Dental fractures of both incisors and cheek teeth are relatively common in equids (Pollaris et al, 2020). This article looks at the anatomy of equid teeth, the pathophysiology of dental fractures and their investigation and management.
Causes of dental fractures
External trauma is often suspected or observed for incisor fractures (Figure 1) but is less commonly the cause of cheek teeth fractures. The normal high masticatory forces (up to 1758N recorded in one study (Staszyk et al, 2006)) may result in primary fracture of healthy cheek teeth in some instances, but more commonly pre-existing underlying dental abnormalities such as infundibular caries, pulp disease or occlusal fissure lines (Pollaris et al, 2020) can lead to secondary fractures.
Fracture classification
Fractures which communicate with the endodontic (vital) structures of the tooth have the potential to result in endodontic infection or inflammation, are termed ‘complicated’ while others are termed ‘uncomplicated’. Knowledge of equid dental anatomy is important to help determine which type of fracture has occurred and the likelihood of endodontic involvement.
Equid endodontic anatomy
Equid endodontic anatomy and how it changes with age have been well described (Dacre et al, 2008; Windley et al, 2009; Kopke et al, 2012; Englisch et al, 2018) with simpler endodontic anatomy in incisors than cheek teeth. The pulp horns of incisors and cheek teeth continually lay down secondary dentine (commonly stained brown at the occlusal aspect), which prevents the endodontic structures from being exposed during normal eruption and attrition. The depth of subocclusal secondary dentine has been shown to vary (2–33 mm in cheek teeth (White and Dixon, 2010)), but in general, fractures that extend further towards the apical aspect of the tooth are more likely to be ‘complicated’ than those that are contained within the clinical crown (the part of the tooth found in the mouth, outside the alveolus) (Figure 2).
Pathophysiology
Insults to the endodontic system (such as dental fractures) result in an inflammatory response (pulpitis) that has the potential to protect the tooth from infection by controlling haemorrhage, killing bacteria and clearing necrotic tissue. If the inflammatory response is successful, the pulp tissues (odontoblasts) can then lay down a layer of hard tissue (tertiary or ‘reparative’ dentine) that seals the pulp canal and protects the tooth from further insult (Dixon et al, 2022). The location of tertiary dentine deposition depends on the site of insult and how the tooth responds – it is sometimes observed focally within a pulp canal a short distance apical to the fracture site (some pulpar necrosis occurs immediately adjacent to the insult) but may also be confined to a single pulp horn (or pulp horn compartments (Kopke et al, 2012)) or be more extensive around the apical aspect of a tooth (Figure 3; 6).
In some cases, the tooth is unable to deal with an endodontic insult effectively, for example when there is overwhelming bacterial contamination. Because of the hard structure of teeth, endodontic inflammation can result in avascular necrosis, with resultant pulp death. As teeth age, the apical foramen (blood supply to the tooth) narrows, and so avascular necrosis is more likely in older teeth (Figure 5) (Dixon et al, 2022).
Pulp death results in exposure of the pulp canals from the occlusal aspect (non-vital pulp exposure) which leads to progressive caries from food impaction. This caries, in combination with the lack of secondary dentine deposition (because the pulp is no longer vital), weakens the tooth and predisposes it to fracture. The extent of pulp death varies (it may be just part of 1 or 2 pulp horns), but even if a tertiary dentine bridge is formed and the tooth remains vital, caries can develop occlusal to the bridge which weakens that part of the tooth.
Investigation
Having identified a fractured tooth, several things need to be considered.
- Which dental structures are involved? Determining whether a fracture has entered the vital part of the tooth is important. In some cases, usually incisors with traumatic fractures, it is possible to see open pulp horns, which bleed acutely. For more chronic fractures, especially those that have occurred as a result of existing endodontic disease and caries, the pulp canals may be filled with feed or necrotic tissue. The use of fine picks and dental files can be useful, as can careful debridement with dental drills and oroscopic evaluation (Figure 4). Certain findings can provide additional information to help guide further investigation and treatment planning. For example, defects in the secondary dentine over pulp horns of the fractured tooth that are not involved in the fracture site suggest chronic (possibly widespread) endodontic disease of that tooth (Figure 4-C). Infundibular caries-related complete midline sagittal fractures invariably kill the tooth, limiting treatment options, while buccal slab fractures over the 1st and 2nd pulp horns (a common fracture configuration (Dacre et al, 2007)) were shown to be related to apical infections in 73% of cases in one recent computed tomography study (Rowley et al, 2021). Diagnostic imaging is often necessary, with radiographic evaluation useful for incisors but not so useful for the complex 3D structure of the cheek teeth endodontics (particularly in acute cases), for which computed tomography scans provide much more information (Figure 3).
- Does the animal have associated clinical signs? Oral pain may not always be recognised in equids, but it is not uncommon to be presented with cases that have been avoiding chewing on a painful tooth; signs such as steep occlusal angles (shear mouth), staining of the occlusal surface and calculus deposition (indications that these haven't been cleared by normal chewing) may be seen. In cases with displacement of loose fracture fragments, signs of oral pain (such as quidding) are normally more pronounced – in these cases the loose fracture fragment(s) should be removed as soon as possible. Animals should be carefully examined for signs of apical infection such as: swellings, draining tracts (both externally and in the mouth) and nasal discharge and any history of these should be determined. If apical infection is present then this needs to be treated, frequently by extraction of the affected tooth.
- How old is the animal? Because of the wider apical foramina, younger animals are perhaps less likely to undergo pulpar avascular necrosis, so may have a better prognosis for tooth survival following fractures. However, based on the author's experience, full endodontic (root canal) treatments are less likely to be successful in young equids, because of the volume of pulp tissue that needs to be removed (leaving a tooth with a large amount of filling material) and because of the challenges in stimulating and achieving an apical seal (sealing the apex of the tooth from the body) when the apical foramen is large (Figure 5).
- How old is the fracture? Acute fractures can be managed to help promote the body's response – reducing bacterial load (such as debridement of the site and application topical or systemic antimicrobials), reducing inflammation (anti-inflammatory administration) and encouraging formation of a tertiary dentine bridge (such as application of calcium hydroxide). More chronic fractures should be examined to determine whether any treatment is necessary, which can include steps to preserve the tooth (such as endodontics), or tooth extraction. Determining chronicity of dental fractures can be difficult; signs such as feed staining of the fractured part of the tooth and evidence of gingival healing around the site suggest longer presence but are not definitive. Accurate dental history can be helpful; fractured teeth that have been present for many years may be of less clinical concern than more acute ones.
Treatment
Treatment options for fractured teeth include extraction (fractured part or whole tooth), endodontics and monitoring, the choice of which will depend on clinical signs (monitoring would not be appropriate for cases with clinical signs of apical infection, as these will not resolve without treatment), fracture extent and chronicity and the age of the horse.
Tooth extraction
Extraction of any loose, displaced fractured dental fragments is very important, as these are frequently displaced into the soft tissues (cheek or tongue) causing trauma and discomfort when moving on their periodontal attachments. Retained fractured fragments frequently result in food entrapment in the fracture line, which can contribute to localised infections and discomfort. Extraction of fractured fragments is performed by cutting their soft tissue attachments (with elevators) and carefully grasping (specialist flat forceps are available for cheek teeth fragments) and is facilitated by application of local anaesthetic into the soft tissue attachments and topically onto traumatised areas while the patient is under standing sedation.
Extraction of the entire fractured tooth is indicated in many cases. Oral tooth extraction carries a low complication rate (Kennedy et al, 2020); however, in some cases fracture configurations result in minimal or no clinical crown, so alternate techniques such as minimally-invasive transbuccal extraction, repulsion or tooth sectioning are required. These techniques carry higher complication rates, as reviewed by Kennedy et al (2020). Regular (6 monthly) dental treatments are required post-extraction to manage the inevitable opposing tooth overgrowth.
Endodontic techniques
Endodontic treatments can be used to preserve fractured teeth in some cases. Because of the complicated endodontic anatomy and challenging access to cheek teeth, these treatments can be difficult. Techniques fall into two broad classes: one aiming to protect the underlying vital pulp structures (vital pulp therapy) and the other aiming to remove necrotic tissue and impacted food material from the affected endodontic structures (which may be just part of the tooth, if the pulp chambers have produced their own seal) and replace it with restorative material (non-vital pulp therapy).
Vital pulp therapy can include: ‘pulp capping’ where a dressing is placed directly onto exposed pulp and ‘partial vital pulpotomy’ where part of the exposed pulp is removed, and a dressing is applied that is covered in restorative material; the latter technique is more likely to be successful.
Non-vital pulp therapy (‘full pulpectomy’ or ‘root canal treatment’) involves obtaining access to the endodontic structures, removal of necrotic tissue (debriding, instrumenting lavaging and sterilising), then filling the space (obturation). This may be done in one stage or over a number of treatments. Endodontic access can be obtained from the occlusal (orthograde) or apical aspect (retrograde) of the tooth, the latter of which can be done with the tooth in-situ or following extraction prior to re-implantation (although re-implantation is not normally attempted with fractured teeth). Orthograde access appears to carry a better prognosis, based on current knowledge. There is limited published research on endodontic treatment in equids; although one case series reported good success rates of up to 80% over 3–6 years (Lundström and Wattle, 2016).
If endodontic techniques are used, it is important that the teeth are carefully monitored post treatment (clinically and with diagnostic imaging) for signs of treatment failure and appropriate action taken (normally tooth extraction) if required. Further detailed information on endodontic treatments of incisors, canines and cheek teeth are well described in recent publications (Pearce and Lundstrom, 2022; Rice and Limone, 2022).
Careful monitoring
In horses without clinical signs, leaving a fractured non-vital tooth in-situ may be considered, as this would have the benefit of stopping dental drift and opposing tooth overgrowth. However, this course of action carries the risk of extension of apical infection (which could be into the paranasal sinuses for caudal maxillary cheek teeth), and animals should be monitored closely as signs of oral pain may be subtle and are often masked by the horse as a prey animal response. It is also important to note that non-vital teeth, without continued deposition of dentine, can become brittle and may disintegrate over time with the normal forces of mastication and may deposit additional peripheral cementum (Figure 6) which can make them more difficult to extract subsequently. Also, once non-vital pulp canals become exposed occlusally, the inevitable food impaction will result in progressive caries that more rapidly weakens the tooth structure and will challenge any reparative dentine bridges or apical seals that have formed previously.
Conclusions
Fractured teeth are common in equids. Careful evaluation of the fractured tooth will allow selection of an appropriate diagnostic and treatment approach. Endodontic techniques can be used to preserve teeth in some cases, while certain fracture configurations inevitably necessitate extraction in others. Knowledge of treatment and diagnostic options and the ability to seek further advice is very helpful when dealing with fractured teeth.
KEY POINTS
- Fractured teeth are common in equids.
- Knowledge of equid dental anatomy is critical for assessing fractured teeth.
- Complicated crown fractures are more likely to result in adverse sequelae.
- Understanding dental pathophysiology allows appropriate treatment planning.