Effects of curing systems and light units on cytotoxicity of dental composites
Abstract
The objective of this study was to examine and compare the cytotoxicity behavior of commercial two restorative (light-cured) and three adhesive composites (dual-cured) polymerized by using two different light curing units (LCU). Commercial composites Filtek Z250, Filtek Supreme XT, Rely X Arc, Rely X U100 and Variolink II were polymerized using different light densities of halogen (H) and Light Emitting Diod (LED) curing units. After the polymerization process samples sterilized under UV light for 15 minutes. Dulbecco's Modified Eagle's Minimal Essential Medium (DMEM) containing 200 µL of serum was placed in 96 well cell plates and samples were added in the wells. They were incubated 5% CO2 incubator for 48 hours at 37°C. Sample surface area/solution volume was adjusted to 2.5 cm2/ml. Cytotoxicity of samples was examined by the extraction method and the results were evaluated using the MTS test. The extracts of the samples were collected for 24 hours and incubated in L-929 mouse fibroblast cells (MFCs). The data was analyzed with the SPSS statistics program. Samples polymerized by H light source were generally cytotoxic than the samples polymerized by LED light source. Rely X Arc in dual-cure system is the most biocompatible material and Variolink II-LED combination is the most cytotoxic one. Furthermore, there was no statistically significant difference between the cytotoxicity levels of composites using H and LED light sources (p>0.05).This study showed that the curing treatment used power density LED affects biocompatibility positively and nano-structures increase the biocompatibility.
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Introduction
Light- and dual-curing composite materials have been used with increasing interest as fillers, luting cements and adhesive resin cements in restorative dentistry for many years [1-5]. Increasing usage of these composite materials has recently provided to improvement of new formulations, simplification of bonding procedures and decreasing of aesthetic concern. Therefore physical properties, clinical performance and polymerization degree of resin composites developed. Halogen (H) and light-emitting diode (LED) light-curing units are the most widely used light sources to achieve the sufficient polymerization degree for restorative composites.
Recently, several research teams reported that usage of both composite and light curing unit can influence the cytotoxicity of the material [1-11]. Influence of light curing on the toxic behaviour of composite materials is the interest issue for dental restoration [1-5]. The relation between the type of light curing unit and the degree of polymerization of dental composites is currently being discussed in the literature [1-3]. Recently Siguscha et al. reported on the influence of different light curing units on the cytotoxicity of various dental composites. They proved that the combination of a high power LCU with various composites caused the lowest cell toxicity [4]. Goldberg explained that cytotoxicity mechanisms effected by the short-term release of residue monomers during polymerization and long-term release of soluble substances after polymerization process [12].
Conclusion
In general all materials used in experimental studies decreased the biocompatibility in certain amounts. Cytotoxicity test results of composite samples indicated that biocompatibility of dual cure system was higher than light curing system. When H and LED light sources effects on in vitro biocompatibility compared, less cytotoxicity was observed in the samples polymerized with the LED light source. The most biocompatible material-curing method combination was Rely X Arc polymerized by LED curing unit in all composites.
According to composite types of materials using H and LED light sources, no significant statistical difference was found between the levels of cytotoxicity (p>0.05).
One of the most important features of restorative materials used in dental practice is biocompatibility. In vitro biocompatibility study results showed chemical structure of material, degree of polymerization, residual monomer amount in the structure, clinical setting conditions (temperature, humidity, etc.) and properties of the curing method (light source type, curing type etc.) stimulate the cytotoxicity formation.
These results revealed the necessity of determination of residual monomer amount and effects on in vitro biocompatibility. In conclusion, it was well understood that in vivo experiments should be done beside in vitro studies to achieve the closest data as in clinical practice. We were able to prove that the combination of a high power LCU with various composites caused the lowest cell toxicity.