The Effect of Thermocycling on the Shear Bond Strength of Flash-free Brackets and Healing Dynamics of Enamel Microcracks: An In vitro Study.

Abstract

Aim: This study evaluates long-term shear bond strength (SBS) and enamel micro cracks (MCs) healing after using adhesive pre-coated brackets (APC).

Materials and methods: A total of eighty extracted human premolar teeth were randomly divided into four experimental groups (n = 20 per group): Control group: Teeth underwent indentation but no bracket bonding; group II : Teeth were subjected to indentation without exposure to thermocycling; group III: Teeth experienced both indentation and thermocycling; group IV: No indentation was applied to the teeth; groups III and IV were further divided into two subgroups to simulate different clinical timelines: Subgroup A (n = 10): Teeth underwent 5,000 thermocycles, equivalent to six months of clinical use. Subgroup B (n = 10): Teeth were subjected to 10,000 thermocycles, representing 12 months of use. All precoated brackets underwent debonding with a universal testing machine to assess the SBS, and the adhesive remnant index (ARI) was scored to evaluate the amount of adhesive left on the tooth surface. The study also examined horizontal and vertical enamel cracks, both pre- and post-intervention, across all groups. Crack healing was quantitatively assessed using computer-assisted digital image analysis to ensure precision. For statistical evaluation, ANOVA, Kruskal-Wallis H-test, and Tukey's post-hoc tests were applied to assess differences among the groups.

Results: The Kruskal-Wallis H-test demonstrated no significant ARI difference between the groups (p = 0.790). A one-way ANOVA showed a significant difference among all groups (p < 0.001), with lower values observed in the group with indentation without thermocycling compared to all other groups and the groups with 5,000 thermocycles compared to the groups with, 10,000 thermocycles. Crack healing was observed in the control and second groups, and cracks were directly proportional to the number of thermocycles and SBS values.

Conclusion: The study showed that APC FF's SBS increased, and thermal aging did not change the failure pattern. Thermocyclers and SBS affected enamel cracks.

Clinical significance: The bond strength of pre-coated brackets and microcrack healing gradually increased with time, while the pattern of bond failure did not change. How to cite this article: Shamsan H, Albelasy NF, Farahat DS, et al. The Effect of Thermocycling on the Shear Bond Strength of Flash-free Brackets and Healing Dynamics of Enamel Microcracks: An In vitro Study. J Contemp Dent Pract 2024;25(9):836-845.