Objective:The purpose of this study was to analyze the resin-dentin interface in cavities prepared with laser or bur in primary teeth. Background data:Erbium, chromium:yttrium-scandium-gallium-garnet (Er, Cr:YSGG) laser was expected to be an alternative cavity preparation method, enhancing surface alterations and producing morphological changes. Methods:Twenty extracted primary molar teeth were divided to four groups according to one of four cavity preparation and pretreatment regimens:Er, Cr:YSGG laser (G1), Er, Cr:YSGG laser + acid-etching (G2), bur (G3), and bur + acid-etching (G4). After applying composite resin to the cavities, the teeth were sectioned. The resin-dentin interface was analyzed under scanning electron microscopy (SEM) and ion analysis was performd with SEM-energy-dispersive X-ray spectroscopy (EDX) after immersion in ammoniacal silver nitrate solution. Results:In G1 and 2, the surfaces were wavy, and in G3 and 4, the surfaces were smooth. Microcracks were seen in some of the lased cavities. In G1 and 2, dentin tubules were exposed and there was lack of a smear layer. In G3, there were gaps and a smear layer in the resin-dentin interface, but no gaps or smear layer were observed in G4. In G2, the resin tags were increased, and some resin tags were broken in cavities, which were prepared with laser (G1 and 2). Conclusions:According to the results of this study, acid-etching was recommended after laser preparations, to have a better adhesion.