[High frequency cinematographic investigations of the mode of operation of common drilling instruments on bone and cartilage (author's transl)].

High frequency cinematographic films were made of the mode of operation of common oto-surgical drilling instruments on bone and cartilage. Rose bits and surgical fraises of different sizes were used at 5,000-80,000 R.P.M. The evaluation of the slow motion pictures was performed on the running films and by review of single frames. In detail: The preparation of the drilling head on the bone without simultaneous flushing leads to a filling of the cutting channel and decreased cutting. Drop flushing only prevents the increasing soiling of the drilling head if the drop sequence is rapid and which must be markedly increased with increasing R.P.M. of the drilling instrument. Flushing with a stream of water, which definitely prevents soiling, is preferable. Both drop flushing as well as the water stream must continuously wet the drilling head, i.e. must be absolutely centric in every case. Safest is the automatic spray flusing which is mounted on the handpiece, but which has so far not been used in oto-surgery. During the preparation, the air space of the working area is always filled with drilling dust or haze. Cutting is always performed tangenitally. The cutting speed lies between 2,9 m/s to 16 m/s. It depends on the R.P.M. of the drilling instrument. A drill head running out of true, even with a gently percussing shaft, touches the bone only with a part of its cutting surface which strikes more vigorously than desired and easily gets soiled, despite flushing. Cutting is therefore less and uncontrolled. An increased feeding energy (pressure on the support) in order to speed up cutting leads to heavy wear of the drilling instrument and unsafety in handling due to jumping of the drilling head. During each contact of a cutter with the bone, coarse fraises with low R.P.M. (5,000 R.P.M. = 83 R/s) show a short stopping of the rotation which results in a jerk and vibration of the whole preparation and can thus lead to a damage of the inner ear.