Merck Manual

Please confirm that you are a health care professional

honeypot link

Congenital and Developmental Anomalies of the Mouth and Dentition in Large Animals


Jack Easley

, DVM, MS, DABVP (Equine),

Last full review/revision Dec 2013 | Content last modified Jun 2016

In horses, the most commonly diagnosed oral congenital deformity is parrot mouth (class 2 malocclusion), in which the maxilla is relatively longer than the mandible. In early embryonic development, the first branchial arch extends as a solid hyaline cartilaginous rod surrounded by a fibrocellular capsule from the temporal region to the midline of the fused mandibular processes. If the first branchial arch fails to close properly in the equine fetus, tooth germ can displace and result in the formation of a dentigerous cyst in the temporal region and a draining tract from the rostral pinna of the ear. In equids and cattle, many anomalies of dental development may result from exposure to teratogenic toxins. However, underlying genetic factors should always be considered.

Dental irregularities accompany systemic fluorosis in both cattle and sheep. In the milder forms of fluorosis, only the dentition may be involved. In extreme fluorosis (eg, 40 ppm in the diet for several years), other skeletal abnormalities may be seen (phalanx fracture). (Also see Fluoride Poisoning Fluoride Poisoning read more .)

Supernumerary teeth (polyodontia) are seen occasionally. In both horses and cattle, double rows of incisor teeth or extra cheek teeth may be seen. Missing teeth (oligodontia) in a dental arcade is less common and can be developmental or secondary to trauma or previous tooth removal. Treatment is determined on a case-by-case basis and may require extraction or frequent crown reduction of the unopposed teeth.

Others also read
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Test your knowledge
Various Obstructions
A 7-year-old gelding undergoes sedation for a standing surgery to clean and close a wound on the left forelimb. He is returned to his stall afterward, and several hours later he is observed to have nasal discharge containing feed material. He is also drooling, grinding his teeth, and intermittently coughing or retching. Which of the following conditions is most likely causing these clinical signs?
Become a Pro at using our website 

Also of Interest

Become a Pro at using our website