Curing Characteristics of a Polyester Methacrylate Oligomer for Dental Application

Designer Molecules Inc. has recently introduced a cyclohexyl methacrylate terminated polyester oligomer PEM-665.This oligomer is considered a promising candidate material in place of BisGMA oligomer based on BisPhenol-A, which is now considered as an endocrine disruptor with health hazard implications. Objective: The goal of this study was to characterize the curing characteristics of PEM-665 oligomer under visible light activation. Method: PEM-665 (PEM) and BisGMA (Bis) solutions were prepared with TEGDMA (Triethylene glycol dimethacrylate) diluent in different proportions under a factorial design. The initiators were CQ (DAEMA was used as amine accelerator for CQ) and DPO in 0.5% concentration. Eight solutions were prepared in a factorial design: PEM/TEGDMA 70/30 DPO; PEM/TEG 70/30 CQ; PEM/TEG 50/50 DPO; PEM/TEG 50/50 CQ; Bis/TEG 70/30 DPO; Bis/TEG 70/30 CQ; Bis/TEG 50/50 DPO; Bis/TEG 50/50 CQ. BISCO VIP visible light was used to cure the liquid solutions using 30 and 60 sec exposure times. TA Instruments Differential Scanning Calorimeter (DSC 2910) was used to determine molar heat of cure. Thermo-Nicolet (AVATAR 370) FT-IR was used to evaluate conversion of C=C double bonds (using 1637 cm^-1 spectral peak). Results: Molar heat of cure (KCals/mole) values ranged between 16.79 and 19.79. ANOVA and Tukey HSD pairwise contrast showed statistically significant differences between main effects [(Monomer (M), Proportion (Pro), Time (T), Initiator (In)); P= .0043, .0282, 0.0246, and <.0001 respectively].  There were also significant interaction effects [M*Pro, P=.0241,,T*In, P=.0075]. Initial conversion of double bonds after cure ranged between 50 to 60%. PEM cure behavior was similar to that of BisGMA under optimized exposure conditions used in this study. Dark cure (continued ambient polymerization after initial cure) needs further study. Conclusion: The results suggest that PEM-665 appears to be a promising candidate material for dental polymer applications.