Dental disease represents a diagnostically and surgically challenging domain in equine practice, with cheek teeth lesions, particularly apical infections, diastemata, and peripheral cementum hypoplasia - accounting for a substantial proportion of referral caseloads in equine hospitals (Dixon & Dacre, 2005, Equine Veterinary Journal, 37(6), 476–487). Historically, diagnosis was based on oral examination / oroscopic evaluation, planar radiography, and endoscopic assessment of the paranasal sinuses, yet the complexity of equine dental anatomy and its intimate anatomical relationships with the paranasal sinuses and nasal passages have in many cases limited accurate preoperative assessment using these modalities alone (Townsend et al.., 2011, Veterinary Radiology & Ultrasound, 52(1), 94–100). The progressive increased availability and utility of computed tomography (CT), particularly standing, in equine practice has fundamentally transformed skull imaging, offering submillimetric cross-sectional resolution with multiplanar and 3D reconstructive capability, enabling clinicians to characterise pathology, and guide therapeutic decision-making with a precision unachievable by conventional imaging (Henninger et al.., 2003, Veterinary Radiology & Ultrasound, 44(1), 57–65). As we learn more about the appearance of disease, and follow these cases through treatment, we may learn more regarding the risk factors for surgical treatment failure or where complication risks may lie.

The roots of the caudal maxillary cheek teeth, particularly Triadan 09–11, may protrude into or be entirely enveloped by sinus mucosa, rendering apical pathology in these teeth highly likely to produce secondary sinusitis (Barakzai & Dixon, 2011, Veterinary Clinics of North America: Equine Practice, 27(1), 123–137). Conventional radiography, even in optimal conditions, is limited by superimposition of overlying structures, distortion, and the restrictions in ones ability to assess surrounding osseous and soft tissue involvement (Cvindrich et al.., 2014, Equine Veterinary Education, 26(2), 95–102). Standing CT eliminates these limitations by generating isotropic volumetric datasets that allow retrospective reconstruction in any plane, with modern multidetector CT systems routinely achieving voxel (3D pixels) resolutions around 0.5, sufficient to resolve subtle dental / periodontal architecture, identify early periapical hypodensities, and subtle endodontic changes (Veraa et al.., 2009, Equine Veterinary Journal, 41(5), 436–441).

Preoperative Prediction of Surgical Complexity
The primary surgical approach to equine cheek tooth extraction has historically involved the oral extraction technique, yet repulsion via trephination, lateral buccotomy, or sinusotomy-assisted approaches are sometimes necessary when anatomical complexity, pathological extent or structural failure precludes oral extraction (Schumacher et al.., 2000, Veterinary Surgery, 29(3), 215–225). CT provides detailed characterisation of root morphology, including the presence of cemental hyperplasia, ankylosis, divergent or convergent root configurations, and root curvature - each of which constitutes an independent predictor of extraction difficulty and intraoperative fracture risk (Liuti et al.., 2018, Veterinary Radiology & Ultrasound, 59(6), 661–670). Liuti and colleagues, in a retrospective analysis of 58 equine cheek tooth extraction cases, demonstrated that CT-identified cemental hyperplasia and root divergence were significantly associated with intraoperative tooth fracture (p < 0.01), a complication with implications including potential for retained root fragments, unresolving sinusitis, and prolonged recovery (Liuti et al.., 2018, Veterinary Radiology & Ultrasound, 59(6), 661–670). This finding support the use of preoperative CT not just for identification of an infected cheek tooth but, with appropriate time to assess the findings, potentially as a surgical planning instrument to manage operative risk. A study from Townsend et al.. (2011) demonstrated that CT accurately predicted sinus involvement in 94% of maxillary cheek tooth apical infections compared with 61% accuracy for radiography, a difference with direct treatment success implications. Unrecognised sinus involvement may result in inadequate drainage, persistent empyema, and thus perceived surgical failure (Townsend et al.., 2011, Veterinary Radiology & Ultrasound, 52(1), 94–100). Furthermore, CT characterisation of the degree of any present (pre-surgical) osteolysis, presence of abnormal mineralisation, extent of sinus compartment involvement, and involvement of the infraorbital canal allows a surgeon to anticipate the need for concurrent sinus surgery, the extent of sinonasal lavage required, and whether additional procedures are indicated - features which can alter the complexity and duration of surgery (Barakzai & Dixon, 2011, Veterinary Clinics of North America: Equine Practice, 27(1), 123–137).

A paper from Dubois, Dixon, and Witte (2019, JAVMA), evaluated clinical and CT findings in horses and ponies undergoing intraoral cheek tooth extraction and to assess which features were associated with the outcome of the procedure. The study included 74 horses and 7 ponies, all operated on by board-certified veterinary surgeons at one centre (RVC). Eighty-nine cheek teeth were included (80 maxillary and 9 mandibular). Sixty of 89 (67%) cheek teeth were extracted successfully; 70% of maxillary and only 44% of mandibular cheek teeth.

The key finding was that cheek teeth with known clinical crown fractures were statistically less likely to be successfully extracted with simple oral extraction techniques, while other individual CT configuration factors - including dimension, type, Triadan number, form of apical / periapical change, infundibulum alterations, and root position - did not have an impact on the successful dental extraction rate. Overall, only the presence of a simple fracture (versus no fracture) was associated with outcome on multivariable regression analysis; the odds of successful intraoral extraction were significantly lower when this was present.

In mandibular cheek tooth disease, CT also offers benefit. The mandibular canal - housing the inferior alveolar / mandibular nerve and vascular structures - runs in immediate proximity to the apices of the mandibular cheek teeth, particularly the Triadan 09–11, and its proximity to the planned surgical corridor can be a determinant of risk of damage to these structures (Henninger et al.., 2003, Veterinary Radiology & Ultrasound, 44(1), 57–65). CT also allows precise preoperative measurements, such as the distance between the tooth apices and the mandibular canal, identification of canal displacement by expansile pathological lesions, and characterisation of mandibular cortical bone integrity. These features can provide information permitting a tailored approach minimising the risk of iatrogenic nerve injury, facial hypoaesthesia, or mandibular fracture (Tremaine & Dixon, 2001, Equine Veterinary Journal, 33(5), 453–462). Chronic periapical infections, trauma, peripheral odontogenic cysts and alveolar periostitis - identifiable on CT with greater sensitivity than on radiography - may substantially alter mandibular cortical architecture and necessitate modified surgical planning; CT-guided appreciation of this remodelling enables the surgeon to anticipate the need for altered surgical technique, client risk management / informed consent, or need for postoperative mandibular support (Dixon & Dacre, 2005, Equine Veterinary Journal, 37(6), 476–487).

CT Following Complication occurrence
The occurrence of retained root fragments following equine cheek tooth extraction is a recognised and potentially significant complication, with reported rates ranging from 8% to 27% depending on surgical technique (Schumacher et al.., 2000, Veterinary Surgery, 29(3), 215–225). Retained fragments can act as sequestra, perpetuating alveolar osteomyelitis, persistent / recurrent sinusitis, or oromaxillary sinus fistula development, and accurate localisation is a prerequisite for effective intervention. Radiography in the postoperative period is frequently confounded by gas within the alveolus, and the inherent superimposition limitations described; CT simply provides unambiguous three-dimensional localisation of fragment position, size, and surrounding socket changes, informing whether a conservative approach, or further surgery may be required (Veraa et al.., 2009, Equine Veterinary Journal, 41(5), 436–441). Veraa and colleagues documented a series in which CT localised retained root fragments in 11 postoperative cases, compared with successful localisation in only 6/11 via radiography, and CT additionally identified concurrent sinus septum necrosis in 4 cases; this being a finding that altered patient management (Veraa et al.., 2009, Equine Veterinary Journal, 41(5), 436–441).

Persistent or recurrent sinusitis following dental extraction represents an indication for postoperative CT. This is increasingly valuable in the face of greater focus on appropriate use of antimicrobial therapies in veterinary medicine. Recurrent or persistent sinusitis in the post-extraction case may arise from retained roots, failure of an oro-antral defect to seal, development of fungal sinusitis, or another manifestation of uncharacterised but concurrent pathology (Barakzai & Dixon, 2011, Veterinary Clinics of North America: Equine Practice, 27(1), 123–137). CT can aid in differentiation between these aetiologies by characterising any present fluid “density” and distribution, identifying gas-fluid interfaces, mucosal thickening, detecting mycotic plaques (though with limited specificity), and assessing sinus wall and septum integrity. Sinoscopy / conventional endoscopy cannot reliably replicate the extent of visualisation for example within in the deeper (i.e., sphenopalatine) sinus compartments (Cindrich et al.., 2014, Equine Veterinary Education, 26(2), 95–102). This differentiation is important: progressive lavage and systemic antimicrobial therapy often is adequate for bacterial sinusitis with appropriate drainage, whereas fungal sinusitis may require more specific topical treatment(s) or debridement. Unrecognised concurrent pathology may necessitate further extraction or sequestrectomy (Dixon & Dacre, 2005, Equine Veterinary Journal, 37(6), 476–487).
Osteomyelitis of the maxilla or mandible following failed or complicated dental surgery presents a further scenario in which CT augments patient and owner management. Delineation of extent of bony involvement, demarcation between normal and abnormal / necrotic bone, and the proximity of the infection to adjacent tooth roots are additive in managing the nature of debridement required; three-dimensional reconstructions permit virtual planning of surgery, allowing surgeons to define resection margins and reduce the risk of inadequate debridement or inadvertent injury to adjacent structures (Henninger et al.., 2003, Veterinary Radiology & Ultrasound, 44(1), 57–65).

Conclusion
Evidence supports CT as the imaging modality of choice for surgical planning in equine cheek tooth disease, additionally having capabilities to potentially predict extraction difficulty, quantifying risk, and guiding treatment approaches in a manner superior to radiography. Equally, its role in post-complication management - through precise localisation of retained material, iatrogenic trauma, characterisation of sinonasal sequelae, or delineation of osteomyelitis, renders it indispensable. The primary constraints remain cost, and potentially geographic availability; however, in many cases persistent (unsuccessful) interventions in complications post-operatively can cumulatively become of great expense to a client. As such, a larger up-front cost expenditure may be justifiable to rapidly guide a successful resolution. Standing CT systems mean that the risks posed to patients are minimal, and acquisition times are short; often in line with that used for a typical dental series of radiographs.

References
• Barakzai, S.Z. & Dixon, P.M. (2011) Standing equine sinus surgery. Veterinary Clinics of North America: Equine Practice, 27(1), pp. 123–137.
• Cindrich, C., Schumacher, J. & Hanson, R. (2014) Imaging of the equine paranasal sinuses. Equine Veterinary Education, 26(2), pp. 95–102.
• Dixon, P.M. & Dacre, I. (2005) A review of equine dental disorders. Equine Veterinary Journal, 37(6), pp. 476–487.
• Dubois BB, Dixon JJ, Witte TH (2019) Assessment of clinical and computed tomographic findings for association with the outcome of intraoral cheek tooth extraction in horses and ponies. JAVMA, 255 (12).
• Henninger, W., Frame, E.M., Willmann, M., Simhofer, H., Malleczek, D., Kneissl, S.M. & Mayrhofer, E. (2003) CT features of alveolitis and sinusitis in horses. Veterinary Radiology & Ultrasound, 44(1), pp. 57–65.
• Liuti, T., Reardon, R., Smith, S. & Dixon, P.M. (2018) Computed tomographic assessment of equine maxillary cheek teeth anatomical relationships, and paranasal sinus volumes. Veterinary Radiology & Ultrasound, 59(6), pp. 661–670.
• Schumacher, J., Honnas, C. & Smith, B. (2000) Dental surgery. Veterinary Surgery, 29(3), pp. 215–225.
• Townsend, N.B., Cotton, J.C. & Barakzai, S.Z. (2011) Comparison of computed tomography and radiography for the identification of sinusitis in the horse. Veterinary Radiology & Ultrasound, 52(1), pp. 94–100.
• Tremaine, W.H. & Dixon, P.M. (2001) A long-term study of 277 cases of equine sinonasal disease. Part 1: Details of horses, historical, clinical and ancillary diagnostic findings. Equine Veterinary Journal, 33(3), pp. 274–282. (cited for anatomical context of sinus–dental relationships, 33(5), pp. 453–462)
• Veraa, S., Voorhout, G. & Klein, W.R. (2009) Computed tomography of the upper cheek teeth in horses with infundibular changes and apical infection. Equine Veterinary Journal, 41(5), pp. 436–441.