HORSE’ HE S M T O M U 3 CE O T R H CREDITS CE Article 1 F From the Horse’s Mouth features important topics on equine dentistry NEW I Y M R P T O S R I T T A N N E T D TO PIC The First Premolar Teeth S ON EQUINE ❯❯ Cleet Griffin, DVM, DABVP Abstract: The first premolar teeth (wolf teeth) of horses are considered a component of the Texas A&M University permanent dentition and may be identified as Triadan ‘05. Through study of the fossil record, it has been determined that wolf teeth are dental vestiges from ancestors of the modern horse. Although wolf teeth may not be problematic for the horse, many believe that harm arising from the presence of wolf teeth in some horses may account for oral discomfort, abnormal behaviors during performance, and bitting problems. Rationale exists for veterinarians to remove wolf teeth when necessary to alleviate discomfort and bitting problems. orphologic features of the mod- upper and lower jaws.3 Over time, the sec- ern horse’s teeth represent adap- ond, third, and fourth premolars as well Mtations to ecologic changes.1 as the three molars progressively became In the Eocene period, the first ancestor (through “molarization”) long-crowned, of the horse—a small, leaf-eating mam- complex, well-developed grinders as the mal called Hyracotherium—had four horse adapted to prolonged periods of toes on each front foot and three toes grazing.1,3 The first premolar progressively on each hind foot2 and bore little resem- became smaller and is now small, cone blance to modern horses. Fossils show shaped, and usually situated just rostrally that Hyracotherium had three incisors; to the first well-developed cheek tooth3–5 one canine tooth; and seven primitive, (FIGURE 1). Thus, the first premolar (wolf short-crowned cheek teeth (four premo- tooth) is a functionless remnant from lars and three molars) in each side of the ancestors of the modern horse.1–5 FIGURE 1 At a Glance Triadan Tooth Numbering System Page 70 Anatomy and Eruption Page 71 Rationale for Removing Wolf Teeth Page 75 The maxillary dental arcades. Upper wolf teeth (arrows; Triadan 105 and Triadan 205) are just rostral to each row of the upper cheek teeth. 68 Compendium Equine: Continuing Education for Veterinarians® | March 2009 | CompendiumEquine.com FREE CE From the Horse’s Mouth There are several possible origins of the teeth were retrogressive representatives of pre- term wolf tooth, some of which appear to be historic horses’ premolars that were degenerat- based on superstition. In one publication from ing under the influence of selection. He further the 1700s, the term wolves’ teeth was used as a theorized that the use of the bit over many general description of teeth with sharp edges generations had rid the interdental space of that could prick and wound the oral mucosa premolars.10 Easley11 retold a remarkable story or tongue while eating.6 At about the same about a 16th-century military general’s horse time, Daubenton7 described the horse’s first that had turned and reared, refusing to move premolars as “supplementary premolars,”8 and forward into a battle. According to the story, some early 20th-century texts suggested that removal of a small tooth in the area of bit con- the term wolf teeth may have originated from tact alleviated the embarrassing behavior of the resemblance of these teeth to the incisors the general’s horse, which became a favorite of carnivores.8,9 Merrillat10 used the terms rem- mount for battle. Unable to leave well enough nant teeth and supernumerary teeth as syn- alone, the general’s horseman concluded that onyms for wolf teeth. He suggested that these the horse had sensed the presence of wolves when the bit was worked against the tooth, BOX 1. which instinctively caused the horse to shy in CriticalPo nt Triadan Tooth Numbering System order to protect the general.11 In some older publications, the first pre- Wolf teeth are Using the three-digit nomenclature system, the molar teeth were blamed for eye problems, functionless dental first digit designates the quadrant of the mouth including excessive watering, inflammation, remnants from and whether a tooth is deciduous or permanent. and blindness.12,13 It was even speculated that ancestors of the The numbering sequence for permanent teeth wolf teeth adversely influenced ophthalmic modern horse. is right maxilla, 1; left maxilla, 2; left mandible, branches of the fifth cranial nerve.12 Therefore, 3; and right mandible, 4. The deciduous teeth wolf teeth were commonly removed from are designated as quadrants 5 through 8 in the horses to alleviate eye ailments, resulting in same order. The subsequent digits in the num- use of the synonym eye tooth.5,10,12,13 bering system designate each tooth within the Apart from these myths and misconceptions, quadrant, starting with the central (first) inci- the presence of wolf teeth in horses remains sor, which is designated as 01. The incisors are an area of importance and interest to veteri- designated as 01 to 03; the canine teeth, 04; narians. In general, wolf teeth are not consid- the premolars, 05 to 08; and the molars, 09 to ered to serve a useful purpose. Although wolf 11 (e.g., the central incisor of the upper right teeth may not be problematic for the horse, arcade is 101, the intermediate incisor of the many horsemen and horsewomen believe that 21,22 same arcade is 102) (FIGURE 2). harm caused by the presence of wolf teeth FIGURE 2 Triadan classification of equine teeth. (From Floyd MR. The modified Triadan system nomenclature for veterinary dentistry. J Vet Dent 1991. Reprinted with permission from Baker GJ, Easley J, eds. Equine Dentistry. 2nd ed. Philadelphia: Elsevier; 2005) 70 Compendium Equine: Continuing Education for Veterinarians® | March 2009 | CompendiumEquine.com FREE The First Premolar Teeth CE FIGURE 3 The upper wolf tooth (green arrow; Triadan 205) is near the erupting second premolar (black arrow; Triadan 206). A deciduous premolar cap (blue arrow; Triadan 606) is present. A small lower wolf tooth (yellow arrow; Triadan 305) is present. (Skull specimen.) may account for oral discomfort, problems mately 30 months of age), some wolf teeth with the bit, and abnormal behavior of some may undergo root resorption or be shed.4,24,25 horses at work.11,14–20 This normal shedding process may account, in CriticalPo nt part, for the 13% to 32% reported incidence of Wolf teeth were Anatomy and Eruption wolf teeth in mature horses22,25,26 (FIGURE 3). Anatomically, the wolf tooth is a component of In my experience, the incidence of man- once superstitiously the permanent dental formula of the horse and dibular wolf teeth (Triadan 305 and Triadan and incorrectly is designated as Triadan ’05. Because practi- 405) is very low; however, it has been reported associated with a tioners are using the modified Triadan tooth that these teeth may be more common in variety of conditions. numbering system more frequently to identify some lines of Standardbred horses.27 Lower specific teeth, a review of the numbering sys- wolf teeth are usually very small but can be tem is provided21,22 (BOX 1 and FIGURE 2). The first premolars have a simple short- FIGURE 4 crown (brachyodont) structure22 and are com- posed of enamel, dentine, cementum, and a pulp chamber.23 These teeth usually erupt between 6 and 12 months of age and may be present in up to 90% of yearlings.11,22 When horses are approximately 3 years of age, sup- porting structures of the wolf tooth become sclerosed and calcified and the pulp chamber starts to obliterate with secondary dentine.23 Wolf teeth are usually no more than 1 to 2 cm in length and have a single root of vari- able length and substance, ranging from short, loose attachments to the gingiva to 30 mm in length.4,14,22 During eruption of the adjacent second premolar (which occurs at approxi- An erupted lower wolf tooth (arrow; Triadan 305). CompendiumEquine.com | March 2009 | Compendium Equine: Continuing Education for Veterinarians® 71 FREE CE From the Horse’s Mouth FIGURE 5 FIGURE 6 The upper left interdental space of a 3-year-old Quarter horse gelding. The commissure of the lips is retracted by the clinician to demonstrate the location of a nodular submucosal enlargement (arrow) that was detected by palpation of the interdental space. FIGURE 7 A small, lower wolf tooth (arrow) is adjacent to the first cheek tooth. (Skull specimen.) large with a sharp point25 (FIGURE 4). Careful examination is required to detect short, small, splinter-like lower wolf teeth because they can be positioned close to the second premolar CriticalPo nt and may be partially concealed by the mucosa of the cheek and gingiva (FIGURE 5). It is generally The upper wolf teeth usually erupt in a accepted that wolf vertical plane close to the first cheek tooth. teeth probably do Occasionally, the crown of the upper wolf not cause problems tooth may be positioned further rostral to or for most horses; palatal or buccal to the second premolar. The however, in some crown may also be angled slightly in some cases, discomfort instances.22 Wolf teeth have been reported due to the pres- to be quite large and even “molarized” in 16,25 Oblique radiograph of the upper left inter- ence of wolf teeth Clydesdale horses or other draft breeds. In some horses, a wolf tooth can be large, ros- dental space (of the same horse in FIGURE 6). may cause bitting trally displaced, and mistaken for a supernu- An unerupted wolf tooth is situated at an angle (within the white circle) just rostral to the larger problems and merary canine tooth.28 Supernumerary wolf first cheek tooth.