An overjet—also known as “parrot mouth,” in which the top incisors are more advanced than the bottom incisors—can create health and welfare issues in horses, say German researchers. Surgically implanted “braces,” essentially a wire over the top teeth, can correct the issue. However, by X raying foals’ heads in exactly the same position several times over their first year of life, scientists can follow jaw growth and gain clues about whether affected foals need surgery.
“The main issues with overjet are chewing problems and improper grazing, which can lead to weight loss,” said Natalia Domanska-Kruppa, DrMedVet, of the University of Veterinary Medicine in Hannover and the Lewitz Stud, Neustadt-Glewe, Germany.
“Riding horses with overjet have bitting problems, which makes them uncomfortable when ridden,” she added.
For these reasons, scientists developed special “braces” that foals can wear to restrict upper jaw growth until the lower jaw catches up. “Surgically placed braces for horses are common in equine orthodontics and are worldwide available in equine clinics,” said Domanksa-Kruppa.
In their recent study, though, Domanska-Kruppa and her fellow researchers recorded, for the first time, radiographic evidence that foals can spontaneously correct their own overjets within the first year of life, she said. On the flip side, they also noted that foals born without overjets can develop them within the first few months of life.
In doing so, Domanska-Kruppa and her team used a new radiographic monitoring system called cephalometry, which they developed based on human orthodontics. By immobilizing a foal’s head in a specially designed restraint (with sedation), the researchers could standardize head position to ensure they could accurately and precisely compare a series of X rays in the same foal over time. The result gives a sort of time lapse look into how a foal’s facial bones evolve over a period of months, she said.
Nearly 70% of the overjet cases in her study resolved spontaneously, Domanska-Kruppa said. And those that did tended to follow certain growth patterns that differed from unresolved cases. This information could be vital for deciding whether it’s necessary to intervene in overjet situations, she said.
“It’s important to screen overjet-affected foals to decide whether surgery needs to be done or if there is a possibility that the overjet resolves spontaneously,” she said.
In their study, Domanska-Kruppa and her fellow researchers followed 13 foals with measurable overjets out of a population of 650 Warmblood foals. They first identified the foals by clinical exam at age two weeks. The scientists placed these 13 foals’ heads, while sedated, in a head-holder they designed (based on an earlier study about ideal head angles for equine orthodontic imaging) and took identical side radiographs of each foal’s head five times over 12 months. For comparison and as controls, they selected 13 foals born the same day as the 13 study foals to follow the same radiograph protocol.
Domanska-Kruppa’s team found that nine of the 13 foals (69%) no longer had overjet by nine to 29 weeks of age. However, four of the 13 control foals developed an overjet between nine and 22 weeks of age.
The angle measurements the researchers took during the study period helped them identify specific ratios that corresponded to a tendency to spontaneously resolve—or spontaneously develop—overjets, she said.
Overjets occur in about 2% of Warmblood foals, but their rates are “much higher” in Quarter Horses, explained Domanska-Kruppa.
That doesn’t mean all foals should be systematically screened with sedation and cephalometry, however, she added. Rather, foals with clinically diagnosed overjet or descending from a genetic line of horses having overjet could benefit from cephalometric measurements.
“My suggestion to owners is to control their foals for any dental abnormalities regularly and not to wait for the first dental check until the horses are being ridden,” said Domanska-Kruppa. “For breeders, I recommend excluding overjet mares and stallions from breeding.”