A modern approach to equine dentistry 1. Oral examination
Recent developments in our understanding of dental anatomy, pathology and the effects of specific dental techniques have advanced the current status of equine dental care. This article, the first in a series of four to review these developments, describes how to carry out a thorough oral examination in horses. Subsequent articles, to be published in consecutive issues of In Practice from February to April, will describe the different lesions that might be seen in equine patients (Part 2) and how these might be investigated further using appropriate imaging techniques (Part 3). Part 4 will consider the techniques available for the prevention and treatment of equine dental disease.
Henry Tremaine graduated from the Royal Veterinary College in 1989. He worked in mixed and equine practice before undertaking an MPhil to study equine upper respiratory tract diseases, and surgical training at Edinburgh and Ohio State University. He is currently a senior lecturer at Bristol. He is a diplomate of the European College of Veterinary Surgeons and an RCVS specialist in equine surgery.
Miriam Casey graduated from Dublin in 2004. After a spell in mixed practice, she undertook a clinical scholarship in equine studies (dentistry) sponsored by the Horse Trust and an MSc by research at Bristol. She is currently working towards a PhD for studies on epidemiology at Glasgow.
Changing approach to equine dentistry
Scientific articles in veterinary journals in the past few years have expanded our knowledge about equine dentition, dental disease and also the application of both historical and new techniques to treat and prevent dental disease in horses, ponies and donkeys.
Although historically equine dental care may have involved a veterinarian or lay person blindly waving some rusty rasps in a horse's mouth to remove perceived sharp points, this approach is no longer justifiable for a mature profession.
Published research has enabled a workable set of guidelines to be drafted, revised and agreed by the relevant parties (available on the BEVA and RCVS websites). This guidance sets out which acts of dental care remain invasive acts of veterinary surgery and which might be delegated to a suitably trained and accredited equine dental technician (EDT). Dental technicians can offer a service which complements that provided by veterinary surgeons. The British Association of Equine Dental Technicians provides a training and accreditation programme for dental technicians and sets out ethical guidelines for managing dental problems in horses. In addition, technological advances in powered dental instruments mean it is difficult to justify any treatment of cases with dental disease by individuals without suitable accreditation from a scientific, legal or welfare perspective. The law does not yet accommodate the diagnosis and treatment of animals to be performed by non-veterinarians, although, the RCVS has recognised that delegation of selective non-invasive procedures to EDTs can benefit horses and their owners.
Oral health in horses
Dentistry must be considered as a speciality within the concept of ‘one medicine’ as applied to horses and not as a separate independent service. Examination of the oral cavity is therefore a worthy inclusion in the investigation of many gastrointestinal complaints, abnormal masticatory or bitting behaviour, weight loss, some equitation problems and any suspected cases of sinonasal disease. Examination of the oral cavity includes an assessment of the dentition, gingiva, tongue and salivary systems, and the mucosa of the buccal cavity. Veterinary surgeons are best prepared for recognising and diagnosing non-dental oral inflammatory and neoplastic disease as well as diseases of the teeth.
In some cases, the oral examination will be a part of a routine health check, although it is not currently an obligatory component of prepurchase examinations. In other cases, horses will be presented with a signalment that indicates an oral examination would be appropriate. Some owners may well be expecting a cursory examination of the horse's mouth before a brief ‘drive through’ the horse's mouth with manual or quiet mechanical instruments. As this may be based on their previous experience, the benefits of performing a thorough professional detailed examination of the horse's mouth may need explaining.
Horses with clinical signs of dental disease (Table 1) deserve a full and complete examination. This should be followed by a discussion with the owners to determine the most appropriate treatment within their financial constraints. Those horses with no signs of dental disease that are undergoing a maintenance examination and removal of minor wear overgrowths may forgo a thorough examination if owners prefer. However, many clinically asymptomatic lesions, which can progress and potentially require more invasive and expensive treatment when they become clinically significant, will inevitably be missed on a cursory examination.
Before embarking on an oral examination a detailed history should be taken. This will reveal key information about the onset and progression of signs of dental disease, which may not be apparent to the owner, and is particularly important when dealing with insured or recently purchased horses. All findings should be documented on a suitable dental chart (see Fig 1), which should be added to the horse's medical file.
The horse's temperament and demeanour should also be assessed at this time and an external palpation of the structures surrounding the oral cavity should be carried out to check for signs of focal pain, soft tissue or bony swellings, lymphadenopathy, asymmetry, discharges or salivary distension (Fig 2). The colour of the mucous membranes should also be evaluated. In addition, careful palpation of the submandibular lymph nodes, temporomandibular areas, lips and the cheeks along the outside of the maxillary arcades should be performed to check for any focal swelling or pain. This initial assessment will reveal a head shy horse or one that resents oral examination. A horse or pony's compliance to this will indicate the level of sedation required for a more detailed examination within the buccal cavity (Box 1).
Box 1: Restraint and sedation
From a horse's perspective, an oral examination represents an invasive procedure to which it may be completely unaccustomed. Many compliant horses will tolerate a cursory examination of their mouth when held open, while some will tolerate the speculum and others the use of manual rasps and quiet more modern powered instruments. It should be borne in mind that an unsedated horse wearing a speculum is capable of inflicting serious injury to itself and staff, so handlers should consider wearing protective headgear when carrying out dental procedures.
In many cases, horses, owners and veterinary surgeons will all benefit greatly from the appropriate administration of sedatives to the horse to facilitate the oral examination. Unsedated horses have a highly muscular mobile tongue and many have a tendency to toss their heads away from noxious stimuli. Therefore, where there is a need to examine the occlusal and periodontal aspects with a mirror, or to use powered instruments safely and with absolute precision, there is a very strong case for sedating such animals. There may be some initial resistance to the use of sedation from some owners, possibly due to misinformed perceptions of the complications, or concern about additional costs and unrealistic expectations about what is actually possible in unsedated horses. The owner's consent should be obtained before sedation (especially when given to facilitate dental examination by non-veterinarians). In addition, a cardiovascular examination must be performed before any sedative drugs are given to identify horses that are at greater than average risk of problems associated with sedation (eg, some older animals). In certain situations, when sedation is deemed undesirable, such as routine rasping in young performance racehorses or minor treatments in geriatric horses, treatments can be performed without additional chemical restraint.
Sedative combinations vary widely and should be tailored to the temperament and age of the horse, the nature of the procedure and the environment. An empirical ‘one dose fits all’ approach will yield highly variable and unsatisfactory results. The most popular drugs are xylazine (0·5 to 1 mg/g), detomidine (10 to 20 μg/kg) and romifidine (0·5 to 1 mg/kg) and these can be used in combination with butorphanol (all administered intravenously) or buprenorphine. More fractious horses can also be given 0·05 to 1 mg of acepromazine 30 minutes before the alpha-2 agonist or the drugs can be administered intramuscularly to enable subsequent intravenous access. Diazepam can also contribute additional muscle relaxation for selected treatments. Oral sedative drugs such as acepromazine achieve minor tranquilisation but are rarely effective in enabling treatment of painful lesions. Recent marketing suggests a new oral product containing detomidine to be effective but thorough evaluation of its suitability for dentistry has yet to be established.
The mandible should be articulated and displaced side-to-side to evaluate the lateral excursion to molar contact (Fig 3). By displacing the mandible laterally, this movement brings the upper and lower dental arcades into contact, one side at a time, as they would be during chewing. The distance the mandible is displaced to do this should be should be approximately equal on each side.
A dental speculum is an essential device that enables visual and digital examination of the teeth without injury to an operator's arm. A variety of patterns are available, many of which are modern interpretations of traditional models (Figs 4, 5, 6). A dental speculum should be self-retaining, facilitate examination of all teeth, be well tolerated by the horse and be safe for the operator, all of which are essential features. An unsedated frisky horse wearing a 500 g steel speculum represents a greater danger to nearby staff than a horse without one. Versions of the traditional Hausman's pattern are suitable for most field use, and routine examinations and procedures. Over the years, these specula have been modified to make them more comfortable for horses. Modifications include the insertion of wider spacers between the side bars and the incisor plates to reduce the pressure exerted by the side bars on the cheeks, and also smoothing of the ridges on the incisor plates. A good-quality speculum will have stainless steel components, several teeth on the ratchet to enable a good range of opening settings, replaceable springs and washable straps. Many models come supplied with an excess of superfluous straps, which are made from materials such as leather which cannot be disinfected adequately.
The Millennium Speculum (WWED) type of speculum has many small teeth (Fig 7) on the ratchet to enable a smooth opening mechanism and good tolerance. The large Meister type patterns (eg, Alumispec; Veterinary Dental Products) (Fig 8) provide better access to the cheeks and sides of the mouth and enable a wide field of view, but are heavy and bulky which makes them more suitable for use in clinics rather than peripatetic work.
Cleaning and servicing of the speculum, and especially the springs, is necessary for repeatable safe opening and closing. If maintained well, these essential instruments do not need to be replaced for many years.
The equine oral cavity is deep and is only penetrated by bright natural light when the horse yawns into the sun! External illumination is therefore required to allow thorough examination of the dentition and other structures (Fig 9). Historically, hand torches and weak pen torches were used for this, but the advent of a wide range of easily available, inexpensive light sources have rendered these obsolete. A good compromise is to use bright portable halogen/LED head torches, which are available from adventure shops (Fig 10). These emit up 10 to 20 W, have a long battery life and the added advantage of freeing up the hands while retaining the beam in the visual axis. More expensive surgical head lights run from halogen arthroscopy light sources are slightly superior but often less practical.
LED light sources that attach to the speculum are also available and these are convenient for demonstrations although their bulk can obscure access into the oral cavity.
Cheek retractor or basket forceps
Cheek retractors or basket forceps are inexpensive devices that are used to retract the cheek from the maxillary arcades to permit examination of occluded cheek teeth at rest and during a lateral excursion test (Fig 11). In addition, they allow the buccal aspects of these teeth and any ulceration of the gingiva to be easily seen. These devices are well tolerated by horses and extremely useful for showing lesions to owners.
Dental mirrors, constituting a stout-handled mirror with a 5 cm diameter angled lens, are an essential tool for any equine dental examination (Fig 12). An angled head is much more useful than a straight one for examining the occlusal surfaces and the interproximal spaces from a buccal and lingual/palatal aspect. When assessing the mandibular teeth, the back of the mirror can be used to retract the powerful caudal muscles of the tongue. When positioning the mirror, its end should be placed against an interproximal space and the handle rotated in order to prevent the tongue from knocking the lens on to the teeth resulting in breakage. Dextrous use of the mirror and coordination between mirror and head light will require some practice.
Some head support for sedated horses will greatly facilitate a detailed oral examination using dental mirrors and picks (Fig 13). Most sedated horses will rest their head willingly on a headstand. Many owners fatigue quickly when asked to support their horse's head and the use of a stand is also safer, enabling lesions to be demonstrated to others more easily. If the horse is placed in stocks, alternative systems of support, such as a suspended head collar (Fig 13c), can be used.
Dental picks allow careful oral examination to reveal sharp dental prominences and painful or loose dental fragments. In addition, they facilitate a more detailed examination of the interproximal spaces between the teeth and can be used to remove any accumulated food. Dental picks are available in a range of shapes and sizes with different ends for different purposes (Fig 14). A straight, graduated periodontal probe (Fig 14a) is useful for measuring the depth of lesions, while a stronger probe is helpful for removing impacted food in the interproximal region. Exploration of the occlusal surface necessitates the use of a flexible fissure probe and a strong occlusal scraper (Fig 14b) to remove food from infundibulae and carious lesions and to identify microscopic occlusal defects or exposed pulp. Probes are most useful when used together with a dental mirror (or endoscope) in sedated horses with the head supported.
Before performing a dental examination in horses, it is important to remove all free food from the mouth. This can be achieved by washing the horse's mouth with a weak (<0·1 per cent) oral disinfectant solution of chlorhexidine or povidone–iodine using a hose pipe, dental syringe or horticultural sprayer (Fig 15). Ideally, the solution used should not contain detergent, as this causes syringes to seize up quickly, thus reducing their life span. The horse's nose should be held ventrally to the larynx when irrigating the oral cavity to avoid any aspiration of the solution and any residue disinfectant should be collected in a bucket.
Oral dental examination
The incisors can be examined before a speculum is applied (Fig 16). This involves parting the lips and closely inspecting the labial aspects. The colour of the peripheral cementum should be evaluated, as should the health of the gingiva and mucosa. In addition, the presence of incisor diastema gum recession and any gingival lesions (eg, sinus tracts or scars) should be noted as they might signal the presence of a historical apical discharging tract. The commissures of the lip should be carefully inspected for trauma associated with the bit and the bars of the mouth should be palpated for any non-erupted wolf teeth (vestigial first premolar) mucosal ulcers or exotoses, which may indicate bit trauma to these structures. Changes to the colour of the incisors, which can indicate intrapulp haemorrhage after trauma or pulp necrosis, should also be noted.
The occlusal surfaces can be examined by digital pressure in the interdental space, which stimulates most horses to open their mouths. Occlusal defects, such as fractures, dentinal defects with pulp exposure or severe carie, should be noted and may warrant further investigation. It should be remembered that incisors are extremely sensitive compared with cheek teeth and apparently small lesions may cause severe discomfort resulting in increased sensitivity to dental examinations and speculum placement or when the bit is being introduced into the mouth before being ridden.
Once a horse is suitably restrained, the oral speculum should be placed by slipping the brow band behind the ears and applying the incisor plates between the lips, after which pressure on the hard palate in the interdental space will relax the jaws. This permits the incisor plates to be introduced without resistance from the muscles of mastication.
Once placed, the speculum should be opened sufficiently to allow examination of the occlusal surfaces without causing the cheeks to press too tightly on the buccal aspects of the maxillary arcades. The mouth should be rinsed with an oral disinfectant using a hose, syringe or horticultural spray to remove any food (see page 8). If the horse is sedated sufficiently, there will be some tongue relaxation and the horse's head can be placed on a support. It is often convenient to perform a careful digital examination before a visual examination (Fig 17). The teeth should be individually palpated between the finger and thumb, counting each tooth to detect the presence of supernumerary dentition. Focal peripheral edges and points, any fractured teeth and large diastema should all be noted. In addition, the practitioner should check the occlusal table angles as well as the dental alignment along the rows, making note of any painful foci. A visual examination of the mouth is achieved much more easily with the horse's head rested on a head stand or suspended at eye level. Where occlusal or periodontal lesions are suspected, examination with a mirror should follow by angling the mirror to facilitate inspection of the interproximal spaces. Effective examination with a mirror is almost impossible to perform in a horse that is inadequately sedated. The motor muscles of the tongue relax with adequate sedation and hence do not resist retraction of the tongue using the mirror when inspecting the caudal mandibular teeth. Horse with focally painful lesions, such as deep periodontal pockets, may resist the use of the mirror in this way and require additional analgesia. It is difficult to achieve good visualisation of the occlusal surfaces of the cheek teeth in a horse's mouth using a direct orthogonal view, and many occlusal and periodontal lesions will be missed if examination with a mirror is omitted.
The presence or absence of wolf teeth can be noted and the option of their removal discussed with the owner.
After performing a visual examination, the dental chart should be completed (see page 4), and a treatment plan suggested and discussed with the owner. It should be noted that many dental lesions are the consequence of chronic wear disorders and decay, so it may be unrealistic to carry out all the treatments indicated in a single consultation.
Endoscopic devices can be used to:
■ Improve the visibility of oral lesions;
■ Magnify the lesions and view them on a screen, which is useful when highlighting problems to owners, students and other clinicians;
■ Record lesions for monitoring the response to treatments.
The use of oral endoscopy in horses is likely to expand greatly in future years. The better visibility and magnified image provided using endoscopic viewing systems compared with using a mirror allows even small lesions to be detected. In addition, endoscopy provides a much improved view of occlusal tables and interproximal spaces, especially caudally in the mouth (Fig 18).
Various endoscopic systems are available. These are usually linked to chip cameras or have built-in chip cameras, some with LED illumination. It is also possible to use rigid laparoscopes modified to incorporate chip cameras or engineering inspection telescopes adapted for veterinary work. However, such technology comes at a price, which often puts it beyond routine oral examinations. While these systems are potentially portable, they are usually used for clinic-based examinations and performed with the horse heavily sedated and supported in stocks. These devices provide a detailed magnified view of occlusal surfaces.
Ancillary diagnostic tests
The oral examination represents just the first stage in the investigation of suspected dental disease in horses. Any lesions suspected to involve the apical regions and reserve crowns of the tooth cannot be visualised directly and require radiographic examination (Fig 19). In such cases, it will be necessary to schedule the horse for an additional visit in ambulatory circumstances or to be transported to the clinic for imaging to be planned and executed expediently. Computed tomographic examinations are also available at selected referral institutions. Part 2 of this series will illustrate common oral and dental diseases, while Part 3 will review the radiographic techniques required to aid their diagnosis.
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