Effect of LED curing modes on cusp deflection and hardness of composite restorations

This in vitro study measured cusp deflection associated with MOD resin composite restorations in maxillary premolars with different curing light modes. Soft-start polymerization may reduce cusp deflection by reducing polymerization shrinkage stress. Forty maxillary premolars were mounted in stone and slot MOD cavities were prepared. The teeth were randomized into four groups: Group A--cavities were etched, bonded and restored with two increments of Z-100 composite. Each increment was cured with an LED curing light (fast curing mode). Group B--similar to Group A except that the LED curing light with pulse curing mode was used. Group C--similar to Group A except that the LED curing light with stepped curing mode was used. Group D--a visible curing light was used for curing the composite. The distance between the indexed cusp tips was measured before the restorations were completed and five minutes after, 24 hours after and two weeks after completion of the restorations. The mean contraction of the cusps in microm at five minutes, 24 hours and two weeks, respectively, for each group was A: 25.4, 16.2 and 8.2, B: 6.4, 3.4 and 2.2, C: 11.6, 7.0 and 4.4, D: 33.0, 21.6 and 15.8. Group D resulted in the highest deflection, Group A was intermediate and Groups B and C were the lowest. Ten samples of the composite for each group with 2-mm thickness were prepared for the Vickers hardness test. No difference among the samples was found.