Influence of light intensity from different curing units upon composite temperature rise

The unavoidable consequence of composite resin photopolymerization is temperature rise in tooth tissue. The temperature rise depends not only on the illumination time, but also on light intensity, distance of light guide tip from composite resin surface, composition and shade of composite resin and composite thickness. The most commonly used units for polymerization today are halogen curing units, which emit a large spectrum of wavelengths. A proportion of the spectrum has no influence on degree of conversion and therefore causes unnecessary temperature rise. Units based on light source - blue light emitting diodes (LED), as an alternative for halogen curing units, have been introduced in clinical practice. The aim of this study was to show the influence of the light intensity of curing units Elipar Trilight, Astralis 7 and Lux-o-Max unit on temperature rise in composite resin sample of Tetric Ceram. The temperature was measurement with Metex M-3850 D multimeter with the tip of temperature probe put into unpolymerized composite resin sample 1 mm depth. The highest temperature rise was recorded with standard curing mode for Elipar Trilight halogen curing unit (13.3 +/- 1.21 degrees C after 40 s illumination), while the lowest temperature rise was recorded for the Lux-o-Max unit based on LED technology (5.2 +/- 1.92 degrees C after 40 s illumination).     

Effect of LED and halogen light curing on polymerization of resin-based composites

The clinical performance of light polymerized resin-based composites (RBCs) is greatly influenced by the quality of the light curing unit (LCU). A commonly used unit for polymerization of RBC material is the halogen LCUs. However, they have some drawbacks. Development of new blue superbright light emitting diodes (LED LCU) of 470 nm wavelengths with high light irradiance offers an alternative to standard halogen LCU. The aim of this study is compared the effectiveness of LED LCU and halogen LCU on the degree of conversion (DC) of different resin composites [two hybrid (Esthet-X, Filtek Z 250), four packable (Filtek P60, Prodigy Condensable, Surefil, Solitaire), one ormocer-based resin composite (Admira)]. The DC values of RBCs polymerized by LED LCU and halogen LCU ranged approximately from 61.1 +/- 0.4 to 50.6 +/- 0.6% and from 55.6 +/- 0.7 to 47.4 +/- 0.5%, respectively. Significantly higher DC of RBCs except Surefil and Filtek Z 250 was obtained for LED LCU compared with halogen LCU (P < 0.05). Surefil and Filtek Z 250 exhibited no statistically significant difference values between LED LCU and halogen LCU (P > 0.05). As a result, it was observed that the performance of LED LCU used in the study was satisfactory clinically and had sufficient irradiance to polymerize RBCs (hybrid, packable and ormocer based) at 2 mm depth with a curing time of 40 s.     

Composite conversion and temperature rise using a conventional,plasma arc,and an experimental blue LED curing unit

The objective of this study was to evaluate the degree of conversion and temperature rise in three different composite materials when illuminated by an experimental light source [blue superbright light emitting diodes (LEDs)] and compared with plasma light and traditional photopolymerization unit. The degree of conversion and temperature rise were measured using Fourier transform infrared (FTIR) spectroscopy and digital multimeter, respectively. The results revealed significantly higher degree of conversion values in case of conventional curing than with other two light sources whereas temperature rise was significantly lower when blue LEDs and plasma light were used. There were great differences in light intensities between blue LEDs of only 9 mW cm-2 compared with plasma light of 1370 mW cm-2 and Elipar II of 560 mW cm-2. Better match of LED spectral distribution peak to camphorquinone absorption distribution peak probably explains much lower intensities used for similar photopolymerization effect like in the case of rapid plasma lamp curing.     

Degree of conversion and in vitro temperature rise of pulp chamber during polymerization of flowable and sculptable conventional,bulk-fill and short-fibre reinforced resin composites

ObjectiveDetermine the degree of conversion (DC) and in vitro pulpal temperature (PT) rise of low-viscosity (LV) and high-viscosity (HV) conventional resin-based composites (RBC), bulk-fill and short-fibre reinforced composites (SFRC).MethodsThe occlusal surface of a mandibular molar was removed to obtain dentine thickness of 2 mm above the roof of the pulp chamber. LV and HV conventional (2 mm), bulk-fill RBCs (2–4 mm) and SFRCs (2–4 mm) were applied in a mold (6 mm inner diameter) placed on the occlusal surface. PT changes during the photo-polymerization were recorded with a thermocouple positioned in the pulp chamber. The DC at the top and bottom of the samples was measured with micro-Raman spectroscopy. ANOVA and Tukey’s post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).ResultsThe PT changes ranged between 5.5–11.2 °C. All LV and 4 mm RBCs exhibited higher temperature changes. Higher DC were measured at the top (63–76%) of the samples as compared to the bottom (52–72.6%) in the 2 mm HV conventional and bulk-fill RBCs and in each 4 mm LV and HV materials. The SFRCs showed higher temperature changes and DC% as compared to the other investigated RBCs. The temperature and DC were influenced by the composition of the material followed by the thickness.SignificanceExothermic temperature rise and DC are mainly material dependent. Higher DC values are associated with a significant increase in PT. LV RBCs, 4 mm bulk-fills and SFRCs exhibited higher PTs. Bulk-fills and SFRCs applied in 4 mm showed lower DCs at the bottom.     

Evaluation of photopolymerization efficacy and temperature rise of a composite resin using a blue diode laser (445 nm)

The purpose of this study was to evaluate the photopolymerization efficacy of a diode laser (445 nm) for use with a composite containing camphorquinone and to estimate the safety of the method related to the temperature rise. Five cylindrical composite specimens were prepared for each thickness: 1, 2, and 3 mm. Three light-curing modes were investigated: a light emitting diode (LED) unit and a diode laser (445 nm) with output powers at 0.7 W or 3 W. Evaluation of the polymerization efficacy was based on Vickers hardness measurements, and the highest temperatures at the bottom of the specimens were recorded using a K-type thermocouple. The highest microhardness was observed after the diode laser curing operating at 3 W. A comparison of the microhardness of the 0.7 W laser cured specimens with the LED cured specimens showed a statistically significant difference in favor of the laser curing. Laser curing operating at 3 W resulted in extremely high temperatures. Laser curing at 0.7 W resulted in statistically significantly higher maximum temperatures than did LED curing for both 1 mm thick (52.9°C against 45.4°C) and 3 mm thick (43.6°C against 40.9°C) specimens. Diode laser (445 nm) may be an alternative for photopolymerization of composite materials and may result in a higher degree of conversion and depth of cure of composites than what has been seen with LED curing units when they emit at the same energy density.     

Correlation between depth of cure and temperature rise of a light-activated resin

The temperature rise, caused by 10 different curing units, in a prepolymerized resin specimen was examined. For all units, the temperature increase in a 60s cycle followed a logarithmic curve, with the most effective light sources giving the highest temperature rise. In the surface layer the change of temperature ranged between 3.6 and 29.2°C, and 3.2 mm below the irradiated surface between 1.5 and 12.3°C. The use of a 2-mm-thick isolating layer of glass ionomer resulted in a significant reduction in the temperature increase. The correlation between the depth of cure and the temperature rise was of an exponential or power nature; i.e., a small increase of the depth of cure was followed by a disproportionately high increase in temperature.     

Effect of light source and time on the polymerization of resin cement through ceramic veneers

PURPOSE: The purpose of this study was to evaluate the efficiency of 3 different light sources to polymerize a light curing resin cement beneath 3 types of porcelain veneer materials. MATERIALS AND METHODS: A conventional halogen light, a plasma arc light, and a high intensity halogen light were used to polymerize resin cement (Variolink II; Ivoclar North America Inc, Amherst, NY) through disks of veneer materials. Equal diameter and thickness disks of feldspathic porcelain (Ceramco II; Ceramco Inc, Burlington, NJ), pressable ceramic (IPS Empress; Ivoclar North America Inc), and aluminous porcelain (Vitadur Alpha; Vident Inc, Brea, CA) were used as an interface between the curing light tips and the light polymerized resin cement. The resin cement/veneer combinations were exposed to 4 different photopolymerization time protocols of 5 seconds, 10 seconds, 15 seconds, and 20 seconds for high intensity light units (Apollo 95E [Dental Medical Diagnostic Systems Inc, Westlake Village, CA] and Kreativ 2000 [Kreativ Inc, San Diego, CA]), and 20 seconds, 40 seconds, 60 seconds, and 80 seconds for conventional halogen light (Optilux; Demetron Research Inc, Danbury, CT). A surface hardness test (Knoop indenter) was used to determine the level of photopolymerization of the resin through the ceramic materials with each of the light sources. The data were analyzed by one-way analysis of variance and a post-hoc Scheffe test (p < .05). RESULTS: The data indicates that the Variolink II Knoop Hardness Number values vary with the light source, the veneer material, and the polymerization time. For a given light and veneer material, Knoop Hardness Number increases with longer polymerization times. The Kreativ light showed statistically significant differences (p < .05) between all test polymerization times. Use of this light required a polymerization time of greater than 20 seconds to reach maximum resin cement hardness. For samples polymerized with the Apollo light, there were statistically significant (p < .05) differences in surface hardness between samples polymerized at all times, except for the 15-second and 20-second times. Samples polymerized with the halogen light showed no statistically significant (p < .05) differences in hardness between polymerization times of 60 seconds and 80 seconds. CONCLUSIONS: High intensity curing lights achieve adequate polymerization of resin cements through veneers in a markedly shorter time period than the conventional halogen light. However, the data in this report indicate that a minimum exposure time of 15 seconds with the Kreativ light and 10 seconds with the Apollo 95E light should be used to polymerize the Variolink II resin, regardless of the composition of the veneer. Conventional halogen lights required a correspondingly greater polymerization time of 60 seconds.     

Correlation between recordings obtained with a light-intensity tester and degree of conversion of a light-curing resin

The present study evaluated the ability of a light-intensity tester (CL-Tester) to predict the degree of conversion of a resin. A light-curing resin was mixed from 25 mol-% BISGMA and 75 mol-% TEGDMA. The resin was cured with one of five different curing units whose light intensity varied from poor to very good when recorded with the CL-Tester. The degree of conversion was found by determination of the number of remaining double bonds (RDB) from transmission infrared spectra of the resin. The five mean values of RDB varied with statistical significance. A significant linear correlation was found between recordings of the CL-Tester and degree of conversion. It was concluded that the CL-Tester was able to predict the degree of conversion to such a degree that it may be expected to constitute a useful means of regular control of curing units.     

Degree of polymerization of resin composites by different light sources

The purpose of this study was to determine the effectiveness of polymerization in the newly introduced blue light emitting diode (LED) (Experimental, SNU, Korea), and plasma arc curing (PAC) (Apollo 95E, Elite, DMD, USA) compared with conventional halogen lamp (Spectrum 800, Dentsply, USA). Various irradiation time with fixed intensity of light-curing units (LCUs) were irradiated to produce the same total light energy. The degree of double bond conversion (DC) of three resin composite (shade A3) was measured with a Fourier-transform infrared (FT-IR) spectrophotometer at various depths from the surface. Immediately after exposure to light, 100 microm thickness of resin composite was sectioned at the 1, 2, 3 and 4 mm from the top surface. The infrared spectrum of uncured resin and each wafer specimen were then obtained. The results were as follows: DC was significantly influenced by three variables of material, depth from the surface, and light source and energy level (P < 0.01). When the same light energy was irradiated, DC by plasma arc and LED was not significantly different from the halogen lamp (P > 0.05). When light energy was increased twice, no significant difference in DC was observed up to 2 mm from the surface (P > 0.05), but DC increased significantly from 3 mm (P < 0.05).     

Temperature change, dentinal fluid flow and cuspal displacement during resin composite restoration

Dentin-bonding agents and resin composite materials typically require light activation for polymerization. Light curing generates heat, which may influence dentinal fluid flow (DFF) and cuspal displacement. This study investigated the relationship among temperature increase, DFF and cuspal displacement in extracted human maxillary premolars with a mesial occlusal distal (MOD) cavity preparation. Two types of curing light were compared. Temperature changes were measured using thermocouples located on the occlusal cavity floor and at the pulp-dentine junction, during polymerization of bonding agent and resin composite material. DFF and cuspal displacement were measured simultaneously using automated flow measurement apparatus and direct current differential transformers respectively. Temperature increases of up to 15 degrees C were recorded during the restoration procedures. A quartz tungsten halogen (QTH) unit produced a significantly greater temperature increase than a light-emitting diode unit and curing of the bonding agent generated less temperature increase than curing of the resin composite. Heating due to exothermic reaction during polymerization of bonding agent and resin was not significantly different between light sources or between bonding and curing (P > 0.05). The QTH unit produced both greater inward fluid flow and cuspal displacement during the irradiation of bonding agent and resin composite than the light-emitting diode unit. There was not a simple relationship between temperature increase, fluid movement and cuspal displacement. From a clinical point of view, the light-emitting diode unit can be considered preferable to the QTH light, because it caused significantly smaller temperature increase, fluid shift and cuspal displacement.     

牙科发光二极管光固化灯和普通卤光灯临床应用效果评价

目的：了解牙科发光二极管光固化灯应用于患牙备洞树脂充填固化后的临床效果.方法：按纳入标准选择门诊就诊患者患牙160颗,龋损和楔状缺损各80颗.随机分为试验组和对照组,使用牙科树脂材料充填后,实验组应用发光二极管光固化灯固化20sec,对照组应用普通卤光灯固化40sec,打磨抛光;12个月后复诊,评价.结果：楔状缺损实验组有1颗充填物脱落,1颗边缘密合度缺陷,1颗边缘着色,成功率92.1%;对照组有1颗充填物脱落,1颗边缘着色,成功率94.4%;无统计学意义上的差异（P＞0.05）.龋损实验组有3例边缘密合度缺陷,2颗边缘着色,成功率87.5%;对照组有2颗边缘密合度缺陷,1颗边缘着色,成功率91.7%;无统计学意义上的差异（P＞0.05）.结论：发光二极管光固化灯与普通卤光灯临床效果没有区别,但操作时间更短,使用更为轻巧.     

How light irradiance and curing time affect monomer conversion in light-cured resin composites

We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s x mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.     

Influence of specimen diameter on the relationship between subsurface depth and hardness of a light-cured resin composite

In pilot studies of the relationship between subsurface depth and hardness of a light-cured resin composite, it was found that the resin composite was softer at a depth of 0.5 mm than at, for example, a depth of 1.0 mm. It is possible that the increase in hardness at intermediate subsurface depths compared with the hardness at small depths is due to the heat of polymerization, causing a greater increase in temperature at intermediate depths than at small depths. As the temperature rise increases with volume of the test specimen, it was hypothesized that the increase in hardness would increase with the diameter of the irradiated specimen. The hardness of a resin composite was measured as a function of subsurface depth for cylindrical specimens of 3, 4, and 6 mm diameter. It was found that the resin composite was softer at 0.5 mm than at 1.0-1.5 mm depth independent of specimen diameter. Possible explanations are oxygen inhibition of polymerization and high rate of cure of material at small subsurface depth. It was also found that, corresponding with increasing specimen diameters, the specimens became significantly softer at depths of 3.0 mm, 3.5 mm, and 4.0 mm, respectively. The heat production and reflection of light from the walls of the molds may explain the latter, but not the former finding.     

3种光固化灯照射不同颜色复合树脂的固化深度比较

目的探讨LED光固化灯与传统卤素灯对不同颜色复合树脂的固化深度的影响。方法选取FiltekTMZ350和Premisa两种树脂,FiltekTMZ350组选取A1B,A2B,A3B 3种颜色,Premisa组选取A1E,A2E,A3E 3种颜色,自制实验模具,将树脂填入模具。每种颜色树脂制作60例试件,分为3组,每组20例,分别用2种新型LED光固化灯Demi LED和Bluephase20i与传统卤素灯ALC-50在标准条件下照射试件,检测固化深度。结果 Demi LED光照10 s、Bluephase20i光照10 s树脂的固化深度均达到3 mm,与传统的卤素光固化灯ALC-50光照40 s有显著差异,但前两者之间无显著差异。Premisa树脂中2种LED照射组A1E,A2E和A3E 3种颜色之间固化深度有统计学差异。结论在相同条件下,Demi LED和Bluephase20i照射10 s树脂固化深度大于传统卤素灯ALC-50照射同一树脂40 s,适合临床应用。树脂颜色的加深对树脂固化深度有影响。     

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提要：光固化复合树脂应用于口腔医学已经有30年历史,光固化灯作为固化光源直接影响了复合树脂的性能及修复效果。目前临床常用的固化灯类型有传统卤光灯、速效卤光灯、发光二极管灯、等离子弧光灯、氩激光灯。本文主要介绍了每种光固化灯的特点、对复合树脂聚合固化的影响因素及使用注意事项。     

Photopolymerization of composite resins with plasma light

Everyday improvements in components and characteristics of composite materials have induced faster development of curing units. Besides standard halogen curing units and soft-start photopolymerization light sources, some experiments with argon and pulsed laser light and low intensity blue superbright light emitting diodes have been made. On the other hand, rapid polymerization with strong plasma light is also clinically applicable. The aim of this study was to measure the degree of conversion and temperature rise for three restorative composite materials: Tetric Ceram (Vivadent, Schaan, Liechtenstein), Pertac II (ESPE, Seefeld, Germany) and Z100 (3M Dental Products, St Paul, MN, USA) during polymerization with plasma light Apollo 95E (DMDS, Dental/Medical Diagnostic Systems, Fleury d'Aude, France) and compare it with the results of polymerization with a halogen curing unit, Elipar Trilight (ESPE, Seefeld, Germany). The results revealed the degree of conversion values in the case of polymerization with plasma light to be almost equal to those obtained by curing with the halogen curing unit, whereas the temperature rise was almost negligible.     

不同温度及不同光固化灯对光固化复合树脂硬度的影响

目的:探讨不同温度处理后的光固化复合树脂用卤素光固化灯和第2代LED光固化灯照射后复合树脂硬度的差别.方法:设5℃(冷藏)、23℃(常温)、40℃(加热)3种不同温度处理光固化复合树脂Clearfil AP-X.再分别用卤素光固化灯Translux CL和LED灯Elipar FreeLight2照射,采用显微维氏硬度计测量树脂试件表面和底部的硬度.结果采用SPSS 17.0软件包进行方差分析.结果:40℃加热处理后的树脂试件表面和底部的硬度值均较其他2种温度处理后的树脂硬度值增高(P＜0.01).3种温度处理后.LED灯照射树脂试件表面和底部硬度值比卤素灯照射后的硬度值高(P＜0.01).结论:树脂试件使用前预加热处理,可以增强树脂的硬度;第2代LED灯的固化效率优于卤素灯.     

Degree of conversion of dual-cured resin cement light-cured through three fibre posts within human root canals: an ex vivo study

Aim  To evaluate the degree of conversion of one dual-cured resin cement light-cured through three fibre posts within extracted human teeth.
Methodology  Fifteen mandibular premolars were root filled and then divided into three groups. Variolink II was light-cured through the posts (LP, D.T. Light-Post; PP, FRC Postec Plus; SP, Snowpost) within the root canal. The degree of conversion was obtained at 1 mm intervals in 9 mm-deep longitudinally sectioned root canals using an optical microscope connected to an FTIR spectrophotometer ( n  =   10). The light transmission of each post tested was also examined using UV–Vis spectroscopy. Data were analysed using anova and Tukey's test ( α  = 0.05).
Results  The LP and PP posts revealed a light transmission of 10.2% and 7.7%, respectively, whereas the SP post exhibited a significantly lower value of 0.5%. The degree of conversion mean value ranged from 32.78% to 69.73% depending on the depth and type of post. For all the groups, there were significant decreases in the degree of conversion values for the middle region when compared with those for the cervical region ( P  <   0.05). Except at a depth of 1 mm, the SP group consistently exhibited significantly lower degree of conversion values than the other groups ( P  <   0.05). The linear regression analysis revealed a strong correlation between the light transmission of the posts and the overall degree of conversion value for each group ( R ² = 0.9888).
Conclusions  The decrease in the degree of conversion for Variolink II relative to the depth was dependent on the light transmission capacity of the posts tested.     

Polymer structure of a light-cured resin composite in relation to distance from the surface

The aim of the investigation was to study the polymer structure of a light-cured resin composite in relation to the distance from the irradiated surface. Ten cylinders (4 x 8 mm) of composite were light-cured in a mold at 580 mW cm-2 for 40 s. The cylinders were expressed from the mold and, after 1 wk of dry storage at 37 degrees C, embedded in dental stone. Grinding parallel to the long axis of the cylinders on carborundum paper exposed the resin composite. The Wallace hardness in relation to distance from the irradiated surface was measured before and after 1 d of ethanol storage. Before ethanol storage and at distances from the surface of 0.5-3.5 mm, no difference in hardness was recorded. The ethanol storage gave rise to a softening of the resin composite. The softening recorded at 3.0-3.5 mm was significantly more pronounced than the softening taking place at 0.5-2.5 mm. This result was explained by a slower polymerization occurring at the greater distances from the irradiated surface, resulting in a polymer with reduced crosslink density.     

Effect of temperature on composite polymerization stress and degree of conversion

Objective

To test the following hypotheses: (1) degree of conversion (DC) and polymerization stress (PS) increase with composite temperature (2) reduced light-exposure applied to pre-heated composites produces similar conversion as room temperature with decreased PS.

Methods

Composite specimens (diameter: 5 mm, height: 2 mm) were tested isothermally at 22 °C (control), 40 °C, and 60 °C using light-exposures of 5 or 20 s (control). DC was accessed 5 min after light initiation by FTIR at the specimen bottom surface. Maximum and final PS were determined, also isothermally, for 5 min on a universal testing machine. Non-isothermal stress was also measured with composite maintained at 22 °C or 60 °C, and irradiated for 20 s at 30 °C. Data were analyzed using two-way ANOVA/Tukey and Student's t-test (α = 5%).

Results

Both DC and isothermal maximum stress increased with temperature (p < 0.001) and exposure duration (p < 0.001). Isothermal maximum/final stress (MPa) were 3.4 ± 2.0b/3.4 ± 2.0A (22 °C), 3.7 ± 1.5b/3.6 ± 1.4A (40 °C) and 5.1 ± 2.0a/4.0 ± 1.6A (60 °C). Conversion values (%) were 39.2 ± 7.1c (22 °C), 50.0 ± 5.4b (40 °C) and 58.5 ± 5.7a (60 °C). The reduction of light exposure duration (from 20 s to 5 s) with pre-heated composite yielded the same or significantly higher conversion (%) than control (22 °C, 20 s/control: 45.4 ± 1.8b, 40 °C, 5 s s: 45.1 ± 0.5b, 60 °C, 5 s s: 53.7 ± 2.7a, p < 0.01). Non-Isothermal conditions showed significantly higher stress for 60 °C than 22 °C (in MPa, maximum: 4.7 ± 0.5 and 3.7 ± 0.4, final: 4.6 ± 0.6 and 3.6 ± 0.4, respectively).Clinical significance: Increasing composite temperature allows for reduced exposure duration and lower polymerization stress (both maximum and final) while maintaining or increasing degree of conversion.