The effect of composite type on microhardness when using quartz-tungsten-halogen (QTH) or LED lights

This study evaluates the Knoop microhardness of resin composites cured with different light-emitting diode (LED) based light curing units (LCU) or with a conventional quartz-tungsten-halogen light (QTH). Ten experimental groups with 10 specimens each were used. The specimens were prepared by placing two light-cured resin composites with similar VITA shade A2-microhybrid Filtek Z250/3M ESPE and microfill Durafil VS/Heraeus Kulzer--in a 2.0 mm-thick disc shaped mold. The specimens were polymerized for 40 seconds with the use of one QTH LCU (Optilux 501/Kerr-Demetron) and four LED LCUs: Elipar FreeLight 1 Cordless LED (3M ESPE), Ultrablue II LED with cord (DMC), Ultrablue III LED cordless (DMC) and LEC 470 I (MM Optics). Knoop microhardness was determined at the top and bottom surfaces of the specimens 24 hours following curing. Microhardness values in the microhybrid resin composite group showed no statistically significant differences when cured with LED FreeLight 1 LCU and QTH LCU (p<0.05). The other LED devices evaluated in the study presented lower microhardness values in both surfaces (p<0.05) when compared to QTH. In the microfill resin composite group, no statistically significant differences were observed among all LCUs evaluated on the bottom surfaces (p<0.05). However, on the top surfaces, QTH presented the highest KHN values, and the LED devices presented similar results when compared with KHN values relative to each other (p<0.05).     

Depth of cure and surface microhardness of composite resin cured with blue LED curing lights.

OBJECTIVES: This study examined the depth of cure and surface microhardness of Filtek Z250 composite resin (3M-Espe) (shades B1, A3, and C4) when cured with three commercially available light emitting diode (LED) curing lights [E-light (GC), Elipar Freelight (3M-ESPE), 475H (RF Lab Systems)], compared with a high intensity quartz tungsten halogen (HQTH) light (Kerr Demetron Optilux 501) and a conventional quartz tungsten halogen (QTH) lamp (Sirona S1 dental unit). METHODS: The effects of light source and resin shade were evaluated as independent variables. Depth of cure after 40 s of exposure was determined using the ISO 4049:2000 method, and Vickers hardness determined at 1.0 mm intervals. RESULTS: HQTH and QTH lamps gave the greatest depth of cure. The three LED lights showed similar performances across all parameters, and each unit exceeded the ISO standard for depth of cure except GC ELight for shade B1. In terms of shade, LED lights gave greater curing depths with A3 shade, while QTH and HQTH lights gave greater curing depths with C4 shade. Hardness at the resin surface was not significantly different between LED and conventional curing lights, however, below the surface, hardness reduced more rapidly for the LED lights, especially at depths beyond 3 mm. SIGNIFICANCE: Since the performance of the three LED lights meets the ISO standard for depth of cure, these systems appear suitable for routine clinical application for resin curing.     

The influence of temperature on the efficacy of polymerization of composite resin

AIM: The purpose of this study was to investigate the effect of different temperatures on the efficacy of polymerization during the insertion of composite resin using different light curing units. METHODS AND MATERIALS: A total of 45 disc-shaped specimens were fabricated from Z250 composite resin (3M/ESPE, St. Paul, MN, USA) with 15 each prepared at three different temperatures (refrigerated to 5 masculineC, room temperature at 25 masculineC, and preheated to 37 masculineC). Each of these temperature-controlled specimen groups of 15 were then subdivided into three groups of five specimens, according to the type of curing light used to polymerize them. Curing lights included a conventional halogen light (QTH) in two modes (continuous and soft-start polymerization) and a light emitting diode (LED). The microhardness of the top and bottom surfaces of the specimens was determined using a Buehler Micromet II digital microhardness tester (Buehler, Dusseldorf, Germany). Data obtained was analyzed using two-way analysis of variance (ANOVA)/Post Hoc Tukey's test at a 0.05 significance level. RESULTS: As the temperature of composite resin increased, the top and bottom microhardness of the specimens also increased regardless of the type of polymerizing light used. The LED light produced a significantly better hardness on top and bottom surfaces of composite resin specimens polymerized at the three different temperatures. Effectiveness of cure at top and bottom surfaces of composite specimens was significantly reduced by using soft-start curing. CONCLUSION: The use of pre-warmed composite resins might help to improve polymerization of composite resin especially at the deeper areas of a restoration which could result in an increase in the expected life of a composite restoration.     

Bond strength of resin-based restorations polymerized with different light-curing sources

PURPOSE: To evaluate the influence of different light-curing units on microtensile bond strength of resin composite restorations. MATERIALS AND METHODS: Standardized Class I preparations (6.0 x 4.5 mm, 2.5 mm deep) were made in extracted human third molars after abrading the cusps. Resin was inserted in bulk using a 3M ESPE restorative system [Adper Single Bond (DBA)/ Filtek Z250 (RC)]. Both materials were polymerized using different light-curing units: QTH at 540 mW/cm(2) (XL 3000, 3M ESPE); LED at 750 mW/cm(2) (Elipar FreeLight2, 3M ESPE); PAC at 2130 mW/cm(2) (Arc Light II, Air Techniques). Nine different light combinations were developed to polymerize both DBA and RC: QTH/QTH; QTH/LED; QTH/PAC; LED/LED; LED/QTH; LED/PAC; PAC/PAC; PAC/QTH; PAC/LED. Restored teeth were stored in distilled water for 24 h at 37 degrees C and then sectioned, yielding stick-shaped specimens with a bonded area of approximately 0.9 mm(2). Specimens were assessed in a testing machine at a crosshead speed of 1 mm/min. The results were analyzed using two-way ANOVA and Tukey's test at a pre-set alpha = 0.05. RESULTS: The combinations PAC/QTH and QTH/QTH presented the highest bond strength values, and LED/QTH the lowest (p < 0.05). Significantly lower values were observed in combinations when the LED light was used to polymerize DBA compared to QTH and PAC lights, irrespective of the light source used to polymerize RC (p < 0.05). Same light combinations presented similar bond strength values. CONCLUSIONS: Different light sources influence restoration bond strength. Bond strength is more dependent on the light source used for DBA than for curing RC.     

The Knoop hardness of a composite resin polymerized with different curing lights and different modes

AIM: The purpose of this study was to compare the surface hardness of a hybrid composite resin polymerized with different curing lights. METHODS AND MATERIALS: Two 3.0 mm thick composite resin discs were polymerized in a prepared natural tooth mold using: (1) a conventional quartz-tungsten halogen light (QTH- Spectrum 800); (2) a high-intensity halogen light, Elipar Trilight (TL)-standard/exponential mode; (3) a high-intensity halogen light, Elipar Highlight (HL)-standard/soft-start mode; (4) a light-emitting diode, Elipar Freelight (LED); and (5) a plasma-arc curing light, Virtuoso (PAC). Exposure times were 40 seconds for the halogen and LED lights, and three and five seconds for the PAC light. Following polymerization, the Knoop hardness was measured at the bottom and the top surfaces of the discs. RESULTS: Significant differences were found between top and bottom Knoop Hardness number (KHN) values for all lights. The hardness of the top and bottom surfaces of both specimens cured by the PAC light was significantly lower than the other lights. No significant hardness differences were observed between the remaining curing units at the top of the 2.0 mm specimens. Significant differences were found between the LED and two modes of HL on the bottom surfaces. For the 3.0 mm thick samples, while significant differences were noted between LED and TL standard mode and between the two TL curing modes on the top, significant differences were only observed between QTH and the standard modes of TL and HL at the bottom.     

Influence of different light curing units on the bond strength of indirect resin composite restorations

The aim of this study was to evaluate the influence of different light sources on the bond strength of indirect resin composite restorations cemented with a dual-cure resin cement. The superficial dentin of human third molars was exposed and acid-etched and an adhesive system was applied (Single Bond 2). Four-mm-thick indirect resin composite restorations (Gradia) were fabricated and cemented using a dual-cure resin cement (Rely X). Four light sources were used to polymerize the cement: QTH - Optilux 401; LED1 - L.E.Demetron 1; LED2 - Optilight CL; and LED3 - Ultralume 5. The teeth were stored for 24 h and then sectioned, yielding stick-shaped specimens for each group with a bonded area of 1.0 mm(2). The specimens were then tested in a universal testing machine, at a crosshead speed of 1 mm/min. Data were analyzed using ANOVA. Bond strength mean values were: QTH: 22.5 (+/- 8.4); LED1: 22.7 (+/- 9.4); LED2: 21.4 (+/- 10.2); and LED3: 27.3 (+/- 13.8). No statistically significant difference was observed among the experimental groups. The bond strength values when the cement was polymerized using different LED lights were equivalent to the values when the QTH light was used. It can be concluded that the variety of light sources used in the present study did not influence the bond strength of indirect resin composite restorations cemented with a dual-cure resin cement.     

INFLUENCE OF THE DISTANCE OF THE CURING LIGHT SOURCE AND COMPOSITE SHADE ON HARDNESS OF TWO COMPOSITES

This study evaluated the influence of curing tip distance, shade and filler particle size on Vickers microhardness (VHN) of composite resins. Two composites were tested: Filtek Z250 microhybrid (3M ESPE; shades A1 and A3.5) and Filtek Supreme nanofilled (3M ESPE; shades A1B and A3.5B). For each resin, 42 specimens (5 mm in diameter and 2 mm height) were prepared being 21 for each shade. The specimens were exposed using a 20-second exposure to a quartz-tungsten-halogen light source with an irradiance of approximately 560 mW/cm², at the following distances: 0 mm (surface contact), 6 mm and 12 mm from composite surface. Effectiveness of cure of different resins, shades and curing distances was determined by measuring the top and bottom hardness (VHN) of specimens using a digital microhardness tester (load: 50 g; dwell time: 45 seconds) 24 hours following curing. The hardness ratio was calculated by dividing VHN of the bottom surface by VHN of top surface. Three-way ANOVA and Tukey''s post-hoc test (p<0.05) revealed statistically significant differences for all analyzed factors. As for top hardness, as microhardness ratio (bottom/top), the factors shade, distance and composite filler particle size exerted influence on resin curing. Lighter shade composites (A1 and A1B) showed higher hardness values. At 6 and 12 mm curing tip distances, hardness was lower when compared to 0 mm. The microhybrid composite resin presented higheer hardness, being its microhardness ratio satisfactory only at 0 mm for both shades and at 6 mm for the lighter shade. The nanofilled composite resin did not present satisfactory microhardness at the bottom while the microhybrid composite resin had higher hardness than the nanofilled. Composite''s curing tip distance and shade can influence hardness.     

EFFECT OF LIGHT CURING UNIT ON RESIN-MODIFIED GLASS-IONOMER CEMENTS: A MICROHARDNESS ASSESSMENT

Objective:

To evaluate the microhardness of resin-modified glass-ionomer cements (RMGICs) photoactivated with a blue light-emitting diode (LED) curing light.

Material and Methods:

Thirty specimens were distributed in 3 groups: Fuji II LC Improved/GC (RM1), Vitremer/3M ESPE (RM2) and Filtek Z250/ 3M ESPE (RM3). Two commercial light-curing units were used to polymerize the materials: LED/Ultrablue IS and a halogen light/XL3000 (QTH). After 24 h, Knoop microhardness test was performed. Data were submitted to three-way ANOVA and Tukey''s test at a pre-set alpha of 0.05.

Results:

At the top surface, no statistically significant difference (p>0.05) in the microhardness was seen when the LED and QTH lights were used for all materials. At the bottom surface, microhardness mean value of RM2 was significantly higher when the QTH light was used (p<0.05). For RM1, statistically significant higher values (p<0.05) were seen when the LED light was used. No statistically significant difference (p>0.05) was seen at the bottom surface for RM3, irrespective of the light used. Top-to-bottom surface comparison showed no statistically significant difference (p>0.05) for both RMGICs, regardless of the light used. For RM3, microhardness mean value at the top was significantly higher (p<0.05) than bottom microhardness when both curing units were used.

Conclusion:

The microhardness values seen when a LED light was used varied depending on the restorative material tested.     

Microhardness of a Resin Cement Polymerized by Light-Emitting Diode and Halogen Lights through Ceramic

Purpose: This study evaluated the curing efficiency of light-emitting diode (LED) and halogen [quartz tungsten halogens (QTH)] lights through ceramic by determining the surface microhardness of a highly filled resin cement.
Materials and Methods: Resin cement specimens (Variolink Ultra; with and without catalyst) (5-mm diameter, 1-mm thick) were condensed in a Teflon mold. They were irradiated through a ceramic disc (IPS Empress 2, diameter 5 mm, thickness 2 mm) by high-power light-curing units as follows: (1) QTH for 40 seconds (continuous), (2) LED for 20 seconds, and (3) LED for 40 seconds (5-second ramp mode). The specimens in control groups were cured under a Mylar strip. Vickers microhardness was measured on the top and bottom surfaces by a microhardness tester. Data were analyzed using analysis of variance (ANOVA) and a post hoc Bonferroni test at a significance level of p < 0.05.
Results: The mean microhardness values of the top and bottom surfaces for the dual-cured cement polymerized beneath the ceramic by QTH or LED (40 seconds) were significantly higher than that of light-cured cement ( p < 0.05). The top and bottom surface microhardness of dual-cured cement polymerized beneath the ceramic did not show a statistically significant difference between the LED and QTH for 40 seconds ( p > 0.05).
Conclusions: The efficiency of high-power LED light in polymerization of the resin cement used in this study was comparable to the high-power QTH light only with a longer exposure time. A reduced curing time of 20 seconds with high-power LED light for photopolymerizing the dual-cured resin cement under ceramic restorations with a minimum 2-mm thickness is not recommended.     

Thermal emission and curing efficiency of LED and halogen curing lights

The purpose of this study was to compare the thermal emission and curing efficiency of LED (LEDemetron 1, SDS/Kerr) and QTH (VIP, BISCO) curing lights at maximum output and similar power, power density and energy density using the same light guide. Also, another LED curing light (Allegro, Den-Mat) and the QTH light at reduced power density were tested for comparison. Increase in temperature from the tips of the light guides was measured at 0 and 5 mm in air (23 degrees C) using a temperature probe (Fluke Corp). Pulpal temperature increase was measured using a digital thermometer (Omega Co) and a K-type thermocouple placed on the central pulpal roof of human molars with a Class I occlusal preparation. Measurements were made over 90 seconds with an initial light activation of 40 seconds. To test curing efficiency, resin composites (Z100, A110, 3M/ESPE) were placed in a 2-mm deep and 8-mm wide plastic mold and cured with the LED and QTH curing lights at 1- and 5-mm curing distances. Knoop Hardness Numbers (KHN) were determiped on the top and bottom surfaces (Leco). Bottom hardness values were expressed as a percentage of maximum top hardness. No significant differences were found in maximum thermal emission or KHN ratios between the LED (LEDemetron 1) and the QTH (VIP) at maximum output and similar energy densities (ANOVA/Tukey's; alpha=0.05).     

Hardening of a dual-cure resin cement using QTH and LED curing units

Objective

This study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light-emitting diode (LED) or quartz tungsten halogen (QTH) light source.

Material and Methods

Eighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons.

Results

Increased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness.

Conclusions

Mean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.     

Effect of light curing tip distance and resin shade on microhardness of a hybrid resin composite

Resin composite shades and resin composite polymerization performed with a distanced light tip are factors that can affect polymerization effectiveness. This in vitro study aimed to evaluate the influence of curing tip distance and resin shade on the microhardness of a hybrid resin composite (Z250-3M ESPE). Forty-five resin composite specimens were randomly prepared and divided into nine experimental groups (n = 5): three curing tip distances (2 mm, 4 mm, and 8 mm) and three resin shades (A1, A3.5, and C2). All samples were polymerized with a continuous output at 550 mW/cm(2). After 24 hours, Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample, with a load of 25 grams for 10 seconds. Five indentations were performed on each surface of each sample. Results showed that bottom surface samples light-cured at 2 mm and 4 mm presented significantly higher hardness values than samples light-cured at 8 mm. The resin shade A1 presented higher hardness values and was statistically different from C2. The resin shade A3.5 did not present statistical differences from A1 and C2. For the top surface, there were no statistical differences among the curing tip distances. For all experimental conditions, the top surface showed higher hardness values than the bottom surface. It was concluded that light curing tip distance and resin shade are important factors to be considered for obtaining adequate polymerization.     

Surface microhardness of a resin composite: a comparison of a tungsten halogen and a LED light curing unit, in vitro

A comparison has been made between published surface microhardness numbers (VHN) of a commercial resin composite for different exposure times to a quartz tungsten halogen (QTH) and light-emitting diode (LED) light-curing unit (LCU). Both LCUs produced comparable hardness at both top and bottom surfaces, respectively, and similar bottom/top hardness ratios, for a specimen thickness of 1.5 mm, given sufficient exposure time (40 s) and an elapsed time of 24 h before measurement (for hardness numbers). However, some data are significantly different. There is no advantage in either LCU regarding optimal hardness and hardness ratios given an appropriate protocol. Immediate finishing (1 h) was more appropriate to the use of the LED LCU (with adequate exposure time). The effect of elapsed time after exposure on microhardness was more pronounced with the QTH LCU.     

INFLUENCE OF LIGHT CURING SOURCE ON MICROHARDNESS OF COMPOSITE RESINS OF DIFFERENT SHADES

Introduction:

The evolution of light curing units can be noticed by the different systems recently introduced. The technology of LED units promises longer lifetime, without heating and with production of specific light for activation of camphorquinone. However, further studies are still required to check the real curing effectiveness of these units.

Purpose:

This study evaluated the microhardness of 4 shades (B-0.5, B-1, B-2 and B-3) of composite resin Filtek Z-250 (3M ESPE) after light curing with 4 light sources, being one halogen (Ultralux – Dabi Atlante) and three LED (Ultraled – Dabi Atlante, Ultrablue – DMC and Elipar Freelight – 3M ESPE).

Methods:

192 specimens were distributed into 16 groups, and materials were inserted in a single increment in cylindrical templates measuring 4mm x 4mm and light cured as recommended by the manufacturer. Then, they were submitted to microhardness test on the top and bottom aspects of the cylinders.

Results:

The hardness values achieved were submitted to analysis of variance and to Tukey test at 5% confidence level. It was observed that microhardness of specimens varied according to the shade of the material and light sources employed. The LED appliance emitting greater light intensity provided the highest hardness values with shade B-0.5, allowing the best curing. On the other hand, appliances with low light intensity were the least effective. It was also observed that the bottom of specimens was more sensitive to changes in shade.

Conclusion:

Light intensity of LED light curing units is fundamental for their good functioning, especially when applied in resins with darker shades.     

Transdental photo-activation technique: hardness and marginal adaptation of composite restorations using different light sources

This study investigated the influence of different light sources associated with a transdental photoactivation technique on the marginal adaptation and hardness of composite restorations. Cavities (3 mm wide x 3 mm long x 1.5 mm in deep) were prepared on flattened bovine dentin and filled with Z250 composite (3M ESPE). Nine groups (n=10) were defined according to the curing technique (direct; transdental--photo-activation through 1 mm of enamel and 2 mm of dentin; mixed--transdental + direct) and light source (QTH XL2500, 3M ESPE; PAC Apollo 95E, DMD; LED Ultrablue Is, DMC) combination. Marginal adaptation was evaluated using a dye staining method, and the percentage of stained margins was recorded. Knoop Hardness readings were made across the transversal section of the fillings. Data were submitted to two-way ANOVA and Tukey's test (p< or =0.05). For margin analysis, although none of the curing conditions provided perfect adaptation, the mixed technique showed lower gap formation. No significant differences were detected between the transdental and other techniques, and no significant differences were detected among the light sources. For hardness, the direct technique showed slightly greater hardness than the mixed technique. Also, the mixed technique yielded greater hardness than the transdental technique. Among the light sources, the LED showed greater hardness than the PAC; whereas, no significant differences between the QTH and other sources were detected. The mixed technique might improve the marginal adaptation of restorations, while not being detrimental to composite hardness.     

Analysis of the degree of conversion of LED and halogen lights using micro-Raman spectroscopy

This study determined the degree of conversion of two LED (light-emitting diodes) (Elipar FreeLight [FL], 3M ESPE; GC e-Light [EL], GC), a high intensity (Elipar TriLight [TL], 3M ESPE) and a very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen light. The degree of conversion of these lights was compared to a conventional halogen light (Max [MX] (control), Dentsply-Caulk). Ten different light curing regimens, including pulse (EL1), continuous (FL1, EL2, TL1), turbo (EL3, AS1) and soft-start (FL2, EL4, TL2) modes of various lights were also investigated. Composite specimens of dimensions 3 x 3 x 2 mm were cured with the 10 different light curing regimens investigated. Micro-Raman spectroscopy was used to determine the degree of conversion at the top and bottom surfaces of a composite restorative (Z100, [3M ESPE]) at 60 minutes post-light polymerization. Five specimens were made for each cure mode. The results were analyzed using ANOVA/Scheffe's post-hoc test and Independent Samples t-tests at significance level 0.05. The degree of conversion ranged from 55.98 +/- 2.50 to 59.00 +/- 2.76% for the top surface and 51.90 +/- 3.36 to 57.28 +/- 1.56% for the bottom surface. No significant difference in degree of conversion was observed for the 10 light curing regimens when compared to MX (control). The curing efficiency of LED lights was comparable to halogen lights regardless of curing modes.     

Composite depth of cure obtained with QTH and LED units assessed by microhardness and micro-Raman spectroscopy

This study analyzed the depth of cure of a composite assessed by microhardness and the degree of conversion as a function of the light cure unit (LCU) used. Two light cure units, one LED (Ultraled-Dabi Atlante) and one quartz-tungsten-halogen (QTH, Optilux 401-Demetron) unit were used to cure 4.0 x 4.0 mm and 5.0 mm deep composite specimens (Filtek Z250, 3M ESPE). After 24 hours storage at 37 degrees C, Knoop microhardness and degree of conversion were measured on the irradiated surface and at each millimeter of the sample's depth. The degree of conversion was determined by using micro-Raman spectroscopy. The specimens cured with the QTH unit presented uniform decay in microhardness up to 4 mm in depth. Beyond 4 mm, the drop was abrupt. With LED photoactivation, uniform decay was observed only up to 2 mm. At higher depths, the decay in microhardness increased rapidly, especially beyond 3 mm. Depth of cure assessed by micro-Raman revealed that the degree of conversion behaved similarly to microhardness for both LCUs. A strong linear regression between microhardness and the degree of conversion, including both LCUs, was established with R2 = 0.980.     

Effect of dual-peak LED unit on the polymerization of coinitiator-containing composite resins

The purpose of the present study was to evaluate the effect of dual-peak LED on the polymerization of coinitiator-containing composite resins. For this, microhardness, degree of conversion (DC), and polymerization shrinkage were evaluated. Specimens (coinitiator-containing: Aelite LS Posterior, Tetric EvoCeram, and Vit-l-escence; only camphorquinone-containng: Filtek Z350 and Grandio) were light cured using a quartz-tungsten-halogen (QTH: OP), a single-peak light-emitting diode (LED) (L. E. Demetron: DM), and a dual-peak LED (G-light: GL), respectively. All specimens light cured using GL showed the highest microhardness both on the top and bottom surfaces compared with the values obtained using the rest light-curing units (LCUs). DC had no consistent trend correspond to the LCU, but rather product specific. OP yielded the lowest polymerization shrinkage on the specimens. The coinitiatorcontaining composite resins achieved the highest microhardness by the dual-peak LED (GL). However, the influence of GL on DC and polymerization shrinkage of the specimens was not consistent.     

Effect of exposure time on curing efficiency of polymerizing units equipped with light-emitting diodes

A study was conducted to evaluate the top and bottom hardness of two composites cured using polymerizing units equipped with light-emitting diodes [LED] (LEDemetron; Elipar FreeLight, Coltolux LED) and one quartz-tungsten halogen device [QTH] (Optilux 501) under different exposure times (20, 40 and 60 sec). A matrix mold 5 mm in diameter and 2 mm in depth was made to obtain five disc-shaped specimens for each experimental group. The specimens were cured by one of the light-curing units (LCUs) for 20, 40 or 60 sec, and the hardness was measured with a Vickers hardness-measuring instrument (50 g/30 sec). Data were subjected to three-way ANOVA and Tukey's test (alpha = 0.05). LED LCUs were as effective as the QTH device for curing both composites. A significant increase in the microhardness values were observed for all light LCUs when the exposure time was changed from 20 sec to 40 sec. The Z250 composite showed hardness values that were usually higher than those of the Charisma composite under similar experimental conditions. LED LCUs are as efficient for curing composites as the QTH device as long as an exposure time of 40 sec or higher is employed. An exposure time of 40 sec is required to provide composites with a uniform and high Knoop hardness when LED light-curing units are employed.     

Polymerization efficiency of LED curing lights

ABSTRACT: Purpose: The purpose of this study was to compare the curing efficiency of three commercially available light‐emitting diode (LED)‐based curing lights with that of a quartz tungsten halogen (QTH) curing light by means of hardness testing. In addition, the power density (intensity) and spectral emission of each LED light was compared with the QTH curing light in both the 380‐to 520‐nm and the 450‐ to 500‐nm spectral ranges. Materials and Methods: A polytetrafluoroethylene mold 2 mm high and 8 mm in diameter was used to prepare five depth‐of‐cure test specimens for each combination of exposure duration, composite type (Silux Plus [microfill], Z‐100 [hybrid]), and curing light (ZAP Dual Curing? Light, LumaCure?, VersaLux?, Optilux 401?). After 24 hours, Knoop hardness measurements were made for each side of the specimen, means were calculated, and a bottom/top Knoop hardness (B/T KH) percentage was determined. A value of at least 80% was used to indicate satisfactory polymerization. A linear regression of B/T KH percentage versus exposure duration was performed, and the resulting equation was used to predict the exposure duration required to produce a B/T KH percentage of 80% for the test conditions. The power densities (power/unit area) of the LED curing lights and the QTH curing light (Optilux 401?) were measured 1 mm from the target using a laboratory‐grade, laser power meter in both the full visible light spectrum range (380–780 nm) and the spectral range (between 450 and 500 nm), using a combination of long‐ and short‐wave edge filters. Results: The emission spectra of the LED lights more closely mirrored the absorption spectrum of the commonly used photoinitiator camphorquinone. Specifically, 95% of the emission spectrum of the VersaLux, 87% of the LumaCure, 84% of the ZAP LED, and 78% of the ZAP combination LED and QTH fell between 450 and 500 nm. In contrast, only 56% of the emission spectrum of the Optilux 401? halogen lamp fell within this range. However, the power density between 450 and 500 nm was at least four times greater for the halogen lamp than for the purely LED lights. As I a result, the LED‐based curing lights required from 39 to 61 seconds to cure a 2‐mm thick hybrid I resin composite and between 83 and 131 seconds to adequately cure a microfill resin composite. By I comparison, the QTH light required only 21 and 42 seconds to cure the hybrid and microfill resin I composites, respectively.