Evaluating intensity output of curing lights in private dental offices

Light Polymerization through Glass-ceramics: Influence of Light-polymerizing Unit's Emitted Power and Restoration Parameters (Shade, Translucency, and Thickness) on Transmitted Radiant Power

Background

This in vitro study assessed light transmission through ceramic discs varying in shade, translucency, and thickness using light-polymerizing units with different radiant power/flux (RP) outputs.

Methods

Disc-shaped specimens (0.5 mm, 1.0 mm, and 2.0 mm) were made from high and low-translucency glass-ceramic ingots (IPS e.max Press) in shades A1 and A4, totaling 60 discs. Two light-polymerizing units with different power outputs were used, and their emission spectra were verified. The transmitted RP values for each ceramic specimen were measured and irradiance and radiant energy influx were calculated. Differences between the light-polymerizing units and the influence of the three ceramic parameters were evaluated using an independent-samples t-test and three-way analysis of variance (ANOVA) tests (α = 0.05).

Results

A statistically significant difference was observed in the mean transmitted RP values between the two light-polymerizing units. Furthermore, the three-way ANOVA test showed a significant effect of shade, translucency, and thickness, as well as a significant interaction between each pair of variables and all three variables on the transmitted RP (P < 0.05).

Conclusions

Despite the significant attenuation in the transmitted RP, especially in ceramics with higher shade chromaticity and thickness and lower translucency, the calculated minimal irradiance values for both light-polymerizing units (their emitted power ≥ 500 mW) were greater than the minimum recommended irradiance threshold (100 mW/cm2). However, the exposure duration needs to be increased to provide the resin with sufficient radiant exposure for adequate polymerization.

Effect of different curing times and distances on the microhardness of nanofilled resin-based composite restoration polymerized with high-intensity LED light curing units

Purpose

This study examined the effect of different distances and curing times on the microhardness (VHN) of nanofilled resin-based composite (RBC) restorations polymerized with high-intensity LED LCUs.

Materials and methods

Seventy-five RBC specimens (2 mm thickness and 5 mm diameter) were fabricated from Tetric-N-Ceram (Ivoclar Vivadent). Each of the 25 specimens was polymerized by means of one of three types of high-intensity LED LCUs: (B) Blue-Phase-G2 (polywave LED, Ivoclar Vivadent), (E) Elipar S10 ^TM (single-peak, 3 M ESPE), and (P) Planmica Lumion (single-peak, Mectron) at three different distances (0 mm, 2 mm, and 4 mm) at 20 sec, 40 s, and 60 sec. A microhardness tester (NOVA, Innovatest, The Netherlands) was used to measure the VHN from the top and bottom surfaces. Data for VHN were analyzed using mixed ANOVA, followed by post hoc analyses with p-values < 0.05.

Results

A significant difference was found in VHN between all three LED LCUs, where (B) specimens had the highest means, followed by (E) and (P). Bottom surface VHN values were reduced significantly (p < 0.05) compared to top surface values in all LCU types. With increasing distances up to 2 mm and 4 mm, VHN values with (E) and (P) were significantly reduced on the top and bottom surfaces (p < 0.05). When the curing times were increased for 40 and 60 sec, the VHN values were significantly improved (p < 0.05). Meanwhile, increasing the distance with (B) did not significantly reduce the VHN. Moreover, increasing the curing times did not significantly improve the VHN of the bottom surfaces.

Conclusion

High-intensity LCUs have variable effects on the surface (top/bottom) hardness of Tetric-N-Ceram nanofilled RBC restoration. With increasing distance, VHN was reduced; therefore, compensation with more curing time (2 mm/40 sec and 4 mm/60 sec) is highly recommended with Elipar S10 and Planmica Lumion LCUs to improve the material surface hardness.

Minimum Radiant Exposure and Irradiance for Triggering Adequate Polymerization of a Photo-Polymerized Resin Cement

This study aimed to establish the minimum radiant exposure and irradiance to trigger an adequate polymerization of a photo-polymerized resin cement. In total, 220 disc-shaped specimens (diameter of 10 mm and thickness of 0.1 mm) were fabricated using a photo-polymerized resin cement (Variolink N-transparent, Ivoclar Vivadent). To investigate the minimum radiant exposure, the specimens were polymerized with radiant exposures of 1, 2, 3, 4, 5, 6, and 18 J/cm² (n = 20). During polymerization, the irradiance was maintained at 200 mW/cm². To investigate the minimum irradiance, the specimens were polymerized with irradiances of 50, 100, 150, and 200 mW/cm² (n = 20). During polymerization, the radiant exposure was maintained at the previously determined minimum radiant exposure. The Vickers microhardness (HV) and degree of conversion (DC) of the carbon double bond of the specimens were measured to determine the degree of polymerization of the specimens. The results were analyzed using one-way analysis of variance (ANOVA) and Tukey’s test (p < 0.05). In the investigation of the minimum radiant exposure, the HV and DC of the specimens polymerized with a radiant exposure from 1 to 5 J/cm² were significantly lower than those with 18 J/cm² (all p < 0.05). However, no significant difference in HV and DC was found between the specimens polymerized with 6 J/cm² and 18 J/cm² (p > 0.05). In the investigation of the minimum irradiance, the specimens polymerized with an irradiance of 50 mW/cm² had significantly lower HV and DC than the specimens polymerized with an irradiance of 200 mW/cm² (p < 0.05). However, no significant difference in the HV and DC was found among the specimens cured with irradiances of 100, 150, and 200 mW/cm² (p > 0.05). In conclusion, the minimum radiant exposure and irradiance to trigger an adequate polymerization of the light-cured resin cement were 6 J/cm² and 100 mW/cm², respectively.

Types of polymerisation units and their intensity output in private dental clinics of twin cities in eastern province, KSA; a pilot study

Objectives

Light-cured resin-based composites (RBCs) are the preferred option to restore teeth. Dental light-curing units (LCUs) should deliver adequate light energy to ensure good mechanical properties, dimensional stability, and biocompatibility of the RBC. The aim of this study was to determine the types of LCUs and their intensity output in private dental clinics.

Methods

A form was developed to record information related to the type of curing lights and their intensity output. A total of 400 curing devices were evaluated using a digital radiometer in 58 private dental clinics. For each device, three separate 10-s readings were taken and the average was calculated. For quartz tungsten halogen (QTH) units, a light intensity below 300 mW/cm² was considered unsatisfactory, whereas for light-emitting diode (LED) units, a reading below 600 mW/cm² was considered unsatisfactory.

Results

Out of 400 curing lights, 354 were LEDs and 46 were QTH units. A total of 13% of the lights were considered unsatisfactory. Of the LED units, 12.4% had a light intensity of less than 600 mW/cm², whereas QTH had 17.3% units with an intensity of less than 300 mW/cm².

Conclusion

The frequency of LCUs showed a trend towards LED units in private dental clinics, whereas the mean intensity value from the LED was higher than that from QTH units. Overall, the radiometer is a good tool to assess the intensity output of LCUs.

Efficiency of light curing units in a government dental school

The light intensity of a light-curing unit is a crucial factor that affects the clinical longevity of resin composites. This study aimed to investigate the efficiency of light-curing units in use at a local governmental dental school for curing conventional and bulk-fill resin materials. A total of 166 light-curing units at three locations were examined, and the brand, type, clinic location, diameter of curing tip, tip cleanliness (using a visual score), and the output (in mW/cm² using a digital radiometer) were recorded. Only 23.5% of the units examined had clean tips, with the graduate student clinical area containing the highest percentage of clean tips. Further, tips with poor cleanliness score values were associated with significantly lower output intensities. A small percentage (9.4%) of units was capable of producing intensities higher than 1,200 mW/cm² and lower than 600 mW/cm² (7.6%). The majority of the low intensity units were located in the undergraduate student area, which also contained the highest number of units with intensities between 900 and 1,200 mW/cm². The output of all the units in service was satisfactory for curing conventional resin composites, and most units were capable of curing bulk-fill resin materials.

Intensity output and effectiveness of light curing units in dental offices

BACKGROUND

The aims of the study were measuring the light intensity of light curing units used in Qazvin's dental offices, determining the relationship between the clinical age of these units and their light intensity, and identifying the reasons for repairing them.

MATERIAL AND METHODS

In this cross-sectional study, the output intensity of 95 light curing devices was evaluated using a radiometer. The average output intensity was divided up into four categories (less than 200, 200-299, 300-500, and more than 500 mW/cm2). In addition, a questionnaire was designed to obtain information mainly about the type, clinical age, and frequency of maintenance of the units and the reasons for fixing them. Data were analyzed using Kolmogorov-Smirnov, chi-squared, and t-tests (p< 0.05) on SPSS 24.

RESULTS

A total of 95 light curing units were examined, with 61 (64.2%) of them being of the LED type and 34 (35.8%) of the QTH type. While average light intensity in LED units was significantly higher than in QTH devices, the two device types were not significantly different regarding desirable light intensity (i.e., ≥ 300 mw/cm2). A negative correlation was observed between clinical age and light intensity. In addition, bulb replacement in QTH devices was over three times as much as in LED units. Also, repairing QTHs was more than twice as much frequent as fixing LEDs. The most common reason for repair was the breakage of the tip of the device.

CONCLUSIONS

The light intensity of LED units is significantly higher than that of QTH devices, and the frequency of repairing in QTHs was significantly more than in LEDs. Furthermore, light intensity decreases with aging, and dentists should regularly monitor the conditions of light units. Key words:Light curing unit, radiometer, light intensity, dental equipment, dental offices.

The effect of interincisal opening, cavity location and operator experience on the energy delivered by a light-curing unit to a simulated dental restoration

BACKGROUND

Curing of resin-based composites depends on the delivery of adequate total energy, which may be operator dependent. Aim To determine the effect of interincisal opening, cavity location and operator experience on the total energy delivered to simulated cavity preparation sites.

DESIGN

Three cohorts were included: junior dental nurses, senior dental nurses and qualified dentists (N=5, each cohort). Each operator (participant) followed the same procedure and light-cured two simulated restorations in a MARC patient simulator using a Demi light-curing unit for 20 seconds in each of the following situations: left upper second molar (UL7), interincisal opening at both 25 mm and 45 mm; upper central incisor (UR1), interincisal opening at 45mm. The light energy delivered by each operator in each situation was recorded. Five readings for each operator were taken at each interincisal distance. Statistical comparisons of delivered energy (J/cm2) between interincisal openings, location and groups in the total energy delivered were performed using the Kruskal-Wallis nonparametric test: alpha = 0.05.

RESULTS

Less total energy was delivered to the posterior cavity at 25mm (12.0 +/- 5.3 J/cm2) than at 45mm (16.9 +/- 5.6 J/cm2) by all operators (P < 0.05). At 45 mm, less total energy was delivered to the posterior cavity compared to the anterior cavity (25.1 +/- 7.4 J/cm2; P < 0.05). There was no statistically significant difference between junior nurses and qualified dentists (P > 0.05) but there was a significant difference in the total energy delivered between senior nurses (20.1 +/- 7.8 J/cm2) and junior nurses (17.5 +/- 7.6 J/cm2) and between senior nurses and qualified dentists (16.6 +/- 8.7 J/cm2) (P < 0.05).

CONCLUSIONS

Interincisal mouth opening, location of the cavity and operator experience affected the total energy delivered to cavities in a simulated clinical environment.

Effect of emitted wavelength and light guide type on irradiance discrepancies in hand-held dental curing radiometers

The purpose of this study was to determine any discrepancies in the outputs of five commercial dental radiometers and also to evaluate the accuracy of these devices using a laboratory-grade spectroradiometer. The power densities of 12 different curing light sources were repeatedly measured for a total of five times using each radiometer in a random order. The emission spectra of all of the curing light sources were also measured using the spectroradiometer, and the integral value of each spectrum was calculated to determine the genuine power densities, which were then compared to the displayed power densities measured by the dental radiometers. The displayed values of power density were various and were dependent on the brand of radiometer, and this may be because each radiometer has a different wavelength sensitivity. These results cast doubt upon the accuracy of commercially available dental radiometers.

A survey of power density of light-curing units used in private dental offices in Changchun City, China

This study investigated power density and relevant information related to light-curing units used in private dental offices in Changchun City, China. The power density of 196 light-curing units used in private dental offices in Changchun City was measured using a simple random sampling method. Relevant information included the brand, type, years of operation, frequency of use, model numbers and types of light guide, resin buildup on the light guides, damage caused by the light guides, required maintenance of the curing lights, and ratio of the unit and chair number. There were 132 quartz tungsten halogen (QTH) units and 64 light-emitting diode units. The power density range was defined as 0-1,730 mW/cm(2). The mean power density was 453.1 mW/cm(2). The mean years of operation of the light-curing units were 3.96. The majority of dentists never tested the power density of the light-curing units and a considerable number of light guide surfaces showed resin buildup and damage. In Changchun City, the majority of light-curing units were QTH. Some units needed to be replaced due to aging. The majority of dentists were not aware that the light-curing units require periodic testing and maintenance. The data herein indicate the importance of periodic testing of the power density of light-curing units and timely replacement of the components and then guarantee the quality of medical services and their benefits to patients.

A clinical survey of the output intensity of 200 light curing units in dental offices across Maharashtra

AIM

The purpose of this study is to examine the intensity of light curing units and factors affecting it in dental offices.

MATERIALS AND METHODS

The output intensity of 200 light curing units in dental offices across Maharashtra were examined. The collection of related information (thenumber of months of use of curing unit, the approximate number of times used in a day, and presence or absence of composite build-ups) and measurement of the intensity was performed by two operators. L.E.D Radiometer (Kerr) was used for measuring the output intensity. The average output intensity was divided into three categories (<200 mW/cm(2), 200-400 mW/ cm(2)and >400 mW/cm(2)).

RESULTS

Among the 200 curing units examined, 81 were LED units and 119 were QTH units. Only 10% LED machines and 2% QTH curing units had good intensities (>400 mW/cm( 2)).

CONCLUSION

Most of the examined curing lights had low output intensity ranging from 200 to 400 mW/cm(2), and most of the curing units had composite build-ups on them.

Evaluation of Light Intensity Output of QTH and LED Curing Devices in Various Governmental Health Institutions

Evaluating the intensity of a light curing unit regularly prior to the application of tooth-colored restorative materials is essential to assure the quality of restorative procedures.

Influence of light curing units on failure of directcomposite restorations

Light polymerizable tooth colored restorative materials are most widely preferred for advantages such as esthetics, improved physical properties and operator's control over the working time. Since the introduction of these light polymerizable restorative materials, there has been a concern about the depth of appropriate cure throughout the restoration. Photopolymerization of the composite is of fundamental importance because adequate polymerization is a crucial factor for optimization of the physical and mechanical properties and clinical results of the composite material. Inadequate polymerization results in greater deterioration at the margins of the restoration, decreased bond strength between the tooth and the restoration, greater cytotoxicity, and reduced hardness. Therefore, the dentist must use a light curing unit that delivers adequate and sufficient energy to optimize composite polymerization. Varying light intensity affects the degree of conversion of monomer to polymer and depth of cure.

Evaluation of different LED light-curing devices for bonding metallic orthodontic brackets

The aim of this study was to assess the influence of different light-emitting diodes (LED) light-curing devices for bonding orthodontic brackets, using the shear bond strength and analysis of adhesive remnant index (ARI). Crowns from 60 bovine incisors received brackets bonded with Transbond XT. Specimens were divided into 4 groups (n=15) according to the light-curing procedures: HL = control, halogen light; OR = Ortholux LED; UL = Ultraled XP, and RD = Radii LED. All light-curing procedures were performed for 40 s. Shear bond strength test was evaluated using an universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by ANOVA and Tukey's test. The ARI scores were evaluated with a stereoscopic magnifying glass and analyzed statistically by Kruskal-Wallis test. A significance level of 5% was set for all analyses. Shear bond strength means in MPa and standard deviations were 9.82 (3.28), 12.70 (3.35), 9.04 (2.80) and 11.22 (2.36) for HL, OR, UL and RD, respectively. OR presented the highest shear bond strength mean value. HL differed significantly (p<0.05) from Groups OR and RD. However, these groups did not differ significantly from each other (p>0.05). Regarding the ARI scores, no statistically significant difference was observed (p>0.05) among the groups. In conclusion, Ortholux LED and Radii LED units provided the highest values of bracket adhesive strength.

Cytotoxic effects of halogen- and light-emitting diode-cured compomers on human pulp fibroblasts

OBJECTIVE

The aim of this study was to determine the cytotoxic effects of three different compomers (Dyract AP, Compoglass, and Hytac) cured using a halogen light-curing unit (LCU) and a light-emitting diode (LED) LCU on human pulp fibroblasts.

METHODS

Specimens of three compomers were added to human pulp fibroblast cultures. Cytotoxicity was evaluated over 96 h using the agar overlay method.

RESULTS

All three compomers tested were found to be moderately cytotoxic to human pulp fibroblasts, regardless of whether they were cured using halogen or LED LCUs. The decolorization zone of Hytac was significantly larger than those of the other compomers tested (P < 0.05). Dyract AP and Compoglass specimens showed greater decolorization when cured with LED than with halogen LCUs (P < 0.05).

CONCLUSION

Compomers are potentially toxic to human pulp fibroblasts, and the type of curing unit may affect compomer toxicity.

Microleakage under Orthodontic Brackets Using High-Intensity Curing Lights

Objective: To compare the microleakage of the enamel-adhesive-bracket complex at the occlusal and gingival margins of brackets bonded with high-intensity light curing lights and conventional halogen lights.

Materials and Methods: Forty-five freshly extracted human maxillary premolar teeth were randomly separated into three groups of 15 teeth each. Stainless steel brackets were bonded in all groups according to the manufacturer's recommendations. Specimens (15 per group) were cured for 40 seconds with a conventional halogen light, 20 seconds with light-emitting diode (LED), and 6 seconds with plasma arc curing light (PAC). After curing, the specimens were further sealed with nail varnish, stained with 0.5% basic-fuchsine for 24 hours, sectioned and examined under a stereomicroscope, and scored for microleakage for the enamel-adhesive and bracket-adhesive interfaces from both the occlusal and gingival margins. Statistical analyses were performed using Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction.

Results: The type of light curing unit did not significantly affect the amount of microleakage at the gingival or occlusal margins of investigated interfaces (P &gt;.05). The gingival sides in the LED and PAC groups exhibited higher microleakage scores compared with those observed on occlusal sides for the enamel-adhesive and adhesive-bracket interfaces. The halogen light source showed similar microleakage at the gingival and occlusal sides between both adhesive interfaces.

Conclusions: High-intensity curing units did not cause more microleakage than conventional halogen lights. This supports the use of all these curing units in routine orthodontic practice.

Effect of Distance from Curing Light Tip to Restoration Surface on Depth of Cure of Composite Resin

Aims

While light-activating composite resins, the light tip may not always be close to the surface of the restoration. This may be intentional in an attempt to create a ramp cure. The aim of this study was to determine the effect of a range of separation distances between the light tip and the restoration surface on the depth of composite cure for different types of light-curing units with a broad range of outputs.

Methods

Three halogen light units, one plasma arc-curing (PAC) light unit and two light-emitting diode (LED) curing lights in clinical use were tested, and a total of 570 restorations cured in a two-part human tooth model at separations ranging from 0 to 15 mm. The tooth was disassembled and depth of cure determined using the scrape test ISO 4049. Light intensity was also measured at each separation distance for each light.

Results

The depth of cure was generally found to decrease as the separation distance increased for all lights at the various cure times. However, the effect of increasing the separation distance was less than anticipated. The depth of cure was also related to the light output.

Conclusions

Depth of composite cure was directly related to intensity and duration of light exposure and inversely related to distance of the light source from the surface for halogen and plasma lights. However, the effect of increasing the separation distance up to 15 mm was less than expected. Altering the separation distance in order to modify the polymerisation characteristics is unlikely to be effective.

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).

Change of shade by light polymerization in a resin cement polymerized beneath a ceramic restoration

OBJECTIVES

The aim of this in vitro study was to examine the effect of the color changes of a resin cement material (Variolink II) polymerized beneath a simulated ceramic restoration (IPS Empress II) by two different light polymerizing units.

METHODS

A conventional halogen light and a light emitting diode unit were used to polymerize resin cement with catalyst. A pressable ceramic block (10mm in diameter, 2 or 1mm in height) was used as an interface between the polymerizing light tip and resin cement. Colorimetric values of the specimens before and after polymerization were measured using a spectrophotometer (Easy Shade). The CIE L*a*b color system was used for the determination of the color difference. Differences between measurements were calculated as delta E*(ab). Repeated measurements analysis of variance (ANOVA) was used to analyze the data (polymerization of resin cement, polymerizing unit and ceramic thickness) for significant differences. The Tukey HSD test and paired two-tailed tests were used to perform multiple comparisons (alpha=.05).

RESULTS

L*a*b values of ceramic system were affected by the polymerization of resin cement (before and after) (P<.01). The a* value was affected by polymerization unit (P<.05), however L* and b* values were not affected by the light polymerization unit (P>.05). The b* value was affected by ceramic thickness (1 or 2mm) (P<.05), but L* and a* values were not affected by ceramic thickness (P>.05). The specimens polymerized beneath 1mm ceramic thickness with conventional halogen light induced a significantly higher color changes than any other specimen (P<.05).

CONCLUSIONS

The results of this in vitro study suggest that light polymerization of the resin cement (Variolink II) used in this study is an important factor for the color of the definitive restoration and should be considered during shade selection and fabrication.

Shear bond strength of metallic brackets photo-activated with light-emitting diode (LED) at different exposure times

The purpose of this study was to compare the shear bond strength of orthodontic metallic brackets photo-activated with two different light-curing sources at different exposure times: halogen light (XL 1500, 3M ESPE) and LED light (Ortholux, 3M Unitek). Sixty bovine permanent lower incisors were inserted into PVC tubes containing plaster. The buccal surfaces were cleaned with pumice and water, and then etched with 37% phosphoric acid gel. The XT Primer bonding agent (3M Unitek) was applied to the enamel surfaces and the metallic pre-coated brackets (Transbond APC II system, 3M Unitek) were attached to upper central incisors. The teeth were randomly divided into four groups (n=15). In Group I (Control), halogen light was used for 40 seconds, while in Groups II, III, and IV were light-cured with LED light unit for 40, 10, and 5 seconds, respectively. The teeth were stored in distilled water at 37°C for 24 hours. The brackets were submitted to shear bond strength test in universal testing machine (Instron) at a crosshead speed of 0.5 mm/minute. Shear bond strength means (MPa) were 4.87 for Group I; 5.89 for Group II; 4.83 for Group III, and 4.39 for Group IV. Tukey's test detected no statistically significant differences among the groups regarding the shear bond strength (p>0.05). Neither of the types of light-curing sources or exposure times influenced the shear bond strength of metallic brackets.

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.

Effective single-charge end point of cordless light-emitting diode light-curing units

INTRODUCTION

The purpose of this study was to evaluate the battery lives of cordless light-emitting diodes (LEDs) and their effect on orthodontic bracket bond strength.

METHODS

One hundred eighty-six metal orthodontic brackets were bonded to extracted molars. Two LED light-curing units (L. E. Demetron [SDS/Kerr, Orange, Calif] and Ortholux [3M Unitek, Monrovia, Calif]) were evaluated. Each light was used to bond 93 specimens. One bracket was bonded every 5 minutes until the battery ran out. The lights were activated for 20 seconds, then automatically turned off for 40 seconds every minute (33% duty cycle) without recharging. Bonded specimens were stored in water at 37 degrees C for 24 hours and then subjected to shear force with a universal testing machine until bracket failure.

RESULTS

Repeated measures ANOVA detected significantly weaker mean shear bond strength and fewer consecutive cures with the Ortholux compared with the L. E. Demetron light-curing unit. However, when the first 5 time points were excluded, there were no differences between the 2 lights, demonstrating that the lights performed similarly after the first 20 minutes of operation Just before battery failure, both lights still provided the same power density as at the beginning.

CONCLUSIONS

Both light-curing units provided adequate power density for up to 2 hours without recharging at a 33% duty cycle. There was no significant decrease in power in cordless LED light-curing units as the battery life approached its end point.

Curing effectiveness of a light emitting diode on dentin bonding agents

This study tested the hypothesis that dentin bonding agents (DBAs) cured with a light emitting diode (LED) light curing unit (LCU) would not show a statistically significant different dentin shear bond strength (DSBS) relative to a halogen LCU, when the LED and halogen LCUs had a supposedly similar irradiance. Five commercial DBAs were tested: ScotchBond Multipurpose, Single Bond, One Step, Clearfil SE Bond, and Adper Prompt. The LCUs used in this study were a VIP (Bisco) for the halogen light and an Elipar FreeLight (3M ESPE) for the LED. First, the emission spectrum and spectral irradiance of both LCUs were investigated. Next, the DSBS of the DBAs cured with each LCU was measured. Two-way analysis of variance was used to analyze whether there were differences in DSBS resulting from the type of LCU and DBA used. The halogen LCU showed a higher total irradiance value relative to the LED LCU, but the difference of spectral irradiance was reduced in the efficient wavelength ranges for camphoroquinone activation. Although the DBAs cured with both types of LCUs showed similar DSBS values, Clearfil SE Bond showed the highest DSBS value when cured with a halogen light. Therefore, the null hypothesis of this study was rejected, indicating that the curing effectiveness of the LED LCU on some DBAs can be lower than that of a halogen LCU in terms of bond strength.

Effect of light-curing method on marginal adaptation, microleakage, and microhardness of composite restorations

The objective of this study was to investigate the effects of different light-curing methods on microleakage, marginal adaptation, and microhardness of composite restorations. Slot-type preparations were made in bovine teeth, with gingival margins on dentin. Specimens were divided into 12 groups (n = 12) according to composite-light-curing unit (LCU) combinations. Three composites were used: Filtek Supreme, Herculite XRV, and Heliomolar. All restorations were placed using the same adhesive. Four LCUs were used: a quartz-tungsten-halogen (QTH) LCU (Optilux 501), a first-generation light-emitting diode (LED) LCU (FreeLight 1), and two second-generation LED LCUs (FreeLight 2 and Translux Power Blue). After finishing and polishing, specimens were subjected to mechanical load cycling (100,000 cycles). Gingival margin adaptation was determined as a function of gap formation using epoxy replicas. Microleakage was evaluated by measuring dye penetration across the gingival wall in cross-sectioned specimens. Microhardness was measured as Knoop Hardness number (KHN) at different occluso-gingival locations in cross-sectioned specimens. Data were analyzed for statistical significance (p = 0.05) using appropriate statistical tests. Marginal adaptation was affected by load-cycling in most specimens, but no significant differences were observed among composites and LCUs. Microleakage was not affected by LCU, except for Heliomolar specimens which when cured with Optilux 501 resulted in higher microleakage scores than those obtained with the other LCUs. For microhardness, Translux Power Blue generally produced the highest values and the FreeLight 1 produced the lowest. The performance of the second-generation LED LCUs generally was similar to that of the QTH control, and better than that of the first-generation LED unit.

Accuracy of LED and Halogen Radiometers Using Different Light Sources

PURPOSE

To determine the accuracy of commercially available, handheld light-emitting diode (LED) and halogen-based radiometers using LED and quartz-tungsten-halogen (QTH) curing lights with light guides of various diameters.

METHODS

The irradiance of an LED curing light (L.E. Demetron 1, SDS/Kerr, Orange, CA, USA) and a QTH curing light (Optilux 501, SDS/Kerr) were measured using multiple units of an LED (Demetron L.E.D. Radiometer, SDS/Kerr) and a halogen radiometer (Demetron 100, SDS/Kerr) and compared with each other and to a laboratory-grade power meter (control). Measurements were made using five light guides with distal light guide diameters of 4, 7, 8, 10, and 12.5 mm. For each light guide, five readings were made with each of three radiometers of each radiometer type. Data were analyzed with two-way analysis of variance/Tukey; alpha = 0.05.

RESULTS

In general, both handheld radiometer types exhibited significantly different irradiance readings compared with the control meter. Additionally, readings between radiometer types were found to differ slightly, but were correlated. In general, the LED radiometer provided slightly lower irradiance readings than the halogen radiometer, irrespective of light source. With both types of handheld radiometers, the use of the larger-diameter light guides tended to overestimate the irradiance values as seen in the control, while smaller-diameter light guides tended to underestimate.

CLINICAL SIGNIFICANCE

The evaluated LED or halogen handheld radiometers may be used interchangeably to determine the irradiance of both LED and QTH visible-light-curing units. Measured differences between the two radiometer types were small and probably not clinically significant. However, the diameter of light guides may affect the accuracy of the radiometers, with larger-diameter light guides overestimating and smaller-diameter guides underestimating the irradiance value measured by the control instrument.

Curing capability of halogen and LED light curing units in deep class II cavities in extracted human molars

Class II cavities were prepared in extracted lower molars filled and cured in three 2-mm increments using a metal matrix. Three composites (Spectrum TPH A4, Ceram X mono M7 and Tetric Ceram A4) were cured with both the SmartLite PS LED LCU and the Spectrum 800 continuous cure halogen LCU using curing cycles of 10, 20 and 40 seconds. Each increment was cured before adding the next. After a seven-day incubation period, the composite specimens were removed from the teeth, embedded in self-curing resin and ground to half the orofacial width. Knoop microhardness was determined 100, 200, 500, 1000, 1500, 2500, 3500, 4500 and 5500 microm from the occlusal surface at a distance of 150 microm and 1000 microm from the metal matrix. The total degree of polymerization of a composite specimen for any given curing time and curing light was determined by calculating the area under the hardness curve. Hardness values 150 microm from the metal matrix never reached maximum values and were generally lower than those 1000 microm from the matrix. The hardest composite was usually encountered between 200 microm and 1000 microm from the occlusal surface. For every composite-curing time combination, there was an increase in microhardness at the top of each increment (measurements at 500, 2500 and 4500 microm) and a decrease towards the bottom of each increment (measurements at 1500, 3500 and 5500 microm). Longer curing times were usually combined with harder composite samples. Spectrum TPH composite was the only composite showing a satisfactory degree of polymerization for all three curing times and both LCUs. Multiple linear regression showed that only the curing time (p < 0.001) and composite material (p < 0.001) had a significant association with the degree of polymerization. The degree of polymerization achieved by the LED LCU was not significantly different from that achieved by the halogen LCU (p = 0.54).

Polymerization efficiency of different photocuring units through ceramic discs

This study compared the ability of a variety of light sources and exposure modes to polymerize a dual-cured resin composite through ceramic discs of different thicknesses by depth of cure and Vickers microhardness (VHN). Ceramic specimens (360) (Empress 2 [Ivoclar Vivadent], color 300, diameter 4 mm, height 1 or 2 mm) were prepared and inserted into steel molds according to ISO 4049, after which a dual-cured composite resin luting material (Variolink II [Ivoclar Vivadent]) with and without self-curing catalyst was placed. The light curing units used were either a conventional halogen curing unit (Elipar TriLight [3M/ESPE] for 40 seconds), a high-power halogen curing unit (Astralis 10 [Ivoclar Vivadent] for 20 seconds), a plasma arc curing unit (Aurys [Degré K] for 10 seconds or 20 seconds) or different light emitting diode (LED) curing units (Elipar FreeLight I [3M/ESPE] for 40 seconds, Elipar FreeLight II [3M/ESPE] for 20 seconds, LuxOmax [Akeda] for 40 seconds, e-Light [GC] for 12 seconds or 40 seconds). Depth of cure under the ceramic discs was assessed according to ISO 4049, and VHN at 0.5 and 1.0 mm distance from the ceramic disc bottom was determined (ISO 6507-1). Medians and the 25th and 75th percentiles were determined for each group (n=10), and statistical analysis was performed using the Mann-Whitney-U-test (p < or = 0.05). The results showed that increasing ceramic disc thickness had a negative effect on the curing depth and hardness of all light curing units, with hardness decreasing dramatically under the 2-mm thick discs using LuxOmax, e-Light (12 seconds) or Aurys (10 seconds or 20 seconds). The use of a self-curing catalyst is recommended over the light-curable portion only, because it produced an equivalent or greater hardness and depth of cure with all light polymerization modes.

Effect of shorter polymerization times when using the latest generation of light-emitting diodes

INTRODUCTION

Recent studies have suggested that a 10-second cure time with a high-energy quartz-tungsten-halogen (QTH) or a light-emitting diode (LED) light might be adequate when bonding orthodontic brackets to tooth enamel. The purpose of this study was to evaluate the ability of the latest generation of QTH and LED light-curing units (LCUs) to bond orthodontic brackets to teeth at decreased polymerization times.

METHODS

Two LED LCUs (Ortholux LED, 3M Unitek, Monrovia, Calif; UltraLume LED 5, Ultradent Products, South Jordan, Utah) and a QTH LCU (Optilux 501, Demetron, Danbury, Conn) were evaluated. One hundred eighty metal orthodontic brackets were bonded to extracted human molars. The specimens were divided into 9 groups (3 lights and 3 curing times) of 20 teeth each. Each group was cured with 1 of the 3 lights for 20, 10, or 6 seconds. Thirty minutes after polymerization, the specimens were subjected to shear force on a universal testing machine until bracket failure.

RESULTS

Two-way ANOVA detected significant differences among the main effects of light type and cure time. Tukey post-hoc tests determined that brackets bonded by all light types had lower bond strengths with the 6-second cure than the 20-second cure (P < .001). The highest bond strengths were obtained with the Optilux 501 QTH LCU and the UltraLume LED 5 LCU at the longest cure time of 20 seconds.

CONCLUSIONS

It is recommended that orthodontic brackets be photopolymerized for at least 20 seconds with the QTH or the LED LCU before the archwires are engaged.

Influence of ceramic thickness and polymerization mode of a resin luting agent on early bond strength and durability with a lithium disilicate–based ceramic system

STATEMENT OF PROBLEM

Attenuation of polymerization light energy by translucent all-ceramic materials may result in insufficient polymerization of underlying resin luting agents and inadequate early bond strength and durability. There is little information regarding the selection of an appropriate polymerization mode for cementing translucent all-ceramic restorations.

PURPOSE

The purpose of this study was to evaluate the influence of ceramic thickness and polymerization mode on the early bond strength and bond durability of a lithium disilicate-based ceramic system.

MATERIAL AND METHODS

The occlusal surfaces of 120 extracted, intact, human third molars were sectioned to expose a flattened area of dentin. The surface was etched with 32% phosphoric acid, and a single-step adhesive (One-Step) was applied to the etched dentin surfaces. Ceramic specimens (Empress 2), 6 mm in diameter and 1 mm, 1.5 mm, or 2 mm thick (n=40 per group), were fabricated using fluoropolymer resin matrixes. Each specimen was ground flat. Following hydrofluoric acid etching and silane treatment, ceramic discs of each thickness were further divided into 2 groups (n=20 per group) and bonded to the dentin surfaces with a dual-polymerized resin luting agent (Illusion), either with a catalyst (dual polymerization) or without a catalyst (light polymerization). A shear bond test was performed after 10 minutes (n=10) or after 24 hours following 1000 thermal cycles between 5 degrees C and 55 degrees C and a dwell time of 30 seconds (n=10). Debonded dentin surfaces were examined with SEM. The data were analyzed with 3-way analysis of variance (ANOVA) (alpha=.05).

RESULTS

The shear bond strengths ranged between 13.2 +/- 4.1 MPa and 15.9 +/- 2.0 MPa. Three-way ANOVA revealed that ceramic thickness, polymerization mode, storage time, or combinations of these parameters did not influence shear bond strength. The location of failure for all specimens was adhesive, between the dentin surface and bonding agent.

CONCLUSION

Both light polymerization and dual polymerization provided similar early shear bond strengths for the lithium disilicate-based ceramic system (Empress 2). The bond strength was not dependent on the thickness of the ceramic material tested. Durability of the bond was similar for both of the polymerization modes.

Effect of LED curing on the microleakage, shear bond strength and surface hardness of a resin-based composite restoration

To determine the effect of Light emitting diode (LED) curing on dental resins, microleakage, shear bond strength and surface hardness of a dental composite cured with different LEDs were determined and compared with conventional halogen curing. For microleakage, Class V cavities were restored with Esthet-X, divided into groups, and exposed to one of the curing protocols (Elipar Freelight in soft start and standard modes; Ultra-Lume 2; Spectrum 800). Standard dye penetration tests were performed and the data summarised in a 2-way contingency table of observed frequencies. The Chi-square test was used (p<0.05) to test for significant differences between the lights. For surface hardness, samples of Esthet-X were exposed to the light-curing units (LCUs). Vickers hardness was determined on the upper and the bottom surfaces. Data was subjected to statistical analysis using ANOVA (p<0.05). Shear bond strength was determined using a push out method. Comparisons (ANOVA, p<0.05) were made between the different curing protocols. No significant difference in microleakage could be demonstrated between the different LCUs at the enamel side (p=0.60). At the dentin side only the Elipar Freelight (soft start), could significantly reduce microleakage (p<0.01). The hardness score for the halogen light was significantly lower than for the LED lights (p<0.01). The Spectrum 800 and the Elipar Freelight (soft start) have significantly higher shear bond strengths than the others (p<0.01). It was concluded that the LED source is more efficient for a comparable overall power output.

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 effect of infection-control barriers on the light intensity of light-cure units and depth of cure of composite

AIM

Dental curing lights are vulnerable to contamination with oral fluids during routine intra-oral use. This controlled study aimed to evaluate whether or not disposable transparent barriers placed over the light-guide tip would affect light output intensity or the subsequent depth of cure of a composite restoration.

METHODS

The impact on light intensity emitted from high-, medium- and low-output light-cure units in the presence of two commercially available disposable infection-control barriers was evaluated against a no-barrier control. Power density measurements from the three intensity light-cure units were recorded with a radiometer, then converted to a digital image using an intra-oral camera and values determined using a commercial computer program. For each curing unit, the measurements were repeated on ten separate occasions with each barrier and the control. Depth of cure was evaluated using a scrape test in a natural tooth model.

RESULTS

At each level of light output, the two disposable barriers produced a significant reduction in the mean power density readings compared to the no-barrier control (P<0.005). The cure sleeve inhibited light output to a greater extent than either the cling film or the control (P<0.005). Only composite restorations light-activated by the high level unit demonstrated a small but significant decrease in the depth of cure compared to the control (P<0.05).

CONCLUSION

Placing disposable barriers over the light-guide tip reduced the light intensity from all three curing lights. There was no impact on depth of cure except for the high-output light, where a small decrease in cure depth was noted but this was not considered clinically significant. Disposable barriers can be recommended for use with light-cure lights.

Effect of light guide tip diameter of LED-light curing unit on polymerization of light-cured composites

OBJECTIVE

The aim of this study was to investigate the influence of the diameter of the light guide tip on the polymerization of light cured composites when light guide tips of different diameters were used with an light-emitting diode (LED)-unit.

METHODS

An LED-unit was used with three light guide tips of 4, 8 and 10 mm diameter. Variations of light illuminance with irradiation time of each light guide tip were measured with a lux meter. Two Composites were exposed for 10, 20, 30 or 40 s. Thereafter, the depths of cure of the specimens were measured by the scraping method, and Knoop hardness was measured at 0.5 mm intervals.

RESULTS

The relative light illuminances from the 8 mm tip and 10 mm tip were 45 and 32% of that of the 4 mm tip. The depth of cure for the 4 mm tip was significantly greater than the others. At a depth of 2.0 mm, the 4 mm tip produced significantly greater hardness than the others. The depth of cure of composite irradiated for 10 s using the 4 mm tip corresponded to those of composites irradiated for 20 s using the 8 mm tip and for 30 s using the 10 mm tip. Thus, when the irradiation time was extended, Knoop hardness of the 4 mm tip was not significantly different from the others.

SIGNIFICANCE

This study showed that the polymerization of light cured composite was affected by the diameter of the light guide tip of the LED-unit.

Shear bond strength of orthodontic brackets bonded with light-emitting diode curing units at various polymerization times

Light emitting diode (LED) light-curing units have recently been used to polymerize resin-based orthodontic adhesives, and preliminary studies indicate their use has been successful. The purpose of this study was to evaluate the relationship between the shear bond strength of orthodontic brackets bonded to enamel and the duration of photopolymerization with LEDs and conventional quartz-tungsten-halogen light-curing units. Three LED light-curing units (GC e-light, GC America, Alsip, Ill; Elipar FreeLight, 3M ESPE Dental Products, St Paul, Minn; and UltraLume LED 2, Ultradent Products, South Jordan, Utah) and 1 halogen-based light-curing unit (Ortholux XT, 3M Unitek, Monrovia, Calif) were evaluated. Two hundred forty metal orthodontic brackets were bonded to extracted molars. Specimens were divided into 12 groups of 20 teeth each. Each group was cured with a different light-curing unit for 40, 20, or 10 seconds. The specimens were stored in water at 37 degrees C for 24 hours and then subjected to a shear force with a universal testing machine until bracket failure. Two-way ANOVA detected significantly weaker mean shear bond strength with the GC e-light at 10 and 40 seconds (P<.001) and higher mean shear bond strength for the UltraLume LED 2 at 40 seconds (P<.001). All experimental groups had laboratory mean shear bond strengths greater than 8 MPa, even with a 10-second cure.

Effect of LED curing on microleakage and microhardness of Class V resin-based composite restorations

BACKGROUND

Polymerisation shrinkage is a critical limitation of dental composites and may contribute to microleakage, postoperative pain, tooth fracture, and secondary caries. It has been shown that curing methods play a significant role in polymerisation shrinkage of light-cured dental resins. The purpose of this study was to investigate the effect of a LED curing light on microleakage as well as microhardness of a dental composite.

METHOD

For the microleakage test 32 Class V cavities were prepared in human premolars, conditioned with 35% phosphoric acid and treated with the bonding agent Prime & Bond NT. They were then incrementally filled with the composite Esthet-X and randomly divided into two groups of 16 each. The first group was cured by means of a Spectrum 800 set at 500 mW/cm2 for 40 seconds and the second group with the GC E-Light in standard mode. The specimens were thermo-cycled in a 0.5% basic fuchsin solution, sectioned and evaluated for dye penetration. For the microhardness test two groups of 6 specimens each were exposed using either the LED- or the Halogen curing unit. Vickers microhardness tests were performed immediately after curing as well as 24 hours later, on the top, and at the bottom surface.

RESULTS

At the dentine/cementum interface, significantly less microleakage (p=0.004) was found when the restorations were cured with the LED-unit. At the enamel interface no significant difference (p=0.340) in microleakage was found between curing methods. Immediately after exposure significantly harder surfaces were found at the top (p<0.001) as well as at the bottom (p<0.001), using the halogen unit (p<0.05).

CONCLUSION

Although a reduction in microleakage could be demonstrated exposing the composite restoration to an LED LCU, an effective microhardness ratio was not achieved.

Polymerization of resin composite restorative materials: exposure reciprocity

OBJECTIVE

To examine whether there is reciprocity between irradiation time and irradiance with regard to the mechanical properties of filled, resin composite restorative materials (RCs).

METHODS

Four visible light-cured RCs, all of shade A3, were used: Heliomolar Radiopaque (HR) and Tetric Ceram (TC) (Ivoclar, Schaan, Liechtenstein), Filtek Z250 (FZ) (3M, St Paul, MN, USA) and Prodigy condensable (PR) (Kerr, Orange, CA, USA). Bar specimens (1.0 x 1.5 x 16.0 mm(3)) were cured at irradiances (I) ranging from 25-1500 mW/cm(2) and irradiation times (t) of 1-3000 s. Six specimens at 250 combinations of t and I were prepared and stored in artificial saliva of pH 6, at 37 degrees C for 7d before performing three-point bend tests for flexural strength (F), flexural modulus (E) and total energy to failure (W). Contour plots of property value vs. t and I on log scales were prepared.

RESULTS

The contour plots showed three regions: unset at low I.t, a plateau corresponding to more or less full property development, and connecting ramp. The boundary between the plateau and the ramp suggests the minimum acceptable exposure. No practical lower limit to irradiance was detected, but there may be no benefit from increasing I beyond about 1,000 mW/cm(2). The slopes of the contours in the log-log plots provided a test of the hypothesis of reciprocity. These slopes were approximately -1.5 for HR, TC and PR; and approximately -1 for FZ, compared with the expected value of -1. The general hypothesis therefore fails. The existence of localized maxima in property values is further evidence of that failure, even for FZ.

SIGNIFICANCE

Dentists may use any lamp, including LED sources, and attain satisfactory results providing irradiation time is long enough. Manufacturers ought to supply a graph indicating the minimum acceptable exposure for each product for specified curing lamps. Calculations based on total energy delivered to guide irradiation protocols are invalid and do not recognize product behavior.

Knoop hardness depth profiles and compressive strength of selected dental composites polymerized with halogen and LED light curing technologies

After the first light-emitting diode (LED) light curing units (LCUs) became available commercially, a comparison of mechanical properties between materials polymerized with conventional halogen lamps and this new technology was required. This study, therefore, investigated the curing performance of two conventional commercial halogen LCUs (Translux CL, Spectrum800), a custom-made LED LCU prototype, and one of the first commercially available LED LCUs (LUXoMAX). The Spectrum800 was adjusted to a similar irradiance to the custom-made LED LCU prototype. Both technologies were compared by measuring compressive strength and Knoop hardness depth profiles for selected dental composites polymerized for 20 or 40 s. Four dental composites (Z100, Spectrum TPH, Solitaire2, and Definite) were used. Two of these composites (Solitaire2 and Definite) contain co-initiators in addition to the standard photoinitiator camphorquinone. In general, the material hardness obtained with the LUXoMAX was statistically significantly (p < 0.05) lower at the depths of 0.1, 1.0, 1.9, and 3.1 mm, for all composites and curing times, than for the other three LCUs. The LED LCU prototype achieved, with one exception, up to a depth of 1.9 mm a material hardness for the composites Z100, Spectrum TPH and Solitaire2 that was not statistically significant different (p < 0.05) from the hardness obtained with the halogen LCUs. At a greater depth (3.1 mm), however, the LED LCU prototype showed statistically significantly lower hardness values than the halogen units. The compressive strength test showed at a 95% confidence level that similar compressive strengths were achieved with the LCUs LUXoMAX and Spectrum800, and the Translux and LED LCU prototype.

Polymerization efficiency of LED curing lights

PURPOSE

The purpose of this study was to compare the curing efficiency of three commercially available light-emitting diode (LED)-based curing lights with that of a quartz tungsten halogen (QTH) curing light by means of hardness testing. In addition, the power density (intensity) and spectral emission of each LED light was compared with the QTH curing light in both the 380- to 520-nm and the 450- to 500-nm spectral ranges.

MATERIALS AND METHODS

A polytetrafluoroethylene mold 2 mm high and 8 mm in diameter was used to prepare five depth-of-cure test specimens for each combination of exposure duration, composite type (Silux Plus [microfill], Z-100 [hybrid]), and curing light (ZAP Dual Curing Light, LumaCure, VersaLux, Optilux 401). After 24 hours, Knoop hardness measurements were made for each side of the specimen, means were calculated, and a bottom/top Knoop hardness (B/T KH) percentage was determined. A value of at least 80% was used to indicate satisfactory polymerization. A linear regression of B/T KH percentage versus exposure duration was performed, and the resulting equation was used to predict the exposure duration required to produce a B/T KH percentage of 80% for the test conditions. The power densities (power/unit area) of the LED curing lights and the QTH curing light (Optilux 401) were measured 1 mm from the target using a laboratory-grade, laser power meter in both the full visible light spectrum range (380-780 nm) and the spectral range (between 450 and 500 nm), using a combination of long- and short-wave edge filters.

RESULTS

The emission spectra of the LED lights more closely mirrored the absorption spectrum of the commonly used photoinitiator camphorquinone. Specifically, 95% of the emission spectrum of the VersaLux, 87% of the LumaCure, 84% of the ZAP LED, and 78% of the ZAP combination LED and QTH fell between 450 and 500 nm. In contrast, only 56% of the emission spectrum of the Optilux 401 halogen lamp fell within this range. However, the power density between 450 and 500 nm was at least four times greater for the halogen lamp than for the purely LED lights. As a result, the LED-based curing lights required from 39 to 61 seconds to cure a 2-mm thick hybrid resin composite and between 83 and 131 seconds to adequately cure a microfill resin composite. By comparison, the QTH light required only 21 and 42 seconds to cure the hybrid and microfill resin composites, respectively.

CLINICAL SIGNIFICANCE

The first-generation LED-based curing lights in this study required considerably longer exposure durations than the QTH curing light to adequately polymerize a hybrid and a microfill resin composite.

Optical power outputs, spectra and dental composite depths of cure, obtained with blue light emitting diode (LED) and halogen light curing units (LCUs)

OBJECTIVE

To test the hypothesis that a prototype LED light curing unit, (LCU), a commercial LED LCU and a halogen LCU achieve similar cure depths, using two shades of a camphorquinone photoinitiated dental composite. To measure the LCUs' outputs and the frequency of the LED LCU's pulsed light, using a blue LED array as a photodetector.

DESIGN

Cure depth and light output characterisation to compare the LCUs.

SETTING

An in vitro laboratory study conducted in the UK.

MATERIALS AND METHODS

The LCUs cured A2 and A4 composite shades. A penetrometer measured the depth of cure. Analysis was by one-way ANOVA, two-way univariate ANOVA and Fisher's LSD test with a 95% confidence interval. A power meter and spectrograph characterised the LCUs' emissions. A blue LED array measured the pulsed light frequency from an LED LCU.

RESULTS

Statistically significant different LCU irradiances (119 mW/cm2 to 851 mW/cm2) and cure depths (3.90 mm SD +/- 0.08 to 6.68 mm SD +/- 0.07) were achieved. Composite shade affected cure depth. A blue LED array detected pulsed light at 12 Hz from the commercial LED LCU.

CONCLUSIONS

The prototype LED LCU achieved a greater or equal depth of cure when compared with the commercial LCUs. LEDs may have a potential in dentistry for light detection as well as emission.

Polymerization of orthodontic resin cement with light-emitting diode curing units

Commercially available light-emitting diode (LED) light-curing units recently have been introduced to the dental products market. No published studies have evaluated the adequacy of cure of commercially available LEDs. The purpose of this study was to compare the shear bond strength of orthodontic brackets bonded to teeth with conventional halogen-based light-curing units and commercially available LED curing units. Two LED light-curing units (LumaCure and VersaLux) and 2 halogen-based light-curing units (Optilux 501 and ProLite) were tested. One hundred standard metal orthodontic brackets were bonded to extracted human third molars with a light-cured adhesive system. The specimens were divided into 4 groups of 25 teeth each. In each group, the brackets were cured for 40 seconds with a different light-curing unit. The specimens were stored in water at 37 degrees C for 24 hours and then tested in shear with an Instron universal testing machine at a crosshead speed of 1 mm/min until the brackets debonded. One-way analysis of variance detected no differences in bond strength between the 4 groups (P =.78). Chi-square analysis detected no difference in the adhesive remnant index scores of the 4 groups (P =.89). Under the conditions of this study, the LED light-curing units bonded brackets to etched tooth enamel as well as the halogen-based light-curing units. Additional clinical studies are necessary before routine use of commercial LED light-curing units can be recommended.

High power light emitting diode (LED) arrays versus halogen light polymerization of oral biomaterials: Barcol hardness, compressive strength and radiometric properties

The clinical performance of light polymerized dental composites is greatly influenced by the quality of the light curing unit (LCU) used. Commonly used halogen LCUs have some specific drawbacks such as decreasing light output with time. This may result in a low degree of monomer conversion of the composites with negative clinical implications. Previous studies have shown that blue light emitting diode (LED) LCUs have the potential to polymerize dental composites without having the drawbacks of halogen LCUs. Since these studies were carried out LED technology has advanced significantly and commercial LED LCUs are now becoming available. This study investigates the Barcol hardness as a function of depth, and the compressive strength of dental composites that had been polymerized for 40 or 20s with two high power LED LCU prototypes, a commercial LED LCU, and a commercial halogen LCU. In addition the radiometric properties of the LCUs were characterized. The two high power prototype LED LCUs and the halogen LCU showed a satisfactory and similar hardness-depth performance whereas the hardness of the materials polymerized with the commercial LED LCU rapidly decreased with sample depth and reduced polymerization time (20 s). There were statistically significant differences in the overall compressive strengths of composites polymerized with different LCUs at the 95% significance level (p = 0.0016) with the two high power LED LCU prototypes and the halogen LCU forming a statistically homogenous group. In conclusion, LED LCU polymerization technology can reach the performance level of halogen LCUs. One of the first commercial LED LCUs however lacked the power reserves of the high power LED LCU prototypes.

[Microhardness of resins as a function of color and halogen light]

The aim of this study was to evaluate the influence of light intensity and the influence of the color of a composite resin on Knoop hardness. Samples were confected utilizing polyester matrices with 6 mm of diameter and 2 mm of depth. The matrices were filled with composite resin (Fill Magic - Vigodent), colors A3, B3, C3, D3 and I, and light-cured by means of an Elipar light-curing unit in three different light intensities: 450 mW/cm2, 800 mW/cm2 and an increasing intensity setup of 100 mW/cm2 to 800 mW/cm2. Ninety test specimens were confected, with the standard curing time of 40 seconds. The specimens were stored at 37 +/- 1 degrees C and immersed in distillate water. The Knoop test was carried out in superficial and deep areas of the specimens. The results revealed that there was no statistical difference (Tukey) between the tested colors. However, there was statistical difference between different light intensities. The authors concluded that the color of the composite resin did not influence Knoop hardness and that the progressive intensity setup led to the best Knoop hardness.

The use and maintenance of visible light activating units in general practice

AIM

The present study to investigate the use, care and maintenance of light units in everyday clinical practice was undertaken to complement light unit emission surveys, with a view to developing a protocol for light unit use and care in everyday clinical practice.

METHOD

The investigative work comprised a survey of selected practices in the Blackburn area with follow-up practice visits to examine light units in situ, and to glean additional information in respect of light unit use and care in the practice environment.

RESULTS

Completed questionnaires were returned by 54 of 77 selected practices--a 70% response, including information in relation to 164 light units. Subsequently, 100 (61%) of these light units were examined in 42 practices according to a standardised protocol. The use and care of the light units included in the study was found to be very variable. In addition to finding that 28 (28%) had inadequate light output (<300 mW/cm2), many of the light units were found to be damaged or repaired (47, 47%). Thirty five (35%) of the light units inspected were found to have varying amounts of material adherent to the light guide exit portal.

CONCLUSION

It is concluded that practitioners should address practical aspects of their increasing reliance on light units, and to this end, guidance is offered on visible light curing and the care and maintenance of light units.

Microdureza de resina composta: efeito de aparelhos e tempos de polimerização em diferentes profundidades

As propriedades das resinas compostas têm sido estudadas com freqüência, bem como os fatores que podem influenciar seu grau de polimerização. Diante da evolução desses materiais e da necessidade de buscarmos melhora do seu comportamento na cavidade bucal, objetivamos, por meio deste estudo avaliar a eficácia de dois aparelhos fotopolimerizadores do tipo pistola (de alta intensidade de luz), comparando com a de um aparelho a cabo (de baixa intensidade de luz), com tempos de exposição de 20 e de 40 segundos e em profundidades de 1 a 4 milímetros. Os testes avaliaram o grau de polimerização da resina por meio de testes de microdureza Knoop. Os resultados mostraram haver diferença estatisticamente significante entre os tempos, sendo que com 40 segundos a dureza foi maior que com 20 segundos para as 4 diferentes profundidades. Para o fator aparelhos, os dois aparelhos tipo pistola se comportaram superiores ao do tipo cabo Fibralux (Dabi Atlante), e entre eles, o XL 1500 (3M) promoveu dureza maior que o Optilight II (Gnatus) no tempo de polimerização de 40 segundos. As profundidades de 1, 2, 3 e 4 milímetros mostraram estatisticamente diferença entre si tendo sido encontrada maior dureza para as menores profundidades (p < 0,05).

Depth of cure and compressive strength of dental composites cured with blue light emitting diodes (LEDs)

OBJECTIVE

The primary objective of this pilot study was to test the hypotheses that (i) depth of cure and (ii) compressive strength of dental composites cured with either a light emitting diode (LED) based light curing unit (LCU) or a conventional halogen LCU do not differ significantly. The second objective of this study was to characterise irradiance and the emitted light spectra for both LCUs to allow comparisons between the units.

METHODS

Dental composite (Spectrum TPH, shades A2 and A4) was cured for 40 s with either a commercial halogen LCU or a LED LCU, respectively. The LED LCU uses 27 blue LEDs as the light source. The composites' depth of cure was measured for 10 samples of 4 mm diameter and 8 mm depth for each shade with a penetrometer. The results were compared using a Student's t-test. Compressive strengths were determined after 6 and 72 h, for six samples of 4 mm diameter and 6 mm depth for each shade after being polymerised for 40 s from each end of the mould. Groups were compared using a three way ANOVA.

RESULTS

The conventional halogen LCU cured composites significantly (p < 0.05) deeper (6.40 mm A2, 5.19 mm A4) than did the LED LCU (5.33 mm A2, 4.27 mm A4). Both units cured the composite deeper than required by both ISO 4049 and the manufacturer. A three way ANOVA showed that there were no significant differences in the compressive strengths of samples produced with either the LED LCU or the halogen LCU (p = 0.460). Significant differences in compressive strength of samples stored for 6 and 72 h (p = 0.0006) and of samples of different shades (p = 0.035) were found as confirmed by the three way ANOVA. The light spectra of both units differed strongly. While the halogen LCU showed a broad distribution of wavelengths with a power peak at 497 nm, the LED LCU emitted most of the generated light at 465 nm. The LED LCU produced a total irradiance of 350 mW cm-2 whereas the halogen LCU produced a total irradiance of 755 mW cm-2.

SIGNIFICANCE

The results showed that both units provided sufficient output to exceed minimum requirements in terms of composites' depth of cure according to ISO 4049 and the depth of cure and the composites' compressive strength stated by the manufacturer. Compressive strengths of dental composites cured under laboratory conditions with a LED LCU were statistically equivalent to those cured with a conventional halogen LCU. With its inherent advantages, such as a constant power output over the lifetime of the diodes, LED LCUs have great potential to achieve a clinically consistent quality of composite cure.

Dental composite depth of cure with halogen and blue light emitting diode technology

OBJECTIVES

To test the hypothesis that a blue light emitting diode (LED) light curing unit (LCU) can produce an equal dental composite depth of cure to a halogen LCU adjusted to give an irradiance of 300 mWcm-2 and to characterise the LCU's light outputs.

MATERIALS AND METHODS

Depth of cure for three popular composites was determined using a penetrometer. The Student's t test was used to analyse the depth of cure results. A power meter and a spectrometer measured the light output.

RESULTS

The spectral distribution of the LCUs differed strongly. The irradiance for the LED and halogen LCUs were 290 mWcm-2 and 455 mWcm-2, when calculated from the scientific power meter measurements. The LED LCU cured all three dental composites to a significantly greater (P < 0.05) depth than the halogen LCU.

CONCLUSIONS

An LED LCU with an irradiance 64% of a halogen LCU achieved a significantly greater depth of cure. The LCU's spectral distribution of emitted light should be considered in addition to irradiance as a performance indicator. LED LCUs may have a potential for use in dental practice because their performance does not significantly reduce with time as do conventional halogen LCUs.