The influence of drill wear on cutting efficiency and heat production during osteotomy preparation for dental implants: a study of drill durability.

PURPOSE: The authors evaluated, under conditions simulating implant placement, the cutting efficiency, durability, heat production, and wear of implant drills.
MATERIALS AND METHODS: Osteotomies were performed on bovine ribs using a surgical unit mounted in a testing apparatus. A software program controlled the apparatus and recorded temperatures, depths, and drilling times. Seven brands of drills were tested (Nobel Biocare, 3i/Implant Innovations, Steri-Oss, Paragon, Implamed, Lifecore, and ITI). Spade, twist, tri-flute, and TiN-coated drill designs were evaluated and compared during 100 successive osteotomies. Scanning electron microscopic and energy-dispersive x-ray spectroscopic examinations were performed, and hardness was measured.
RESULTS: Two 2-mm drills (Nobel Biocare and 3i/Implant Innovations) had mean removal rates significantly greater than the others (P < .05). The 2-mm twist drill design with a low hardness (Implamed) exhibited plastic deformation at the cutting edge, loss of cutting efficiency, and drill fracture. The TiN-coated drills (Steri-Oss and Paragon) showed greater wear and significantly lower removal rates (P < .05) than noncoated drills. Temperature increases with different drills were not significantly different at depths of 5 or 15 mm or between 2-mm or 3-mm drills. With 1 exception (the 2.3-mm Paragon drill at a depth of 15 mm), the temperatures generated by the different types of drills were not significantly different. Clinically harmful temperatures were detected only at a depth of 15 mm during 5 osteotomies and coincided with a marked decrease in the rate of drill advancement with a resulting continuous drilling action. DISCUSSION: Temperatures generated at depths of 5 and 15 mm by the different drill types and diameters were not significantly different and, with only 5 exceptions, were clinically safe. Several differences between brands were noted in regard to cutting efficiency and durability, underscoring the importance of material selection and quality on drill performance.
CONCLUSIONS: Drill design, material, and mechanical properties significantly affect cutting efficiency and durability. Coolant availability and temperature were the predominant factors in determining bone temperatures. Implant drills can be used several times without resulting in bone temperatures that are potentially harmful. Continuous drilling in deep osteotomies can produce local temperatures that might be harmful to the bone.