Normally, a rabbits top 2 teeth should overlap the bottom 2 teeth slightly. If the rabbits' bite is not aligned properly, the rabbit is unable to wear the teeth down normally and the teeth continue to grow.
Rabbits teeth grow approximately 1/2" a month, and the rabbit will wear down its' teeth through chewing on things such as wood.
Malocclusion is when the rabbits teeth continue to grow. For one reason or another the rabbit is unable to wear its' teeth down normally. A rabbit may be born with its jaw not in correct alignment. A rabbit that pulls on wire can also "pull" his teeth out of alignment. Also, a rabbit can break a tooth and cause the opposing tooth to grow unchecked. I have also had a rabbit have a run in with a wall and "knock" himself into malocclusion.
If you breed rabbits, never breed a rabbit with malocclusion. If you have a rabbit with great depth and malocclusion, put the rabbit down(or find a home for the rabbit, but make sure the person knows about the rabbits teeth and how to care for it) and find another rabbit with great depth and good teeth.
If you breed the rabbit, you may get 1/2 of all the rabbits offspring with bad teeth.A rabbit with malocclusion will be disqualified at a show.
Another form of malocclusion is called "peg" teeth or "butting" teeth. This is where the rabbits bite is flat or the teeth hit exactly on top of one another. This is not a disqualification at a show, but it is a fault. If you have a rabbit with peg teeth, watch his bite very carefully, it can turn into full blown malocclusion. I also have some netherlands between 1 and 4 months have peg teeth and then go on to develop a normal bite. Netherlands and other rabbits with "flat" or "squished" faces are more prone to malocclusion that other breeds of rabbits.
What can you do for a rabbit with malocclusion? If this is a pet, you can trim the teeth. If this is new to you get someone to help. Hold the head still and trim the teeth down to about 1/4". I've used scissor-like nail trimmers that you can buy for very thick toenails. It doesn't hurt the rabbit at all. Another suggestion is every day to press in on the rabbits lower teeth, to try forcing the teeth into alignment. Also, provide the rabbit with a small block of untreated wood, some people have used the chew bones that are marketed for dogs.