Degree of conversion of resin-based orthodontic bonding materials cured with single-wave or dual-wave LED light-curing units

Aim: To evaluate the degree of conversion (DC) of orthodontic adhesives (RBOAs) cured with dual peak or single peak light-emitting diode (LED) light-curing units (LCUs). Materials and methods: Standardized samples of RBOAs, APCPlus, Opal (R) Bond (R) and LightBond (TM) were prepared (n=3) and cured with one of two dual peak LCUs (bluephase (R) G2-Ivoclar-Vivadent or Valo-Ultradent) or a single peak control (bluephase (R) Ivoclar-Vivadent). The DC was determined using micro-Raman spectroscopy. The presence or absence of initiators other than camphorquinone was confirmed by high-performance liquid chromatography and nuclear magnetic resonance spectroscopy. Data were analysed using general linear model in Minitab 15 (Minitab Inc., State College, PA, USA). Results: There was no significant difference in DC between APCPlus, and Opal (R) Bond (confidence interval: -3.89- to -2.48); significant difference between APCPlus and LightBond (TM) (-18.55 to -12.18) and OpalH Bond and Lightbond (TM) (-17.85 to -11.48); no significant difference between bluephase (single peak) and dual peak LCUs, bluephase G2 (-4.896 to 1.476) and Valo (-3.935 to -.437) and between bluephase G2 and Valo (-2.225 to 4.147). APCPlus and Opal (R) Bond showed higher DC values than LightBond (TM) (P<0.05). Lucirin (R) TPO was found only in Vit-l-escence. Conclusion: Lucirin (R) TPO was not identified in the three orthodontic adhesives. All three LCUs performed similarly with the orthodontic adhesives: orthodontic adhesive make had a greater effect on DC than the LCUs. It is strongly suggested that manufacturers of resin-based orthodontic materials test report whether or not dual peak LCUs should be used with their materials. Dual peak LED LCUs, though suitable in the majority of cases, may not be recommended for certain non Lucirin (R) TPO-containing materials.