How to Recognize and Clinically Manage Class 1 Malocclusions in the Horse

Robert M. Baratt, DVM, MS, FAVD

Class 1 malocclusions are a frequent ﬁnding in the dentition of the horse. These malocclusions often result in tooth elongations that can be detrimental to normal mastication, cause pathologic orthodontic tooth movements, and predispose to painful periodontal disease. Odontoplasty, the removal of tooth material with manual or motorized instrumentation, is generally used in a conservative manner to correct the malocclusion or prevent it from becoming worse over time. Author’s address: Salem Valley Veterinary Clinic, 12 Center Street, Salem, Connecticut 06420; e-mail: rbaratt1dvm@ gmail.com. © 2010 AAEP.

1. Introduction tooth wear are frequently seen and often described as 4 A malocclusion is defined as any deviation from nor- waves, steps, hooks, and ramps. Although these mal occlusion.1 In the horse, the normal occlusion types of occlusal abnormalities have not been previ- (orthooclusion) is a level incisor bite. In humans ously classified as a type of malocclusion, their descrip- (and many breeds of dog and cat), the incisors have tion as a class 1 malocclusion is justified and lends a normal overbite. The hypsodont dentition, an- credence to the idea that occlusal adjustment is an orthodontic procedure. Similarly, abnormal incisor gled conformation of the temporomandibular joints, wear, given the descriptive terms smile, diagonal, and anisognathism (mandibular jaw width narrower stepped or irregular, and frown, can be considered than the maxillary counterpart) result in the normal another type of class 1 malocclusion.5 10–15° angle to the occlusal surface of the cheek A malpositioned tooth, in the horse with normal teeth and enamel points on the lingual aspect of the jaw lengths, is another type of class 1 malocclusion. mandibular cheek teeth and buccal aspect of the 2 Rotations, embrications (crowding), displacements, maxillary cheek teeth. The normal horse has a and versions (tilting) are seen in both the incisor and curvature of the occlusal surfaces of the cheek teeth cheek teeth, with the highest incidence in the Min- in the longitudinal plane, called the curvature of iature Horse. An overjet is a facial projection of the Spee (Fig. 1). The rostral angulation of the distal maxillary incisors, whereas an overbite is the verti- cheek teeth and the caudal angulation of the mesial cal overlap of the maxillary incisors over the man- cheek teeth maintain tight interproximal contact dibular incisors.6 The overbite (parrot mouth) is until very late in life.3 most commonly seen in the class 2 malocclusion, in A class 1 malocclusion (neutroclusion) occurs in which the mandible is short relative to the maxilla horses with normal jaw lengths and teeth in their (Fig. 2). The maxillary incisor overbite or overjet normal mesiodistal location. Abnormalities of cheek may be accompanied by abnormalities in cheek tooth

NOTES

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Fig. 1. Quarter Horse gelding, 7-yr-old. Normal development of sharp enamel points on the buccal side of the maxillary cheek teeth and the lingual aspect of the mandibular cheek teeth (left). Buccal mucosal lacerations (arrows). Normal curvature of Spee gives the false impression of a hook on the lower third molars (311, 411). Conservative management: ﬂoating of the enamel points; note that very little rasping of the occlusal surface has occurred.

wear, such as hooks on the rostral maxillary and sedation, noting the horse’s body score, rectal tem- caudal mandibular cheek teeth. However, normal perature, and in some cases, observation of the cheek tooth occlusion is often observed with these horse’s chewing behavior and whether quidding is incisor malocclusions (Fig. 3). The class 3 maloc- present. An extraoral examination should include clusion, in which the mandible is of greater length the observation of any facial swelling, nasal than the maxilla-incisive bones, is most commonly discharge, malodorous breath, ocular discharge, pty- seen in the Miniature Horse. Mandibular incisor alism, painful response to palpation of the temporo- overjet or overbite may occur in the absence of mandibular joint region, and lymphadenopathy. cheek teeth abnormalities but is most commonly After sedation, and before placement of the full- associated with ramped mandibular ﬁrst cheek mouth speculum, oral examination of the lips, oral teeth (306, 406). mucosa and gingiva of the lips and incisors, incisor The etiology of class 1 malocclusions generally can malocclusions, and periodontal disease and assess- be determined by physical examination and radio- ment of the lateral excursion to molar contact is graphic imaging. Because malocclusions can be re- performed. After placement of the full-mouth sponsible for poor mastication, periodontal disease, speculum, the diastema between the incisors and and poor athletic performance related to oral pain, the cheek teeth is examined, and the presence of proper diagnosis and management is important. canine teeth and ﬁrst premolars (wolf teeth) is noted. The examination of the cheek teeth requires 2. Materials and Methods both an overall evaluation of the occlusion for pat- The equipment needed and method of performing a terns of abnormal tooth wear and a detailed, tooth thorough physical examination of the horse’s head by tooth examination with a good headlight, dental and mouth have been described.7 The clinician mirror, dental explorer, and periodontal probe. should perform a brief physical examination before Mobility of teeth can be assessed digitally and using

Fig. 2. Quarter Horse mare, 11-yr-old. Class 2 malocclusion (short mandible). Incisor overbite in conjunction with a normal Fig. 3. Warmblood X gelding, 14-yr-old. Incisor overjet, with cheek tooth occlusion. ramp overgrowth of 206 and 311.

AAEP PROCEEDINGS ր Vol. 56 ր 2010 459 RESPIRATORY/DENTISTRY menting the efficacy of widening the diastema between cheek teeth in cases where feed impaction is the cause of painful periodontal disease.14,15 Burs of various sizes and shapes are available from the manufacturer of some models of motorized dental floats. Instrumentation for the reduction of tooth overgrowths is largely a matter of personal preference. Although there is no substitute for direct visual oral examination, some practitioner’s prefer to use instruments (floats) to rasp tooth overgrowths with digital rather than visual guidance and assessment. In the author’s opinion, the use of motorized instrumentation allows easier direct visualization of the Fig. 4. Quarter Horse gelding, 18-yr-old. Tooth overgrowth of odontoplasty procedure and a more precise adjust- 408, with expired 108 (center). Odontoplasty of 408 (right). ment of occlusal abnormalities. The procedure is generally faster with motorized equipment, and often the ergonomics are improved. A scanning a variety of forceps. It is important to carefully electron microscopy study indicated that live odon- examine the tooth opposite from any overly long toplastic processes were exposed by routine odonto- tooth. Although crown reduction of the overlong plasty procedures and that motorized floats resulted tooth may be indicated, the pathology is generally in in less trauma to the treated surface of the tooth.16 the opposing tooth (Fig. 4). Of course, the two types of instrumentation can be The pulp horn numbering system devised by Da- used in conjunction with each other. Regardless of cre has been generally adopted.8 Particular atten- the instrumentation used, care must be taken not to tion to the presence of pulpar exposure in all cheek cause iatrogenic trauma to soft tissues or teeth. teeth is important. Any “catch” of the dental ex- Removal of excessive tooth material can cause irre- plorer on the occlusal aspect of a pulp horn should be versible pulpitis either from direct pulp exposure or noted. The depth of pulp horn and infundibular thermal damage.17,18 The clinician should always cavities can sometimes be assessed using 25- to 27- bear in mind that the equine hypsodont tooth is gauge hypodermic needles, but computed tomogra- a vital structure, which continuously erupts. phy studies have shown that these estimates Although removal of sharp enamel points on a young generally underestimate the apical extent of the le- (Ͻ15 yr old) horse may be necessary at 6- to 12-mo sions.9 Recording of these findings on a dental intervals, the older horse may require this only ev- chart is recommended and should be kept as part of ery 2 yr or even less frequently. Tooth wear is also the medicolegal records. Fewer errors and omis- significantly affected by the horse’s access to pasture sions will be made if an assistant records the findings that are dictated by the clinician as he performs the oral examination. The use of standard abbreviations approved by the Academy of Veterinary Dentistry10 and the American Veterinary Dental College11 will facilitate communication with col- leagues and specialists. Meticulous evaluation of any sites of feed impaction is important. A variety of instruments may be required to accomplish the removal of impacted feed material and cleansing and sounding of the diastemata and periodontal pockets. Long-handled straight and right-angled alligator forceps, long-handled picks and scalers, marked (in millimeters) periodontal probes, and irrigation devices are often needed. Accurate periodontal disease assessment requires the introduction of sharp instruments into the horse’s mouth and therefore adequate sedation Fig. 5. Quarter Horse gelding, 27-yr-old. Wave complex with needs to be used to prevent iatrogenic injury to the tooth overgrowth of 408 (left) and excessive wear and diastema oral soft tissues. Radiographic evaluation is cer- between 107 and 108, with food packing and periodontal disease (center). Conservative odontoplasty of 408 (right) takes this tainly indicated when probing depths exceed 10 mm tooth out of occlusion. In a younger horse, this would permit or there is significant tooth mobility or clinical evi- closure of the diastema and resolution of the periodontal disease. 12 dence of apical infection. Techniques for obtain- In this geriatric horse, the diastema will persist, and re-evaluation ing diagnostic dental radiographs have been of periodontal disease will be necessary to determine whether fur- described.13 There have been several papers docu- ther management is needed.

460 2010 ր Vol. 56 ր AAEP PROCEEDINGS RESPIRATORY/DENTISTRY It is not possible to predict with any degree of cer- tainty how much tooth overgrowth can be removed without the risk of pulp exposure. Conservative odontoplasty, the removal of Ͻ4 mm of clinical crown at any time, can be performed at 2-mo intervals when large tooth overgrowths must be corrected. The apical retraction of the vital pulp and coronal deposition of secondary dentine in the pulp horns will occur in response to this staged odontoplasty procedure. The coronal extend of the mesial pulp horn (#6) of the first maxillary and mandibular cheek teeth is not likely to extend beyond the occlusal surface of the body of the premolar. If the base of the hook is narrow, the entire hook can be removed at one visit, because the #6 pulp horn is not at Fig. 6. Thoroughbred, mare, 11-yr-old. The large hook, with a risk (Fig. 6). However, if the base of the hook is narrow base, was reduced in one session. broader, a more conservative crown reduction is justified (Fig. 7). Once the cheek teeth overgrowths have been addressed, the full-mouth speculum should be re- and the proportion of concentrate to roughage in the moved, and the excursion to molar contact should be diet. Because an unopposed cheek tooth will erupt reassessed. If there is excessive excursion to molar more quickly and has less wear than a normal cheek contact, conservative incisor crown reduction can be tooth, occlusal adjustment, in the form of crown performed.20 Some diagonal incisor malocclusions height reduction, may be required at frequent (6 mo) have recently been shown to have accompanying intervals in a young horse and yearly in an older deformation of the incisive bone.a In the author’s horse. opinion, it is not necessary and potentially deleteri- Once a diastema has formed between adjacent ous (inadvertent pulp exposure) to perform occlusal cheek teeth, an excessive transverse ridge tends to adjustments of these cases in an effort to recreate a form on the opposing cheek tooth (Fig. 5). This level bite. Odontoplasty of incisors is generally not dental overgrowth acts as a wedge, perpetuating or needed if there is normal excursion to molar contact 19 even increasing the diastema width. In some (Fig. 8). early cases, the associated feed packing and peri- odontitis may be adequately addressed by removal 3. Results of the excessive transverse ridge/tooth overgrowth Sharp enamel points are normal in the horse. at shorter intervals (3–6 mo) than the routine re- Although there is no doubt they are occasionally moval of sharp enamel points. Removal of the the cause of painful buccal or lingual lacerations tooth overgrowth will often allow closure of the di- in the horse, removal of enamel points (floating) astema (by mesial drift) and resolution of the peri- has not been shown to affect either feed digestibil- odontal disease. Similarly, a hook on the mesial ity or performance in a limited number of stud- aspect of the maxillary second premolar will some- ies.21,22 However, it is generally accepted that, times result in mesial orthodontic movement of this for many performance horses, the removal of tooth that will correct when the hook is removed. sharp enamel points on the cheek teeth results in

Fig. 7. Quarter Horse gelding, 7-yr-old. 106 hook with a broad base (left). Odontoplasty of ϳ5 mm (center). Further odontoplasty of ϳ5 mm the following year (right).

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Fig. 8. Arabian gelding, 20-yr-old. Diagonal incisor malocclusion with normal cheek tooth occlusion and normal excursion to molar contact in both directions. This diagonal bite form of malocclusion has resulted in acquired skeletal deformation of the incisive bone and/or rostral mandible. improved “rideability.” The author believes that occlusions are commonly observed in the horse, the this procedure should be conservative and in gen- practitioner should bear in mind that the vast ma- eral should not reduce the occlusal surface of the jority of these horses have an occlusion that is quite cheek tooth (Figs. 1 and 9). functional, with a normal excursion to molar con- Conservative management of class 1 malocclu- tact. In these cases, the goal of intervention is as sions has, in the author’s experience, been success- follows: reduce dental overgrowths that are causing ful in the vast majority of cases presented in general orthodontic movement of teeth, diastemata, feed practice for a “routine ﬂoat” (Fig. 10). With the exception of the geriatric patient, conservative management of diastema between cheek teeth is proba- bly preferred over diastema widening, because the risk of iatrogenic pulp exposure is signiﬁcant.23 Removal of the opposite tooth overgrowths and ad- dressing any tooth overgrowths that are exerting orthodontic forces that tend to create the diastema should be attempted before diastema burring in most cases. In the author’s experience, mesial drift will often close the diastemata in horses Ͻ20 yr of age, if tooth overgrowths are corrected.

4. Discussion The hypsodont dentition of the horse is always in a state of eruption and wear. Although class 1 mal-

Fig. 10. Thoroughbred gelding, 19-yr-old. Initial exam and odontoplasty of 411 step (upper left and right). Over the next 3 yr, the tooth overgrowths were addressed on four visits. The Fig. 9. Oldenberg gelding, 11-yr-old. Neutrocclusion; sharp lower photos are the before (left) and after (right) on the occasion enamel points, buccal lacerations; before (left) and after (right) of the last odontoplasty, which returned the 411 to a nearly ﬂoating. normal crown height.

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Fig. 11. Thoroughbred mare, 12-yr-old. Chief complaint of dysphagia, anorexia, and rapid weight loss after teeth were floated. Full lateral excursion of the mandible with no molar contact (left); overfloated cheek teeth with flat occlusal angles (right). packing, and periodontal disease and reduce dental premolars or molars. This may predispose to in- overgrowths that are the cause of traumatic soft fundibular caries and a crown that is relatively tissue contacts or excessive wear of opposing dis- weaker than the mandibular counterpart. Exces- eased teeth. sive wear is recognized as a prematurely expired With mesial drift and continued eruption of cheek (cupped) crown opposite the overgrown mandibular teeth, conservative management of many class 1 tooth. In this case, regular reduction of the man- malocclusions will be enough to eliminate the mal- dibular cheek tooth overgrowth will be needed for occlusion in young horses with undamaged cheek the life of the horse. teeth. The frequent occurrence of asynchronous Step overgrowths, ramps, and large hooks on eruption of the maxillary and mandibular fourth cheek teeth not only impede normal mastication, premolars is presumed to be a common etiology of they exert orthodontic forces that move the over- the wave complex in which there is relative tooth grown teeth, with creation of diastemata. The re- overgrowth of the mandibular fourth premolars. sultant feed impaction in turn causes periodontal In the horse Ͻ15 yr of age, correction of this maloc- disease. Some hooks are so large that they cause clusion may be possible with several crown reduc- significant trauma to the opposite soft tissues. tions of 3–4 mm over the course of 1–2 yr, because In the author’s experience, removal of large hooks the short (infracluded) maxillary cheek tooth erupts back to the level of the normal occlusal surface may without the occlusal contact of the opposite mandib- need sequential reduction to avoid pulp exposure. ular cheek tooth. On the other hand, in the older Pulp exposure has been documented when removing horse, there may not be significant reserve crown the normal occlusal surface along the mesial aspect eruption of the infracluded maxillary cheek tooth to of the second premolars (the so-called “bit seat”).24 permit correction of the wave malocclusion. Again, Basic dental principles dictate that the occlusal ta- very conservative odontoplasty is generally all that bles should be preserved. In regard to large tooth is needed. overgrowths, until more scientific evidence is avail- Complex malocclusions, such as waves, should not able, a conservative reduction of 3–4 mm every 2–3 be corrected to a theoretical normal anatomical con- mo is recommended. The use of molar cutters is dition by trying to reduce the height of all overgrown not recommended, because these instruments can teeth in an effort to create a “textbook” occlusion. cause vertical tooth fracture. In cases where the This results in unnecessary removal of crown, runs mandibular third molar has a very large distal hook, the risk of iatrogenic irreversible pulpitis, would a motorized float can still be used by placing the often require excessive incisor crown reduction to instrument cutting disc on the lingual or buccal allow normal excursion to molar contact, and may aspect of the tooth overgrowth and pressing it coro- result in quidding or even anorexia (Fig. 11). In the nally until enough space is created so the float can case of a mild to moderate wave, when the most be placed on top of the tooth overgrowth. overgrown tooth is opposed by a diseased tooth, then In the author’s opinion, if there is normal excur- annual reduction of 3–5 mm of this “peak” of the sion to molar contact, diagonal incisor bite malocclu- wave is enough to keep the weakened tooth out of sions need not be corrected. In these instances, occlusion and to protect it from traumatic contact. there has likely been adaptive remodeling of the This degree of crown reduction is not associated with incisive bone and/or rostral mandible (axial rotation quidding or a measurable change in excursion to and/or lateral deviation). Shortening of overgrown molar contact teeth will not change this skeletal adaptation. On Another proposed etiology is the presence of in- the other hand, if incisor overgrowth has precluded fundibular cemental hypoplasia of the maxillary molar contact, crown reduction of the overlong inci-

AAEP PROCEEDINGS ր Vol. 56 ր 2010 463 RESPIRATORY/DENTISTRY sors can be done in a conservative manner (3–4 mm, of the American Association of Equine Practioners 2007;460– every 2 mo). 465. 14. Dixon PM, Barakzai S, Collins N, et al. Treatment of equine References and Footnote cheek teeth by mechanical widening of diastemata in 60 horses (2000–2006). Equine Vet J 2008;40:22–28. 1. Wiggs RB, Loprise HB. Basics of orthodontics. In: Veteri- 15. Collins NM, Dixon PM. Diagnosis and management of nary dentistry, principles & practice. Philadelphia: Lip- equine diastemata. Clin Tech Equine Pract 2005;4: pencott-Raven, 1997;435–481. 148–154. 2. Carmalt JL. Observations of the cheek tooth occlusal angle 16. Kempson SA, Davidson MES, Dacre IT. The effect of three of the horse. J Vet Dent 2004;21:70–75. types of rasps on the occlusal surface of equine cheek teeth: 3. Dixon PM. Dental anatomy. In: Baker GJ, Easley J, eds. a scanning electron microscopic study. J Vet Dent 2003;20: Equine dentistry, 2nd ed. Edinburgh: Elsevier, 2005;25– 19–27. 48. 17. Wilson GJ, Walsh LJ. Temperature changes in dental pulp 4. Baker GJ. Abnormalities of wear and periodontal disease. associated with use of power grinding equipment on equine In: Baker GJ, Easley J, eds. Equine dentistry, 2nd ed. Edi- teeth. Austr Vet J 2005;83:75–77. nburgh: Elsevier, 2005;111–119. 18. Allen ML, Baker GJ, Freeman DE, et al. In vitro study of 5. Easley J. Corrective dental procedures. In: Baker GJ, Eas- heat production during power reduction of equine mandibu- ley J, eds. Equine dentistry, 2nd ed. Edinburgh: Elsevier, lar teeth. J Am Vet Med Assoc 2004;224:1128–1132. 2005;221–248. 19. Easley, J. Corrective dental procedures. In: Baker GJ, Ea- 6. Wiggs RB, Loprise HB. Basics of Orthodontics. In: Veteri- sley J, eds. Equine dentistry, 2nd ed. Edinburgh: Elsevier, nary dentistry, principles and practice. Philadelphia: Lip- 2005; 221–248. pencott-Raven, 1997;442. 20. Rucker BA. Utilizing cheek teeth angle of occlusion to de- 7. Gieche J. How to assess the equine periodontium, in Pro- termine length of incisor shortening, in Proceedings. 48th ceedings. 56th Annual Meeting of the American Association of Equine Practitioners 2010; 441–449. Annual Meeting of the American Association of Equine Prac- 8. Dacre IT. Equine dental pathology. In: Baker GJ, Easley tioners 2002;448–452. J, eds. Equine dentistry, 2nd ed. Edinburgh: Elsevier, 21. Ralston SL, Foster DL, Divers T, et al. Effect of dental 2005;91–109. correction on feed digestibility in horses. Equine Vet J 2001; 9. duToit N, Burden FA, Kempson SA, et al. Pathological in- 33:390–393. vestigation of caries and occlusal pulpar exposure in donkey 22. Carmalt JL, Carmalt KP, Barber SM. The effect of occlusal cheek teeth using computerised axial tomography with his- equilibration on sport horse performance. J Vet Dent 2006; tological and ultrastructural examinations. Vet J 2008;178: 23:226–230. 387–395. 23. Rucker BA, Carmalt JL. Measurement of equine cheek 10. American Veterinary Dentistry. http://www.fvvds.com/ﬁles/ teeth pulpcavities from mesial and caudal tooth edges, in Equine_Application_2010.docx. Accessed August 30, 2010. Proceedings. 50th Annual Meeting of the American Associ- 11. American Veterinary Dental College. http://avdc.org/ ation of Equine Practioners 2004;41–46. abbreviations.pdf. Accessed August 30, 2010. 24. Klugh DO. Principles of occlusal equilibration. In: Prin- 12. Klugh DO. Equine periodontal disease. Clin Tech Equine ciples of equine dentistry. London: Manson, 2010;75. Pract 2005;4:135–147. 13. Baratt RM. How to obtain equine dental radiographs in ambulatory practice, in Proceedings. 53rd Annual Meeting aEarley E. Unpublished data, 2009.

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