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Objective: To assess light irradiance (LI) delivered by two light-curing units (LCU's) and to measure the degree of conversion (DC) of three composite cements, when cured through different thicknesses of two novel CAD-CAM block materials., Methods: 100-μm-thick films of a dual-curable composite cement (G-CEM LinkAce, GC), a light-curable flowable resin-based composite (RBC) (G-ænial Universal Flo, GC) and a micro-hybrid RBC (G-ænial Posterior, GC) were investigated as luting agents. Two 'polymer-ceramic' CAD-CAM blocks (Cerasmart, GC; Enamic, Vita Zahnfabrik) were sectioned in slabs with different thicknesses (1, 3 and 5mm). LI at the bottom of the specimens was measured using a calibrated spectrometer, while being light-cured through the CAD-CAM block slabs for 40s with a low- (±500mW/cm 2 ) or high- (±1,600mW/cm 2 ) irradiance LCU (n=5). After light-curing, micro-Raman spectra of the composite films were acquired to determine DC at 5min, 10min, 1h and 24h. LI data were statistically analyzed by Kruskal-Wallis followed by post-hoc comparisons, while a linear mixed-effect model was applied for the DC analysis. In addition, the CAD-CAM blocks ultrastructure was characterized upon argon-ion slicing using scanning transmission electron microscopy (STEM). Finally, light transmission (LT) through each CAD-CAM block material was assessed using a spectrophotometer., Results: Curing-light attenuation and DC were significantly influenced by thickness and type of the overlying material. LCU only had a significant effect on DC of the micro-hybrid RBC. DC significantly increased over time for all composite cements. CAD-CAM block structural analysis revealed a relatively small and homogenous filler configuration (mean filler size of 0.2-0.5μm) for Cerasmart, while Enamic contained ceramic grains varying in shape and size (1-10μm), which were interconnected by the polymer-based network. LT was much higher at a wavelength range of 300-800nm for Cerasmart than for Enamic., Significance: Light-curable composite cements can be cured through a restoration up to 2.7-mm thickness, depending on the kind of CAD-CAM material. A high-irradiance LCU only has a limited effect on the maximum thickness of the polymer-ceramic CAD-CAM material that can be cured through., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: The photoinitiator diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) is more reactive than a camphorquinone/amine (CQ) system, and TPO-based adhesives obtained a higher degree of conversion (DC) with fewer leached monomers. The hypothesis tested here is that a TPO-based adhesive is less toxic than a CQ-based adhesive., Methods: A CQ-based adhesive (SBU-CQ) (Scotchbond Universal, 3M ESPE) and its experimental counterpart with TPO (SBU-TPO) were tested for cytotoxicity in human pulp-derived cells (tHPC). Oxidative stress was analyzed by the generation of reactive oxygen species (ROS) and by the expression of antioxidant enzymes. A dentin barrier test (DBT) was used to evaluate cell viability in simulated clinical circumstances., Results: Unpolymerized SBU-TPO was significantly more toxic than SBU-CQ after a 24h exposure, and TPO alone (EC50=0.06mM) was more cytotoxic than CQ (EC50=0.88mM), EDMAB (EC50=0.68mM) or CQ/EDMAB (EC50=0.50mM). Cultures preincubated with BSO (l-buthionine sulfoximine), an inhibitor of glutathione synthesis, indicated a minor role of glutathione in cytotoxic responses toward the adhesives. Although the generation of ROS was not detected, a differential expression of enzymatic antioxidants revealed that cells exposed to unpolymerized SBU-TPO or SBU-CQ are subject to oxidative stress. Polymerized SBU-TPO was more cytotoxic than SBU-CQ under specific experimental conditions only, but no cytotoxicity was detected in a DBT with a 200μm dentin barrier., Significance: Not only DC and monomer-release determine the biocompatibility of adhesives, but also the cytotoxicity of the (photo-)initiator should be taken into account. Addition of TPO rendered a universal adhesive more toxic compared to CQ; however, this effect could be annulled by a thin dentin barrier., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: To investigate the variation in water sorption and solubility across a range of different core build-up materials., Methods: Five materials were tested, four of which are resin-based materials (Grandio Core, Core.X Flow, Bright Flow Core, Speedee) and one resin-modified glass ionomer (Fuji II LC). All specimens (n=10) were immersed in 10ml distilled water in individual glass containers and weighed at one week, 14 and 28 days. After a total immersion time of 28 days, 7 specimens were dried to a constant mass, in a desiccator for 28 days. Three samples of each material were not dried, but were left in distilled water for 1 year, to determine the long-term water sorption properties. Specimens were weighed at monthly intervals until 6 months and then at the 9th and 12th months. Each specimen was measured using a digital electronic caliper (Mitutoyo Corporation, Japan)., Results: After 28 days immersion, the change in water sorption and solubility of the materials ranged from 12.9 to 67.1μg/mm(3) (P<0.001) and 0.9-6.4μg/mm(3) respectively (P<0.001). Except for Fuji II LC, an independent T-test showed significantly higher water sorption and solubility for the other materials after 1-year total immersion in water compared to 1 month (P<0.05). Using repeated measures ANOVA, all materials showed mass changes over time (1 month) (P<0.001)., Significance: Grandio Core had the lowest water sorption and solubility among the tested materials. According to the ISO 4049 standards, all the tested materials showed acceptable water sorption and solubility, apart from the water sorption behavior of Fuji II LC., (Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: The latest LED dental curing devices claim sufficient curing of restorative materials with short curing times. This study evaluates mechanical and chemical properties as a function of curing time of two commercial composite filling materials cured with three different LED lamps., Methods: The composites were Filtek Z250 (3M ESPE) and Tetric EvoCeram (Ivoclar Vivadent) and the LED curing devices were bluephase 16i (Ivoclar Vivadent), L.E.Demetron II (Kerr) and Mini L.E.D. (Satelec). Control samples were cured with a QTH-lamp (VCL 400, Kerr). The wear resistance after simulated tooth brushing, degree of conversion, curing depth, and amounts of residual monomers were measured after different curing times., Results: The results of this study show that short curing time with high-intensity LEDs may influence the bulk properties of the materials, resulting in lower curing depth and increased residual monomer content. The measured surface properties of the materials, degree of conversion and wear resistance, were not affected by short curing times to the same extent., Significance: This study demonstrates that reduced exposure time with high intensity LEDs can result in composite restorations with inferior curing depth and increased leaching of monomers. Dentists are recommended to use sufficient curing times even with high intensity LEDs to ensure adequate curing and minimize the risk of monomer leaching., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: To assess the depth of cure claims of two bulk-fill flowable RBC bases (SDR and x-tra base) using Fourier transform infrared (FTIR) spectroscopy, biaxial flexure strength (BFS), and Vickers hardness number (VHN) for specimen depths of 8mm (in 1mm increments)., Methods: The degree of conversion (DC) was measured by monitoring the peak height (6164cm(-1)) of specimens (11.0±0.1mm diameter, 1.0±0.1mm thickness) during light irradiation for 20s using a quartz tungsten halogen light curing unit at 650±26mW/cm(2). DC was measured up to 120s post irradiation and repeated (n=3) for irradiation depths up to 8mm (in 1mm increments). Further series (n=20) of eight discs were prepared, stacked, light irradiated and numbered from one to eight (distance from the LCU). The specimens were stored at 37±1°C for 24h and BFS tested with the fracture fragments used to determine the VHN for each specimen., Results: X-tra base can be irradiated to 8mm without a change in DC, something the SDR material cannot claim. However, the DC results confirm both bulk-fill flowable RBC bases have a depth of cure in excess of 4mm. One-way ANOVAs of BFS and VHN data showed significant differences between irradiation depths for x-tra base and SDR with increasing irradiation depth (4mm) resulting in significant reductions in mean BFS and VHN., Significance: The claims that the bulk-fill flowable RBC bases have a depth of cure in excess of 4mm can be confirmed but the differing chemistry of the resin formulations and filler characteristics contribute to significant differences in DC, BFS and VHN data between the two materials tested., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: Light cured materials are increasingly used in orthodontic clinical practice and concurrent with developments in materials have been developments in light curing unit technology. In recent years the irradiances of these units have increased. The aim of this study was to determine the safe exposure times to both direct and reflected light., Methods: The weighted irradiance and safe exposure times of 11 dental curing lights (1 plasma arc, 2 halogen and 8 LED lights) were determined at 6 distances (2-60 cm) from the light guide tip using a spectroradiometer. In addition, using the single most powerful light, the same two parameters were determined for reflected light. This was done at a distance of 10 cm from the reflected light, but during simulated bonding of 8 different orthodontic brackets of three material types, namely stainless steel, ceramic and composite., Results: The results indicate that the LED Fusion lamp had the highest weighted irradiance and the shortest safe exposure time. With this light the maximum safe exposure time without additional eye protection for the patient (at 10 cm), the operator (at 30 cm) and the assistant (at 60 cm) ranged from 2.5 min, 22.1 min and 88.8 min respectively. This indicates a relatively low short term risk during normal operation of dental curing lights. For reflected light at a distance of 10 cm the risk was even lower, but was affected by the material and shape of the orthodontic bracket under test., Significance: The short term risks associated with the use of dental curing lights, halogen, LED or plasma, appear to be low, particularly if as is the case adequate safety precautions are employed. The same is true for reflected light from orthodontic brackets during bonding. What is still unclear is the potential long term ocular effects of prolonged exposure to the blue light generated from dental curing lights., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed., Methods: Non-polymerized and polymerized samples of the composites Grandio(®) (VOCO, Cuxhaven), Solitaire(®) (Heraeus Kulzer, Hanau) and Filtek Z 250(®) (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM--Dulbecco's Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test., Results: With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p<0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher., Significance: The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed., (Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: Light-curable polymers are commonly used in restorative surgery, prosthodontics and surgical procedures. Despite the fact of wide application, there are clinical problems due to limitations of blue light penetration: application is restricted to defects exposed to the light source, layered filling of defect is required., Methods: Combining photo-activation and up conversion allows efficient polymer hardening by deep penetrating near-infrared (NIR) light. The prerequisite 450 nm blue light to polymerize dental resins could be achieved by filler particles, which absorb the incident NIR irradiation and convert it into visible light., Results: The on spot generated blue light results in uniform polymer hardening. Composite samples of 5mm thickness were cured two times faster than pure polymer cured by blue light (30 and 60 s, respectively). Overall degree of monomer conversion resulted in higher values of more than 40%. The enhanced transmission of NIR light was confirmed by optical analysis of dentin and enamel. The NIR transmittance surge in the 800-1200 nm window could improve sealing of complex and deep caries lesions., Significance: We demonstrate faster curing and an improved degree of polymerization by using upconversion filler particles as multiple light emission centers. This study represents an alternative approach in curing dental resins by NIR source., (Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)