Introduction: Resin composites are bonded to tooth-dentin via the formation of a resin-impregnated dentinal collagen, known as the hybrid layer (HL). Unprotected ester linkages of resin composites and adhesives, such as bis-phenyl glycidyl dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-Hydroxyethyl methacrylate (HEMA) are hydrolyzed by salivary and bacterial esterases, generating degradation by-products (BBPs), such as bis-hydroxy-propoxyphenyl propane (BisHPPP) and triethylene glycol (TEG) at the HL. The HL could also be degraded by dentinal endogenous matrix metalloproteinases (MMPs). Galardin has been suggested as a specific MMP-inhibitor for preservation of HL. However, its long-term inhibitory effect has not been investigated. The objectives of the study were to investigate the effect of resin composites monomers and their BBPs on soluble recombinant human MMPs and to assess the long-term inhibitory effect of galardin on activated human dentinal MMPs.
Materials and methods: BisGMA, TEGDMA, TEG, Bis-HPPP, and HEMA solutions in relevant concentrations to in vivo conditions (0.1 mM) were prepared. Three samples of each experimental solution were used to study their effect on MMP-1 (collagenase), MMP-2 (gelatinase), MMP-8 (collagenase) and MMP-9 (gelatinase). A Fluorimetric assay was used to measure MMP activity at Ex/Em=490 nm/520 nm. Dentin beams (3×1×3mm) were prepared from human extracted third molars. Half of the specimens were sterilized using γ-irradiation (25kGy). In a simulation of a total-etch adhesive system procedure that activates dentinal MMPs, the beams were etched with 37% phosphoric acid gel for 15 seconds, and washed for 30 seconds with distilled water. Then, 0.2 mM galardin was applied to the etched dentin for 30 seconds. Specimens were incubated in distilled water for up to 180 days at 37°С. A colorimetric assay was used to measure dentinal MMP activity via absorbance at 415 nm.
Results and Discussion: MMP-8 and MMP-9 activities were significantly (p˂0.05) increased in the presence of Bis-GMA and TEGDMA, while TEGDMA was the only substance that increased the activity of MMP-2 (p<0.05) (Fig.1).
MMP-1 activity was not significantly increased in the presence of any experimental solutions vs. the control. Galardin exhibited significant (P< 0.05) inhibitory effect on non-sterile and γ-irradiated dentin beams after 0, 7 & 30 days and 0, 7, 30 & 60 days respectively (Fig. 2).
However, no significant inhibition was detected for both groups between the control and the inhibitory groups for 90, 135 and 180 days.
Conclusions: These results indicate that certain components of resin composites and their BBPs could affect MMPs’ activity, modulating the latter’s degradative activity toward the hybrid layer, potentially affecting the longevity of resin composite restorations. Application of galardin has only short-term effect on dentinal MMP activity that should be supplemented for long-term effect.