[Histological examinations about possible heat lesions of bone and cartilage during boring and grinding (author's transl)].

In skull bone and septum cartilage holes were bored with rose trepans and diamond cutters of various sizes (2-20) and at different revolutions (5,000-42,0000 rev/min) with and without the use of cooling fluid. The specimens were examined histologically. Borings with rose trepans without cooling fluid cause sometimes considerable heat lesions up to a depth of 30 mu. Bone shows the more severe lesions. The use of cooling fluid reduces the damage quite considerably (burns zone up to a maximum depth of 12 mu). In the normal range of up to 10,000 rev/min practically no heat lesions occur. In the high range above 20,000 rev/min the lesions are often only plaque-shaped. Water jet or spray cooling is superior to droplet cooling. Diamond cutters cause more severe lesions. Boring and grinding in the highest range (up to 300,000 rev/min) without cooling fluid cause very deep burns (up to 56 mu),