Curing efficiency of orthodontic adhesives polymerized by different curing units

Objective: The purpose of this study was to compare the percentage degree of cure (%DC) of orthodontic adhesive resins irradiated with three different types of light sources of various intensities: plasma arc, halogen, and LED. Methods: Twenty maxillary incisor stainless steel brackets (0.018-slot) were divided into four groups of five brackets each (n=5). A standardized amount of composite resin (Eagle Spectrum, American Orthodontics) was applied to each bracket base with a method simulating the clinical application of material. Brackets of group A were light-cured with a halogen unit (TriLight, 3M ESPE, 800 mW/cm2) for 20 seconds (10 seconds each from the incisal and cervical bracket edges); group B with LED unit (TC-100-2, The Cure, Spring Health Products, 1100 mW/cm2) for 20 seconds (10 seconds per edge); group C with plasma unit (Virtuoso, Den-Mat, 2040 mW/cm2) for 10 seconds (5 seconds per edge); and finally the group D with the same LED unit for 10 seconds (5 seconds per edge). The %DC was assessed using micro-multiple internal reflectance FTIR spectroscopy and results were analyzed with one-way ANOVA (a=0.05). Results: The results of the %DC (mean±SD) are: for group A 48.35±1.87, for group B 46.16±1.92, for group C 35.35±1.87 and finally for group D 32.34±6. Overall, LED and halogen lights, when used with the 20-second regimen, produced the higher %DC. No significant difference was found in %DC between the plasma light source and 10 seconds of the LED light source, whereas both showed lower %DC compared to 20 seconds of halogen or LED lights. Conclusion: Significant variation in %DC are associated with the use of various light curing units, which must be considered in selecting light source and irradiation time.