Persistent Deciduous Teeth

When deciduous teeth exfoliate improperly or incompletely, the deciduous tooth and the permanent tooth are present in the mouth at the same time. No tooth of the same type should be present in the mouth at the same time. If this occurs, the deciduous tooth should be extracted immediately. Persistent deciduous teeth are never normal and should be extracted as soon as a diagnosis is made. Persistent deciduous teeth are also a common cause of malocclusion because they can cause the permanent teeth to erupt in an abnormal location. The permanent premolar teeth generally erupt to the inside (lingually or palatally) of the deciduous counterpart. The exception to this is the upper canine teeth, which erupt in front (mesial) of the deciduous teeth. Figure 35-3 shows an example of a dog with a persistent deciduous left upper canine tooth. The permanent tooth has erupted in an abnormal position because of the failure of the deciduous tooth to exfoliate. This abnormal mesioversion (the tooth is angled toward the front of the mouth) of the canine tooth has also been termed a “lance canine” tooth.

Figure 35-3 Photos of the left upper arcade in a Beagle dog showing a persistent deciduous canine that has caused the permanent canine tooth to erupt mesially. This is also called a lance canine tooth. Left untreated, these teeth develop severe periodontal problems over time, which can result in oronasal fistulas.

Treatment for persistent deciduous teeth consists of complete extraction of the deciduous tooth. Preoperative intraoral dental radiographs identify location and shape of the tooth to be extracted. A gingival flap may be appropriate to allow adequate visualization and minimize chance of root fracture. Extraction techniques are covered in detail in other texts (see Suggested Reading list); however, it is important to note that deciduous teeth have deceptively long roots compared with crown size, very thin enamel walls, and break easily with overzealous extraction technique (Figure 35-4). It is essential to remove the entire deciduous tooth root when extraction is performed. Incomplete extraction may lead to infection, pain, or malocclusion. Postoperative dental radiographs should be obtained to ensure complete extraction. When performing deciduous tooth extractions, special care should be exercised to avoid trauma to the permanent tooth bud as this can cause damage to the permanent tooth enamel (Figure 35-5).

Figure 35-4 The crown length of a deciduous canine demonstrates the deceptively short crown compared with root length. The bracket is outlining the crown. The remainder of the tooth is root. It is imperative to extract the root entirely. This may require creating a gingival flap for increased exposure and visualization. Complete extraction should always be verified radiographically.

Figure 35-5 Enamel dysplasia of the permanent teeth after extraction of the deciduous teeth in a dog. If the permanent tooth bud is traumatized during the extraction procedure, dysplasia will occur. Dysplasia exposes the dentin tubules to the environment and may weaken the tooth, possibly requiring composite or crown restoration to avoid further damage to the teeth. Enamel dysplasia may also result from a puppyhood illness or facial trauma while the permanent tooth is still developing.

Missing and Impacted Teeth

Normal tooth eruption occurs in two stages: the intraosseous stage and the supraosseous stage. In the first stage, the overlying bone and the deciduous tooth root (if present) are resorbed. In the second stage, the permanent tooth erupts through the soft tissues. This process can be delayed or interrupted by a number of local and systemic causes, including genetic and congenital problems, trauma, persistent deciduous teeth, thickened fibrous tissue (operculum) covering the unerupted tooth, and failure of bone resorption. It is important to note there are no deciduous precursors to the permanent first premolar teeth in the canine or the molar teeth in both the canine and feline. Knowledge of normal permanent tooth eruption times in addition to dental radiography can differentiate between congenital absence of teeth (oligodontia or anodontia) and impaction. Impaction occurs when a tooth is covered by a tough gingival tissue called the operculum that prevents eruption. When a tooth is embedded, the tooth is not only covered by the operculum but also is covered by bone (Figures 35-6 and 35-7). It is not uncommon to see lower first premolar teeth that are impacted or in an abnormal position, particularly in brachycephalic breeds. Unerupted teeth are prone to developing destructive cystic lesions. These cysts can cause significant damage to the soft and hard tissues surrounding them, including loss of surrounding permanent teeth (Figure 35-8). Because impacted lower first premolar teeth are often in an abnormal position, extraction is usually appropriate.

Figure 35-6 Intraoral photo of missing teeth in a 14-week-old puppy. Dental radiographs must be obtained to ascertain whether the teeth are truly missing or are impacted.

Figure 35-7 Intraoral radiographs of the puppy in Figure 35-6. This radiograph demonstrates that although the teeth are missing clinically, they are present under the gingiva. Left untreated, dentigerous cysts are likely to follow.

Figure 35-8 Radiograph of a dentigerous cyst caused by an impacted right lower first premolar in a 5-year-old Japanese Chin. Timely diagnosis and treatment early in life could have prevented the extensive damage and tooth loss caused by this pathology. All puppies and kittens should be monitored for full dentition by 6 months of age, and abnormalities should be investigated radiographically.

Breeders may request preeruption dental radiographs to determine whether a particular dog has a full complement of permanent teeth. In some breeds, such as the Doberman Pinscher, Rottweiler, and German Shepherd Dog, absence of teeth may be grounds for elimination in the show ring because of the hereditary component of this problem. Preeruption radiographs are most diagnostic after 8 to 10 weeks of age.

It is simple to diagnose these abnormalities at the time of routine well puppy exams or spay and neuter appointments. At this time, any missing teeth should be noted in the medical record, and dental radiographs should be obtained. Treatment of impacted or embedded teeth involves making mesial and distal releasing incisions on both the buccal and lingual or palatal surfaces, and then elevating a full-thickness mucoperiosteal flap on both surfaces. The fibrous tissue (operculum) covering the crown is excised with a No. 15 blade, and any overlying bone is gently removed with rongeurs. A high-speed dental bur should not be used to remove bone as it may cause trauma to the underlying tooth. The releasing incisions are closed using 4-0 or 5-0 absorbable suture, leaving the coronal aspect of the flap open.

Supernumerary, Fusion, and Gemination Teeth

Abnormalities of the developing tooth bud can result in abnormal numbers of roots or crowns or entire teeth in the dog and the cat. Supernumerary teeth occur when two of the same tooth are present in the mouth. It is not uncommon to see supernumerary incisors in breeds such as the Boxer and Mastiff. Supernumerary first premolar teeth are common in many dog breeds as well. Cats can have supernumerary premolars. These teeth should be extracted if they cause crowding or impingement on adjacent teeth.

Fusion and gemination teeth are seen in many breeds of dogs and cats. A fusion tooth typically has two fused crowns, a common pulp chamber, and separate root canal systems. In contrast, gemination teeth have two crowns and pulp chambers but a single root canal system. Intraoral dental radiographs can differentiate the two. These teeth are often extracted because of the frequency of enamel, dentin, and root canal system abnormalities that may lead to endodontic disease.