Objective: This study was carried out to determine the effect of polyNIPAM microgel particles
on the microtensile bond strength (µTBS) of universal adhesive to dentin before and after thermocycling.
Materials and methods: Superficial dentin discs were prepared from young human upper premolars. Specimens were divided into three groups GI: All-Bond Universal adhesive was applied directly to etched dentin. G2: 2% polyNIPAM microgel was added to the adhesive before being applied to etched dentin. G3: polyNIPAM microgel was applied on etched dentin before application of the adhesive. In all groups, after light activation of the adhesive, resin composite (Filtek Z350 XT), was applied incrementally on the treated dentin specimens. A total of 120 beams were prepared. Half of these beams were subjected to 5000 cycles of 5 °C to 55 °C using a PCR thermocycler. Microtensile bond strength testing was performed on all specimens. The fractured dentin side of all specimens was inspected using a scanning electron microscope (SEM) at 200X magnification. Three sticks from each group were gold sputter coated and examined with SEM at 2000X. Results: The statistical analysis showed that before thermocycling, there was a statistically significant difference in the mean µTBS values of all the tested groups p <0.001. G1T0 showed the highest statistically significant mean µTBS values. After thermocycling, G1T1 showed the lowest statistically significant mean µTBS values. Failure mode analysis and SEM analysis confirmed and explained the µTBS results. Conclusion: The addition of p(NIPAM) microgel to etched dentin preserved the bond durability, particularly after thermocycling.