Ok, bunnies have two sets of teeth- their incisors and the molars (no canines because they are herbivores). All their teeth constantly grow.
The front ones (incisors) normally wear down on each other as they eat and chew things. (I hope this link works).
http://www.google.co.uk/imgres?imgu...age=1&ndsp=24&ved=1t:429,r:1,s:0&tx=60&ty=103
That is what the incisors should look like. The bottom ones should go behind the front ones.
Sometimes they are not lined up in the mouth properly (sometimes due to jaw shape, genetics, injury) and so grow out of line like these poor bunnies. When they don't meet properly, they don't wear down properly, thus causing these problems. This is Malocclusion (the second link is not for the faint hearted because there are some removed incisors further down the page).
http://www.google.co.uk/imgres?imgu...jLAL&esq=6&page=1&ndsp=24&ved=1t:429,r:19,s:0
http://www.vet-magazin.com/wissenschaft/veterinary-dentistry/Articles/Malocclusion-Rabbits.html
Rabbits with these problems can have their teeth clipped (more in the olden days), or burred down to keep them level, or in extreme cases (although it is becoming more and more common), the teeth can be extracted.
Those teeth can obviously been seen and checked and looked at, so its very easy to tell if your bunny has an incisor issue.
With the molars it is very different. The molars are not visible to the naked eye. A bunnies mouth is very long and the only way to see in in with an otoscope (what the doctor looks in a persons ear with). However, checking teeth even with an otoscope is not 100% accurate. The only way to fully check the teeth is under a general anaesthetic when the jaw is not tense and can be opened far wider.
This is what an xray of a rabbits skull looks like. It gives you an idea of where the teeth are placed in the skull and why they are not visible.
http://www.google.co.uk/imgres?imgu...page=1&ndsp=21&ved=1t:429,r:1,s:0&tx=99&ty=74
Molars also constantly grow. When they line up perfectly, and the rabbit has a good diet (i.e. plenty of hay and other fibrous foods), the teeth just rub down on each other and cause no problems.
If the molars don't line up properly (i.e. through genetics, injury or illness- head tilt can cause this problem because of how a rabbit has to eat with a tilted head), or if the diet is not good enough then the teeth may not wear down properly. This may mean that 'spurs' will form. This is when part of the tooth is being worn down, but another part is not so continues growing, eventually forming a spike.
When these spurs grow they can either grow vertically up and down (which is less problematical), or they can grow sideways into the tongue or into the cheek, which, as you can imagine, is pretty painful. The way they grow depends on the reasons behind the dental problems in the first place and how the teeth are wearing down.
When rabbits get spurs and they cause problems, then they need to be burred down under a general anaesthetic. It is not accepted that they can be removed, although there are some very gummy bunnies about with no molars- but that's not the standard treatment and one most vets won't consider.
If a rabbit needs one dental, it will invariably need another, but the time in between can vary depending on the problem and how its managed. Some rabbits need them every 3-4 weeks (these are generally the ones with misaligned teeth where the spurs grow into the tongue or cheek), whereas others can go for many months or years without needing one. Most of mine fall into the second category and can go anywhere from 6 months up to over a year, without needing another dental. I do have one girl who at 17 weeks had her first dental and she was unfortunately brewing again only a week after, although with some major changes she is now almost 5 months since her last dental- now aged 18 months.
The following link shows the first two pictures of a rabbit with mild/moderate spurs pointing in to the tongue. The second two pictures show the teeth burred and back to looking like normal teeth again.
http://www.google.co.uk/imgres?imgu...page=1&ndsp=21&ved=1t:429,r:5,s:0&tx=49&ty=71
Dental problems can be easy to identify if you know your bunny, or bunnies in general.
Typical dental signs are drooling, weightloss, not eating, not pooing (in short, gut stasis- which means the gut has shutdown and is not functioning. This can be fatal to bunnies because toxic levels of the wrong bacteria will grow).
The more subtle signs to see before that (or around the time the drooling may appear) would be aggression that is not normally there, smaller poos, 'doughy' stomach, acting out of character, excessive drinking, boney spine, running to food then looking like they want to eat and then running away again, eating but bits falling out of their mouth, selective eating (such as less hay, more pellets or greens, but what rabbits can and will eat will depend on the spurs).
Other signs you might see, which tally in, could be runny eyes, running nose, sneezing, lumps on the face, and those would all be associated with tooth root problems.
Obviously many of those symptoms can present for other reasons as well and be caused by other problems, so its a case of looking at the overall picture.
My vet has been amazed by how early I can pick up my bunnies problems. Normally when he sees dental bunnies they are seriously ill, not eating, drooling, lost a lot of weight, had their mouth all cut up inside from the spurs, and the owner has not realised. I have never had an injury inside my bunnies mouths because I can spot it so early, just from the slight behaviour changes. I will turn up at the vets and say 'I think X needs a dental' and my vet will be like 'how do you know' and I'll say 's/he is not himself, and I have noticed that s/he is more withdrawn, or has small poo, or whatever' and he will look at me doubtfully, then check the tummy and identify it doesn't feel right, then check the mouth and tel me that yes, said bunny needs a dental. I think he's learning that you can pick things up so early, which gives the bunny the best chance of recovery and the best chance of a long gap between dentals (if the spurs are pushing on the teeth and causing them to move slightly, that can make them more prone to more problems in the longer run- so the sooner they are sorted the better).
As rabbits age, their teeth become looser in their mouth, making them more prone to dental problems. If a rabbit is getting them young, then that is not a good sign for the future, and things are likely to get worse with age, although while the rabbit is young, it is sometimes possible to manage the problem, thus reducing the amount of dentals a rabbit needs.
Tooth roots are also common problems with rabbits, but a completely different board game to spurs. With spurs you can treat them periodically for as long as the bunny needs (or wants) you to. Roots are pretty untreatable, so its a case of managing the symptoms (be them runny eyes, abscesses, pastuerella- which is an upper respiratory infection, and most importantly, pain) which is often anti inflammatories, burring the teeth down to gumline and then treating additional symptoms and problems as they arise.'