Objectives: New tungsten-halogen light curing units are continuously introduced to the dental market. The purpose of this study was to compare the flexural strengths of three resin composite materials, activated with different light curing units at different intensities and for different activation times. Methods: 375 resin bars were produced from the composites Admira (ADM) (Voco, Germany), Herculite (HER) (Kerr, Germany), Venus (VEN) (Heraeus Kulzer, Germany), and Tetric Ceram (TEC) (Ivoclar-Vivadent, Liechtenstein) following the procedure specified in EN ISO 4049. Polymerization times with the halogen curing devices Optilux 501 (OPT) (Kerr) and Polofil Lux (POL) (Voco) were 10, 20, 30 and 40 s, and with the high intensity Xenon-light instrument aurys (AUR) (degré K, France) 5, 10 and 15 s, respectively. In addition, the effects of three high intensity and ramp modes of the OPT on flexural strengths were investigated. Differences in flexural strengths recorded were analyzed by multiple analysis of variance followed by Duncan's multiple comparison tests on the 0.05-level. Results: All samples fulfilled the ISO standard requirements of 50 MPa. No significant difference between POL (105.8 MPa) and OPT (107.3 MPa) could be detected after standard activation (p=0.52). The values recorded for AUR were significantly lower (89.2 MPa). Three homogeneous Duncan groups were identified for the composites: a) ADM (95.5 MPa) and VEN (98.1 MPa), b) TEC (107.5 MPa) and c) HER (118.1 MPa). Significantly lower flexural strengths were found for activation times shorter than 20 s and with the ramp curing modes. Conclusion: Under the conditions of this study the curing effect with halogen curing units on resin composite flexural strengths was highest when operated in the standard mode for at least 20 s. Ramp curing or activation with the Xenon instrument resulted in lower flexural strengths and is thus not advisable.

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