The wall-to-wall contraction of the cementing layer of bonde restorations is compensated for mainly by elastic and plastic tooth substrate-cement deformation but may result in adhesive fracture. Occlusally flattened teeth and corresponding computer-designed onlays, both positioned in a special device, were used to study marginal and intenal seal of the adhesive interface with respect to four variables: rigidity of the restoration-substrate setup, cement thickness, adhesive configureation (enamel-dentin ratio and bonding agent), and luting agent. The results of dye infiltration tests revealed the significant influence of the adhesive configureation and rigidity of the setup. A high enamel-dentin ratio, use of a dentinal adhesive on dentinal margins and relative restoration-substrate mobility are required to preserve satisfactory marginal seal. However, in the present experimental conditions, no statistically significant differences were found among the diverse cement thicknesses or the luting agents evaluated.