incubated for 24 h. Their secondary enamel microhardness was subsequently measured, and the change in microhardness of the specimens was calculated and analyzed by one-way analysis of variance (ANOVA; α = 0.05). Results: The mean percentage of change in microhardness was -0.73% ± 16.8%, -5.28% ± 27.32%, and -7.27% ± 32.28% following the application of APF gel at 4, 25, and 37°C, respectively. The difference among the three groups was not significant regarding the percentage of change in microhardness (p  > 0.05). Conclusion: Increasing the temperature of 1.23% APF gel from 4 to 25°C and 37°C did not cause a significant change in enamel microhardness of permanent teeth.