Use of a specific MMP-inhibitor (galardin) for preservation of hybrid layer

Objective: Dentinal MMPs have been claimed to contribute to the auto-degradation of collagen fibrils within incompletely resin-infiltrated hybrid layers and their inhibition may, therefore, slow the degradation of hybrid layer. This study aimed to determine the contribution of a synthetic MMPs inhibitor (galardin) to the proteolytic activity of dentinal MMPs and to the morphological and mechanical features of hybrid layers after aging. Methods: Dentin powder obtained from human molars was treated with galardin or chlorhexidine digluconate and zymographically analyzed. Microtensile bond strength was also evaluated in extracted human teeth. Exposed dentin was etched with 35% phosphoric acid and specimens were assigned to (1) pre-treatment with galardin as additional primer for 30 s and (2) no pre-treatment. A two-step etch-and-rinse adhesive (Adper Scotchbond 1XT, 3M ESPE) was then applied in accordance with manufacturer's instructions and resin composite build-ups were created. Specimens were immediately tested for their microtensile bond strength or stored in artificial saliva for 12 months prior to being tested. Data were evaluated by two-way ANOVA and Tukey's tests (α = 0.05). Additional specimens were prepared for interfacial nanoleakage analysis under light microscopy and TEM, quantified by two independent observers and statistically analyzed (χ² test, α = 0.05). Results: The inhibitory effect of galardin on dentinal MMPs was confirmed by zymographic analysis, as complete inhibition of both MMP-2 and -9 was observed. The use of galardin had no effect on immediate bond strength, while it significantly decreased bond degradation after 1 year (p < 0.05). Interfacial nanoleakage expression after aging revealed reduced silver deposits in galardin-treated specimens compared to controls (p < 0.05). Conclusions: This study confirmed that the proteolytic activity of dentinal MMPs was inhibited by the use of galardin in a therapeutic primer. Galardin also partially preserved the mechanical integrity of the hybrid layer created by a two-step etch-and-rinse adhesive after artificial aging.