The relatively low bond strengths of resin cements to dentin may result in poor interfacial adaptation of composite inlays. This study determined whether the interfacial adaptation of composite inlays could be improved by applying an adhesive system and a low viscosity microfilled resin to the prepared cavity walls before making an impression. Ten MOD cavities were prepared on extracted human premolars with gingival margins located above and below the cemento-enamel junction. A "resin coat" consisting of a self-etching primer system (Clearfil SE Bond) and a low viscosity microfilled resin (Protect Liner F) was applied to the cavities of half of the prepared teeth, while the remaining teeth served as non-coated control specimens. All the teeth were restored with composite inlays (Estenia) fabricated by the indirect method and cemented with a dual-cured resin cement (Panavia F). After finishing the margins with superfine burs, the bonded inlays were thermocycled between 4 degrees C and 55 degrees C for 400 cycles. Specimens were sectioned with a diamond saw and the tooth-restoration interfaces were observed with a confocal laser scanning microscope. The data were analyzed with two-way ANOVA and Fisher's PLSD test (p < 0.05). The percentage length of gap formation at the dentin-restoration interface of the "resin coated" teeth (7.1 +/- 3.5) was significantly less than that of the non-coated teeth (85.7 +/- 6.7) (p < 0.05). The concept of coating the prepared cavity with an adhesive system and a low viscosity microfilled resin resulted in observing fewer gaps at the internal dentin-restoration interface compared with the non-coated specimens.