Purpose: Endogenous dentin enzymes degrade collagen fibrils in the restoration-dentin interface. Zinc has been identified as a potential enhancer of adhesive interface stability of adhesive interface by inhibiting enzymatic activity. The present study aimed to investigate the degradation resistance of adhesive interfaces created by a resin adhesive containing zinc zeolite nanoparticles.

Materials and methods: Dentin beams (1 mm x 2 mm x 6 mm), completely demineralized in 0.5 M EDTA and treated with 10 % phosphoric acid for 15 min (control), were immersed in experimental resin (40 % bis-GMA, 30 % TCDM, 28.75 % TEGDMA, and 1 % EDMAB) modified with 0, 2, 5 and 10 wt% zinc zeolite nanoparticles for 2 h. Each beam was then incubated in artificial saliva medium for 1, 3, 7, 14 and 30 days, with dry mass loss measured at each time-point. Hydroxyproline and CTX contents were analyzed in the incubation medium. Zinc release from zinc zeolite-containing resin disks was measured with atomic emission spectroscopy. The microtensile bond strength (μTBS) of zinc zeolite-modified adhesive resin (All Bond Universal, Bisco Inc.) to dentin was also tested. The data were analyzed using repeated measures of ANOVA, and ANOVA and post-hoc Tukey HSD tests at p = 0.05.

Results: Zinc zeolite at 10 wt% showed higher mass loss at all time-points, except on the 1-day (p < 0.05). No significant difference was found in hydroxyproline contents of the incubation medium (p > 0.05), however, the CTX quantity was higher in the zinc zeolite 10 % group (p < 0.05). Zinc release was confirmed for zeolite groups, reaching the maximum level at the 7 days of incubation. Zinc zeolite at 10 wt% resulted in significantly lower μTBS (p < 0.05).

Conclusions: Zeolite nanoparticles incorporated in dentin adhesives may serve as ion reservoirs. However, zinc content of zeolite particles should be adjusted according to the optimum levels for the inhibition of dentin enzymes.