Front view of a dog's teeth showing incisors and canines, with normal occlusion.Puppies normally have 28 deciduous (primary or baby) teeth, which erupt during the first six months of life. Adult dogs have 42 permanent teeth. Dogs have four types of teeth:
- Incisors are the teeth located between the canines on the upper and lower jaws. They are used for grasping food and, along with the lower canines, they help keep the tongue within the mouth.
- Canine teeth are located on the sides of the incisors and are used to grasp food and other objects. The lower canines help keep the tongue within the mouth.
- Premolars are located behind the canines in both the upper and lower jaws and work together to shear or cut food.
- Molars are behind the premolars and are the teeth found at the back of the mouth. They are used for grinding food to prepare it for swallowing.
What does occlusion mean?
Side view of a dog's teeth showing incisors, canines, premolars, and molars, with normal occlusion.Occlusion describes the way teeth align with each other. “Normal” occlusion occurs when:
- the upper incisors just overlap the lower incisors (called a “scissor bite”),
- the lower canines are located at an equal distance between the upper third incisors and the upper canine teeth, and
- when the premolar crown tips of the lower jaw point between the spaces of the upper jaw teeth.
Flat-faced breeds (brachycephalics), such as boxer dogs, shih-tzus, Boston terriers, and lhasa apsos, have “abnormal” bites that are recognized as being “normal” for their breed, where the lower jaw protrudes in front of the upper jaw and alters the above tooth-to-tooth relationships.
What is malocclusion?
Dog's teeth showing a skeletal malocclusion (lower jaw is longer than upper jaw, creating malalignment).Malocclusion refers to abnormal tooth alignment. There are two types of malocclusion: skeletal and dental.
A skeletal malocclusion results when an abnormal jaw length creates a malalignment of the teeth. A dental malocclusion, or malposition, occurs when the upper and lower jaw lengths are considered normal, but there may be one or more teeth out of normal alignment (malpositioned tooth/teeth).
When a dental or skeletal malocclusion causes trauma to other teeth or to the oral soft tissues, the condition is termed non-functional or traumatic, and treatment is needed. Therapy options include extraction, moving the offending or offended tooth/teeth, or surgically creating additional space for the malpositioned tooth to occupy.
What are some common forms of skeletal malocclusion?
Mandibular distoclusion or Class 2 Malocclusion (MAL2). Also known as an overbite, overjet, overshot, and mandibular brachygnathism, it occurs when the lower jaw is shorter relative to the length of the upper jaw. When the mouth is closed, the teeth of the lower jaw do not occlude (align normally) with the corresponding teeth in the upper jaw. There is a space between the upper and lower incisors when the mouth is closed and the lower incisors may traumatically contact the roof of the mouth behind the upper incisors. The upper premolars are aligned too far toward the nose compared to their counterparts in the lower jaws.
Mandibular mesioclusion or Class 3 Malocclusion (MAL3). Also known as an underbite, undershot, reverse scissor bite, and mandibular prognathism. It occurs when the lower jaw is too long relative to the upper jaw and the lower teeth protrude in front of the corresponding upper teeth. If the jaw length discrepancy is minimal, then the upper and lower incisor teeth may meet each other edge to edge, resulting in an occlusion referred to as an even or level bite.
Dog's teeth showing a skeletal malocclusion (maxillomandibular asymmetry).Maxillomandibular asymmetry. The asymmetry may occur in several different ways. It is important to keep in mind that there are two upper jaws and two lower jaws. All four jaws grow and develop independently. Therefore, asymmetry may occur in the lower and/or upper jaws. When there is a length disparity between the right and left sides, it is referred to as a rostrocaudal asymmetry (upper and/or lower).
When the asymmetry results in a lack of centering of the upper and lower jaws over each other, causing a midline shift, it is referred to as a side-to-side asymmetry.
Finally, an asymmetry may be exhibited as an abnormal (increased) space between the upper and lower jaws (may affect one or both sides) and is referred to as an open bite.
What are some common forms of dental malocclusion?
Rostral crossbite. This occurs when the canine and premolar teeth on both sides of the mouth are normally aligned, but one or more of the lower incisors are positioned in front of the upper incisors when the mouth is closed.
Caudal crossbite. This occurs when one or more of the lower cheek teeth are more towards the cheek than the opposing upper cheek teeth when the mouth is closed.
Linguoverted mandibular canines (also known as lingually displaced canines or base narrow canines). In this malocclusion, the lower canine tooth (one or both) is angled inward. The linguoverted canine is then often in traumatic contact with the roof of the mouth. Often, this condition is due to persistent deciduous canine teeth and can usually be corrected through various options such as tooth movement, crown reduction and restoration, or extraction.
Mesioverted maxillary canines. This dental malocclusion may be inherited (e.g., shelties) or developmental, secondary to persistent deciduous teeth.
