THE EFFECT OF DRILLING PARAMETERS ON BONE .3. THE RESPONSE TO POROUS HYDROXYAPATITE IMPLANTS

For biocompatibility testing, cylindrical specimens are often inserted into drilled cortical defects. However, little attention has been pai d to the drilling conditions. Our previous experience revealed that bo ne formation in drilled cortial defects was delayed by 5000 r.p.m. dri lling due to thermal necrosis around the hole compared with 500 r.p.m. , and the use of irrigation was effective in reducing the degree of lo cal ischaemia. Therefore, this experiment was performed to investigate the short- and long-term effects of the drilling conditions on bone r esponse to cylindrical porous hydroxyapatite implants. Two holes were drilled in rabbit tibia diaphysis with two different drilling conditio ns: 500 r.p.m. with irrigation and 5000 r.p.m. without irrigation. Rab bits were killed at 2 or 12 weeks post-operatively. The bone formation on the hole edge, on the implant surface and within the implant pores was investigated. At 2 weeks post-operatively the area of newly forme d bone within the implant pores at 500 r.p.m. was significantly greate r, whereas there was no difference at 1 2 weeks. These results indicat e that the drilling conditions affect the short-term bone response to the implants. Therefore, the drilling conditions must be taken into co nsideration when investigating the early bone response to materials im planted into drilled cortical defects.