Is it more appropriate to start rotary files before entering the canal, or to enter the canal orifice and then start them?

When you start rotary files outside the canal before entering it, the file may initially enter at an angle that does not suit the canal, and this may cause instrument fracture or ledge formation in the tooth. For this reason, we place rotary instruments in the canal, advance them and start them at the point where we feel binding. This is similar to our principle of operating hand files in the canal. Starting a rotary instrument where it binds sounds frightening at first, but because the binding here is passive, it does not cause the instruments to fracture; on the contrary, it is very helpful in preventing fracture.