Introduction: With advances in technology, other options besides the traditional cavity preparation with diamond and carbide burs have emerged; among them are laser and sono-abrasive systems.
Objectives: The aim of this study was to compare in vitro the effect of (Er:YAG) laser with different radiation distances, sono-abrasion and rotary cutting on  the surface roughness of dentin and the shear bond strength of resin composite to dentin using self-etching adhesive system.
Materials and methods: 50 extracted human molars were randomly divided into 5 groups (n=10) received the following treatments. Group 1: carbide bur, Group 2: diamond bur, Group 3: sono-abrasion, Group 4: contact Er:YAG laser, Group 5: non-contact Er:YAG laser. Average surface roughness (Ra) was determined with a profilometer. Specimens in all groups were treated with self-etching adhesive system and composite build ups were done with Filtek Z-250. Bonding of resin composites to the dentine specimens was tested in shear mode. For morphological analysis; two extra teeth from each group were examined using a scanning electron microscope (SEM).
Results:The shear bond strength of composite to the laser irradiated dentine (contact and non-contact) ranged from 6.64 ± 5.24 MPa and 6.29 ± 2.08 MPa respectively, and were significantly lower than the bond strength seen in other groups. However, the surface roughness of the laser irradiated dentine was significantly higher than that of the sono-abraded dentine and bur-cut dentine. SEM revealed that, the dentine surfaces irradiated by laser showed a scaly and rugged appearance and open dentinal tubules without smear layer production.
Conclusions: It was concluded that Er:YAG laser treatment reduced shear bond strength of resin composite to dentin in comparison with conventional treatment with high speed rotary and treatment with sono-abrasion. Different Er:YAG laser distance irradiations did not influence the shear bond strength of composite to dentin.