Novel crescent drill design and mechanistic force modeling for thrust force reduction in bone drilling

Bone drilling tends to cause mechanical damages and thermal necrosis in the vicinity of the drilled hole, which can deteriorate the surgery quality and patients' recovery. Understanding the cutting forces generation mechanism is crucial in controlling thrust force and bone temperature for optimum tool design. In this study, a novel crescent drill bit featuring an improved positive rake angle distribution was designed to reduce the thrust force and temperature elevation. On this basis, a mechanistic model for predicting thrust force and torque was proposed for drill bits with different geometries (twist drill and crescent drill). The proposed model was established in the polar coordinate system to precisely calculate the curvilinear integral of the crescent cutting edges. Drilling experiments were carried out using two types of drill bit under different cutting conditions and results showed that our proposed model agrees well with the experimental data. The experimental results also demonstrated that our tool design can significantly reduce the thrust force and reduce the bone temperature below the thermal threshold without coolant, providing a clinical option for coolant free drilling.