An optimal preparation technique should meet the following requirements: a cavity that does not extend beyond the carious lesion; maximum preservation of sound tooth substance, preparation and margin design adapted to the requirements of the restorative material and its adhesion properties, prevention of adjacent tooth damage, and low technique sensitivity. Oscillating instruments with one diamond-coated and one polished surface have been developed to overcome the limitations of conventional preparation designs dictated by rotary burs. Previously untreated carious lesions were prepared using a modified air-scaler handpiece (Sonicsys) with various working tips allowing interproximal cavity preparation with minimal extension and a low risk of damaging the neighboring tooth. Another oscillating system is based on the EVA-System. It uses files for the preparation of interproximal bevels and for the finishing of margins of interproximal box, crown and veneer preparations. These oscillating instruments overcome the major limitations of rotary burs for tooth preparation and facilitate conventional cavity preparation. In addition, they allow the use of cavity designs that could not be achieved with conventional instruments.