Synthesis of none Bisphenol A structure dimethacrylate monomer and characterization for dental composite applications

In this study, new dimethacrylate monomer SiMA without Bisphenol A (BPA) structure was synthesized and used as base resin of dental composite materials with the aim of reducing human exposure to BPA derivatives.

SiMA was synthesized through ring-opening addition reaction between 1,3-bis[2(3,4-epoxycyclohex-1-yl)ethyl]tetra-methyldisiloxane and methacrylic acid, and its structure was confirmed by FT-IR and (1)H NMR spectra. SiMA was mixed with TEGDMA (50/50, wt/wt) and photoinitiation system (0.7 wt% of CQ and 0.7 wt% of DMAEMA) to form resin system. Experimental composite EC was then prepared by SiMA based resin loading with BaAlSiO2 microfillers (72wt%). Double bond conversion (DC) was determined by FT-IR analysis. Volume shrinkage (VS) was measured through variation of density before and after irradiation. Water sorption (WS) and solubility (SL) were obtained until the mass variation of polymer in distilled water kept stable. Flexural strength (FS) and modulus (FM) of the polymer were measured using a three-point bending set up. Extract of composite was used to evaluate its cytotoxic effect on humane dental pulp cells, and relative growth rate (RGR) was obtained by CCK-8 assay. Bis-GMA/TEGDMA (50/50, wt/wt) resin system and universal dental restorative materials 3M ESPE Filtek™ Z250 were used as references for neat resin system and composite material, respectively.

FT-IR and (1)H NMR spectra showed that structure of SiMA was the same as designed. For the neat resin systems: DC of SiMA based resin was higher than that of Bis-GMA based resin (p<0.05); SiMA based resin had lower VS than Bis-GMA based resin; WS of SiMA based resin was lower than that of Bis-GMA based resin (p<0.05), while SL of SiMA based resin was nearly the same as that of Bis-GMA based resin (p>0.05); FS and FM of SiMA based resin were lower than those of Bis-GMA based resin (p<0.05). For the composite materials: DC of EC was higher than that of Z250 (p<0.05); EC and Z250 had same VS; WS of EC was lower than that of Z250 (p<0.05), and SL of EC was higher than that of Z250 (p<0.05); FS and FM of EC were lower than those of Z250 (p<0.05); RGRs of EC were lower than those of Z250 after the cells were incubated with relative extract for 24h and 48h (p<0.05), while after being incubated for 72 h, RGR of EC and Z250 had no obvious difference (p>0.05).

SiMA had potential to replace Bis-GMA as base resin of dental composite materials. However, formulation of SiMA based resin and composite should be optimized in terms of mechanical strength to satisfy the requirements of resin based dental materials for clinical application.