THE EFFECT OF DRILLING PARAMETERS ON BONE .1. GENERAL HEALING RESPONSE

For biocompatibility evaluation, orthopaedic and dental biomaterials a re often implanted into bone after drilling. Bone repair in the drille d hole may be affected by bone damage attributed to drilling, thus inf luencing the bone response to biomaterials. The drilling parameters (t he speed of rotation and irrigation) were investigated histologically. Three holes were drilled in each rabbit tibia with different conditio ns; three speeds (200, 500 and 5000 r.p.m.) and the use of central irr igation or not. Rabbits were killed immediately, 3 days, 2 weeks or 4 weeks post-operatively. India ink was injected in several rabbits just after drilling to investigate the extent of local ischaemia. The dril ling quality was evaluated with regard to hole geometry, initial therm al damage and later bone healing process. For 500 or 200 r.p.m. the in itial thermal damage, shown by the degree of ischaemia, was less than for 5000 r.p.m. drilling, but the hole edge was not always cleanly cut . This uneven cut edge was considered not to influence the bone-healin g process. Drilling at 200 r.p.m. introduced a lower degree of circula rity. The subsequent bone formation was retarded by 5000 r.p.m. drilli ng, presumably due to thermal damage and vascular obstructions, The ir rigation was effective in reducing the ischaemic area. These results s uggest that a speed of about 500 r.p.m. may be recommendable for intra osseous implantation of biomaterials. The central irrigation system is considered effective in reducing the ischaemic area.