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.     

Effectiveness of composite cure associated with different curing modes of LED lights

This study compared the effectiveness of cure of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M-ESPE; GC e-Light [EL], GC) to conventional (Max [MX], Dentsply-Caulk [control]), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen lights. The 10 light-curing regimens investigated were: FL1 400 mW/cm2 [40 seconds], FL2 0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds], EL1 750 mW/cm2 [10 pulses x 2 seconds], EL2 350 mW/cm2 [40 seconds], EL3 600 mW/cm2 [20 seconds], EL4 0-600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds], TL1 800 mW/cm2 [40 seconds], TL2 100-800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds], AS1 1200 mW/cm2 [10 seconds], MX 400 mW/cm2 [40 seconds]. Effectiveness of cure with the different modes was determined by measuring the top and bottom surface hardness (KHN) of 2-mm thick composite (Z100, [3M-ESPE]) specimens using a digital microhardness tester (n=5, load=500 g; dwell time=15 seconds). Results were analyzed using one-way ANOVA/Scheffe's post-hoc test and Independent Samples t-test (p<0.05). At the top surface, the mean KHN observed with LED lights ranged from 55.42 +/- 1.47 to 68.54 +/- 1.46, while that of halogen lights was 62.64 +/- 1.87 to 73.14 +/- 0.97. At the bottom surface, the mean KHN observed with LED and halogen lights ranged from 46.90 +/- 1.73 to 66.46 +/- 1.18 and 62.26 +/- 1.93 to 70.50 +/- 0.87, respectively. Significant differences in top and bottom KHN values were observed between different curing regimens for the same light, and between LED and halogen lights. Although curing with most modes of EL resulted in significantly lower top and bottom KHN values than the control, no significant difference was observed for the different modes of FL. Hence, the effectiveness of composite cure with LED LCUs is product dependent.     

The effectiveness of cure of LED and halogen curing lights at varying cavity depths

This study compared the effectiveness of cure of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M-ESPE and GC e-Light [EL], GC) to conventional (Max [MX] (control), Dentsply-Caulk), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen lights at varying cavity depths. Ten light curing regimens were investigated. They include: FL1-400 mW/cm2 [40 seconds], FL2-0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds], EL1-750 mW/cm2 [10 pulses x 2 seconds], EL2-350 mW/cm2 [40 seconds], EL3-600 mW/cm2 [20 seconds], EL4-0-600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds], TL1-800 mW/cm2 [40 seconds], TL2-100-800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds], AS1-1200 mW/cm2 [10 seconds], MX-400 mW/cm2 [40 seconds]. The effectiveness of cure of the different modes was determined by measuring the top and bottom surface hardness (KHN) of 2-mm, 3-mm and 4-mm thick composite (Z100, [3M-ESPE]) specimens using a digital microhardness tester (n = 5, load = 500 g; dwell time = 15 seconds). Results were analyzed using ANOVA/Scheffe's post-hoc test and Independent Samples t-Test (p < 0.05). For all lights, effectiveness of cure was found to decrease with increased cavity depths. The mean hardness ratio for all curing lights at a depth of 2 mm was found to be greater than 0.80 (the accepted minimum standard). At 3 mm, all halogen lights produced a hardness ratio greater than 0.80 but some LED light regimens did not; and at a depth of 4 mm, the mean hardness ratio observed with all curing lights was less than 0.80. Significant differences in top and bottom KHN values were observed among different curing regimens for the same light and between LED and halogen lights. While curing with most modes of EL resulted in significantly lower top and bottom KHN values than the control (MX) at all depths, the standard mode of FL resulted in significantly higher top and bottom KHN at a depth of 3 mm and 4 mm. The depth of composite cure with LED LCUs was, therefore, product and mode dependent.     

Hardness of a bleaching-shade resin composite polymerized with different light-curing sources

The microhardness of a bleaching-shade resin composite polymerized with different light-curing units was evaluated. Composite samples (3M ESPE Filtek Supreme) were applied to brass rings (2 mm in thickness, 5 mm in diameter). Three commercial LED lights were used to polymerize the specimens and the results were compared to those of a conventional halogen light. The light sources used in the present study were: Demetron Optilux 401 (QTH), 3M ESPE Elipar FreeLight (LED 1); Kerr L.E. Demetron I (LED 2), and ColtoluxLED lights (LED 3). The microhardness of the top and bottom surfaces was assessed with a digital Vickers hardness-measuring instrument, under load. At the bottom surface, no significant difference among the light sources was observed (two-way ANOVA). At the top surface, the QTH light source presented significantly higher hardness values compared to the values observed when LED 1 and LED 3 were used. There were no significant differences between the QTH and LED 2 light sources. Significantly higher hardness values were also found at the top surface when compared to the values observed at the bottom surface. The power density of the polymerization light sources seemed to be responsible for the observed resin composite hardness, not their irradiance.     

Curing efficacy of a new generation high-power LED lamp

This study investigated the curing efficacy of a new generation high-power LED lamp (Elipar Freelight 2 [N] 3M-ESPE). The effectiveness of composite cure with this new lamp was compared to conventional LED/halogen (Elipar Freelight [F], 3M-ESPE; Max [M], Dentsply-Caulk) and high-power halogen (Elipar Trilight [T], 3M-ESPE; Astralis 10 [A], Ivoclar Vivadent) lamps. Standard continuous (NS, FS, TS; MS), turbo (AT) and exponential (NE, FE, TE) curing modes of the various lights were examined. Curing efficacy of the various lights and modes were determined by measuring the top and bottom surface hardness of 2-mm thick composite specimens (Z100, 3M-ESPE) using a digital microhardness tester (n=5; load=500 g; dwell time=15 seconds) one hour after light polymerization. The hardness ratio was computed by dividing HK (Knoops Hardness) of the bottom surface by HK of the top surface. The data was analyzed using one-way ANOVA/Scheffe's test and Independent Samples t-test at significance level 0.05. Results of the statistical analysis were as follows: HK top--E, FE, NE > NS and NE > AT, TS, FS; HK bottom--TE, NE > NS; Hardness ratio--NS > FE and FS, TS > NE. No significant difference in HK bottom and hardness ratio was observed between the two modes of Freelight 2 and Max. Freelight 2 cured composites as effectively as conventional LED/halogen and high-power halogen lamps, even with a 50% reduction in cure time. The exponential modes of Freelight 2, Freelight and Trilight appear to be more effective than their respective standard modes.     

Thermal emission by different light-curing units

This study quantified and compared the thermal emission of different light curing units (LCU). Three LED (Elipar Freelight [3M]; GC e-light [GC]; Coolblu [Dentalsystems.com]) and three halogen (Max [Dentsply-Caulk]; Elipar Trilight [3M]; Astralis 10 [Ivoclar-Vivadent]) lights were selected for the study. Thermal emission of the LCUs, when used in various curing modes, was assessed using a K-type thermocouple and a digital thermometer at distances of 3 mm and 6 mm compared to the conventional halogen LCU (Max). The temperature profiles and mean maximum temperature change (n = 7) generated by each LCU were obtained. Data was subjected to ANOVA/Scheffe's post-hoc test and Independent Samples t-test at significance level 0.05. At 3 mm, temperature rise observed with LED lights ranged from 4.1 degrees C to 12.9 degrees C, while halogen lights ranged from 17.4 degrees C to 46.4 degrees C. At 6 mm, temperature rise ranged from 2.4 degrees C to 7.5 degrees C and 12.7 degrees C to 25.5 degrees C for LED and halogen lights, respectively. Thermal emission of LED lights was significantly lower than halogen lights. Significant differences in temperature rise were observed between different curing modes for the same light and between different LED/halogen lights.     

Effect of pre-heating on depth of cure and surface hardness of light-polymerized resin composites

PURPOSE: To evaluate the depth of cure and surface hardness of two resin composites when subjected to three preheating temperatures, three polymerization times and two types of curing lights. METHODS: Two resin composites were used in this study (Esthet-X and TPH), three polymerization times (10, 20, 40 seconds), three preheating temperatures (70, 100, 140 degrees F/21.1, 37.7 and 60 degrees C), and two curing lights (halogen and LED). For depth of cure measurements, 180 specimens (4 mm in diameter and 2 mm in depth) were made for 36 combinations of variables. Four Knoop hardness measurements were obtained from both the top and bottom surfaces. For the surface hardness, another 180 (4 x 6 mm) cylindrical specimens were fabricated. Each specimen was sectioned in half and hardness measurements were made at 0.5 mm intervals. Statistical analyses were performed using the multifactor ANOVA at a level of significance of alpha = 0.05. RESULTS: For depth of cure, there was a statistical difference among all the main effects (time, temperature and curing light) for both composites (P > 0.001) when the % difference from the top was analyzed. Results indicate that there was an increase in hardness as the temperature of the composite was increased from 70 to 140 degrees F for both composites for either the top or the bottom. The percent difference in hardness was greater when the LED curing light was used compared to the halogen curing light. Overall there was a greater change in hardness when the resin composite was polymerized at 140 degrees F. Although the ISO standard was not met in many cases, there was a significant increase in hardness on both the top and bottom as temperature and curing time increased (P < 0.001). Results for the surface hardness showed that there was a significant statistical difference (P < 0.001) in hardness when the surface hardness at 0.5 and 3.5 mm were analyzed separately. There was a general increase in surface hardness for both the hybrid and microhybrid as time and temperature increased. For both hybrid and microhybrid groups, as the temperature increased, there was an increase in hardness and it was statistically different (P < 0.001). When the percent difference between 70 and 100 degrees F or 70 and 140 degrees F was evaluated, the greatest increase occurred between the 70 and 140 degrees F and minimal increase between 100 and 140 degrees F. Overall, the LED curing light provided a greater surface hardness for the hybrid at both depths than the halogen curing light. For the microhybrid, the halogen curing light provided the greatest surface hardness when the resin was polymerized for 40 seconds.     

The influence of storage and indenter load on the Knoop hardness of dental composites polymerized with LED and halogen technologies.

OBJECTIVES: The mechanical properties of light cured dental composites are greatly influenced by the light curing unit (LCU) used for the polymerization. Previous studies have shown that for some composites lower mechanical properties were obtained if light emitting diode (LED) LCUs were used for the polymerization instead of halogen LCUs. Previous studies have also shown that light cured composites improve their mechanical properties through a post-curing process after the initial illumination with the LCUs. Therefore, this study investigated the post-curing process, to ascertain if it can compensate for the lower mechanical properties of composites polymerized with LED LCUs. METHODS: The Knoop hardness was measured for four dental composites (Z100, Spectrum, Definite, Solitaire2) polymerized with an LED LCU (LED63 prototype) or a halogen LCU (Trilight), directly after the curing process and after 5 days of storage. In addition, the load on the indenter was varied from 200 to 400 gf to investigate the influence of the load on the measured hardness on the top and bottom of the 2 mm thick samples. RESULTS: In general the Knoop hardness at the bottom of the stored samples, cured with the LED LCU, was the same or statistically significantly greater than for the samples cured with the halogen LCU. A statistically significantly lower (p<0.0001) Knoop hardness was obtained on the top of the samples if the composite Definite was polymerized with the LED LCU instead of the halogen LCU. The load of 200 or 400 gf on the indenter had a statistically significant influence (p<0.0001) on the measured Knoop hardness for the composite Z100. The Knoop hardness measured with an indenter load of 400 gf increased statistically significantly (p<0.0001) for all composites after the 5 days' storage, whether cured with the LED LCU or halogen LCU. SIGNIFICANCE: The post-curing effect cannot compensate for the lower hardness of composites containing co-initiators if polymerized with an LED LCU instead of a halogen LCU. The indenter load had a statistically significant influence on the measured Knoop hardness of composites and has the potential to falsify results if not selected carefully.     

Post-gel shrinkage with different modes of LED and halogen light curing units

This study compared the post-gel shrinkage of two LED (light-emitting diodes) lights (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 to a conventional (Max [MX] (control), Dentsply-Caulk) halogen light. Ten light curing regimens were investigated. These included continuous (FL1, EL2, MX, TL1 and AS1), soft-start (FL2, EL4, TL2), pulse activation (EL1) and turbo (EL3) modes. A strain-monitoring device and test configuration was used to measure the linear polymerization shrinkage of a composite restorative (Z100, [3M ESPE]) during and post-light polymerization up to 60 minutes when cured with the different modes. Five specimens were made for each cure mode. Results were analyzed using ANOVA/Scheffe's post-hoc test and independent sample t-tests at significance level 0.05. Shrinkage associated with the various modes of EL was significantly lower than MX immediately after light polymerization and at one-minute post-light polymerization. No significant difference between MX and the various lights/cure modes was observed at 10, 30 and 60-minutes post-light polymerization. At all time intervals, post-gel shrinkage associated with continuous light curing mode was significantly higher than the soft-start light curing mode for FL and TL.     

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.     

Second generation LEDs for the polymerization of oral biomaterials.

OBJECTIVES: New blue, so called second generation light emitting diodes (LEDs) are now available with a high optical power output. These LEDs will potentially find widespread application in commercially available light curing units (LCUs). This study, therefore, investigated the curing performance of a prototype LCU containing one high power LED and a conventional halogen LCU (Polofil). METHODS: The performances of the LCUs were evaluated by measuring the Knoop hardness and depth of cure of the composites. Three dental composites were selected (Z100, Admira and Revolcin Flow) in a light (A2) and a dark shade (A3.5 or A4), respectively, and were polymerized for 40 s each. RESULTS: The LED prototype (irradiance=901 mW/cm2) achieved a statistically significantly greater (p<0.05) depth of cure than the halogen LCU (irradiance=860 mW/cm2) for all composites. Generally, there was no statistically significant difference in Knoop hardness on the top and bottom of a 2 mm thick disk for the composites Z100 and Admira if polymerized with the LED prototype or halogen LCU. The composite Revolcin Flow, however, showed in general a statistically significant lower Knoop hardness if polymerized with the LED LCU. SIGNIFICANCE: The present study shows that second generation LEDs have the potential to replace halogen LCUs if the composites are selected carefully. Furthermore, this study confirmed that the depth of cure test does not discriminate between LCU's performance for composites containing co-initiators, but the Knoop hardness test does.     

Effect of light curing modes and light curing time on the microhardness of a hybrid composite resin

AIMS: The aim of this in vitro study was to evaluate the influence of light curing modes and curing time on the microhardness of a hybrid composite resin. METHODS AND MATERIALS: Forty-five Z250 composite resin specimens (3M-ESPE Dental Products, St. Paul, MN, USA) were randomly divided into nine groups (n=5): three polymerization modes (conventional-550 mW/cm2; light-emitting diodes (LED)-360 mW/cm2, and high intensity-1160 mW/cm2) and three light curing times (once, twice, and three times the manufacturer's recommendations). All samples were polymerized with the light tip 8 mm from the specimen. Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample. RESULTS: Conventional and LED polymerization modes resulted in higher hardness means and were statistically different from the high intensity mode in almost all experimental conditions. Tripling manufacturers' recommended light curing times resulted in higher hardness means; this was statistically different from the other times for all polymerization modes in the bottom surface of specimens. This was also true of the top surface of specimens cured using the high intensity mode but not of conventional and LED modes using any of the chosen curing times. Top surfaces showed higher hardness than bottom surfaces. CONCLUSIONS: It is important to increase the light curing time and use appropriate light curing devices to polymerize resin composite in deep cavities to maximize the hardness of hybrid composite resins.     

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).     

Composite cure and pulp-cell cytotoxicity associated with LED curing lights

This study compared the cure and pulp-cell cytotoxicity of composites polymerized with light-emitting diode (LED) and halogen-based light curing units. A mini-filled resin composite (Tetric Ceram, Vivadent), two LED (E-light [EL], GC and Freelight [FL], 3M-ESPE), a conventional halogen (Max [MX], Dentsply) and a high-intensity halogen light (Astralis 10 [AS], Vivadent) were evaluated. Cure associated with the different lights was determined by measuring the top and bottom surface hardness (KHN; n = 5) of 2-mm thick specimens using a digital microhardness tester (load = 500 gf; dwell time = 15 seconds). Pulp-cell cytotoxicity was assessed using a direct contact method involving incisor tooth slices dissected from 28-day old Wistar rats maintained in Dulbecco's Modified Eagle's Medium (DMEM) and 1% agarose. The bottom surfaces of the cured composite specimens (7-mm diameter and 2-mm deep) were placed in contact with the openings of each tooth slice. After incubation in 5% CO2 atmosphere at 37 degrees C for 48 hours, the tooth slices were fixed, demineralized and processed for histological examination. Pulp fibroblasts and odontoblasts were counted histomorphometrically at 400x magnification within a 1500 microm2 area using a computerized micro-imaging system. Eighteen readings were obtained for each curing light. Data was subjected to ANOVA/Scheffe's test and Pearson's correlation at significance level 0.05 and 0.01, respectively. At the top surfaces, the cure with AS was significantly greater than the other curing lights, with MX and FL being significantly greater than EL. At the bottom surfaces, MX, AS and FL had significantly better cure than EL. Specimens cured with MX were less cytotoxic than those polymerized with other curing lights. Specimens cured with AS and EL were significantly less cytotoxic than FL. Composite cure and cytotoxicity associated with LED lights is device dependent. Composite cure was not correlated to pulp-cell cytotoxicity. The response of pulpal fibroblasts to unreacted/leached components of composites differs somewhat from odontoblasts.     

Influence of curing lights and modes on cross-link density of dental composites

This study investigated the influence of curing lights and modes on the cross-link density of dental composites. Four LED/halogen curing lights (LED-Elipar Freelight [FL], 3M-ESPE and GC e-light [EL], GC; high intensity halogen-Elipar Trilight [TL], 3M-ESPE; very high intensity halogen-Astralis 10 [AS], Ivoclar Vivadent) were selected for this study. Pulse (EL1), continuous (FL1, EL2, TL1), turbo (EL3, AS) and soft-start (FL2, EL4, TL2) curing modes of the various lights were examined. A conventional, continuous cure halogen light (Max [MX], Dentsply-Caulk) was used for comparison. Six composite (Z100, 3M-ESPE) specimens were made for each light-curing mode combination. After polymerization, the specimens were stored in air at 37 degrees C for 24 hours and subjected to hardness testing using a digital microhardness tester (load=500 g; dwell time=15 seconds). The specimens were then placed in 75% ethanol-water solution at 37 degrees C for 24 hours and post-conditioning hardness was determined. Mean hardness (HK)/change in hardness (deltaHK) was computed and the data subjected to analysis using one-way ANOVA/Scheffe's test and Independent Samples t-test (p<0.05). Softening upon storage in ethanol (deltaHK) was used as a relative indication of cross-link density. Specimens polymerized with AS, TL2 and all modes of both LED lights were significantly more susceptible to softening in ethanol than specimens cured with MX. No significant difference in cross-link density was observed among the various modes of EL and FL. For TL, curing with continuous mode resulted in specimens with significantly higher cross-link density than curing with the soft-start mode.     

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.     

Influence of curing tip distance on resin composite Knoop hardness number,using three different light curing units

This in vitro study evaluated the influence of curing tip distance on the Knoop Hardness Number (KHN) of a resin composite when using three different light curing units: (1) a halogen light (XL 1500 curing unit-3M), (2) a "softstart-polymerization" (Elipar Trilight curing in an exponential mode-ESPE) and (3) a PAC (Apolo 95E curing unit-DMD). The resin composite, Filtek Z250 (3M), was cured by these curing units at three light-tip distances from the resin composite: 0 mm, 6 mm and 12 mm. The resin composite specimens were flattened to their middle portion and submitted to 18 KHN measurements perspecimen. The results showed that for the Elipar Trilight unit, the hardness of the resin composite decreased as the light tip distance increased. The XL 1500 unit presented a significant decrease in hardness as the depth of cure of the resin composite increased. Apolo 95E caused a decrease in the resin composite hardness values when the depth of cure and light tip distance increased.     

Microhardness of resin-based materials polymerized with LED and halogen curing units

The purpose of this study was to evaluate the microhardness of resin-based materials polymerized with a LED (light-emitting diode) light-curing unit (LCU) and a halogen LCU. Twenty cylindrical specimens (3.0 mm in diameter and 2.0 mm high) were prepared for each tested material (Z100, Definite and Dyract). Specimens were light-cured with two LCUs (Ultraled and Curing Light 2500) for either 40 or 60 s on their top surfaces. Hardness was measured on top and bottom surfaces of each specimen. Statistical analysis was done by ANOVA and Tukey's test (p<0.05). There was no significant difference in hardness between LED LCU and halogen LCU for Z100 and Dyract on top surface. Conversely, lower hardness was recorded when Definite was light-cured with the LED LCU than with the halogen lamp. On bottom surface, hardness was significantly lower for all materials light-cured with LED LCU. Z100 was harder than Dyract and Definite regardless of the light curing unit. There was no significant difference in hardness between the exposure times on top surface. Higher hardness was obtained when the materials were light-cured for 60 s on bottom surface. The tested LED was not able to produce the same microhardness of resin-based materials as the halogen LCU.     

Degree of conversion and surface hardness of resin cement cured with different curing units.

OBJECTIVE: The aim of this study was to evaluate the degree of conversion and Vickers surface hardness of resin cement under a simulated ceramic restoration with 3 different curing units: a conventional halogen unit, a high-intensity halogen unit, and a light-emitting diode system. METHODS AND MATERIALS: A conventional halogen curing unit (Hilux 550) (40 s), a high-intensity halogen curing unit used in conventional and ramp mode (Optilux 501) (10 s and 20 s, respectively), and a light-emitting diode system (Elipar FreeLight) (20 s, 40 s) were used in this study. The dual-curing resin cement (Variolink II) was cured under a simulated ceramic restoration (diameter 5 mm, height 2 mm), and the degree of conversion and Vickers surface hardness were measured. For degree of conversion measurement, 10 specimens were prepared for each group. The absorbance peaks were recorded using the diffuse-reflection mode of Fourier transformation infrared spectroscopy. For Vickers surface hardness measurement, 10 specimens were prepared for each group. A load of 200 N was applied for 15 seconds, and 3 evaluations of each of the samples were performed. RESULTS: Degree of conversion achieved with Optilux 501 (20 s) was significantly higher than those of Hilux, Optilux 501 (10 s), Elipar FreeLight (20 s), and Elipar FreeLight (40 s). For Vickers surface hardness measurement, Optilux 501 (20 s) produced the highest surface hardness value. No significant differences were found among the Hilux, Optilux 501 (10 s), Elipar FreeLight (20 s), and Elipar FreeLight (40 s). CONCLUSION: The high-intensity halogen curing unit used in ramp mode (20 s) produced harder resin cement surfaces than did the conventional halogen curing unit, high-intensity halogen curing unit used in conventional mode (10 s) and light-emitting diode system (20 s, 40 s), when cured through a simulated ceramic restoration.     

Effect of reduced exposure times on the microhardness of nanocomposites polymerized by QTH and second-generation LED curing lights

This study investigated the effectiveness of polymerization of various curing regimes on five nanocomposite restorative materials—Z350, Grandio, Clearfil Majesty Esthetic, Ice and Tetric EvoCeram—by utilizing microhardness measurements. Five (n=5) disc-shaped specimens of each material were subjected to one of three curing regimes: curing with a halogen light for 20 seconds, curing with an LED light for 20 seconds and curing with an LED light for 10 seconds. Immediately following curing, hardness measurements were made with a Vickers indenter at five different locations on both the top and bottom surfaces of each disc. The mean for each surface was calculated. Data were analyzed using a one-way ANOVA and post-hoc Tukey HSD (α=0.05). The results demonstrated that among the Z350 composite samples, top and bottom microhardness values showed no statistical differences when cured with the halogen 20 second or LED 20 second regimes (p>0.05). Comparison of the top and bottom values of discs cured with the LED 10 second regime demonstrated significant differences (p<0.0001). Grandio samples cured with the halogen 20 second regime showed no statistical differences between top and bottom microhardness values (p>0.05); however, the bottom values of Grandio discs cured with the LED 20 second and 10 second regimes were significantly lower when compared with top surface values (p=0.001 and p<0.0001, respectively). Clearfil Majesty Esthetic, Ice and Tetric Evo Ceram samples cured with the halogen 20 second regime produced significantly lower bottom microhardness values, while both LED regimes produced top and bottom surfaces that were statistically comparable. The conclusion may be drawn that LED 10 second curing regimes were insufficient to cure Z350 and Grandio, while they were adequate for curing Clearfil Majesty Esthetic, Ice and Tetric EvoCeram.