Experimental evaluation of cortical bone substitute materials for tool development, surgical training and drill bit wear investigations.

Surgeons, scientists and development engineers of surgical devices require phantoms and materials for testing and training purposes. Human or animal bones are the gold standard, but difficult to obtain, prepare and handle. While polyurethane foams can be used as a substitute for trabecular bone, cortical bone substitutes have not been evaluated. In this study, a standard surgical drill bit (⌀ 3.2 mm) with clinical process parameters was used to compare 5 different materials with bovine cortical bone: polyurethane with three different densities, short-fiber-filled epoxy and an artificial bone material. Drillings were repeated 100 times with 6 drill bits for each material. The results indicate that none of the substitute materials can be used without compromises. Axial drilling thrust forces in short-fiber-filled-epoxy are similar to bone. However, its hard fibers significantly deteriorate the chisel edge and flank face and increases the thrust force with each drilling (doubles within the first 10 repetitions) so that drill bits should only be used very limited times. The densest polyurethane (Renshape BM-5166) has the advantage of comparable torque values with bovine cortical bone (up to 60 repetitions). Additionally to these findings, a significant and potentially clinical relevant increase of axial drilling force (80%) and torque (56%) was found during 100 drillings in bovine cortical bone.