Quartz Tungsten Halogen Curing Units Research Articles

Factors affecting marginal integrity of class II bulk-fill composite resin restorations.

Background. Bulk-fill composite resins are a new type of resin-based composite resins, claimed to have the capacity to be placed in thick layers, up to 4 mm. This study was carried out to evaluate factors affecting gap formation in Cl II cavities restored using the bulk-fill technique. Methods. A total of 60 third molars were used in this study. Two Cl II cavities were prepared in each tooth, one on the mesial aspect 1 mm coronal to the CEJ and one on the distal aspect 1 mm apical to the CEJ. The teeth were divided into 4 groups: A: The cavities were restored using the bulk-fill technique with Filtek P90 composite resin and its adhesive system and light-cured with quartz tungsten halogen (QTH) light-curing unit. B: The cavities were restored similar to that in group A but light-cured with an LED light-curing unit. C: The cavities were restored using the bulk-fill technique with X-tra Fil composite resin and Clearfil SE Bond adhesive system and light-cured with a QTH curing unit. D: The cavities were restored similar to that in group C but light-cured with an LED light-curing unit. The gaps were examined under a stereomicroscope at ×60. Data were analyzed with General Linear Model test. In cases of statistical significance (P<0.05), post hoc Bonferroni test was used for further analyses. Results. The light-curing unit type had no effect on gap formation. However, the results were significant in relation to the composite resin type and margin location (P<0.001). The cumulative effects of light-curing unit*gingival margin and light-curing unit*composite resin type were not significant; however, the cumulative effect of composite rein type*gingival margin was significant (P=0.04) Conclusion. X-tra Fil composite exhibited smaller gaps compared with Filtek P90 composite with both light-curing units. Both composite resins exhibited smaller gaps at enamel margins.

Leaching of monomers from bulk-fill composites: An in vitro study.

Aim and Objectives:To evaluate the elution of bisphenol A-glycidyl methacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) from two bulk-fill composites at different polymerization times, for different storage periods when cured with quartz-tungsten-halogen (QTH) curing unit.Materials and Methods:Tetric N-Ceram bulk fill and EverX Posterior were analyzed using high-performance liquid chromatography unit. Totally, 68 samples were prepared, two groups (n = 17) from both the composites, one for each tested polymerization time. Each sample was cured with a QTH curing unit, using soft-start curing technique and stored in 2 ml of ethanol for 24 h. Storage medium was renewed and then stored again for 1 week. Data acquired were statistically analyzed.Results:The elution of BisGMA was significantly higher from Tetric N-Ceram bulk fill and BisGMA and TEGDMA from EverX Posterior composite at the end of 24 h, irrespective of the curing time. In EverX Posterior, a higher amount of TEGDMA was eluted at the end of 24 h, while at the end of 1 week, significantly higher amount of BisGMA was released.Conclusion:A significant amount of the release of BisGMA as well as TEGDMA was seen from both the composites when stored for different time intervals.

Argon-Ion Laser Vs Quartz-Tungsten-Halogen Curing of Polyacid Modified Composite Resin Restorative Materials

This study evaluated the differences in mechanical properties (flexural strength, surface roughness, and micro hardness) of three commercially available compomer restorative materials (Compo glass F, F2000, and Dyract AP), that were cured by argon laser (AL) and the traditional visible light quartz-tungsten-halogen (QTH) sources. Twenty eight nominally identical disc-shaped specimens, from each material, were prepared in a cylindrical split Teflon mold (6mm diameter, 2 mm thickness; to allow for one-step curing regime). Half of the specimens were cured by 40s. Exposure to a QTH curing unit and the other half by 10s. Exposure to AL on top and bottom surfaces. Fourteen samples from each material (seven for each curing type) were subjected to surface profile-measuring instrument. Samples used for surface roughness were also used to measure Knoop Hardness Number (KHN). The bi-axial flexure strength, of the remaining disc-shaped specimens was determined using the 'piston on ball' technique using the universal testing instrument to apply a compressive load perpendicularly through a ball indenter 4 mm in diameter at a crosshead speed of 1 mm/min. Results of the work showed that there was no statistical significant difference between the two techniques of compomer curing (P > 0.05). It was concluded that the argon laser cured compomer effectively as traditional visible light but with time saving.

Photo-polymerization efficiency of self-etch dental adhesives composed of camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide

Unique design of self-etch adhesive monomers combines acidic functional group and double bond into a single molecule, which presents complexity as using the environmentally-sensitive photoinitiators in such a system. The objective of this study was to evaluate the kinetics of polymerization for self-etch adhesives cured with two different photoinitiators camphorquinone (CQ) and trimethylbenzoyl-diphenyl-phosphine oxide (TPO). Model self-etch adhesives contained bis[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) (mass ratio of 2MP:HEMA=1:1). Different contents of water from 0wt% to 60wt%, or NaOH from 0.2wt% to 2wt% were incorporated to the system. The adhesives were cured using quartz–tungsten–halogen (QTH) or light-emitting diode (LED) light curing units. The degree of conversion (DC) and polymerization rate (PR) of the model self-etch adhesives were determined using ATR/FT-IR with a time-based spectrum analysis. TPO generally outperformed CQ/4E to initiate the self-etch adhesives when using the QTH curing unit. In addition, the DC of the TPO-initiated adhesives displayed increasing trend with water content, in contrast to a decreasing trend for the CQ/4E-initiated system. Furthermore, polymerization of the TPO-initiated system was independent of pH of the self-etch adhesives, whereas the DC and PR of the CQ/4E-initiated system were strongly influenced by the pH. As the LED curing unit was used, polymerization of both TPO and CQ/4E-initiated adhesives was greatly depressed. However, the DC and PR of the CQ/4E initiated adhesives could be improved by increasing pH of the system. In summary, the TPO-initiated system exhibits superior polymerization performance to the CQ/4E system as well as water-favorable and pH-independent features as using QTH curing unit.

Effect of light sources and curing mode techniques on sorption, solubility and biaxial flexural strength of a composite resin

Adequate polymerization plays an important role on the longevity of the composite resin restorations.Objectives The aim of this study was to evaluate the effect of light-curing units, curing mode techniques and storage media on sorption, solubility and biaxial flexural strength (BFS) of a composite resin. Material and Methods Two hundred and forty specimens were made of one composite resin (Esthet-X) in a stainless steel mold (2 mm x 8 mm Ø), and divided into 24 groups (n=10) established according to the 4 study factors: light-curing units: quartz tungsten halogen (QTH) lamp and light-emitting diodes (LED); energy densities: 16 J/cm2 and 20 J/cm2; curing modes: conventional (CM) and pulse-delay (PD); and permeants: deionized water and 75% ethanol for 28 days. Sorption and solubility tests were performed according to ISO 4049:2000 specifications. All specimens were then tested for BFS according to ASTM F394-78 specification. Data were analyzed by three-way ANOVA followed by Tukey, Kruskal-Wallis and Mann-Whitney tests (α=0.05). Results In general, no significant differences were found regarding sorption, solubility or BFS means for the light-curing units and curing modes (p>0.05). Only LED unit using 16 J/cm2 and PD using 10 s produced higher sorption and solubility values than QTH. Otherwise, using CM (16 J/cm2), LED produced lower values of BFS than QTH (p<0.05). 75% ethanol permeant produced higher values of sorption and solubility and lower values of BFS than water (p<0.05). Conclusion Ethanol storage media produced more damage on composite resin than water. In general the LED and QTH curing units using 16 and 20 J/cm2 by CM and PD curing modes produced no influence on the sorption, solubility or BFS of the tested resin.

Comparison of the Heat Generation of Light Curing Units

The aim of this study was to evaluate the heat generation of three different types of light curing units. Temperature increases were recorded from a distance of 1 mm from a thermocouple to the tip of three different types of light curing units including one quartz-tungsten halogen (QTH), one plasma arc (PAC), and one light emitting diode (LED) unit. An experimental model was designed to fix the 1 mm distance between the tip of the light curing units and the thermocouple wire. Temperature changes were recorded in 10 second intervals up to 40 seconds. (10, 20, 30, and 40 seconds). Temperature measurements were repeated three times for every light curing unit after a one hour standby period. Statistical analysis of the results was performed using the analysis of variance (ANOVA) and the Bonferroni Test. The highest temperature rises (54.4+/-1.65 degrees C) occurred during activation of a PAC light curing unit for every test period (p<.05). The least temperature increase (11.8+/-1.3 degrees C) occurred with a LED curing unit for each tested period except for the measurement of the temperature rise using the QTH curing unit at the tenth second interval (p<.05). These results indicate the choice of light activation unit and curing time is important when polymerizing light activated resin based restorations to avoid any thermal damage to the pulp.

Degree of conversion of adhesive systems light-cured by LED and halogen light

This study evaluated the effect of blue light emitting diode (LED) and quartz tungsten halogen (QTH) on the degree of conversion (DC) of an etch-and-rinse Single Bond adhesive system (SB) and a mixture composed of primer solution and resin bond from Clearfil SE Bond self-etching adhesive system (CB) using Fourier transform infrared analysis (FTIR). Adhesives were applied to potassium bromide pellet surfaces and FTIR analyses were performed before and after photo-activation for 10 s with either LED (Freelight 1 - 400 mw/cm(2)) or QTH (XL 3000 - 630 mw/cm(2)) light-curing units (n=8). Additional FTIR spectra were obtained from photo-activated samples stored in distilled water for 1 week. The DC was calculated by comparing the spectra obtained from adhesive resins before and after photo-activation. The results were analyzed by two-way split-plot ANOVA and Tukey's test (p<0.05). Both adhesive systems exhibited low DC (%) immediately after photo-activation (SB/QTH: 18.7 +/- 3.9; SB/LED: 13.5 +/- 3.3; CF/QTH: 13.6 +/- 1.9; CF/LED: 6.1 +/- 1.0). The DC of samples light-cured with LED was lower than DC of those light-cured with QTH, immediately after light curing and after 1 week (SB/QTH: 51.3 +/- 6.6; SB/LED: 50.3 +/- 4.8; CF/QTH: 56.5 +/- 2.9; CF/LED: 49.2 +/- 4.9). The LED curing unit used to photo-activate the adhesive resins promoted lower DC than the QTH curing unit both immediately after light curing and 1 week after storage in water.

Temperature rise beneath a light–cured materials using two types of curing machines

Aim: To measure the temperature rise induced by a light emitting diode (LED) curing unit and by quartz tungsten halogen (QTH) curing unit using two types of composite resin XRV Herculite and Venus. Materials and Methods: Forty extracted non–carious single canal premolars were cleaned and bisected longitudinally. Class V preparations were cut on the buccal surfaces. The teeth were divided into four groups; each of ten. The teeth in the first and second groups were restored with XR–Herculite composite resin. The teeth in the third and fourth groups were restored with Venus composite resin. The composite resin in the first and third groups were polymerized using QTH curing unit “Astralis” for 40 seconds; the light intensity was 502 mW/cm2. The distance between the tip of the light and the composite was 3 + 1 mm. The composite resin in the second and fourth groups was polymerized using LEDs “Ultra–Lite 200 E plus” curing unit for 20 seconds; the light intensity was 536 mW/cm2 using the same distance as the first and third groups. The temperature rise at the pulpal wall was recorded by placing a thermocouple on the pulpal wall directly under the restoration. Results: The lowest temperature rise during LED irradiation with Venus composite resin followed by LED irradiation with XRV Herculite composite resin. Whereas QTH curing units with XRV Herculite composite resin produced higher values, QTH curing units with Venus composite resin produced the highest temperature rise. Conclusion: The temperature rise of LED curing units and QTH curing units used in this study was under the limits that affect the integrity of the dental pulp.