Tooth eruption and exfoliation in dogs and cats

Tooth eruption and exfoliation in dogs and cats

Keep in mind that eruption is controlled by genetic, environmental, infectious and traumatic factors
Jan 01, 2011

Table 1 Normal eruption times for deciduous and permanent teeth in dogs and cats
Puppies and kittens initially develop a set of teeth collectively referred to as the primary, or deciduous, dentition. These primary teeth generally erupt or emerge into the oral cavity between the ages of 3 to 6 weeks. At 3 months of age, the permanent teeth begin to erupt, and the primary teeth are shed or exfoliated (Table 1). The first premolars and molars erupt as permanent teeth without deciduous predecessors.

As permanent teeth develop within the jaws, resorption causes the roots of the deciduous teeth to be absorbed by the surrounding tissues. This process of exfoliation of primary teeth and eruption of permanent teeth is usually complete by 6 months of age. The time when the mouth contains both primary and permanent teeth in functional positions is called the period of mixed dentition.

Tooth eruption is facilitated by osteoclasts that resorb alveolar bone, forming an eruption pathway for the tooth to exit its bony crypt. Eruption is controlled by genetic, environmental, infectious and traumatic factors.

As noted, in most dogs and cats, the deciduous teeth are fully erupted by 2 months of age, and usually by 6 months they're replaced by permanent (secondary or adult teeth). In dogs, the canines erupt first, followed by the incisors, then the fourth, third and second premolars, for a total of 28 primary teeth. In cats, the incisors erupt before the canines, followed by the premolars for a total of 26 deciduous teeth. As in dogs, cats do not have deciduous molar teeth.

4 problems with deciduous teeth

The following are common problems associated with deciduous teeth and suggestions for proper patient care.

Photo 1: An intraoral radiograph revealing a deciduous mandibular second premolar without a permanent underlying counterpart
1. Delayed eruption of deciduous teeth. A delay is usually caused by dense, overlying, fibrous gingival tissue preventing normal eruption. Small-breed dogs are predisposed to this problem. Diagnosis is confirmed by radiography. An operculectomy is performed by removing a small gingival window with a No. 11 surgical blade to remove the impediment. Ideally, this is performed before nine months while the tooth still has the ability to erupt.

Photo 2: Retained deciduous maxillary and mandibular canines.
2. Missing underlying permanent teeth. Occasionally, the permanent tooth is not present to facilitate exfoliation of its deciduous counterpart. When this occurs, the deciduous tooth may remain functional for years. However, once resorption is clinically or radiographically evident (Photo 1), extraction is indicated.

Photo 3A: A retained maxillary canine creating malposition of the mandibular canine in a dog.

Photo 3B: A retained deciduous canine in a cat.
3. Fractured deciduous teeth. Compared with their permanent successors, the roots of deciduous teeth are longer and thinner and may be partially resorbed. Coupled with the fact that puppies and kittens enjoy chewing objects that often are not tooth-friendly, deciduous teeth occasionally fracture, exposing the pulp. Once exposed to the oral environment, the pulp becomes infected and necrotic. The infection may affect the area surrounding the root, including the permanent tooth. Treatment for fractured deciduous teeth is extraction. Radiology is advised before extraction to evaluate the degree of root resorption present and proximity to the permanent underlying tooth.

Photo 4: An intraoral radiograph revealing a deciduous canine root fragment (white arrows) with periapical lucency consistent with inflammation as well as iatrogenic penetration of a permanent canine during a deciduous canine extraction attempt.

Photo 5: A retained deciduous canine without radiographic evidence of resorption.
4. Retained (persistent) deciduous teeth. Occasionally, the deciduous tooth does not exfoliate, causing the permanent tooth, if present, to erupt in the same gingival collar (Photo 2). The maxillary deciduous canine is usually distal to the permanent canine, and the mandibular deciduous canine is labial to the permanent canine. These two erupted teeth in one gingival collar commonly cause the permanent tooth to become positioned in a nonfunctional location. Problems may also arise due to lack of periodontal attachment with two teeth present (Photos 3A & 3B, p 4S). Immediate removal of the retained deciduous tooth is indicated; note, this is a delicate surgical procedure. Most commonly, the canine is retained, followed by incisors and premolars. Extraction of the tooth in total is often difficult because of the increased length of the root, the thin walls that may be affected by resorption or ankylosis. In these cases, extraction may result in iatrogenic damage to the erupting permanent canine (Photo 4).

Photo 6: A retained deciduous tooth with resorption evidence.

Photo 7: An extracted retained resorbing deciduous canine.
Examination of intraoral dental films while the patient is anesthetized is recommended to view the condition of the deciduous tooth root and proximity to the permanent tooth. For deciduous teeth that do not have radiographic evidence of internal or external resorption (Photo 5), a closed surgical technique can be used to deliver the tooth from the oral cavity. If there is radiographic evidence of resorption (Photo 6), an open surgical technique facilitates total tooth extraction without fracture. Examine a postoperative dental radiograph to confirm complete extraction of the deciduous tooth, as well as to document the continued presence and proper condition of the permanent tooth (Photo 7).