Sinus tract and apical infection in a mare with a fractured incisor
A 9-year-old Thoroughbred mare is presented for a persistent facial swelling over the left maxilla and a small draining tract below the left eye that has been treated with two courses of trimethoprim-sulfonamide without resolution. The mare is in training and has had a reduced appetite for 2 weeks. Oral examination shows a fractured upper left third incisor with a discolored crown; the fracture is old and smooth. The left maxillary cheek teeth appear normal on gross inspection, but the fourth premolar has a slightly widened periodontal space on the buccal aspect. There is no nasal discharge. Radiographs of the skull show a soft tissue opacity in the left caudal maxillary sinus and a possible periapical lucency at the fourth premolar.
1. Explain why the sinus tract has not resolved with antibiotics and outline the diagnostic steps needed to identify the source.
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Antibiotics alone cannot resolve a draining tract of dental origin because the source is a necrotic pulp space and periapical infection that antibiotics cannot sterilize. The tract persists as long as the infected tooth remains. The discolored fractured incisor is a plausible source, but the sinus opacity and the widened periodontal space at the fourth premolar raise concern for a cheek tooth apical infection. Diagnostic steps include a detailed oral examination under sedation with a full-mouth speculum to assess the incisor and cheek teeth, periodontal probing, and radiographs from multiple angles. Additional imaging such as computed tomography is often needed in the horse because the maxillary sinus and tooth roots overlap on plain films. Sinoscopy can allow direct visualization and sampling of the sinus. A positive response to a local anesthetic block or a positive sinus centesis would help localize the source. A complete blood count and fibrinogen may support the presence of chronic infection.
2. Compare the options for managing a confirmed periapical infection of a maxillary cheek tooth in this mare, considering that she is in training.
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Options include extraction, endodontic treatment, and, in some cases, conservative management with sinus lavage. Extraction of a maxillary cheek tooth is technically demanding because of the size and curvature of the roots and the risk of sinus communication or fracture of the alveolar bone. It is usually performed under general anesthesia with a oral extraction technique using a dental extractor, and post-operative sinus lavage and packing may be required. Return to training is typically several weeks. Endodontic treatment of a cheek tooth is feasible in selected cases but requires specialist equipment, multiple visits, and a compliant patient, and success in horses is less predictable than in dogs. Sinus lavage alone does not address the infected tooth and is only supportive. Given the training schedule, extraction with careful aftercare may be the most definitive option, but the owner should be counseled about the risks and the recovery time.
3. The owner wants to know whether the fractured incisor must also be treated. How would you decide?
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The incisor should be assessed for vitality and periapical disease. A discolored crown with an old smooth fracture may be non-vital, but without radiographic evidence of periapical lucency or a sinus tract tracing to that tooth, it may be an incidental finding. Pulp testing in horses is unreliable, so radiographs and clinical signs guide the decision. If the incisor is confirmed as the source, options include extraction or root canal therapy; incisor extraction is simpler than cheek tooth extraction and usually well tolerated. If it is not the source, it can be monitored with radiographs at recheck. The priority is to identify and treat the actual source of the sinus tract, so the incisor should not be extracted without evidence linking it to the drainage. A thorough examination and imaging of both the incisor and the cheek tooth are needed before committing to treatment.