Case of the Missing Tooth

QUESTION

During a routine visit, it is discovered that the patient—a pug—is missing a mandibular first premolar (Figure 1); there is no swelling or discharge in the area. Based on the physical examination findings, what are your differential diagnoses and thoughts on further diagnostics and treatment?

Figure 1

ANSWER

It is exceedingly common for teeth to be absent in the dental arcades of veterinary patients. If the tooth is not seen above the gumline, do not assume it is truly absent or previously extracted.

Possible etiologies for “missing” teeth include:¹

1. Congenitally missing:²
   This is generally considered to be a genetic problem, but can also occur secondary to significant in utero or neonatal issues. Congenitally missing teeth are common in small, toy, and brachycephalic breeds,³ with a predisposition in the Chinese Crested and Mexican hairless breeds.¹ Teeth most typically affected include premolars, maxillary second and mandibular third molars, and incisors. No specific therapy is necessary.
2. Previously exfoliated or extracted:
   While rare in juvenile patients, this cause is common in mature to geriatric animals. Exfoliation (ie, the tooth has fallen out “on its own”) typically results from periodontal disease, but may also be trauma related. In older animals, extraction is a more likely cause. In these cases, radiographs will usually reveal evidence of a healing alveolus. Again, no specific therapy is necessary.
3. Fracture below the gingival margin:
   This condition is also rare in the juvenile patient, but common in adults. Subgingival tooth fractures may occur as a result of an incomplete extraction attempt, and retained roots are actually far more common than thought.⁴ Dental radiographs can confirm retained roots and potential infectious lesions. Surgical extraction is generally recommended to alleviate pain and endodontic infection.
4. Impacted or embedded:
   These teeth may be malformed or normal, but do not erupt into the dentition because they are blocked by a structure, such as bone or tooth (deciduous or permanent) or, most commonly, by an area of thick and firm gingiva called an operculum. This condition is most common in the first and second premolars of brachycephalic breeds.

It is critical to note that the first two causes for “missing” teeth require no therapy, because the teeth are truly absent. However, the remaining two causes can be associated with significant pathology. Therefore, all “missing” teeth should be radiographed to determine whether the cause is true absence versus subgingival pathology.⁵

QUESTION

Figure 2 is a dental radiograph of the area of the absent mandibular first premolar. Based on the physical examination findings and radiograph, what is your diagnosis and treatment plan?

Figure 2

ANSWER

The radiographic image reveals an unerupted mandibular first premolar tooth (white arrow). In addition, there is a significant, smooth-edged lytic lesion surrounding the tooth (red arrows). Finally, many of the teeth have been displaced (blue arrows).

The primary diagnosis is a dentigerous cyst.

Treatment recommendations include:

• Surgical enucleation (removal) of the cyst and all affected teeth¹
• Sampling and submitting the cyst lining for histopathology
• Addition of an osseopromotive substance, which benefits treatment of large lesions, such as this
• Referral to a qualified veterinary dentist for best surgical outcome.

What are dentigerous cysts?

Dentigerous cysts arise from the enamel forming organ of the unerupted/impacted tooth. The incidence of dentigerous cyst development from impacted teeth is unknown in veterinary patients, but anecdotally is approximately 50%. In a human study, pathologic changes were noted in 32.9% of cases of unerupted/impacted teeth.⁶

Do dentigerous cysts negatively impact dental health?

As a dentigerous cyst grows, this pressure causes bone loss. Cysts can grow quite large in a short period of time, resulting in weakened bone and, possibly, pathologic fractures of the jaw. In addition, the cyst can become infected and create significant swelling and pain. Malignant transformation can also occur.⁷

What therapeutic measures should be pursued?

Therapy for impacted teeth is surgical extraction. If cyst formation has occurred, en bloc removal or extraction of the tooth and meticulous curettage of the lining will prove curative.