Rabbit teeth are described as elodont meaning they continuously grow throughout their lifetime at an approximated rate of 2-2.4mm per week. This happens to the rabbit's adult 28 teeth once the 16 deciduous ones have been shed off.
Also, they have open-rooted (aradicular) teeth and they have a long crown (hypsodont) that extends into their gums, a feature they share with rodents, horses and so on.
The ever-growing is an adaptation to continuously replace the wearing down by attrition as they chew a lot of grassy, tough and fibrous foods that have silicate as well as they rub against each other during the mastication process.
Note that these foods are high-fiber, low energy diets meaning these animals must eat a lot of them to be able to survive making the wearing substantial. This is why Kaytee Timothy Hay, Oxbow Timothy Hay, Small Pet Select 2nd Cutting "Perfect Blend" Timothy Hay Pet Food among others are critical to this pet and must be given in unlimited amounts.
Finally, for their teeth to remain the same size, the rate of wearing must be equal to the rate at which they are growing. However, sometimes, they may grow faster than they are being ground down during masticating and chewing. This is the phenomenon we are referring to as overgrown teeth.
Rabbit overgrown teeth symptoms
The symptoms noted will depend on how severe the overgrowth is. Some of the common symptoms that may be shown include:
- Excessively long or crooked teeth especially the incisors which are easy to see.
- Drooling will cause a wet dewlap, chin, front paws and below their mouth. Mattered fur, moist dermatitis and hair loss may also occur if not treated for a long time.
- Oral lacerations including on the tongue and cheeks in case of rabbit teeth spurs. A laceration can also occur to other oral soft tissues.
- Loss of appetite followed by weight loss
- Inability to groom characterized by poor hair coat, a sticky perianal area, and increased cases of fur mites.
- Chewing difficulties and preference of soft foods
- Excessive tearing especially if there is root intrusion that is obstructing the tear duct. Root intrusion can be due to pressure exerted by the elongation.
- “Palpable swellings along the ventral border of the mandible.” 
- Nasal discharge
- Food dropping from their mouth as they try to eat
There may be severe symptoms including osteomyelitis, tooth abscesses, overall distortion of the affected tooth, breakages, and so on depending on the level of overgrowth.
The most common cause of overgrown teeth especially the incisors and sometimes premolars and molars is malocclusion. This refers to misaligned upper and lower teeth, i.e., they are not correctly aligned as they are supposed to align and consequently they cannot wear down during the chewing and grinding. There could be an overbite, and underbite or crowded teeth.
The causes of malocclusion can be genetic, commonly noted in dwarf rabbit including the Dwarf lop and Netherland lop. These dwarf bunnies may have a shorter upper jaw (maxillary brachygnathism)
However, malocclusion can also be due to overgrown cheek teeth, trauma (especially those that cause fractures), dietary issues (low fiber diet) among other causes.
Besides malocclusion, this problem can be a result of giving your bunnies diets with low fiber content, especially soft foods and not giving them chew toys and chew items. Note that fiber is important not only in ensuring a healthy gut and enhancing gut motility, but it helps in wearing down teeth.
Also, metabolism problems such as a wrong balance of calcium and phosphorus, lack of calcium and deficiency of Vitamin D have been associated with osteomalacia that makes bones weak and they may not be able to hold teeth well. This is likely to cause malocclusion.
Diagnosis will involve looking at the various clinical signs, dental observation using a speculum after your bunny has been restrained on sternal recumbency. When examining the premolars and molars, sedation might be required.
Sometimes, radiographs such as X-ray may be recommended, should your vet suspect issues such as dental abscesses, the intrusion of the root, and so on.
How to keep rabbit teeth short - rabbit teeth trimming
When it comes to trimming your bunnies teeth, all the overgrown ones must be trimmed, i.e., both the incisors, premolars and molars to bring occlusal equilibration for a correct bite.
If not caused by an acquired condition such as poor diets, then trimming should be done regularly.
Various trimming techniques will be used depending on how long the teeth have overgrown Common techniques that will be employed include:
“The best technique to trim incisors is to use a highspeed dental handpiece with a diamond grit fissure bur”  It does not require cooling and can be performed with or without sedation. Also, you can use a “low-speed latch grip contra-angle handpiece (RA class burs) and a straight handpiece (HP class burs).” 
For the case of molars, you should consider using a dental bur that has a soft tissue guard to minimize injuries.
Rabbit teeth clipping
Secondly, you can use the rabbit teeth clippers like Hanchen Stainless Steel Tooth Cutter Scissor or canine nail clippers to cut them shorter, especially the incisors. Afterward, filing might be necessary to make to get rid of sharp edges.
However, this is not the most preferred method of trimming since the teeth may crack, fracture, split, or injury your rabbit or yourself. Also, splitting or clipping it too close to the nerve (pulp) may cause a lot of pain and increase the chances of infections that may result in abscesses.
Rabbit teeth filing
Another way to trim them is by using a file. This is a course file that has smooth edges that will gently wear down teeth. It should be used for cases where the overgrowth is still small, and it may present various challenges including injuring the various oral cavity tissues.
Cutting discs are also not recommended as they may present similar challenges as clippers as they may also cause fractures, cracks, splits or injuries. Also, they may be hard to use in trimming premolars and molars owing to their position.
When using any method of trimming bunny teeth, you need to ensure you do not trim so close to the gum for the lower incisors as their pulp often extends beyond the gum line due to their rapid eruption. A trans-illumination will reveal the pulp as a pink triangle and you need to cut at least 1mm above this pink triangle.
We have a detailed discussion on rabbit teeth trimming including costs that has an in-depth discussion of the various methods.
Rabbit teeth extraction or removal
The second option you should consider extraction. This is only considered in cases where the teeth have been damaged severely. Both the incisor, premolars, and molars can be extracted under anesthesia.
Painkillers to relieve pain afterward as well as the use of antibiotics to prevent secondary infections may also be recommended.
This is a method used to arrest further growth of your rabbit’s cheek teeth. It is done by removing the apex that keeps them growing. Once done, the affected tooth may stay in place but eventually fall off and you will need to maintain the opposite tooth.
Cases caused primarily by skeletal or congenital malocclusion may require regular trimming or extraction. Other causes of overgrowth may be managed by the following methods:
High fiber diets
Provide unlimited grassy hay. Hay should account at least 80% of the daily rabbit food requirement. Chewing it will help grind the growing teeth being very abrasive. You can also include tough and fibrous greens that these animals eat.
Always ensure you monitor your rabbit’s teeth while grooming them. Do this at least weekly. Additionally, look at some of the clinical signs this condition presents.
Chew toys and items
Provide chew toys and items including the commercial ones such as Peter’s Woven Grass Ball and mats or Kaytee Perfect Chews for Rabbits or homemade ones including cardboards, pinecones, apple branches or twigs, among others.
Selecting your bunny carefully
Go to reputed breeders who will sell you a rabbit that is not predisposed to dental malocclusion and overgrowth. A pedigreed one will be good as you can see if it is genetically predisposed to this problem.