CVD micro/nanocrystalline diamond (MCD/NCD) bilayer coated odontological drill bits

Dental implants replace the damaged teeth, including the root, in a surgical procedure that begins with the drilling of the bone to create a hole of adequate dimension, before placing the implant. The temperature rise during drilling is a major factor, because overheating above 42–47 °C leads to tissue death and implant failure. Commercial steel drill bits are inefficient at low speeds and cause overheating at high speeds. To overcome these limitations, a novel CVD diamond coated tool is hereby presented consisting of a bilayer coating of micro/nanocrystalline diamond (MCD/NCD) on silicon nitride (Si3N4) ceramic drill bit. The hot filament CVD technique was employed for the diamond deposition, using H2/Ar/CH4 gas mixtures.For the drilling experiments a variable speed drill was coupled to a universal mechanical testing machine. A laminated test block formed by a solid rigid polyurethane foam with a 2 mm thick upper layer of E-Glass-filled epoxy sheet was used to simulate the human mandible and maxilla. The feed force, spindle speed and temperature rise during drilling, which are key parameters for the success of the implant, were monitored during the experiments. The spindle speed varied in the range 50 to 1400 rpm, and the infeed rate between 7.5 and 30 mm/min. The temperature oscillation during cutting was evaluated by two thermocouples placed in the polymer at different levels. By using the MCD/NCD bilayered coating it was possible to drill with significantly lower forces (fourfold smaller), lower rise in temperature (4 °C less), lower spindle speeds (100 rpm) and higher infeed rates (30 mm/min), when compared to the commercial steel (AISI 420) drill bit.