Tooth eruption and exfoliation 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.

Table 1 Normal eruption times for deciduous and permanent teeth in dogs and cats

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.

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 1: An intraoral radiograph revealing a deciduous mandibular second premolar without a permanent underlying counterpart

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 2: Retained deciduous maxillary and mandibular canines.

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

Photo 3B: A retained deciduous canine in a cat.

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 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.

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).

Photo 6: A retained deciduous tooth with resorption evidence.

Photo 7: An extracted retained resorbing deciduous canine.

Extraction recommendations

1. Use a No. 11 surgical blade (not a No. 10 or 15) to circumferentially incise the proximal periodontal ligament attachment.

Photo 8: Using a No. 11 blade, incise the proximal periodontal ligament.

Photo 9: Place a wing-tipped elevator between the permanent and deciduous canines.

2. Choose a closed or an open extraction technique based on degree of resorption visible on radiographs. The closed extraction technique (Photos 8-9, 10-11) is indicated in cases without radiographic evidence of resorption. The open extraction technique (Photos 12-15) is indicated with radiographic evidence of resorption to decrease the chance of root fracture.

Photo 10: Use an elevator to loosen the maxillary canine.

Photo 11: Extract the deciduous maxillary canine.

3. Use an appropriately sized, presharpened, thin-faced, wing-tipped elevator to further excise the periodontal attachment and loosen the tooth.

Photo 12: Incise the gingiva overlying the deciduous canine.

Photo 13: Use a wing-tipped elevator to loosen the deciduous canine from attachment.

4. Use a small rongeur, which wraps around the crown and proximal root, in a pull stroke to extract the tooth. Do not use rotational force, as this often will result in deciduous tooth root fracture.

Photo 14: Extract the maxillary canine.

Photo 15: Suture the incision.

5. If the root fractures during the extraction, examine an intraoral radiograph to determine the degree of resorption present in the root fragment. If little radiographic evidence of root resorption exists, the root fragment should be visualized and removed. This is facilitated with gingival flap exposure and removal of the overlying alveolus.

Dr. Bellows owns All Pets Dental in Weston, Fla. He is a diplomate of the American Veterinary Dental College and the American Board of Veterinary Practitioners. He can be reached at (954) 349-5800; e-mail: dentalvet@aol.com

SUGGESTED READING

1. Reiter AM. Dental surgical procedures. In: Tutt C, Deeprose J, Crossley DA, eds. BSAVA manual of canine and feline dentistry. Gloucester: BSAVA, 2007;178-195.

2. Harvey CE, Emily PP. Occlusion, occlussal abnormalities, and orthodontic treatment. In: Harvey CE, Emily PP, eds. Small animal dentistry. St. Louis, Mo: Mosby, 1993;278-280.

3. Wiggs RB, Lobprise HB. Oral anatomy and physiology. In: Wiggs RB, Lobprise HB, eds. Veterinary dentistry: principles and practice. Philadelphia, Pa: Lippincott-Raven, 1997;69.

4. Wiggs RB, Lobprise HB. Pedodontics. In: Wiggs RB, Lobprise HB, eds. Veterinary dentistry: principles and practice. Philadelphia, Pa: Lippincott-Raven, 1997;169-174.

5. Hale FA. Juvenile veterinary dentistry. Vet Clin North Am Small Anim Pract 2005;35(4):789-817.

6. Amimoto A, Iwamoto S, Taura Y, et al. Effects of surgical orthodontic treatment for malalignment due to the prolonged retention of deciduous canines in young dogs. J Vet Med Sci 1993;55(1):73-79.