The present invention relates to dental instruments used in tooth restoration and replacement including dental burs, dental discs, tapes, endodontic files, surgical drills and taps, having abrading working surfaces coated or embedded with diamond particles or chips onto the substrate or shank, the abrading surfaces having a flexible diamond-like carbon coating. When there occurs abnormality in detection of any of HP marks, an alternate signal is generated in place of a signal associated with a mark the detection of which is determined to be abnormal, and image formation is carried out with reference to the time of normal HP mark detection and the alternate signal. If the user is not authorized to access the computer system, a packet is sent by the trusted server to instruct the hypervisor to stop any boot process on the computer system.