Easley explained that a foal's first deciduous incisors erupt at about six days of age, followed by the second incisors at about six weeks and the third incisors at about nine months.
Photo: Anne M. Eberhardt/The Horse
Most horse owners are privy to caring for their adult horses' teeth and diligent in obtaining proper dental care. But caring for foals' and young horses' deciduous (or simply put, baby) teeth is a little different, at least from a veterinary standpoint.
At the American Association of Equine Practitioners Focus on Dentistry meeting, held Sept. 18-20 in Albuquerque, N.M., Jack Easley, DVM, MS, Dipl. ABVP, a private practitioner from Equine Veterinary Practice LLC, in Shelbyville, Ky., discussed what to watch for when dealing with deciduous teeth, and what veterinarians look for when examining them.
"Knowledge of eruption times of deciduous and permanent dentition should be second nature to veterinarians working in the equine mouth," Easley said. "The shedding of deciduous teeth is an entirely natural process that generally does not require human intervention to proceed normally."
However, he noted, as with any other natural occurrence, sometimes things don't go as planned. Some veterinary intervention could be required to put the young horse's mouth on track for a healthy life.
Basics of Tooth Eruption
"Horses under five years of age have mixed hypsodont dentition," Easley began. "From 12 months to six years, equids shed 24 deciduous teeth and erupt 36 to 44 permanent teeth."
Easley explained that a foal's first deciduous incisors erupt at about six days of age, followed by the second incisors at about six weeks and the third incisors at about nine months. These deciduous incisors are smaller than the horse's permanent teeth and are shaped like a dome.
"They have a flattened root, short crown, and shallow infundibulum (a crescent- shaped depression in the central crown of a tooth) on the occlusal (chewing) surface," he noted.
The incisor caps begin shedding when the horse is about two-and-a-half years of age and continue to shed until the horse reaches about four-and-a-half years.
Horses' deciduous premolars begin erupting shortly after birth, Easley noted.
"As the juvenile horse matures, the crowns of deciduous premolars wear thin and the roots resorb, forming a flat premolar cap as the underlying permanent teeth erupt," he added.
The juvenile horse's permanent teeth will erupt starting at about a year old and continuing until the animal is four years of age.
Easley explained that horses have vertically successional teeth, meaning that each deciduous tooth and its associated permanent tooth reside in the same alveolar crypt (the sockets from which horses' teeth erupt). The mechanisms behind equine tooth eruption have not been studied in great detail, he noted, but it's likely that eruption is a multifactorial (having multiple causes) process fueled by eruptive, resorptive, and hydrostatic forces.
He also relayed that between the deciduous tooth and the permanent tooth lies a layer of soft tissue that contains osteoprogenator cells (loosely organized cells that become osteoblasts, or cells that can form bone), cytokines (inflammatory mediators), and odontoclasts (cells that aid in the resorption of deciduous teeth roots). This layer of soft tissue plays a major role in helping the horse's body transition successfully from deciduous teeth to permanent dentine.
"The combined action of resorption of the deciduous tooth roots, development and eruption of permanent successors, and attrition of the clinical crown results in the shedding or exfoliation of a wafer of the deciduous tooth, often referred to as a cap," Easley explained.
"Deciduous premolar caps close to natural exfoliation should: 1) be digitally loose; 2) have partial loss of the crown; or 3) have a palpable demarcation noted on the lingual (tongue) or palatal (the palate, or middle part of the roof of the mouth) aspect of the clinical crown with little or no gingival attachment to the remainder of the cap," Easley noted, adding that malodor often arises as the teeth draw near to shedding.
Easley reported veterinarians often encounter eruption pseudocysts--bony enlargements located on the lower jaw or the upper cheek bone--when dealing with juvenile teeth.
"These pseudocysts (or eruption bumps) normally result from erupting permanent premolars and are most prominent in 3- and 4-year-old horses," he said, adding that the growths generally regress and disappear within a year or so.
Maleruption in Juvenile Horses
Easley reviewed several types of maleruption (eruption of a tooth out of its normal position) juvenile horses can face when their permanent teeth develop.
Worn Deciduous Teeth Crowns--When the crowns of deciduous teeth become worn, they loosen to the point they are displaced or shed into the horse's mouth. Easley noted these worn caps and their aftereffects are often associated with gingivitis or periodontal disease.
Retained Deciduous Incisors--As the name suggests, this occurs when one or more incisor does not shed as the permanent teeth arrive. Often, this abnormality is caused by "the permanent tooth erupting slightly (nearer the inside of the horse's mouth) to the deciduous, resulting in failure of the deciduous root to completely resorb."
Easley explained that retained deciduous incisors cause clinical signs including head tossing during eating, rubbing incisors on fixed objects, quidding (dropping chewed food from the mouth), and bitting problems. He noted that in some cases a narrow space can develop between the deciduous tooth and the permanent tooth, a precursor for periodontal disease in horses.
Loose incisor caps are often easily removed in standing horses, he said; however, some instances require sedation to successfully remove the cap.
Retained Premolar Caps--"Premolar caps can appear much like a table with four legs lying over the top of the permanent tooth," Easley said. Gingivitis and periodontal disease can result if the premolar cap's roots remain in the gum after the cap is shed, and it also predisposes horses to developing dental problems later in life.
Retained premolar caps can cause gingival irritation, dysmastication (abnormal chewing), anorexia, loss of appetite, and a predisposition to malocclusion (abnormal relationships between opposing teeth). Further, he explained, eruption bumps can result from the delayed eruption of permanent teeth, an occasional side effect of retained dentation.
Easley said these are primarily cosmetic problems; however, he warned that in some cases they can be caused by anachoretic pulpitis--a condition in which blood-borne bacteria become lodged within the pulp of the tooth, necessitating immediate treatment.
Easley noted that, similar to loose incisor caps, these caps can usually be removed easily.
Malocclusions--Several different types of malocclusion can affect juvenile horses as they shed their deciduous teeth, Easley noted. Permanent teeth can erupt misaligned with the rest of the teeth, spaces can develop between permanent teeth, and overcrowding can occur in young equine mouths.
In some cases of malocclusion (i.e., with asynchronous eruption of permanent teeth--permanent teeth in close proximity that erupt at different times) a veterinarian will recommend removing deciduous teeth.
"As a general rule in equine practice, if one cap has shed, the cap in the same position on the opposite side of the jaw should be evaluated and, if loose or close to exfoliation, it should be removed," he explained.
To Remove, or Not to Remove?
"The practice of methodically removing deciduous teeth at set ages results in premature removal in some horses," Easley noted.
In cases like these, when the deciduous teeth are removed prematurely, the dental sac covering the underlying permanent tooth is exposed and quickly destroyed by mastication, Easley said. This leads to loss of blood supply to the chewing surface, where active cement deposition might still be occurring, he added, which can result in conditions that predispose the animal to the development of caries (cavities) later in life.
For these reasons most veterinarians opt to let healthy deciduous teeth shed on their own.
Although many horses' deciduous teeth shed without incidence, there are times when maleruptions, retentions, or malocclusions develop in the juvenile mouth. In these cases, a veterinarian familiar with equine dentition is the best resource for keeping a young horse on the road to life-long health and wellness.
About the Author
Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.
POLL: University Equine Hospitals