Effect of Light Sources on Bond Strength of Different Composite Resins Repaired with Bulk-Fill Composite

The aim of this study was to evaluate and compare the effects of different light sources on shear bond strength when bulk-fill composite was used for the repair of different composite resins. A total of 126 samples made from six resin composites with different properties were aged (thermal-cycling with 5000 cycle), exposed to the same surface treatments and adhesive procedure. Then, they were repaired with a bulk-fill composite. At the polymerization step, each group was divided into three subgroups (n=7) and light cured with a QTH light source for 40s and two different LED light sources for 20s. Subsequently, the specimens were aged in distilled water at 37 ºC for 4 weeks and then subjected to shear bond strength test. Then, the specimens were examined under a stereomicroscope to identify modes of failure and visualized by Scanning Electron Microscope. Data obtained from the study were analyzed using ANOVA and Tukey HSD Test (α=0.05). In all groups, the light curing units had an impact on shear bond strength (p<0.05). Among the study groups, the greatest bond strength values were observed in the specimens repaired using the LED and the specimens repaired with the QTH light curing unit had the lowest bond strength values. It was concluded that the content of composite resins and light curing units may influence bond strength of different composites repaired with the bulk-fill composite.

Pengaruh Penyinaran Qth Dan Led Pada Kekuatan Tekan Resin Komposit Bulkfilldengan Berbagai Ketebalan

The incremental layering technique with a 2mm maximum depth is a standard procedure to produce a perfect resin composite with a high mechanical strength. Recent studies has developed bulkfill composite resin that can be done to a depth of more than 4mm. Composite resin polymerization process through irradiation can be obtained by the use of Quartz-Tungsten-Halogen (QTH) and Light Emitting Diodes (LED). One of the mechanical properties needed for the restorative material is good compressive strength to withstand a load of chewing time during the process of mastication function. The purpose of this study to determine the effect of irradiation QTH and LED on the compressive strength of composite resin bulkfill with thickness variations of 4 and 6mm. Teflon mold were used to prepare the resin bulkfill spesimen (6mm in diameter x 4mm in length) bulkfill disk 6mm diameter with a thickness of 4mm (n=5) and 6mm (n=5). Samples were soaked in distilled water with a temperature of 37ºC for 24 hours and then do the pressure test measurements by using Universal Testing Machine (UTM) with 250kgf load and speed of 0.5 mm/min. Shapiro-Wilk normality test and unpaired t-test used in this study.The results of the study there is no influence thickness was statistically significant (a=0.05) in the composite resin bulkfill thickness of 4mm and 6mm in LED and QTH irradiation group with a value of compressive strength 4mm group (147.82 ± 24,35MPa) and sample 6mm (133.76±30.63 MPa), QTH light source sample 4mm (158,21 ± 18,61Mpa), 6mm (154,23±21,43Mpa). LED and QTH no significant difference (p>0.05) in a thickness of 4mm and 6mm. Conclusion, bulkfill composite resin can be applied to the LED and QTH to a depth of 6mm without effecting the bulkfill compressive strength.

Effect of High Irradiance on Depth of Cure of a Conventional and a Bulk Fill Resin-based Composite

SUMMARY Objectives This study evaluated the effect of using three commercial light curing units (LCUs) delivering a range of irradiance values, but delivering similar radiant exposures on the depth of cure of two different resin-based composites (RBCs). Methods A conventional hybrid RBC (Z100 shade A2, 3M ESPE) or a bulk fill RBC (Tetric EvoCeram Bulk Fill shade IVA, Ivoclar Vivadent) was packed into a 10-mm deep semicircular metal mold with a 2-mm internal radius. The RBC was exposed to light from a plasma-arc-curing (PAC) light (Sapphire Plus, DenMat) for five seconds, a quartz-tungsten-halogen (QTH) light (Optilux 501, Kerr) for 40 seconds, or a light-emitting-diode (LED) light (S10, 3M ESPE) for 20 seconds and 40 seconds (control). The Knoop microhardness was then measured as soon as possible at the top surface and at three points every 0.5 mm down from the surface. For each RBC, a repeated measures analysis of variance (ANOVA) model was used to predict the Knoop hardness in a manner analogous to a standard regression model. This predicted value was used to determine at what depth the RBC reached 80% of the mean hardness achieved at the top surface with any light. Results The PAC light delivered an irradiance and radiant exposure of 7328 mW/cm2 and 36.6 J/cm2, respectively, to the RBCs; the QTH light delivered 936 mW/cm2 and 37.4 J/cm2 and in 20 seconds the LED light delivered 1825 mW/cm2 and 36.5 J/cm2. In 40 seconds, the control LED light delivered a radiant exposure of 73.0 J/cm2. For Z100, using 80% of the maximum hardness at the top surface as the criteria for adequate curing, all light exposure conditions achieved the 2.0-mm depth of cure claimed by the manufacturer. The LED light used for 40 seconds achieved the greatest depth of cure (5.0 mm), and the PAC light used for five seconds, the least (2.5 mm). Tetric EvoCeram Bulk Fill achieved a 3.5-mm depth of cure when the broad-spectrum QTH light was used for 40 seconds delivering 37.4 J/cm2. It required a 40-second exposure time with the narrow-spectrum LED, delivering approximately 73 J/cm2 to reach a depth of cure of 4 mm. Conclusions When delivering a similar radiant exposure of 37 J/cm2, the QTH (40 seconds) and LED (20 seconds) units achieved a greater depth of cure than the PAC (five seconds) light. For both resins, the greatest depth of cure was achieved when the LED light was used for 40 seconds delivering 73 J/cm2 (p&lt;0.05).

Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin

ABSTRACTObjectives: The aim of this study was to evaluate the effects of different light sources and curing time on the degree of conversion and microhardness of two surfaces within a nanofilled composite resinMethods: Four experimental groups (n=10) were formed in accordance with the light source (quartz-tungsten halogen (QTH – 600mW/cm2), or light-emitting-diode (LED -800mW/cm2)) and the time of curing (20 s or 40 s). The specimens were prepared with a circular mould (5 mm Ø and 2 mm thick), according to the respective protocol, and the Knoop microhardness and degree of conversion was measured at the top and the base of the specimens. The degree of conversion was evaluated by the Fourier transform infrared spectrometer (FTIR). The results were analyzed by ANOVA two-way repeated measures and Tukey’s test (α=,05)Results: Both the degree of conversion and microhardness were higher at the top than at the bottom of the specimens. The QTH light source presented better values on the degree of conversion evaluation, but this result was not observed in the microhardness evaluation. Although forty seconds of curing promotes an increased level of microhardness, it did not influence the degree of conversionConclusion: It could be concluded that increasing the time of curing to 40 s promotes an increase in microhardness, but it does not influence the degree of conversion of a nanofilled composite resin. QTH promote better monomeric conversion; however, the microhardness values are similar to LED curing. For all situations tested, the bottom of the specimens presented lower results than the top. (Eur J Dent 2012;6:153-157)

Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization

ABSTRACT Aims The purpose of this study was to evaluate the effect of light intensity and curing cycle of quartz tungsten halogen (QTH) and plasma arc curing (PAC) lights on the microleakage of class V composite restorations. Materials and methods A total of 60 freshly extracted human maxillary premolars were used for this study. Standardized class V cavities were prepared and restored with microhybrid resin composite. According to the curing protocol, the teeth were then divided into three groups (n = 20): QTH curing (standard and soft start mode) and PAC high intensity irradiation. The microleakage was evaluated by immersion of the samples in 50% silver nitrate solution. The samples were then sectioned, evaluated under a stereomicroscope and scored for microleakage. Statistical analysis used Dye leakage scores were obtained, and analysis was done using Student's t-test. Results Light curing with QTH light in the soft start mode, showed the least leakage in the composite restoration, which was highly significant when compared with the other groups (p < 0.01). Light curing with QTH light in the standard mode, showed moderate microleakage, which was statistically significant (p < 0.05), when compared with the PAC high intensity curing. Curing with PAC light in high intensity mode resulted in severe microleakage along the cavity margins. Conclusion Within the limitations of the study, it may be concluded that: 1. The high intensity PAC light resulted in maximum leakage, when compared to the other groups in the study. 2. The soft start polymerization mode offers a distinctive advantage over the standard curing protocol, in terms of microleakage, for the QTH curing lights. Clinical significance In the clinical scenario, soft start curing regimen offers a distinctive advantage over the conventional mode of the QTH curing and the high intensity rapid curing offered by the PAC light. How to cite this article Chandurkar AM, Metgud SS, Yakub SS, Kalburge VJ. Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization. Int J Prosthodont Restor Dent 2012;2(1): 10-15.

Effect of light-activation with different light-curing units and time intervals on resin cement bond strength to intraradicular dentin

The aim of this study was to assess the bond strength of a resin cement to intraradicular dentin varying the light-curing unit and the moment at which the light was applied. Post spaces of endodontically treated canines were prepared. The roots were distributed into 6 groups (n=10) according to the light-curing unit and the moment of light exposure: I) Quartz tungsten halogen-600 mW/cm² (QTH) + immediate light activation (t0); II) QTH + light activation after 10 min (t10); III) Light-emitting diodes (LED)-800 mW/cm² (LED-800)+ t0; IV) LED-800 + t10; V) LED-1,500 mW/cm² (LED-1500)+ t0; VI) LED-1500 + t10. After post cementation, slices from coronal, middle and apical post/root regions were submitted to the push-out test and failure evaluation. It was verified that LED-800 (4.40 ± 3.00 MPa) and LED-1500 (4.67 ± 3.04 MPa) provided bond strength statistically superior to QTH (3.13 ± 1.76 MPa) (p<0.05), and did not differ from each other (p>0.05). There was no significant difference between t0 and t10 (p>0.05). Coronal post/root region (4.75 ± 3.10 MPa) presented significantly higher bond strength than the apical (3.32 ± 2.30 MPa) (p<0.05) and middle regions (4.14 ± 2.99 MPa) showed intermediate values. Adhesive failures were predominant when using QTH. Adhesive and mixed failures occurred more frequently in the apical region. Higher adhesion of the resin cement to intraradicular dentin was observed in the coronal region with LED light-activation, regardless of the moment of light exposure.