Effect of light intensity and exposure duration on cure of resin composite.
ABSTRACT Of the many factors under their control, clinicians can manipulate light-exposure duration but must deal with a set intensity of light emitted from the dental curing unit. This research investigates the interdependence of exposure duration and source intensity on resin cure at various depths within a simulated light-cured resin composite restoration. This wafers of composite were obtained from a simulated cylindrical restoration such that the wafer could be removed from the top or from a distance of 1, 2, and 3 mm beneath the surface. The composites used in this study were a microfill and hybrid of Universal and Gray shades. All the data concerning filler type and shade were pooled so that generalized statements could be made regarding curing of light-activated composite in general. Specimens were cured using various source intensities and for different durations at each level within the cured cylinder. The cure of the specimens resulting from the different treatments was determined using infrared spectroscopy. The results indicate a dramatic effect of depth on the cure of composite. At depths greater than 2 mm, poor cure results, and polymerization is very susceptible to changes in light intensity and exposure duration. From these results, routine exposure times of 60 seconds are recommended using light-source intensities of at least 400 mW/cm2 as measured with a commercial dental light intensity meter. Incremental layer thickness should not exceed 2 mm, with 1 mm being ideal. Sources with intensity values less than 233 mW/cm2 should not be used because of their poor cure characteristics.
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ABSTRACT: Objectives: The purpose of this study was to observe the reaction kinetics and the degree of polymerization of composite resins when cured by different light sources and to evaluate the effectiveness of the blue Light Emitting Diode Light Curing Units (LED LCUs) compared with conventional halogen LCUs. Materials and Methods: First, thermal analysis was performed by a differential scanning calorimeter (DSC). The LED LCU (Elipar Freelight, ) and the conventional halogen LCU (XL3000, ) were used in this study for curing three composite resins (SureFil, Z-250 and AEliteFLO). Second. the degree of conversion was obtained in the composite resins cured according to the above curing mode with a FTIR. Third, the measurements of depth of cure were carried out in accordance with ISO 4049 standards. Statistical analysis was performed by two-way ANOVA test at 95% levels of confidence and Duncan's procedure for multiple comparisons. Results: The heat of cure was not statistically different among the LCUs (p > 0.05). The composites cured by the LED (Exp) LCUs were statistically more slowly polymerized than by the halogen LCU and the LED (Std) LCU (p < 0.05). The composite resin groups cured by the LED (Exp) LCUs had significantly greater degree of conversion value than by the halogen LCU and the LED (Std) LCU (p =0.0002). The composite resin groups cured by the LED (Std) LCUs showed significantly greater depth of cure value than by the halogen LCU and the LED (Exp) LCU (p < 0.05).Restorative Dentistry and Endodontics. 01/2004; 29(4).
Article: Résines composites[Show abstract] [Hide abstract]
ABSTRACT: Les résines composites à usage dentaire ont pris une part prépondérante dans les restaurations coronaires par technique directe. La phase organique est composée de plusieurs monomères qui copolymérisent sous l'influence d'initiateurs chimiques ou photoniques. La photopolymérisation présente de nombreux avantages : temps de prise court, propriétés mécaniques améliorées, plus grande stabilité de la teinte. Les sources lumineuses se sont diversifiées. Divers programmes visant à réduire les contraintes de rétraction de polymérisation sont actuellement disponibles. Les light emitting diode (LED) s'imposent progressivement. La phase organique constitue le point faible du matériau. Elle est renforcée par des charges inorganiques dont les dimensions, la composition et la répartition varient. Plusieurs propriétés importantes sont directement en rapport avec le pourcentage de charges. L'esthétique et l'usure sont améliorées lorsque la taille des particules est réduite. L'évolution de ces deux paramètres a abouti aux composites microhybrides souvent qualifiés d'universels suite à leurs nombreuses indications cliniques. La tendance actuelle est le développement de charges générées par la nanotechnologie et à la recherche de monomères à très faible rétraction de prise qui reste, malgré des progrès manifestes, un des défauts majeurs du matériau. Les propriétés mécaniques et physiques se sont améliorées, mais des différences importantes persistent au sein de chaque groupe.
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ABSTRACT: In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 nW/ light intensity and a 7 mm diameter turbo light guide with 1100 nW/. Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers' hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p < 0.05). The results of this study suggest that, when projecting tooth material over a specified thickness, the increase of polymerization will be limited even if light intensity or curing time is increased.Restorative Dentistry and Endodontics. 01/2005; 30(2).