Depending on which tooth is being treated, it may have anywhere from 1-3 roots. This is a big factor when it comes to the length of your appointment (treating fewer roots takes less time.)
Additionally, some teeth have unique root anatomy, making them more challenging to treat. For example, a root may be curved or hooked at the end, requiring special resources to clean out the nerve canal and fill it.
Your dentist or endodontist will use a soft mouth prop to help you relax your jaws and facial muscles throughout the process.