What is Overshot and Undershot Jaw?
Occlusion refers to the contact and alignment of the teeth in the upper and lower jaws. In normal occlusion, the lower incisors are overlapped by the upper incisors, called a scissor bite, the lower canines are equidistant between the upper canine teeth and the third lower incisor, and the premolars point to the spaces between the upper jaw teeth. Malocclusions occur when there are variations from the classic scissor bite, and can be caused by a misalignment of the jaws or teeth.
Overshot and undershot jaws are types of misalignments of the mandible, or lower jaw, and the maxilla, or upper jaw. Overshot refers to an upper jaw that is longer than the lower jaw, while undershot is when the lower jaw is longer. These misalignments, or malocclusions, can cause trauma, discomfort, and problems with eating in affected dogs.
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Symptoms of Overshot and Undershot Jaw in Dogs
If your dog has an overshot or undershot jaw, he may have trouble closing his mouth. The slightly open mouth has sometimes been called salmon jaw, as it can resemble the open mouth of a fish. The longer upper jaw associated with overshot jaw can cause a parrot beak-like appearance. Besides looking unusual, a misaligned jaw can cause trauma and discomfort to various parts of the mouth as the misaligned teeth come into contact with tissues that would not be touched in normal occlusion. Signs your dog may have a misaligned upper or lower jaw include:
- Protruding lower jaw
- Abnormal jaw growth
- Incisors that meet edge to edge
- Inability to close mouth
- Slightly open mouth
- Difficulty chewing food
- Preference for certain kinds of foods, such as bigger pieces
- Inability to keep food in mouth while chewing
- Rubbing at face
- Oral pain
- Hard palate trauma
- Defects in the hard palate
- Lip or soft tissue trauma
- Oral ulcers
- Tooth wear
- Exposure of tooth pulp
- Tooth loss
Overshot and undershot jaws are two types of malocclusions seen in dogs. Some defining features of each include:
This is a Class II malocclusion that is also called mandibular brachygnathism, mandibular distoclusion, or an overbite. This type of misalignment is characterized by a shorter lower jaw and a longer upper jaw, which causes the lower canine teeth to strike the palate or upper canines. All dogs are born with an overshot jaw that allows them to nurse as new puppies. As the puppies grow, the lower jaw grows to catch up to the upper jaw. If the jaw does not have that growth spurt, it can cause displacement of the canines, which can then also inhibit the mandible growth.
This is a Class III malocclusion that is also referred to as mandibular prognathism, maxillary brachygnathism, mandibular mesioclusion, or an underbite. This malocclusion is characterized by a shorter upper jaw and a longer lower jaw, resulting in lower teeth that are in front of the upper teeth. While this condition is normal for some breeds, such as Bulldogs, in many breeds it is unusual. An undershot jaw occurs when the lower jaw grows faster than normal and becomes longer than the upper jaw, and is usually evident around 8 weeks of age in puppies. This misalignment can cause soft tissue trauma, such as to the lips. When the incisors meet instead of fitting next to each other, it is called a level bite. When the malocclusion causes the lower incisors to be placed in front of the upper incisors, it is called a reverse scissors bite.
Causes of Overshot and Undershot Jaw in Dogs
The cause of overshot and undershot jaws in dogs relate to the increased or decreased rate of growth of the upper and lower jaws in relation to one another. This can occur due to a:
- Genetic disorder
- Systemic infection
- Nutritional disorder
- Endocrine disorder
- Abnormal setting of puppy teeth
- Early or late loss of puppy teeth
Diagnosis of Overshot and Undershot Jaw in Dogs
If you have noticed that your dog’s jaw seems abnormally shaped, or that he is having a hard time chewing or keeping food in his mouth, you may need to take your dog in to your veterinarian. After a quick physical exam, your vet may have to sedate your dog in order to perform a thorough oral exam. This will assess your dog’s skull type and teeth location in relation to the teeth on the opposite jaw.
Often, the placement of the upper and lower incisors in relation to one another can determine what type of malocclusion your dog has. Your vet will note any areas of trauma due to teeth striking those areas, and any cysts, tumors, abscesses, or remaining puppy teeth that may be present. A dental X-ray can also help to assess the health of the jaws and teeth. These diagnostic methods will lead to a diagnosis of an overshot or undershot jaw in your dog.
Treatment of Overshot and Undershot Jaw in Dogs
Treatment of a jaw misalignment will depend on the severity of the condition. If your dog has a misalignment, but can still bite and chew food without problems, no treatment may be needed. If the misalignment is caught early in a puppy’s life, it may only be temporary and may correct itself over time.
However, there are times when intervention may be needed. If your puppy’s teeth are stopping the normal growth of his jaws, then surgery to remove those puppy teeth may be performed. This may allow the jaws to continue to grow, but will not make them grow.
For older dogs who are experiencing pain and trauma due to misaligned jaws and teeth, oral surgery is generally performed to extract teeth that are causing trauma, to move teeth so that they fit, or to create space for a misaligned tooth to occupy. Other therapies include crown reductions or braces.
Recovery of Overshot and Undershot Jaw in Dogs
Overshot and undershot jaws in dogs are often genetic defects that cannot be controlled. As such, the earlier the intervention, the better the outcome for your dog. While the condition can be severe if the misalignment causes your dog to be unable to eat, in many cases, orthodontic intervention can lessen the pain and trauma associated with malocclusion and help your dog to comfortably live with the condition. Recovery will depend on how early the condition was treated and how mild or severe it is, but is generally fair.
If your dog is genetically programmed to have an overshot or undershot jaw, intervention can help, but will not slow or stop the abnormal growth of either jaw. Prevent jaw misalignments in puppies by not breeding dogs who have overshot or undershot jaws.
Overshot and Undershot Jaw Questions and Advice from Veterinary Professionals
Ruby first displayed excessive drooling at about 2-3 months old, and it has not let up since. We initially assumed she was teething and that the drooling would stop when her permanent teeth came in. Of course, we were wrong, and now Ruby has an underbite. There is about a 3/4-inch space between the upper and lower incisors.
I also noticed her upper incisors line up straight rather than adhering to the shape of the jaw, if that makes sense (her bottom incisors are arranged in an arc, so they're fine).
As a consequence, she has a poor grip on her food and water, making a big mess near her feeding area. She's also not inclined to play with dog toys that require teeth (she'll chase a ball but won't grab it).
Thankfully, she's adapted to smacks and body-slamming when playing with our other GSD.
Ruby also has a littermate who lives nearby. This puppy has a normal muzzle, which makes Ruby's appearance more noticeable when juxtaposed by her sister.
I could email pictures if you'd like a more tangible description.
Oh, forgot my question. Will Ruby's condition worsen with age? Is treatment still an option at this time?
Also, her lips are very loose, which exacerbates the drooling. Are any of these correlated (underbite, drooling, poor grip, loose lips)?
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Hi, I'm BNu sister living in Seoul, Korea. In Seoul, there are only 2 dental vets, so hard to make a decision with the limited information. Your answer would be great, big help for me..
BNu has undershot Bite, her bottom 3 front teeth are loose , gum has been going down. Diagnosed that the 3 must be extracted and other front 7 teeth (top 4, bottom 3) are better to be removed. But she eats well by now, I could touch her mouth and brush her teeth so I guess it is not that much painful yet. Nontheless her front teeth should be extracted? If necessary, I'll send you some pictures of her teeth. My email address is this: [email protected]
There are a few criteria for tooth extraction including are the teeth healthy? Are they loose? Are they affecting any soft tissues of the mouth (irritating gums or palate for example)? Do they cause problems when eating? So you can see there are many different viewpoints which need to be considered, generally if a tooth is healthy we’ll do as much as we can to keep the tooth but if it is malpositioned, loss of bone surrounding the tooth (based on x-ray) or it is causing pain or discomfort a healthy tooth may need to be removed. Your Veterinary Dentist will (should) try to retain all healthy teeth but in some instances it is best to removal all teeth in an affected area. The decision may also be varied by professional preference or a different standpoint to treatment, the link below gives a good indication for the criteria for tooth extraction. Regards Dr Callum Turner DVM
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