Skeletal Malocclusion

February 2006
Dr Gerhard Steenkamp

A client presents his dog for evaluation after it was disqualified at a recent dog show. The complaint of the judges was that the dog has an overbite which is heritable (Fig D Mand Brachy . . . . )

a) What are the components of a normal occlusion in the dog?
b) Broadly classify malocclusion in 2 categories

Memo (Fig. Dog chart lateral…..)

a) The normal bite or occlusion of a dog is known as a scissor bite and consists of 4 components:

1 The maxillary incisors are just rostral to the mandibular incisors; the incisal edge
of the mandibular incisors contacts the cingulum( a ridge on the caudal aspect of the maxillary incisor cusp) of the maxillary incisors.
2 The mandibular canine is centred between the maxillary canine and third incisor,
without touching either of them.
3 The tips of the crowns of the mandibular premolars fit into the interdental spaces of
the maxillary premolars, with each mandibular premolar placed mesial to (in front
of) the maxillary premolar [i.e. the "pinking shear" effect].
4 The palatal surface of the maxillary fourth premolar (carnassial) occludes with
buccal surface of the mesial (rostral) part of the mandibular first molar; the
occlusal surface present on the distal (caudal) part of the mandibular first molar
occludes with occlusal surface of the maxillary first molar.

b) Malocclusion can broadly be classiefied as being of Dental or Skeletal origin.

Dental - can be due to abnormal development of a tooth (i.e. odontoma), trauma to a tooth(avulsion) or abnormal eruption of a tooth.

Skeletal - these cases have an abnormal jaw length which is generally associated with an inheritable condition (In this example a too short mandible - mandibular brachygnathism). These animals should not be used for breeding and correctly should be prevented from being shown.


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