Influence of photoinitiator type on the rate of polymerization, degree of conversion, hardness and yellowing of dental resin composites

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Objectives. To evaluate the degree of conversion (DC), maximum rate of polymerization (R-P(max)), Knoop hardness (KHN) and yellowing (b-value) of resin composites formulated with phenylpropanedione (PPD), camphorquinone (CQ), or CQ/PPD at different concentrations. The hypotheses tested were (i) PPD or CQ/PPD would produce less R-P(max) and yellowing than CQ alone without affecting DC and KHN, and (ii) R-P(max), DC, and KHN would be directly related to the absorbed power density (PDabs). Methods CQ/amine, PPD/amine and CQ/PPD/amine were used at low, intermediate and high concentrations in experimental composites. Photoinitiator absorption and halogen-light emission were measured using a spectrophotometer, R-P with differential scanning calorimetry (DSC), DC with DSC and FTIR, KHN with Knoop indentation; and color with a chromameter. The results were analyzed with two-way analysis of variance (ANOVA)/Student-Newman-Keul's test (p < 0.05). Correlation tests were carried out between PDabs and each of DC, R-P(max) and KHN. Results. The PDabs increased with photoinitiator concentration and PPD samples had the lowest values. In general, maximum DC was comparable at intermediate concentration, while R-P(max) and KHN required higher concentrations. DC was similar for all photoinitiators, but R-P(max) was lower with PPD and CQ/PPD. PPD produced the lowest KHN. Yellowing increased with photoinitiator concentration. PPD did not reduce yellowing at intermediate and/or high concentrations, compared to CQ-formulations. PDabs showed significant correlations with DC, R-P(max) and KHN. Conclusion. PPD or CQ/PPD reduced R-P(max) in experimental composites without affecting the DC. The use of PPD did not reduce yellowing, but reduced KHN. DC, R-P(max) and KHN were dependent on PDabs. (c) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.24911691177Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPES [BEX 3667/05-7

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

Effect of irradiance and light source on contraction stress, degree of conversion and push-out bond strength of composite restoratives

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Purpose: To evaluate the influence of five curing methods on contraction stress, stress rate, and degree of conversion (DC) of a composite and on bond strength of composite restoratives. Methods: For the stress test, composite was applied between two 5-mm diameter glass rods, mounted in a servohydraulic machine. Stress rates were calculated as the change in stress vs. time. DC was measured by FTIR. Bond strength testing was performed using a push-out test in bovine incisors. The C-factor was 3.0 for all tests. Five methods were evaluated: High Intensity LED (LED HI), Continuous Halogen Light (QTH CL), Medium Intensity LED (LED MI), Low Intensity LED (LED LI), and Pulse Delay Halogen Light (QTH PD). Results were analyzed by ANOVA and Tukey's test (alpha = 0.05). Results: Stress values ranged from 9.25 MPa (QTH PD) to 10.46 MPa (LED MI). No statistical difference was observed among the methods. Bond strength values ranged from 24.6 MPa (LED HI) to 35.4 MPa (QTH PD), with the QTH PD presenting a statistically higher value compared to the other methods. Stress rate and bond strength presented an inverse linear correlation ( = 0.79). LED HI presented the highest maximum stress rate, followed by LED MI, QTH CL, LED LI, and QTH PD. The reduction in stress rate observed for the low intensity groups was associated with a general increase in bond strength, with no adverse effect on the degree of conversion of the restorative composite. (Am J Dent 2009;22:165-170).223165170Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPES [BEX3428/04-4