[Investigations on the shape and size of bone-chips produced during boring and grinding (author's transl)].

Examinations of the shape and size of chips produced during boring and grinding of dry macerated and fresh temporal bone by various drills and grinders at different revolutions show that rose trepans mainly scrape fresh bone, producing large rolled-up chips, but knock off dry macerated bone, producing more compact chips of bizarre shape. In either case the chip waste also contains plenty of fine and finest compact chips which are broken off and splinter during the removal or knocking-off of the chips from solid bone. The size of the chip depends on the size of the drill head. Diamond cutting heads produce fine and finest compact bone chips. Bone milling produces plenty of scrapes even from dry macerated temporal bone. The rate of revolutions (10,000-80,000 per min) had no influence on the shape and size of chips. Clinically the scraped chip seems to be the most favourable in the drilling of bone because it causes least damage. The use of a drill head with sharp-edged, intact cutting surfaces seems important for this, with continuous rinsing during the boring process to prevent soiling of the interspaces between the cutters and to ensure full performance in accordance with their construction.