Light-emitting Diode Light-curing Research Articles

Comparative evaluation of third-generation LED-light curing units and their effect on bulk-fill composites—An in vitro study

Abstract Aim: Comparing the effectiveness of third-generation light-emitting diode light-curing devices and their impact on bulk-fill composites is the primary purpose of this study. Materials and Methods: In vitro investigation was carried out on a total of 32 samples of two bulk-fill composites. Four groups (n = 8) were formed. Half of the specimens of Tetric® N-Ceram Bulk Fill and Palfique Bulk Flow composites were randomly selected and cured from top with Bluephase® N LED light curing unit (LCU), and the remaining half with FlashMax P3 WS 4W LED LCU, following instructions provided by the manufacturer. The samples were assessed for degree of conversion (DoC) and microhardness after being submerged in distilled water solution and kept in an incubator for 24 h at 37°C. The two LED LCUs were compared. Standard deviation and mean were used to describe the data. Utilizing the Kruskal–Wallis test, the groups were compared. The independent sample t test was used to evaluate the differences in values between the top and bottom surfaces, and the Bonferroni post hoc test was used for multiple comparisons. The DoC and microhardness were correlated, and this was evaluated using Pearson’s correlation test. Results: The mean values for both parameters were statistically different when the two composites were cured with the LED-LCUs. Both the bulk-fill composites showed better mechanical properties when cured with Bluephase N® LED-LCU. Conclusions: Bluephase N® LED-LCU showed better performance than FlashMax P3 WS 4W. The bulk-fill composites showed significant differences in both parameters when cured with the two LED-LCUs.

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.

Effects of LED curing light on silver diamine fluoride penetration into dentin.

This ex-vivo study investigated the effect of a light-emitting diode (LED) curing light on the depth of penetration of Silver Diamine Fluoride (SDF) into carious lesions. Twenty-four primary teeth with untreated caries lesions were allocated into groups and treated within 5 min after extraction: (1) n = 6 treated for 1 min with one drop of SDF followed by 10 sec rinse with tap water, (2) n = 6 treated for 10 sec with one drop of SDF and exposed to LED light for 20 sec (30 sec total SDF exposure) followed by 10 sec rinse with tap water, (3) n = 6 treated for 10 sec with one drop of SDF followed by a 10 sec rinse with tap water, (4) n = 3 untreated, and (5) n = 3 untreated but exposed to LED light for 20 sec. Samples were prepared, embedded, sectioned and silver penetration was measured using backscattered electron imaging in the scanning electron microscope and energy-dispersive X-ray spectroscopy analysis. Results were expressed as the average relative depth of penetration (%) = Ag depth/lesion depth × 100 from 5 sites in each lesion. Group means were compared using mixed model analysis. Mean ± standard deviation (SD) penetration was: 86.4 ± 20.7% in Group 1, 94.3 ± 13.7% in Group 2, and 26.7 ± 13.9% in Group 3. Groups 1 and 2 were statistically similar and different from Group 3 (p < 0.001). Groups 4 and 5 had no silver present. Use of LED light for 20 sec after 10 sec SDF application appears to facilitate silver penetration, similar to a 1 min SDF application. Clinical studies are needed to define the role of silver penetration in sustained caries arrest.

Effect of thickness of CAD/CAM materials on light transmission and resin cement polymerization using a blue light-emitting diode light-curing unit.

Evaluate the effect of thickness of high-translucency (HT) CAD/CAM materials on irradiance and beam profile from a blue light-emitting diode light-curing unit (LCU) and on the degree of conversion (DC) and maximum polymerization rate (Rpmax ) of a light-cured resin cement (LCC). The direct output from the LCU, the light transmission and irradiance ratio (IR) through one conventional composite and nine HT CAD/CAM materials (0.5, 1.0, 1.5, or 2.0-mm thick; n=5) were measured with a integrating sphere coupled to a spectrometer. The light beam was assessed with a beam profiler camera. The DC at 600 s and the Rpmax of one LCC was determined using a Fourier transform infrared spectrometer (n=5). Data were analyzed by ANOVA followed by Tukey's tests, and Dunnett's test was also used for irradiance data (α=0.05). A significant decrease in irradiance through all materials occurred as thickness increased. Thin CAD/CAM materials improved light homogeneity, which decreased with the increase in thickness. The DC of the LCC directly exposed to light was the same as when exposed to 45%, 25%, 15%, or 5% IRs. Rpmax decreased with the decrease in IR. Although the HT CAD/CAM materials reduced the irradiance from the LCU, minor effects were observed in the LCC's DC. Despite the light attenuation of blue light through different CAD/CAM materials that were up to 2-mm thick, the degree of conversion of one brand of light-cured resin cement was clinically acceptable when the LCU was used for 30 s.

The potential ‘blue light hazard’ from LED headlamps

Many dental personnel use light-emitting diode (LED) headlamps for hours every day. The potential retinal ‘blue light hazard’ from these white light headlamps is unknown. MethodsThe spectral radiant powers received from direct and indirect viewing of an electronic tablet, an LED curing light, a halogen headlamp, and 6 brands of LED headlamps were measured using integrating spheres attached to fiberoptic spectroradiometers. The spectral radiant powers were measured both directly and indirectly at a 35 cm distance, and the maximum daily exposure times (tMAX) were calculated from the blue weighted irradiance values. ResultsThe headlamps emitted very different radiant powers, emission spectra, and color temperatures (K). The total powers emitted at zero distance ranged from 47 mW from the halogen headlamp to 378 mW from the most powerful LED headlamp. The color temperatures from the headlamps ranged from 3098 K to 7253 K. The tMAX exposure times in an 8 h day when the headlamps were viewed directly at a distance of 35 cm were: 810 s from the halogen headlamp, 53 to 220 s from the LED headlamps, and 62 s from the LED curing light. Light from the LED headlamps that was reflected back from a white reference tile 35 cm away did not exceed the maximum permissible exposure time for healthy adults. Using a blue dental dam increased the amount of reflected blue light, but tMAX was still greater than 24 h. ConclusionsWhite light LED headlamps emit very different spectra, and they all increase the retinal ‘blue light hazard’ compared to a halogen source. When the headlamps were viewed directly at a distance of 35 cm, the ‘blue light hazard’ from some headlamps was greater than from the LED curing light (tMAX = 62 s). Depending on the headlamp brand, tMAX could be reached after only 53s. The light from the LED headlamps that was reflected back from a white surface that was 35 cm away did not exceed the maximum permissible ocular exposure limits for healthy adults. Clinical relevanceReflected white light from dental headlamps does not pose a blue light hazard for healthy adults. Direct viewing may be hazardous, but the hazard can be prevented by using the appropriate blue-light blocking glasses.

The Effect of Curing Modes and Times of Third-Generation Led LCU on the Mechanical Properties of Nanocomposites

This study evaluates the effect of curing modes and times on the mechanical properties of nanocomposites. Two nanocomposite resins were investigated: supra-nanohybrid (Estelite Posterior Quick; EP) and nanohybrid (Solare X; SX). They were polymerized with a light-emitting diode light-curing units (LED LCU, Valo) as follows: standard mode for 20s (ST20), high power mode for 12s (HP12), high power mode for 20s (HP20), extra power mode for 6s (XP6), and extra power mode for 20s (XP20). For Vickers microhardness (HV), disc-shaped specimens were fabricated (n=10). For the three-point bending test, bar-shaped specimens were fabricated (n=10). Flexural strength and resilience modulus were calculated. The fractured surfaces and specimen surfaces of composites were observed using scanning electron microscopy. The data were analyzed with repeated measures ANOVA, two-way variance, and Bonferroni tests (p&lt;0.05). On the top and bottom surfaces of the EP nanocomposite resin, ST20 and HP12 revealed statistically higher HV than with XP6. Moreover, HP20 and XP20 had statistically higher HV than HP12 and XP6. For the SX nanocomposite resin, HP20 had statistically higher HV than HP12. For EP and SX, there were no significant differences in flexural strength and resilience modulus regarding the curing modes and times. Furthermore, SX demonstrated lower mechanical properties than EP. Scanning electron microscopy indicated that both nanocomposites had similar surface appearances. However, with all curing modes and times, SX exhibited layered fractures and more crack formations than EP. Different curing modes and times could influence the microhardness of nanocomposites.

Assessment of Streptococcus mutans biofilms on orthodontic adhesives over 7 days

The purpose of this study was to compare the metabolism of Streptococcus mutans biofilms after 1-7days of growth on different orthodontic adhesives. Specimens of 6 commercial orthodontic adhesives were fabricated in custom-made molds and polymerized using a light-emitting diode light-curing unit. Bioluminescent S mutans (UA159:JM10) biofilms were grown on ultraviolet-sterilized specimens for 1, 3, 5, and 7days (n=18 biofilms/d/product) in anaerobic conditions at 37°C. The metabolism of biofilms (relative luminescence unit [RLU]) was measured 0, 2, 4, and 6minutes after exposure to D-luciferin solution using a microplate reader. A linear mixed-effects model was used to analyze the logarithm of RLU (log RLU). The model included fixed effects of products, days, and minutes. Tukey-Kramer post-hoc tests were then performed on the significant predictors of log RLU (α=0.05). Days (P<0.0001) and minutes (P<0.0001) were independent predictors of log RLU, but the products were not (P=0.5869). After adjusting for minutes, the log RLU was analyzed with a post-hoc test, and all differences between days were significant with the exceptions of day 3 from day 5 (P=0.0731) and day 5 from day 7 (P=0.8802). After adjusting for day, log RLU was analyzed with a post-hoc test and all differences in minutes were significant. No significant differences in the metabolism of S mutans biofilms were observed among the 6 orthodontic adhesives. Biofilms that were grown for 3days demonstrated the highest levels of biofilm metabolism as evidenced by higher mean log RLU values relative to 1, 5, and 7-day growth durations.

The Effect of Irradiance on the Degree of Conversion and Volumetric Polymerization Shrinkage of Different Bulk-Fill Resin-Based Composites: An In Vitro Study.

Objective The influence of different light-emitting diode (LED) curing light intensities on the degree of conversion (DC) and volumetric polymerization shrinkage (VPS) of bulk-fill resin-based composite (RBC) restorative materials was evaluated. Materials and Methods Twenty-four specimens of each RBC material (Filtek one bulk-fill posterior, Reveal HD Bulk, Tetric N-Ceram, and Filtek Z350) were prepared. The RBCs were shaped in molds and cured using an LED curing light unit at high-intensity (1,200 mW/cm 2 ) for 20 seconds and low-intensity (650 mW/cm 2 ) for 40 seconds Fourier-transform infrared (FTIR) spectroscopy was used to determine the DC and microcomputed tomography was used to evaluate VPS. Data were analyzed using one- and two-way ANOVA, independent t -test, and Tukey’s and Scheffe’s post hoc multiple comparison tests. Results With high-intensity curing light, Reveal HD showed the highest DC (85.689 ± 6.811%) and Tetric N-Ceram the lowest (52.60 ± 9.38%). There was no statistical difference in VPS when using high- or low-intensity curing light. The highest VPS was observed for Reveal HD (2.834–3.193%); there was no statistical difference ( p > 0.05) among the other RBCs. Conclusion Curing light intensities do not significantly influence the VPS of RBC materials. Reveal HD bulk cured with high-intensity light had the highest DC.

The Effects of Irradiance on Translucency and Surface Gloss of Different Bulk-Fill Composite Resins: An in vitro Study.

PurposeThe influence of different light-emitting diode (LED) curing light intensities on the translucency and surface gloss of bulk-fill resin-based composite (RBC) restorative materials was evaluated.Materials and MethodsForty specimens of each RBC (Filtek One bulk-fill posterior, Reveal HD bulk, Tetric N-Ceram, and Filtek Z350) were prepared. The RBCs were shaped into molds and cured using an LED curing light unit at high intensity (1,200 mW/cm2) for 20 s and low intensity (650 mW/cm2) for 40 s. A spectrophotometer was used to determine the translucency, and a gloss meter was used to evaluate surface gloss. Data were analyzed using one- and two-way analysis of variance (ANOVA), independent t-test, and Tukey’s and Scheffe’s post hoc multiple comparison tests.ResultsThe highest translucency value was observed for Reveal HD (7.688 ± 0.861) with a high curing intensity, while Filtek One showed the lowest value (1.750 ± 0.376) with a low curing intensity. The materials showed no significant difference in surface gloss with a high curing intensity. With low-intensity light curing, Filtek One showed the highest gloss value (55.270 ± 10.106), while Tetric N-Ceram and Reveal HD showed the lowest gloss values (35.560 ± 6.533 and 35.680 ± 6.648, respectively).ConclusionCuring light intensity had no effect on both the gloss and translucency for all the materials tested, although for Tetric N-Ceram, higher intensity corresponded to higher gloss values while for Filtek One, higher intensity corresponded to a higher translucency value.

The effect of repeated preheating on diametral tensile strength of composite resin with different fillers

Background: The development of adhesive systems has made the removal of carious lesion a minimally invasive procedure. Composite resin is the material of choice today, but the filler composition of the resin varies. Packable composite resin has good mechanical properties, but its high viscosity makes it hard to manipulate. Several methods, such as preheating, are used to decrease this viscosity. A syringe of composite resin might be preheated several times, but the effect of repeated preheating is unknown. Objectives: The purpose of this research was to analyze the effect of repeated preheating on the mechanical properties of a composite resin with different fillers. Method: Microhybrid, nanohybrid, and nanofill composite resins were preheated (ten times, twenty times, and control), molded into cylinder molds 6 mm in diameter and 3 mm in height, flattened with a celluloid strip, and polymerized with an light-emitting diode light-curing unit for 40 s. A total of 180 specimens were tested. The specimens were divided into two groups: Group 1 was immediately tested using a universal testing machine. Group 2 was soaked in 37°C artificial saliva for 24 h before testing. Each specimen was tested using the universal testing machine with the pressure side with a 1 mm/s crosshead speed. Result: Nanohybrid composite resin had the most stable diametral tensile strength after repeated preheating, whereas nanofill composite had the weakest strength. The increase and decrease in the diametral tensile strength in each group were not statistically significant. Conclusion: Repeated preheating does not significantly affect the diametral tensile strength of composite resin.

Comparison of shear bond strength of orthodontic bracket bonding to teeth using light-curing units between halogen and LED: An in vitro study

Background: Light-cured bonding systems have been widely accepted among orthodontists. Various light curing units are available now. Recently, the light emitting diode (LED) has been introduced alongside halogen light curing units. There is lack of information on the advantages and disadvantages of different light curing systems. The aim of this in vitro study was to compare the shear bond strength of orthodontic brackets and adhesive remnant index (ARI) of an adhesive cured with two different orthodontic light sources i.e. LED and halogen.&#x0D; Methods: Forty four (22 in each group) extracted human premolars without any defects were etched with 37% phosphoric acid and cleansed with water spray and air dried. The sealant (Ortho Solo) was applied on the tooth surface and the brackets were bonded using adhesive (Enlight). Adhesives were cured with Halogen (Litex) and LED (D-LUX) for 40 seconds. Then the specimens were debonded later using a universal testing machine, with crosshead speed of 0.2 mm/min until the brackets were detached. Adhesive remnant index (ARI) scores were assessed under stereomicroscope at ×10 magnification.&#x0D; Results: The shear bond strength in Halogen group was 19.73 ± 3.44 MPa and in the LED group 20.81±3.02 MPa which is little higher than halogen group. The proportion of being adhesive remaining index for ARI Score 1 in Halogen group was 5 (22.7%) and in LED group 7 (31.8%). While ARI Score 2 in the Halogen group was 13 (59.1%) compared to LED group 8 (36.4%). However, ARI Score 3 in Halogen group was 4 (18.2%) and in LED group 7 (31.8%). The overall model showing no significant difference.&#x0D; Conclusion: Within limitations, this in vitro study showed the shear bond strength of orthodontic adhesives cured with a LED was statistically equivalent to those cured with a halogen light curing unit. There were significant differences in the ARI scores of the light-curing units tested. LED light-curing units can be suggested for the polymerization of orthodontic bonding adhesives because it showed a balanced effect on ARI index.&#x0D; Bangladesh Med Res Counc Bull 2019; 45: 17-22

Bulk-fill versus conventional composite: A comparative analysis on degree of conversion

Abstract Aim: This study aimed to determine the degree of conversion (DC) of two resin-based composites: a conventional nanohybrid composite and a bulk-fill flowable composite (SureFil® SDR™ flow). Materials and Methods: DC was evaluated at 1-, 2-, 3-, and 4-mm depths at varying irradiation times (20 and 40 s) by Fourier-transform infrared spectroscopy. Disc-shaped specimens of varying depths were prepared and photoactivated with a third-generation light-emitting diode light-curing unit. The specimens were stored for 24 h in the dark at ambient temperature and pulverized into a fine powder which was mixed with potassium bromide. After homogenization, the mixture pressed to form a pellet. All pellets were evaluated by an infrared spectrometer equipped with a triglycine sulfate detector using diffuse reflectance. The percentage of monomer conversion was determined from the ratio of the absorbance intensities of the aliphatic carbon–carbon double bonds (C = C) and the internal standard before and after the curing of the composite, represented by the aromatic carbon–carbon single bonds (C-C). Results: The DC data for the bulk-fill resin showed no significant difference (P &gt; 0.05) for different irradiation depths, whereas for the conventional nanohybrid resins, statistical analyses revealed a significant result of the variables time and depth as well as the interaction between them. Conclusions: The results indicated that SDR™ achieves a 4-mm depth of cure with both 20- and 40-s light exposures.

Rapid Antibiofilm Effect of Ag/ZnO Nanocomposites Assisted by Dental LED Curing Light against Facultative Anaerobic Oral Pathogen Streptococcus mutans.

The integration of nanomaterials with clinical therapeutic instruments is a promising approach to improve the effects of nanomaterials. We reported an efficient synergistic antibacterial strategy formed through the combination of Ag/ZnO nanocomposites with a light-emitting diode (LED) curing light, which is a commonly used small instrument in dental clinics. The as-designed integration depicted a significantly enhanced bactericidal effect on facultative anaerobic oral pathogen Streptococcus mutans (S. mutans) both in planktonic and biofilm phases over a very short irradiation time (≤5 min). Further study showed that the combination of LED and Ag/ZnO nanocomposites induced more ·OH and ·O2- generation, which is responsible for the enhanced antibacterial activity. Moreover, this combination could destroy S. mutans biofilm by killing the bacteria embedded within biofilm, inhibiting exopolysaccharide production and down-regulating the biofilm-related gene expression. Therefore, it is proposed that this combination could be applied in dental clinics to realize dental caries prevention and dental restoration simultaneously.

Pulp Temperature Rise Induced by Light-Emitting Diode Light-Curing Units Using an Ex Vivo Model.

The aim of this research was to compare the pulp temperature (PT) rise induced by four light-emitting diode light-curing units (LED LCUs) (Bluephase 20i, Demi Ultra, SPEC 3, and Valo) in different curing modes. Immediately after extraction, the pulp chamber of 11 premolars was accessed from the palatal cervical third of the crown for insertion of fiber Bragg grating (FBG) sensors for temperature measurement and kept in a 37.0° water bath. The teeth were then submitted to a random sequence of curing modes with four irradiations at 30 s intervals. Care was taken to ensure complete pulp temperature reset between curing modes. The curing modes were classified as high-energy (above 80 J/cm2) or low-energy (below 40 J/cm2) according to the total energy density delivered. Statistical analysis was performed with repeated ANOVA measures and Pearson’s correlation for the association between energy density and temperature variation. The significance level was set to 0.05. All curing units promoted a statistically significant PT rise (p < 0.01). After four emissions, the PT rise was higher than 5.0 °C for the high-energy curing modes. The low-energy modes induced approximately a 2.5 °C rise. A strong positive correlation was found between energy density and PT increase (R = 0.715; p = 0.01). Exposure of intact premolars to LED LCUs induced significant and cumulative PT rise. Curing modes emitting high energy densities produced higher PT variations. Radiant exposure was positively correlated to PT variation.

Evaluation of Different Light-Curing Units—Light-Emitting Diodes and Quartz–Tungsten–Halogen-Based Light-Curing Units in Polymerization of Posterior Composite: An In Vitro Study

Abstract Objective To assess the adequacy of various light-curing units to polymerize the posterior composite resin. Materials and Methods Specimens were prepared by placing a single increment of posterior composite resin in split cylindrical metallic mold of dimension (6.0 mm in diameter and 5 mm in depth). Polymerization was done by utilizing one quartz-tungsten-halogen and three light-emitting diode light-curing units of different powers. The specimens of composite resin were then mounted on metallic molds utilizing autopolymerizing acrylic resin. After polishing, the complete setting of composite resin material was analyzed using Vickers hardness test. Results Showed in each group, hardness reduced as we moved from upper to lower surface of composite resin. Furthermore, hardness increased as intensity of light was increased. The maximum hardness was detected when light-emitting diode light-curing unit having intensity of 1,250 mW/cm2 was utilized and least hardness was detected when halogen lamp having intensity 418 mW/cm2 was utilized and results were found to be highly significant (p &lt; 0.01). Conclusion It was concluded that increased top and bottom hardness can be accomplished by utilizing the light-curing unit of high intensity.

Effect of Mold Type and Diameter on the Depth of Cure of Three Resin-Based Composites.

To evaluate the effects of different mold materials, their diameters, and light-curing units on the mechanical properties of three resin-based composites (RBC). A conventional nano-filled resin composite (Filtek Supreme Ultra, 3M Oral Care, St Paul, MN, USA) and two bulk-fill composites materials, Tetric Evoceram Bulk fill (Ivoclar Vivadent, Schaan, Liechtenstein) and Aura Bulk Fill (SDI, Bayswater, VIC, Australia), were tested. A total of 240 specimens were fabricated using metal or white semitransparent Delrin molds that were 4 or 10 mm in diameter. The RBCs were light cured for 40 seconds on the high-power setting of either a monowave (DeepCure-S, 3M Oral Care) or polywave (Bluephase G2, Ivoclar Vivadent) light-emitting diode (LED) curing unit. The depth of cure was determined using a scraping test, according to the 2009 ISO 4049 test method. Data were analyzed using multivariate analysis of variance followed by Tukey multiple comparison test ( p<0.05). In general, when used for 40 seconds, both LED curing lights achieved the same depth of cure ( p=0.157). However, the mold material and its diameter had a significant effect on the depth of cure of all three RBCs ( p<0.0001). Curing with either the polywave or monowave LED curing light resulted in the same depth of cure in the composites. The greatest depth of cure was always achieved using the 10-mm-diameter Delrin mold. Of the three RBCs tested, both Tetric Bulk Fill and Aura achieved a 4-mm depth of cure when tested in the 10-mm-diameter metal mold. Tetric Bulk Fill was the most transparent and had the greatest depth of cure, and the conventional composite had the least depth of cure. Very little violet (<420 nm) light penetrated through 6 mm of any of the RBCs.

Effect of Sonic Resin Composite Delivery on Void Formation Assessed by Micro-computed Tomography.

The aim of this study was to quantify the internal void volume formation in commercially available, resin composites inserted using conventional or sonic insertion methods, and analyzed using three-dimensional (3D) micro-computed tomography (μCT). Four resin composites were evaluated: one conventional (Herculite, Ultra, Kerr Corporation, Orange, CA, USA), one flowable bulk fill (SureFil SDR Flow, Dentsply International, York, PA, USA), and two packable bulk fill (SonicFill, Kerr Corporation, and Tetric EvoCeram Bulk Fill, Ivoclar Vivadent Inc, Schaan, Liechtenstein). Eight groups were evaluated according to each resin composite type and insertion method (conventional or sonic; n=5). Forty ABS 3D-printed cylindrical molds, 5.0 mm in diameter and 4.0 mm in depth, were fabricated. For the conventional resin composite, the mold was filled incrementally (two layers), while for bulk-fill resin composites, insertion was performed in a single increment. The sonic insertion method was performed using a specific handpiece (SonicFill Handpiece, Kerr Corporation). Resin composites were light cured using a multipeak light-emitting diode light-curing unit (VALO, Ultradent Products Inc, South Jordan, UT, USA) in its regular mode. Samples were evaluated by μCT, and data were imported into software (Amira, version 5.5.2, VSG, Burlington, MA, USA) for 3D reconstruction, from which the percentage of void volume was calculated. Data were analyzed using two-way analysis of variance and Tukey post hoc test at a preset alpha of 0.05. The conventional insertion method resulted in reduced porosity, compared with sonic insertion, for SureFil SDR Flow and Tetric EvoCeram bulk fill. The sonic insertion method did not demonstrate any influence on void formation for Herculite Ultra or SonicFill. Results suggest that the sonic insertion method might increase void formation during resin composite delivery, depending on restorative material brand.

Battery Charge Affects the Stability of Light Intensity from Light-emitting Diode Light-curing Units.

This study investigated the influence of battery charge levels on the stability of light-emitting diode (LED) curing-light intensity by measuring the intensity from fully charged through fully discharged batteries. The microhardness of resin composites polymerized by the light-curing units at various battery charge levels was measured. The light intensities of seven fully charged battery LED light-curing units-1) LY-A180, 2) Bluephase, 3) Woodpecker, 4) Demi Plus, 5) Saab II, 6) Elipar S10, and 7) MiniLED-were measured with a radiometer (Kerr) after every 10 uses (20 seconds per use) until the battery was discharged. Ten 2-mm-thick cylindrical specimens of A3 shade nanofilled resin composite (PREMISE, Kerr) were prepared per LED light-curing unit group. Each specimen was irradiated by the fully charged light-curing unit for 20 seconds. The LED light-curing units were then used until the battery charge fell to 50%. Specimens were prepared again as described above. This was repeated again when the light-curing units' battery charge fell to 25% and when the light intensity had decreased to 400 mW/cm2. The top/bottom surface Knoop hardness ratios of the specimens were determined. The microhardness data were analyzed by one-way analysis of variance with Tukey test at a significance level of 0.05. The Pearson correlation coefficient was used to determine significant correlations between surface hardness and light intensity. We found that the light intensities of the Bluephase, Demi Plus, and Elipar S10 units were stable. The intensity of the MiniLED unit decreased slightly; however, it remained above 400 mW/cm2. In contrast, the intensities of the LY-A180, Woodpecker, and Saab II units decreased below 400 mW/cm2. There was also a significant decrease in the surface microhardnesses of the resin composite specimens treated with MiniLED, LY-A180, Woodpecker, and Saab II. In conclusion, the light intensity of several LED light-curing units decreased as the battery was discharged, with a coincident reduction in the units' ability to polymerize resin composite. Therefore, the intensity of an LED light-curing unit should be evaluated during the life of its battery charge to ensure that sufficient light intensity is being generated.

Degree of Conversion and Polymerization Shrinkage of Bulk-Fill Resin-Based Composites.

This study evaluated the degree of conversion (DC) and polymerization shrinkage (PS) of contemporary bulk-fill resin-based composites (RBCs) including giomer materials. Two giomer bulk-fill (Beautifil Bulk Restorative [BBR], Beautifil Bulk Flowable [BBF]), two nongiomer bulk-fill (Tetric N-Ceram Bulk-fill [TNB], Smart Dentin Replacement [SDR]), and three conventional non-bulk-fill (Beautifil II [BT], Beautifil Flow Plus [BF], Tetric N-Ceram [TN]) RBCs were selected for the study. To evaluate the DC, disc-shaped specimens of 5-mm diameter and 2-mm, 4-mm, and 6-mm thickness were fabricated using customized Teflon molds. The molds were bulk filled with the various RBCs and cured for 20 seconds using a light-emitting diode curing light with an irradiance of 950 mW/cm2. The DC (n=3) was determined by attenuated total reflectance Fourier transform infrared spectroscopy by computing the spectra of cured and uncured specimens. PS (n=3) was measured with the Acuvol volumetric shrinkage analyzer by calculating specimen volumes before and after light curing. The mean DC for the various materials ranged from 46.03% to 69.86%, 45.94% to 69.38%, and 30.65% to 67.85% for 2 mm, 4 mm, and 6 mm, respectively. For all depths, SDR had the highest DC. While no significant difference in DC was observed between depths of 2 mm and 4 mm for the bulk-fill RBCs, DC at 2 mm was significantly greater than 6 mm. For the conventional RBCs, DC at 2 mm was significantly higher than at 4 mm and 6 mm. Mean PS ranged from 1.48% to 4.26% for BBR and BF, respectively. The DC at 2 mm and PS of bulk-fill RBCs were lower than their conventional counterparts. At 4 mm, the DC of giomer bulk-fill RBCs was lower than that of nongiomer bulk-fill materials.

Guidelines for the selection, use, and maintenance of LED light-curing units - Part 1.

Light curing is a critical step in the restorative process when using light-activated resin-based composites, but it is frequently not given the attention it deserves. The selection of a reliable light curing unit (LCU) that meets the practitioner's needs is an important equipment purchase. Using an inappropriate LCU may seriously compromise the quality of care without the practitioner realising their mistake until years later. The importance of the subject is reflected by the rapidly increasing use of light-cured composites and the decline in the use of amalgam. Many changes have occurred in the equipment and materials available for making light-cured restorations in the last twenty years. This article is part of a two-part series that will describe those changes and recommend guidelines for the selection, use, and maintenance of light emitting diode light-curing units (LED LCUs). This paper (Part 1) discusses terminology, clinical studies, the development of LCUs in dentistry, the aims of light-curing, and the need to deliver an adequate amount of energy. The interaction between light source and material is briefly described to demonstrate the complex nature of the resin photopolymerisation process.