Alternative monomer for BisGMA-free resin composites formulations.

OBJECTIVE: Water sorption, high volumetric shrinkage, polymerization stress, and potential estrogenic effects triggered by leached compounds are some of the major concerns related to BisGMA-TEGDMA co-monomer systems used in dental composites. These deficiencies call for the development of alternative organic matrices in order to maximize the clinical lifespan of resin composite dental restorations. This study proposes BisGMA-free systems based on the combination of UDMA and a newly synthesized diurethane dimethacrylate, and evaluates key mechanical and physical properties of the resulting materials. METHODS: 2EMATE-BDI (2-hydroxy-1-ethyl methacrylate) was synthesized by the reaction between 2-hydroxy-1-ethyl methacrylate with a difunctional isocyanate (1.3-bis (1- isocyanato-1-methylethylbenzene) - BDI). The compound was copolymerized with UDMA (urethane dimethacrylate) at 40 and 60wt%. UDMA copolymerizations with 40 and 60wt% TEGDMA (triethylene glycol dimethacrylate) were tested as controls, as well as a formulation based in BisGMA (bisphenol A-glycidyl methacrylate)-TEGDMA 60:40% (BT). The organic matrices were made polymerizable by the addition of DMPA (2.2-dimethoxyphenoxy acetophenone) and DPI-PF6 (diphenyliodonium hexafluorophosphate) at 0.2 and 0.4wt%, respectively. Formulations were tested as composite with the addition of 70wt% inorganic content consisting of barium borosilicate glass (0.7µm) and fumed silica mixed in 95 and 5wt%, respectively. All photocuring procedures were carried out by a mercury arc lamp filtered to 320-500nm at 800mW/cm2. The experimental resin composites were tested for kinetics of polymerization and polymerization stress in real time. Flexural strength, elastic modulus, water sorption, and solubility were assessed according to ISO 4049. Biofilm formation was analyzed after 24h by luciferase assay. Data were statistically analyzed by one-way ANOVA and Tukey's test (α≤0.05). RESULTS: In general, the addition of 2EMATE-BDI into the formulations decreased the maximum rate of polymerization (RPMAX), the degree of conversion at RPMAX (DC at RPMAX), and the final degree of conversion (final DC). However, these reductions did not compromise mechanical properties, which were comparable to the BT controls, especially after 7-day water incubation. The incorporation of 60wt% 2EMATE-BDI reduced water sorption of the composite. 2EMATE-BDI containing formulations showed reduction in polymerization stress of 30% and 50% in comparison to BT control and TEGDMA copolymerizations, respectively. Biofilm formation was similar among the tested groups. SIGNIFICANCE: The use of the newly synthesized diurethane dimethacrylate as co-monomer in dental resin composite formulations seems to be a promising option to develop polymers with low-shrinkage and potentially decreased water degradation.

Effect of the combination of a crosslinking agent and a thiourethane additive on the properties of acrylic denture bases processed with microwave energy.

Thiourethane (TU) additives and difunctional, polymerizable crosslinking agents have been demonstrated to increase toughness in methacrylate-based materials. The aim of this study was to evaluate the potential reinforcement of acrylic denture bases by combining thiourethane additives and 1,6 hexanediol dimethacrylate (HDDMA) as an additional crosslinking agent. One commercial acrylic resin (Nature-Cryl MC; GC America) was tested by adding 0 (control) or 10 wt% TU, each of them combined with 0 (control), 10, 20 and 30 wt% HDDMA, for a total of 8 experimental groups. Materials were processed using microwave energy (500 W for 3 min) using microwave-safe molds and flasks. Flexural strength, modulus and toughness were obtained in 3-point bending (ISO 4049) using bars measuring 2 × 2x25 mm (n = 6). Dynamic mechanical analysis was used to determine glass transition temperature (Tg), breadth of tan delta (as a measure of polymer heterogeneity) and crosslinking density in 1 × 3x15 mm bars (n = 6) tested in tension, using a 3 °C/min heating rate (-30 to 180 °C). Viscosity samples were evaluated in a parallel plate reometer. Data were analyzed by two-way ANOVA and Tukey's test (α = 0.05). Results showed that on the samples not containing TU, HDDMA up to 20 wt% increased the flexural strength and thoughness (and up to 30 wt% HDDMA increased the modulus). The addition of TU did not affect those properties (except for the increase in elastic modulus), but the combination TU + HDDMA led to decreased properties overall. The addition of HDDMA decreased the viscosity for all materials, and the presence of TU did not affect viscosity. The Tg increased linearly with the concentration of HDDMA, except in the groups containing TU - in general, the addition of TU reduced Tg. The crosslinking density increased with the addition of HDDMA for all materials, regardless of the presence of TU. The addition of TU significantly decreased crosslinking density. The breadth of tan delta was not affected by the addition of HDDMA, but significantly increased with the addition of TU. In conclusion, the chain-breaking effect of TU on polymerizing methacrylates was deleterious in the case of methyl methacrylate, since it forms a linear polymer. The addition of HDDMA up to 20 wt% and not combined with TU significantly improved the tested properties.

Mechanical and biological characterization of resin-modified glass-ionomer cement containing doxycycline hyclate.

OBJECTIVES: To characterize the mechanical and biological properties of a resin-modified glass ionomer cement (RMGIC) containing doxycycline hyclate. METHODS: The antibacterial effect of RMGIC containing 1.5, 3.0 and 4.5% doxycycline hyclate was assessed using two experiments - agar diffusion test for 24h and biofilm assay for 24h and 7 days - against some cariogenic bacteria. Briefly, base layers of BHI agar and 300µL of each inoculum were prepared in Petri dishes with 6 wells that were completely filled with materials. After 24h incubation, zones of bacterial growth inhibition were measured using a digital caliper. Biofilm assays were conducted using RMGIC specimens immersed in 24-well plates containing the inoculum in BHI broth. After 24h and 7 days, each specimen were removed, vortexed and the suspension diluted and inoculated in BHI plates for subsequent bacterial counting. Cytotoxicity tests used 50 specimens made in sterilized metal molds, including Vitrebond as positive control. Extracts from every specimen were applied on the MDPC-23 odontoblast-like cells for 24h. The MTT assay and SEM evaluation determined cell metabolism and morphology, respectively. 80 cylindrical specimens were made from the previously cited groups, and were submitted to testing with a universal testing machine (Instron 4411) using a crosshead speed of 1.0mm/min for compressive strength and 0.5mm/min for diametral tensile strength, respectively. Data from antibacterial and cytotoxic effects, and mechanical properties were submitted to appropriated statistical tests. RESULTS: All tested groups showed growth inhibition of all tested strains (p<0.05) in 24h for both microbiological tests, but only 4.5% doxycycline have antibacterial effect after 7 days. None of doxycycline concentrations caused toxic effect to the MDPC-23 cells or presenting alterations to mechanical properties. CONCLUSION: The incorporation of up to 4.5% doxycycline hyclate into RMGIC inhibits important oral microorganisms, without modifying biological and mechanical characteristics of the dental material, suggesting a new alternative for the treatment of dental caries.