Possible causes of missing teeth (i.e. teeth that do not erupt) include
1. Congenital: This abnormality is generally considered to be a genetic problem but can be secondary to in utero or neonatal problems. It
is common in small, toy, and brachycephalic dog breeds. No specific therapy is necessary in these cases, but the patient should
not be bred if a full dentition is standard.
2. Previously exfoliated: This condition is rare in juvenile patients, but it is possible. In these cases, radiographs will usually reveal evidence
of a healing alveolus. Again, no specific therapy is necessary.
3. Fractured below the gingival margin: This condition is also rare in juvenile patients but common in adults. Dental radiographs will confirm a retained root (Figures 17A & 17B). If the root appears relatively normal (i.e. it is not being resorbed), surgical extraction is generally recommended to avoid pain and endodontic infection. If the tooth
is showing marked resorption and no evidence of infection (periapical lucency), it can be radiographically monitored.
4. Impacted: Any tooth that remains unerupted beyond its normal eruption time is considered impacted.12 These teeth can 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 the operculum.4 This condition most commonly involves the first and second premolars of brachycephalic dogs. If caught early (before root
end closure), removing the offending structure may allow the tooth to erupt normally. This procedure is called an operculectomy. Dental radiographs will confirm the unerupted tooth (Figures 18A & 18B).
The biggest concern with impacted teeth is the development of odontogenic cysts. These cysts originate from the enamel-forming
organ of the unerupted tooth. The incidence of cyst development is unknown in veterinary medicine, but pathologic changes
were noted in 32.9% of cases in one human study.13 In some cases, the cysts grow quickly and cause bone loss by pressure (Figure 19). This may result in a pathologic fracture. In addition, cysts can become infected and create marked swelling and pain.
Finally, malignant transformation has occurred in some cases.14
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.
Note that two of the causes of missing teeth require no therapy and that the other two can lead to serious pathology. So radiograph
all missing teeth to ensure that they are truly missing.
Enamel is a thin (< 1 mm) material on the surface of teeth.15 It is deposited on the dentin of the developing tooth by the enamel-forming organ. Enamel is only formed before tooth eruption
and cannot be naturally repaired after eruption into the mouth. Hypocalcification results from a malformation of the enamel
during its development. The malformed enamel will be easily lost, exposing the underlying dentin.
The most frequent cause of enamel hypocalcification in veterinary patients is trauma imposed on the unerupted tooth. This
trauma is most commonly associated with the extraction of a deciduous tooth. In these cases, only one or several adjacent
teeth will be affected. Other causes of this pattern of enamel hypocalcification include infection or inflammation from an
overlying deciduous tooth.6