Quartz Tungsten Halogen Units Research Articles

Performance of Multiple Light-curing Units used by Dental Students

Aim: To investigate the performance of multiple Light-curing Units (LCUs) of different manufacturers used in a dental student clinical setting. Background: Manufacturers claim that the irradiance values of the LCUs stay stable over time. However, this may not be accurate among the different units. Objective: This study investigated the performance in terms of the irradiance, radiant exposure, and DOC of multiple LCUs of different types used in a dental student clinical setting. Methods: Four different LCU were investigated (n=5 units/LCU manufacturer): three Light-Emitting-Diodes (LED) units (Demi Ultra, Mini LED, and E-Morlit) and one quartz-tungsten-halogen (QTH) (PolyluxII). Irradiance and radiant exposure were collected [Managing Accurate Resin Curing-Patient Simulator (MARC-PS)](n=5 readings/unit/tooth). Depth of Cure (DOC) was performed (ISO 4049:2009standards) using a micro-hybrid composite (n=5/unit). Data were analyzed using Kruskal-Wallis and ANOVA followed by Student-Newman-Keuls and Tukey post hoc methods, respectively (α=0.05). Results: Using the MARC-PS anterior and posterior teeth sensors, respectively, the mean irradiance for Demi Ultra was (1625.7±38.8) and (1250.4±25.2); Mini LED (1381.1±37.8) and (1058.1±27.3); E-Morlit (1831.1±294.7) and (1545.2±176.0); and Polylux II (932.4±368.5) and (840.4±353.4)mW/cm2. The radiant exposure range was 16-38 J/cm2 for all LCUs. LCUs’ mean DOC ranged from 2.9 to 3.1 mm. Significant differences in irradiance and radiant exposure values were detected among the multiple units and manufacturers. Significant differences in DOC values among the Demi Ultra and Polylux II units were detected. DOC met the standards except for onePolylux II unit. Conclusion: The irradiance and radiant exposure values were not the same among the different units, regardless of the manufacturers’ claim of the irradiance values stability over time. Polymerization was not compromised except for one QTH unit per the DOC measurements. Itis highly recommended to closely monitor LCUs used in dental student clinical areas due to the high demand in this type of setting.

The effect of curing time by conventional quartz tungsten halogens and new light-emitting diodes light curing units on degree of conversion and microhardness of a nanohybrid resin composite.

Background:Little is known about the relationship between the minimal light-curing time required for proper polymerization on various quartz–tungsten–halogen (QTH) and light-emitting diode (LED) light-curing units that have different light intensities.Aim:To evaluate the effects of curing time by QTH and LED light-curing units on the degree of conversion (DoC) and surface microhardness of a nanohybrid resin composite.Setting and Design:Experimental design.Materials and Methods:One hundred and twenty cylindrical specimens (4.0 mm in diameter, 2.0 mm thick) of shade A2 resin composite were prepared and polymerized with either QTHs or LEDs for 20 and 40 s. The DoC and the top and bottom surface microhardness were recorded.Statistical Analysis Used:Two-way analysis of variance, Tukey's test, and the t-test (α = 0.05) were used.Results:Surface microhardness and DoC values were affected by light intensity and curing time (P < 0.05). In terms of microhardness and DoC, LED groups gave significantly more values than QTH groups (P < 0.05).Conclusion:Curing time affected surface microhardness and DoC values of a nanohybrid resin composite in both conventional QTH and new LED light-curing units.

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

ObjectivesLight-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.MethodsA 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.ResultsOut 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.ConclusionThe 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.

Surface microhardness and depth of cure of composite resin cured with LED and Halogen units

The aim of this study was to evaluate the surface hardness and depth of cure ofresin composites cured with a quartz tungsten halogen (QTH) lamp or a light emittingdiodes (LED) unit.Swiss Tec (colten/whaledent AG, Switzerland) resin composite was placed in1, 2,3, and 4 mm depth and 8 mm width metallic molds and cured using the QTH light orthe LED unit for 40s.A total of 40 samples were made that divided into two groups according to thetype of curing light with 20 samples each. Each group was subdivided into 4 groupsaccording to the height of the mold with 5 samples each. Microhardnessmeasurements were performed using a calibrated Vickers indenter (100 g load and30s dwell time). Measurement of depth of cure was carried out by means of hardnessratio (bottom/top × 100).Results were analyzed by paired student's t-tests (P &lt; 0.05). Results showed thatLED exhibited higher microhardness values than QTH unit and the difference wasstatistically significant (P = 0.03) at the top surface and highly significant (P = 0.001)at the bottom surface.Further more the results revealed that LED produced samples with hardness ratio(depth of cure) higher than QTH unit and the difference was highly significant (P =0.004) at 3 mm depth. Both curing lights inadequately cure samples at 4 mm depth.Conclusions: Curing effectiveness of resin composite is better with LED thanQTH unit especially when the composite thickness exceed 2 mm.

Temperature changes under demineralized dentin during polymerization of three resin-based restorative materials using QTH and LED units.

ObjectivesLight-curing of resin-based materials (RBMs) increases the pulp chamber temperature, with detrimental effects on the vital pulp. This in vitro study compared the temperature rise under demineralized human tooth dentin during light-curing and the degrees of conversion (DCs) of three different RBMs using quartz tungsten halogen (QTH) and light-emitting diode (LED) units (LCUs).Materials and MethodsDemineralized and non-demineralized dentin disks were prepared from 120 extracted human mandibular molars. The temperature rise under the dentin disks (n = 12) during the light-curing of three RBMs, i.e. an Ormocer-based composite resin (Ceram. X, Dentsply DeTrey), a low-shrinkage silorane-based composite (Filtek P90, 3M ESPE), and a giomer (Beautifil II, Shofu GmbH), was measured with a K-type thermocouple wire. The DCs of the materials were investigated using Fourier transform infrared spectroscopy.ResultsThe temperature rise under the demineralized dentin disks was higher than that under the non-demineralized dentin disks during the polymerization of all restorative materials (p < 0.05). Filtek P90 induced higher temperature rise during polymerization than Ceram.X and Beautifil II under demineralized dentin (p < 0.05). The temperature rise under demineralized dentin during Filtek P90 polymerization exceeded the threshold value (5.5℃), with no significant differences between the DCs of the test materials (p > 0.05).ConclusionsAlthough there were no significant differences in the DCs, the temperature rise under demineralized dentin disks for the silorane-based composite was higher than that for dimethacrylate-based restorative materials, particularly with QTH LCU.

Thermographic analysis of temperature rise in the pulp chamber with LED and QTH light curing units: Anin vitroinvestigation

Aims: To compare the temperature rise in the pulp chamber with light-emitting diode (LED) and Quartz-Tungsten-Halogen (QTH) light curing units by infrared thermography. Materials and Methods: Class V cavity was prepared in 20 freshly extracted maxillary first premolars measuring 2 mm depth, 4 mm width, and 1 mm above the cement enamel junction. The samples were divided into two groups (n = 10). Cavity was etched with 37% phosphoric acid, rinsed and bonding agent was applied over the etched cavity surface on both the groups. In group I the samples were cured with LED curing unit, whereas group II were cured with QTH unit, which was followed by two incremental curing of composite. Thermal emission for QTH and LED (fast mode) light curing units were noted by Fluke Ti32 infrared thermography after 20 s bonding agent curing and first and second increment composite curing for 40 s each. Statistical Analysis: Data were analyzed with Student t-test and Friedman test using SPSS version 11.5 software. Results: The statistical analysis revealed that the temperature rise was significantly minimal with LED fast mode (Group I) in all stages of curing compared with QTH unit (Group II). There is significant rise of temperature during first incremental curing of composite, whereas insignificant increase of temperature during curing of second increment of composite (P < 0.001%). Conclusions: Temperature rise caused due to both QTH and LED light curing units does not result in irreversible pulpal damage and thermography is a viable means of quantifying the temperature changes during photo polymerization.

Effect of Energy Density on Low-Shrinkage Composite Resins: Diode-Pumped Solid State Laser Versus Quartz-Tungsten-Halogen Light-Curing Unit

The purpose of the present study was to evaluate the effect of energy density on the polymerization of low-shrinkage composite resins. The number of photons needs to initiate the polymerization process can be controlled by light intensity and curing time through the form of energy density. For the study, two methacrylate-based (Premise [PR] and Venus Diamond [VE]) and one silorane-based (Filtek LS [LS]) composite resins were light cured using a quartz-tungsten-halogen (QTH) light-curing unit (LCU) and a 473 nm diode-pumped solid state (DPSS) laser. Degree of conversion (DC), microhardness, refractive index, and polymerization shrinkage were evaluated under different energy densities. Through the study, the feasibility of DPSS laser as a light source was tested as well. LS showed the highest DC and refractive index both on the top and bottom surfaces, and the least polymerization shrinkage among the tested specimens. For the same or similar energy density, QTH and DPSS showed insignificant DC difference (p>0.05). On the other hand, for microhardness, except for one case at the bottom surface, QTH and DPSS showed significant difference (p<0.001). DPSS generated slightly lower polymerization shrinkage than that by QTH. DC, microhardness, refractive index, and polymerization shrinkage were linearly correlated with energy density. In most cases, there was a strong linear correlation among DC, mirohardness, and refractive index. The DPSS laser of 473 nm could polymerize low-shrinkage composite resins to the level that was achieved by the conventional QTH unit.

Temperature Increase at the Light Guide Tip of 15 Contemporary LED Units and Thermal Variation at the Pulpal Floor of Cavities: An Infrared Thermographic Analysis

In this study, a comprehensive investigation on the temperature increase at the light guide tip of several commercial light-emitting diode (LED) light-curing units (LCUs) and the associated thermal variation (ΔT) at the pulpal floor of dental cavities was carried out. In total, 15 LEDs from all generations were investigated, testing a quartz-tungsten-halogen (QTH) unit as a reference. The irradiance level was measured with a power meter, and spectral distribution was analyzed using a spectrometer. Temperature increase at the tip was measured with a type-K thermocouple connected to a thermometer, while ΔT at the pulpal floor was measured by an infrared photodetector in class V cavities, with a 1-mm-thick dentin pulpal floor. The relationship among measured irradiance, ΔT at the tip, and ΔT at the pulpal floor was investigated using regression analyses. Large discrepancies between the expected and measured irradiances were detected for some LCUs. Most of the LCUs showed an emission spectrum narrower than the QTH unit, with emission peaks usually between 450 and 470 nm. The temperature increase at the tip followed a logarithmic growth for LCUs with irradiance ≥1000 mW/cm(2), with ΔT at the tip following the measured irradiance linearly (R(2)=0.67). Linear temperature increase at the pulpal floor over the 40-second exposure time was observed for several LCUs, with linear association between ΔT at the pulpal floor and measured irradiance (R(2)=0.39) or ΔT at the tip (R(2)=0.28). In conclusion, contemporary LED units show varied irradiance levels that affect the temperature increase at the light guide tip and, as a consequence, the thermal variation at the pulpal floor of dental cavities.

Evaluation of light-curing units in rural and urban areas

To evaluate the distribution of light-curing units (LCU) used in an urban area (Riyadh) and a rural area (Kharj) of Saudi Arabia, and to compare their irradiance values. The study involved three dental centers in urban areas and two in rural areas, all of which were parts of a single healthcare institution providing dental services. The light outputs (power mW) from 140 LCUs were measured by laboratory-grade spectrometry, and the irradiance (mW/cm(2)) was calculated from the tip area of each LCU. The minimum acceptable irradiance outputs for the quartz-tungsten-halogen (QTH) and light-emitting diode (LED) units were set at 300 and 600mW/cm(2), respectively. The ages of these units and the protocol used to light-cure the resins were also determined. The total number of LCUs was 140, 112 (78%) in urban areas, and 28 (22%) in rural areas. In rural areas, only 7 of the 22 (32%) QTH units delivered irradiances greater than 300mW/cm(2) and were therefore considered clinically acceptable, whereas 4 of the 6 (66.7%) LED units delivered values greater than 600mW/cm(2). In urban centers, 43 of 61 (70.5%) LED units and 25 of 61 (49%) QTH units were considered clinically acceptable. Irradiance values for both QTH (P<0.01) and LED (P<0.05) units were significantly better in urban than in rural areas. Urban areas had a greater distribution of LCUs than rural areas. Overall, irradiance values were significantly higher in urban areas.

Analysis of the Effect of Dental Chair Light on the Knoop Hardness of Composite Resin While Light Curing with QTH and LED Light Units

ABSTRACT Dental chair lights have been known to rapidly polymerize lightcured composites beyond the point of workability. Often in our dental clinics we are advised to switch off the dental chair light while light curing of dental composites. The purpose of this study was to determine whether the dental chair light causes any effect on the degree of polymerization of light cured composites using the quartz tungsten halogen (QTH) and the light emitting diode (LED) light curing units (LCUs). Filtek Z350 composite samples of 2 × 5 mm were prepared in an acrylic mold. Four groups were made having 20 samples each. In group I and II light curing was done using QTH LCU with and without the dental chair light respectively. Similarly in group III and IV LED LCU was used. Microhardness was measured and compared using Knoop's hardness Test. Data was submitted to ANOVA and Tukey's test. Results showed that the average microhardness was significantly higher in group 4 (LED light curing with dental chair light on). Thus, it was concluded that the dental chair light can be left on while using QTH and LED LCU's during light curing of composite material. How to cite this article Parekh B, Sathe S, Hegde V. Analysis of the Effect of Dental Chair Light on the Knoop Hardness of Composite Resin While Light Curing with QTH and LED Light Units. World J Dent 2012;3(2):156-160.

Effect of different light sources in combination with a light-transmitting post on the degree of conversion of resin composite at different depths of simulated root canals

The aim of this study was to evaluate the degree of conversion (DC) of composite resin at different depths of simulated immature root canals using light-transmitting plastic post (LTPP) and three different light sources. Composite resin was packed into 60 black plastic cylinders 12mm in length with 4mm internal diameters to simulate immature root canals. LTPPs were inserted into half of the simulated canals and the other half acted as controls. Both the simulated canals with LTPPs and the controls were divided into three groups of 10, and each group was cured using either a quartz-tungsten-halogen (QTH), light-emitting diode (LED), or plasma arc (PAC) curing unit. Specimens were sectioned in three horizontally 24h after curing to represent cervical, middle, and apical levels. DC for each section of composite resin was measured using a Fourier transform infrared spectrophotometer, and data were analyzed using three-way anova and Tukey tests. At the cervical level, no significant differences were found between specimens cured using different light sources or between specimens with and without LTPPs (P>0.05). However, DC was significantly higher in specimens with LTPPs than in those without LTPPs at both the middle and apical levels (P<0.05). The mean DC of all specimens with LTPPs was significantly higher than that of specimens without LTPPs (P<0.05). PAC unit showed lower DC than QTH and LED units at both the middle and apical levels; however, the differences were not statistically significant (P > 0.05). The results of this study suggest that the use of a LTPP increased the DC of composite resin at the middle and apical levels of simulated immature root canals, but that DC was independent of type of light source.

Hardening of a dual-cure resin cement using QTH and LED curing units

ObjectiveThis study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light-emitting diode (LED) or quartz tungsten halogen (QTH) light source.Material and MethodsEighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons.ResultsIncreased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness.ConclusionsMean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.

Effects of High-Intensity Curing Lights on Microleakage under Bonded Lingual Retainers

To evaluate the effects of high-intensity light curing units (light-emitting diode [LED] and plasma arc curing [PAC]) on the microleakage of flexible spiral wire retainers (FSWRs) at the composite/enamel and composite/wire interfaces. Forty-five human mandibular incisor teeth were separated into three groups of 15 teeth. Multistranded PentaOne wire of .0215 inch diameter was bonded to enamel and was cured with three different light curing units: a quartz-tungsten-halogen (QTH) unit and two high-intensity units (ie, LED and PAC). A conventional halogen light served as the control. Samples were sealed with nail varnish, stained with 0.5% basic fuchsine, and sectioned. Transverse sections were evaluated under a stereomicroscope and were scored for microleakage for the composite/enamel and composite/wire interfaces. Statistical analysis was performed by Kruskal-Wallis and Mann-Whitney U-tests with Bonferroni correction. Little or no microleakage was detected at the composite/enamel interface of the FSWR cured with three different light sources. However, at the composite/wire interface, statistically significant differences were found between the QTH (mean, 1.10 +/- 1.05 mm) and high-intensity curing units. The PAC resulted in the greatest amount of microleakage (mean, 2.63 +/- 1.49 mm), whereas no statistically significant difference was noted between the PAC and the LED (mean, 2.35 +/- 1.28 mm). High-intensity light curing units show statistically significant microleakage at the composite/wire interface and therefore may not be safe for use in bonding FSWRs.

The Effect of Different Light-Curing Methods on Temperature Changes of Dual Polymerizing Agents Cemented to Human Dentin

This in vitro study aims to measure the temperature changes of resin luting cements cemented to human dentin when using different light curing systems for photo-activation. The three different types of light-curing units (LCUs) used for photoactivation were quartz-tungsten halogen (QTH), light emitting diode (LED), and plasma arc (PAC). Two types of dual cure resin cements were used [Variolink II (VL) and Choice (CH)]. Feltik Z250 composite resin material was used to prepare composite discs. Thirty human dentin specimens were prepared for each resin luting cement (ten for each light source). A total of 60 specimens were fabricated. Resin cement was applied on a dentin bridge and covered with the prepared composite disc where specimens were fabricated. Temperature change was recorded with a digital thermometer. The lowest temperature was recorded when VL and CH were photo-activated with the PAC unit. The PAC unit produced significantly lower recorded temperatures than the LED and QTH units. No significant difference appeared between QTH and LED units in terms of recorded temperature. The PAC unit produced significantly lower temperature changes compared to QTH and LED curing units. The risk for temperature rise should be taken into consideration during photo-polymerization of adhesive resins with LED or QTH in deep cavities when dentin thickness is 0.5 mm.

Temperature change, dentinal fluid flow and cuspal displacement during resin composite restoration

Dentin-bonding agents and resin composite materials typically require light activation for polymerization. Light curing generates heat, which may influence dentinal fluid flow (DFF) and cuspal displacement. This study investigated the relationship among temperature increase, DFF and cuspal displacement in extracted human maxillary premolars with a mesial occlusal distal (MOD) cavity preparation. Two types of curing light were compared. Temperature changes were measured using thermocouples located on the occlusal cavity floor and at the pulp-dentine junction, during polymerization of bonding agent and resin composite material. DFF and cuspal displacement were measured simultaneously using automated flow measurement apparatus and direct current differential transformers respectively. Temperature increases of up to 15 degrees C were recorded during the restoration procedures. A quartz tungsten halogen (QTH) unit produced a significantly greater temperature increase than a light-emitting diode unit and curing of the bonding agent generated less temperature increase than curing of the resin composite. Heating due to exothermic reaction during polymerization of bonding agent and resin was not significantly different between light sources or between bonding and curing (P > 0.05). The QTH unit produced both greater inward fluid flow and cuspal displacement during the irradiation of bonding agent and resin composite than the light-emitting diode unit. There was not a simple relationship between temperature increase, fluid movement and cuspal displacement. From a clinical point of view, the light-emitting diode unit can be considered preferable to the QTH light, because it caused significantly smaller temperature increase, fluid shift and cuspal displacement.

The effect of a light-emitting diode on shear bond strength of ceramic brackets bonded to feldspathic porcelain with different curing times

The aim of this study was to evaluate different curing times of a light-emitting diode (LED) unit on shear bond strength (SBS) of ceramic brackets bonded to feldspathic porcelain. Ceramic brackets were bonded with a light-cured adhesive to 96 feldspathic porcelain facets. Air-borne particle abrasion was performed using 25 mum aluminium trioxide (Al(2)O(3)) with an air abrasion device from a distance of approximately 10 mm at a pressure of 2.5 bars for 4 seconds, then the porcelain surfaces were etched with 9.6 per cent hydrofluoric acid for 2 minutes. After surface preparation of the porcelain specimens, silane was applied. In groups 1 and 2, the adhesive was cured with a quartz-tungsten-halogen (QTH) unit for 10 and 20 seconds, respectively. The LED was used in the standard mode for 3, 5, and 10 seconds for groups 3, 4, and 5, respectively. For the other three groups, the LED was used in the fast mode for 3, 5, and 10 seconds, respectively. The SBS of the brackets was measured on a universal testing machine. The adhesive remnant index (ARI) scores, damage to the porcelain, and fracture of the ceramic bracket bases were determined. No significant differences were observed for SBS between the eight groups (P=0.087). There was no significant difference between the groups' ARI scores, porcelain damage, and bracket base fracture (P=0.340, P=0.985, and P=0.340, respectively). There was a greater frequency of ARI scores of 0 for all groups. Fifty per cent of the porcelain facets displayed damage. Nineteen ceramic bracket base fractures were observed. No significant difference was found for the SBS of the groups with QTH and LED units and curing times. It is reliable to use LED with a 3-second curing time since it provided adequate bond strength for ceramic brackets bonded to porcelain surfaces.

Color stability of composites subjected to accelerated aging after curing using either a halogen or a light emitting diode source

The purpose of this study was to evaluate, in vitro, the color stability of three composite resins of two different shades (A3 and C3) cured with either a quartz tungsten halogen (QTH) or a light emitting diode (LED) source. Forty specimens (20 x 2 mm) were prepared for each composite (Tetric Ceram, Heliomolar and Esthet-X), being 20 for each shade. In each group, 10 specimens were light-cured using the QTH unit and 10 with the LED source. The shade of the materials was evaluated before and after submitting the specimens to artificial accelerated aging (4 h UV-B/4 h condensing vapor), using a reflection spectrophotometer. deltaE means were calculated and analyzed statistically by 2-way ANOVA and Tukey's test at 5% significance level. Both A3 and C3 shades of Esthet-X composite resin showed the lowest color change when cured with the QTH light, while Tetric C3 cured with the QTH light showed the highest color change.

The Linear Shrinkage and Microhardness of Packable Composites Polymerized by QTH or PAC Unit

This study evaluated the effectiveness of a plasma arc curing (PAC) unit for packable resin composite curing. The amount and speed of polymerization shrinkage and the microhardness of packable composites were evaluated in order to compare the PAC unit's effectiveness with a quartz tungsten halogen (QTH) unit. Sure Fil (Dentsply Caulk), Pyramid (BISCO Inc) and Synergy Compact (Colténe/Whaledent) were used as the packable composites. In the case of curing with the PAC unit, the composites were light cured with Apollo 95E (DMD System Inc) for 1 second (Group 1), 2 seconds (Group 2), 3 seconds (Group 3), 6 seconds (Group 4) and 12 seconds (Group 5). For light curing with the QTH unit, the composites were light cured for 60 seconds using XL3000 (Group 6). The linear polymerization shrinkage of each composite was measured using a custom made linometer, and the data was stored in a computer every 0.5 to 0.55 seconds for a total of 60 seconds. For each composite, the amount of polymerization was compared using one-way ANOVA with Tukey at the 95% confidence level. In order to compare the speed of polymerization, the peak time (PT), showing the highest speed of polymerization and maximum speed of polymerization (Smax), were determined from the data and compared using one-way ANOVA with Tukey at the 95% confidence level for each material. Based on the statistical analysis among the PAC-cure groups (Groups 1 through 5), the group that was not statistically different from the QTH-cure group (Group 6) in the amount of linear polymerization shrinkage was determined for each material, and the corresponding curing time of the group was defined as the tentative minimum PAC-curing time (TMPT). For microhardness measurements, the samples were placed in a 2-mm thick Teflon plate. Twenty specimens, randomly divided into the PAC-cure group (Group 1) or the QTH-cure group (Group 2), were prepared for each material. In Group 1, each composite was light cured for TMPT with the PAC unit. In Group 2, each composite was light cured for 60 seconds with the QTH unit. Microhardness was measured on the upper and lower surface. For each material, the microhardness of the upper and lower surface of Groups 1 and 2 was analyzed using two-way ANOVA with Tukey at the 95% confidence level. The amount of polymerization was Group 1<Group 2<Group 3<Group 4<Groups 5, 6 in the Sure Fil composite (p<0.05); Groups 1, 2<Group 3<Groups 4, 6<Group 5 in the Synergy Compact composite (p<0.05) and Group 1 <Group 2 <Group 3 <Groups 4, 6 <Group 5 in the Pyramid composite (p<0.05) Regarding the speed of polymerization, the order of PT was G1, G2, G3<G4, G5<G6 (p<0.05). The order of Rmax was G6<G1, G2, G3, G4, G5 in Sure Fil; G6<G1<G2, G3, G4<G5 in Synergy Compact (p<0.05) and G6<G1<G2, G3<G4, G5 in Pyramid (p<0.05) On the upper surface, there was no statistical difference in microhardness between Groups 1 and 2 in all materials. On the lower surface, the microhardness of Group 2 was significantly higher than Group 1 in all materials. In all materials in Group 1 and the Synergy Compact of Group 2, microhardness of the upper surface was significantly higher than the lower surface (p<0.05). In Sure Fil and Pyramid of Group 2, there was no difference in microhardness between the upper and lower surfaces.

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

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. 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. 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. 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.

Shrinkage behavior of a resin-based composite irradiated with modern curing units

The present study determined the influence of different light curing regimes (four light-emitting diode (LED) units (Freelight 1 and 2, 3M-ESPE; e-light, GC; Bluephase (prototype), Ivoclar Vivadent), two quartz-tungsten-halogen (QTH) lights (Astralis 10, Ivoclar Vivadent; Swiss Master Light, EMS) and one plasma-light curing unit (Easy Cure, DMDS)) on the curing behavior of a resin-based composite material (InTen-S, Ivoclar Vivadent). Polymerization shrinkage was induced by light curing the tested material with 14 different regimes of the curing units mentioned above. The contraction stress was recorded for 300 s at room temperature with a Stress-Strain-Analyzer (c(FACTOR)=0.3). The maximum contraction stresses after 300 s, the time until gelation (t(0.5N)), and the coefficient of near linear fit of contraction force/time (gradient) were analyzed. The statistical analysis was conducted using ANOVA (alpha=0.05) and Tukey's post hoc test. The five tested regimes of the LED unit e-light revealed the lowest statistically significantly maximum contraction stress followed by the low intensity LED unit Freelight 1 and the plasma curing unit Easy Cure. The high intensity LED unit Freelight 2 exhibited a significantly higher contraction stress compared to Freelight 1. No significant differences between the standard and exponential modes within these curing units were found. No significant differences were found between the LED unit Freelight 2 and the pulse program of the halogen light curing unit Astralis 10. The highest polymerization stresses were observed for the high energy curing units, either QTH (Swiss Master Light and Astralis 10) or LED (Bluephase). Fast contraction force development, high contraction stress and an early start of stress build-up cause tension in the material with possible subsequent distortion of the bond to the tooth structure. The lowest polymerization stress was observed for the low energy LED lamps, while the plasma unit and the high energy QTH and LED curing units produced two to three times higher stress.