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:
- Overbite
- 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
- Salivation
- 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
Types
Overshot and undershot jaws are two types of malocclusions seen in dogs. Some defining features of each include:
Overshot
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.
Undershot
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.