Investigation of physio-mechanical properties of cross-linked Bis-GMA/TEGDMA dental resins: A molecular dynamics study

Abstract

In this work, molecular dynamics simulation was employed to investigate the cross-linked network structure formation and resulting physio-mechanical properties of typical Bis-GMA/TEGDMA dental resin models. An automated polymerization protocol was initially proposed to mimic the curing process and cross-linked Bis-GMA/TEGDMA models were constructed with different degrees of conversion (DCs). The network structure of the cured chains was then characterized by examining radial distribution function (RDF) and molecular weight fraction profiles. The RDF peaks at ∼1.54 Å indicated the polymerization successfully proceeds, and the molecular weight fraction of the largest cross-linked chain increases with DC, while that of the second largest molecule starts to decrease around a DC of 40 %, signifying the formation of the cross-linked network. In addition, the effects of the 3D network formation on the physio-mechanical properties, i.e., density, volume shrinkage, glass transition temperature (Tg), and elastic modulus, were also investigated. As the DC rises, both the density and volume shrinkage exhibit a significant increase due to the double bond conversion. Furthermore, Tg was evaluated and adjusted at various DCs and their relation (Tg vs. DC) agrees well with the DiBenedetto’s equation. More intriguingly, the elastic modulus was found to increase almost linearly with DC; while discrepancy still exists for models with DC < 40 % as the dental resins present a rubber-like state (T > Tg). The findings in this work are believed to provide a robust automated polymerization protocol as well as the atomic/molecular scale understanding of the cross-linked network structure and physio-mechanical properties of Bis-GMA/TEGDMA dental resins.