Objective:This study evaluated the effect of the margin location and an adhesive system on
the marginal adaptation of composite restorations.Material and Methods:Class V cavities were prepared in bovine teeth with the gingival margin on the
dentin and the incisal margin on the enamel. The cavities were restored with a
micro-hybrid composite resin using an etch-and-rinse [Single Bond 2 (SB)] or a
self-etching adhesive [Clearfil SE Bond (CL)]. After finishing and polishing the
restorations, epoxy replicas were prepared. The marginal adaptation was analyzed
using scanning electronic microscopy (SEM, 500 x magnification). The higher gap
width in each margin was recorded (T0). After the first evaluation, the samples
were submitted to thermal cycling (2,000 cycles of 5ºC±2ºC followed by 55ºC±2ºC -
T1) and mechanical cycling (100,000 cycles of 50 kN and 2 Hz - T2). Replicas of
samples were rebuilt after each cycling and analyzed under SEM. The data were
submitted to Mann-Whitney, Wilcoxon and Friedman testing (a=0.05).Results:The SB presented higher gaps in the dentin than the enamel, while there was no
difference between the substrate for the CL. In the dentin, the CL showed better
marginal sealing than the SB. The opposite occurred in the enamel. There were no
significant differences between the baseline, thermal and mechanical cycling for
any experimental condition.Conclusions:The outcomes of the present study showed that the adhesive system and margin
location have an important effect on the marginal adaptation of composite
restorations.