Light-curing-unit influence on the conversion degree of composite luting materials

Objectives: The physical and chemical properties of luting agents are strictly related to polymer conversion. Aim of this study was to evaluate the degree of conversion (DC) of four different composite luting materials cured below composite inlays by means of two LED curing devices. Methods: One-hundred and twenty onlays (Signum composite – Heraeus - A2 shade) of different thickness (2 mm, 3 mm, 4 mm) were prepared in a custom template then split into 24 groups (n = 5) and luted on laboratory glass slides with 4 different composites: a)Multilink Automix (Ivoclar-Vivadent); b)Variolink II (Ivoclar-Vivadent); c)Calibra (Dentsply); d)54°C-heated Venus (Heraeus) with two different curing units (Bluephase C8 and Bluephase G2, Ivoclar-Vivadent). Specimens were cured interposing the luting composite between a glass plate and an indirect restoration; the curing tip was shielded so that the light reached the composite material only passing through the onlay. DC was then assessed with a micro Raman Dilor HR Labram spectrometer, then ANOVA test was performed (α=0.05). Results:Mean DC are shown in Tab.1. As expected and shown by the Literature, the degree of conversion decreases as the onlay thickness increases. Comparing our results with previous data obtained with the same experiment using a halogen lamp, it was observed that: a)Multilink Automix and Variolink II reached significant higher results when cured with both LED lamps; b) Calibra shows to be slightly influenced by the nature of the LCU, always maintaining constant DCs. Conclusion: Modifying the LCU employed during the polymerization process, even when the same amount of energy is provided, changes are observed in the DC of the luting materials tested.