Amorphous films of poly(vinylidene fluoride)-poly (methyl methacrylate) were prepared by initial precipitation from a solvent and rapid solidification at ~ 15 ~ from the molten state. The PVDF/PMMA compositions studied were 25/75, 45/55, 50/50, 55/45, 60/40 and 75/25. X-ray scattering analysis suggests that mixture of the two components throughout the composition range studied occurs at a molecular level. The parallel decrease of the microhardness, which obeys a simple expression: Hblen d = HpMMA(1 --~) (~ being the PVDF concentration) and the glass transition temperature, Tg, following the predictions, of Gordon and Taylor, reveals that the depression of microhardness is caused by the shift of Tg towards lower temperatures. It is pointed out that the effect of PVDF molecules is to act as a softening agent within the PMMA component.
Background To evaluate in vitro the influence of photoinitiators on the microtensile strength of adhesive systems and composite resins in bovine dentin. Material and Methods Forty dentin obtained from bovine teeth were randomly distributed in four groups (n = 10) according to the different adhesive systems and composite resins used: G1 - AAPS + VAPS (Ambar APS + Vittra APS); G2- AAPS + O (Ambar APS + Opallis); G3 - A + VAPS (Ambar + Vittra APS) and G4 - A + O (Ambar + Opallis). After restoration with the composite, the samples were sectioned to obtain toothpicks that were subjected to the microtensile and nanofiltration test (1.0 mm/min). Results The Kruskal-Wallis test did not show significant differences between the groups ( p <0.05). The values in MPa were: AAPS + VAPS - 19.56 MPa; AAPS + O - 19.77 MPa; A + VAPS - 17.78 MPa; A + O - 22.44 MPa. The result of the Mann-Whitney test showed no significant differences depending on the adhesive (Ambar Universal- 19.11 MPa, Ambar APS Universal- 21.70 MPa) and the composite resin used (Vittra APS- 18.75 MPa, Opallis - 23.75 MPa). The AAPS + VAPS and AAPS + O groups showed intense silver nitrate infiltration. The A + APS group showed a moderate infiltration and the A + O group had a mild infiltration in the adhesive system/dentin interface. Conclusions The use of different photoinitiators in the composition of adhesive systems and restorative composites did not affect their bond strength values and the presence of water in the solvent of the APS photoinitiator system had a negative influence, increasing the degree of infiltration in the hybrid layer when compared to the camphorquinone photoinitiator. Key words: Dentin, adhesive systems, composite resin, photoinitiators, tensile strength, nano-infiltration.
A combined X-ray diffraction and microhardness investigation of the 70/30 polyvinylidene fluoride-trifluorethylene copolymer was carried out as a function of temperature. The changes in microhardness are interpreted in terms of variations in lattice spacing of the ferro-and paraelectric phases, crystallinity and long period. The changes of microhardness with temperature show four distinct temperature regions. In addition to a low temperature range, in which microhardness decreases exponentially with temperature, the ferroparaelectric Curie transition involves a faster hardness decrease. At higher temperature, the sudden microhardness rise is ascribed primarily to an increase of crystal thickness within the remnant paraelectric phase. Near the melting point, the fusion of thinner crystals leads to a range in which microhardness decreases exponentially again.
Background To evaluate the microtensile bond strength of indirect resin composite bonded to dentin using five different adhesives strategies. Material and Methods Forty specimens (Solidex) were produced and randomly into five groups with different adhesives strategies: (G1)- Single Bond Universal + etch + silane + RelyX Ultimate, (G2)- Single Bond Universal + silane + RelyX Ultimate, (G3)- Single Bond Universal + etch + RelyX Ultimate, (G4)- Single Bond Universal + RelyX Ultimate, and (G5)-Scotchbond Multi-purpose + RelyX ARC. After cementation the specimens were stored in 100% humidity for 24hours at 37°C. The specimens were sectioned perpendicular to the adhesive interface to obtain beams and submitted to microtensile test. Microtensile values were expressed in MPa and analyzed by one-way ANOVA and multiple comparison Tukey tests (α=0.05). Results The mean bond strength in MPa groups were: G1=11,48, G2=14,15, G3=16,95, G4=17,03 and G5=16,80. Statistical analysis showed that the bond strength values were not significantly affected by the different adhesive strategies. Conclusions Cementation of dentin to indirect resin composite cannot be significantly affected by different adhesive strategies used. The specimens treated with silane, etch associated with Single bond universal did not increase bond strength values. Key words: Adhesives, dental cements, dentin.
Background To evaluate the microtensile strength in the adhesive interface depending on the volume of the composite resin used to restore class I cavities. Material and Methods Forty-eight human third molars received a standardized class I cavity preparation and they were separated into six experimental groups: G1 – single-bottle adhesive system; G2 - bonding system with load; G3 – single-bottle adhesive associated with low-viscosity composite resin; G4 – loaded adhesive associated with low-viscosity composite; G5 - resin-modified glass ionomer associated with single-bottle adhesive; and G6 - resin-modified glass ionomer associated with loaded adhesive. All cavities were restored with a universal restorative composite. After completing the restorations, the samples were stored for seven days in a stove (37°C) and the microtensile bond strength was evaluated by producing slices and applying axial loading in an Instron universal testing machine at a speed of 0.5 mm/min. The thickness of the intermediate layer formed on the cavity floor to verify the relationship between the volume of restorative composite and the concentration of stresses in the buccal wall. With the data obtained in the microtensile strength test, an Analysis of Variance (ANOVA) was performed entirely at random. Results Duncan’s test showed that group 4 (Filtek Flow/Optibond Solo Plus) obtained the highest mean of microtensile strength with no statistically significant difference to groups 3 (Filtek Flow/Single Bond), 5 (Vitremer/Single Bond), and 6 (Vitremer/Optibond Solo Plus). It also showed a statistically significant difference to groups 2 (Optibond Solo Plus) and 1 (Single Bond), with no statistical difference between the other groups studied. Conclusions The highest mean of microtensile strength was obtained when the volume of the restorative material decreased through the interposition between the material and the adhesive system of a base with low elasticity modulus. Key words: Adhesion, microtensile, composite resin.
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