This study aimed to evaluate the effects of simulated pulpal pressure on the durability of microtensile bond strength (µTBS) and analyze the micro-morphological structure of the resin-dentin interface of dentin treated with Single Bond Universal; a universal adhesive.

Dentin discs were prepared from forty extracted human mandibular third molars by cutting above and below the CEJ 2 mm into the tooth segment model with 1 mm remaining dentin thickness. The bonding and resin composite placement processes were done under 2 different conditions between a group using a simulated pulpal pressure device (Simulated pulpal pressure: S) and a group without a simulated pulpal pressure device (Non-simulated pulpal pressure: N). The bonded specimens were longitudinally sectioned into the sticks with dimensions approximately 1x1 mm². Two sticks obtained from the center of each specimen were used for µTBS testing with different conditions: immediate testing (n=10) and testing after the 10,000-cycles thermocycling process (n=10).  The failure mode of the fractured specimens was observed under a scanning electron microscope (SEM). The remaining slabs were further stained with silver nitrate, embedded, and polished for resin-dentin interface observation under the SEM. The data were analyzed using the 2-way ANOVA at the 95% significant level with SPSS software.

                The NI group presented the highest µTBS values (30.15±3.08 MPa) follow by the SI group (25.96±3.90 MPa), NT group (25.25±2.44 MPa), and ST group (22.47±1.75 MPa) (p<0.05). The failure mode of all testing groups was an adhesive failure, in which the S group showed a fracture pattern at the top of the adhesive layer while the N group was broken at the bottom of the adhesive layer. The study of the resin-dentin interface revealed that the thickness of the hybrid layers ranged from 0.94-1.02 µm. The deposition of silver nitrate particles in the immediate testing group was presented both in SI and NI groups. After the thermocycling process, more accumulation of silver nitrate was observed in both ST and NT groups. In conclusion, the µTBS values and nanoleakage of resin-dentin interface obtained from Single Bond Universal could be affected by simulated pulpal pressure and 10,000-cycle thermocycling process.