RESUMEN
Aim: This in vitro study evaluates the influence of marginal sealing methods in composite restorations with different adhesive systems submitted to mechanical load. Materials and Methods: Eighty bovine incisor crowns were embedded in Polyvinyl chloride (PVC) molds with the buccal surface exposed, where cavities (4mm x 4mm x 3mm) were made. Samples had the adhesive systems, Single Bond or Clearfil SE Bond, applied according to the manufacturer's recommendations. The cavities were filled with a Z-250 composite according to the restoration technique (bulk filling or three increments) and photoactivation (conventional, soft start, pulsatile light or light-emitting diode [LED]). The samples were duplicated with epoxy resin for scanning electron microscopy observations. Samples were also submitted to mechanical load (200,000 cycles; 2 Hz) and new replicas were made. Results: The results, in percentages, were submitted to ANOVA followed by Tukey's test (P < 0.05). There was statistical difference between the cycle group (23.84%) and the non cycle group (18.63%). Comparing the restoration technique, there was no statistical difference between bulk filling (19.62%) and three increments (22.84%). There was no statistical difference among the groups: Pulsatile light (24.38%), soft start (22.75%), LED (21.47%) or conventional (16.34%). Furthermore, there were no statistical differences between the adhesive systems: Clearfil SE Bond (21.32%) and Single Bond (20.83%). Conclusions: The photoactivation methods, the restorative techniques and the adhesive systems did not influence gap formation.