Treating dentin with silver-containing solutions: 2-years bonding and ultramorphological evaluation

Purpose To evaluate the microtensile bond strength (µTBS) with a morphological and chemical characterization (SEM/EDS) of fractured sticks, and the endogenous enzymatic activity (MMPs) of dentin after application of two silver-containing primer solutions prior bonding with a universal adhesive after 2 yrs of artificial aging. Methods and Materials Human extracted molars were cut perpendicular to the long axis to obtain middle/deep dentin blocks (N=60) and the following groups were formed, according to the dentin surface pre-treatment and universal adhesive (Zipbond, SDI; ZB) application mode (n=10): 1) ZB applied in the self-etch mode (SE); 2) Riva Star (R) + SE (RSE); 3) Riva Star Aqua (A) + SE (ASE); 4) ZB applied in the total-etch mode (TE); 5) R + TE (RTE); 6) A + TE (ATE). After 24h, specimens were cut to obtain 1x1-mm thick slices. The µTBS test was performed at baseline (T0) and after 2 yrs (T2) of storage in artificial saliva at 37°C and 100% relative humidity. Fractography analysis and chemical characterization of debonded specimens were performed with SEM/EDS. To investigate the effect of silver-containing solutions on MMPs activity, 3 additional molars per group were processed for the in situ zymography analysis at T0 and T2. Data were statistically analyzed (p<0.05). Results The dentin pre-treatment, etching mode and aging significantly influenced bond strength (p<0.05). The control groups showed significantly higher bond values among groups, irrespective of the application mode and storage time (p<0.001). No bonding differences were found between R and A at T0 or T2. Artificial aging negatively affected the bond strength values among groups, with T0 > T2 (p<0.001). Total-etch application mode provided higher bond strength (p=0.014). Silver ions were present in the adhesive interfaces of specimens treated with R and A. Dentin pre-treatment significantly influenced the endogenous enzymatic activity (p<0.05). Specifically, A groups recorded the highest collagenolytic activity among groups (A>C>R) (p<0.05). Conclusion Bonding performance and endogenous enzymatic activity were influenced by pre-treatment with the silver-containing solutions tested, in particular after the use of Riva Star Aqua. Riva Star showed long term MMPs inhibitory effects comparable to the control groups. Further studies are warranted to validate these results.