Background/Objectives: Bond reliability is essential in orthodontic treatment, as temperature fluctuations in the oral environment can weaken adhesive interfaces and increase the risk of bracket failure. However, direct comparison of the long-term durability of commonly used orthodontic resin cements under thermocycling conditions is limited. Therefore, the present study aimed to evaluate and compare the shear bond strength (SBS) and failure modes of Transbond™ XT and Orthomite™ LC before and after thermal cycling (Tc). Methods: A total of 60 bovine enamel specimens were used in this study. Specimens were bonded with either Transbond XT or Orthomite LC under standardized conditions. SBS was measured at 24 h (Tc0) and after 5000 thermal cycles (Tc5000). Failure modes were classified as adhesive (A), enamel cohesive (B), or bracket cohesive (C) failure. Statistical analyses included the Mann–Whitney U test for SBS and Fisher’s exact test for failure mode distribution. Results: At Tc0, there was no significant difference in SBS between the two cements (p > 0.05). After Tc5000, Orthomite LC showed significantly higher SBS than Transbond XT (p = 0.00368). Failure mode analysis revealed that, after Tc, Transbond XT exhibited a higher incidence of adhesive failures (A), whereas Orthomite LC predominantly demonstrated bracket cohesive failures (C) (p = 0.00020). Conclusions: Orthomite LC demonstrated greater resistance to thermal cycling–induced bond degradation compared with Transbond XT, likely due to differences in resin monomer composition and interface stability.
Okazaki et al. (Wed,) studied this question.