Unlike dogs/cats (and us), the teeth of rabbits continue to grow throughout the life of the rabbit. They are kept at the proper length and shape by the action of the teeth wearing against each other. When anything interferes with the ability of the teeth to wear normally, teeth actually overgrow, and can cause a host of problems, such as inability to eat, and pain due to laceration of soft tissues. Some rabbits are unlucky enough to be born with congenital jaw malformations that prevent the incisors from wearing against each other normally.
While these teeth can be trimmed back to a more reasonable length, they will only continue to regrow.
Fortunately, rabbits do not absolutely have to have incisors to eat. They need the incisors to cut large food items into smaller pieces, or to cut growing good such as grass or weeds. But they aren't required to eat hay, pellets, and smaller bits of greens, which are crushed with the sharp premolars and molars (also called cheek teeth).. For this reason, incisor extraction is a great option that will prevent the need for frequent re-trimming. Extraction is done under general anesthesia with several kinds of medication to control any discomfort.
Here is our rabbit after extraction. He was eating normally within the next few days.