Section 882.4305 - Powered compound cranial drills, burrs, trephines, and their accessories(a)Identification. Powered compound cranial drills, burrs, trephines, and their accessories are bone cutting and drilling instruments used on a patient's skull. The instruments employ a clutch mechanism to disengage the tip of the instrument after penetrating the skull to prevent plunging of the tip into the brain.(b)Classification. Class II (performance standards).