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Malocclusion is common in the dog, but also occurs in cats.
Malocclusion is common in the dog, but also occurs in cats.
==Malocclusion==
==Malocclusion Types==
Malocclusion can result from jaw length and/or width discrepancy (skeletal malocclusion), from tooth malpositioning (dental malocclusion), or a combination of both. The development of the occlusion is determined by both genetic and environmental factors. Specific genetic mechanisms regulating malocclusion are unknown. A polygenic mechanism, however, is likely and explains why not all siblings in successive generations are affected by malocclusion to the same degree, if at all. With a polygenic mechanism, the severity of clinical signs is linked to the number of defective genes. The most reasonable approach to evaluate whether malocclusion is hereditary or acquired is as follows:
Malocclusion can result from jaw length and/or width discrepancy (skeletal malocclusion), from tooth malpositioning (dental malocclusion), or a combination of both. The development of the occlusion is determined by both genetic and environmental factors. Specific genetic mechanisms regulating malocclusion are unknown. A polygenic mechanism, however, is likely and explains why not all siblings in successive generations are affected by malocclusion to the same degree, if at all. With a polygenic mechanism, the severity of clinical signs is linked to the number of defective genes. The most reasonable approach to evaluate whether malocclusion is hereditary or acquired is as follows:
* Skeletal malocclusion is considered inherited unless a developmental cause can be reliably identified.
* Skeletal malocclusion is considered inherited unless a developmental cause can be reliably identified.
'''Narrow mandible''': In some animals, the mandible is too narrow with respect to the upper jaw. The result is that the lower canines impinge on the maxillary [[Gingiva|gingivae]] or the [[Hard Palate|hard palate]] instead of fitting into the diastema between the upper third incisor and upper canine on either side. The animal may not be able to close its mouth and injury to the gingivae or palatal mucosa commonly occurs. In untreated severe cases, an oronasal communication may develop over time. This condition is seen in both the primary (deciduous) and permanent dentition. Persistent mandibular primary canines will further exacerbate the condition, as the permanent mandibular canines erupt medially to their primary counterparts. The incorrect dental interlock will interfere with the normal growth in width and length of the developing mandible. The condition can also be caused by persistent primary mandibular canines in a mandible of normal width. <font color="red">(pic 7 malocclusion)</font color>
'''Narrow mandible''': In some animals, the mandible is too narrow with respect to the upper jaw. The result is that the lower canines impinge on the maxillary [[Gingiva|gingivae]] or the [[Hard Palate|hard palate]] instead of fitting into the diastema between the upper third incisor and upper canine on either side. The animal may not be able to close its mouth and injury to the gingivae or palatal mucosa commonly occurs. In untreated severe cases, an oronasal communication may develop over time. This condition is seen in both the primary (deciduous) and permanent dentition. Persistent mandibular primary canines will further exacerbate the condition, as the permanent mandibular canines erupt medially to their primary counterparts. The incorrect dental interlock will interfere with the normal growth in width and length of the developing mandible. The condition can also be caused by persistent primary mandibular canines in a mandible of normal width. <font color="red">(pic 7 malocclusion)</font color>
===Dental Malocclusion===
Dental malocclusion is malpositioning of [[:Category:Teeth - Anatomy & Physiology|teeth]] where there is no obvious skeletal abnormality, i.e. there is no jaw length or width discrepancy.
'''Anterior crossbite''': This is a clinical term used to describe a reverse scissor occlusion of one, several or all of the incisors. The condition can be secondary to persistent primary incisors. However, there is probably a skeletal origin as well, since affected animals often develop a mandibular prognathic bite. In other words, an anterior crossbite in an immature animal may be the first sign of a developing mandibular prognathism. The cause can be either a dental malocclusion (i.e. linguoversion of the upper incisors) or a skeletal malocclusion (i.e. mandibular prognathism or maxillary brachygnathism). <font color="red">Pic8 malocclusion</font color>
==Class 1 malocclusion==
'''Malocclusion of the canine teeth''': The two most common abnormalities in canine tooth position are:
* Rostral displacement (mesioversion) of the maxillary canines. Persistent primary canines may be responsible for this condition. A breed predisposition has been reported in the Shetland sheepdog. <font color="red">(pic9malocclusion)</font color>
* Medial displacement of the lower canines. <font color="red">(pic10mal)</font color>
'''Malocclusion of the premolars and molars''': Posterior crossbite is used to describe an abnormal relationship of the carnassial teeth, seen commonly in the dolicocephalic breeds, where the normal buccolingual relationship is reversed.
==Classification of Malocclusion==
===Class 1 malocclusion===
Also called neutroclusion, this describes a normal rostral-caudal relationship of the maxillary and mandibular dental arches but there is '''malposition of one or more individual teeth'''.
Also called neutroclusion, this describes a normal rostral-caudal relationship of the maxillary and mandibular dental arches but there is '''malposition of one or more individual teeth'''.
==Class 2 malocclusion==
===Class 2 malocclusion===
This is also called '''mandibular distoclusion, mandibular brachygnathism''' or mandibular retrognathism.
This is also called '''mandibular distoclusion, mandibular brachygnathism''' or mandibular retrognathism.
Breeds commonly affected include the Rough Collie and the Borzoi.
Breeds commonly affected include the Rough Collie and the Borzoi.
==Class 3 malocclusion==
===Class 3 malocclusion===
This is also called '''mandibular mesioclusion, mandibular prognathism'''.
This is also called '''mandibular mesioclusion, mandibular prognathism'''.