Table 3.
Guidelines for bone drilling with minimum bone tissue injury.
| Guideline for bone drilling | Literature review recommendation | Reason |
|---|---|---|
| High drill speed with larger force (of the order so that the bursting of the bone should not take place) | No clear indication from the past studies but majority of the studies recommends high drill speed with larger force for minimum heat generation | Increase in speed and force increases the rate of heat generation but reduces the time of drilling. Hence overall less total heat is generated |
| Supply of coolant | Coolant should be used whenever it is feasible | Coolant helps in dissipating the heat through conduction. Besides taking away the heat by conduction, the coolant also provides lubrication and irrigation (excluding closed loop internal cooling system). Lubrication reduces the friction during drilling and hence less heat is generated. Irrigation causes the effective removal of chips and debris which avoids clogging of flutes during bone drilling and facilitates less heat generation |
| High drill rake angle | Rake angle of 20°–30° is recommended | Higher the rake angle, lower are the cutting forces which increases its cutting efficiency and reduces the heat generation |
| Use of split point | Can be used effectively for bone drilling as the friction between the flank and the bone is reduced by increasing the clearance angle half way along the surface | Split point causes reduction of the friction of the flank with workpiece so less heat is generated |
| Quick helix or worm spiral | Temperature decreases uniformly with increasing helix angle. The recommended ranges are 25°–35° or drill bit with parabolic flutes can be used | High helix/parabolic flutes provides an excellent clearance of debris which reduces the friction and hence reduces the heat generated |
| Two phase drill bit (step drill bit) | Step drilling is highly effective method of minimizing temperature elevation | Material removal from drilling site takes place gradually which lowers the temperatures generated during drilling |
| Large point angle | Point angle in the range of 100°–130° is recommended by most of the researches | Larger point angles provide full contact of the cutting lip with the bone as soon as drilling starts and hence less total heat is produced due to the faster cutting action |