Influence of cutting force on temperature, microcracks and chip morphology during rotary ultrasonic bone drilling: An in-vitro study

Mechanical and thermal damage due to cutting force and temperature rise during bone drilling plays a significant role in implant failure during osteosynthesis. High cutting force results in hole inaccuracy and weakens the stability between bone and implant. In comparison, temperature above 47 degrees C during drilling of bone results in the permanent death of regenerative bony cells consequences of thermal osteonecrosis. Microcracks at the drill site result in bone delamination and affect the holding strength at the bone-screw interface, resulting in implant failure. Accumulation of bone chips produced during drilling may cause chip clogging. The cutting force, microcracks, bone chip accumulation, and temperature rise are significant reasons for implant instability and revision surgery. Therefore, the present work uses the rotary ultrasonic bone drilling (RUBD) technique of the pig femur bone to monitor cutting force, temperature, microcracks and bone debris generated during the drilling. The results were also compared with conventional bone drilling (CBD). The twisted surgical drill bit was used during CBD and the diamond-impregnated tool was used during RUBD with the same diameters of 3.5 mm. The histopathological analysis was conducted at the drilled site to observe the tissue damage and the effect of heat generation on bone morphology. The output parameters were correlated, and the influence of cutting force on temperature rise, microcracks, and chip morphology was observed. This study showed that the increase in cutting force from 35.63 to 57.66 N in RUBD, and 54.83 to 78.7 N in CBD, resulted in a decrease in temperature rise by 51.5 and 32.7%, respectively. In contrast, the intensity of microcracks and chips size increased with the increase in cutting force for both RUBD and CBD techniques. Moreover, the RUBD technique reduces cutting force, temperature rise, microcracks and bone chip morphology as compared to CBD.