Object: To quantify the relationship 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 and maximum temperature).
Methods: Ten millimeters cortical bovine samples were used to determine the effects of four independent parameters i.e. two drills bit diameter, six different feed rates, three various resting times and three different exit rates on thrust force and maximum temperature. Twenty-eight stainless steel orthopedic drill bits with a diameter of 2.5 and 3.2 mm as well as orthopedic handpiece attached to the 500 N load cell and an accurate linear variable differential transformer (LVDT) to obtain forces. Two k- type thermocouples were used to record the temperature-time curve adjacent to the drilling site. ANOVA two-way and post hoc Tukey-Kramer honesty tests were applied statistically.
Results: Maximum thrust force (MTF) decreased by almost 230% by increasing drill bit diameter from 2.5 to 3.2 mm in the lowest feed rate. MTF increased by 335% while the maximum temperature (MT) decreased by 69% by increasing feed rates from 0.5 to 3 mm/sec. Also, MT decreased by 67% by increasing exit rate from 1 to 3 mm/sec. A slight increase was observed in MT by increasing the resting time from 0 to 2 seconds (p>0.05).
Conclusions: The desire drilling is drilling with lower thrust force and lower final temperature of bone. Increasing feed rate can cause an increase in thrust force while decreasing the final temperature. The maximum final temperature is highest in two first feed rate values, thus the desired value for feed rate would be 90 mm/min. Resting time has no significant effects on final temperature. So for a more accurate, efficient and uniform drill hole, resting time will be helpful.