Abstract 23

AN IN VITRO EVALUATION OF 2- AND 3-FLUTED DRILL BITS: AN INVESTIGATION OF THERMAL DAMAGE, HOLE PLACEMENT ACCURACY AND MECHANICAL PROPERTIES.

Milne, H R M; Gillies, R M; Bertollo, N; Ellis L P; Stephens, P C; Butler A M; Walsh, WR

Orthopaedic Research Laboratories, University of New South Wales, Sydney, Australia

This study compared the drilling characteristics of a 2-fluted Smith and Nephew (S&N) drill bit, a Synthes 3-fluted drill bit and a new 3-fluted 'SurgiBit' drill bit from Orthopedic Innovation (OI).

The in-vitro characteristics studied were;
   · Stiffness
   · Accuracy
   · Feed-rate
   · Torque
   · Heat generation

The bending stiffness, load and energy to failure were tested. A comparison of the characteristic feed-rate of each drill was made at a range of forces. A thermal camera measured temperature elevations in the bone during drilling. Drill accuracy was examined by measuring skiving distances at drill bit entry angles between 0° and 60°.

The 3- fluted designs showed higher stiffness and maximum force to failure (P<0.05). Feedrates measured during testing were greater in the 3- fluted designs (P<0.05). The 3- fluted designs were the most accurate throughout all angle tested. The accuracy of the OI drill bit was consistent at all the angles tested (p=0.114). The 2-fluted design became increasingly less accurate at higher angles (p<0.0005). Mean torques measured were higher and more variable in the 2- fluted drill bit (p<0.05). The 2-fluted drill bits produced a greater thermal increase during drilling.

Higher stiffness may reduce breakage during procedure. The higher feed-rates experienced by the 3- fluted drills reduces drilling time. This may reduce thermal damage. The 2-fluted torque profile suggests a more jarring cutting action which may create micro-damage. This could lead to a structurally compromised drill hole. The results of this study suggest the there may be clinical advantages derived from adopting 3-fluted drill bits.

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