Effect of delivering light in specific narrow bandwidths from 394 to 515nm on the micro-hardness of resin composites.

OBJECTIVES: This study investigated the wavelength-dependent photosensitivity of eleven resin composites (Admira A2, Heliomolar A2, Herculite XRV A2, Pyramid Dentin A2, Solitaire 2 A2, Z250 A2, AElite LS A2, Vit-l-escence A2, Tetric Ceram Bleach XL, Tetric Ceram A2, Pyramid Enamel Neutral). METHODS: Resin composites 1.6mm thick were exposed to narrow bandwidths of light at the following peak wavelengths: 394, 400, 405, 410, 415, 420, 430, 436, 442, 450, 455, 458, 467, 470, 480, 486, 493, 500, 505, and 515+/-5nm. A spectroradiometer was used to ensure that the same irradiance (mW/cm(2)) and total energy density (J/cm(2)) was delivered through each filter. For each resin composite, three specimens were exposed through each filter. The Knoop micro-hardness at the top and bottom of the composites was then measured. The wavelength-dependent photosensitivity of each resin composite was analyzed by plotting the mean hardness achieved at each wavelength. RESULTS: The composites responded variably when they received light through the narrow bandpass filters. Six resin composites had a single peak of wavelength-dependent photosensitivity at approximately 470nm. Four resin composites had two peaks of wavelength-dependent photosensitivity at approximately 470 and approximately 405nm. One resin composite had a single peak of wavelength-dependent photosensitivity at approximately 405nm and was only sensitive to light below 436nm. SIGNIFICANCE: Using light delivered through narrow bandpass filters is a convenient method to determine the wavelength-dependent photosensitivity of resins and can be used to predict the performance of dental curing lights.

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).

Effect of reduced exposure times on the microhardness of 10 resin composites cured by high-power LED and QTH curing lights.

PURPOSE: To compare the effect of reduced exposure times on the microhardness of resin composites cured with a "second-generation" light-emitting diode (LED) curing light and a quartz-tungsten-halogen (QTH) curing light. METHODS: Ten composites were cured with a LED curing light for 50% of the manufacturers" recommended exposure time or a QTH light at the high power setting for 50% of the recommended time or on the medium power setting for 100% of the recommended time. The composites were packed into Class I preparations in extracted human molar teeth and cured at distances of 2 or 9 mm from the light guide. The moulds were separated, and the Knoop microhardness of the composites was measured down to 3.5 mm from the surface. RESULTS: The LED light delivered the greatest irradiance at 0 and 2 mm, whereas the QTH light on the standard (high power) setting delivered the highest irradiance at 9 mm. According to distribution-free multiple comparisons of the hardness values, at 2 mm from the light guide the LED light (50% exposure time) was ranked better than or equivalent to the QTH light on the high power setting (50% exposure time) or on the medium power setting (100% exposure time). At 9 mm, the LED light was ranked better than or equivalent to the QTH light (both settings) to a depth of 1.5 mm, beyond which composites irradiated by the LED light were softer (p < 0.01). At both distances, the QTH light operated on the high power setting for 50% of the recommended exposure time produced composites that were as hard as when they were exposed on the medium power setting for 100% of the recommended exposure time. CONCLUSIONS: The ability to reduce exposure times with high-power LED or QTH lights may improve clinical time management.

Evaluation of a dual peak third generation LED curing light.

This study compared 3 light-emitting diode curing lights (UltraLume 5, FreeLight 2, LEDemetron I) with a quartz-tungsten-halogen light (Optilux 401) to determine which was the better at photopolymerizing 5 resin composites. The composites were 2 mm thick and were irradiated for the manufacturers' recommended curing times at distances of 2 mm and 8 mm from the light guide. The Knoop hardness at each of 22 points over a 10-mm diameter footprint at the top and bottom of the composites was used to compare the lights. The 4 curing lights and irradiation distances did not have the same effect on all the composites (P < .001). It was concluded that overall the UltraLume 5 dual peak third generation LED curing light was able to polymerize these 5 resin composites as well as or better than the other curing lights.

Knoop hardness of ten resin composites irradiated with high-power LED and quartz-tungsten-halogen lights.

This study compared a high-power light-emitting-diode (LED) curing light (FreeLight 2, 3M ESPE) with a quartz-tungsten-halogen (QTH) light (TriLight, 3M ESPE) to determine which was the better at photo-polymerising 10 resin composites. Class I preparations were prepared 4-mm deep into human teeth and filled with 10 different composites. The composites were irradiated for 50% or 100% of their recommended times using the LED light, and for 100% of their recommended times with the QTH light on either the high or medium power setting. Fifteen minutes later, the Knoop hardness of the composites was measured to a depth of 3.5 mm from the surface. When irradiated by the LED light for their recommended curing times, the Knoop hardness of all 10 composites stayed above 80% of the maximum hardness of the composite to a depth of at least 1.5 mm; three composites maintained a Knoop hardness that was more than 80% of their maximum hardness to a depth of 3.5 mm. Repeated measurements analysis of variance indicated that all the two-way and three-way interactions between the curing light, depth, and composite were significant (p < 0.01). To eliminate the choice of composite as a factor, an overall comparison of the lights was performed using the Kruskal-Wallis test and distribution free multiple comparisons of the ranked hardness values. The LED light, used for the composite manufacturer's recommended time, was ranked the best at curing the composites to a depth of 3mm (p < 0.01). The LED light used for 50% of the recommended time was not significantly different from the QTH light used for 100% of the recommended time on the high power setting.

Effects of resin composite composition and irradiation distance on the performance of curing lights.

This study determined the effect of using five resin composites and two irradiation distances to test the performance of dental curing lights. Three types of curing lights with similar spectral distributions, but each delivering a different power density, were used for irradiation times ranging from 3 to 60 s. Power densities were measured at 2 and 9 mm from the tip of the light guide. Five composites 1.6 mm thick and of the same shade were irradiated at 2 and 9 mm from the light guide with energy densities of 1.2-38.0 J/cm(2). The Knoop hardness at the top and bottom of the composite specimens was measured 15 min after irradiation and again after immersion in water at 37 degrees C for 24 h. There was a linear relationship between the hardness and the logarithm of the energy density received by the composite (r2 > 0.81). The analysis of variance showed that the composite, the side tested, the distance from the light guide, and the curing light/irradiation time combination all had a significant effect on the hardness (p < 0.01). Plots of the hardness at the bottom 15 min after irradiation by each light were generated for all the composites. These plots illustrated that the effects of the different curing light/irradiation time combinations on hardness were not the same for each composite. The effects of each curing light/time combination on hardness were also different at 2 and 9 mm from the light guide. In conclusion, when comparing the effects of different light sources on resin polymerization, several different composites should be irradiated at clinically relevant distances from the light guide. Using high-powered curing lights for 3 or 5 s did not deliver sufficient energy to cure the 1.6-mm thick specimens of composites used in this study.

Effect of disposable infection control barriers on light output from dental curing lights.

PURPOSE: To prevent contamination of the light guide on a dental curing light, barriers such as disposable plastic wrap or covers may be used. This study compared the effect of 3 disposable barriers on the spectral output and power density from a curing light. The hypothesis was that none of the barriers would have a significant clinical effect on the spectral output or the power density from the curing light. METHODS: Three disposable barriers were tested against a control (no barrier). The spectra and power from the curing light were measured with a spectrometer attached to an integrating sphere. The measurements were repeated on 10 separate occasions in a random sequence for each barrier. RESULTS: Analysis of variance (ANOVA) followed by Fisher's protected least significant difference test showed that the power density was significantly less than control (by 2.4% to 6.1%) when 2 commercially available disposable barriers were used (p < 0.05). There was no significant difference in the power density when general-purpose plastic wrap was used (p > 0.05). The effect of each of the barriers on the power output was small and probably clinically insignificant. ANOVA comparisons of mean peak wavelength values indicated that none of the barriers produced a significant shift in the spectral output relative to the control ( p > 0.05). CONCLUSIONS: Two of the 3 disposable barriers produced a significant reduction in power density from the curing light. This drop in power was small and would probably not adversely affect the curing of composite resin. None of the barriers acted as light filters.

Comparison of quartz-tungsten-halogen, light-emitting diode, and plasma arc curing lights.

PURPOSE: This study determined which light source was best at photopolymerizing five representative brands of resin composite. The hypothesis was that there would be no difference in the hardness of the composites when irradiated by any of the lights. MATERIALS AND METHODS: Six curing light/tip combinations were used to photopolymerize five resin composites. In accordance with the manufacturer's instructions, the PAC light was used for 3 s and the high intensity QTH light was used for 5 s. The other QTH and LED lights were used for 40 s. To represent the clinical environment, the samples were irradiated at a distance of 2 and 9 mm away from the tip of the light guide. The Knoop hardness was measured at the top and bottom of the composites after 15 min and again at 24 h. The hardness data were compared using a general linear model analysis with Sidak's adjustment for multiple comparisons with p < 0.01 as the level of significance. RESULTS: The 6 curing light/tip combinations had different effects on the hardness of the 5 composites (p < 0.01). The two LED lights could not cure the neutral shade of Pyramid Enamel in 40 s. As the distance increased from 2 to 9 mm, the decrease in hardness was not similar amongst the different light/tips and composite combinations (p < 0.0012). The curing light/tip combination which delivered the greatest total energy produced the hardest specimens. CONCLUSION: 1) The 6 curing light/tip combinations had different effects on the hardness of the 5 composites (p < 0.01). 2) Neither of the two LED lights used was able to adequately polymerize the five resin composites tested. 3) The QTH light, which delivered the greatest total energy, always produced the hardest resin composite. 4) When the distance of the composites from the light guides was increased, the effect on their hardness was not the same for all light/tip combinations. It is therefore not possible to predict the performance of a curing light at 9 mm based upon power density measurements or hardness data recorded when the tip of the light guide is 2 mm away.

Evaluation of a second-generation LED curing light.

BACKGROUND: Light-emitting diode (LED) curing lights offer advantages over quartz-tungsten-halogen (QTH) lights, but the first-generation LED lights had some disadvantages. PURPOSE: This study compared a second-generation LED light with a QTH light to determine which was better at photopolymerizing a variety of resin composites. METHODS: The ability of a LED light used for 20 and 40 seconds to cure 10 resin composites was compared with that of a QTH light used for 40 seconds. The composites were 1.6 mm thick and were irradiated at distances of 2 and 9 mm from the light guide. The Knoop hardness at the top and the bottom of each composite was measured at 15 minutes and 24 hours after irradiation. RESULTS: The different curing lights and irradiation times did not have the same effect on all of the composites (p < 0.01). For specimens analyzed 24 hours after irradiation, the LED light used for 20 seconds cured 5 of the composites as well as when the QTH light was used for 40 seconds (p > 0.01). When used for 40 seconds, the LED light cured 6 of the composites as well as when the QTH light was used (p > 0.01), and all 10 composites achieved more than 80% of the hardness produced with the QTH light. CONCLUSIONS: This LED light could not polymerize all of the composites as well as the QTH light. However, when used for 40 seconds, it cured more than half of the composites as well as when the QTH light was used, and all of the composites achieved a hardness comparable to that produced with the QTH light.

The effect of distance from light source on light intensity from curing lights.

PURPOSE: To investigate how light intensity changes as the distance increases from the tip of the light guide. MATERIALS AND METHODS: Ten different curing light/light guide combinations were used. Light intensity was measured at 0, 3, 6, and 10 mm from the tip of the light guide with a radiometer. Measurements were repeated in five separate trials and the mean light intensity +/- standard deviation was calculated. The fiber density was measured at the entrance and exit of all ten light guides and the light dispersion patterns were recorded. RESULTS: Light intensity decreased as distance increased for all lights tested; however, the rate and extent of this decrease was not similar for all lights (p < 0.0001). Turbo light guides exhibited a more rapid decrease in intensity as the distance increased than standard light guides. At 10 mm, all the turbo light guides had lost over 80% of their intensity recorded at 0 mm. CONCLUSION: 1. The rate and extent of the decrease in intensity is not similar among curing lights (p < 0.0001). 2. It is not possible to predict light intensity at 10 mm from measurements made at 0 mm. 3. Curing light manufacturers should state intensity over clinically relevant distances (0 to 10 mm).