DOI: 10.1111/ipd.12102
Depth of cure of sealants polymerized with high-power light emitting diode curing lights BRANDON KITCHENS1, MARTHA WELLS2, DARANEE TANTBIROJN3 & ANTHEUNIS VERSLUIS4 1 Department of Pediatric Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, 2Department of Pediatric Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, 3Department of Restorative Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, and 4Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA
International Journal of Paediatric Dentistry 2015; 25: 79–86 Objective. To determine whether recommended
short curing times of three high-power light emitting diode (LED) curing lights are sufficient to polymerize sealant materials. Methods. Opaque-unfilled sealant (Delton LC Opaque), opaque-filled sealant (UltraSeal XT plus), and clear-filled sealant (FluroShield) were light cured in a covered slot-mold using the manufacturers’ shortest recommended curing times with three high-power LED lights (3-s VALO, 5-s Fusion, 10-s Smartlite). A 40-s cure with a quartz-tungsten halogen (QTH) light was used as control. Vickers hardness was measured 24 h after curing at the sealant surface and through the depth (0.5 mm
Introduction
Well-placed resin-based sealants have proved to be effective in preventing pit-and-fissure caries when the sealant remains intact1. Among others, adequate polymerization is a prerequisite for longevity and clinical success of a sealant. Resin-based materials with poor polymerization have increased cytotoxicity and leach more monomers2,3. Lower degree of conversion also adversely affects bond strength of dental adhesives and compromises marginal integrity4,5. Polymerization of light-cured sealants occurs when photoinitiators, most commonly camphoroquinone (CQ), absorb blue light with a wavelength in the region of 470 nm6. This absorption facilitates the conversion of low-viscosity monomers into a polymer Correspondence to: Martha Wells, 875 Union Ave, Memphis, TN 38163, USA. E-mail: [email protected]
increments) (N = 10). Results were analyzed with two-way ANOVA (pair-wise multiple comparisons, significance level 0.05). Results. The high-power LEDs did not cure the sealants as deep as the QTH. Delton LC Opaque showed the least depth of cure as hardness values beyond a depth of 0.5 mm were not measurable regardless of the curing light. Even for UltraSeal XT plus, when surface hardness was about the same with all lights, hardness decreased more rapidly with depth for the LEDs. FluroShield showed the slowest decline in hardness through the depth for all lights. Conclusions. Manufacturers’ recommendations for shortest possible curing time with high-power LEDs were not sufficient for adequate polymerization of the tested sealants.
matrix. The extent of light-initiated polymerization depends on light source intensity (power density), wavelength or spectral emission, exposure duration, and light penetration through the material7,8. Factors affecting light penetration include distance of the light source, shade or opacity, and thickness of the material9,10. Quartz tungsten halogen (QTH) curing lights, introduced in the 700 s, have proved to be effective and were the mainstay for nearly 30 years in dentistry11. Utilizing QTH curing lights with power density of around 400 mW/ cm2 and with exposure times of 40 s have been the standard for curing 2 mm thick composite12. These traditional QTH curing units, however, inherit some disadvantages. The QTH spectrum includes a broad range of wavelengths that contribute to heat buildup, even though a band-pass filter is used to allow only light between 400 and 550 nm to pass11,13. The light from QTH units also diminishes in intensity over time due to
© 2014 BSPD, IAPD and John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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degradation of the bulb, and if left unchecked, it could end up delivering less than the minimum required power density13. Advances in technology have led to the introduction of alternatives to the conventional QTH lights by using light-emitting diode (LED) technology. LED curing lights have a narrow spectral range (440–500 nm), require less operating power, generate less heat, cause less gingival/pulpal irritation, have long lasting bulbs, and are often cordless featuring rechargeable batteries8,14–16. A study showed that the emission peak of blue LED at 465 nm coincided with the absorption peak of camphoroquinone at 467 nm15, although early generation LED lights sometimes did not perform well compared with QTH when the material contained a photoinitiator that absorbs light at lower wavelengths than CQ16. Manufacturers are currently promoting and selling newer generation LED lights with high power/high intensity modes and a wider range of wavelengths. These ‘second generation’ LED units offer from 600 to 800 mW/ cm2, whereas the most recent LEDs on the market offer outputs up to 4000 mW/ cm2.17,18 High-power LEDs are claimed to cure resin-based materials within a few seconds19. These shorter curing times are especially advantageous for pediatric patients. Not only is the isolation technique for sealant placement demanding, but sealants must be adequately polymerized to reach their purported clinical properties before contamination occurs. Polymerization performance does not only depend on the curing light source, it also depends on the material to be cured. Although traditional resin systems have contained CQ, new photointiators, proprietary photoinitators, have been introduced and may absorb light energy in lower regions of the visible spectrum20. Besides the polymerization chemistry, sealant materials can be filled or unfilled and clear or opaque. Each property can affect its light-curing ability10,21. It remains to be determined whether highpower LED units with shorter curing times will cure all sealants sufficiently. The purpose of this study was to evaluate the depth of
cure of sealant materials cured with highpower LED units at manufacturers’ shortest recommended curing times. The depth of cure was determined by hardness measurements. Methods
Sealant materials and curing lights The ability of three high-power LED curing lights to cure sealants was examined for three different sealant materials. The sealant materials were (i) UltraSeal XT plus (Ultradent, South Jordan, UT, USA), a filled, fluoridereleasing, opaque sealant; (ii) Delton LC Opaque (Dentsply International, York, PA, USA), an unfilled opaque sealant; and (iii) FluroShieldâ VLC (Dentsply International, York, PA, USA), a filled, fluoride releasing, clear sealant. Sealant compositions are shown in Table 1. Light-curing units and curing durations used in the study are listed in Table 2. Sealants cured with the QTH unit for 40 s served as controls. The number of specimens was 40 for each sealant, with 10 specimens per group for each sealant/curing light combination (For example, 10 specimens of UltraSeal XT plus were cured with the VALO light, 10 with the Smartlite, 10 with the Fusion light, and 10 with the QTH light). Sealants were injected into a rectangular slot, approximately 2 9 2 9 5 mm in a plaster mold. The top of the slot was covered with an orange glass plate (Fig. 1a) to ensure that the curing light entered the slot only from the end of the slot, which was covered with a clear glass slip (0.15 mm thick). The sealants were cured for the manufacturer recommended minimum time (Table 2) with the light tip placed against the clear thin (0.15 mm) glass slip (Fig. 1b). After light-curing, any uncured sealant in the slot was removed (Fig. 1c), and the samples were stored in a dry and dark container at room temperature for 24 h. Depth of cure The extent of cure throughout the bulk of the sealant (‘depth of cure’) was determined by
© 2014 BSPD, IAPD and John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Sealant depth of cure
measuring microhardness. Hardness measurements have been shown to be a practical method to indirectly determine the degree of conversion for resin materials, and hardness Table 1. Sealants used in the study. Sealant & Composition*
Percentage
Function
81
profiles can thus be used as alternative indication for depth of cure22,23. Vickers hardness at 25 g load (MicrometTM 2103, Buehler, Lake Bluff, IL, USA) was measured at the end surface (0 mm) and at 0.5 mm intervals down the depth (i.e., length of the slot) of the sealant (Fig. 1c).
Type
Statistical analysis UltraSeal XT plus (Ultradent, South Jordan, UT, USA) Diurethane
Depth of cure of sealants polymerized with high-power light emitting diode curing lights BRANDON KITCHENS1, MARTHA WELLS2, DARANEE TANTBIROJN3 & ANTHEUNIS VERSLUIS4 1 Department of Pediatric Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, 2Department of Pediatric Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, 3Department of Restorative Dentistry, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA, and 4Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA
International Journal of Paediatric Dentistry 2015; 25: 79–86 Objective. To determine whether recommended
short curing times of three high-power light emitting diode (LED) curing lights are sufficient to polymerize sealant materials. Methods. Opaque-unfilled sealant (Delton LC Opaque), opaque-filled sealant (UltraSeal XT plus), and clear-filled sealant (FluroShield) were light cured in a covered slot-mold using the manufacturers’ shortest recommended curing times with three high-power LED lights (3-s VALO, 5-s Fusion, 10-s Smartlite). A 40-s cure with a quartz-tungsten halogen (QTH) light was used as control. Vickers hardness was measured 24 h after curing at the sealant surface and through the depth (0.5 mm
Introduction
Well-placed resin-based sealants have proved to be effective in preventing pit-and-fissure caries when the sealant remains intact1. Among others, adequate polymerization is a prerequisite for longevity and clinical success of a sealant. Resin-based materials with poor polymerization have increased cytotoxicity and leach more monomers2,3. Lower degree of conversion also adversely affects bond strength of dental adhesives and compromises marginal integrity4,5. Polymerization of light-cured sealants occurs when photoinitiators, most commonly camphoroquinone (CQ), absorb blue light with a wavelength in the region of 470 nm6. This absorption facilitates the conversion of low-viscosity monomers into a polymer Correspondence to: Martha Wells, 875 Union Ave, Memphis, TN 38163, USA. E-mail: [email protected]
increments) (N = 10). Results were analyzed with two-way ANOVA (pair-wise multiple comparisons, significance level 0.05). Results. The high-power LEDs did not cure the sealants as deep as the QTH. Delton LC Opaque showed the least depth of cure as hardness values beyond a depth of 0.5 mm were not measurable regardless of the curing light. Even for UltraSeal XT plus, when surface hardness was about the same with all lights, hardness decreased more rapidly with depth for the LEDs. FluroShield showed the slowest decline in hardness through the depth for all lights. Conclusions. Manufacturers’ recommendations for shortest possible curing time with high-power LEDs were not sufficient for adequate polymerization of the tested sealants.
matrix. The extent of light-initiated polymerization depends on light source intensity (power density), wavelength or spectral emission, exposure duration, and light penetration through the material7,8. Factors affecting light penetration include distance of the light source, shade or opacity, and thickness of the material9,10. Quartz tungsten halogen (QTH) curing lights, introduced in the 700 s, have proved to be effective and were the mainstay for nearly 30 years in dentistry11. Utilizing QTH curing lights with power density of around 400 mW/ cm2 and with exposure times of 40 s have been the standard for curing 2 mm thick composite12. These traditional QTH curing units, however, inherit some disadvantages. The QTH spectrum includes a broad range of wavelengths that contribute to heat buildup, even though a band-pass filter is used to allow only light between 400 and 550 nm to pass11,13. The light from QTH units also diminishes in intensity over time due to
© 2014 BSPD, IAPD and John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
79
80
B. Kitchens et al.
degradation of the bulb, and if left unchecked, it could end up delivering less than the minimum required power density13. Advances in technology have led to the introduction of alternatives to the conventional QTH lights by using light-emitting diode (LED) technology. LED curing lights have a narrow spectral range (440–500 nm), require less operating power, generate less heat, cause less gingival/pulpal irritation, have long lasting bulbs, and are often cordless featuring rechargeable batteries8,14–16. A study showed that the emission peak of blue LED at 465 nm coincided with the absorption peak of camphoroquinone at 467 nm15, although early generation LED lights sometimes did not perform well compared with QTH when the material contained a photoinitiator that absorbs light at lower wavelengths than CQ16. Manufacturers are currently promoting and selling newer generation LED lights with high power/high intensity modes and a wider range of wavelengths. These ‘second generation’ LED units offer from 600 to 800 mW/ cm2, whereas the most recent LEDs on the market offer outputs up to 4000 mW/ cm2.17,18 High-power LEDs are claimed to cure resin-based materials within a few seconds19. These shorter curing times are especially advantageous for pediatric patients. Not only is the isolation technique for sealant placement demanding, but sealants must be adequately polymerized to reach their purported clinical properties before contamination occurs. Polymerization performance does not only depend on the curing light source, it also depends on the material to be cured. Although traditional resin systems have contained CQ, new photointiators, proprietary photoinitators, have been introduced and may absorb light energy in lower regions of the visible spectrum20. Besides the polymerization chemistry, sealant materials can be filled or unfilled and clear or opaque. Each property can affect its light-curing ability10,21. It remains to be determined whether highpower LED units with shorter curing times will cure all sealants sufficiently. The purpose of this study was to evaluate the depth of
cure of sealant materials cured with highpower LED units at manufacturers’ shortest recommended curing times. The depth of cure was determined by hardness measurements. Methods
Sealant materials and curing lights The ability of three high-power LED curing lights to cure sealants was examined for three different sealant materials. The sealant materials were (i) UltraSeal XT plus (Ultradent, South Jordan, UT, USA), a filled, fluoridereleasing, opaque sealant; (ii) Delton LC Opaque (Dentsply International, York, PA, USA), an unfilled opaque sealant; and (iii) FluroShieldâ VLC (Dentsply International, York, PA, USA), a filled, fluoride releasing, clear sealant. Sealant compositions are shown in Table 1. Light-curing units and curing durations used in the study are listed in Table 2. Sealants cured with the QTH unit for 40 s served as controls. The number of specimens was 40 for each sealant, with 10 specimens per group for each sealant/curing light combination (For example, 10 specimens of UltraSeal XT plus were cured with the VALO light, 10 with the Smartlite, 10 with the Fusion light, and 10 with the QTH light). Sealants were injected into a rectangular slot, approximately 2 9 2 9 5 mm in a plaster mold. The top of the slot was covered with an orange glass plate (Fig. 1a) to ensure that the curing light entered the slot only from the end of the slot, which was covered with a clear glass slip (0.15 mm thick). The sealants were cured for the manufacturer recommended minimum time (Table 2) with the light tip placed against the clear thin (0.15 mm) glass slip (Fig. 1b). After light-curing, any uncured sealant in the slot was removed (Fig. 1c), and the samples were stored in a dry and dark container at room temperature for 24 h. Depth of cure The extent of cure throughout the bulk of the sealant (‘depth of cure’) was determined by
© 2014 BSPD, IAPD and John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Sealant depth of cure
measuring microhardness. Hardness measurements have been shown to be a practical method to indirectly determine the degree of conversion for resin materials, and hardness Table 1. Sealants used in the study. Sealant & Composition*
Percentage
Function
81
profiles can thus be used as alternative indication for depth of cure22,23. Vickers hardness at 25 g load (MicrometTM 2103, Buehler, Lake Bluff, IL, USA) was measured at the end surface (0 mm) and at 0.5 mm intervals down the depth (i.e., length of the slot) of the sealant (Fig. 1c).
Type
Statistical analysis UltraSeal XT plus (Ultradent, South Jordan, UT, USA) Diurethane
