The Degree of Conversion of Composites Using Different Light-Curing Sources

Objectives: The purpose of this study was to investigate the effect of different light-curing units and irradiation modes on degree of conversion (DC) in resin composite polymerization. Further aim was to evaluate the depth of cure of resin composite layers with the above mentioned different curing units. Materials and methods: 2 x 4 mm and 4 x 4 mm sized composite model resins were prepared from Filtek Z250 (3M, St Paul, MN, USA). The standard supplements were irradiated with 6 different curing units (conventional halogen, high power halogen, plasma arc (PAC) and 3 blue LED light-curing units) in different curing methods. After irradiation the specimens were stored in ethanol for 72 hours in dark at 25C°. The ethanol solutions containing unpolymerized, dissolved monomer were analyzed with reversed phase high performance liquid chromatography (RP-HPLC). Results: The highest DC was observed from LED curing devices. There was no difference between DC used standard mode and soft-start extended curing intervals. The PAC and the high power halogen unit showed the lowest DC in fast cure mode. Higher DC was produced by increasing curing time. At 4 mm depth all curing units and methods showed lower curing efficiency, than at 2 mm. Conclusion: Degree of polymerization shows direct correlation with total energy of irradiation. The LED light provides the highest DC in standard and soft-start methods, while exposure time is not enough for complete polymerization recommended for PAC and high power halogen sources. Photo-activated composite in thickness higher than 2 mm should not be utilized in clinical situations. Acknowledgements: This work was supported by Grants PD 76395 and PD 78599 of the Hungarian National Science Foundation (OTKA).