Depends on how long you take off for leave and which specialty. The Commission on Dental Accreditation requires a certain amount of months in residency and if you are going to be out for 3+ months I think you will need to program extend, at least for OMS. Luckily, this year the OMS standards eliminated the issues of extending your program and the program taking a hit because of this. So residents who extend are not causing the PD more paperwork.