Back to Basics: Equine Dental Terminology and Anatomy

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Originally published on TheHorse.com

When discussing our dental health, we are familiar with commonly used terms such as plaque, cavity, or root canal. But discussing our horses' teeth can be a bit more confusing: Mesial. Occlusal surface. Interproximal space. What does it all mean? Fortunately, at the 2013 Western Veterinary Conference, held Feb. 17-21 in Las Vegas, Nev., Cleet Griffin, DVM, Dipl. ABVP, a clinical assistant professor in the Texas A&M University College of Veterinary Medicine and Biomedical Sciences, reviewed the basics of equine dental anatomy, beginning with common terms and their definitions:

• Rostral—located toward the front of the mouth (For example, incisors are positioned rostral to molars in horses' mouths)
• Caudal—located toward the back of the mouth (For example, molars are positioned caudal to premolars in horses' mouths)
• Mesial—located toward the midline of the mouth, or closer to the space between the first incisors (For example, horses' canine teeth are positioned mesial to their premolars)
• Distal—located away from the midline of the mouth
• Occlusal—located toward the occlusal (or chewing) surface of the tooth
• Apical—located away from the occlusal surface and closer to the tooth roots
• Labial—the surface of the incisors facing the lips
• Buccal—the surface of the cheek teeth facing the cheek
• Lingual—the surface of the lower teeth facing the tongue
• Palatal—the surface of the upper teeth facing the palate
• Interproximal space—the space between adjacent teeth in a row
• Vestibule—the space inside the horse's mouth between the cheeks, lips, and teeth

Dental Basics

During his lecture, Griffin described some interesting and important points to remember about horse teeth.

He explained that horses have hypsodont teeth, meaning they have long crowns divided into two regions: the clinical crown (the short length visible in the mouth) and the reverse crown (the longer portion located under the gums). The reverse crowns are situated in sockets called alveoli, he said, and the surrounding gum prevents feed from accumulating in tiny gaps between the teeth and the alveoli.

"An important anatomic concept to remember is that the horse is anisognathic, which means the upper and lower jaws are different widths," Griffin said. The maxilla (the upper jaw or cheek) is about 30% wider than the mandible (the lower jaw), and the maxillary teeth are slightly wider than the mandibular teeth, he said.

"The differing width of the jaws and the chewing motion of the horse leads to formation of sharp enamel points along the buccal edge of the upper cheek teeth and the lingual edge of the lower cheek teeth," Griffin explained. "These sharp areas can cause discomfort to the horse when eating or when bridled and working."

Horses' cheek teeth (the premolars and molars) are tightly wedged together to prevent feed from compacting in the interproximal areas, Griffin explained. Additionally, each row of cheek teeth has an angled grinding surface (generally about 10 to 15 degrees) to help break down feedstuffs, he said.

Horses' teeth grow and erupt continuously throughout their lives, generally at a rate of two to three millimeters per year, Griffin explained; this continues until the horse has aged into his 20s. This continuous tooth growth is needed to counteract dental wear resulting from "long hours of consuming tough, fibrous feedstuffs," he said.

Griffin explained that young horses develop and erupt 24 deciduous (or baby) teeth, including the incisors and premolars. Starting at about one year of age and continuing approximately through age five, horses sequentially erupt 36 to 44 permanent teeth, including incisors, canine teeth, wolf teeth, premolars, and molars. "The total number of permanent teeth depends on the presence or absence of canine teeth and wolf teeth," Griffin noted.

Griffin reviewed how the horse's teeth are organized within the mouth:

• The incisors are located at the front of the mouth, visible when you lift up the horse's lips. The permanent incisors initially have an infundibulum (a crescent-shaped depression in a tooth's crown) filled with cementum (the tissue that covers much of the visible portion of the tooth). Over time, the infundibulum wears away and disappears when the horse reaches about 15 years of age, Griffin said.
• Canine teeth are located in the space between the incisors and the premolars, with the lower canines generally positioned more rostrally than the upper ones. Male horses generally have four permanent canine teeth, Griffin said; canine teeth often do not fully develop in mares, however, and might not erupt.
• Griffin said wolf teeth are located just mesial to the first cheek teeth in both the upper and lower jaws. Horses can have anywhere from four wolf teeth to none at all; however, it's common for horses to erupt one or two upper wolf teeth.
• The most caudal group of teeth in an equine mouth are the cheek teeth. Three premolars and three molars make up each row, Griffin said. As described previously, the cheek teeth are situated close together and form an angled occlusal surface. Similar to the incisors, upper cheek teeth have infundibulae that "wear out" over time, he said, leaving very sharp buccal and lingual tooth edges in senior horses.

Take-Home Message

While equine dentistry can be complicated, having a basic understanding of dental anatomy and terminology can help owners better comprehend this complex and important topic.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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