Abstract
The organic phase of resin composites is constituted by dimethacrylate resins, the most common monomers being the bisphenol A diglycidildimethacrylate (BisGMA), its ethoxylated version (BisEMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA). This study compared the homopolymers formed from the monomers used in restorative dental composites in terms of their degree of conversion (DC) and reaction kinetics (by near infra-red spectroscopy, n=3), mechanical properties (flexural modulus and strength in three point-bending, FM and FS, respectively, n=15), water sorption and solubility (WS and SL, respectively - ISO 4049, n=5). Materials were made photopolymerizable by the addition of camphoroquinone/dimethylamine ethyl methacrylate. TEGDMA showed the highest DC, followed by BisEMA, UDMA and BisGMA, both at 10 min and at 24h (p<0.001). UDMA showed the highest rate of polymerization, followed by TEGDMA, BisEMA and BisGMA (H(0)=13.254, p<0.001). UDMA and TEGDMA presented similar FM, significantly higher (p<0.001) than BisEMA and BisGMA, which in turn present statistically similar values (p>0.001). For FS, UDMA presented the highest value (p<0.001), followed by TEGDMA, then by BisEMA and BisGMA, which were statistically similar (p>0.001). BisGMA showed the highest WS, and TEGDMA and BisEMA the lowest. UDMA was statistically similar to all (H(0)=16.074, p<0.001). TEGDMA presented the highest SL, followed by UDMA, BisGMA and BisEMA (p<0.001). The tested homopolymers presented different behaviors in terms of polymerization kinetics, flexural properties, water sorption and solubility. Therefore, the use of copolymers is justified in order to obtain high DC and mechanical properties, as well as good resistance to water degradation.
Highlights
Dimethacrylate-based resins find many applications in restorative dentistry
Dimethacrylate copolymerization through light or heat activation in the presence of an initiator results in a crosslinked polymer whose physicochemical properties depend on the degree of conversion (DC) and final network structure [1]
urethane dimethacrylate (UDMA) copolymers in general present higher flexural strength, elastic modulus and hardness [7]. Another alternative is the ethoxylated version of bisphenol A diglycidildimethacrylate (BisGMA), known as BisEMA with higher molecular weight (MW=540 g/mol), without the strong secondary molecular interactions given by hydroxyl groups, which reduces its viscosity and allows for higher DC and better mechanical properties to be achieved [8]
Summary
Dimethacrylate-based resins find many applications in restorative dentistry They are used as adhesives, pit-and-fissure sealants, and can be combined with silane-coated glass fillers to render the most widely used esthetic direct restorative material, as well as cementation agents and veneering materials. UDMA copolymers in general present higher flexural strength, elastic modulus and hardness [7] Another alternative is the ethoxylated version of BisGMA, known as BisEMA (ethoxylatedbisphenol A dimethacrylate; η=0.9 Pa; Fig. 1) with higher molecular weight (MW=540 g/mol), without the strong secondary molecular interactions given by hydroxyl groups, which reduces its viscosity and allows for higher DC and better mechanical properties to be achieved [8]. This study compares the homopolymers used in restorative dental composites in terms of their DC, reaction kinetics, mechanical properties (flexural modulus and strength), water sorption and solubility
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