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Purpose: The aim of this study was to evaluate the tensile bond strength (TBS) of repairs in recent fillings of methacrylate- (MBC) or silorane-based composites (SBC) subsequent to different surface treatments. Materials and Methods: Fifty slabs of Filtek P60 (3M ESPE, St Paul, USA) and Filtek P90 (3M ESPE) were stored for 10 days in distilled water at 37°C. The surface of adhesion was abraded with a 600-grit silicone paper and repaired using each respective composite: G1, no treatment (control); G2, application of adhesive; G3, application of silane and adhesive; G4, sandblasting (Al2O3) and adhesive; and G5, sandblasting (Al2O3), silane, and adhesive. Further 10 slabs of each composite were also evaluated for cohesive strength (G6). After 30 days immersion in distilled water at 37°C, the TBS was determined. Results: TBS results were higher for MBC than for SBC (P = 0.00012). The experimental groups were similar for SBC and the TBS was 27% of its cohesive strength. For P60, sandblasting significantly improved the TBS compared to other groups. With MBC, G4 and G5, the TBS was approximately 47% of its cohesive strength. Conclusion: Sandblasting (Al2O3) improves the repair-strength of MBC, whilst for the SBC all treatments succeed. MBC presents higher repair strength than SBC. [ABSTRACT FROM AUTHOR]

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The material's shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or postoperative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature. [ABSTRACT FROM AUTHOR]

Though many advances have been made in the development of dental adhesives, the immediate, or short-term, disruption created by stress — due to polymerization of resin composite restorative materials within dental cavities — is still a challenge yet to be completely solved in restorative dentistry. Therefore, the aim of this paper is to present a general overview of the subject, concerning resin composite formulations, origins of stress, clinical consequences of stress development, in vitro methods used for its measurement and methods used to reduce stress magnitudes and rates of development. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Stress development during the polymerization process continues to be a major factor that limits predictability and longevity of resin composite restorations. This study evaluated the effect of the photoinitiator type on the maximum rate of polymerization , stress development (final stress and maximum rate, ), degree of conversion (DC) and cross-link density (CLD) of materials containing camphorquinone (CQ), phenylpropanedione (PPD) or CQ/PPD. Materials and methods: was evaluated via differential scanning calorimetry (DSC). Contraction force measurement was assessed with a single cantilever device for 5min. The samples were subsequently tested by infrared spectroscopy (FTIR) to evaluate the DC. After, samples were soaked in ethanol to evaluate the swelling coefficient (α) as a way to estimate the CLD. The results were analyzed by one-way ANOVA and Tukey''s test (p =0.05). Results: CQ showed the highest and . PPD produced the lowest DC and the highest α. The mixture CQ/PPD produced statistically lower and than CQ alone, but similar DC and CLD. Conclusion: CQ/PPD reduced the and without a reduction in DC and CLD. Therefore, the use of alternative photoinitiator systems could be a promising way to reduce the stress developed during the composite''s polymerization without affecting the final properties. [Copyright &y& Elsevier]

Abstract: Objectives: To evaluate the effect of amine ratio (ethyl 4-dimethylaminobenzoate, EDMAB) on the maximum rate of polymerization (), degree of conversion (DC), Knoop hardness (KH), water sorption (Wsp), water solubility (Wsl) and color changes (ΔE) over time of resin composites formulated with the photoinitiators camphorquinone (CQ), phenylpropanedione (PPD) and CQ-PPD in combination. Materials and methods: Experimental resin composites were made with photoinitiator:amine ratios of 2:1, 1:1, 1:1.5 and 1:2 by weight. was evaluated with differential scanning calorimetry (DSC), DC with DSC and Fourier transformed infrared (FTIR) spectroscopy, KH with Knoop indentation, Wsp and Wsl adapted from ISO 4049; and color with a chromameter. The results were analyzed with two-way ANOVA/Tukey’s multiple comparison test (p <0.05). Results: The higher the amine ratio in the composite, the higher was DC, , and KH, and the lower was Wsl, regardless of the photoinitiator type. The use of PPD alone resulted in poorer properties than CQ and CQ-PPD. Many factors seem to affect the color changes and the b-axis data revealed that the higher the amine ratio, the higher was the +b value (yellowing) for CQ and CQ-PPD formulations. Conclusions: Higher amine ratios led to improved polymer properties, but also produced more yellowing in resin composites with CQ and CQ-PPD. The use of PPD alone was not advantageous for producing good final properties when compared to CQ and CQ-PPD. [Copyright &y& Elsevier]

Abstract: Objectives: To evaluate the degree of conversion (DC), maximum rate of polymerization (), 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 and yellowing than CQ alone without affecting DC and KHN, and (ii) , 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, 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 and KHN required higher concentrations. DC was similar for all photoinitiators, but 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, and KHN. Conclusion: PPD or CQ/PPD reduced in experimental composites without affecting the DC. The use of PPD did not reduce yellowing, but reduced KHN. DC, and KHN were dependent on PDabs. [Copyright &y& Elsevier]

Regular composites could produce less polymerization stress than resin cements when luting laminate veneers but there is no proper evidence to support this theory. The current study aimed to determine the degree of conversion, volumetric shrinkage, polymerization stress and the resultant elastic moduli of materials currently used for adhesive cementation and to determine possible correlations. The study considered (i) regular resin composites (Admira Fusion, Gradia, Grandioso, Palfique, Sirius Z, Viscalor and Z100) at room and pre-warmed (PW) at 69ºC, (ii) flowable composites (Sigma Flow and Grandioso Flow); (iii) solely light-activated cements (AllCem Veneer, Variolink Esthetic and RelyX Veneer); and (iv) one dual-activated resin cement (SpeedCEM). Degree of conversion (DC, n = 3) was accessed with FTIR 1 h after irradiation. Bonded-disk and Bioman II instruments were used to access polymerization shrinkage strain and shrinkage stress, respectively, for 60 min at 23 ± 1◦C (n = 3). The elastic modulus was determined by 3-point bending flexural test (n = 6). The results were submitted to analyse s of variance, Tukey's, and correlation tests. For regular composites, the pre-warming did not affect DC, shrinkage and modulus but significantly increased the stress magnitude. Correlation tests indicated a significant relationship only between stress and polymerization shrinkage (r = 0.811343). Regular composites can produce less polymerization stress than resin cements when luting laminate veneers. Polymerization stress was dependent on the shrinkage magnitude, but not on the degree of conversion nor the elastic modulus. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to formulate materials with high color stability and reduced degradation by using photoinitiator systems derived from phosphine oxides alternative to the traditional camphorquinone (CQ)/amine system. Methods: Materials were formulated with the monomers BisGMA and TEGDMA as organic matrix. The photoinitiators tested were CQ+ amine (EDMAB), phenylbis(2,4,6-trimethylben-zoyl)phosphine oxide (BAPO), BAPO + EDMAB, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and TPO + EDMAB. A 60% mass of silanated glass filler particles was added. Degree of CC conversion was evaluated by Fourier-transformed infrared spectroscopy 10 min after photopolymerization. The color properties were evaluated by a digital spectrophotometer, applying the CIELab parameters, either before photoactivation, immediately after photoacti-vation, 24 h after dry storage, and one month after water immersion. Water sorption and solubility were assessed by mass gain or loss after storage in water for 30 days. Data were analyzed using ANOVA and Tukey's test (5%). Results: Degree of conversion did not differ statistically among all the tested formulations. Regarding color, only groups with TPO presented satisfactory color stability after one month of water storage (ΔE < 3.3). Water sorption and water stability did not differ among the groups. Conclusions: Degree of conversion, water sorption and water solubility did not differ among all the tested groups. The TPO-based groups were the only materials with satisfactory color stability after one month of water storage. [ABSTRACT FROM AUTHOR]