Entering the antrum

The size of the burr required for this task depends on the space between the external ear canal and the dura. Use a burr that is sufficiently small to fit within this space. Not to do so will likely damage the external ear canal.

Also it is important to have the external ear canal sitting in an orientation where you can see the posterior aspect of the canal wall. If you are looking straight down the external ear canal, you need to be aware that there is a posterior bowing of this canal, which means that there is still a chance that the drill could go through the mastoid and completely drill away a portion of the canal and damage this structure.