Biomechanical Evaluation of Temperature Rising and Applied Force in Controlled Cortical Bone Drilling: An Animal in Vitro Study

The present study was conducted to quantify the relationships between bone drilling process parameters(i.e., feed rate, resting time, exit rate, and drill bit diameter) and drilling outcome parameters (i.e., thrust force andmaximum temperature).

This study utilized 10-cm cortical bovine samples to evaluate the effects of four independent parameters,including drill bit diameters, six different feed rates, three various resting times, and three different exit rates on thrustforce and maximum temperature (MT). A total of 28 stainless steel orthopedic drill bits with a diameter of 2.5 and 3.2mm, as well as an orthopedic handpiece were attached to the 500N load cell and an accurate linear variable differentialtransformer to obtain forces. Moreover, two k-type thermocouples were utilized to record the temperature-time curvenear the drilling site. The data were analyzed using the two-way analysis of variance and post hoc Tukey-KramerHonest test.

Maximum thrust force (MTF) decreased by almost 230% as the drill bit diameter increased from 2.5 to 3.2mm in the lowest feed rate. The MTF showed a 335% increase, whereas a decrease of 69% was observed as the feedrates rose from 0.5 to 3 mm/sec. Moreover, the MT decreased to 67% with an increasing exit rate from 1 to 3 mm/sec.Furthermore, a slight increase was observed in MT when the resting time increased from 0 to 2 seconds (P>0.05).

The desired drilling is drilling with lower thrust force and lower final temperature of bone. Increasing feedrate can cause an increase and decline in thrust force and final temperature, respectively. The highest rates of MT were0.5 and 1 mm/min, and the optimum feed rate would be 1.5 mm/min due to the averaged thrust force. Moreover, theresting time had no significant effects on the final temperature. Attentions to resting time would be useful to provide amore accurate, efficient, and uniform drill hole.Level of evidence: V