Evidence-Based Equine Dentistry: Preventive Medicine

Vet Clin Equine 23 (2007) 519–524 Evidence-Based Equine Dentistry: Preventive Medicine James L. Carmalt, MA, VetMB, MVetSc, MRCVS* Scone Veterinary Hospital, 106 Liverpool Street, Scone, NSW 2337, Australia Equine dentistry is one of the most common tasks performed by large animal practitioners [1]. Dental publications exist from circa 600 BC. By the time of Aristotle (330 BC), ageing horses by their teeth and the effects of periodontal disease had been noted and treatments described. Knowledge progressed slowly, and it was not until Markham (1610–1723) that the technique to remove sharp overgrowths on the lateral edges of the upper cheek teeth to prevent soft tissue damage was reported. Despite this incredible history, equine dentistry sadly remains an art and not a science. An evidence-based approach to equine dentistry is poorly used because of the perceived importance of the intervention by veterinarians and owners. Consequently, a critical evaluation of what is being achieved by so-called ‘‘occlusal equilibration’’ or other routine procedures is often not performed. The benefits of interventional dentistry (ie, oral extraction, repulsion in cases of diseased teeth) are obvious and preclude the need for randomized controlled trials, whereas the importance of routine dental floating (also known as occlusal equilibration) has not been fully determined. The purpose of this article is to review the veterinary literature to evaluate the evidence supporting the role of equine dentistry in weight loss or gain and as a cause of poor performance. Several modern equine texts cite dental disease as a possible cause of oral pain, colic, gastrointestinal impaction, weight loss, and poor performance [2–7]. It has also been stated that horses focus on the pain rather than on performance when experiencing oral discomfort, which supposedly leads to a failure to respond to bit cues by evading the action of the bit or by ignoring it completely. The research behind these accepted statements is completely lacking. The literature does not conclusively define oral pain in the horse, nor does it confirm that poor * Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK, S7N5B4, Canada. E-mail address: [email protected] 0749-0739/07/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.cveq.2007.03.002 vetequine.theclinics.com 520 CARMALT dentition affects performance or weight loss or is a factor in the pathogenesis of colic. In addition to this, a recent prospective, matched, case-controlled study examining dietary and other management factors associated with colic in horses did not find a statistical association between horses floated at least once yearly and control horses [8]. Occlusal equilibration (floating, rasping, or filing) is the most common equine dental procedure performed [9], the goal of which has been stated as ‘‘. to maintain the symmetry and balance of the arcades and to allow a free elliptical chewing motion’’ [10]. This single goal has subsequently been refined to focus on four separate but integrated goals: (1) to relieve discomfort associated with oral soft tissue injuries caused by sharp enamel points, (2) to improve mastication and digestion of feedstuffs, (3) to alleviate stresses on abnormally worn teeth, and (4) to prevent discomfort associated with the bit, [11] all of which should hopefully improve mastication, maintain proper alignment, and increase the longevity of the dental arcade. Nowhere in this definition does it state that occlusal equilibration improves performance or weight gain. Occlusal equilibration and weight loss Consider a 15-year-old horse that is presented to a veterinary practice in poor body condition. The history is one of insidious weight loss over the past 6 months. Most readers have automatically formulated a differential diagnosis list and treatment plan during the preceding two sentences. The author would suggest that most veterinarians would have parasites and dental disease at the top of the list, with deworming and a dental float as a treatment plan. The literature would suggest that dental malocclusions alone play a limited role in weight loss. Staggeringly, despite a 2600-year history of dental publications, publication of the results of the first clinical trial only occurred in 1995. Trials in 1995 [12] and 2001 [13] examined the role of dentition in equine nutrition using clinical trials. The former study pronounced a benefit of dental floating on feed digestibility, whereas the latter did not. Careful examination of the former study reveals the use of historical controls and small numbers of animals in the study, which questions the validity of the conclusions reached. Numerous studies have been published subsequently. These suggest that although occlusal equilibration increases the rostrocaudal mobility (RCM) of the mandible, it does not improve feed digestibility, fecal particle size, or weight gain in the pregnant mare. Cheek tooth occlusal angle and molar occlusion percentage also have no discernable effect on the same outcome variables [14–17]. In the first of these studies, the authors found that it was the feed group and not the treatment group (floated or controls) that had a significant effect on weight gain. There was also no statistical interaction between feed and treatment group. This information suggests that it is EVIDENCE-BASED EQUINE DENTISTRY 521 the feed and not the occlusal equilibration that accounts for the weight gain. This is significant, because in clinical cases of weight loss where occlusal equilibration has been performed, it is common veterinary practice to alter the nutrition in favor of a higher quality feed. Credit for improvement may go to the procedure when, in fact, the nutritional changes are responsible. Studies showing a lack of effect of routine dental procedures [13,15] have been subjected to a certain amount of criticism. One of the major critiques has been that normal horses were used for the study, and thus do not represent the population as a whole. Although the first portion of the argument is certainly true, current legislation rightly precludes the use of cachectic animals in a clinical trial. With respect to a trial conducted in 2004, investigators knew categorically that the horses had never had their teeth floated. Horses ranging in age from 3 to 18 years that had a variety of dental malocclusions commonly cited as needing correction (and potentially the cause of weight loss) [15]. If these normal horsesdhorses that had never had dental procedures but had a variety of dental abnormalitiesdwere not to show benefit from treatment, perhaps the definition of a clinically significant malocclusion or ‘‘normal’’ should be adjusted. It is important to note that the aforementioned reports have focused on dental malocclusions, namely because this is the main focus of occlusal equilibration and the portion of equine dentistry that is most easily understood. Nevertheless, this is likely to prove a shortsighted view of the oral cavity; it is soft tissue pathologic conditions (and the prevention thereof) that should be under scrutiny. The interaction between dental malocclusions and periodontal disease is complex, however, and not fully understood in most cases. One dental malocclusion consistently leading to the development of periodontal disease is a valve diastema. Congenital or acquired in nature, diastemata are abnormal gaps between teeth and refer (in the horse) almost exclusively to the cheek teeth. Subcategorization of the pathologic findings into open or closed/valved is based on the architecture of the boundary walls of the space [18]. The open diastema allows cycling of feed material through the space with little to no concurrent bacterial putrefaction and periodontal disease. Conversely, the valve diastema prevents egress of feed material and leads to periodontal disease, which itself has been described as ‘‘one of the most painful conditions in the horse’s mouth’’ and ‘‘one which is difficult to treat’’ [19]. In select cases, treatment of the diastema (a dental malocclusion) may to lead to resolution of periodontal disease and, in early cases, to cessation of clinical signs and weight gain. Occlusal equilibration and performance There is a strong anecdotal history of the link between equine performance and dentition. ‘‘Performance’’ is a difficult word to define fully in respect to the horse. It may mean feed conversion ratios in feedlot animals, speed in the racehorse (eg, Thoroughbred, trotter/pacer, barrel horse), or 522 CARMALT judged score in the show and dressage horse. Making claims as to the effectiveness of a dental procedure with respect to performance is difficult and should be tightly defined to avoid exaggeration. The detrimental effect of ‘‘wolf teeth’’ (rudimentary first premolars) on performance is the focus of heated debate among veterinarians involved in equine dentistry. Even among ourselves, veterinarians can come to no common understanding with regard to the importance of this tooth. Some may state that ‘‘no wolf tooth has ever done a horse any good,’’ and others may claim that they have ‘‘never seen a wolf tooth cause a problem with respect to performance.’’ As a result of their personal perspective, some clinicians routinely remove wolf teeth of all horses going into training, whereas others reserve the right to wait until a problem develops and then remove the offending tooth. Once again, however, there are no clinical data to substantiate either of these views. Occlusal equilibration increases the RCM of the mandible, and authors have suggested that the amount of RCM may be correlated with height or weight (because heavy-breed horses have a greater range of motion than do light-breed horses). They have theorized further that RCM of the mandible is an important aspect of performance, especially in those equine disciplines that require extreme poll flexion, such as dressage [14]. Sharp lateral cingulae and other perceived dental abnormalities on the upper cheek teeth have been linked statistically to the presence of buccal ulceration in the horse [15]. Theoretically, soft tissue pathologic conditions may have a negative effect on performance. A recent blind, randomized, controlled clinical trial examining the effect of occlusal equilibration on dressage horse performance failed to find a correlation between treatment group (occlusal equilibration and placebo treatment) and performance or between increased RCM and improved performance [20]. Some criticisms of this study are that the judged scores are wholly subjective (as is the nature of the dressage discipline) and that there was only a short time between preand posttreatment testing, possibly negating the positive benefits of the procedure if such benefits were to require time to be recognized. The horses in this study had not had occlusal equilibration performed in more than a year, they did have dental abnormalities, and any immediate relief should have been apparent. The major problem, insofar as conducting good studies on the necessity for and the benefits of commonly advocated dental procedures is concerned, is that performance horses (however defined) are kept and trained within their chosen discipline to win. For this reason, randomized, controlled, performance-related clinical trials are difficult to perform in equine dentistry. Owners or trainers are unwilling to accept or become enrolled in a clinical trial, especially if they perceive a performance-limiting condition in their horse. This is especially true when winning comes with financial gain or prestige. As a result, many upper level performance horses may have their teeth ‘‘done’’ at least every 6 months and more frequently in some cases. The EVIDENCE-BASED EQUINE DENTISTRY 523 ‘‘benefit’’ in these cases may be to the rider and not to the horse, even possibly resulting in subconscious adjustments of bit-induced cues by the former. Summary In spite of the difficulties posed in evaluating the effect of occlusal equilibration on performance and weight loss or gain, the current resurgence of interest in equine dentistry is driving the need for knowledge. Routine occlusal equilibration is commonly performed. The treatment interval and abnormalities that constitute ‘‘malocclusions of significance’’ are still not known. There is obviously a level of malocclusion that is clinically silent. It is certainly possible that these malocclusions will continue to develop and may lead to further problems. Currently, however, it is not fully understood what is normal. Nor is it understood whether it is pain or a mechanical impediment to jaw motion (or a combination of the two) that purportedly leads certain malocclusions to affect feed digestibility or performance. This leaves the most basic question unanswered: when should occlusal equilibration be performed and on what basis? It is of paramount importance that the equine veterinarian approach dental problems in the horse with an open mind. Equine dentistry can generate a significant portion of practice income. Although that, in itself, makes dentistry attractive, veterinarians also have an ethical responsibility to justify not only the procedure, but also the extent and frequency by which they are performed. The author believes that a complete oral examination (comprising sedation and the use of a full-mouth speculum, mirror, and some method of illumination) every 6 to 12 months is acceptable to identify dental malocclusions or other dental pathologic conditions that may become clinically significant in time. In the author’s opinion, blanket statements as to the need for biannual occlusal equilibration are not acceptable and can certainly not be supported by any evidence. The field of equine dentistry would benefit from multifaceted research. There is a lack of basic biomechanical research with respect to dentition and the temporomandibular joint. Tightly controlled studies investigating the effect of occlusal equilibration on performance across different disciplines and the true effect of wolf teeth on performance in the horse need to be done. It is incredible in that in the field of clinical equine dentistry, so much is performed in the face of so little published research. 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