A single implant can be used as a root to hold a new tooth/crown in place. This is a relatively simple and straight forward treatment whose success compares really favourable to the other options.
Lost tooth due to decay/infection/gum disease/failed root filling/tooth breaking/trauma
Crown keeps falling out, or potentially there’s not enough tooth left to hold a crown
Missing teeth from birth (hypodontia)
Want to be able to chew as normal
Don’t want to have to remove a false tooth
Bone and gum tissue in the area shrinks away