This study compares the effects of Er:YAG laser radiation and classical prepa- ration with acid treatment of hard dental tissues. The study was divided into two parts. At first oval cavities on the buccal surface were prepared in twenty human teeth. The edges of cavities were irradiated with Er:YAG laser. The energy of the laser was 105 mJ and repetition rate 1 Hz. Ten control samples were etched with 35% phosphoric acid. The cavities were filled with composite resin according to the manufacturer's directions. The quality of connection between composite resin and margin of the cavity was similar. The aim of the second study was to evaluate the shear bond strength of both types of treatment and examine the effect of Er:YAG laser and classical preparation on the bond of composite resin and hard dental tissues. It was confirmed that laser and acid etching have the same effect on the bond of composite resin to enamel and dentin.

        Key words: dentistry – laser therapy – Er:YAG laser – etching – enamel – dentin