As with many other fields of modern equine surgery the use of sedative and local anaesthesia regimes has meant that almost all dental procedures in the equine are performed with the patient standing. The days of routinely repulsing teeth with a hammer and punch under general anaesthesia are long gone. Advances in dental equipment and surgical techniques allow most teeth, or fragments of teeth, to be extracted quickly and efficiently via the oral cavity, thus reducing collateral damage and complications. However, extraction of teeth should never be undertaken lightly and should only be attempted when confirmation of disease is made by thorough diagnosis and ideally when more conservative methods have proved ineffective. Endodontic treatment of equine cheek teeth is still embryonic in its development but, as in other species, may offer a useful alternative in the future.
Indication for extraction
Periapical infection is by far the most common indication for extraction of teeth, especially in younger horses. Periapical infections have a variety of aetiologies, including periodontal disease, fractures, infundibular caries of the maxillary cheek teeth, iatrogenic pulpar exposure and anachoretic infection of the pulp tissues. The clinical signs of a periapical infection depend on the affected tooth and its position in the head, and include facial and mandibular swellings, draining tracts, sinusitis with nasal discharge and quidding of food. Idiopathic cheek tooth fractures are relatively common and patients may present with clinical signs of quidding and halitosis, as well as bitting and behavioural problems. A number of fracture configurations can be observed, but lateral slab fractures (Figure 1) and upper cheek teeth midline sagittal fractures (Figure 2) are seen more frequently, the latter of which invariably mandate extraction due to pain and inevitable periapical disease. Supernumerary, misaligned, dysplastic and impacted teeth can all cause clinical signs of disease and their removal may be indicated in many cases.
Diagnosis of diseased teeth
Using a light source and mirror or, ideally, an oral endoscope, the occlusal, buccal and palatal/lingual aspects of the teeth are carefully examined and will allow disease of most equine cheek teeth to be identified. Careful visual inspection of the secondary dentine overlying the pulp horns is essential, accompanied by probing of the pulp horn occlusal surfaces with a suitable instrument to allow identification of any secondary dentine defects (Figure 3), which may indicate endodontic disease of the tooth in question.
Diagnostic imaging is indicated in cases in which extraction is anticipated. It is not only used to confirm the presence of periapical and periodontal disease, but also helps surgical planning and helps determine the most suitable method of extraction. Radiography is the mainstay of dental imaging, and modern digital systems allow good radiographs of the dental apices and surrounding alveoli to be obtained in both the clinic or field setting. Rostral maxillary and mandibular cheek teeth with periapical infections may present with a bony swelling, which is often seen on radiographs as an area of sclerosis and periosteal new bone formation usually surrounding a distinct lucent zone (Figure 4). In some cases, cutaneous draining tracts may also be present, and placement of a radiodense metallic probe within the tract can pinpoint the source of the tract to a specific dental apex. Similarly, placement of a metallic ring around a bony swelling can be used (Figure 5). These changes may also be identified in disease associated with the caudal upper cheek teeth, and often observed as local densities (encapsulated abscesses and granulomas) in the otherwise lucent adjacent sinus. Obvious fluid lines may also be present in the sinuses (Figure 6) in cases of cheek teeth fractures that are involved in a secondary dental sinusitis.
When the oral examination and radiography are inconclusive then other imaging modalities may be indicated, of which computed tomography (CT) and scintigraphy are the most commonly used. CT uses X-ray beams and reconstructive computer software to allow tomographic slices of the area imaged to be created and displayed on a computer monitor (Figure 7). CT has higher contrast resolution when compared to conventional radiography allowing for a more accurate differentiation between soft tissues and fluids. CT imaging negates problems caused by superimposition, which is often encountered with radiography of complex anatomical locations such as the head and oral cavity.
Scintigraphy is unique among the imaging modalities because the images reflect active physiological processes rather than the structural features portrayed by other imaging modalities. It can, therefore, detect changes in bone that precede radiographic changes, and this makes it a very useful imaging modality for diagnosis of early periapical infection. Periapical infections of the cheek teeth typically result in focal and intense increased radionuclide uptake (IRU) located in the periapical region of the affected tooth. When partnered with radiography, a high sensitivity and specificity for detection of periapical infections is achievable.
Routine oral extraction
The initial stage of the extraction involves elevation of the gingiva from the tooth on the lingual, palatal and buccal aspect, as far apically as possible. Interdental spreading of the tooth from its neighbouring teeth, using sequentially increasing size of spreaders (Figure 8), is particularly useful in breaking down the periodontal ligament and hastening the procedure. Care must be taken, however, to not damage the adjacent healthy teeth or disturb the ’06 teeth when attempting an ’07 extraction, and similarly the ’11 tooth when attempting a ’10 extraction. The next step is manipulation of the tooth in the alveolus using forceps. The choice of forceps is very much dependent upon the veterinary surgeon’s preference as well as the tooth in question. For example, serrated jaw forceps are adequate for most extractions, but three-pronged forceps can be useful for fractured teeth and finer tooth forceps for fracture fragments. Once gentle sustained rotational pressure within the alveolus and intermittent rocking of the tooth has loosened the tooth to a point that frothing blood and “squelching” is heard then extraction of the tooth from the alveolus can be attempted. This involves placing a fulcrum between the forceps and the adjacent rostral tooth, and applying gentle firm pressure to extract the tooth in an occlusal direction from the alveolus.
Once removed, the tooth and alveolus should be carefully inspected to ensure that the tooth has been extracted in its entirety. Curetting and extraction with finer forceps allow removal of loose fragments. Oblique radiography of the apical region is useful to determine the presence of any remnants and provide a record of complete extraction. Once empty, the alveolus is usually packed to provide haemostasis and prevent food contamination in the early stages of tissue healing. The choice of material is usually determined by the surgeon and clinic preference and often includes: gauze packing, cotton tampons, polysiloxane impression material or dental wax.
Variations on this technique allow the extraction of the majority of cheek teeth; however, in teeth that are fractured, become fractured during oral extraction attempts, have no clinical crown or have other malformations preventing routine extraction alternative methods will be needed.
Periodontal elevation extraction technique
Specially engineered periodontal elevators (Figure 9) have been developed to facilitate extraction of problematic and fractured teeth, and teeth that have no clinical crown remaining to allow forceps placement. The elevators are usually placed under endoscopic guidance, sometimes in pairs, with one on the buccal aspect and one on the lingual or palatal aspect of the tooth. It can then be manipulated disrupting any remaining periodontal tissues and using fine fragment forceps the fragments can be removed.
Minimally invasive transbuccal extraction (MTE)
This is a recently developed technique that utilises a direct approach to the tooth with a “key-hole” cannula placed through the tissues of the cheek (Figure 10). The correct positioning of the cannula is paramount to the success of this technique, and is usually assisted with a combination of oral endoscopy, ultrasonography and radiography. A good working knowledge of the neurovascular anatomy of the head is essential not only to ensure the cannula is placed in the best position to allow access to the alveolus, but also to prevent inadvertent neurovascular and ductal damage that may be catastrophic in some horses.
Once the cannula is placed then the tooth can be manipulated further, under endoscopic guidance, directly in the alveolus using specifically designed periodontal elevators inserted directly from the occlusal aspect of the tooth. Once the dental tissue appears adequately loose, it can be drilled and tapped using oral endoscopic and radiographic guidance. A screw extraction device is then inserted in the hole and tightened, and using a specially designed hammer, successive percussion on the end of the screw extractor will pull the dental tissue from the alveolus (Figure 11). Any small fragments can be removed using fine forceps passed through the cannula, and curettage of the alveolar bone can also be performed through the cannula.
A minimally invasive trephination and repulsion (MITR) technique using small diameter Steinmann pins has been described and provides a method of dental repulsion with fewer reported complications than traditional methods using large punches. This technique is often performed using sedation and local anaesthesia, with the horse standing. The pins are placed through carefully positioned drill holes in the bones of the face, or the mandible, under strict radiographic, and in some cases sinoscopic, guidance, and the dental remnants carefully repulsed often while observing via oral endoscopy.
This technique is a major surgical undertaking, mandating general anaesthesia, and is usually reserved for teeth with abnormal apical anatomy or changes preventing routine extraction from the alveolus. It is often associated with a number of peri- and post-operative complications, mainly resulting from the close proximity of a number of neurovascular structures.
Using accurate diagnosis, surgical planning and modern methods and equipment, most teeth requiring extraction can successfully be removed with the horse standing, and with complications being much less common than with traditional repulsion techniques.