Effects of simulated pulpal pressure, mechanical and thermocycling challenge on the microtensile bond strength of resin luting cements

This study aimed at comparing the microtensile bond strength (μTBS) of three simplified luting strategies after different aging processes. Sixty human molars were prepared to expose flat middle dentin surfaces which received the following luting procedures: (i) SB+ARC - two-step etch-and-rinse adhesive+conventional resin cement (Adper Singlebond 2+RelyX ARC, 3M-ESPE); (ii) S3+PAN - one-step self-etch adhesive+conventional resin cement (Clearfil S3+Panavia F2.0, Kuraray Medical); (iii) U200 - self-adhesive resin cement (RelyX U200,3M-ESPE). The specimens were finally restored by indirect resin composite procedures (Filtek Z100,3M-ESPE). The aging regimens were water storage at 37 °C for one week (control), one week of 20 cm H₂O simulated pulpal pressure (SPP), 200,000 mechanical loading (ML) cycles, or 5000 thermal cycles (TC). The μTBS data was analyzed by two-way ANOVA and Tukey's test (α=0.05). SB+ARC showed significantly higher μTBS for control and all aging processes (p<0.001). Nevertheless, TC had no effect on the bond strength of SB+ARC. No difference in μTBS was observed between S3+PAN and U200 after SPP (p=0.251), but significant lower values were found for U200 after ML (p=0.010) besides being superior in the control groups (p<0.001). For U200, all ageing regimens induced significant reductions in the bond strength (p<0.001) with a more pronounced negative effect after ML. S3+PAN showed significant lower bond strength (p=0.010) only after ML aging. Two-step etch-and-rinse adhesive associated with dual-curing conventional resin cement may present the highest overall μTBS. However, the use of S3 one-step self-etch adhesive along with conventional resin cements may provide the most stable luting performance under the tested aging strategy.