Say you knock your tooth out in space, you can 3D print a fake tooth. Dentists call this fake tooth a flipper. This would be extremely important because astronauts lose 1-2% of their bone density per month. If you leave the empty space blank, the bone loss would be even worse and the bone would be even weaker! It is important that the missing tooth is replaced to help the astronaut have better bone strength in that space.
The flipper would help the astronauts eat (keeping their nutrition up) and it would help with their bone density. Before launch they would leave an impression of their mouth with the NASA dentist. If they knocked out a tooth, the dentist would send over a 3D file to print. When the astronaut returns to Earth they will visit their dentist and have the dentist drill in a real fix.