Variation of depth of cure and intensity with distance using LED curing lights.

OBJECTIVES: The purpose of the study was to determine the correlation between intensity of light-emitting diode (LED) and tungsten-halogen light sources, and depth of cure of a resin composite at different distances. METHODS: Four LED curing lights (Flashlite 1001, Freelight 2, Smartlite IQ and Ultralume 5) and one tungsten halogen (Optilux 501, with 8 and 11 mm tips) were evaluated. Intensity was measured according a modified ISO Standard 10650 at distances of 0, 2, 4, 6, 8, 10 mm between the light tip and detector. Depth of cure (DOC) of TPH Spectrum shade A2 was measured according to the international standard ISO 4049 at the same distances. RESULTS: For all lights, intensity decreased as distance increased. The authors documented a logarithmic correlation between intensity and distance for all lights except the Smartlite IQ, Ultralume 5 and the Optilux 501 with the 11 mm tip, which showed a linear relationship between intensity and distance. All lights demonstrated a logarithmic correlation between intensity and DOC, and a linear correlation between DOC and distance. Smartlite IQ and Optilux 501 (11 mm tip) also had the least reduction in intensity and DOC at 10 mm. SIGNIFICANCE: Clinicians often an experience difficulty placing the light tip close to the resin surface when curing resin composites. While both intensity and DOC decrease with increasing distance, the relationship between these factors and distance may not be similar for all lights and may depend on the characteristics of individual lights.     

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).     

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.     

Third-generation vs a second-generation LED curing light: effect on Knoop microhardness

Third-generation light-emitting diode (LED) curing lights use several different types of LEDs within the light to deliver a broader spectral output compared with the narrower spectral output of second-generation curing lights. This study determined the benefits of this broader spectral output. A third-generation LED curing light was modified so that the 4 peripheral LEDs, which provide the lower wavelengths, could be turned on or off, allowing the light to be used as a third- or a second-generation LED curing light. Twelve composites of A2 and lighter shades were packed into molds 2 mm deep with an internal diameter of 12 mm, and then irradiated for 20 seconds. A laboratory-grade spectroradiometer was used to ensure that all the specimens received the same irradiance and total energy (16.82 J/cm2) from the curing light in both the second- and third-generation modes. The results showed the benefits of using a broader spectrum third-generation LED curing light. This light produced composites that were as hard as when the narrower spectrum second-generation LED curing light was used (P < or = .01). In 7 of the 12 resin composites, the top surface was harder when the third-generation LED curing light was used (P < or = .01).     

三种光固化灯在不同照射距离对复合树脂固化的影响

目的通过检测比较三种具有较高光密度的光固化灯固化树脂试片的表面硬度值,以评价不同的照射距离对树脂固化程度的影响。方法采用3盏光固化灯聚合90个圆柱形光固化复合树脂试片,固化时间均为40s,聚合时固化灯头与试片表面的距离分别为0mm,3mm,6mm,9mm,12mm,15mm。将固化试片浸泡在蒸馏水中,避光37°C保存24h,测量试片表面和底面的努氏硬度(KHN)。对数据进行统计学分析,计算试片底面与表面最大硬度的百分率,检测试片表面在不同的照射距离所获得的光密度值,取对数后与相应的距离进行直线相关分析。结果光密度的对数值与固化距离呈明显负相关。光固化灯与固化距离对试片的硬度有显著影响。Mini LED AutoFocus固化的硬度值比LEDemetronⅠ和Optilux 401更高,LEDemetronⅠ和Optilux 401的硬度比较没有显著意义。随着固化距离的增加样品的努氏硬度显著下降。大多数实验组都能达到有效的硬度百分率。结论光固化灯灯头与树脂表面距离的微小改变会导致光密度发生显著变化。只有采用具有较高光密度的光敏灯才能满足临床较长照射距离的复合树脂充分固化。     

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.     

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.     

Irradiance effects on the mechanical properties of universal hybrid and flowable hybrid resin composites.

OBJECTIVES: A potential problem with high-intensity lights might be failure of polymer chains to grow and cross-link in a desired fashion, thereby affecting the structure and properties of the polymers formed. The purpose of this study was to evaluate mechanical properties of resin composites polymerized using four different light-curing units. METHODS: A conventional quartz-tungsten-halogen (QTH) light, a soft-start light, an argon-ion laser, and a plasma-arc curing light were used to polymerize disk-shaped (9.0mm diameter x 1.0 mm high) and cylinder-shaped (4mm diameter x 8 mm high) specimens of a universal hybrid and a flowable hybrid composite. Biaxial flexure strength, fracture toughness, hardness, compressive strength, and diametral tensile strength were determined for each composite. RESULTS: The use of the plasma-arc curing light, a high-intensity light, resulted in significantly lower hardness for the universal hybrid composite compared with the hardness obtained using the conventional QTH and the soft-start units. Hardness was the only mechanical property that was adversely affected by the use of a high-intensity light. SIGNIFICANCE: High-intensity lights might affect some resin composite mechanical properties, but this effect cannot be generalized to all resin composites and all properties.     

Effect of light-tip distance on the shear bond strengths of composite resin

The purpose of this study was to assess the effect of light-tip distance on the shear bond strength and failure site of brackets cured with three different light curing units: a high-intensity halogen (Astralis 10, 10-second curing), a light-emitting diode (LED, e-Light, six-second curing), and a plasma arc (PAC System, four-second curing). One hundred and thirty-five bovine permanent mandibular incisors were randomly allocated to nine groups of 15 specimens each. Stainless steel brackets were bonded with a composite resin to the teeth, and each curing light was tested at zero, three, and six mm from the bracket. After bonding, all samples were stored in distilled water at room temperature for 24 hours and subsequently tested for shear bond strength. When the three light curing units were compared at a light-tip distance of zero mm, the three lights showed no significantly different shear bond strengths. At light-tip distances of three and six mm, no significant differences were found between the halogen and plasma arc lights, but both lights showed significantly higher shear bond strengths than the LED light. When evaluating the effect of the light-tip distance on each light curing unit, the halogen light showed no significant differences between the three distances. However, the LED light produced significantly lower shear bond strengths at a greater light-tip distance, and the plasma arc lamp showed significantly higher shear bond strengths at a greater light-tip distance. In hard-to-reach areas, the use of PAC system is suggested, whereas the LED evaluated in this study is not recommended.     

Curing efficiency of three different curing modes at different distances for four composites

This study investigated the influence of the different curing distances with three polymerization modes in terms of the surface microhardness of four resin composites as a function of energy density. A hybrid resin composite and flowable composite from each of two manufacturers were evaluated. The specimens were polymerized with one of two light-curing units: 1) Mini LED AutoFocus (1500 mW/cm2) with a fast curing mode, for which two polymerization regimens were used: a) one AutoFocus function cycle and b) two AutoFocus function cycles, and 2) LEDemetron I (950 mW/cm2) with a 20-second curing time. Polymerization was performed with the curing tip at a distance of 0 mm, 3.0 mm, 6.0 mm, and 9.0 mm from the top surface of the specimen, and the power density of each light source was measured with a spectrophotometer. All specimens were stored in distilled water in a light-proof container at 37°C for 24 hours, and their top and bottom surface Knoop hardness numbers were determined. Microhardness data were submitted to two-way analysis of variance and multiple comparisons with a Tukey test. All statistical analyses were performed at a significance level of 0.05. Though the curing lights tested exhibited a decrease in power density with distance, the rate and extent of power density loss were not the same. The polymerization mode and curing tip distance had a significant effect on the composite microhardness. There was also a significant interaction among polymerization mode, curing tip distance, and microhardness. The curing ability of the three polymerization modes was ranked in terms of the hardness percent values: the LEDemetron I > two cycles of the Mini LED AutoFocus > one cycle of the Mini LED AutoFocus.     

The Effect of Different Light Curing Units and Tip Distances on Translucency Parameters of Bulk fill Materials

ObjectivesTo evaluate the effect of light curing unit (LCU) types and distance from light curing unit tip on the translucency parameters (TP) of bulk fill composite materials.Materials and MethodsTwo bulk-fill resin composites and one nanohybrid composite were used in this study. The specimens were divided into groups based on the type of curing unit used, and further subdivided based on the distance of the curing source to the surface of the resin composite. Translucency was evaluated at 4 mm thickness (for the bulk-fill) and 2 mm thickness (for nanohybrid) after curing using two different light curing units at zero, 2 mm, and 4 mm distance. The results were analyzed using two-way ANOVA at the significance level of a p-value of < 0.05.ResultsAmong all the tested materials, Filtek Bulk Fill Posterior RBC showed the highest TP at 0 mm distance when cured with Blue phase G2 LED LCU and it was the least affected by the differences in distances. However, Filtek Z350 nanohybrid composite had no significant differences between the three distances when cured with Blue phase G2 LCU.ConclusionTranslucency values among the studied bulk-fill materials are affected by material composition, curing units and the distance of the tip of the light source to the restoration surface.     

Comparison between a plasma arc light source and conventional halogen curing units regarding flexural strength, modulus, and hardness of photoactivated resin composites

The plasma arc curing light Apollo 95 E (DMDS) is compared to conventional curing lights of different radiation intensities (Vivalux, Vivadent, 250 mW/cm²; Spectrum, DeTrey, 550 mW/cm²; Translux CL, Kulzer, 950 mW/cm²). For this purpose, photoactivated resin composites were irradiated using the respective curing lights and tested for flexural strength, modulus of elasticity (ISO 4049), and hardness (Vickers, Knoop) 24 h after curing. For the hybrid composites containing only camphoroquinone (CQ) as a photoinitiator (Herculite XRV, Kerr; Z100, 3 M), flexural strength, modulus of elasticity, and surface hardness after plasma curing with two cycles of 3 s or with the step-curing mode were not significantly lower than after 40 s of irradiation using the high energy (Translux CL) or medium energy conventional light (Spectrum). However, irradiation by only one cycle of 3 s failed to produce adequate mechanical properties. Similar results were observed for the surface hardness of the CQ containing microfilled composite (Silux Plus, 3 M), whereas flexural strength and modulus of elasticity after plasma curing only reached the level of the weak conventional light (Vivalux). For the hybrid composites containing both CQ and photoinitiators absorbing at shorter wavelengths (370–450 nm) (Solitaire, Kulzer; Definite, Degussa), plasma curing produced inferior properties mechanical than conventional curing; only the flexural strength of Solitaire and the Vickers hardness of Definite reached levels not significantly lower than those observed for the weak conventional light (Vivalux). The suitability of plasma arc curing for different resin composites depends on which photoinitiators they contain. Received: 5 July 1999 / Accepted: 16 March 2000     

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.     

Advances in light curing units and curing techniques: a literature review.

There exists a constant need for a dental curing light that works reliably and conveniently in the general practitioner's office and can be used effectively for all the different curing procedures. Due to the need for improved physical properties of resin based composites (RBCs) and less stress at the marginal interface, light curing units (LCUs) experienced significant advances in the past years. The dental industry has focused on reducing the curing time by developing higher intensity curing lights and by altering the resin composition and photo-initiator concentration. As a result the dentist can now choose from a vast variety of curing lights, light intensities and curing methods. This article presents a review of the advances in light curing units and curing techniques, as well as the scientific principles that guided past developments and that will influence future advances.     

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.     

Light curing of resin-based composites in the LED era

This review thoroughly accumulated information regarding new technologies for state-of-the-art light curing of resin composite materials. Visible light cured resin-based composites allow the dentist to navigate the initiation of the polymerization step for each layer being applied. Curing technology was regularly subjected to changes during the last decades, but meanwhile the LED era is fully established. Today, four main polymerization types are available, i.e. halogen bulbs, plasma are lamps, argon ion lasers, and light emitting diodes. Additionally, different curing protocols should help to improve photopolymerization in terms of less stress being generated. Conclusions were: (1) with high-power LED units of the latest generation, curing time of 2 mm thick increments of resin composite can be reduced to 20 seconds to obtain durable results; (2) curing depth is fundamentally dependent on the distance of the resin composite to the light source, but only decisive when exceeding 6 mm; (3) polymerization kinetics can be modified for better marginal adaptation by softstart polymerization; however, in the majority of cavities this may not be the case; (4) adhesives should be light-cured separately for at least 10 seconds when resin composite is applied directly; (5) photocuring through indirect restorations such as ceramics is still a problem, therefore, both dual-cured adhesives and dual-cured composites and resin coating in any way are recommended; and (6) heat generation with high-power photopolymerization units should not be underestimated as a biological problem for both gingival and pulpal tissues.     

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.     

Evaluation of curing light distance on resin composite microhardness and polymerization

This study evaluated the influence of the curing tip distance on cure depth of a resin composite by measuring Vickers microhardness and determining the degree of conversion by using FT-Raman spectroscopy. The light curing units used were halogen (500mW/cm2) and LED (900mW/cm2) at a conventional intensity and an Argon laser at 250mW. The exposure time was 40 seconds for the halogen light, 20 seconds for the LED and 20 and 30 seconds for the Argon laser. The curing tip distances of 0, 3, 6 and 9 mm were used and controlled via the use of metal rings. The composite was placed in a black matrix in one increment at a thickness of 1 mm to 4 mm. The values of microhardness and the degree of conversion were analyzed separately by ANOVA (Analysis of Variance) and Tukey test, with a significance level set at 5%. Correlations were analyzed using the Pearson test. The results obtained conclude that greater tip distances produced a decrease in microhardness and degree of conversion values, while increasing the resin thickness decreased the microhardness and degree of conversion values. A higher correlation between microhardness and the degree of conversion was shown. This study suggests that the current light curing units promote a similar degree of conversion and microhardness, provided that the resin is not thicker than 1 mm and the light source is at a maximum distance of 3 mm from the resin surface.     

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.     

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.