Thermal damage of osteocytes during pig bone drilling: an in vivo comparative study of currently available and modified drills

The Gekkou-drill® is an industrial drill that is highly efficient due to reduced cutting resistance resulting from its characteristic drill point shape. In this experiment, we compared the degree of thermal damage to bone tissue caused by conventional medical drills and these same drills with Gekkou modifications. Holes were created in the tibias of living pigs using two different 3.2-mm diameter drills and their modified versions. Regarding the drilling parameters, the thrust force was 10 N and the drilling speeds were 800 revolutions per minute (rpm) and 1500 rpm. We compared the original and modified drills in terms of the bone temperature around the drill bit and the total time necessary to create each hole, the latter calculated using imaging data captured during drilling. In histopathological examination, the percentages of empty lacunae in osteocytes of the cortical bone beneath the periosteum were evaluated at 400 × magnification with an optical microscope. Compared to the original drills, the modified drills required significantly less time to create each hole and caused a significantly lower temperature rise during bone drilling. With the modified drills, the percentages of empty lacunae around the drilling holes were about 1/2–1/3 of those with the original drills, and were significantly lower for both drilling speeds. Gekkou-modified medical drills shortened drilling times despite low thrust force, and histopathological assessment demonstrated a significant reduction in osteocyte damage.