The effect of pre-curing waiting time of different bonding resins on micro-tensile bond strength to dentin

Objective: To evaluate the effect of 30 s waiting time of different bonding resins on their micro- tensile bond strength (μTBS) to dentin. Method: The occlusal enamel of freshly extracted human third molars was removed to expose the middle dentin. The specimens were randomly assigned into four groups namely, Group I, two-steps-total-etch bonding system (Adper Single Bond 2/Filtek Supreme XT, ASB2/FSXT), Group II, two-steps-self-etch bonding system (Silorane System Adhesive/Filtek Silorane, SSA/FS), Group III, two-steps-self-etch bonding system (Adper SE Plus/Filtek Supreme XT, ASEP/FSXT) and Group IV, one-step-self-etch bonding system (Adper Easy One/Filtek Supreme XT, AEO/FSXT). Each group was further divided into two sub-groups according to the application time of the bonding resin (following manufacturer recommendation and 30s more than manufacturer recommendation). The corresponding resin composite (shade A3) was applied in 4 increments of 0.5-1 mm thickness each to build resin composite stump of 3-4 mm height. Each increment was light polymerized for 20 s using LED at intensity 1000 mW/cm^2. The specimens were stored in deionized water at 37 ℃ for 24 hrs. The specimens were cut into bars according to the non-trimming technique (n = 20/group) with surface area of 0.81 mm^2. The mTBS of the bars was tested using a micro-tensile device on a Universal testing machine at a crosshead speed of 1 mm/min. Result: Two-way ANOVA revealed a statistical significant difference in the two main effects, the types of bonding systems (P = 0.0024) and the application times of bonding resins (P = 0.0005). There was no statistical significant interaction between the two main effects (P = 0.9257). The methacrylate-based two-steps-total-etch bonding system and two-steps-self-etch bonding system showed significant higher values than that of the one-step-self-etch bonding system. Conclusion: i. Thirty-seconds pre-curing waiting time for bonding resins has a role in achieving higher mTBS to dentin. ii. Onestep- self-etching bonding system ranked as the lowest bonding system.