<pedantic git mode>
As a vet I can say that unfortunately malocclusion is not a “once in a while” thing in rabbits - apart from vaccinations malocclusion related problems are probably the single biggest reason why they come into the practice*.
Although incisor malocclusion is the most obvious form (the main reason being that the incisors frequently grow out of the rabbit’s mouth and thus become visible) it is by far the easier to treat. You can indeed clip the teeth back, although once in a while this will cause a tooth to shatter longditudinally and cause a tooth root abscess (bad news). It is considered better to cut them down to size using an air powered bit (which most vets have these days) - this avoids fractures and means that theoretically you can maintain the chiselled edge. Some rabbits don’t seem to need these doing very often; if we’re having to do it every month then we’d normally recommend removal of the incisors to avoid stressing the rabbit out every few weeks with a trip to the vet; rabbits can manage very well without these incisors (which in any case don’t work properly any more) as long as they don’t actually have to cut their own grass to eat)
Sometimes the incisor overgrowth doesn’t stop the rabbit eating, but because the roots change position / size as well they can push on and block the nasolacrimal duct, the small tube that drains tears from the eye into the nose. As a result you get overspill of tears down the face. This doesn’t look very nice, and can cause dermatitis on the always - wet skin.
More of a serious problem is molar malocclusion (the molars are the big teeth at the back of a rabbit’s mouth and thus impossible to see without sedation and / or some kind of scope). The molars rarely become completely maloccluded but it only takes a slight malocclusion for them to form chisel points. The problem is that the molars are supposed to be flat (well, ridged, but blunt ridges rather than sharp points) - any points that form can cut into the rabbit’s tongue and cheeks which is obviously pretty painful.
The molars are absolute hell to remove surgically, partially because of the poor access (the rabbit’s oral opening is a lot smaller than in other animals or humans) and the fact that the roots are big, but also because each molar rubs against two of the molars in the opposite jaw, and if you remove one molar there is nothing to stop the two molars that used to wear on it from growing until they stick into the opposite gum. So we normally have to file them down periodically under sedation.
Again the roots can become malformed and in some cases actually start to break out of the bottom of the lower jaw; this can cause tooth root abscesses which again are a nightmare to fix.
Cecil is absolutely right that normal rabbit teeth are self adjusting (although some breeds such as the dwarves have a congenital tendency to brachygnathism) given an adequate supply of chewing material. Carrots though are not the answer! Rabbits are designed to eat high fibre plant material such as grass (hay is also fine), with the occasional leafy vegetable. About the closest they get to the “energy store” parts of plants is if they eat the occasional blackberry or windfall or (prehaps) dig up a dandilion root. So keep treats down to an occasional disc of carrot or eighth of an apple please!
(rabbit teeth actually wear by rubbing on one another through the fibrous material rather than through the fibrous material, so a block of softwood isn’t a good idea the way it is for rodents, by the way)
One other issue with T-shirt chewing, incidentally, is the possibility of a blockage. Rabbits digest cellulose using bacteria in their hindgut, so if the blockage occurs before this area being able to theoretically digest cotton isn’t going to be much use to it)
</pedantic git mode>
*“Fly strike” (myiasis) is another common (and particularly horrible) problem in the summer, but it in turn is often caused by either diarrhoea (too many high sugar foods?) or lack of caecotrophy (bored now, check out Cecotrope - Wikipedia for more info) due to dental pain, obesity or possibly too high a plane of nutrition.
:eek: