Quartz Tungsten Halogen Research Articles

Evaluation of the Impact of Irradiance Lamps and Storage Media on Elution of TEGDMA from Dental Composites.

The aim of this study was to evaluate and compare the effect of irradiance light and storage media on the elution of triethylene glycol dimethacrylate (TEGDMA) from conventional Filtek Z350XT 3M ESPE and two bulk-fill composites Shofu Beautifil-Bulk and Filtek Bulk fill flowable 3M ESPE using high-performance liquid chromatography (HPLC). Shofu Beautifil-Bulk, Filtek Bulk fill flowable 3M ESPE, and Filtek Z350XT 3M ESPE were the three types of composites used in this study. Disk shaped samples of 4-mm thickness and 10-mm diameter were fabricated using a stainless steel mold and were polymerized using light emitting diode (LED) and quartz tungsten halogen (QTH) lamps. After polymerization, the samples were immersed in ethanol, artificial saliva with betel quid extract, and distilled water for 1, 7, and 30 days, respectively. The elution of monomer TEGDMA was evaluated using HPLC. To evaluate the mean concentration difference, mixed way analysis of variance (ANOVA) was applied. Between different light, materials, and within the time duration, Tukey's post hoc test was used. A p value of 0.05 was considered significant. During the first day of storage, a significant amount of monomer TEGDMA elution was seen in all the materials. The highest values observed to be in the disks cured with QTH lamp. However, the highest elution was seen when the disks were immersed in ethanol/water solution. While the most stable medium was distilled water, artificial saliva with betel nut extract also had a significant effect on the elution of TEGDMA. The highest value obtained was of Filtek Bulk fill flowable 3M ESPE after 30 days of immersion in both LED and QTH cured disks. Filtek Bulk fill flowable 3M ESPE shows better properties in relation to the release of monomer TEGDMA as it releases less amount of monomer in the storage media. The release of monomer was highest in ethanol as compared to artificial saliva and distilled water with the passage of time.

Novel Time-Saving Technique to Measure the 2D Complex Profile of Spectral Transmittance of Linearly Variable Filters and Assessing Homogeneity of Optically Transparent Materials

Emerging technologies for coating new types of filters, such as linearly variable bandpass filters, urges new kind of measurement systems requiring accurate and time-saving spatially resolved transmittance measurements. On the other hand, one of the main uses of coated filters is standardization use; e.g., as certified reference materials (CRMs) for transmittance and absorbance standards. In this case, the homogeneity assessment is of great interest. To do such measurements with low uncertainty, spatial scanning methods using reference double-beam spectrophotometers are routinely used. High time consumption and relatively high-cost are disadvantages of this traditional method. In this work, we propose a new system based on an imaging technique. The newly developed system comprises a quartz tungsten halogen (QTH)-based illuminator, with collimator and coupling optics, a double-grating monochromator, customized integrating sphere, and scientific highly digitized, high-resolution and dynamic range Si-based CCD (monochrome) camera. The system is time-saving: in one-shot we may measure the spatial transmittance distribution of the samples (e.g. filters) without separately measuring the reference (air), which has many instability issues. Validation measurements using standard filters are presented. Systematic errors may be studied and corrected for. Many types of filters and liquids, for instance chemical reference materials (RMs), may be measured and reported. Uncertainty of spatial, spectral and radiometric components are studied carefully and estimated. The combined uncertainty evaluation has shown that relatively low uncertainty levels may be achieved, specially in the visible range (U < 1 %, k=2 ). Spatially-resolved data with different curves at different positions (spatial points) are shown in the spectral range of 380 nm through 950 nm. The combined uncertainties at some spectral points are presented and proved to be sample- and wavelength-dependent at all the points in the field-of-view (FOV) of the CCD camera.

COOMET key comparison COOMET.PR-K1.a.2018 for spectral irradiance 250 nm to 2500 nmm, final report

Main textThis report describes the Key Comparison COOMET.R-K1.a.2018 for spectral irradiance in the wavelength range of 250 nm to 2500 nm, conducted by the Regional Metrology Organization "Euro-Asian Cooperation of National Metrological Institutions" (COOMET). The comparison was, in fact, a combination of three bilateral comparisons with the same link/pilot laboratory - the All-Russian Research Institute for Optical and Physical Measurements (VNIIOFI), the Russian Federation. The non-link laboratories were the Belarusian State Institute of Metrology (BelGIM), Belarus, the National Scientific Centre "Institute of Metrology" (NSC IM), Ukraine, and the National Metrology Institute of Türkiye (TÜBİTAK UME), Türkiye.The aim of the comparison was to link the BelGIM, NSC IM and TÜBİTAK UME measurement results to the CIPM key comparison CCPR-K1.a.2017, conducted by the Consultative Committee for Photometry and Radiometry (CCPR).Tungsten quartz halogen lamps of the FEL type (1000 W) were used as artefacts. Each participant used its own set of lamps. The sequence of measurements was participant - pilot - participant. The pilot measurements of the described here COOMET comparison were performed in a short time (within three months) after completing the measurements of CCPR-K1.a.2017, where VNIIOFI also was a pilot, which provided a high quality link.NSC IM performed measurements in the full spectral range, from 250 nm to 2500 nm, while BelGIM and TÜBİTAK UME managed to cover the range from 250 nm to 1100 nm only.The analysis of the comparison was performed following the approach described in the Appendix A of the Guidelines for CCPR and RMO Bilateral Key Comparisons (CCPR-G5). Differences from KCRV of BelGIM and TÜBİTAK UME, for the most of the measured wavelengths, do not exceed 2% and are within the expanded uncertainties. For NSC IM the differences from KCRV are within or comparable with the uncertainties in the IR range, from 900 nm to 2500 nm, but become larger with decreasing wavelength in the visible and UV reaching 9% at 250 nm.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Temperature Changes in Primary and Permanent Teeth Dentine of Varying Thicknesses Following Irradiation by Two Light Curing Units.

This study was performed to determine the temperature rise under human dentin discs of different thicknesses from primary and permanent teeth during the photo-curing process using quartz tungsten halogen (QTH) or light-emitting diode (LED). The current experimental study sample consisted of 160 dentin discs of different thicknesses (0.5, 1, 1.5, and 2 mm), of which 80 dentin discs were prepared from sound lower second primary molars, and the remaining 80 dentin discs were prepared from sound lower third permanent molars extracted surgically for various reasons. A "K" type of thermal tentacle was placed in the center of an acrylic resin base, followed by the placement of a dentin disc. Then, the thermal changes were measured during the photo-curing of the composite using a second LED or QTH light curing unit for 20 s. Statistical evaluation was performed using the IBM SPSS Statistics® Version 20.0 software system (SPSS Inc., Chicago, IL, USA). The current study found that the temperature rise in primary teeth (1.17-2.96°C) is significantly lower compared to the rise in permanent teeth (1.55-3.33°C), regardless of the dentin disc thickness or light curing unit used. The temperature rise decreases significantly when the thickness of dentin discs increases, regardless of the type of teeth or light curing unit used (P<0.05). Furthermore, QTHcauses less temperature rise (1.17-2.65°C) compared to LED (1.61-3.33°C). The temperature rise during polymerization of the resin composite with the second-generation LED appeared to be below 5.5°C. Hence, it appears to be safe for use during the restoration of primary teeth. Primary teeth dentin might be more effective than permanent teeth dentin in protecting the dental pulp.

Microleakage of Class II Bulk-Fill Resin Composite Restorations Cured with Light-Emitting Diode versus Quartz Tungsten-Halogen Light: An In Vitro Study in Human Teeth

Background: Resin composites undergo a certain degree of shrinkage when light-cured with different light sources available on the market, resulting in microleakage of dental restorations. The aim of the present study was to assess microleakage of class II restorations with bulk-fill resin composites cured with LED (light-emitting diode) and QTH (quartz tungsten-halogen light) units, both in cervical and occlusal areas of cavity preparations. Materials and Methods: In the present in vitro experimental study, a total of 30 human molar teeth were used, in which 60 class II cavities were prepared (mesial and distal) and restored with Filtek bulk fill resin composite. Restorations were equally distributed in 3 groups according to type of curing light: A, QTH (Litex 680A Dentamerica®); B, LED (Bluephase N® 3rd generation); and C, LED (Valo® 3rd generation). Each group was further subdivided into subgroups 1 and 2 according to IV-A or IV-B resin composite color. Restored teeth were subjected to 20,000 thermal cycles between 5° and 55 °C, then immersed in 1M silver nitrate solution for 24 h. Subsequently, the teeth were sectioned mesiodistally to obtain samples for observation under stereomicroscope in order to determine microleakage degree. Kruskal-Wallis H and Mann-Whitney U statistical tests were applied with a significance level of 5% (p < 0.05). Results: No statistically significant differences were found in the degree of microleakage of bulk-fill resin composites light-cured with LED and QTH units for both occlusal (p > 0.05) and cervical areas (p > 0.05). Additionally, no significant differences were found when comparing microleakage between occlusal and cervical areas (p > 0.05), regardless of lamp type. In addition, significant differences in microleakage degree were found between bulk-fill resins with IV-A and IV-B shades when they were light-cured with QTH at cervical level (p = 0.023). However, there were no significant differences when comparing these bulk-fill resin composite shades at occlusal level with LED (p > 0.05) and QTH (p > 0.05) units. Conclusions: Class II restorations with bulk-fill resin composite in IV-A and IV-B shades light-cured with third generation LED lamp and QTH showed no significant differences in microleakage when compared in both occlusal and cervical areas. On the other hand, significantly more microleakage was found at the cervical level when a darker shade of resin composite was used and light-cured with the QTH unit.

Assessment of the functional efficacy of various light-curing units of different manufacturers

Background: Light plays an important role in polymerizing a light-cured resin-based composite as a hard restorative material. The present study was conducted to assess the functional efficacy of various light-curing units (LCUs) available to us. Materials and Methods: The present study was conducted in the Department of Endodontics on 60 different LCUs of different manufacturers. Parameters such as type of light-curing unit, the curing protocol, and frequency of bulb replacement were also recorded. Results: Out of 60 LCUs, 26 were quartz–tungsten–halogen (QTH) and 34 were light-emitting diodes (LEDs). The mean intensity of QTH was 486.3 W/cm2 and of LED was 612.1 W/cm2. The difference was significant (P &lt; 0.05). Nineteen QTH and 22 LEDs were satisfactory, while 7 QTH and 12 LEDs were unsatisfactory. The difference was nonsignificant (P &gt; 0.05). Conclusion: The authors found that maximum satisfactory results were seen with QTH type as compared to LED type.

CIPM key comparison CCPR-K1.a.2017 for spectral irradiance 250 nm to 2500 nm. Final report

Main textThis report describes the Key Comparison of the Consultative Committee for Photometry and Radiometry CCPR-K1.a.2017 for Spectral Irradiance in the wavelength range of 250 nm to 2500 nm. Tungsten quartz halogen lamps of the FEL type (1000 W) were used as artefacts. Each participant used its own set of lamps. The star scheme of measurements was applied with the sequence participant - pilot - participant. Twelve National Metrology Institutes participated in the comparison. Each participant's measurement data were based on a totally independent spectral irradiance scale realisation. VNIIOFI (the Russian Federation) served as a pilot. The measurements were carried out from 2017 - 2020.The analysis of the comparison was performed following the step-by-step approach described in Appendix B of the Guidelines for CCPR Key Comparison Report Preparation (CCPR-G2 Rev.4). The key comparison reference values (KCRV) were calculated independently at each wavelength as the weighted means with cut-off. The measurement data of all participants were used for the KCRV excluding just a few outliers in the wavelength range of 1700 nm to 2500 nm. The relative uncertainties of the KCRV were minimal, 0.08 %, at the wavelengths of 900 nm to 1500 nm and increasing towards the limits of the spectral range up to 0.28 % at 250 nm and 0.20 % at 2500 nm. Consistency checks were satisfied at 17 of the 28 measured wavelengths, but failed at 11 wavelengths, mostly in the infrared range. For the latter wavelengths the Mandel-Paule method was applied resulting in an additional uncertainty that varied depending on wavelength from 0.11 % to 0.89 %.In general, the measurement uncertainties submitted by the participants in this comparison were less than those submitted in the previous CCPR-K1.a comparison. This is evidenced by the values of the cut-off, which had decreased at all wavelengths by a factor of 1.2 to 3.0 depending on wavelength. However, only for seven participants the degrees of equivalence do not exceed the expanded uncertainties at almost all wavelengths. About 80 % of all results (all participants at all wavelengths) agree with the KCRV within 1 % over the whole spectral range and within 0.7 % in the visible, which is comparable with the results of the previous CCPR-K1.a comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

How the Duration and Mode of Photopolymerization Affect the Mechanical Properties of a Dental Composite Resin.

Composite materials are the most common materials in use in modern dentistry. Over the years, the methods of photopolymerization of composite materials have been improved with the use of various devices, such as quartz tungsten halogen lamps (QTHs), light-emitting diode units (LEDs), plasma-arc lamps and argon-ion lasers. This study aimed to compare the mechanical properties of a composite material, depending on the time and mode of photopolymerization. One hundred and forty rectangular specimens (25 × 2 × 2 mm) and forty-two disc-shaped samples (5 mm diameter and 2 mm thickness) were prepared from shade A2 Boston composite resin. Samples were cured using the following seven photopolymerization protocols: four fast-cure modes (full power for 3, 5, 10, and 20 s), two pulse-cure modes (5 and 10 shots of 1 s exposures at full power), and one step-cure mode (soft start with a progressive cycle lasting 9 s). Specimens were subjected to a flexural strength test, Vickers microhardness test, and FTIR spectroscopy test. A 2-factor ANOVA and post-hoc tests were carried out to assess the differences in the flexural strength parameter between the tested groups of samples before and after aging. A mixed-model ANOVA was carried out to assess the differences in the Vickers microhardness parameter between the tested groups of samples before and after aging. The lowest values of flexural strength (p < 0.001) and Vickers microhardness (p < 0.001) were obtained for the 3 s mode for the pre- and post-aging groups. The FTIR mapping tests showed a much more homogeneous chemical structure of the composite after 20 s of continuous irradiation, compared to the sample irradiated for 5 s in the continuous mode. The mode and cure time affects the mechanical properties of the composite resin. Appropriate selection of the cure mode and time ensures better mechanical properties of composite resin. This suggests that the survival of dental restorations within the oral cavity could be extended by using longer photopolymerization durations.

Measurement of Spectral Match and Spatial Non-uniformity for Indoor Solar Simulator

This paper presents a study on the measurement of spectral match and spatial non-uniformity of the indoor solar simulator available in Universiti Teknikal Malaysia Melaka (UTeM). This indoor solar simulator which was successfully fabricated at the Applied Solar Energy Laboratory (ASEL) had used the quartz tungsten halogen lamp as its only light source. Upon its fabrication, the reliability of ASEL’s solar simulator has not been proved yet as there is no concrete evidence that it had followed the international standard set for solar simulator. Therefore, the motivation of this study had been set to determine the characteristics of the indoor solar simulator in term of its spectral match and spatial non-uniformity. The literature review conducted has revealed that there are few methods that been practiced to determine both cases. For the spectral match test, the experimental works chosen for this research was the mathematical modelling method. Meanwhile, for the spatial non-uniformity test, irradiance mapping method was used where the reading of irradiance intensity at each coordinate across the map was measured. At the end of this study, it shows that at 400-500nm and 500-600 wavelength range, the value of spectral match value obtained was 0.40 and 1.46 respectively; whereas for 600-700nm range, the spectral match measured was beyond the standard range set. On the other hand, this study also reveals that the solar simulator was capable to produce 8.42% of spatial non-uniformity across the tested area of 104cm x 80cm. The average irradiance intensity recorded for this test was 981.98 W/m2.

Effects of aging and light-curing unit type on the volume and internal porosity of bulk-fill resin composite restoration

This study explores the effects of aging (thermal cycling and cyclic loading–TC/CL) and different light-curing unit (LCU) types on the volume characteristics and internal porosity of a bulk-fill resin-based composite restoration. Occlusal cavities (4 × 4 × 3 mm) were prepared on extracted human molars (n = 5). Tetric N-Bond Universal was applied, and the cavities were restored using Tetric-N-Ceram Bulk Fill. Photoactivation was performed using a quartz-tungsten halogen (QTH) or a multiple-emission peak light-emitting diode (MLED). Digital images for all restorations were obtained using microcomputed tomography (micro-CT) before (baseline) and after (post-aging) TC/CL (5,000 TC cycles in 5–55 °C baths and a dwell time of 30 s followed by 10,000 sinusoidal CL load cycles in an Instron B3000 at 2 Hz and 10–110 N) and storage (37 °C) for three months. For the micro-CT analysis, three-dimensional images were used to determine the restoration volume and internal porosity. Data were analyzed using a two-way ANOVA and Tukey’s test (p < 0.05). Restorations photoactivated with QTH exhibited a higher object volume than the LED group at baseline and in post-aging conditions without any significant differences in the other evaluated characteristics. All volume/porosity characteristics increased considerably after TC/CL aging, except for the object volume of the QTH group and the closed porosity of the MLED group. The change in all the volume/porosity characteristics between both LCU groups after TC/CL were not significantly different. Thus, the aging process simulated herein increased the volume and porosity characteristics of the bulk-fill restoration, and no significant differences were obtained between the QTH and MLED equipment.

Effects of Light-Curing Techniques on Dental Resins - A Cross-Sectional Study

Background: Commonly used dental resin composites are used as dental filling materials with the help of light induced polymerization reaction. The purpose of this cross-sectional research was to compare the results of different light intensities on the hardness of different dental composites. Following light treatment units were used.&#x0D; &#x0D; QTH also called Quartz Tungsten Halogen&#x0D; LED also called Light Emitting Diodes&#x0D; &#x0D; Methods: This one-month cross-sectional, in-vitro study was carried out in the Dental Materials Laboratory in Saudi Arabia. Using non-probability, convenient sampling, a single trained operator prepared 60 dental restorative composites (DRC) samples in steel molds with a diameter of 10mm and each mold was 2mm thick. During the polymerization of DRCs, the effects of light intensities, sorption and solubility, and microhardness were all measured. SPSS was used for statistical analysis and a p-value of &lt;0.05 was declared striking.&#x0D; Results: When QTH and LED lamps were used, the average micro hardness of DRC was estimated to be 15.480.46 and 18.260.53, respectively. The mean light intensity of QTH was 434 mW/cm2 and for LED lights it was 925mW/cm2. There was no notable difference in DRC sorption and solubility capability (p=0.001) during the polymerization reaction (p=0.128).&#x0D; Conclusion: When it came to increasing the surface micro hardness of DRC, LED light was found to be more effective than QTH light.

INVESTIGATION OF LIGHT INTENSITY OF LIGHT CURING UNITS AFTER DIFFERENT PERIODS OF USE

Quartz-tungsten halogen light curing units (LCUs) have been the main source of light for the polymerization of resin based composites (RBCs) for several decades. Since the beginning of the 20th century, however, their use has been reduced due to the invention and improvement of LED LCUs. Various factors can cause a decrease in the light intensity of LED LCUs, one of which is diode aging. The aim of the present paper is to study the change in light intensity of LCUs after different periods of intensive use. For this purpose, the light intensity of 94 regularly used LED LCUs aged between 1 and 10 years was measured with a digital radiometer. The devices were used in conventional mode with maximum light intensity. It was found that regardless of the type and model of LCU, there is a direct relationship between the time of use and light intensity - the longer the operation period of a device is and the more used it is, the lower its intensity is. The decrease in light intensity as devices age is different for different models, as well as for different devices of the same model. In the studied LCUs with a 10-year period of use, 77.5% have light intensity lower than the required minimum of 400 mW/cm2, which makes them unusable. It can be concluded that dentists should regularly monitor and measure the light intensity of their LCUs, especially as they age, to ensure the longevity of their restorative procedures.

Effect of Light-Sources and Thicknesses of Composite Onlays on Micro-Hardness of Luting Composites.

The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.

Optimal design and experimental test of a solar simulator for solar photovoltaic modules

AbstractSolar simulators have been widely used to characterize the performance of solar photovoltaics cells, which typically have a size of 156 × 156 mm2. In order to amplify the testing area, a flexible optimal design method for solar simulators is presented in this study. In this work, 20 quartz tungsten halogen lamps are used with a light filter composed of a mixture of distilled water and cyan ink. The methodology includes the measurements of the irradiance nonuniformities, spectral profile, and explores the effects of light filters on the primary light source used. During this stage, the power source of the lights should be selected, where direct current is usually assumed. As soon as the primary light source is characterized by its corresponding model, a layout is defined by optimizing the nonuniformity of the irradiance. The constructed solar simulator presents a spectral match of 1.69%, a spatial nonuniformity of irradiance of 1.66%, and a temporal instability of irradiance lower than 0.1%. In addition, the current‐voltage curves are compared under indoor and outdoor test showing a root‐mean‐squared error lower than 3%. A class CAA solar simulator is achieved according to the International Electrotechnical Commission and American Society for Testing and Materials standards over an area of 270 × 270 mm2, suitable for testing small size solar photovoltaic modules.

Effect of Additional Light Curing on Colour Stability of Composite Resins

AimThe objective of this study was to evaluate the effect of additional light curing on the colour stability of composite resins. Materials and methods: Four different composite resins—a nanofill, a nanohybrid, a microhybrid, and a bulk-fill composite resin—were tested. Eighty disc-shaped specimens were prepared from each material using either a quartz tungsten halogen or a light-emitting diode light source and were randomly divided into 2 groups according to the surface treatment: no polishing (nonpolished) or polishing with aluminum oxide discs (polished). Then additional light curing was applied to half of the specimens in each group. All specimens were immersed in coffee solution for 1 week. Colour was measured with a spectrophotometer at baseline and after 1 week of storage in coffee solution. Results: Statistically significant differences in colour stability were observed in the restorative materials according to the composition of composite resin, the polishing protocol, and additional light curing, whilst there were no significant differences according to the light source. Additional light curing reduced discolouration in all groups tested. Conclusions: Additional light curing may be beneficial after finishing and polishing in order to maintain aesthetics and increase the resistance of composite resins to discolouration.

Pre-Launch Radiometric Characterization of EMI-2 on the GaoFen-5 Series of Satellites

The environmental trace gas monitoring instrument (EMI) is a space-borne imaging spectrometer onboard GaoFen-5, which was launched in May 2018, covering wavelengths in the range of 240–710 nm to measure NO2, O3, HCHO, and SO2. An advanced EMI-2 instrument with a higher spatial resolution and sufficient signal-to-noise is currently planned for launch on the GaoFen-5(02) satellite in 2021. The EMI-2 instrument bidirectional scattering distribution function (BSDF) is obtained from the absolute irradiance and radiance calibration on-ground. Based on EMI-2 earth and sun optical paths, the key factors of BSDF parameters are introduced. An NIST-calibrated 1000 W FEL quartz tungsten halogen lamp and a 2D turntable are adopted for the absolute irradiance calibration. A large aperture integrating sphere system is used for the absolute radiance calibration. Based on absolute irradiance and radiance calibration functions, the BSDF parameters are obtained, with accuracy of 4.9% for UV1, 4.3% for UV2, 4.1% for VIS1, and 4.2% for VIS2. The on-ground measurement results show that the reflectance spectrum can be calculated from BSDF parameters. On-orbit application of the EMI-2 instrument BSDF are also discussed.

A measurement of irradiance of light-curing units in dental offices in three Croatian cities.

Aim To determine irradiance of light-curing units (LCUs) in dental offices in three Croatian cities and to compare irradiance values with the age and model of LCUs. Methods Private and public dental offices in three most prominent cities in Croatia (Rijeka, Split and Zagreb) were included in this study. In total, 195 LCUs were tested, using radiometer Ivoclar Bluephase Meter 2 for irradiance (mW/cm2 ). The minimum acceptable value was set at 400 mW/cm2 . The age, model and difference between declared and measured irradiance of the LCUs were also determined. Of the total of 195 LCUs, 190 (98%) were LED (light-emitting diode) and 5 (2%) were QTH (quartz-tungsten - halogen). Results The mean age of tested LCUs was 4.43±3.4 years; the oldest was in Rijeka, 5.2±3.8 years. The overall mean irradiance for all three cities was 806.4 mW/cm2 (p=0.0004). Of all LCUs, 11.3% were considered clinically unacceptable with irradiance of less than 400 mW/cm2 . Of all tested LCUs 42% (p=0.0005) had a 30% lower value of irradiance than the manufacturer of the LCU declared. In 73% tested LCUs, there was a matching between measured and declared irradiance. The age and model of LCUs had the most significant impact on irradiance. Conclusion The most commonly used LCU included in dental offices was LED. Mean irradiance was good enough to secure adequate polymerization of resin-based materials. Irradiance decreases with usage time of LCU.

Effects of curing lights on human gingival epithelial cell proliferation

BackgroundLight-emitting diode (LED) and quartz-tungsten-halogen (QTH) curing lights are used commonly in clinics. The aim of this study was to assess the effect of these lights on the proliferation of human gingival epithelial cells. MethodsSmulow-Glickman (S-G) cells were exposed to a VALO LED (Ultradent) or an XL3000 QTH (3M ESPE) light at 1 millimeter or 6 mm distance for 18, 39, 60, and 120 seconds. Untreated and Triton X-100 treated cells were used as controls. At 24, 48, and 72 hours after light exposure, cell proliferation was evaluated via a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. ResultsThe authors first evaluated the performances of these 2 lights. Both LED and QTH lights generated heat. The LED light generated less heat than the QTH light and could save approximately two-thirds of the curing time. When used for 18 seconds at a 6 mm distance, the LED light did not inhibit the proliferation of S-G cells. However, if the exposure time was longer (for example, 39, 60, or 120 seconds), the LED light inhibited cell proliferation. The inhibitory effect increased when the exposure time was increased to 39, 60, or 120 seconds. The QTH light did not inhibit S-G cell proliferation if the exposure time was less than 120 seconds. ConclusionsProlonged exposure to a blue curing light (both LED and QTH) inhibits the proliferation of gingival epithelial cells and may cause damages to oral soft tissues. Practical ImplicationsIn dental practices, a balance should be struck in consideration of curing time not only to cure the composites completely but also to minimize unnecessarily prolonged light exposure.

Degree of conversion and microhardness of resin cements photoactivated through glass ceramic.

BackgroundTo assess whether glass-ceramic shade, thickness and translucency affect degree of conversion (DC) and Knoop microhardness (KHN) of resin cements photoactivated using light-emitting diode (LED) or quartz-tungsten-halogen (QTH) units. Material and MethodsGlass-ceramic blocks were cut (2, 3 and 4mm) and sintered. For DC FT Raman spectroscopy (n=3), film specimens of cements (RelyX ARC, U200, Veneer, C&B) were obtained. For KHN test (n=3), cements were inserted in cylindrical matrix and covered by polyester strip. Specimens were photoactivated (30s) using LED or QTH according to each group: direct photoactivation (DP), interposing ceramic specimens or no photoactivation (NP). Data were analysed by ANOVA and Tukey’s test, Kruskal-Wallis and Dunn’s tests (p<0.05). ResultsCeramic features had significant effect on DC of RelyX ARC, U200 and Veneer (p<0.0017). Light source had no effect (p=0.9512). C&B and Veneer had higher DC, followed by dual cements. NP dual cements showed the lowest DC. For KHN, ceramic shade (p=0.1717) and light source (p=0.1421) were not significant, but ceramic translucency, thickness and resin cement were significant (p=0.0001). KHN was higher for U200 followed by ARC, and lowest for Veneer. ConclusionsDC was affected by ceramic shade, translucency and thickness. KHN was dependent on ceramic translucency and thickness. Higher DC and KHN were achieved for dual-cured cements photoactivated through 2mm-thick low translucent or 3mm-thick high translucent glass-ceramic. Key words:Cementation, composite resin cements, dental curing lights, glass ceramics.

The effect of different curing units on the degree of polymerization of different composite resins

Objective: The aim of this study was to investigate the degree of polymerization of composite resins cured with different light-curing units (LCUs). Materials and Methods: Three bulk-fill composite (Beautifil Bulk-Fill Giomer, Filtek Bulk-Fill, and X-Tra Fill) and a methacrylate-based composite (Filtek Z250) were used in this study. Thirty disc-shaped specimens, 4 mm thick, were prepared from each composite resin. Specimens were divided into three groups and polymerized with light-emitting diode (LED), Plasma arch curing unit (PAC), and quartz-tungsten halogen LCU. The bottom and top surface microhardness of the specimens stored in distilled water for 24 h at 37°C after polymerization was measured with a universal test device. The hardness ratio (HR) of specimens was calculated by the bottom surface microhardness/top surface microhardness formula. Data were analyzed by two-way ANOVA and Tukey's least significant difference post hoc tests (α = 0.05). Results: Statistically significant differences were detected between the mean HR values of the specimens polymerized with different LCUs (P Conclusion: The degree of polymerization of the composite resin restoration may be affected by the structural properties of the resin and the type of LCU. The clinician may use alternative techniques, especially in deep cavities.