Doxycycline as a dentin pretreatment agent for MMP-2 inhibition and maintaining hybrid layer stability over time

The aim of this study was to evaluate the effect of doxycycline (DXC) as a dentin pretreatment agent on the inhibition of matrix metalloproteinase 2 (MMP-2) and preservation of microtensile bond strength (μTBS) of the adhesive-dentin interface over time. MMP-2 was analyzed by gelatin zymography in buffers containing 5 mM CaCl2 (Tris-CaCl2) in 50 mM Tris-HCl buffer with the addition of DXC at 2, 0.2 and 0.02% (v/v). The effect of DXC at 0.2% (concentration defined after MMP-2 inhibition analysis) on the μTBS of the adhesive-dentin interface was evaluated after 24 h and 6 months. Data (MPa) were analyzed by two-way ANOVA followed by pairwise comparison within groups at different time-points of water-storage (24 h and 6 months) (α = 0.05). DXC was able to completely inhibit MMP-2 expression at 2% and 0.2%, whereas at 0.02% there was only a partial inhibition. Dentin pretreatment with DXC at 0.2% was capable of maintaining μTBS values up to 6 months. Under visual inspection, an evident staining of the adhesive interface was observed for DXC. DXC had positive effects on MMP-2 inhibition and μTBS up to 6 months. However, the staining of the adhesive interface with DXC may be expected. Although DXC may improve in vitro bond stability in dentin, the clinical impact of the staining of the adhesive interface should be clarified.