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Abstract: Objectives: Since photoinitiator systems for dental resins based on camphorquinone (CQ) present color disadvantages, trimethylbenzoyl-diphenyl-phosphine oxide (TPO) has been proposed as an alternative. However, there are remaining considerations about its curing efficiency. The aims of the present investigation were: to characterize the relationship between the photoinitiator absorption spectra and the light spectrum emitted from a QTH light (absorbed power density, PDabs); to evaluate the kinetics of polymerization, and the depth of cure for filled dimethacrylate resins formulated with different photoinitiator systems. Methods: CQ+EDMAB (control); TPO and TPO+EDMAB were used in 50:50 Bis-GMA/TEGDMA resins. Photoinitiator absorption and QTH-light emission were evaluated using a spectrophotometer and kinetics of polymerization with differential scanning calorimetry (DSC) (n =3). Depth of cure was analyzed by the scraping method (n =5), as recommended by ISO4049. One-way ANOVA/Tukey''s (p <0.05) was used to analyze the results. Results: CQ presented higher PDabs than TPO (364 and 223mW/cm3, respectively). The DSC revealed that TPO and TPO+EDMAB produced a faster reaction than CQ+EDMAB. Composite formulated with CQ+EDMAB produced higher depth of cure (6.3±0.4mm) than those with TPO (4.3±0.1) or TPO+EDMAB (4.2±0.3). Significance: Although CQ presented higher PDabs than TPO, formulations containing TPO exhibited higher reactivity than that with CQ. On the other hand, materials formulated with TPO demonstrated lower depth of cure than that with CQ. Therefore, its use as an alternative photoinitiator requires further investigation, with higher concentrations. [Copyright &y& Elsevier]

Abstract: Objective: To investigate the surface integrity of solvent-challenged ormocer-matrix composites, photoactivated by different light exposure modes, through surface-hardness measurements at different periods of time; and to compare such behavior with dimethacrylate-based materials. Methods: One hundred percent ormocer-based matrix (experimental ormocer (ORM)), a commercial mixed dimethacrylate-ormocer-based matrix (Admira (ADR)) and two commercial dimethacrylate-based matrix composites (experimental controls, (Grandio (GRD) and Premise (PRE)) were evaluated. Disk specimens (4mm×2mm) were prepared from each material and light-activated using either a standard (S) or soft-start (SS) light exposure protocol with an LED-curing unit. Top, irradiated surface Knoop hardness (KHN) was measured within the following experimental groups (n =5): Group 1: immediately after exposure; Group 2: after dry and dark storage, Group 3: after storage in distilled water, and Group 4: immersion in absolute ethanol. Hardness of Groups 2–4 were measured after 7 days storage. Immediate hardness values were submitted to Student''s t-tests separately for each material. Hardness values after treatments were submitted to two-way ANOVA and Tukey''s post hoc test to compare values among different storage media and light exposure mode protocols. Comparisons among materials were described using percentage of hardness change. Statistical testing was performed at a pre-set alpha of 0.05. Results: Immediate hardness values were not affected by the light exposure mode, regardless of the material. In general, exposure mode did not significantly affect hardness after 7 days storage, regardless of storage media or material. After 7 days dry storage, hardness values increased for all materials relative to immediate testing, and decreased after water and ethanol storage, with ethanol showing the greatest effect. The experimental ormocer-based material had the lowest percentage hardness change and thus proved more resistant to solvent degradation than the other materials, regardless of the light exposure method. Significance: Irradiated surface hardness values and surface integrity were unaffected by light exposure mode, regardless of the material tested. The experimental ormocer-based material presented the least change in hardness as a result of solvent challenge than any of the commercial products: ormocer or conventional resin-based, and thus showed better surface integrity. [Copyright &y& Elsevier]

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 The aim of this study was to determine the influence of the monomer type and photoinitiator systems on the degree of C=C conversion and color stability of model self-adhesive flowable composites (SAFCs). Three sets of flowable composites were formulated varying the monomer type: set 1 (control), with bisphenol-A glycidyl methacrylate and triethylene glycol dimethacrylate (BisGMA/TEGDMA) at 50/50 wt%; set 2, with BisGMA/TEGDMA/bis[2(methacryloyloxy)ethyl]phosphate (2MP) at 30/30/40 wt%; and set 3, with BisGMA/TEGDMA/4-ethyl-methacryloxy-trimetilato anhydride (4-META) at 30/30/40 wt%. For each set, different initiator systems were added: camphorquinone (CQ) + ethyl-4-dimethylamino benzoate (EDMAB); diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO); phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO); and the combinations CQ + EDMAB + TPO and CQ + EDMAB + BAPO. Degree of C=C conversion was determined by Fourier-transformed infrared spectroscopy with an attenuated total reflectance device (ATR-FTIR). The color stability was determined by CIE 00 color difference formula (∆ E * 00), after water (T 1) and coffee (T 2) storages for 30 days. Data was submitted to two-way analysis of variance (ANOVA) followed by Student-Newman-Keuls test (α = 0.05). Degree of conversion and color stability were dependent on the resin matrix composition and the photoinitiator system. The 2MP-based set showed the highest DC, but also the poorest color stability. For the 4-META-base set, TPO and BAPO produced the highest degree of C=C conversion. The use of BAPO produced the best color stability for the acidic-monomer-based sets. [ABSTRACT FROM AUTHOR]

Objective This study has investigated the influence of BisGMA, BisEMA, BisEMA 30, and two UDMA-based monomers (UDMA and Fit 852), with TEGDMA as co-monomer, on the degree of conversion, water sorption, water solubility, and optical properties of experimental dental composites. Methods Materials were formulated at 70/30 molar rations using BisGMA, BisEMA, BisEMA 30, UDMA or FIT 852, as base monomers, combined with TEGDMA. 60 wt% of silanated-glass particles was added. Degree of conversion (DC) and polymerization kinetics were monitored using Fourier-transformed infrared spectroscopy in the near-IR range. Water sorption (Wsp) and solubility (Wsl) were assessed using mass variation after 60 days water storage. Color was evaluated using a digital spectrophotometer, applying the CIELab parameters 24 h after dry storage and 60 days after water immersion to calculate ΔE values. All data were analyzed using ANOVA and Tukey’s test (pre-set alpha = 0.05). Results The BisGMA-based co-monomer mixture presented the lowest DC (62 ± 1%), whereas BisEMA 30 had the highest DC value (95 ± 2%). The highest Wsp was observed for BisEMA 30 (12.2 ± 0.8%), and the lowest for BisEMA (0.4 ± 0.1%). BisEMA has shown the lowest Wsl (0.03 ± 0.01%) and BisEMA 30 the highest one (0.97 ± 0.1%). The ΔE values showed that BisEMA 30 (7.3 color units) and Fit 852 (3.8 color units) altered the color stability providing ΔE > 3.3, which is considered clinically unacceptable. Conclusions The chemical composition and structure of the base monomer influenced the degree of conversion, water sorption, water solubility, and color stability. Considering the overall results, it is possible to state that the base monomer BisEMA mixed with the co-monomer TEGDMA presented the best performance in terms of all the parameters tested. Significance The resin matrix composition might influence physical property degradation processes and color stability of dental resin composites. Formulations based on BisEMA seem most promising for materials’ development. [ABSTRACT FROM AUTHOR]