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

Abstract

Background: The present study was conducted to quantify the relationships between bone drilling process parameters<br />(i.e., feed rate, resting time, exit rate, and drill bit diameter) and drilling outcome parameters (i.e., thrust force and<br />maximum temperature).<br />Methods: This study utilized 10-cm cortical bovine samples to evaluate the effects of four independent parameters,<br />including drill bit diameters, six different feed rates, three various resting times, and three different exit rates on thrust<br />force and maximum temperature (MT). A total of 28 stainless steel orthopedic drill bits with a diameter of 2.5 and 3.2<br />mm, as well as an orthopedic handpiece were attached to the 500N load cell and an accurate linear variable differential<br />transformer to obtain forces. Moreover, two k-type thermocouples were utilized to record the temperature-time curve<br />near the drilling site. The data were analyzed using the two-way analysis of variance and post hoc Tukey-Kramer<br />Honest test.<br />Results: Maximum thrust force (MTF) decreased by almost 230% as the drill bit diameter increased from 2.5 to 3.2<br />mm in the lowest feed rate. The MTF showed a 335% increase, whereas a decrease of 69% was observed as the feed<br />rates 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.<br />Furthermore, a slight increase was observed in MT when the resting time increased from 0 to 2 seconds (P>0.05).<br />Conclusion: The desired drilling is drilling with lower thrust force and lower final temperature of bone. Increasing feed<br />rate can cause an increase and decline in thrust force and final temperature, respectively. The highest rates of MT were<br />0.5 and 1 mm/min, and the optimum feed rate would be 1.5 mm/min due to the averaged thrust force. Moreover, the<br />resting time had no significant effects on the final temperature. Attentions to resting time would be useful to provide a<br />more accurate, efficient, and uniform drill hole.<br />Level of evidence: V