Yeah, but teeth are small. If a drill goes in the same spot twice the damage won't be as great as the first time. (Not taking Pressure or force into the equation.)
But the thing is, you can't bring new information into the affirmative argument ('redundancy never heard anybody' is the resolution). All the negative side needs to do is to prove it wrong once, and the affirmative loses the argument, because if it CAN hurt someone, the the affirmative side loses cause the resolution is negated. By bringing in the new argument about a drill, you are dropping the argument about the teeth, meaning it stands (and if i want to take it further, i can say by not arguing it, you agree to it.) since it stands, i win the argument, as i explained earlier.
just a little debate 101.