The acceptance and use of amalgam as an everyday filling material is decreasing. Today, direct composite fillings are widely used to restore even extensive lesions in premolars and molars. The sonoabrasive method presented here uses special working tip geometries (SONSICSYS approx) to a allow a "finishing preparation" of standardized interproximal cavities. In this process, the "negative shape" of the working tip is transferred to the tooth. It is now possible, for the first time, to accurately restore class II box cavities using prefabricated ceramic inlays. Complicated layering techniques are no longer necessary and there is no risk of compromising interproximal contacts remaining occlusal defects can be restored with conventional composites. The use of special SONICSYS working tips for ceramic and cast gold cavity preparations ensures precise cavity geometries with "close-to-perfect" margins. The sonoabrasive method greatly lowers the technique sensitivity of such difficult types of preparations.