LED Units Research Articles

Evaluating UV-C LED disinfection performance and investigating potential dual-wavelength synergy

A dual-wavelength UV-C LED unit, emitting at peaks of 260 nm, 280 nm, and the combination of 260|280 nm together was evaluated for its inactivation efficacy and energy efficiency at disinfecting Escherichia coli, MS2 coliphage, human adenovirus type 2 (HAdV2), and Bacillus pumilus spores, compared to conventional low-pressure and medium-pressure UV mercury vapor lamps. The dual-wavelength unit was also used to measure potential synergistic effects of multiple wavelengths on bacterial and viral inactivation and DNA and RNA damage.All five UV sources demonstrated similar inactivation of E. coli. For MS2, the 260 nm LED was most effective. For HAdV2 and B. pumilus, the MP UV lamp was most effective. When measuring electrical energy per order of reduction, the LP UV lamp was most efficient for inactivating E. coli and MS2; the LP UV and MP UV mercury lamps were equally efficient for HAdV2 and B. pumilus spores. Among the UV-C LEDs, there was no statistical difference in electrical efficiency for inactivating MS2, HAdV2, and B. pumilus spores. The 260 nm and 260|280 nm LEDs had a statistical energy advantage for E. coli inactivation.For UV-C LEDs to match the electrical efficiency per order of log reduction of conventional LP UV sources, they must reach efficiencies of 25–39% or be improved on by smart reactor design. No dual wavelength synergies were detected for bacterial and viral inactivation nor for DNA and RNA damage.

High Uniformity and Tolerance Design for Direct-Lit LED Backlight Illumination Using Lagrange Interpolation

This paper proposes the use of a Lagrange interpolation polynomial to meet the illumination distribution requirements of single-LED units, in both a square and a triangular arrangement, for direct-lit backlighting to obtain uniform illumination to be used for designing secondary optical lenses. In addition, we propose the use of a wider illumination coverage of LED units to achieve excellent assembly displacement tolerance. We also define an evaluation formula for combining the uniformity and tolerance of the LED unit to select its ideal corresponding light intensity distribution as the target of the lens design in direct-lit LED backlight modules.

Evaluarea in vitro a temperaturii generate în restaurările directe cu răşini compozite

Aim: To assess thermal changes in composite fillings during light-curing process of two types of resin-based composites with low- polymerization shrinkage. Materials and methods: A thermocouple K was introduced apically through the pulp chamber of six extracted human upper premolars till the base of prepared MOD cavities, in order to measure the temperature developed in two restorative systems, a silorane-based composite (Filtek Silorane/3M EPSE - FS) and a dymethacrylate-based composite (Premise Packable/KERR - PP), during 5, 10 and 20 seconds light-curing process. For the light-curing of the adhesive systems and 9 increments of composites of the restorations was used a high power LED unit with a Periodic Level Shifting Light Technology from 1.100 mW/cm2 -1.330 mW/cm2 per second and a wave length of 450-470 nm. Results: The light-curing process caused an increase of the temperature in the restorative materials that was correlated to the increase of exposure time to the light, with almost doubled temperature values recorded for the silorane- based restorations compared to the dimethacrylate-based ones. The peak value was recorded for the horizontal base composite increment after 20 seconds of light-exposure, with a temperature mean value of 10.18 °C for FS composite compared to 4.91 °C mean temperature value recorded in PP composite. Conclusions: The ring opening Silorane cationic curing technology rises a concern regarding general accepted temperature values associated to its exothermic curing reaction during light-curing with a LED high-power and narrow wave length unit, compared to a highly-filled free-radical polymerization dimethacrylate-based resin system.

Polymerization shrinkage kinetics and shrinkage-stress in dental resin-composites

ObjectivesTo investigate a set of resin-composites and the effect of their composition on polymerization shrinkage strain and strain kinetics, shrinkage stress and the apparent elastic modulus. MethodsEighteen commercially available resin-composites were investigated. Three specimens (n=3) were made per material and light-cured with an LED unit (1200mW/cm2) for 20s. The bonded-disk method was used to measure the shrinkage strain and Bioman shrinkage stress instrument was used to measure shrinkage stress. The shrinkage strain kinetics at 23°C was monitored for 60min. Maximum strain and stress was evaluated at 60min. The shrinkage strain rate was calculated using numerical differentiation. ResultsThe shrinkage strain values ranged from 1.83 (0.09) % for Tetric Evoceram (TEC) to 4.68 (0.04) % for Beautifil flow plus (BFP). The shrinkage strain rate ranged from 0.11 (0.01%s−1) for Gaenial posterior (GA-P) to 0.59 (0.07) %s−1 for BFP. Shrinkage stress values ranged from 3.94 (0.40)MPa for TET to 10.45 (0.41)MPa for BFP. The apparent elastic modulus ranged from 153.56 (18.7)MPa for Ever X posterior (EVX) to 277.34 (25.5) MPa for Grandio SO heavy flow (GSO). SignificanceThe nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk-fill materials showed comparable result when compared to the traditional resin-composites.

Comparison of Surface Hardness of Various Shades of Twinky Star Colored Compomer Light-cured with QTH and LED Units.

IntroductionColored compomers are a group of restorative materials that were introduced in 2002 to repair primary teeth, and they provide attractive color and ease of use in pediatric dentistry. The aim of this study was to evaluate the effect of QTH and LED light-curing units on the surface hardness of different colors of Twinky Star compomers.MethodsIn this experimental study, a composite resin (Z250, 3M, and USA), an ionosit compomer (DMG, Germany) with A3 shade and 8 different Twinky Star colored compomer (Voco, Germany) samples were used. In all, 100 samples were prepared with 10 samples in each group, i.e., 10 Z250 composite resin, 10 ionosit compomers, and 10 Twinky Star compomer samples of each color. The samples were prepared in a 4×4-mm Teflon mold. Half of the samples were light-cured with QTH and the other half with LED units. Then, the surface microhardness was measured by Vickers hardness test. The data were analyzed with IBM-SPSS version 22, using the t-test and ANOVA.ResultsTwo-way ANOVA showed that the mean surface hardness of the compomer samples cured with the QTH unit was significantly higher than that cured with the LED unit (p < 0.001). In each curing unit, surface hardness of some materials exhibited significant differences with the highest hardness being observed in the Z250 composite resin (650.35 ± 56.320) and the lowest hardness being detected in the ionosit compomers (461.10 ± 96.170). One-way ANOVA also showed that, among the different colors of the Twinky Star compomer, the lowest hardness with both units (QTH and LED) was observed in the gold color (214.32 ± 22.026 and 175.116 ± 15.918, respectively).ConclusionThe colored compomer and the type of light-curing unit affected the microhardnesses of the surfaces. Different colors of Twinky Star compomers exhibited different surface microhardnesses.

The challenge of scaling up photobioreactors: Modeling and approaches in small scale

Commercial large‐scale application of photobiotechnology calls for acceptable rates and high cell densities. The latter results in self‐shading and a temporally declining growth rate, making the process inefficient. Upscaling phototrophic processes requires knowledge of the reaction kinetics with special attention on the μ‐I relation. Model‐based calculations for studying the effect of self‐shading on growth were performed for three μ(I) concepts. The nonrealistic μ(I0) concept results in exponential growth without limit, the widely used concept exhibits a growth behavior that significantly deviates from real processes, but the sophisticated concept describes real processes best. A Respiration Activity Monitoring System (RAMOS) with CultiLux unit was tested regarding its applicability for exploring the μ‐I dependency of Arthrospira platensis. The results were not satisfactory because of self‐shading due to a high cell density (which was essential for yielding detectable oxygen‐evolution signals). An innovative cultivation system in which self‐shading does not interfere with phototrophic growth was required. A flat‐panel system was constructed (designed by CFD, short light path of 1 cm, uniform planar light supply by LED and OLED units), allowing continuous cultivation of phototrophic microbes at varied light intensities.

Effect of radiant heat and ultrasound on fluoride release and surface hardness of glass ionomer cements.

The purpose of this investigation was to evaluate the influence of radiant heat and ultrasound on fluoride release and surface hardness of 3 glass ionomer cements (GICs). There were 3 experimental groups for each GIC; in group 1, the specimens were left to set without any treatment; in group 2, the specimens were irradiated for 2 minutes using a LED unit; and in group 3, ultrasound was applied using a scaler for 55 seconds on the specimen surface. Fluoride release measurements were performed daily for 7 days and at days 14 and 28. Surface hardness of the tested GICs was determined using Vickers method. The measurements were performed 24 hours and 7 days after mixing. Statistical analysis of the data was made using 1-way ANOVA and Tukey's and Bonferroni post hoc tests (α = 0.05). Radiant heat during setting reduced the fluoride release and increased the surface hardness of GICs (p&lt;0.05). Ultrasonic treatment also reduced the fluoride release and increased the surface hardness (p&lt;0.05) of GICs but in lower extent. Among the GICs there were differences in fluoride release and surface hardness properties depending on their composition (p&lt;0.05). Radiant heat and ultrasonic treatments may be useful methods for GIC restorations in order to achieve faster adequate initial mechanical properties.

Reducing the stroboscopic effects of LED luminaires with pulse width modulation control

Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.

Design and Manufacture of a Novel LED Table Lamp with Flower Decoration

This work involved the design and manufacture of a novel LED table lamp that provides for flower decoration. It is a combination of a normal LED table lamp and attachments holding flower arrangement frogs. In this application the frogs, as used for traditional flower arrangements, became heat sinks for the LED units. They are made of an aluminum alloy to give good heat transfer and dissipation. In any case since they are fixed to the unit they do not need to be very heavy. The design features of this novel flower-arrangement LED table lamp are: (1) the use of a light aluminum alloy flower decoration frog as a heat sink which gives both high heat dissipation and allows decorative flower arrangement; (2) the installation of LED lamps at three points of the same plate above a cylinder covered with a glass lampshade to achieve a beautiful effect; (3) to provide three different lighting modes for reading, use as a night light and for flower decoration. This novel LED table lamp meets all the energy-saving and environmental protection requirements. It has commercial potential in the market for LED lamps.

Marginal integrity of resin composite restorations restored with PPD initiatorcontaining resin composite cured by QTH, monowave and polywave LED units.

This study evaluated the influence of curing devices on marginal adaptation of cavities restored with self-etching adhesive containing CQ and PPD initiators and hybrid composite. Twenty-four class V (3 groups, n=8) with margins located on enamel and dentin were restored with Clearfil S3 Bond and Clearfil APX PLT, light-cured with a monowave LED, multiwave LED and halogen light-curing unit (LCU). Marginal adaptation was evaluated with SEM before/after thermo-mechanical loading (TML). On enamel, significantly lower % continuous margins (74.5±12.6) were found in group cured by multiwave LED when compared to monowave LED (87.6±9.5) and halogen LCU (94.4±9.1). The presence of enamel and composite fractures was significantly higher in the group light-cured with multiwave LED, probably due to an increased materials' friability resulted from an improved degree of cure. The clinician should aware that due to a distinct activation of both initiators, marginal quality may be influenced on the long-term.

Characterizing the output settings of dental curing lights

ObjectivesFor improved inter-study reproducibility and ultimately improved patient care, researchers and dentists need to know what electromagnetic radiation (light) is emitted from the light-curing unit (LCU) they are using and what is received by the resin. This information cannot be obtained from a dental radiometer, even though many studies have used a dental radiometer. MethodsThe light outputs from six LCUs (two QTH and four broad-spectrum LED units) were collected in real-time using an integrating sphere connected to a fiberoptic spectrometer during different light exposures. ResultsIt was found that the spectral emissions were unique to each LCU, and there was no standardization in what was emitted on the various ramp (soft-start) settings. Relative to the normal use setting, using the ramp setting reduced the radiant energy (J) delivered from each LCU. For one of the four broad-spectrum LED LCUs, the spectral emissions in the violet range did not increase when the overall radiant power output was increased. In addition, this broad-spectrum LED LCU emitted no light from the violet LED chip for the first 5s and only emitted violet light when the ramp phase finished. ConclusionsA single irradiance value derived from a dental radiometer or from a laboratory grade power meter cannot adequately describe the output from the LCU. Manufacturers should provide more information about the light output from their LCUs. Ideally, future assessments and research publications that include resin photopolymerization should report the spectral radiant power delivered from the LCU throughout the entire exposure cycle.

Red/Infrared LED Unit with Moderate Light Intensity and Low Heat Generation for Personal Phototherapy Applications

A new phototherapy unit for personal and home application is developed based on red and infrared LEDs. The wavelengths of the LEDs used are 660 nm for red light and 840 nm for infrared. The array of red and infrared LEDs were designed to generate mixture of red and infrared light and the current flowing through red and infrared LEDs were driven by using micro control unit (MCU) so that the light output and the heat generated from LEDs could be controlled in order not to exceed the certain limit. Light output from the personal phototherapy unit depends on the current flowing through red and infrared LEDs. The current can be controlled by MCU and constant current LED driver ICs by adjusting the duty ratio of the driving pulse generated by MCU and the operation time of the phototherapy unit is also controlled by MCU. The average red and infrared light output from the phototherapy unit developed for personal application was set to 50 mW/cm2. The surface temperature of the phototherapy unit after 10 minutes operation did not exceed 41°C at the light output of 50 mW/cm2 while LEDs were in contact with the skin.

Temperature rises during tooth bleaching with different light-curing units

The aim of this study was to evaluate the influence of three different light-curing units on the temperature rise induced in the pulpal cavity, when bleached with 35% hydrogen peroxide (HP). Forty extracted maxillary central incisors were randomly divided into four groups according to photoactivation procedure (n = 10). Whiteness HP (WHP) bleaching agent which contains 35% HP bleach was placed on the facial tooth surface and no photoactivation device was used (control); an blue light-emitting diode (LED, 40 s), a diode laser (4 W, Continous mode, 20 s), and Nd:YAG laser (4 W, 60 Hz frequency, 20 s). Temperature rise in the pulpal chamber was measured with a J-type thermocouple wire that was connected to a data logger before and immediately after each 20–40 s application. One tooth of each group was selected for scanning electron microscope analysis. Data were analyzed using one-way ANOVA followed by the Games Howell post hoc test at a preset α of 0.05. One-way ANOVA revealed that there was a significant difference among the light-curing units (p < 0.05) and between control group and light-curing units (p < 0.05). The Nd:YAG induced significantly, which resulted in higher temperature increase than other light-curing units (10.7 °C). The LED unit produced the lowest temperature changes (3.2 °C) among the light-curing units. The presence of the bleaching gel did not cause a temperature increase in control group (0 °C). The results suggested that using light-curing units caused temperature changes in the intrapulpal cavity during tooth bleaching. The use of LED will be more safer for pulpal health when assisted with WHP bleaching gel.

To Determine The Functional Efficacy of Led Units in Various Clinical Offices

Abstract Aim: Light units used for polymerization of resin composites are subject to deterioration with age, and frequent maintenance is required to maintain optimal efficacy. The aim of this study was to examine the efficacy of LED units in private dental offices in Baddi (H.P) for polymerization of resin composites. Materials and Methods: Twenty dental offices met all selection criteria and agreedto participate in the study. To measure light intensity, an analogue radiometer was used. The probe of each LED unit was placed and then measurements of light intensities were recorded for each light unit and the data was statistically analysed. Results: The light intensity of the individual units varied widely. The results revealed that there was error of 35% and a standard deviation of 155.76 among the intensities of various LED Units checked in the study. Conclusions: Light polymerization units in private dental offices displayed a wide rangein light intensity, and many had below-recommended levels. A positive linear relationship was found between light intensity and photoactivation effectiveness. Dentists should regularly monitor the condition of light units and replace deteriorating parts.

Evaluation of Polymerization Efficacy in Composite Resins via FT-IR Spectroscopy and Vickers Microhardness Test.

Background and aims. Polymerization efficacy affects the properties and performance of composite resin restorations.The purpose of this study was to evaluate the effectiveness of polymerization of two micro-hybrid, two nano-hybrid and one nano-filled ormocer-based composite resins, cured by two different light-curing systems, using Fourier transformation infrared (FT-IR) spectroscopy and Vickers microhardness testing at two different depths (top surface, 2 mm).Materials and methods. For FT-IR spectrometry, five cylindrical specimens (5mm in diameter × 2 mm in length) were prepared from each composite resin using Teflon molds and polymerized for 20 seconds. Then, 70-μm wafers were sectioned at the top surface and at2mm from the top surface. The degree of conversion for each sample was calculated using FT-IR spectroscopy. For Vickers micro-hardness testing, three cylindrical specimens were prepared from each composite resin and polymerized for 20 seconds. The Vickers microhardness test (Shimadzu, Type M, Japan) was performed at the top and bottom (depth=2 mm) surfaces of each specimen. Three-way ANOVA with independent variables and Tukey tests were performed at 95% significance level.Results. No significant differences were detected in degree of conversion and microhardness between LED and QTH light-curing units except for the ormocer-based specimen, CeramX, which exhibited significantly higher DC by LED. All the composite resins showed a significantly higher degree of conversion at the surface. Microhardness was not significantly affected by depth, except for Herculite XRV Ultra and CeramX, which showed higher values at the surface.Conclusion. Composite resins containing nano-particles generally exhibited more variations in degree of conversion and microhardness.

Perceived Discomfort Glare from an Adaptive Driving Beam Headlight system Compared with Three Low Beam Lighting Configurations

Adaptive driving beams (ADB) avoid glare for approaching or leading drivers but otherwise provide high beam lighting. Audi's implementation uses a matrix of LED units to deactivate individual LEDs when it detects leading or approaching vehicles. A test track study measured perceived discomfort glare by having 20 participants view and rate headlight configurations from five roadway approaches. The headlight conditions included an Audi A8 with ADB, the A8 with ADB deactivated (resulting in an LED low beam pattern that met European specifications), a 2013 Mazda 3 with low beam adaptive curve HID headlights, and a 2014 Dodge Durango SUV with low beam HID headlights. Five approaches included left and right gradual and sharp curves and a straight approach. Participants rated glare comfort on a scale from 1 to 9, with higher ratings indicating more acceptable glare. Glare from the Durango was rated as less comfortable (M = 6.15) than the other three systems. The Mazda 3 (M = 6.82) received more acceptable glare ratings than the Durango. The A8 ADB (M = 7.25) received more acceptable glare ratings than the Durango and the Mazda 3 but was not rated differently from the A8 low beam LED condition (M = 7.36). Mean and maximum illuminance measures for the approach vehicles corresponded well with subjective ratings. These findings demonstrate the promise for adaptive driving beam headlight systems, and the tested adaptive driving beam system is presently available for use in the European market. However, FMVSS 108 requires discrete high and low beam settings, which does not allow adaptive driving beam systems in the United States. Measuring illuminance dynamically may provide an alternative regulatory approach.

Does the light source affect the repairability of composite resins?

The aim of this study was to examine the effect of the light source on the microshear bond strength of different composite resins repaired with the same substrate. Thirty cylindrical specimens of each composite resin--Filtek Silorane, Filtek Z550 (3M ESPE), Gradia Direct Anterior (GC), and Aelite Posterior (BISCO)--were prepared and light-cured with a QTH light curing unit (LCU). The specimens were aged by thermal cycling and divided into three subgroups according to the light source used--QTH, LED, or PAC (n = 10). They were repaired with the same substrate and a Clearfil Repair Kit (Kuraray). The specimens were light-cured and aged for 1 week in distilled water at 37 °C. The microshear bond strength and failure modes were assessed. There was no significant difference in the microshear bond strength values among the composite resins, except for the Filtek Silorane group that showed significantly lower bond strength values when polymerized with the PAC unit compared to the QTH or LED unit. In conclusion, previously placed dimethacrylate-based composites can be repaired with different light sources; however, if the composite to be repaired is silorane-based, then using a QTH or LED device may be the best option.

Influence of the composition of different resin composites in the Knoop hardness and bond strength between tooth/restoration

Abstract The aim of this study was to evaluate the Knoop Hardness (KH) and bond strength (BS) among different resin composites. Three composites (Z100- 3 M/ESPE; Filtek Supreme-3 M/ESPE, Filtek Silorane-3 M/ESPE) were tested. Thirty bovine incisors (n = 10) were used. Conical cavities were prepared in the buccal surface of each tooth with a diamond bur (3131KG Sorensen, Barueri, SP, Brazil) with a high-speed water-cooled hand-piece in a standard cavity preparation appliance (2.0 x 2.0 x 1.5 mm), resulting in a C-Factor of 2.2. Two adhesive systems were used according to the manufacturer’s instructions (Single Bond 2 and Silorane System Adhesive - 3 M ESPE). The restorations were made respectively with Z100, Supreme and Silorane. The composites were inserted in a single increment and light cured with a LED unit, Freelight (3 M ESPE) for 40 s. After photo-activation the specimens were stored at 37°C in distilled water during 24 h. KH (HMV-2, Shimadzu) were performed in the top and bottom at each specimen. After that, the push-out test was performed with a universal testing machine (Model 4411, Instron). In the KH test the data were submitted to a two way ANOVA and Tukey’s test (α=5%). The mean of KHN and standard deviations were: Top - Z100 (74.1/9.0); Supreme (58.4/3.6); Silorane (42.8/6.2) and Bottom - Z100 (66.7/13.6); Supreme (61.2/3.6); Silorane (40.0/3.0). In the BS test the data were submitted to one way ANOVA and Tukey’s test (α=5%). The BS mean and standard deviations were: Z100 (12.6/5.2), Supreme (20.9/6.3), Silorane (29.7/9.0). Z100 had the highest KHN at the top and it was statistically different from the bottom. Supreme and Silorane had no differences between top and bottom. Silorane showed the highest BS mean differing statistically from the others. Differences in the composition of composite resins can to influence in the Knoop hardness and bond strength of restorations.

A 1024-channel 6 mW/mm2 optical stimulator for in-vitro neuroscience experiments.

Recent optical stimulation technologies allow improved selectivity and have been widely used in neuroscience research. This paper presents an optical stimulator based on high power LEDs. It has 1024 channels and can produce flexible stimulation patterns in each frame, refreshed at above 20 Hz. To increase the light intensity, each LED has an optical package that directs the light into a small angle. To ensure the light of each LED can reach the lens, the LEDs have been specially placed and oriented to the lens. With these efforts, the achieved power efficiency (defined as the mount of LED light power passing through the lens divided by the LED total power consumption) is 5 × 10(-5). In our current prototype, an individual LED unit can source 60 mW electrical power, where the induced irradiance on neural tissues is 6 mW/mm(2) integrating from 460 nm to 480 nm. The light spot is tunable in size from 18 μm to 40 μm with an extra 5-10 μm separation for isolating two adjacent spots. Through both bench-top measurement and finite element simulation, we found the cross channel interference is below 10%. A customized software interface has been developed to control and program the stimulator operation.

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites. MethodsModel composites based on BisGMA/TEGDMA (60:40mol%) were loaded with 40wt% of 7nm or 16nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α=0.05 significance level. ResultsComposites formulated with 16nm particles had higher CIE L* than those with 7nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO+16nm before storage and all groups with 16nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ+7nm had the lowest and BAPO+16nm the highest hardness values. SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.