How old is the bun approximately?
The teeth will grow back unless they are totally removed. It may be best to have them removed, if they will continue to cause problems when they grow back. Some bunnies have bad genetics when it comes to teeth. Typically with the incisors, the top teeth keep the bottom teeth from being too long, and vice versa, as long as there is a good diet and the teeth are aligned properly. If the bottom teeth are bad, the jaw is misaligned, etc, it may be best to just have them all out. Usually the opposite tooth must be taken out (upper and lower) or trimmed often because all rabbit teeth kind of work in opposition to each other.
Most bunnies will have molars, unless they've also been removed. At least I've never heard of a bunny not being born with molars. It is possible, I suppose. If he had really bad molars for a very long time, they could have been resorbed, according to some sources. It is ok to have a bunny with no teeth. We've had a few on the forum. You do have to keep an eye on their feeding, and cut veggies into smaller pieces, but they do just fine.
Usually bunnies won't have bald spots either, unless there's a scar or they're molting or there's some other overall health issue. A female bunny that is mounted by a male (or an aggressive bunny of any gender mounting a male to establish dominance) may have the fur at the back of her neck ripped out, in which case it would grow back. Other issues that cause hair loss, other than nutrition or overall poor health, are pretty obvious. The skin would look weird, have a big bump under it, or be scaly and dry.
You'll want to make sure the vet is rabbit-savvy. We have a listing of vets that members have approved over the years. So far, yours sounds fine.
http://www.rabbitsonline.net/f21/nm-rabbit-savvy-vets-x-10095/
Here are some helpful links on rabbit dental disease:
http://www.medirabbit.com/EN/Dental_diseases/Dental_diseases_main.htm
http://www.medirabbit.com/EN/Dental_diseases/Stella/Stella.htm
If he's otherwise healthy, it's probably a good idea to do the dental stuff at the same time as his neuter. It may be necessary to do dental help before the neuter because he may need to gain body weight and condition (if the bald patch is due to poor nutrition) before a surgery that is important but not to fix something immediately life-threatening. This is a curious situation. It sounds like the poor guy was in pretty bad shape before you got him. It is cheaper to have the teeth just filed instead of removed, and less painful, and it may be a better option just to get him to be able to eat normally for the time being. The vet may find something more serious going on with his teeth once he gets him under anesthesia and is able to examine well. Sometimes one good tooth trimming will set a bunny on the right path; sometimes they need them frequently for life. Unless it's pretty clear a trim isn't going to cut it (jaw misaligned, etc), I'd try that first instead of removing. Tooth removal is very painful for bunnies.
