Experimental resin-modified calcium-silicate cement containing N-(2-hydroxyethyl) acrylamide monomer for pulp tissue engineering

Abstract

Aim: Our study aimed to measure (1) the flexural strength, (2) shear bond strength to dentin, (3) pH, and (4) calcium (Ca) release of a series of innovative resin-modified calcium-silicate pulp-capping cements (Rm-CSCs). Using an ex-vivo human vital tooth-culture model, we additionally assessed (5) their pulp-healing initiation when brought in direct contact with human dental pulp tissue. Methodology: Three experimental Rm-CSCs, being referred to ‘Exp_HEAA’, ‘Exp_GDM’ and ‘Exp_HEAA/GDM’, contained either 20 wt% N-(2-hydroxyethyl) acrylamide (HEAA), 20 wt% glycerol dimethacrylate (GDM) or 10 wt% HEAA plus 10 wt% GDM, added to a common base composition consisting of 25 wt% urethane dimethacrylate (UDMA), 10 wt% 4-methacryloxyethyl trimellitate anhydride (4-MET), and 5 wt% N,N'-{[(2-acrylamido-2-[(3-acrylamidopropoxy)methyl] propane-1,3-diyl)bis(oxy)]bis-(propane-1,3-diyl)}diacrylamide (FAM-401). As Ca source and radiopacifier, 37 wt% tricalcium silicate powder (TCS) and 3 wt% zirconium oxide (ZrO 2) were respectively added. Results: All three experimental Rm-CSCs revealed a significantly higher flexural strength and shear bond strength to dentin (p < 0.05) than the commercial reference Rm-CSC TheraCal LC (Bisco). Exp_HEAA presented with a significantly higher Ca release and pH at 24 h compared with the other Rm-CSCs (p < 0.05). At 1 week, the Ca release and pH of Exp_HEAA and Exp_HEAA/GDM was significantly higher than those of Exp_GDM and TheraCal LC (p < 0.05). Using the ex-vivo human vital tooth culture model, Exp_HEAA revealed pulp-healing initiation capacity as documented by nestin and collagen-I expression. Conclusions: Depending on the formulation, the innovative Rm-CSCs performed favorably for primary properties of relevance regarding pulp capping, this more specifically in terms of flexural strength, bond strength to dentin, as well as alkaline pH and Ca release. However, only Exp_HEAA revealed pulp-healing initiation in direct contact with human dental pulp tissue in the ex-vivo human vital tooth-culture model. This promising outcome for Exp_HEAA should be attributed to the combined use of (1) a novel hydrophilic acrylamide monomer, enabling sufficient polymerization while maintaining adequate hydrophilicity, with (2) the functional monomer 4-MET, possessing chemical bonding potential to dentin, and (3) tricalcium silicate powder to achieve an alkaline pH and to release Ca in a sufficient and controlled way.