Flexural strengths of fiber-reinforced composites polymerized with conventional light-curing and additional postcuring

Introduction: The purpose of this study was to evaluate the effect of hand light-curing (Optilux 501; SDS Kerr, Danbury, Conn) and secondary oven polymerization (Liculite; Dentsply, Dreieich, Germany) on the mechanical properties of 2 sizes (diameters, 0.6 and 1.2 mm) of fiber-reinforced composites (FRCs) (Ever Stick; Stick Tech, Turku, Finland). Methods: The FRC samples were divided into 8 groups. Each group consisted of 10 specimens. Each FRC sample was evaluated with a 3-point bending test with a universal testing machine. Groups 1, 3, 5, and 7 were hand light-cured with a halogen curing unit for 40 seconds. Groups 2, 4, 6, and 8 were light-cured with the same curing unit for 40 seconds, followed by polymerization for 15 minutes in a light-curing oven. Groups 1 through 4 were tested at 1-mm deflection, and groups 5 through 8 at 2-mm deflection. Results: The results of ANOVA indicated significant differences among the various groups (P =.000). The post-hoc test showed that the 2-mm deflection groups had significantly higher flexural strengths than the 1-mm deflection groups (P =.000). Moreover, the 1.2-mm FRCs showed significantly higher flexural strength than the 0.6-mm FRCs (P =.000). No significant differences (P >.05) were found between the hand light-cured and the oven-polymerized groups. Conclusions: This investigation demonstrated that oven postcuring does not increase the flexural strength values of 0.6- and 1.2-mm FRCs compared with conventional hand light-curing. Thus, hand light-curing of FRCs is recommended directly in the mouth for orthodontic purposes.