Influence of the base and diluent monomer on network characteristics and mechanical properties of neat resin and composite materials.

This study evaluated the effect of the combination of two dimethacrylate-based monomers [bisphenol A diglycidyl dimethacrylate (BisGMA) or bisphenol A ethoxylated dimethacrylate (BisEMA)] with diluents either derived from ethylene glycol dimethacrylate (ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate) or 1,10-decanediol dimethacrylate (D3MA) on network characteristics and mechanical properties of neat resin and composite materials. The degree of conversion, maximum rate of polymerization and water sorption/solubility of unfilled resins and the flexural strength and microhardness of composites (after 24 h storage in water and 3 months storage in a 75 vol% ethanol aqueous solution) were evaluated. Data were analyzed with two-way ANOVA and Tukey's test (α = 0.05). The higher conversion and lower water sorption presented by BisEMA co-polymers resulted in greater resistance to degradation in ethanol compared with BisGMA-based materials. In general, conversion and mechanical properties were optimized with the use of long-chain dimethacrylate derivatives of ethylene glycol. D3MA rendered more hydrophobic materials, but with relatively low conversion and mechanical properties.

Correlation between polymerization stress and interfacial integrity of composites restorations assessed by different in vitro tests.

OBJECTIVE: to correlate polymerization stress data obtained under two compliance conditions with those from different interfacial quality tests. METHODS: Six commercial composites were tested (Filtek Z250/3M ESPE, Heliomolar/Ivoclar Vivadent, Aelite LS Posterior/Bisco, Filtek Supreme/3M ESPE, ELS/Saremco and Venus Diamond/Heraeus Kulzer). Bond strength (BS) was evaluated by push-out test on slices of bovine dentin (2-mm thick) with tapered cavities. For microleakage (ML) and gap analysis, cylindrical cavities in bovine incisors (4-mm diameter and 1.5-mm height) were restored and epoxy replicas of the cavo-surface margins were prepared for analysis under scanning electron microscopy (200×). The same specimens were submitted to a microleakage protocol using AgNO3 as tracer. After sectioned twice perpendicularly, ML was determined under a stereomicroscope (60×). Polymerization stress (PS, n=5) was determined by the insertion of the composite (h=1.5mm) between poly(methyl methacrylate), PMMA, or glass rods (Ø=4 mm) attached to a universal testing machine. Data were analyzed using Kruskal-Wallis (ML and gaps), and ANOVA/Tukey (BS and PS, α=5%). Pearson's correlation test was used to verify correlations between stress and interfacial quality. RESULTS: BS varied from 4.7 to 7.9 MPa. Average ML data ranged from 0.34 to 0.89 mm. Maximum ML varied from 0.61 to 1.34 mm. Gap incidence varied from 13 to 47%. PS ranged from 2.5 to 4.4 MPa in PMMA, and between 2.1 and 8.2 in glass. Statistically significant correlations were observed between stress and interfacial quality, except between BS and PS in glass. These correlations were stronger when PMMA was used as bonding substrate. CONCLUSIONS: PS data obtained using a high compliance testing system showed a stronger correlation with "in vitro" interfacial integrity results, compared to data from a low compliance system.

Monomers used in resin composites: degree of conversion, mechanical properties and water sorption/solubility.

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.

Monomers used in resin composites: degree of conversion, mechanical properties and water sorption/solubility

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 (H0=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 (H0=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.

A fase orgânica de compósitos resinosos é constituída por dimetacrilatos, sendo os mais comuns o dimetacrilato de diglicidilabisfenol A (BisGMA), sua versão etoxilada (BisEMA), dimetacrilato de trietilenoglicol (TEGDMA) e dimetacrilato de uretano (UDMA). Este estudo comparou os homopolímeros formados pelos monômeros utilizados em compósitos restauradores dentários em relação a seus graus de conversão (GC) e cinética de reação (através de espectroscopia no infra-vermelho), propriedades mecânicas (módulo de elasticidade em flexão e resistência à flexão, MF e RF, respectivamente), sorção de água e solubilidade (SA e SL, respectivamente - ISO4049). Os materiais se tornaram fotopolimerizáveis pela adição de canforoquinona/metacrilato de dimetilaminoetila e foram fotoativados utilizando uma fonte de luz de quartzo-tungstênio-halogênio filtrada para 400-500 nm. O TEGDMA apresentou o maior GC, seguido pelo BisEMA, UDMA e BisGMA, tanto aos 10 min quanto após 24 h (p<0,001). O UDMA mostrou a maior velocidade de reação, seguido pelo TEGDMA, BisEMA e BisGMA (H0=13,254, p<0,001). O UDMA e o TEGDMA apresentaram MF semelhantes, estatisticamente superiores ao BisEMA e ao BisGMA (p<0,001), os quais por sua vez apresentaram valores estatisticamente semelhantes (p>0,001). Para RF, o UDMA apresentou o valor mais alto, seguido pelo TEGDMA, BisEMA e BisGMA (p<0,001), sendo os dois últimos estatisticamente semelhantes (p>0,001). O BisGMA apresentou a maior SA, e o TEGDMA e o BisEMA as menores. O UDMA foi estatisticamente semelhante a todos (H0=16,074, p<0,001). O TEGDMA apresentou a maior SL, seguido pelo UDMA, BisGMA e BisEMA (p<0,001). Os homopolímeros demonstraram desempenhos bastante distintos em relação à cinética de polimerização, propriedades em flexão e sorção e solubilidade. Tais diferenças justificam o uso de co-polímeros para a obtenção de materiais com propriedades físicas otimizadas.