Aim: The aim of this study was to evaluate the effects of diode laser irradiation on microleakage of composite restorations in class I cavities.
Material and methods: Twenty human premolar teeth were used in this study. Class I cavities standardized to a size of 3x2x2mm dimensions were prepared in each sample. The cavity of each tooth was acid etched using 37% phosphoric acid gel* for 15 seconds. Then the teeth were rinsed with water spray for five seconds. The adhesives were applied to the entire surface of the cavity and air thinned for 15 seconds then light-cured for 10 seconds with light emitting diodes (LED). Cavities were then filled with nanofilled composite and light-cured for 40 seconds. The filled teeth were divided into two main groups (of 10 each) according to surface treatment by laser application or not. Group A: teeth without treatment, Group B: teeth with surface treatment by diode laser application. Dye penetration was measured under a stereomicroscope (Olympus SZ-PT-Japan).Another twenty specimens was prepared and examined by scanning electron microscope. Result: in microleakage assessment there were no significant difference in the microleakage scores at the buccal and lingual cavosurface margin between conventional and diode laser groups.