A 9-year-old spayed female Pembroke Welsh corgi was presented for evaluation of a complicated crown and root fracture of the left second maxillary incisor (202). No physical examination abnormalities were noted, and the results of a complete blood count and serum chemistry profile were unremarkable. The first incisor from the left maxilla and the first and second incisors from the right maxilla had been previously removed. Two small openings were noted lateral to the incisive papillae:
Dental radiographs of the rostral maxilla were obtained after extraction of the affected tooth:
A dental radiograph of the rostral maxilla was also obtained with a radiopaque file placed into the opening on the right side of the incisive papilla:
Which of the following is the most likely diagnosis?