IADR Abstract Archives
Replacing HEMA with an Alternative Water-compatible Crosslinking Monomer
Objectives: 2-Hydroxyethyl methacrylate (HEMA) is common in dental adhesives for surface wetting and viscosity control. However, it is prone to water-induced phase separation with limited reactivity and strength associated with the water/HEMA-rich domains. This study assesses the potential for partial or complete substitution of a water-miscible monomer capable of dense polymer network formation in place of HEMA in model dental adhesive resins.
Methods: Varied proportions of HEMA and a tetrahydroxy dimethacrylate (THDMA) derived from a tartaric acid core structure were prepared for testing (1:0, 1:3, 1:1, 3:1, 0:1 mass ratios). Bulk photopolymerizations were conducted with evaluations that included reaction kinetics (FT-IR), flexural modulus/strength (MTS universal testing) and water contact angle (goniometer) in addition to other tests such as resin viscosity and water uptake/solubility for the photopolymers.
Results: 1:1 HEMA/THDMA produced the highest conversion (94.3±1.5%) compared to either homopolymer (89.6±0.2% and 87.9±0.5%, respectively). The maximum rate of the HEMA bulk homopolymerization was 2 to 3x slower than any THDMA-containing formulation. HEMA and THDMA homopolymers had similar flexural moduli (1.174±0.2 and 1.289±0.1GPa) and strengths (46.6±7.9 and 49.6±3.7MPa, respectively); however, the 1:1 and 3:1 copolymers produced synergistically enhanced modulus and strength results (1:1=1.662±0.1GPa; 63.4±4.6MPa and 3:1=1.833±0.3GPa; 73.3±5.0MPa). The higher water contact angle of poly(HEMA) (46.3°) relative to poly(THDMA) (43.0°) indicates that THDMA is somewhat more hydrophilic. In the presence of 25wt% water, the THDMA homopolymerization proceeds 18-fold faster than that of HEMA.
Conclusions: THDMA is significantly more viscous than HEMA, which limits its potential to completely replace HEMA in BisGMA-based adhesive resins. However, based on the enhanced polymerization rates, particularly in the presence of water, and improved polymer mechanical properties for HEMA/THDMA copolymers observed here, the partial substitution of THDMA for HEMA in ternary BisGMA/HEMA/THDMA resins, as well as other resins compositions that avoid a poorly cured, water-rich phase with low crosslink density, appear as attractive goals.
Methods: Varied proportions of HEMA and a tetrahydroxy dimethacrylate (THDMA) derived from a tartaric acid core structure were prepared for testing (1:0, 1:3, 1:1, 3:1, 0:1 mass ratios). Bulk photopolymerizations were conducted with evaluations that included reaction kinetics (FT-IR), flexural modulus/strength (MTS universal testing) and water contact angle (goniometer) in addition to other tests such as resin viscosity and water uptake/solubility for the photopolymers.
Results: 1:1 HEMA/THDMA produced the highest conversion (94.3±1.5%) compared to either homopolymer (89.6±0.2% and 87.9±0.5%, respectively). The maximum rate of the HEMA bulk homopolymerization was 2 to 3x slower than any THDMA-containing formulation. HEMA and THDMA homopolymers had similar flexural moduli (1.174±0.2 and 1.289±0.1GPa) and strengths (46.6±7.9 and 49.6±3.7MPa, respectively); however, the 1:1 and 3:1 copolymers produced synergistically enhanced modulus and strength results (1:1=1.662±0.1GPa; 63.4±4.6MPa and 3:1=1.833±0.3GPa; 73.3±5.0MPa). The higher water contact angle of poly(HEMA) (46.3°) relative to poly(THDMA) (43.0°) indicates that THDMA is somewhat more hydrophilic. In the presence of 25wt% water, the THDMA homopolymerization proceeds 18-fold faster than that of HEMA.
Conclusions: THDMA is significantly more viscous than HEMA, which limits its potential to completely replace HEMA in BisGMA-based adhesive resins. However, based on the enhanced polymerization rates, particularly in the presence of water, and improved polymer mechanical properties for HEMA/THDMA copolymers observed here, the partial substitution of THDMA for HEMA in ternary BisGMA/HEMA/THDMA resins, as well as other resins compositions that avoid a poorly cured, water-rich phase with low crosslink density, appear as attractive goals.