Minimal cavity preparation could be achieved with the use of ultrasonic tips. The purpose of this study was to evaluate the required time for opening the proximal cavities using three ultrasonic tips of different sizes and fine diamond burs (inlay burs, Intensive, Switzerland)/ultrasonic tip combinations. Proximal cavities with margins in enamel were prepared in a total of 40 intact molars using ultrasonic tips (SONICSYS approx tips micro torpedo, size #2 and #3, KaVo, Germany; Siplus Instrument approximal U-shaped, Komet, Germany and Piezon Cavity system 408, U-shaped, Electro Medical Sytems, Germany). The same procedure was repeated in another set of 40 molars which were prepared with fine diamond burs and finished with ultrasonic tips. ANOVA was used to analyze the data. The mean time required for opening small cavities recorded with Siplus (15 min, 13 to 17 min) was significantly longer than with diamond bur/Siplus tip combination (5 min, 4 to 6 min). Opening the cavities with only SONICSYS tips size #3 took 17 min (15 to 21 min) and size #4 19 min (16 to 22 min), which were also significantly longer than with diamond bur/SONICSYS tip size #3 combination (5 min, 4 to 8 min), and size #4 (8 min, 7 to 9 min). The mean time for opening the cavities recorded for Siplus tips of different sizes did not differ from the corresponding sizes of the SONICSYS tips (p > 0.05). Piezon cavity system required the least time both with tips (10 min, 8 to 14), and tips in combination with diamond burs (4 min, 3 to 5). Times required for proximal cavity preparation with ultrasonic tips were found to be longer than those with fine diamond bur/ultrasonic tip combinations. Proximal cavities opened with fine diamond burs and finished with ultrasonic tips provide short chairside times which are similar to conventional preparations. Schlagwörter: ultrasonic tips, proximal cavities, required time, diamond burs