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 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.     

Microhardness of different thicknesses of resin composite polymerized by conventional photocuring at different distances

This in vitro study sought to evaluate the influence of photocuring modes and polymerization time on the microhardness of a hybrid composite resin. Sixty composite resin specimens were prepared at random and divided into 12 experimental groups (n=5), consisting of four curing tip distances (2.0 mm, 4.0 mm, 6.0 mm, and 8.0 mm) and three sample thicknesses (0.5 mm, 1.0 mm, and 2.0 mm). All samples were polymerized with a continuous output at 550 mW/cm2. After 24 hours, Knoop microhardness measurements were obtained on top and bottom surfaces of the sample, with a load of 25 g for 10 seconds. Five indentations were made on each surface of each sample. Subdivided parcels ANOVA test and Tukey test were performed (p = 0.05). There were no statistical differences among the experimental groups for the top surface. On the bottom surface, 0.5 mm and 1.0 mm sample thicknesses showed significantly higher hardness means for all photocuring tip distances when compared with the 2.0 mm sample thickness. In terms of the photocuring tip distance, the 2.0 mm and 4.0 mm distances showed significantly higher hardness means for all sample thicknesses when compared with the 8.0 mm distance. For all experimental conditions, the top surface showed higher hardness than the bottom surface. It was concluded that the resin composite increments should be decreased to improve the polymerization of the resin composite bottom surface in deep cavities.     

A Fourier transform Raman spectroscopy analysis of the degree of conversion of a universal hybrid resin composite cured with light-emitting diode curing units

The degree of conversion (DC), of a universal hybrid resin composite cured with LED curing units with low and high power densities and a 510 mW/cm2 quartz tungsten halogen unit, was investigated with Fourier Transform Raman spectroscopy. Three curing depths (0, 2, 4mm) and 0 and 7 mm light guide tip - resin composite (LT - RC) distances were tested. The DC of the LED units varied between 52.3% - 59.8% at the top surface and 46.4% - 57.0% at 4 mm depth. The DC of specimen cured with a 0 mm LT- RC distance at 4 mm depth varied between 50.8% - 57.0% and with 7 mm distance between 46.4% - 55.4%. The low power density LED unit showed a significantly lower DC for both distances at all depth levels compared to the other curing units (p < 0.05). Significant differences between the other curing units were only found at the 4 mm depth level cured from 7 mm distance (p < 0.05). The reduction in DC by increasing LT- RC distance was less than 10% for all curing units. It can be concluded that the improved LED curing units could cure the studied resin composite to the same DC as the control unit.     

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.     

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.     

Evaluation of light curing units used for polymerization of orthodontic bonding agents

This study evaluated the light intensity of various light curing units, the effect of distance of the light guide, and the validity of a tapered light guide. Light curing units tested included (1) four blue light-emitting diode curing units, Lux-O-Max, LEDemetronl, Ortholux LED, and The Cure; (2) two tungsten-quartz halogen curing units, Optilux 501 and Co-bee; and (3) one plasma arc curing unit, Apollo95E. The Optilux 501 was also evaluated for combinations of normal mode and boost mode and Standard tip and Turbo tip light guide. The spectral output of each unit was measured from 300 to 600 nm with a spectroradiometer. The light intensities at distances of zero, five, 10, 15, and 20 mm were determined with the radiometer. The peak value of Ortholux LED and The Cure surpassed that of Apollo95E. The light intensity significantly decreased with distance. Although The Cure showed a higher light intensity than the LEDemetron1 at zero-mm distance, the light intensity of the LEDemetron1 was higher than that of The Cure at five to 20 mm, resulting in no significant difference. The boost mode increased light intensity at any distance. Although the Turbo tip enhanced light intensity at zero-mm distance, reduction of light intensity by Turbo tip was demonstrated at five- to 20-mm distance.     

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.     

Influence of curing tip distance on composite Knoop hardness values

The purpose of this paper was to study the influence of curing tip distance on Knoop hardness values, at different depths, of two composites, Z100 and Silux Plus. Specimens (5 mm in diameter and 2.5 mm in height) were prepared in a copper mold, covered with mylar strip and polymerized for 40 s, at 3 tip-to-composite surface distances: 0 mm (surface contact), 6 and 12 mm, utilizing an XL 3000 curing unit, with 750 mW/cm2 power. The specimens were then stored at 37 degrees C for 24 h. Knoop hardness values were measured using a microhardness tester, with a load of 50 g for 30 s for each indentation. Four specimens were made for each distance and composite and eighteen indentations were made of each specimen. The results were submitted to analysis of variance and Tukey test at 5% significance level. The results indicated that 1) composite Z100: the larger the curing tip distance in relation to the composite, the lower the Knoop hardness values; 2) Silux Plus: increasing the curing tip distance did not produce a statistically significant difference in the Knoop hardness values; however, at 6 and 12 mm, the deeper layers showed lower Knoop hardness values in relation to the surface; 3) Z100: statistically superior in relation to Silux Plus at all three curing tip distances and at all depths (P < 0.05).     

Influence of ceramic translucency on curing efficacy of different light-curing units

PURPOSE: The aim of the study was to examine the influence of dental ceramic translucency under different exposure conditions upon the polymerization rate of a dual-curing composite resin by measuring the depth of cure (DOC) and the Vickers microhardness (VHN). MATERIALS AND METHODS: Three hundred twenty ceramic specimens (160 Empress 2, Ivoclar Vivadent, color 300, and 160 ProCAD, Ivoclar Vivadent, 300, 114; diameter 4 mm, height 1 mm or 2 mm) were inserted into steel molds and overlayed using a composite resin (Variolink II, Ivoclar Vivadent) with and without a self-curing catalyst. Specimens were cured either in contact with or at a 5-mm distance from a conventional halogen curing light (Elipar TriLight, 3M ESPE, exposure duration 40 s, standard mode) and a light-emitting diode (LED: Bluephase 16i, Ivoclar-Vivadent, exposure duration 20 s, high-power mode). DOC under the ceramic specimen was measured following ISO 4049:2000. The VHN of the resin composite was determined at 0.5 mm and 1.0 mm distance from the ceramic using a Vickers hardness tester. Statistical analysis was performed using the Mann-Whitney U-test (alpha = 0.05) and the error-rates method (ERM). RESULTS: Higher translucency of the ceramic restoration resulted in higher DOC and VHN values, which were statistically significant for the halogen light source and in most cases for the LED groups. The use of a self-curing catalyst generally produced an increase in DOC and VHN data, with the exception of DOC data for the highly translucent ceramic and direct contact of the tip of the light source with the ceramic. No significant differences between VHN data of the highly translucent ceramic without catalyst and the opaque ceramic with catalyst were observed in 3 out of 4 pairwise comparisons and according to the ERM. Thus, there are indications that for a highly translucent ceramic with the LED unit tested the catalyst may be waived for a ceramic thickness up to 2 mm. CONCLUSIONS: There are indications that for a highly translucent ceramic with the LED unit tested, the catalyst may be omitted with a ceramic thickness up to 2 mm. High ceramic translucency improves polymerization of luting composite.     

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).     

固化灯及照射距离对纳米树脂显微硬度的影响

目的观察在不同照射距离下,不同固化模式对复合树脂表面显微硬度的影响。方法将复合树脂制备成直径4mm,厚2mm的圆片状实验模块,根据照射距离（2mm、5mm、10mm）与固化模式（430mw／cm^2卤素灯40秒与860mw／cm^2二极管固化灯20秒）分成6组,每组6个,共36个。固化后用硬度计测定每个树脂块顶面与底面的韦氏硬度值。统计分析各组间显微硬度值的差别。结果随照射距离增大,树脂块显微硬度显著降低（p〈0．01）;各组树脂块顶面显微硬度值均高于底面（p〈0．01）;在2mm与5mm照射距离下,不同固化方式对树脂块表面硬度无显著影响（p〉0．05）;在10mm照射距离下,二极管固化灯组底面的显微硬度显著高于卤素灯组（p〈0．01）。结论远距离照射下,要使深层复合树脂充分固化应选择高功率的固化模式。     

Comparison of composite curing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrinkage

This study analyzed the degree of conversion, temperature increase and polymerization shrinkage of two hybrid composite materials polymerized with a halogen lamp using three illumination modes and a photopolymerization device based on blue light emitting diodes. The degree of conversion of Tetric Ceram (TC) (Ivoclar Vivadent) and Filtek Z 250 (F) (3M/ESPE) was measured by Fourier transformation infrared spectroscopy at the surface and 2-mm depth; temperature rise was measured by digital multimeter, and linear polymerization shrinkage was measured during cure by digital laser interferometry. Composite samples were illuminated by quartz-tungsten-halogen curing unit (QTH) (Astralis 7, Ivoclar Vivadent) under the following modes: "high power" (HH) 40 seconds at 750 mW/cm2, "low power" (HL) 40 seconds at 400 mW/cm2 and "pulse/soft-start" (HP) increasing from 150 to 400 mW/cm2 during 15 seconds followed by 25 seconds pulsating between 400 and 750 mW/cm2 in 2-second intervals and by light emitting diodes (LED) (Lux-o-Max, Akeda Dental) with emitted intensity 10 seconds at 50 mW/cm2 and 30 seconds at 150 mW/cm2. A significantly higher temperature increase was obtained for both materials using the HH curing mode of halogen light compared to the HP and HL modes and the LED curing unit after 40 seconds. Significantly lower temperature values after 10-second illumination were obtained when LED was used compared to all halogen modes. For all curing modes, there was no significant difference in temperature rise between 20 and 40 seconds of illumination. Results for the degree of conversion measurements show that there is a significant difference in the case of illumination of resin composite samples with LED at the surface and 2 mm depth. For polymerization shrinkage, lower values after 40 seconds were obtained using LED compared to QTH.     

Effect of curing time and light curing systems on the surface hardness of compomers

This study compared the Vickers hardness of the top and bottom surfaces of two compomers (Compoglass F and Dyract AP) polymerized for 20 and 40 seconds with two different light curing systems. Five samples for each group were prepared using Teflon molds (9x2 mm) and were light-cured either with a conventional halogen lamp (Optilux 501) or LED light (LEDemetron I) for 20 or 40 seconds. After curing, all the samples were stored in distilled water for 24 hours at 37 degrees C. The Vickers hardness measurements were obtained from the top and bottom surfaces of each sample. ANOVA, Scheffé and t-test were used to evaluate the statistical significance of the results. For the top and bottom surfaces, the light curing systems and curing times tested showed no statistical difference, except for Optilux 501, which used 20 seconds for both compomers (p<0.05). There was no significant difference in the microhardness of both surfaces of Compoglass F and Dyract AP cured for either 20 or 40 seconds using LEDemetron I. With Optilux 501, the microhardness of samples cured for 40 seconds was significantly higher than 20 seconds (p<0.05).     

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.     

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.     

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.     

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.