Supernumerary teeth--the presence of more teeth than normal--occurs in less than 3.6 percent of the human population. While the prevalence in horses is unknown, supernumerary teeth in horses is thought to be equally rare.
Researchers suspect that an extra tooth forms when a "tooth germ," the small mass of fetal tissue destined to develop into a tooth, splits in half. Either the incisors or the cheek teeth can be affected, and the extra teeth may erupt either beside or behind them.
In some cases, the teeth require veterinary attention: A 2005 University of Bristol survey of 15 horses with a total of 24 supernumerary cheek teeth found that 13 of the horses showed clinical signs including nasal discharge, facial swelling, bit evasion behavior and difficulty eating. However, two of the horses had no signs, and the teeth were discovered only incidentally during routine examinations.
Supernumerary teeth need to be removed only if they interfere with the horse's health and dental function. In some cases, the extra teeth may be manageable with routine dental care.
In the British study, 13 of the 24 supernumerary teeth were left in place, and six were extracted. (The remaining five teeth belonged to four horses who had to be euthanatized--due to either chronic, untreatable sinus infections related to the condition or because of complications from failed forceps extractions.) The clinical signs improved or resolved in 11 of the 13 teeth treated conservatively and in all six teeth that were extracted.
The optimum course of action for a horse with supernumerary teeth is best decided on a case-by-case basis. Removal is not always necessary and, as the British researchers concluded, both conservative treatments and surgical removal can result in positive results, depending on the particulars of each situation.
Read "One Tooth Too Many" in the June 2006 issue of EQUUS magazine for a related case report.