A dynamic mechanical method to assess bulk viscoelastic behavior of the dentin extracellular matrix

Objectives. To develop a protocol for assessment of the bulk viscoelastic behavior of dentin extracellular matrix (ECM), and to assess relationships between induced collagen cross linking and viscoelasticity of the dentin ECM. Methods. Dentin ECM was treated with agents to induce exogenous collagen cross-linking: proanthocyanidins (PACs) from Vitis vinifera - VVe, PACs from Pinus massoniana PMe, glutaraldehyde - (GA), or kept untreated (control). A dynamic mechanical strain sweep method was carried out in a 3-point bending submersion clamp at treatment; after protein destabilization with 4 M urea and after 7-day, 6-month, and 12-month incubation in simulated body fluid. Tan 8, storage (E'), loss (E"), and complex moduli (E*) were calculated and data were statistically analyzed using two-way ANOVA and post-hoc tests (a = 0.05). Chemical analysis of dentin ECM before and after protein destabilization was assessed with ATR-FTIR spectroscopy. Results. Significant interactions between study factors (treatment vs. time points, p < 0.001) were found for all viscoelastic parameters. Despite a significant decrease in all moduli after destabilization, PAC-treated dentin remained statistically higher than control (p < 0.001), indicating permanent mechanical enhancement after biomodification. Covalently crosslinked, GA-treated dentin was unaffected by destabilization (p = 0.873) and showed the lowest damping capacity (tan 8) at all time points (p < 0.001). After 12 months, the damping capacity of PMe and VVe groups decreased significantly. Changes in all amide IR resonances revealed a partial chemical reversal of PAC-mediated biomodification. Significance. Viscoelastic measurements and IR spectroscopy aid in elucidating the role of inter-molecular collagen cross-linking in the mechanical behavior of dentin ECM. (C) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.