Progressive Changes in Commercial Orthopedic Drill Bits During Repeated Drilling of Synthetic Bone: Drill-Point Geometry, Thrust Force, Feed Work, and Hole Diameter

Repeated use can alter the geometry and functional performance of orthopedic drill bits, yet geometry, process load, and hole dimensions are rarely tracked together. Four integrated commercial drill types—Stryker (3.2 and 3.5 mm), Synthes (4.5 mm), and Zimmer (4.3 mm)—produced successive through-holes in a 6 mm short-glass-fiber-filled epoxy cortical-bone analog at 900 rpm and approximately 40 mm/min. Projected point angle was measured intermittently, maximum thrust force and axial feed work were calculated per hole, and entrance diameter was measured optically. The primary estimand was longitudinal change within each drill type; the design was not factorial, and differences among types cannot be attributed separately to manufacturer, diameter, geometry, intended function, or alloy. Drill-type-specific models included fixed specimen intercepts. Force, work, and diameter were described using constrained monotonic functions selected by AICc, while trend inference used permutation-based Spearman tests. Point angle decreased significantly only for the Stryker drills. Force and work increased in every type, whereas entrance diameter decreased significantly for Stryker 3.5 mm, Synthes, and Zimmer. Pairwise force/work–diameter associations did not remain significant after adjustment for hole number and multiplicity. Repeated-use exposure therefore produced drill-type-specific mechanical and dimensional drift, but the study did not directly quantify cutting-edge wear or establish a causal material mechanism.