Dynamic Mechanical Behavior of Dentin Matrices Under Accelerated Protein De-stabilization

Objectives: Dentin stability is key for durable dental adhesive restorations. Strategies to enhance and sustain the mechanical properties of dentin for this purpose explored plant oligomeric proanthocyanidins (PACs) and synthetic agents (e.g. glutaraldehyde), as mediators of dentin biomodification, with different mechanisms of interactions to dentin. The aim was to investigate the bulk dynamic mechanical behavior of dentin matrix modified by PACs and glutaraldehyde under an accelerated chemical method of protein de-stabilization.

Methods: Demineralized dentin specimens (1.5 x 6 x 0.5 mm) were assigned into groups (n=5) 0.65% vitis vinifera (PAC_VV), 0.65% pinus massoniana (PAC_PM), 5% glutaraldehyde (GD), and control (buffer only). Strain sweep dynamic mechanical analysis (DMA, 1-100 mm amplitude at 1 Hz) were carried out in 3-point bending submersion clamp (Q800 DMA, TA) at baseline, treatment (T1), 4 M urea for 24 h - protein de-stabilization (T2), and after 7-day incubation (T3). Complex modulus (E*, in MPa) and tan δ were calculated and data statistically analyzed using two-way ANOVA and dedicated post-hoc tests (α=0.05).
Results: Significant interactions between study factors (treatment and time points, p<0.001) were found for E* and tan δ. At T1, PAC_VV and PAC_PM groups showed the highest E* among (p<0.008), followed by GD (p<0.003). Despite a significant 50% decrease in E* (p<0.001) at T2, PAC_VV and PAC_PM groups remained statistically higher than control (p<0.001). The E* and tan δ of glutaraldehyde and control groups were not affected by urea (p>0.2). GD showed the lowest tan δ at all time points (T1-T3) (p<0.001), indicating low damping.

Conclusions: DMA is a reliable method to perform repeated bulk dentin measurements. The protein de-stabilization protocol results in reproducible accelerated breakage of noncovalent bonds. Partial stable intermolecular bonds between collagen and PACs (VV and PM) showed irreversible biomodification to the dentin matrix leading to permanent enhanced mechanical properties. Distinct mechanical behavior was apparent between experimental groups.