Influence of Light-curing on Endogenous Dentinal Enzymatic Activity.

Objectives: Dentin collagen fibrils exposed after bonding procedures are possibly subject to degradation through a mechanism mediated by dentinal endogenous enzymes, thus impairing the longevity of the hybrid layer (HL). The aim of this in vitro study was to investigate the ability of a universal adhesive used in combination with dual-cure resin cements with/out light-activation to inhibit enzymatic activity, using in situ zymography. Methods: Composite overlays were prepared to be luted to middle/deep dentin surfaces of non-carious human molars. After bonding application (iBond universal adhesive used in the self-etch modality), the following resin cements were used for luting procedures: 1) RelyX Ultimate (RXU); 2) Panavia V5 (PAN); 3) Variolink EstheticDC (VAR). Resin cements were either used in the self-cure mode (SC; 1h at 37°C) or in the dual-cure mode (DC; 20s light-cure followed by 15 min self-cure at 37°C). After 24h, specimens were cut to expose the HL, glued to glass slides, polished and prepared for in situ zymography. Self-quenched fluorescein-conjugated gelatine mixture was placed on top of each specimen, protected with a cover slip and incubated in a dark humidified chamber at 37°C for 12h. Detection of endogenous gelatinolytic enzyme activity within the HL was evaluated with a multi-photon confocal laser scanning microscope. Results: The enzymatic activity, as showed by in situ zymography, was dependent to the polymerization mode of the resin cement. A lower level of fluorescence was present for RXU when DC, and this was statistically significant among all the groups (p<0.05). PAN demonstrated inferior enzymatic activity when only SC (P<0.05). VAR specimens in the SC group completely fractured during preparation procedures. Conclusions: Light-cure influences the dentinal enzymatic activity when a simplified bonding system is used in combination with dual-cure resin cements with a material-dependent trend. Further studies are necessary to investigate whether the enzymatic activity would change over time.