Marginal adaptation of composite restorations photoactivated by LED, plasma arc, and QTH light using low-modulus resin liners

Purpose: The aim of this study was to evaluate the influence of resin liners on the marginal adaptation to dentin of resin composite restorations photoactivated by a conventional quartz-tungsten halogen lamp (QTH), light emitting diodes (LED), and a plasma arc light (PAC). Materials and Methods: The buccal surfaces of 120 bovine incisors were ground until a flat dentin area was obtained. A circular cavity (4 mm in diameter x 1.5 mm in depth) was prepared in this area. Scotchbond Multi Purpose was applied in the cavities following the manufacturer's instructions. The specimens were randomly assigned into 4 groups according to the lining technique: (1) control (1 adhesive layer); (2) three adhesive layers; (3) Filtek Flow; (4) Protect Liner F. Each group was further divided into 3 subgroups according to the light-curing method: (A) QTH; (B) LED; (C) PAC. All cavities were then restored with a single increment of Filtek Z250 restorative composite and polished. Caries Detector was applied to each specimen for 5 s. Images of dye-stained gaps were observed under a stereomicroscope and transferred to a computer measurement program. Gap values were obtained by dividing the dyed margin length by the total cavity length, then multiplying by 100. Data were analyzed using ANOVA and Tukey's test (p<0.05). Results: All the tested lining techniques significantly decreased marginal gap formation when compared with the control group only for the QTH light groups. There was no significant difference among the light-curing methods. Conclusion: The use of resin liners can effectively reduce the gap formation along dentin margins, but only when QTH light is used.8422322

Effect of different photoactivation methods on the bond strength of composite resin restorations by push-out test

Objective: Modulated curing methods could lead to a higher probability of bond preservation. Therefore, the aim of this study was to evaluate the effect of 7 curing methods on bond strength of composite resin restorations. Method and Materials: Seventy bovine incisors were selected. A conical cavity was prepared in the buccal surface. Adper Single Bond adhesive system was applied according to the manufacturer's instructions, and the cavities were filled with a single increment of Esthet X (Dentsply/Caulk). The specimens were randomly assigned into 7 groups (n = 10) according to the photoactivation method: (1) continuous light 700 (700 mW/cm(2)) (control); (2) continuous light 150 (150 mW/cm(2)); (3) continuous light 250 (250 mW/cm(2)); (4) soft-start 75 (75 mW/cm(2) + 700 mW/cm(2)); (5) soft-start 150 (150 mW/cm(2) + 700 mW/cm(2)); (6) pulse-delay (150 mW/cm(2) + 3 minutes + 700 mW/cm(2)); and (7) intermittent light (cycles at 600 mW/cm(2)). The energy density for all groups was 14 J/cm(2). The bond strength of the composite restorations was measured by performing the push-out test in a universal testing machine (Instron). The results were submitted to ANOVA and Tukey test (P < .05). Results: Pulse-delay, soft-start 150, and soft-start 75 methods showed a significant increase in bond strength when compared with the control continuous light 700 method. Low power density and intermittent light groups showed intermediate results. Conclusion: Modulation of the energy density during light curing of composite resins using pulse-delay or soft-start methods increased the bond strength of composite restorations.39324324

Relationship between bond strength and marginal and internal adaptation of composite restorations photocured by different methods

Objective. This study evaluated the relationship between bond strength and marginal and internal adaptation of composite restorations photocured using different methods with a quartz-tungsten-halogen light. Material and Methods. A push-out test was performed to evaluate bond strength of conical restorations in 50 bovine incisors. To evaluate marginal ( external) and internal restoration adaptation, 50 circular all-enamel margin preparations were done in bovine incisors. For both tests, the preparations were filled with Esthet(center dot) X resin composite. Specimens were distributed into 5 groups ( n = 10) depending on photoactivation method: G1: continuous light 700; G2: continuous light 150; G3: soft-start; G4: intermittent light; and G5: pulse-delay. The energy density for each method was standardized: 14 J/cm(2). Caries Detector((R)) ( Kuraray) was placed in restoration margins for detection of marginal adaptation. The percentage of interfaces present as gaps was determined using digital images. Specimens were then sectioned, stained, and the internal adaptation was recorded in a similar manner. Data were submitted to ANOVA and the Tukey HSD test, pre- set alpha = 0.05. Results. Bond strength G5 ( 7.2 MPa +/- 1.3) was significantly greater ( p = 0.00280) than G1 ( 4.6 MPa +/- 1.5). G2, G3, and G4 showed equivalent, intermediate strength values. No significant difference was found in marginal adaptation of any of the groups ( p = 0.16911). Internal adaptation results were the inverse of strength results: G5 ( 2.8% +/- 4.9) showed significantly less ( p = 0.00979) gap formation compared to G1 ( 10.1% +/- 6.2). Conclusion. Some modulated photocuring methods can increase bond strength while decreasing internal gap formation. An inverse relationship was found between push-out bond strength and internal adaptation. Marginal adaptation was not affected by any photoactivation method.64530631

Spectrophotometric determination of caramel content in spirits aged in oak casks

A new methodology was developed for determination of caramel in spirits aged in oak casks. The method is based on differences between the electronic spectra of oak aqueous alcoholic extracts and caramel solutions in the same solvent. The data were treated by 2 different approaches: the simplest one was based on the plot of caramel concentration versus the ratio of absorbance at 210 and 282 nm; the other was based on a partial least squares (PLS) calibration model using the first derivative of the spectral data. Both methodologies were applied to analysis of 159 aged spirit samples. The mean caramel content of several Brazilian sugar cane spirits (cachaga) and all United States whiskies was smaller than that of Scottish whiskies and other brandies from several countries. Correlation was good between caramel concentrations for the same sample calculated by the 2 methods. The uncertainties following PLS and the absorbance ratio method were 0.01 and 0.03 g/L, respectively, for a sample containing 0.45 g/L caramel. Treatment of UV-VIS spectra by pattern recognition using hierarchical clustering analysis and principal components analysis allowed discrimination of the samples as a function of their caramel content. It was possible to distinguish U.S. whiskies from other whiskies, but a clear differentiation among Brazilian cachagas as a function of their geographic origin was not feasible. Small caramel quantities as low as 0.08 g/L were clearly detected by these methodologies.85374475

Contraction stress and physical properties development of a resin-based composite irradiated using modulated curing methods at two C-factor levels

Objectives. The objective of this study was to verify the influence of curing methods on contraction stress, stress rate and degree of conversion (DC) of a restorative composite at two C-factor levels. Methods. For the stress test, composite was applied between two for 15 min from diameter glass rods mounted in a servohydraulic machine, and stress was monitored for 10 min from the beginning of light curing. Stress rates were calculated as the change in stress versus time at each second. DC was measured by micro-FTIR. Four curing methods were tested at two C-factor levels (1.5 and 3.0): continuous light (CL), soft-start (SS) and two pulse delay methods using different initial irradiances-150 mW/cm(2) (PD150) and 80 mW/cm(2) (PD80). Results were analyzed by ANOVA and Tukey's test (alpha = 0.05). Results. For the stress test, at CF 1.5, PD80 presented the lowest mean value, statistically different from the others. PD150 also showed a mean value statistically inferior to CL. At CF 3.0, no statistical difference was observed among CL, SS and PD150. PD80 presented statistically lower stress values compared to CL and SS. Stress values at CF 3.0 were statistically higher than those at CF 1.5 for all curing methods. CL presented the highest maximum stress rate, followed by SS, PD150 and PD80, for both C-factors. In the DC test, no difference was observed among the methods and between the C-factor levels. Significance. Modulated curing methods were shown to be effective in reducing contraction stress rate, without compromising the DC of the restorative composite. C-factor was shown to influence negatively the stress rate and the amount of stress generated. (C) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.24339239