Light-curing considerations for resin-based composite materials: a review. Part I

There has been a continual advent of improved technologies in dentistry. Among these are the material sciences of resin-based composites (RBCs). Since the introduction of light-cured RBCs, the problem of polymerization shrinkage and the methods used to overcome this have concerned clinicians and researchers. Types of curing light and modes of curing have been shown to affect the degree of polymerization and related shrinkage of RBCs. This review, which is divided into two parts, discusses the contemporary light-curing units. Part I explores the evolution in light-curing units and different curing modes. Part II highlights the clinical considerations regarding light curing of RBCs that are important for achieving optimal curing and maximum polymerization of RBCs in a clinical setting.     

A study of temperature rise in the pulp chamber during composite polymerization with different light-curing units

AIM: The study compared pulp temperature rise during polymerization of resin-based composites (RBCs) using halogen and LED light-curing units (LCUs). METHODS AND MATERIALS: A total of 32 teeth extracted from patients aged 11-18 years were used in the study. Thermocouples placed on the roof of the pulp chamber using a novel 'split-tooth' method. In Group 1 a halogen LCU with a light intensity of 450 mW cm(-2) was used and in Group 2, an LED LCU with a light intensity of 1100 mW cm(-2) was used. The teeth were placed in a water bath with the temperature regulated until both the pulp temperature and the ambient temperature were stable at 37 degrees C. Continuous temperature records were made via a data logger and computer. The increase in temperature from baseline to maximum was calculated for each specimen during the curing of both the bonding agent and the RBC. RESULTS: The rise in pulp temperature was significantly higher with the LED LCU than with the halogen LCU for bonding and RBC curing (p<0.05). The major rise in temperature occurred during the curing of the bonding agent. During the curing of the RBC, rises were smaller. CONCLUSIONS: Curing of bonding agents should be done with low intensity light and high intensity used only for curing RBC regardless of whether LED or halogen LCUs are used.     

Comparison of temperature changes in the pulp chamber induced by various light curing units, in vitro

This study compared the temperature increase in a pulp chamber as a result of using various light-curing units during resin composite polymerization, and it determined the effect of remaining dentin thickness on temperature rise. A Class II occlusodistal cavity with a remaining dentin thickness of 2 mm was prepared in an extracted human mandibular molar. A 2-mm layer of fine hybrid resin composite was placed on the floor of the proximal box. A K-type thermocouple was inserted into pulp chambers filled with heat sink compound, and pulp chamber temperature rise (starting temperature: 37.0 +/- 0.1 degrees C) during polymerization of the composite was measured. The light-curing units tested included two halogen lights, Spectrum 800 and Elipar Trilight (Standard and Exponential mode); a light-emitting diode (LED, Elipar Freelight) and a plasma arc (Virtuoso, Xenon Power Arc). Irradiation time was 40 seconds for the halogen and LED lights and 3 seconds for the plasma arc light. Five measurements were carried out for every light-curing unit. The same experimental design was conducted after the cavity preparation was modified, leaving a 1-mm thick dentin layer. The Kruskal-Wallis and multiple comparison tests were used to evaluate the differences among the tested curing units. Mann Whitney-U tests were used to compare the mean temperature rise in each curing unit for different remaining dentin thicknesses. The increase in pulp chamber temperature ranged between 1.40-3.8 degrees C. The highest temperature rise was observed when using Elipar Trilight Standard mode, and the lowest temperature rise was observed with light emitting diode for both remaining dentin thicknesses. The only significant differences in temperature rise were observed between Elipar Trilight Standard mode and LED. No significant difference (p > 0.01) existed for the different modes of Elipar Trilight. A statistically significant higher temperature rise was observed within each curing unit at a depth of 1 mm compared to 2 mm. Although the tested light-curing units caused a temperature rise in the pulp chamber, none exceed the critical value of 5.5 degrees C.     

光照模式对双固化树脂粘接剂聚合程度的影响

目的研究不同光照模式对两种双固化树脂粘接剂聚合程度的影响。方法采用间歇光照、即刻光照、延迟光照和无光照4种不同固化方式,分别制备3MRelyXUnicem和DMGPermaCem2．0双固化树脂试件．24h避光保存后使用显微硬度仪测定样本表面硬度．三点弯曲试验测量挠曲强度．差示扫描量热仪进行玻璃化转变温度测量。数据采用协方差分析进行统计。结果两种树脂粘接剂各组表面硬度和挠曲强度由高到低依次为：间歇光照模式、即刻光照模式〉延迟光照模式〉无光照模式（P〈0．05）。差示扫描量热分析未检测到明显吸热峰,不能确定玻璃化转变温度。除无光照组外．3MRelvX Unicem表面硬度均显著高于DMG PermaCem2．0（P〈0．05）;DMG PermaCem2．0挠曲强度显著高于3MRelyX Unicem（P〈0．05）。结论间歇光照模式比延迟光照模式更有利于提高双固化树脂粘接剂聚合程度：双固化树脂粘接剂在无光照情况下聚合不全;与3MRelyX Unicem相比．DMGPernlaCem2．0抗压性能较差．但韧性较好．且无光照条件下聚合程度更高。     

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.     

The reliability of standardized flexure strength testing procedures for a light-activated resin-based composite.

OBJECTIVES: To investigate the differences in the reliability of three-point flexure strength (TFS) and bi-axial flexure strength (BFS) data of a dental resin-based composite (RBC) irradiated by a hand-held or an oven light-curing unit (LCU). METHODS: Three-point bar-shaped (25 x 2 x 2 mm3) and bi-axial disc-shaped (12 mm diameter, 2 mm thick) specimens of Filtek Z250 were polymerized utilizing either a hand-held (n = 20) or an oven-LCU (n = 20). The mean TFS and BFS, associated Weibull moduli and degree of conversion (DC) for each curing regime were obtained following 24 h immersion in a light-proof water bath maintained at 37 +/-1 degrees C. RESULTS: A significant decrease in TFS (129 +/- 15 and 127 +/- 13 MPa) compared with BFS (140 +/- 12 and 148 +/- 13 MPa) was identified for specimens irradiated with both LCU types (P < 0.001). The Weibull moduli of TFS data associated with the hand-held--was significantly decreased compared with the oven-LCU since confidence intervals did not overlap (7.5-9.4 and 9.5-10.6, respectively). In contrast, the Weibull moduli of the BFS data associated with either LCU were not significant (11.3-12.4 and 11.3-13.5). A significant decrease in the DC of three-point and bi-axial flexure specimens irradiated with the hand-held compared with the oven-LCU was reported (P = 0.031). CONCLUSIONS: The improved experimental reliability combined with the increased clinical relevance in specimen geometry of disc-compared with bar-shaped specimens may advocate bi-axial flexure testing methodology as the standard to assess the strength of light-activated dental RBCs. The differences in extent of polymerization of RBC specimens cured with either LCU were not consistent with an equivalent dose of light energy density. This phenomenon may be attributed to differences in polymerization efficiency associated with the quantity of useful light energy emitted from the hand-held--compared with the oven-LCU.     

Factors affecting polymerization of resin-based composites: A literature review

Aim

The aim of this review was to help clinicians improve their understanding of the polymerization process for resin-based composites (RBC), the effects of different factors on the process and the way in which, when controlled, the process leads to adequately cured RBC restorations.

Photocure attachment lens: its effect on polymerization of visible-light-cure resin composite

The attachment lens for a light-curing unit which disperses light over a larger area was investigated. The effect of polymerization on a composite material was compared with that obtained with a regular light-cured tip. It was found that for similar exposure times, the efficiency of curing was significantly reduced when this lens was used.     

Direct cuspal-coverage posterior resin composite restorations: A case report

The clinical success of direct composite restorations is the result of the correct use and performance of adhesive systems, resin composites and light curing systems. Total-etch adhesive systems and microhybrid resin composites have seen continuous improvement; various clinical techniques have been introduced to address polymerization shrinkage. Manufacturers have introduced sophisticated light-curing devices with the hope of improving performance. Direct resin bonded composites (RBCs) are becoming the first choice in many clinical situations. This article presents an experimental clinical technique that outlines the reconstruction of severely damaged posterior teeth missing multiple cusps; particular attention to incremental and curing techniques is adopted to complete each restoration.     

Investigation of polymerisation shrinkage strain, associated cuspal movement and microleakage of MOD cavities restored incrementally with resin-based composite using an LED light curing unit

OBJECTIVES: To investigate the polymerisation shrinkage strain, associated cuspal movement, degree of conversion (DC) and cervical gingival microleakage of mesio-occlusal-distal (MOD) cavities restored with four resin-based composite (RBC) filling materials placed incrementally using a light emitting diode (LED) light curing unit (LCU). METHODS: Standardised extensive MOD cavity preparations on extracted teeth were performed on 40 sound upper premolar teeth. Restoration of the teeth involved the placement of RBCs in eight increments with the appropriate bonding system before irradiation using an LED LCU. Buccal and palatal cusp deflections at each stage of polymerisation were recorded using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in a 0.2% basic fuchsin dye for 24 h, sagittally sectioned and examined for cervical microleakage. The DC was determined using a Fourier transform infra-red (FT-IR) spectrometer. RESULTS: No significantly difference (P=0.677) in cuspal movement was recorded for Z100 (13.1+/-3.2 microm) compared with Filtek Z250 (8.4+/-3.5 microm), P60 (7.3+/-3.8 microm) and Admira (6.7+/-2.7 microm). The LED LCU deflections were compared with a halogen LCU used in a conventional (Fleming GJP, Hall D, Shorthall ACC, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials of varying reported volumetric shrinkage values. Journal of Dentistry, 2005;33:139-146) and soft-start mode (Fleming GJP, Cara RR, Palin WM, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials cured using 'soft-start' polymerization. Dental Materials, 2006, , in press) and a significant reduction in cuspal movement was identified for curing type and material type (P<0.001 and P=0.002, respectively). No significant differences were noted between the four RBC materials investigated when the DC or microleakage scores were examined for the LED LCU. SIGNIFICANCE: It would appear that irradiation of RBCs using the LED LCU offered a significant reduction in associated cuspal movement in large MOD cavities. However, the microleakage scores following polymerisation were significantly increased with dye penetration into the pulp chamber from the axial wall evident in teeth restored with the LED LCU.     

Effectiveness of composite resin polymerization using light-emitting diodes (LEDs) or halogen-based light-curing units

The clinical performance of composite resins is greatly influenced by the quality of the light-curing unit used. The aim of this study was to compare the efficiency of a commercial light-emitting diode (LED) with that of a halogen-based light-curing unit by means of dye penetration of a micro hybrid composite resin. The composite resin evaluated was Filtek Z250 (3M Dental). The composite was filled into acrylic moulds that were randomly polymerized for 40 seconds by each of the light-emitting systems: light-emitting diode Ultraled (Dabi Atlante) or halogen light Degulux (Degussa Hülls) curing units. Immediately after polymerization, each specimen was individually immersed in 1 ml of 2% methylene blue solution at 37 degrees C +/- 2 degrees C. After 24 hours, the specimens were rinsed under running distilled water for 1 minute and stored at 37 degrees C +/- 2 degrees C at relative humidity for 24 hours. The composite resins were removed from the moulds and individually triturated before being immersed in new test tubes containing 1 ml of absolute alcohol for 24 hours. The solutions were filtered and centrifuged for 3 minutes at 4,000 rpm and the supernatant was used to determine absorbance in a spectrophotometer at 590 nm. To verify the differences between groups polymerized by LED or halogen light t-test was applied. No significant differences were found between composite resins light-cured by LED or halogen light-curing unit (p > 0.05). The commercially LED-based light-curing unit is as effective to polymerize hybrid composite resins as the halogen-based unit.     

Correlation between the beam profile from a curing light and the microhardness of four resins

ObjectiveTo demonstrate the effect of localized irradiance and spectral distribution inhomogeneities of one LED-based dental light-curing unit (LCU) on the corresponding microhardness values at the top, and bottom surfaces of four dental resin-based composites (RBCs), which contained either camphorquinone (CQ) alone or a combination of CQ and monoacylphosphine oxide (TPO) as photoinitiators.MethodsLocalized irradiance beam profiles from a polywave LED-based LCU were recorded five times using a laser beam analyzer, without and with either a 400 nm or 460 nm narrow bandpass filter placed in front of the camera lens. Five specimens of each of the four RBCs (two containing CQ/TPO and two containing CQ-only) were exposed for 5-, 10-, or 30-s with the light guide directly on the top surface of the RBC. After 24 h, Knoop microhardness values were measured at 45 locations across the top and bottom surfaces of each specimen. Microhardness readings for each RBC surface and exposure time were correlated with localized patterns of the LCU beam profile, measured using the 400 nm and 460 nm bandpass filters. Spearman rank correlation was used to avoid relying on an assumption of a bivariate normal distribution for the KHN and irradiance.ResultsThe local irradiance and spectral emission values were not uniformly distributed across the light tip. There was a strong significant positive correlation with the irradiance beam profile values from the LCU taken through bandpass filters and the microhardness maps of the RBC surfaces exposed for 5 and 10 s. The strength of this correlation decreased with increasing exposure time for the RBCs containing CQ only, and increased for the RBCs containing both CQ and TPO.ConclusionsLocalized beam and spectral distributions across the tip end of the light guide strongly correlated with corresponding areas of microhardness in both the top and bottom surfaces among four RBCs with different photoinitiator contents.SignificanceA light-curing unit with a highly inhomogeneous light output can adversely affect localized microhardness of resin-based composites and this may be a contributing factor for premature failure of a restoration.     

Comparison of light transmittance in different thicknesses of zirconia under various light curing units

PURPOSE

The objective of this study was to compare the light transmittance of zirconia in different thicknesses using various light curing units.

MATERIALS AND METHODS

A total of 21 disc-shaped zirconia specimens (5 mm in diameter) in different thicknesses (0.3, 0.5 and 0.8 mm) were prepared. The light transmittance of the specimens under three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) was compared by using a hand-held radiometer. Statistical significance was determined using two-way ANOVA (α=.05).

RESULTS

ANOVA revealed that thickness of zirconia and light curing unit had significant effects on light transmittance (P<.001).

CONCLUSION

Greater thickness of zirconia results in lower light transmittance. Light-emitting diodes light-curing units might be considered as effective as Plasma arc light-curing units or more effective than Quartz-tungsten-halogen light-curing units for polymerization of the resin-based materials.     

LED vs halogen light-curing of adhesive-precoated brackets

OBJECTIVE: To test the hypothesis that bonding with a blue light-emitting diode (LED) curing unit produces no more failures in adhesive-precoated (APC) orthodontic brackets than bonding carried out by a conventional halogen lamp. MATERIALS AND METHODS: Sixty-five patients were selected for this randomized clinical trial, in which a total of 1152 stainless steel APC brackets were employed. In order to carry out a valid comparison of the bracket failure rate following use of each type of curing unit, each patient's mouth was divided into four quadrants. In 34 of the randomly selected patients, designated group A, the APC brackets of the right maxillary and left mandibular quadrants were bonded using a halogen light, while the remaining quadrants were treated with an LED curing unit. In the other 31 patients, designated group B, halogen light was used to cure the left maxillary and right mandibular quadrants, whereas the APC brackets in the remaining quadrants were bonded using an LED dental curing light. The bonding date, the type of light used for curing, and the date of any bracket failures over a mean period of 8.9 months were recorded for each bracket and, subsequently, the chi-square test, the Yates-corrected chi-square test, the Fisher exact test, Kaplan-Meier survival estimates, and the log-rank test were employed in statistical analyses of the results. RESULTS: No statistically significant difference in bond failure rate was found between APC brackets bonded with the halogen light-curing unit and those cured with LED light. However, significantly fewer bonding failures were noted in the maxillary arch (1.67%) than in the mandibular arch (4.35%) after each light-curing technique. CONCLUSIONS: The hypothesis cannot be rejected since use of an LED curing unit produces similar APC bracket failure rates to use of conventional halogen light, with the advantage of a far shorter curing time (10 seconds).     

Curing efficiency of three different curing modes at different distances for four composites

This study investigated the influence of the different curing distances with three polymerization modes in terms of the surface microhardness of four resin composites as a function of energy density. A hybrid resin composite and flowable composite from each of two manufacturers were evaluated. The specimens were polymerized with one of two light-curing units: 1) Mini LED AutoFocus (1500 mW/cm2) with a fast curing mode, for which two polymerization regimens were used: a) one AutoFocus function cycle and b) two AutoFocus function cycles, and 2) LEDemetron I (950 mW/cm2) with a 20-second curing time. Polymerization was performed with the curing tip at a distance of 0 mm, 3.0 mm, 6.0 mm, and 9.0 mm from the top surface of the specimen, and the power density of each light source was measured with a spectrophotometer. All specimens were stored in distilled water in a light-proof container at 37°C for 24 hours, and their top and bottom surface Knoop hardness numbers were determined. Microhardness data were submitted to two-way analysis of variance and multiple comparisons with a Tukey test. All statistical analyses were performed at a significance level of 0.05. Though the curing lights tested exhibited a decrease in power density with distance, the rate and extent of power density loss were not the same. The polymerization mode and curing tip distance had a significant effect on the composite microhardness. There was also a significant interaction among polymerization mode, curing tip distance, and microhardness. The curing ability of the three polymerization modes was ranked in terms of the hardness percent values: the LEDemetron I > two cycles of the Mini LED AutoFocus > one cycle of the Mini LED AutoFocus.     

Effectiveness of composite cure associated with different light-curing regimes

This study investigated the use of various light-curing regimens with standardized light energy density on the effectiveness of cure of a visible light activated resin composite (Z100, 3M-ESPE). A light-cure unit (Variable Intensity Polymerizer (VIP), BISCO Inc) which permitted individual control over time and intensity, was used. The five light-curing modes investigated include Pulse Delay (PD), Pulse Cure (PC), Soft-start (SS), Turbo (T) and Control (C). Effectiveness of cure was established by measuring the top and bottom Knoop hardness of 2-mm thick composite specimens using a digital microhardness tester (n=5, load=500g; dwell time=15 seconds) immediately and at one-day post-polymerization. Data obtained was analyzed using one-way ANOVA/Scheffe's post hoc test and Independent Samples t-tests (p<0.05). Top KHN observed immediately after polymerization with C was significantly lower than PD. At one day post-polymerization, the top KHN obtained with C was significantly lower than PD, SS and T. No significant difference in bottom KHN was observed among the different curing modes immediately after curing. At one day post-polymerization, the bottom KHN obtained with C was significantly lower than SS and T. Regardless of curing regimens, top and bottom values at one day were significantly higher than those observed immediately after light polymerization. No significant difference in mean hardness ratio was observed among the different curing regimens immediately and one day later. Effectiveness of the cure at the bottom surfaces of composites may be increased by soft-start and turbo polymerization regimens.     

Pulp chamber temperature rise during curing of resin-based composites with different light-curing units.

AIMS: The purpose of the present study was to measure the intrapulpal temperature rise occurring during polymerisation of different shades of resin-based composites (RBCs), and two light-emitting diode (LED) units. METHODS: Seventy non-carious permanent molars, that had been extracted for orthodontic purposes and stored in 2% thymol for not more than four months, were selected. Patient age range was 11-18 years. Standard cavity preparation with standardised remaining dentine thickness and placement of thermocouples (TCs) was prepared using a novel split-tooth technique. Cavities were filled with one of two shades of RBC (A2 and C4, Filtek Z250, 3M ESPE, Seefeld, Germany), and cured with two LED high-intensity units (Elipar Freelight2, 3M ESPE, Seefeld, Germany; Bluephase, Ivoclar Vivadent, Schaan, Liechtenstein) and a conventional halogen light-curing unit (LCU) (Prismetics Lite 2, Dentsply, Weybridge, Surrey, UK) as a control. RESULTS: Pulp temperature rises during bonding [A2 results: H;2.67/0.48:E;5.24/1.32;B;5.99/1.61] were always greater than during RBC curing [A2 results: 2.44/0.63;E3.34/0.70;B3.38/0.60], and these were significant for both LED lights but not for the halogen control, irrespective of shade (Mann-Whitney test: 95% confidence limits). Temperature rises were at times in excess of the values normally quoted as causing irreversible pulp damage. Pulp temperature rises during bonding were higher with the LED lights than with the halogen control. There was no significant difference in temperature rise between the two LED lights when bonding but there was a significant difference between the two LED lights and the halogen control LCUs (Kruskal-Wallis Test: 95% confidence limits). CONCLUSIONS: The results support the view that there is a potential risk for heat-induced pulpal injury when light-curing RBCs. The risk is greater during bonding and with high energy, as compared to low-energy output systems. As the extent of tolerable thermal trauma by the pulp tissues is unknown, care and consideration should be given to the choice of LCU and the exposure time when curing RBCs, and especially during bonding.     

In-vitro pulp chamber temperature rise during composite resin polymerization with various light-curing sources.

OBJECTIVES: The purpose of this in vitro study was to measure the pulp chamber temperature increase induced during composite resin polymerization with various visible light-curing units. METHODS: A Class II cavity was prepared in an extracted molar tooth, leaving a dentin layer 1 mm thick between pulp chamber and proximal cavity wall. A 2 mm composite resin layer was applied to the proximal box and light-cured with the selected curing units: Heliolux II (H; 320 mW/cm2), QHL 75 (Q; 505 mW/cm2), Astralis 5 (A; 515 mW/cm2), Optilux 500 (O; 670 mW/cm2), Elipar Highlight (EH; 730 mW/cm2), ADT 1000 PAC (P; 1196 mW/cm2). Light-curing took place for 40 s (H, A, Q, O, EH), 5 and 10 s (P). Measurement of pulp chamber temperature changes (starting temperature: 37.0 +/- 0.1 degrees C) during polymerization was performed with a K-type thermocouple positioned at the pulp-dentin junction. Mean values were calculated from 10 measurements with each light-curing unit. ANOVA and Dunnett t-test were used for statistical analyses. RESULTS: Maximum temperature changes varied significantly depending on the light-curing unit used: 2.9 +/- 0.3 degrees C (H), 4.7 +/- 0.5 degrees C (A), 5.4 +/- 0.3 degrees C (P, 5 s), 5.6 +/- 0.4 degrees C (Q), 6.1 +/- 0.2 degrees C (EH, 2-step mode: 100 mW/cm2 over 10 s, 730 mW/cm2 over 30 s), 6.9 +/- 0.4 degrees C (EH), 7.3 +/- 0.3 degrees C (O), 7.8 +/- 0.9 degrees C (P, 10 s). SIGNIFICANCE: It is concluded that light-polymerization with curing units characterized by high energy output (A,EH,O,P,Q) causes significantly higher pulp chamber temperature changes as compared to the conventional curing light (H). Therefore, clinicians should be aware of the potential thermal hazard to the pulp which might result from visible-light curing of composite resins.     

Evaluation of a new curing light on the shear bond strength of orthodontic brackets

With the introduction of photosensitive (light-cured) restorative materials in dentistry, various methods were suggested to enhance their polymerization and to shorten the curing time including layering and the use of more powerful light-curing devices. The purpose of this study was to determine the effect of using a new light-curing apparatus that uses a light-emitting diode (LED) on the shear bond strength of an orthodontic adhesive. The new light-curing apparatus used in the study was UltraLume 2 (Ultradent USA, South Jordan, Utah) that has an 8-mm footprint and can simultaneously cure two orthodontic brackets. Forty teeth were etched with 37% phosphoric acid, washed and dried, and sealant applied, and then precoated brackets with the Transbond adhesive (APC II, 3M Unitek, Monrovia, Calif) were placed. The teeth were randomly divided into two groups according to the curing light used. In group I (control), 20 brackets were cured using an Ortholux (3M Unitek) halogen curing light for 20 seconds. In group II, 20 brackets were cured using the new LED light for 20 seconds. The findings indicated no significant (P = .343) differences in the shear bond strength between the Ortholux halogen light (5.1 +/- 2.5 MPa) and the UltraLume 2 LED light when the two groups were compared using Student's t-test (t = -0.961). In conclusion, the advantages of the new unit include the ability to cure two brackets at a time and a smaller light-emitting apparatus for the clinician to handle.