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==Signalment==
==Signalment==
With the mesocephalic skull shape, the [[mandible]] is shorter and less wide than the upper jaw. Dolicocephalic breeds have a longer than normal upper jaw. The increased jaw length results in interdental spaces that are wider than normal. Brachycephalic animals have a shorter than normal upper jaw. A short jaw results in reduced interdental spaces with rotation and/or overlap of teeth.
With the mesocephalic skull shape, the [[mandible]] is shorter and narrower than the upper jaw. In dolicocephalic breeds the upper jaw is longer than normal. The increased jaw length results in interdental spaces that are wider than normal. Brachycephalic animals have an upper jaw which is shorter than normal. A short jaw results in reduced interdental spaces with rotation and/or overlap of teeth.
Malocclusion is common in the dog, but also occurs in cats.
Malocclusion is common in the dog, but also occurs in cats.
==Malocclusion Types==
==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. However, a polygenic mechanism 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.
* Pure dental malocclusion, unless known to have breed or family predisposition, should be given the benefit of the doubt and may not necessarily be considered inherited.
* Pure dental malocclusion, unless known to have breed or family predisposition, should be given the benefit of the doubt and is not necessarily considered to be inherited.
An outline of the more common types of malocclusion is given below.
An outline of the more common types of malocclusion is given below.
===Skeletal Malocclusion===
===Skeletal Malocclusion===
'''Mandibular prognathic bite''': In the mandibular prognathic bite <font color="red">(pic4 malocclusion)</font color>, often called ‘undershot’, the [[Skull and Facial Muscles - Anatomy & Physiology|mandible]] is longer than the [[maxilla]] and some or all of the mandibular teeth are rostral to their normal position. If the dental interlock prevents the mandible from growing rostrally to its genetic potential, lateral or ventral bowing of the mandible may occur to accommodate the length. This results in an open bite and is characterized by increased space between the premolar cusp tips. In addition, the caudal angle of the mandible is caudal to the temporomandibular joint to accommodate the extra length of the mandible.
'''Mandibular prognathic bite''': In the mandibular prognathic bite <font color="red">(pic4 malocclusion)</font color>, often called ‘undershot’, the [[Skull and Facial Muscles - Anatomy & Physiology|mandible]] is longer than the [[maxilla]] and some or all of the mandibular teeth are rostral to their normal position. If the dental interlock prevents the mandible from growing rostrally to its full genetic potential, lateral or ventral bowing of the mandible may occur to accommodate the length. This results in an open bite and is characterized by increased space between the premolar cusp tips. In addition, the caudal angle of the mandible is caudal to the temporomandibular joint to accommodate the extra length of the mandible.
'''Mandibular brachygnathic bite''': A mandibular brachygnathic bite, often called ‘overshot’, occurs when the mandible is shorter than normal. This will often result in the mandibular canine [[Category:Teeth - Anatomy & Physiology|teeth]] contacting the [[Hard Palate|palate]], causing trauma. <font color="red">(pic 5malocclusion)</font color>
'''Mandibular brachygnathic bite''': A mandibular brachygnathic bite, often called ‘overshot’, occurs when the mandible is shorter than normal. This will often result in the mandibular canine [[Category:Teeth - Anatomy & Physiology|teeth]] contacting the [[Hard Palate|palate]], causing trauma. <font color="red">(pic 5malocclusion)</font color>
'''Wry bite''': A wry bite occurs if one side of the head grows more than the other side. In its mildest form a one-sided prognathic or brachygnathic bite develops. In more severe cases, a crooked head and bite develop with a deviated midline. An open bite may also develop in the incisor region so that the affected teeth are displaced vertically and do not occlude. <font color="red">(pic6 malocclusion)</font color>
'''Wry bite''': A wry bite occurs if one side of the head grows more than the other side. In its mildest form a one-sided prognathic or brachygnathic bite develops. In more severe cases, a crooked head and bite develop with a deviated midline. An open bite may also develop in the incisor region so that the affected teeth are displaced vertically and do not occlude. <font color="red">(pic6 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>
'''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 severe, untreated 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===
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.
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>
'''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 either be 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>
'''Malocclusion of the canine teeth''': The two most common abnormalities in canine tooth position are:
'''Malocclusion of the canine teeth''': The two most common abnormalities in canine tooth position are:
==Classification of Malocclusion==
==Classification of Malocclusion==
===Class 1 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===
Also called '''mandibular distoclusion, mandibular brachygnathism''' or '''mandibular retrognathism'''.
In layman's terms this is referred to as an overshot jaw or a parrot mouth.
In layman's terms this is referred to as an overshot jaw or a parrot mouth.
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===
Also called '''mandibular mesioclusion, mandibular prognathism'''.
In layman's terms this is referred to as an undershot jaw.
In layman's terms this is referred to as an undershot jaw.
'''Premature loss''' of teeth may be caused by an increased liability to [[periodontitis]].
'''Premature loss''' of teeth may be caused by an increased liability to [[periodontitis]].
Owners should also be counselled with regards the possible '''inheritance''' of the condition. Dogs with severe dental malocclusion should not be bred from.
Owners should also be counselled with regard to the possible '''inheritance''' of the condition. Dogs with severe dental malocclusion should not be bred from.
==Treatment==
==Treatment==
[[Category:Developmental Dental Conditions]]
[[Category:Developmental Dental Conditions]]
[[Category:To Do - Dentistry Images]]
[[Category:To Do - Dentistry Images]]
[[Category:To Do - Dentistry preMars]]
[[Category:To Do - Mars Check]]
[[Category:LisaM reviewing]]
[[Category:LisaM reviewing]]