To know the service life of IMZ drills, repeated drilling tests were done for spiral and cannon drills using pig thighbone under 450 gf static load,<br/> As a result, the following conclusion were obtained.<br/> 1. On the spiral drill, drilling time was extended after every drilling and drilling became impractical after the twenty seventh time drilling.<br/> 2. And the edge of the spiral drill was worn out after twenty seven times' repeated drilling.<br/> 3. Difference in drilling time with cannon drill was not recognized up to fifty times' repeated drilling.<br/> 4. And the edge of cannon drill did not wear out.<br/>