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This is described as '''orthoclusion'''.
This is described as '''orthoclusion'''.
The length of a dog's jaw is most importantly determined by its '''genetic background'''. Problems exist commonly in dogs mainly due to the great variation in skull types within the species. Other factors can influence jaw length during growth, such as diet, metabolism, trauma, infection and forces within the mouth.
The length of a dog's jaw is most importantly determined by its '''genetic background'''. Problems exist commonly in dogs mainly due to the great variation in [[Skull and Facial Muscles - Anatomy & Physiology|skull]] types within the species. Other factors can influence jaw length during growth, such as diet, metabolism, trauma, infection and forces within the mouth.
The clinical significance of malocclusion is that it may cause discomfort and sometimes pain to the affected animal. In some cases, it may be the direct cause of severe oral pathology.
The clinical significance of malocclusion is that it may cause discomfort and sometimes pain to the affected animal. In some cases, it may be the direct cause of severe oral pathology.
==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 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.
Malocclusion is common in the dog, but also occurs in cats.
Malocclusion is common in the dog, but also occurs in cats.
==Malocclusion==
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.
* 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.
An outline of the more common types of malocclusion is given below.
===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 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>
'''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>
[[Category:Expert Review]]
[[Category:Expert Review]]
[[Category:Developmental Dental Conditions]]
[[Category:Developmental Dental Conditions]]
[[Category:To Do - Dentistry Images]]