Dentin Matrix Biomodification: Biomechanics of carious dentin and MMP activity

The biomodification of dentin by multi-functional collagen cross-linkers include reduction of the biodegradation rates of dentin matrix. Caries-affected (CA) dentin is the primary tissue present during dental restorative therapies of caries-infected teeth. The long-term mechanical properties of CA compared to sound dentin are unknown. Objective: To evaluate the long-term ultimate tensile strength (UTS) of sound and CA dentin modified by two collagen cross-linkers and their inhibitory effect on matrix metalloproteinases (MMP-2/9). Method: 15 sound and 30 non-cavitated carious molars had their crowns sectioned in the occlusal-cervical direction and further trimmed to an hourglass shape of 0.5x0.5 mm neck at each respective substrate. Specimens were demineralized (10% phosphoric acid, 5 hours), rinsed and divided into 3 groups (n=24): Control (distilled water), 6.5% grape seed extract (GSE), 5% glutaraldehyde (GD). Specimens were kept in their respective solutions for 30 minutes. UTS was assessed immediately and after 12 month storage in artificial saliva containing zinc at 37^oC. Data (expressed in MPa) were statically analyzed using ANOVA and Games-Howell (α=0.05). Inhibitory activity of recombinant human MMP-2 and MMP-9 were assessed by assay detection kits. Result: Statistically significant interactions were only observed between 2 factors (treatments vs. time, p<0.001) and differences were observed between treatments (p<0.001) and time (p<0.001). Control groups showed statistically significant decrease in the UTS after 12 month (Sound: 1.61±1.57; CA: 0) when compared to immediate (Sound: 12.64±4.92; CA: 10.13±4.98). Dentin matrix biomodified by GSE (sound: 12.25±4.86; CA: 12.34±4.03) and GD (sound: 10.17±4.00; CA: 12.89±4.92) remained remarkably stable. GD and GSE greatly reduced MMP activity; 97% and 90% for MMP-2 and 93%, and 84% for MMP-9, respectively. Conclusion: Degradation of dentin matrix over 12 months due to endogenous proteases activity is more pronounced in CA. Non-enzymatic cross-linking of dentin matrix impaired collagen breakdown and stabilized the UTS of sound and CA dentin.