The role of MMPs inhibitors in the stability of the adhesive interface

Aims: This thesis aimed to investigate the influence of several protease inhibitors/inactivators, as separate primers or blended within the adhesive resin, on the longevity of dental restorations and on the dentinal enzymatic activity immediately, or after aging in vitro. Methods: A series of studies was conducted using several different MMPs inhibitors and several adhesive systems. The first three studies investigated the longevity of the hybrid layer by means of microtensile bond strength test, and the enzymatic activity using gelatin and in situ zymography, immediately or after 1 year of aging in the artificial saliva. Study 4 tested samples bonded with or without an inhibitor-containing-primer, that were previously aged for 10 years. The degradation of the hybrid layer was observed using transmission electron microscopy, the enzymatic activity in the hybrid layer using in situ zymography. Raman spectroscopy was used to investigate whether the active substance was still within the hybrid layer after 10 years. Results: The results of the studies showed that the inhibitors/inactivators of endogenous dentinal enzymes were efficient in preserving bond strength after aging in vitro when used as separate primers. In the cases when the inhibitory agent was introduced within the adhesive resin, bond preservation was adhesive system- and/or bonding mode-dependent. The enzymatic activity was lower in all experimental groups, at baseline, as well as after aging (for 1 and 10 years) with a slight influence of the bonding mode. Conclusions: The tested protease inhibitors used as separate aqueous primers in etch-and-rinse adhesives seem to be clinically applicable, since the procedure is not overly time-consuming and seems to preserve the hybrid layer over time. As for the inhibitors blended within adhesives, comprehensive studies on the mechanical properties of the adhesives as well as their influence on the longevity of the hybrid layer should be performed before clinical use.