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This study evaluated the influence of formulation and thermal treatment on the degree of conversion, fracture toughness, flexural strength, and elastic modulus of experimental composites. Six composites were analyzed at BisGMA : TEGDMA molar ratios of 1 : 1 and 7 : 3 with filler at 30, 50, and 70 wt%. The degree of conversion was analyzed by Fourier transform infrared spectroscopy, fracture toughness was measured using the single-edge notched beam, and flexural strength and elastic modulus were measured with the 3-point bend test. For all tests, one-half of the specimens received thermal treatment at 170°C for 10 min. Data were analyzed by the Kruskal-Wallis or ANOVA/Tukey's test (α = 5%). The 1 : 1 BisGMA : TEGDMA ratio showed higher properties than the 7 : 3 ratio. Although the material with 70% filler had a conversion lower than the one with 50%, it showed higher mechanical properties. The thermal treatment improved all properties in all materials. Therefore, the use of an equimolar ratio of BisGMA : TEGDMA can be paired with 70 wt% filler to design dental composites that possess increased advantageous physical and chemical properties. Furthermore, the simple and low-cost method of thermal treatment proposed for use in clinical dentistry has been shown to effectively improve the properties of all evaluated materials.

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OBJECTIVE: to verify the effect of the addition of dicalcium phosphate dihydrate (DCPD) particles functionalized with di- or triethylene glycol dimethacrylate (DEGDMA or TEGDMA) on the degree of conversion (DC), post-gel shrinkage (PS), mechanical properties, and ion release of experimental composites. METHODS: Four composites were prepared containing a BisGMA/TEGDMA matrix and 60 vol% of fillers. The positive control contained only barium glass fillers, while in the other composites 15 vol% of the barium was replaced by DCPD. Besides the functionalized particles, non-functionalized DCPD was also tested. DC after 24 h (n = 3) was determined by FTIR spectroscopy. The strain gage method was used to obtain PS 5 min after photoactivation (n = 5). Flexural strength and modulus (n = 10) were calculated based on the biaxial flexural test results, after specimen storage for 24 h or 60 days in water. The same storage times were used for fracture toughness testing (FT, n = 10). Calcium and phosphate release up to 60 days was quantified by ICP-OES (n = 3). Data were analyzed by ANOVA/Tukey test (alpha: 5%). RESULTS: Composites containing functionalized DCPD presented higher DC than the control (p < 0.001). The material containing DEGDMA-functionalized particles showed higher PS than the other composites (p < 0.001). After 60 days, only the composite with DEGDMA-functionalized DCPD presented fracture strength similar to the control, while for flexural modulus only the composite with TEGDMA-functionalized particles was lower than the control (p < 0.001). FT of all composites containing DCPD was higher than the control after 60 days (p < 0.005). Calcium release was higher for the composite with non-functionalized DCPD at 15 days and no significant reductions were observed for composites with functionalized DCPD during the observation period (p < 0.001). For all the tested composites, phosphate release was higher at 15 days than in the subsequent periods, and no difference among them was recorded at 45 and 60 days (p < 0.001). CONCLUSIONS: DCPD functionalization affected all the studied variables. The composite with DEGDMA-functionalized particles was the only material with strength similar to the control after 60 days in water; however, it also presented the highest shrinkage. The presence of DCPD improved FT, regardless of functionalization. DCPD functionalization reduced ion release only during the first 15 days.

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OBJECTIVE: To verify the null hypothesis that in a high compliance testing system stress magnitude was not influenced by specimen dimensions and, therefore, by its cavity configuration factor (C-factor) and volume. METHODS: Twelve experimental groups were defined according to the specimen height (0.5, 1, 2 or 4mm) and diameter (4, 6 or 8mm). A selfcure composite (Bisfil 2B, Bisco) was inserted between the flat surfaces of two acrylic rods attached to the opposite ends of a universal testing machine. An extensometer with a gauge length of 10mm was attached to both rods to monitor specimen height. Force development was monitored for 30min and nominal stress was calculated dividing the maximum force value by the crossection of the rod. A second set of data was obtained dividing nominal stress by the corresponding longitudinal compliance (LC) of the system for that particular specimen size. Data was analyzed using two-way ANOVA/Tukey test (nominal stress), Kruskal/Wallis (normalized stress), both at alpha=5%, and regression analysis having either C-factor or volume as independent variable. RESULTS: Regression analysis involving nominal stress did not reveal strong relationships with the independent variables (C-factor: 0.437, volume: 0.662). A strong relationship was found between normalized stress and specimen volume (Radj(2)=0.886). Normalized stress showed no relationship with specimens' C-factor. Pairwise comparisons between groups with similar volumes revealed that normalized stress increased at higher C-factors. SIGNIFICANCE: By eliminating the influence of longitudinal compliance, a strong relationship between polymerization stress and specimen volume was revealed in a high compliance testing system.

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OBJECTIVE: This study determined the volumetric shrinkage, degree of conversion, sorption, solubility, and flexure properties (before and after aging) of commercial dental composites identified as "low shrinkage". METHODS: Six Bis-GMA-based composites (Point 4, ELS, Filtek Supreme, Aelite LS Posterior, Filtek Z250 and Heliomolar), a silorane-based (Filtek LS) and a dimer dicarbamate dimethacrylate-based composite (N'Durance) were studied. Total shrinkage was measured in a mercury dilatometer (n=3). Elastic modulus and flexural strength was determined by the three point bending test before and after 4 months aging in 75% ethanol solution (n=10). Sorption and solubility in water was assessed according to ISO 4049. Additionally, composite degree of conversion was determined using near-IR spectroscopy (n=3). Data were analysed using one-way/two-way ANOVA or Kruskal-Wallis, and Tukey's test. Student's t-test was used to compare storage periods (α=0.05). RESULTS: The volumetric shrinkage values ranged between 1.5% (Filtek LS) and 3.4% (Point 4). The materials presented different behaviors regarding aging in ethanol, as evidenced by the large range in values of percentage reduction for elastic modulus (26-75%) and flexural strength (25-86%). Sorption values ranged from 8.2µg/mm(3) (Aelite LS Posterior) to 38.2µg/mm(3) (Point 4). Solubility values ranged from -1.5µg/mm(3) (Filtek LS) to 5.7µg/mm(3) (Aelite LS Posterior). The degree of conversion values at 10min ranged between 28% (Filtek LS) and 73% (Point 4). At 72h after curing the values ranged between 39% (Filtek LS) and 83% (Point 4). SIGNIFICANCE: Among the materials identified by their manufacturers as "low shrinkage", only Filtek LS presented statistically lower values of shrinkage compared to composites based on conventional dimethacrylates, but lower degree of conversion as well. Overall materials with higher filler content presented higher initial values of flexural properties. However, their resistance to ethanol degradation seems to be influenced by different compositional factors and, therefore, cannot be directly related to water sorption results.

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We evaluated the effect of activation mode (immediate or delayed light activation vs. no light activation) on diametral tensile strength (DTS), elastic modulus, ultimate tensile strength (UTS), and degree of conversion (DC) in dual-cured resin cements. Three resin cements were evaluated: Enforce, RelyX ARC, and Panavia F. The mixed cements were inserted into circular molds for the DTS test and into dumbbell-shaped molds for the UTS test. Inside the molds, the cements were light-activated either immediately or after 5 min (delayed light activation). If no light activation was performed, the materials were protected from light exposure (control). The DTS and UTS tests were performed until fracture. The elastic modulus was calculated using data from the DTS test, and DC was evaluated 24 h after manipulation using near-infrared spectroscopy. Data for each variable were individually analyzed by two-way ANOVA and the post-hoc Tukey test (α = 0.05). Regarding DTS, activation mode influenced only Panavia Fspecimens, which had the lowest DTS values in the absence of light activation. Activation mode did not influence the elastic modulus or UTS of any resin cement evaluated. Immediate light activation yielded higher DC values as compared with the absence of light activation.

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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.

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OBJECTIVES: To verify the hypothesis that crack analysis and a mechanical test would rank a series of composites in a similar order with respect to polymerization stress. Also, both tests would show similar relationships between stress and composite elastic modulus and/or shrinkage. METHODS: Soda-lime glass discs (2-mm thick) with a central perforation (3.5-mm diameter) received four Vickers indentations 500 µm from the cavity margin. The indent cracks were measured (500×) prior and 10 min after the cavity was restored with one of six materials (Kalore/KL, Gradia/GR, Ice/IC, Wave/WV, Majesty Flow/MF, and Majesty Posterior/MP). Stresses at the indent site were calculated based on glass fracture toughness and increase in crack length. Stress at the bonded interface was calculated using the equation for an internally pressurized cylinder. The mechanical test used a universal testing machine and glass rods (5-mm diameter) as substrate. An extensometer monitored specimen height (2mm). Nominal stress was calculated dividing the maximum shrinkage force by the specimen cross-sectional area. Composite elastic modulus was determined by nanoindentation and post-gel shrinkage was measured using strain gages. Data were subjected to one-way ANOVA/Tukey or Kruskal-Wallis/Mann-Whitney tests (alpha: 5%). RESULTS: Both tests grouped the composites in three statistical subsets, with small differences in overlapping between the intermediate subset (MF, WV) and the highest (MP, IC) or the lowest stress materials (KL, GR). Higher stresses were developed by composites with high modulus and/or high shrinkage. SIGNIFICANCE: Crack analysis demonstrated to be as effective as the mechanical test to rank composites regarding polymerization stress.

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OBJECTIVES: The null hypothesis was that mechanical testing systems used to determine polymerization stress (σ(pol)) would rank a series of composites similarly. METHODS: Two series of composites were tested in the following systems: universal testing machine (UTM) using glass rods as bonding substrate, UTM/acrylic rods, "low compliance device", and single cantilever device ("Bioman"). One series had five experimental composites containing BisGMA:TEGDMA in equimolar concentrations and 60, 65, 70, 75 or 80 wt% of filler. The other series had five commercial composites: Filtek Z250 (3M ESPE), Filtek A110 (3M ESPE), Tetric Ceram (Ivoclar), Heliomolar (Ivoclar) and Point 4 (Kerr). Specimen geometry, dimensions and curing conditions were similar in all systems. σ(pol) was monitored for 10 min. Volumetric shrinkage (VS) was measured in a mercury dilatometer and elastic modulus (E) was determined by three-point bending. Shrinkage rate was used as a measure of reaction kinetics. ANOVA/Tukey test was performed for each variable, separately for each series. RESULTS: For the experimental composites, σ(pol) decreased with filler content in all systems, following the variation in VS. For commercial materials, σ(pol) did not vary in the UTM/acrylic system and showed very few similarities in rankings in the others tests system. Also, no clear relationships were observed between σ(pol) and VS or E. SIGNIFICANCE: The testing systems showed a good agreement for the experimental composites, but very few similarities for the commercial composites. Therefore, comparison of polymerization stress results from different devices must be done carefully.

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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.

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OBJECTIVES: Bond strength between adhesive systems and the tooth structure is influenced by a large number of variables, which makes the comparison among studies virtually impossible. Also, failure often times propagates into the dental substrate or the composite, deeming the results questionable at best. In spite of the increased popularity gained by micro-tensile and micro-shear tests, in vitro evaluations using specimens with relatively large bonding areas remain frequent. This review focuses on aspects related to specimen geometry and test mechanics of "macro" shear and tensile bond strength tests. METHODS: Besides information drawn from the literature, the effect of some parameters on stress distribution at the bonded interface was assessed using finite element analysis (FEA). RESULTS: Bond strength tends to increase with smaller bonding areas and with the use of high elastic modulus composites. Stress concentration at the bonded interface is much more severe in shear compared to tension. Among shear methods, the use of the chisel shows the highest stress concentration. Within the limits suggested by the ISO/TS 11405, crosshead speed does not seem to influence bond strength values. Pooled data from currently available adhesives tested in either shear or tension showed 44% of adhesive failures, 31% mixed and 25% cohesive in the substrate (tooth or composite). A comparative bond strength study involving three adhesive systems revealed similarities between "macro" and "micro" counterparts regarding material ranking, whereas "macro" tests presented a higher incidence of cohesive failures. SIGNIFICANCE: Simplicity warrants "macro" bond strength tests an enduring popularity, in spite of their evident limitations. From a mechanical standpoint, knowing the stress distribution at the bonded interface and how it is affected by the materials and loading method used is key to explain the results.

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