In dogs, we may find that permanent teeth are missing on the oral examination and most often this is an incidental finding. However, this is an important finding, as it may cause problems to the animal. Therefore, complete oral examination and dental radiographs under general anaesthesia are recommended to determine the nature of the problem.
Congenitally missing teeth cause no clinical problem to the animal and the reason for a missing tooth is mostly unknown, but may be hereditary. Dental radiographs are needed to confirm the true absence of the teeth (Fig. 1).
The tooth can also be missing if it has exfoliated due to severe periodontitis, or as a result of periodontal trauma (avulsion). Another reason for a missing tooth is previous dental extraction. Healing of the alveolus is rapid and active bone remodeling with radiographic evidence of new bone formation is visible in 6-8 weeks, and (radiographic) healing of the extraction site is completed after 6-8 months. Once the vacated alveolus has (radiographically) healed, it is usually impossible to determine the reason for a clinically missing tooth.
The tooth will also be missing clinically, if it has failed to erupt (e.g., unerupted tooth, impacted tooth), which can also be diagnosed by dental radiographs (Fig. 2). Extraction of an unerupted tooth is usually indicated. Extraction is not necessary easy and it depends on the position of the tooth (impacted or abnormally positioned unerupted teeth). If an unerupted permanent tooth is left in place, chances are this will lead to a formation of a dentigerous cyst (Fig. 2b, c). If untreated, dentigerous cysts expand, which may lead to an extensive bone loss (Fig. 3), possibly resulting in jaw fracture.
A tooth may also be clinically missing after it has fractured, with root remnants persisting in the bone, which can be seen on dental radiographs (Fig. 4). Retained roots are the source of infection and pain and should be removed. Complete removal of the roots should be confirmed radiographically.