To obturate is to block an opening. Your dentist may obturate the hole where she performed a root canal. If she doesn't, you'll be in some serious pain.
The verb obturate is really more formal or technical than an everyday word like "block" or "obstruct," but you can use it as a substitute if you want to. It's more often used to describe the mechanism of a firearm, in which a bullet is designed to obturate the inside of a gun's barrel, increasing the pressure with which it's fired. The Latin root, obturat, means "stopped up."