Malocclusions in Dogs – When Teeth Are Malaligned
Puppies normally have twenty-eight deciduous (primary or baby) teeth, which erupt during the first six months of life, and adult dogs have forty-two 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 they, along with the lower canines, 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 retain 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?
Occlusion is a term used to describe the way teeth align with each other. “Normal” occlusion occurs when the upper incisors just overlap the lower incisors (scissor bite), when 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?
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 that are 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:
- 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 he upper jaw. When the mouth is closed, the teeth of the lower jaw do not occlude (align normally) with their 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 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.
Maxillomandibular asymmetry. The asymmetry may occur in a number of different ways. It is important to keep in mind that there are 2 upper jaws and 2 lower jaws. All 4 jaws grow/develop independently. Therefore, asymmetry may occur in the lower and/or the upper jaws. When there is a length disparity between the right and left side 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, then it is referred to as a side-to-side asymmetry. Finally, there may be an asymmetry that is 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. This malocclusion refers to the situation where the lower canine tooth (one or both may be affected) 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.
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