Evaluation of microtensile bond strength of composite under three aging conditions: A comparative in-vitro study

Objectives: To investigate the effects of different in-vitro artificial aging protocols on the micro tensile bond strength (µTBS) of composite restorations applied to dentin. Methods: A total of 88 teeth were prepared on dentin and divided into three distinct aging conditions and a control group: G1) Control group with no aging (n=22); G2) Thermal Cycling (Thermocycling) involving 10,000 cycles between 5°C and 55°C, with a dwell time of 20 seconds (n=22); G3) Mechanical Loading (Cyclic loading) with a 50 N load, a frequency of 1.5 Hz, and 10,000 cycles (n=22); G4) Combined Thermo-mechanical cyclic loading (TMCL) using the parameters of both Thermocycling and Cyclic loading (n=22). Following the preparation of specimens on dentin using standardized procedures, they were subjected to their respective aging conditions and subsequently underwent micro tensile bond strength µTBS testing. The resulting failure modes were classified into adhesive, mixed, and cohesive failures. Statistical analyses were conducted with α = 0.05 to determine significant differences between groups. Results: All aged groups showed lower µTBS compared to the control group. The TMCL group exhibited a significantly lower µTBS compared to both the Control and cyclic loading groups. However, no significant differences were observed between the Control, Thermocycling, and cyclic loading groups. Adhesive failure emerged as the predominant mode of failure across all aging groups. Conclusions: The combined aging condition of TMCL significantly influenced the µTBS of composite restorations, particularly at the adhesive layer located at the dentin/composite interface. Thermal cycling induced a lower µTBS compared to cyclic loading. These findings underscore the importance of standardized aging protocols for reliable comparison of adhesive performance. Clinical significance: The study establishes that the combined thermo-mechanical cyclic loading (TMCL) condition, evaluated using the micro tensile bond strength (µTBS) test, emerges as the most suitable in-vitro aging protocol for accurately assessing adhesive performance. This finding offers valuable guidance for researchers and clinicians in selecting a standardized aging approach that closely mimics real-world conditions.