ADVANCES IN DENTAL PRODUCTS |
Curing performance of a new-generation light-emitting diode dental curing unit
KIM M. WIGGINS,
MARTIN HARTUNG, Ph.D.,
OLAF ALTHOFF, Ph.D.,
CHRISTINE WASTIAN and
SUMITA B. MITRA, Ph.D.
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ABSTRACT
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Background. Recent technological advances have resulted in the marketing of high-powered, or HP, battery-operated light-emitting diode, or LED, dental curing lights. The authors examine the curing efficiency and peak polymerization temperature, or Tp, of a new HP LED curing light.
Methods. The authors studied four visible light-curing, or VLC, units: HP LED (A), first-generation LED (B), conventional halogen (C) and high-intensity halogen (D). They determined the depth of cure, or DOC; adhesion; and Tp of three types of VLC resin-based composites after exposure to each light. The exposure times for units A and D were one-half those for units B and C.
Results. The power density of unit A was 1,000 milliwatts per square centimeter, which was comparable to that of unit D with turbo charge. The DOC and adhesion attained for all three resin-based composites after being light cured by unit A for a 10-second exposure time were equivalent to those after being light cured by unit D for a 10-second exposure time and to those after being light cured by units B and C for 20-second exposure times. The resin-based composites light cured by unit A attained significantly lower Tps than did those light cured by unit D at equivalent cure, or exposure, times and by unit C at twice the cure time.
Conclusions. The authors found that Unit A effectively cured the resin-based composites at one-half the cure time of units B and C and at the same time as unit D, while maintaining low Tp.
Clinical Implications. The battery-operated HP LED curing light might be an effective, time-saving alternative for clinicians to use in light curing resin-based composites.
The use of visible light-curing, or VLC, units for the polymerization of dental materials is an essential part of a contemporary dental practice. In recent years, many types of VLC lights have been marketed with a view toward making the polymerization process more efficient for dental practitioners. Dental VLC materials generally contain a diketone-type photoinitiator that absorbs light in the 400- to 500-nanometer range covered by blue light from the visible spectrum. The most common photoinitiator used is camphorquinone, or CPQ, which has a peak absorption maximum at 465 nm.
The battery-operated high-powered light-emitting diode curing light might be an effective alternative in light curing resin-based composites.
Tungsten halogen curing lights (often referred to simply as "halogen curing lights") are the most frequently used polymerization source in dental offices.1 The advantage of halogen curing lights is that they are derived from relatively low-cost technology. However, they have low efficiency and present several drawbacks. The light from a halogen curing light is produced by an electric current flowing through a thin tungsten filament.2 The filament functions as a resistor, and when it is heated by the current to temperatures of about 3,000 Kelvin, it becomes incandescent and emits electromagnetic radiation in the form of visible light, as well as a large amount of infrared radiation. The light emitted is not selective; therefore, when blue light is given off, the rest of the spectrum is unused and has to be filtered out.3 Because the filament generates high temperatures, the curing light has to be cooled by a ventilating fan that forces airflow through slots in the casing. This feature causes the handpiece to become cumbersome and noisy, and the slots can make it difficult to disinfect the handpiece completely. The high temperatures attained also can cause the bulb components to have limited lifetimes and requires frequent monitoring and replacement of the curing light’s bulb.4
Newer types of curing lights have been introduced to photopolymerize dental materials. Plasma arc curing, or PAC, lights have been introduced with the claim that they can decrease curing times significantly without a concomitant reduction in mechanical properties and performance of the cured materials.5 Scientific data, however, do not support this claim unequivocally.6 Typically, adequate curing results can be obtained only if the cure, or exposure, times are extended beyond those recommended by the devices’ manufacturers. In PAC lights, a high voltage is applied between two electrodes, resulting in a light arc between them. Like halogen curing lights, PAC lights also have low efficiency, and their power consumption is higher than that of halogen curing lights. PAC lights have high operating temperatures, which makes the use of ventilating fans necessary. In addition, the bulbs of PAC curing lights are located inside a tabletop base that uses rigid light-guiding cables. The lights’ spectral output is continuous and must be filtered to provide the useful blue light. The use of these high-intensity PAC lights can present a danger of increased heat generation in the cured dental materials, which may lead to pulpal damage.7,8
Light-emitting diode curing lights are lightweight, portable and highly efficient and have long life spans.
Laser lights also have been introduced. They have the advantage of having narrow spectral emission characteristics that may be well-adapted to dental photoinitiators. Because of their low energy conversion, they require a larger base for power supplies and cooling.
More recently, the use of light-emitting diodes, or LEDs, that produce blue light have been mentioned in conjunction with curing dental materials.9–11 LED technology is not new, and different versions of it have been used in many common applications, such as indicators in common electronic devices (for example, computer keyboards) and red or green laser pointers. Highly bright blue LEDs have been available only since the mid-1990s. A new semiconductor material system—the gallium nitride—forms the basis for the blue emission, as well as for the high efficiency of devices that use it. Both characteristics are essential requirements for their use in the dental curing application. In LEDs, a voltage is applied across the junctions of two doped semiconductors (n-doped and p-doped), resulting in the generation and emission of light in a specific wavelength range. By controlling the chemical composition of the semiconductor combination, one can control the wavelength range.12 The dental LED curing lights use LEDs that produce a narrow spectrum of blue light in the 400- to 500-nm range (with a peak wavelength of about 460 nm), which is the useful energy range for activating the CPQ molecule most commonly used to initiate the photopolymerization of dental monomers.
LED curing lights are lightweight, portable and highly efficient and have long life spans. Since a narrow band of light is emitted, there is no need for filter systems. Because there is no infrared emission, the curing lights have low amounts of wasted energy, leading to minimum heat generation, which obviates the need for cooling fans. The LED curing light’s power consumption is low, so batteries can be used to power it. The light output is consistent, there is no bulb to change and the service life is long. Studies have been conducted to demonstrate the potential of the blue LED technology for curing of dental materials. The earlier versions of blue LEDs were low in intensity and required the use of a large number of LEDs to provide adequate performance. In 1996, Fujibayashi and colleagues9 reported using 61 LEDs to achieve adequate cure of dental composites. Mills and colleagues11 needed 26 LEDs to do the same in their 1999 study. In their 2002 report on polymerization of a hybrid and a microfill resin-based composite using two commercial LED light-curing units (LumaCure, LumaLite, Spring Valley, Calif., and Versalux, Centrix, Shelton, Conn.), Dunn and Bush13 concluded that the light output of commercially available LEDs for resin-based composite polymerization still required improvement to be able to provide the same adequacy of cure as halogen light-curing units.
Since then, marked improvements in LED technology have resulted in the development of several types of commercial LED light-curing units that have improved intensity output, which results in a depth of cure, or DOC, equivalent to that of conventional halogen lights at about the same length of light exposure.14 Uhl and colleagues15 demonstrated that an LED light-curing unit—Elipar FreeLight (3M ESPE, St. Paul, Minn.)—that had an array of 19 LEDs in its first version represented a viable alternative to halogen light-curing units for light polymerization of dental composites because it generated a generally lower temperature increase within the composite. These older versions of LED light-curing units had intensities of up to 400 milliwatts per square centimeter.
Further advancements in technology have made it possible for manufacturers to produce high-powered, or HP, LED lights. A number of HP LED lights have been marketed recently that claim to reduce curing times.16,17 To achieve this reduction in curing times, this newer generation of curing lights have incorporated the latest advancements in HP LEDs so that they are capable of delivering a power density of about 1,000 mW/cm2. Since all of the spectral output of the LEDs is concentrated in the blue wavelength range, more efficient curing should be possible with the HP LED lights, resulting in reduced curing time compared with the first LED lights and conventional halogen lamps. Thus, they would be comparable to HP or high-intensity halogen curing lights. At the same time, they are lightweight and portable and have long life spans, like the first-generation LED curing lights.
We measured the depth of cure of three visible light–cured dental filling materials and the interfacial adhesion of these materials to dental hard tissue using a common bonding agent and each of the four curing lights studied.
We conducted a study to assess the effectiveness of a new HP LED curing light (unit A) and compare it with a first-generation LED curing light (unit B), a conventional halogen curing light (unit C) and a high-intensity halogen curing light (unit D). We measured the DOC of three VLC dental filling materials and the interfacial adhesion of these materials to dental hard tissue using a common bonding agent and each of the four curing lights. We also compared the temperature rise caused by the curing of a composite by the HP LED curing light with those generated by the other three VLC units. We tested the following hypotheses:
- – The curing efficiency of the HP LED curing light (unit A) would be equivalent to those of the conventional LED curing light (unit B) and the conventional halogen curing light (unit C) at one-half the cure time.
- – The curing efficiency of unit A would be equivalent to that of the high-intensity curing light (unit D).
- – The peak polymerization temperature, or Tp, reached by the composites cured by units A and B would be lower than that of units D and C, respectively.
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MATERIALS AND METHODS
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Light-curing units.
Table 1
lists the VLC units we used in this study, their power densities and their exposure times. Unit A, Elipar FreeLight 2 (3M ESPE, St. Paul, Minn.), has a single HP LED, and unit B, Elipar FreeLight, has an array of 19 LEDs. Unit C is a conventional halogen light-curing unit (Elipar TriLight, 3M ESPE), and unit D is an HP halogen lamp (Optilux 501, KerrLab, Orange, Calif.) with turbo tip and boost mode. We obtained the units’ power densities (Table 1) and the spectral emission characteristics (Figure 1) using a calibrated fiber-optic spectrally resolving radiometer system (S2000 Miniature Fiber Optic Spectrometer, Ocean Optics, Dunedin, Fla., coupled to an integrating sphere).
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Figure 1. Absorption spectrum of the photoinitiator camphorquinone, or CPQ, and emission spectra of the curing lights. Total light intensity is equivalent to area under the emission curve for each light. Total useful light is the extent of overlap of the emitted light of a curing light with the absorption spectrum of the photoinitiator. The values given with the light-curing units are the units’ total power densities. mW/cm2: Milliwatts per square centimeter. nm: Nanometer.
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Resin-based composites.
We used representative examples of three dental filling composites—a microfill (Filtek A110, 3M ESPE), a hybrid (Filtek Z250 Universal Restorative, 3M ESPE) and a nanocomposite (Filtek Supreme, 3M ESPE)—in this study (Table 2, page 1475).
DOC measurement.
We measured DOC according to the procedure defined by the International Organization for Standardization 4049:2000 (E) for resin-based filling materials.18 We packed the filling material into a metal cylinder (4 millimeters diameter, 6 mm length) and cured it for the exposure time recommended by the manufacturer with units B and C or for one-half the recommended time with units A and D. After exposing the resin-based composite with the light-curing units for the times specified in Table 1
, we removed it from the mold and scraped away any uncured material using a plastic instrument. The DOC value we recorded was one-half the height of cured material after scraping back. We used a sample size of five for each resin-based composite for each of the light-curing units.
Adhesion measurement.
We determined the resin-based composites’ adhesion to bovine enamel by measuring shear bond strength using a total etch technique. We ground bovine teeth to enamel with a final 320-grit finish. We applied Scotchbond Etchant Gel (batch 2YR, 3M ESPE) for 15 seconds, and then rinsed the teeth with water and dried them. We applied Single Bond adhesive (batch 2HB, 3M ESPE) to the teeth as recommended by the manufacturer and dried and light cured the teeth for the times shown in Table 3. We placed each resin-based composite to 2 mm depth in the mold and cured it for the times shown in Table 3. Thus, the light-curing time for unit A was only one-half that of unit C. We stored the specimens in distilled water at 37 C for 24 hours. We measured bond strength in the shear mode using a wire loop with an Instron Universal testing machine (model 1123, Instron, Canton, Mass.) at a shear rate of 2 mm/minute. We used a sample size of six for each resin-based composite for each of the light-curing units. We conducted statistical analysis using analysis of variance, or ANOVA, at P < .05.
Tp measurement.
We measured Tp in vitro with a cavity consisting of an aluminum cylinder (2 mm height, 6 mm diameter) filled with resin-based composite material. We incorporated a thermocouple into the bottom of the cavity, and we recorded the temperature increase during the irradiation from the curing lights with a computer-based data acquisition system. We considered the maximum of the temperature rise to be the peak temperature. We light cured five samples of each material with each of the four curing lights, and we conducted statistical analyses (ANOVA, P < .05) to determine significant differences in Tp among the curing lights used. This setup allowed us to measure the amount of relative heat that was produced owing to the polymerization reaction of the resin-based composite sample, as well as the thermal effect due to the radiation from the curing lights. We did not interpret the absolute temperature values in terms of the real temperatures present during a clinical procedure, as the thermal capacity, heat transport and dissipation of a vital tooth may be completely different. The evaluation, however, allowed us to make relative comparisons of the amount of heat that a tooth, and in turn the pulp, had to handle with the different treatments.
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RESULTS
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DOC.
Figure 2 shows the DOC results for units C and B at 20-second cure times for the three resin-based composites. Figure 2 also shows the results of curing using unit A at 10-second cure times, as well as that of unit D at 10-second cure times. We performed statistical analysis using ANOVA for equality of medians at P < .05. We found no significant difference in DOC for all three types of resin-based composites tested using units A and D both at 10-second cure times. In all cases, there was no significant difference in the DOC obtained from unit A at 10 seconds and unit C at 20 seconds, while that obtained from unit B at 20 seconds was significantly lower than that of unit A.
Adhesion.
Table 4 shows the results of adhesion to enamel testing using the adhesive in the total etch technique and each of the three composites cured with the four lights. We recorded the cure time of the resin-based composites for each light. The adhesion values for all three resin-based composites showed no significant difference or greater results between samples cured with unit A and samples cured with each of the other three curing lights (ANOVA, P < .05).
Tp.
Figure 3 shows the results of Tp measurements. Table 5 shows the mean temperature and standard deviation. For each resin-based composite, the numbers with same superscript letters have mean values that are not significantly different from each other (ANOVA, P < .05). We found that the Tp for the nanocomposite and the hybrid were the highest when unit D was used at the 10-second cure time, though the average value was not significantly different from that obtained from unit C at the 20-second cure time. For the microfill, these Tp values were essentially the same. The resin-based composites cured by unit A attained a significantly lower (P < .05) Tp than that reached by unit D at an equivalent 10-second cure time. At the 20-second cure time, unit B produced a Tp that was 65 to 75 percent lower than that of unit C at the same cure time.
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DISCUSSION
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LED technology has advanced significantly since the original use of blue LEDs for curing dental composites.8–10 Unit A is one of the newest curing lights. In contrast to previous generations of LED lights, which used an array of LEDs (for example, there are 19 LEDs in unit B), it uses a single high-intensity blue LED that has a larger semiconductor crystal, which increases both the illuminated area and light intensity with an output of 1,000 mW/cm2. An efficient optical arrangement is required for the delivery of the high-intensity light to the light guide to ensure optimum polymerization. For this, a conical reflector consisting of a highly reflective mirror film (3M Radiant Light Film, 3M) is used at the base of the light guide to ensure maximum light flux.17 This mirror film consists of multilayer polymer film technology, which serves as a perfectly reflective mirror that is only a few micrometers thick.19 Using this film allows for integration of unit A into a slender, ergonomically optimized handpiece that weighs only 220 grams (one-half pound), while providing high optical efficiency. Unit B’s handpiece weighs 320 g, unit C’s weighs 270 g, and unit D’s weighs 280 g.
We used three types of resin-based composites—microfill, hybrid, nanocomposite—to study the efficiency of light curing using unit A, which uses a single high-intensity LED as its energy source. All three resin-based composites use CPQ as the photosensitizer component, as well as a tertiary amine. We found that though there were small differences in curing between the three resin-based composite groups, the overall differences we observed when comparing the four light sources were independent of the type of composite used.
The guiding principle that dictates the efficiency of a photopolymerization reaction is how much light energy is absorbed by the photoinitiator in the system.
The guiding principle that dictates the efficiency of a photopolymerization reaction is how much light energy is absorbed by the photoinitiator in the system. The efficiency of a photopolymerizing device can be described by the total energy concept.3 This means that while light intensity is important, the more important factor is how much of the emitted light effectively matches the absorption spectrum of the photoinitiator (total useful light). Figure 1 shows the light output from all four curing lights. It also shows the absorption spectrum of CPQ. Although the CPQ absorption curve constitutes the total range of light that can initiate a polymerization reaction, the highest probability of light absorption is at the peak maximum of 465 nm. Light at this wavelength is much more likely to start a photopolymerization reaction and, therefore, is more efficient than light at all other wavelengths. The spectral output curves for units C and D (halogen curing lights) were broad and a substantial portion of them were outside the CPQ curve. In contrast, both the spectral output curves for units A and B (LED curing lights) had sharp emission peaks centered around the CPQ absorption maximum of 465 nm, with 95 percent of the photons being emitted between 440 and 480 nm. This is why unit B, which has an intensity of 400 mW/cm2, provided DOC and adhesion values at 20-second cure time for the three resin-based composites comparable with those obtained from unit C, which has an intensity of 700 mW/cm2.
A recent survey showed that while the convenience of LED curing lights such as unit B was appreciated by clinicians, 60 percent said they preferred shorter cure times.16 Manufacturers have moved toward higher-intensity LED curing lights that have shorter curing times. Unit A, with its HP LED light source, has a light intensity of 1,000 mW/cm2, which is more than twice that of unit B (400 mW/cm2). The recommended cure time of unit A is one-half that of units B and C. Uhl and colleagues20 recently demonstrated that the DOC of a resin-based composite correlates with the curing efficiency of the light unit. In our study, we used DOC and adhesion of resin-based composite as measures of curing efficiency. The results of the DOC and adhesion testing indicated that the values for unit A at a 10-second cure time are equivalent to or exceed those obtained from units C or B at 20-second cure times. This supports our first hypothesis for all three resin-based composites. Our second hypothesis also was supported, since we found no significant difference in the DOC values and adhesion results for all three resin-based composites when we used units A and D at 10-second exposure times.
According to the total energy concept, a certain dose (intensity x time) of light is needed to adequately cure a specific material. Thus, if one wants to reduce the curing time of a standard halogen lamp (for example, unit C at intensity of approximately 700 mW/cm2), one would need to use a high-energy halogen light with an intensity of about 1,400 mW/cm2. This is what we saw for unit D, which has an intensity of 1,500 mW/cm2 and cures the resin-based composites in 10 seconds as efficiently as unit C does in 20 seconds. Unit B, which is a first-generation LED curing light with an intensity of 400 mW/cm2 at 20 seconds, provided DOC and equivalent adhesion results comparable with those of unit C at 20 seconds. Hence, to cut down unit B’s cure time by one-half, unit A (a HP LED curing light) would need to have an intensity of about 800 mW/cm2. The measured intensity for unit A was 1,000 mW/cm2, which was slightly higher than the required value, providing an added safeguard against undercuring.
An important factor to consider in regard to increased light intensity of the curing source is the heat generated in the resin-based composite being cured. If excessive heat is generated during the curing of the composite, it could be transmitted to the surrounding tissues and pulp, causing them damage. A low Tp is desirable. As we expected, in all cases, the lowest Tp value was that for unit B; it was significantly less in all instances from those of unit C, even though we used equivalent curing times and obtained similar DOC and adhesion values from both units. The total energy concept we described previously also explains why Tps for unit A were significantly lower than those of unit D at the same light 10-second exposure, even though the DOC and adhesion values were statistically equivalent in all cases. Thus, our third hypothesis also was upheld.
One might have expected that the higher-intensity LED used in unit A would cause substantial heat generation in the handpiece, requiring external cooling. However, a design feature of this unit obviates the need for external cooling fans. Heat generated by the LED is dissipated by a heat sink made of highly thermal conductive aluminum that is integrated in the housing of the unit. The high conductivity of this material ensures that a low LED temperature is maintained when the unit is operating for several minutes, which protects the LED’s longevity. When the unit is turned off, heat temporarily stored in the heat sink dissipates into the environment via interaction with the aluminum composite housing. This design means that fans or other means of air-cooling the device are not needed, which means that the HP LED curing unit (unit A) is lighter weight than the other light-curing units.
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CONCLUSIONS
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We found that unit A effectively cured three representative resin-based composites at 10-second cure times comparable with unit D with turbo charge, while maintaining lower Tp. All three null hypotheses we proposed were upheld by the results of our study. The design features of unit A provided us the option of using a lightweight, battery-powered portable curing light that combines time savings and curing efficiency without excessive heat generation.
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Dr. Mitra is the corporate scientist, 3M ESPE Dental Products, 3M Company, 260-2B-13, 3M Center, St. Paul, Minn. 55144, e-mail "sbmitra{at}mmm.com". Address reprint requests to Dr. Mitra.
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FOOTNOTES
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DISCLOSURE
The authors are employees of 3M ESPE Dental Products, St. Paul, Minn., and 3M ESPE AG, Seefeld, Germany. The study described here was conducted at both 3M ESPE locations.
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REFERENCES
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- Tarle Z, Meniga A, Knezevic A, Sutalo J, Ristic M, Pichler G. Composite conversion and temperature rise using a conventional, plasma arc, and an experimental blue LED curing unit. J Oral Rehabil 2002;29:662–7.[Medline]
- Council on Dental Materials, Instruments, and Equipment. Visible light-cured composites and activating units. JADA 1985;110:100–2.[Abstract]
- Althoff O, Hartung M. Advances in light curing. Am J Dent 2000;13(special issue):77D–81D.[Medline]
- Barghi N, Berry T, Hatton C. Evaluating intensity output of curing lights in private dental offices. JADA 1994;125:992–6.[Abstract]
- Burgess JO, Walker RS, Porche C, Rappold AJ. Light curing: an update. Compend Contin Educ Dent 2002;23:889–96.[Medline]
- Park SH, Krejci I, Lutz F. Microhardness of resin composites polymerized by plasma arc and conventional visible light curing. Oper Dent 2002;27:30–7.[Medline]
- Shortall AC, Harrington E. Temperature rise during polymerization of light-activated resin composites. J Oral Rehab 1998;25:908–13.[Medline]
- Hannig M, Bott B. In-vitro pulp chamber temperature rise during composite resin polymerization with various light-curing sources. Dent Mater 1999;15:275–81.[Medline]
- Fujibayashi K, Ishimaru K, Kohno A. A study on light activation units using blue light emitting diodes. J Jpn Dent Pres Acad 1996; 39(1):180–8.
- Fujibayashi K, Ishimaru K, Takahashi N, Kohno A. Newly developed curing unit using blue light-emitting diodes. Dent Jpn 1998;34: 49–53.
- Mills RW, Jandt KD, Ashworth SH. Dental composite depth of cure with halogen and blue light emitting diode technology. Br Dent J 1999;186:388–91.[Medline]
- Nakamura S, Mukai T, Senoh M. Candela-class high-brightness InGaN/AlGaN double-hetrostructure blue-light-emitting diodes. Appl Phys Lett 1994;64:1687–9.
- Dunn WJ, Bush AC. A comparison of polymerization by light-emitting diode and halogen-based light-curing units. JADA 2002; 133(3):335–41.[Abstract/Free Full Text]
- Hartung M, Kürschner R. Surface hardness and polymerization heat of halogen/LED-cured composites (abstract 1745). J Dent Res 2001;80(special issue):254.
- Uhl A, Mills RW, Jandt KD. Photoinitiator dependent composite depth of cure and Knoop hardness with halogen and LED light curing units. Biomaterials 2003;24(10):1787–95.[Medline]
- Clinical Research Associates. LED resin curing lights: 2002 update. CRA Newsletter 2002;26(3):1–3.
- Clinical Research Associates. LED curing lights: update part 2. CRA Newsletter 2002;26(10):1–2.
- ISO 4049:2000: Dentistry—Polymer-based filling, restorative and luting materials. Geneva, Switzerland: International Standards Organization; 2000.
- Weber MF, Stover CA, Gilbert LR, Nevitt TJ, Ouderkirk AJ. Giant birefringent optics in multilayer polymer mirrors. Science 2000;287(5462):2451–6.[Abstract/Free Full Text]
- Uhl A, Sigusch BW, Jandt KD. Second generation LEDs for the polymerization of oral biomaterials. Dent Mater 2004;20(1):80–7.[Medline]
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ABSTRACT
MATERIALS AND METHODS
