Light-emitting Diode Curing Units Research Articles

Current trends in placing posterior composite restorations: Perspectives from Palestinian general dentists: A questionnair study

Abstract Aim: The success of composite restorations relies on material selection and practitioner-related factors that shape the overall outcome. This study explores the practices of Palestinian general dental practitioners in placing posterior composites, examining the impact of work sector, experience, and gender on their choices. Materials and Methods: The study was conducted as an online cross-sectional questionnaire and involved 351 participants, with a response rate of 69.8%. The survey comprised 18 closed-ended questions covering demographics, material selection, and composite placement in special cases, techniques, and factors influencing the choices. Statistical analyses included descriptive statistics, chi-squared tests, and Fisher’s exact tests. Results: Composite was the predominant choice for small-size (83.7%) and large-size posterior cavities (60.4%). Practitioners commonly opted for composite restorations in cases involving occlusal parafunctional activity (60%), poor oral hygiene (78%), and subgingival cavities (72.2%). Only 19.6% and 5.3% reported occlusal and gingival beveling, respectively. Rubber dams for isolation stood at 30%, one-step self-etch adhesives at 44.9%, and the oblique layering technique at 51%. Light-emitting diode curing units were popular (97.55%), but monitoring output with a radiometer was infrequent (93.5%). Tofflemire metal matrix usage was 46.1%, whereas a sectional matrix system was employed by 29.8%. A 2 mm layer exposure to light curing for 20 s was reported by 62%, and 27.75% utilized additional light-curing postmatrix band removal. Conclusion: The study highlights the need for Palestinian dental professionals to update their clinical approaches in placing composite restorations in posterior teeth. Gender, work sector, and experience influence practitioners’ choices, emphasizing the importance of tailored continuing education programs for improving clinical practices.

Multi-peak Light-emitting Diode Curing Units and Polymerization of 3D-printed Crown and Bridge Resin.

This study aimed to evaluate the substitutive and additive efficacy of multi-peak light-emitting diode (LED) curing units for post-curing of a three-dimensional- (3D-) printed crown and bridge resin. A total of 792 disc- and 180 bar-shaped specimens were printed with a crown and bridge resin (NextDent C&B MFH) and post-cured using two LED curing units (VALO Cordless and Bluephase N G4) in fast and standard modes. Conventional post-curing (LC-3D Print Box, Group PC) was compared with LED-only curing (Groups V1, V2, B1, and B2) and LED-combined curing (Groups PV1, PV2, PB1, and PB2) in terms of microhardness, flexural strength, degree of conversion (DC), and CIE L*a*b* color and translucency parameters. Cytotoxicity of the resin eluates was evaluated using the WST-1 assay. Temperature increases on the resin surface were measured with infrared thermography. Data were statistically analyzed using ANOVA and Kruskal-Wallis tests (α=0.05). The microhardness and flexural strength in Groups V1, V2, B1, and DC in all LED-only groups were lower than in other groups (p<0.05). Larger color disparities existed between Group PC and all LED-only groups than between Group PC and the others (p<0.05). There was no significant difference in cytotoxicity among the groups. The temperature increase was lowest in Groups V1 and PV1 during light curing (p<0.05). Post-curing by multi-peak LED curing units was not as effective as the conventional post-curing device. Additional post-curing by LED curing units did not improve the material properties.

Comparison of the temperature changes in pulp using monophasic light-emitting diode curing unit at different exposure times: An in vivo study

This invivo study evaluated the temperature changes in the pulp chamber at different exposure times using a monophasic light-emitting diode curing unit. Forty-five patients (aged 13-25 years) requiring extraction of maxillary first premolars for orthodontic reasons were included in the study. After access opening, the temperature rise was recorded when exposed to monophasic light-emitting diode curing light (Elipar 3M ESPE; Pymble, New South Wales, Australia) at 5, 10, 15, and 20 seconds with K-type thermocouple probe. Teeth were atraumatically extracted on the same day. The results were analyzed with an analysis of variance and the Bonferroni test. There was a significant increase of 2.1°C ± 0.5°C of pulpal temperature in the maxillary first premolar tooth during exposure to a light curing unit from baseline to 20 seconds. The mean baseline temperature was 35.7°C ± 0.52°C. The highest mean temperature was recorded at 20 seconds (37.8°C ± 0.57°C), and the lowest mean temperature was recorded at 5 seconds (36.1°C ± 0.61°C). There were significant differences among each group (P<0.001) with a mean increase in pulpal temperature from baseline to exposure mode of 5, 10, 15, and 20 seconds. The study results reveal a statistically significant increase in pulpal temperature with a monophasic curing light, which can be used for up to 20 seconds without causing any detrimental effects on the pulp.

Effect of the thickness of CAD-CAM materials on the shear bond strength of light-polymerized resin cement.

This study aimed to investigate the effect of the thickness of computer aided design-computer aided manufacturing (CAD-CAM) restorative materials on the bond strength of light-polymerized resin cement. Ninety specimens were prepared from three different CAD-CAM materials (a leucite-based glass-ceramic [Empress CAD], a polymer-infiltrated ceramic network [Vita Enamic], and a zirconia-reinforced lithium silicate glass-ceramic [Vita Suprinity]) in different thicknesses (1, 2, and 3mm). One surface of each specimen was treated by using a single-step self-etching ceramic primer (Monobond Etch & Prime). Light-polymerized resin cement was bonded to treated surfaces by exposure to a light-emitting diode curing unit from the untreated side of the samples. Shear bond strength (SBS) between the ceramic and the resin cement was measured by using a universal testing machine. The leucite-based glass-ceramic had higher SBS values than the other materials at each thickness. For each material, 1mm-thick specimens had the highest SBS values. The difference between the SBS values of 2mm- and 3mm-thick polymer-infiltrated ceramic network was nonsignificant, whereas the SBS values of 2mm-thick leucite-based glass-ceramic and the zirconia-reinforced lithium silicate glass-ceramic were significantly higher than those of the corresponding 3mm-thick specimens. The choice of the material and its thickness may be highly important for clinical success when light-polymerized resin cements are used for cementation.

An Innovative Light Curing Unit With Multiple Portable Power Sources

The process of attaching brackets to the tooth surface has evolved from brackets being welded to bands to attaching them using light cure composite resin materials. Similarly, the curing lights have advanced from bulky Quartz-Tungsten-Halogen lights to light-emitting diode (LED) curing units. The LED curing units available now have advanced features like high intensity light, reduced curing time, and are very expensive and rely upon prior charging of the unit. The present article describes a curing light which is powered by an external power source like, laptop, smartphone, and power bank and is very compact compared to the present curing lights and is also less expensive.

Effect of Photoinitiator Type and Photoactivation Condition on the Physical-Mechanical Properties of Orthodontic Resins

Purpose: The aim of this study was to evaluate the physical-mechanical properties of experimental orthodontic resins, containing different photoinitiators systems and photoactivated through a ceramic bracket, using a high irradiance and wide spectrum light emitting diode curing unit. Methods: Experimental resin composites (50:50 BisGMA/TEGDMA: 60% feldspar silanized particles) were formulated with different photoinitiators according to the following groups: phenylpropaneamine + amine DMAEMA (PPD), camphorquinone + amine DMAEMA (CQ) or bisacylphosphinic oxide (BAPO). A commercial orthodontic resin composite (Transbond XT) was used as control. The materials were then distributed into two groups, according to the photoactivation condition: directly or through a ceramic bracket, for 20s at 1200 mW/cm2. In the sequence, fifteen composite disks, 5mm of diameter and 1mm of thickness, were made for each of the eight groups. The degree of conversion (DC) was determined by means of Raman spectroscopy. Knoop hardness (KHN) was measured immediately after confection and after 24 hours of storage in 100% ethanol for indirect crosslink density (CLD) evaluation. Data were analyzed using two-way ANOVA followed by Tukey's test (α = 0.05). Results: The DC of the BAPO composite was significantly higher in comparison to the other materials, regardless of the photoactivation condition. The KHN was significantly different between the composite groups in the following sequence: BAPO&gt; Transbond XT&gt; CQ&gt; PPD. The direct photoactivation presented higher KHN values, regardless the type of material. Regarding the CLD, there was statistical difference only for the material factor, as follow: PPD&gt; BAPO = CQ = Transbond XT. Conclusion: The photoinitiator type and the photoactivation condition had a significant influence on the physical-mechanical properties of the evaluated materials.

Evaluation of Color-matching Ability of a Structural Colored Resin Composite.

The present study evaluated the color-matching ability of a structural colored resin composite to compare it with resin composites employing pigments. A structural colored resin composite (Omnichroma [OMC]), a supranano-filled resin composite (Estelite ∑ Quick [ELQ]), and a nano-filled resin composite (Filtek Supreme Ultra [FSU]) were used. Each resin composite was packed into a Teflon mold and pressed down with a clear strip under a glass slide. The specimens were light irradiated through the slide with a light-emitting diode curing unit. The thickness of the specimens (n=6) was measured with a digital caliper before being transferred to distilled water and stored at 37°C for 24 hours. The measurements of the optical characteristics of the specimens on a black-and-white background were performed using a spectrophotometer. D65 (CIE D65) was used as a light source for the spectrophotometer. Measurements were repeated three times for each specimen under each color-measurement condition, and average values for three same-shade specimens were calculated. One-way analysis of variance and Tukey post hoc tests were used (α=0.05). To determine its ability to match the color of artificial teeth, each shade of resin composite was placed in a cavity before performing color measurements. Using a spectrophotometer (CMS-35F S/C) with a flexible sensor, L*, a*, and b* values were obtained. The spectral reflectance curve of OMC showed that it reflected light wavelengths from 430-700 nm regardless of the background color and thickness of the specimens. The percentage of reflectance of ELQ decreased near wavelengths of 550-580 nm. Regarding the influence of background color on CIE L*, a*, b* values, the L* level showed significantly higher values for all tested materials with white backgrounds, and OMC was most affected by the difference in background color. However, a* values of ELQ and FSU were significantly higher with a black background than with a white background, and OMC showed a significantly higher value with a white background than with a black background. The b* values were higher with a white background than with a black background and were significantly higher for all three products, and these tendencies were much greater for ELQ and FSU. The ability of OMC to match the color of artificial teeth showed acceptable color compatibility, regardless of the shade of the artificial teeth and the depth of the cavity. However, ELQ and FSU showed reduced color compatibility, especially for a cavity depth of 3.0 mm. Excellent color matching ability was confirmed for the structural colored resin composite OMC, resulting in reduced color differences and therefore improving the esthetic appearance of the restoration, simplifying shade matching, and compensating for any color mismatch.

Evaluation of photopolymerization efficacy and temperature rise of a composite resin using a blue diode laser (445nm).

The purpose of this study was to evaluate the photopolymerization efficacy of a diode laser (445nm) for use with a composite containing camphorquinone and to estimate the safety of the method related to the temperature rise. Five cylindrical composite specimens were prepared for each thickness: 1, 2, and 3mm. Three light-curing modes were investigated: a light emitting diode (LED) unit and a diode laser (445nm) with output powers at 0.7W or 3W. Evaluation of the polymerization efficacy was based on Vickers hardness measurements, and the highest temperatures at the bottom of the specimens were recorded using a K-type thermocouple. The highest microhardness was observed after the diode laser curing operating at 3W. A comparison of the microhardness of the 0.7W laser cured specimens with the LED cured specimens showed a statistically significant difference in favor of the laser curing. Laser curing operating at 3W resulted in extremely high temperatures. Laser curing at 0.7W resulted in statistically significantly higher maximum temperatures than did LED curing for both 1mm thick (52.9°C against 45.4°C) and 3mm thick (43.6°C against 40.9°C) specimens. Diode laser (445nm) may be an alternative for photopolymerization of composite materials and may result in a higher degree of conversion and depth of cure of composites than what has been seen with LED curing units when they emit at the same energy density.

Effect of Preheating on Micro-hardness of different Composite Resins

Aim: The aim of this study was to assess the effect of preheating on the surface microhardness of different commercially available composite resins (G-aenial, Filtek Z350 and Tetric-N-Ceram). Materials and Methods: Tubes of the composite resins were either kept at room temperature (24 ±10 C) or preheated for 40 min in a commercially preheating device to 40 0 C, 50 0 C and 60 0C, respectively. From composite resin tubes, a total of 120 disk-shaped specimens (40 specimens of each composite resin, 10 disks from each temperature setting) were prepared by inserting uncured preheated composite resin into cylindrical nylon moulds (5 mm diameter × 2 mm height); before light polymerized for 40s with a light emitting diode curing unit. The Vicker’s microhardness number (VHN) of each specimen was measured. Two-way ANOVA and Tukey test were used to analyze the collected data at a significance level of 0.05. Results: In comparison to the room temperature, there was a significant increase in the mean VHNs of each composite resin by preheating to 40 0C, 50 0 C and 60 0 C, respectively (p<0.05). For G-aenial posterior, Filtek Z350XT and Tetric-N-Ceram, at room temperature, the mean VHNs were 51± 4.3, 60.6± 3.7 and 76.6±1.4, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05), while at 400C, the mean VHNs were 65.7±2.5, 86.8±2.3 and 88.4±1.8, respectively with significant differences (p<0.05) between G-aenial posterior and the other two composites. At 500C, the mean VHNs were 109.4±0.9, 104.4±3.4 and 114±0.71, respectively with no significant difference between composite resins. At 600C, the mean VHNs were 122±3.2, 129±3.4 and 136±2, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05). Conclusions: Preheating significantly increased the surface microhardness of all tested composite resins with the highest value observed for Tetric N-Ceram at 600C preheating temperature.

Simple and Low-Cost Thermal Treatments on Direct Resin Composites for Indirect Use.

The aim of this study was to evaluate the influence of three low-cost additional thermal treatments, available in the dental office, on the mechanical, chemical and optical properties of a light-cured resin composite indicated for direct restorations but used as indirect restorative. The direct resin composite TPH3 (Dentsply) was light-polymerized using a light-emitting diode curing unit and submitted to three experimental additional thermal treatments: dry heat at 170 °C for 5 min, autoclave at 121 °C for 6 min, or microwave oven at 450 W for 3 min. The resin composite without any thermal treatment was used as negative control group. An indirect resin composite (Vita CM LC, Vita Zahnfabrik) was tested as a reference. Flexural strength, elastic modulus, microhardness, degree of C=C conversion, roughness before and after simulated toothbrush abrasion, translucency parameter and color difference (ΔE00) were evaluated. Data were analyzed at α=0.05. The indirect resin composite presented lower C=C conversion and mechanical performance. The flexural strength was significantly higher in the dry oven group compared with the control. The roughness was not different among groups before or after brushing, but the thermal treatments caused an increase in C=C conversion, microhardness, and elastic modulus without affecting the translucency parameter or showing visible color alteration (ΔE00<1.8). These results suggest that the use of additional thermal methods of polymerization represents an economical and simple alternative to enhance the mechanical and chemical properties of direct resin composites when used as indirect restoratives.

Depth of cure of high-viscosity bulk-fill and conventional resin composites using varying irradiance exposures with a light-emitting diode curing unit.

The purpose of this study was to determine the depth of cure (DOC) of three resin-based composites (RBCs) using varying irradiance exposures with a corded light-emitting diode curing unit. DOCs for Filtek Z250, TPH Spectra, and Tetric EvoCeram Bulk Fill were determined using the International Organization for Standardization (ISO) Standard 4049. The RBCs were light-polymerized using three different power modes and manufacturer-recommended curing times. Irradiance was determined using a spectrometer sensor and the total energy density was calculated for each power mode and concomitant polymerization time. The DOC data were analyzed with a two-way analysis of variance and Tukey's post hoc test. Tetric EvoCeram Bulk Fill produced significantly greater DOCs than TPH and Z250 (P < 0.05) for all three power mode settings. Overall, the DOC of Tetric EvoCeram Bulk Fill was greater than those of TPH and Z250 at all power settings, but the individual RBCs did not show a significant DOC difference among the three power settings (P > 0.05).

Dimensional Changes of Glass Ionomers and a Giomer during the Setting Time.

ObjectivesThe aim of this study was to evaluate dimensional changes of conventional glass ionomer cements, resin-modified glass-ionomer cement, and a giomer during the setting time using digital laser interferometry. Additionally, the influence of different curing modes (“high”, “soft”, and “low”) of a light-emitting diode (LED) curing unit on dimensional changes was evaluated.Materials and methodsLinear curing shrinkage of conventional glass ionomer cements (CGICs): Fuji IX Extra (F9E), Fuji IX Fast (F9F), Ketac Molar Aplicap (KM), Ketac Molar Quick Aplicap (KMQ), resin-modified glass ionomer cement (RM GIC): Fuji II LC (F2LC) and giomer: Beautifil II (B2) was analyzed. All tested materials were of shade A3, while all of the GIC were encapsulated. Discoid specimens (n=10, d=10 mm, h=0.85 mm) were prepared for each tested material and each curing mode (for light-curable materials) according to the manufacturer’s instructions. Light-curable specimens were cured with LED curing unit (Bluephase G2, Ivoclar-Vivadent, and Schaan, Liechtenstein). Dimensional changes during curing were recorded in real-time. The results were analyzed by ANOVA, and Tukey post hoc test was used for multiple comparisons (α˂ 1%).ResultsAll tested materials showed an initial setting expansion and a subsequent setting shrinkage. KM and KMQ had significantly lower setting shrinkage than RM GIC polymerized using any of the three curing modes. B2 showed lower shrinkage compared to F2LC.ConclusionsThe extent of curing shrinkage in RM GIC measured in this study can affect longevity of restorations.

The effect of a plastic-wrapped LED light curing unit and curing distance variances on diametral tensile strength of composite resin

A method to control infection when using a light-emitting diode (LED) curing unit (LCU) is to wrap it in a transparent plastic barrier (cling wrap). The influence of a plastic-wrapped LCU and curing distance variances on diametral tensile strength of composite resin was evaluated. A total of 60 disc-shaped specimens were formed and cured using plastic-wrapped and unwrapped LCUs. The specimens were divided into six groups with curing distances of 0.5 to 5 mm. The diametral compression test was done using a universal testing machine. A statistically significant difference was found between the wrapped and unwrapped groups. Therefore, the use of a plastic-wrapped LCU influences the diametral tensile strength of composite resin.

Real-time Light Transmittance Monitoring for Determining Polymerization Completeness of Conventional and Bulk Fill Dental Composites.

To monitor the real-time changes in light transmittance during composite curing and to use transmittance data to determine the curing times required for a complete polymerization. Three conventional and three bulk fill composites were cured with two light-emitting diode curing units at layer thicknesses of 2 mm and 4 mm. The real-time light transmittance data were collected by a UV-Vis spectrometer in the wavelength range of 350-550 nm, plotted against time (t) and fitted to an exponential function f(t), whose first derivative ΔT(t) = df(t)/dt represented the rate of transmittance change. As the changing transmittance reflects structural changes that occur during polymerization, ΔT(t) > 0 was considered to indicate an ongoing polymerization, whereas ΔT(t) values approaching zero suggested a complete polymerization. This principle was used to determine times required for a complete polymerization (tcomplete) for each material/thickness/curing unit combination. Light transmittance was significantly influenced by the material type, sample thickness, and curing unit, amounting to 2.9%-27.0% for the bulk fill and 0.7%-16.7% for the conventional composites. The values of tcomplete amounted to 15.3-23.3 seconds for the bulk fill composites at 2 mm, 20.2-33.3 seconds for the conventional composites at 2 mm, 26.9-42.1 seconds for the bulk fill composites at 4 mm, and 40.1-59.8 seconds for the conventional composites at 4 mm. Additionally, an exponential relationship was discovered between the light transmittance and tcomplete. Some of the tcomplete values considerably exceeded the curing times recommended by the manufacturers.

Influence of different wavelengths peaks in LED units on the degree of conversion of orthodontic composites

ObjectiveThe aim of this study was to assess the influence of adding a second wavelength peak (400 nm) to a light-emitting diode (LED) unit on the degree of conversion (DC) of two commercial orthodontic composites, as well as comparing the DC of those two composites. MethodsTransbond XT and Opal Bond MV were the composites used for the tests, cured either with second- or third-generation LED units adjusted to produce the same power density on a given time. Analysis of DC was performed by using the Fourier-transformed infrared spectroscopy in four groups of 5 specimens each divided according to the composites and LED curing units being used. The results, which were normally distributed, were analyzed using a two-way ANOVA test. ResultsThe composites showed very similar degrees of conversion when light-cured with second-generation (74.3%) and third-generation (73.2%) LED light-curing units. The Opal Bond MV composite had a higher degree of conversion (81.9%) than the Transbond XT composite (65.7%). No interaction was found (P = 0.56) between the composites and the LED curing units, regardless of their wavelength, on the degree of conversion. ConclusionThere was no influence of either a second- or third-generation LED curing unit on orthodontic composites.

Color changes in resin cements due to light polymerization with and without all-ceramic restorations

Objective: The aim of this in vitro study was to examine the color changes in resin cements polymerized under lithium disilicate glass ceramic material (IPS Empress 2).Material and methods: A pressable ceramic material (10 mm × 1 mm) placed between the curing unit tip and resin cement was used to simulate the impact of light transmission on restoration. Light-polymerized Variolink II, dual polymerized Variolink II, Multilink Automix, Clearfil Esthetic Cement, Panavia F 2.0, RelyX Veneer, and Nexus 3 resin cement specimens were polymerized by a high-power light-emitting diode curing unit (Demi). A spectrophotometer (Vita EasyShade) was used to measure the colorimetric values of the specimens. Color changes were determined by the CIEL*a*b color system. Total color differences () of the resin cement specimen with or without the ceramic specimen were calculated. Analysis of variance, Tukey’s honestly significant difference and paired t-tests were used to analyze the data (α = 0.05). Results: There were significant differences among values with or without the ceramic specimen (p < 0.05). The light-polymerized Variolink II resin cement specimens induced the greatest color changes with or without the ceramic specimen ( = 14.21 and = 2.32). The values of all resin cements with the ceramic specimen were less than 2.5 and the Panavia F 2.0 specimens induced the smallest color changes ( = 0.95). Conclusions: Light polymerization of resin cements is a significant factor affecting the color of the final restoration, but lithium disilicate glass ceramics of 1-mm thickness appeared to have a masking effect on the color changes in resin cements.

Effect of monolithic zirconia on the degree of conversion of two resin cements analyzed by FT-IR/ATR spectroscopy

Objective: This study aimed to evaluate the degree of conversion (DC) of two different resin cements polymerized under the monolithic zirconia specimens in different thicknesses and colors.Material and methods: Partially stabilized monolithic zirconia blocks (inCoris TZI) were cut into three different thicknesses (0.5, 1.0, and 2.0 mm) and the specimens were divided into four color groups (A1, A2, A3, and A4). The light transmittance of each specimen was measured. Panavia F 2.0 or Variolink N resin cement was applied into teflon mold and irradiated using the light emitting diode curing unit for 20 s under monolithic zirconia specimen (n = 10). The resin cement specimens were stored at room temperature under dry conditions. The DC of each specimen was measured by Fourier transform infrared-attenuated total reflection (FT-IR/ATR) spectroscopy after the 1st and 10th day. Data were analyzed with two-way analysis of variance (ANOVA), two-way repeated measures ANOVA, three-way repeated measures ANOVA, and the Tukey least significant difference (LSD) tests (α = 0.05).Results: The light-cure resin cement groups showed higher DC than the dual-cure resin cement groups (p < 0.05). The DC of both resin cements reduced with an increase in the thickness and darkening of the color of monolithic zirconia specimens. There was a statistically meaningful increase in the 10th-day values for dual-cure resin cement (p < 0.05), whereas there were no significant differences between the 1st- and 10th-day values for light-cure resin cement (p > 0.05).Conclusion: The use of light-cure resin cement can be suggested for the luting of monolithic zirconia restorations.

Curing of pit & fissure sealants using Light Emitting Diode curing units.

Light Emitting Diode (LED) curing units are attractive to clinicians, because most are cordless and should create less heat within tooth structure. However, questions about polymerization efficacy have surrounded this technology. This research evaluated the adequacy of the depth of cure of pit & fissure sealants provided by LED curing units. Optilux (OP) and Elipar Highlight (HL) high intensity halogen and Astralis 5 (A5) conventional halogen lights were used for comparison. The Light Emitting Diode (LED) curing units were Allegro (AL), LE Demetron I (DM), FreeLight (FL), UltraLume 2(UL), UltraLume 5 (UL5) and VersaLux (VX). Sealants used in the study were UltraSeal XT plus Clear (Uclr), Opaque (Uopq) and Teethmate F-1 Natural (Kclr) and Opaque (Kopq). Specimens were fabricated in a brass mold (2 mm thick x 6 mm diameter) and placed between two glass slides (n=5). Each specimen was cured from the top surface only. One hour after curing, four Knoop Hardness readings were made for each top and bottom surface at least 1 mm from the edge. The bottom to top (B/T) KHN ratio was calculated. Groups were fabricated with 20 and 40-second exposure times. In addition, a group using a 1 mm-thick mold was fabricated using an exposure time of 20 seconds. Differences between lights for each material at each testing condition were determined using one-way ANOVA and Student-Newman-Keuls Post-hoc test (alpha=0.05). There was no statistical difference between light curing units for Uclr cured in a 1-mm thickness for 20 seconds or cured in a 2 mm-thickness for 40 seconds. All other materials and conditions showed differences between light curing units. Both opaque materials showed significant variations in B/T KHN ratios dependent upon the light-curing unit.

Temperature rise during polymerization of different cavity liners and composite resins.

Objective:The purpose of this study was to evaluate the thermal insulating properties of different light curing cavity liners and composite resins during light emitting diode (LED) curing.Materials and Methods:Sixty-four dentin discs, 1 mm thick and 8 mm in diameter, were prepared. Specimens were divided into four groups. Calcium hydroxide (Ca[OH]2), resin-modified glass ionomer cement, flowable composite and adhesive systems were applied to dentin discs according to the manufacturers’ instructions. The rise in temperature during polymerization with a LED curing unit (LCU) was measured using a K-type thermocouple connected to a data logger. Subsequently, all specimens were randomly divided into one of two groups. A silorane-based composite resin and a methacrylate-based composite resin were applied to the specimens. Temperature rise during polymerization of composite resins with LCU were then measured again. Data were analyzed using one-way ANOVA and post hoc Tukey analyses.Results:There were significant differences in temperature rise among the liners, adhesives, and composite resins (P < 0.05). Silorane-based composite resin exhibited significantly greater temperature rises than methacrylate-based resin (P < 0.05). The smallest temperature rises were observed in Ca(OH)2 specimens.Conclusion:Thermal insulating properties of different restorative materials are important factors in pulp health. Bonding agents alone are not sufficient to protect pulp from thermal stimuli throughout curing.

AN ADA LABORATORY EVALUATION OF LIGHT-EMITTING DIODE CURING UNITS

AN ADA LABORATORY EVALUATION OF LIGHT-EMITTING DIODE CURING UNITS