The ABCs of veterinary dentistry: "E" is for enamel

Enamel, formed during tooth eruption, is 96% mineral, making it the hardest structure in dog's and cat's bodies. Dentin is the second hardest tissue, being 70% mineral and 30% organic (water, collagen and mucopolysaccharide).

Enamel covers and protects the tooth crown. It is avascular and has no nerve supply. If the enamel is damaged, it cannot self-repair as compared with dentin, which can. On radiographs, enamel appears more radiodense than dentin and pulp tissue since enamel is more mineralized than both (Figure 1).

Figure 1. An intraoral radiograph with arrows pointing to radiodense enamel. (Unless otherwise indicated, photos courtesy of Dr. Jan Bellows)Many conditions can affect enamel, some of which need care while others do not. Treatment generally depends on the proximity of the lesion to the underlying dentin, which, through tubules, communicates with the tooth's sensitive pulp. In a young dog or cat, the pulp is large and close to the enamel. As the animal ages, the dentin produced by amelobasts from the pulp increases the distance between the pulp and enamel, decreasing sensitivity and the possibility of infection (Figure 2).

Figure 2. Tooth anatomy showing the proximity of enamel and pulp. (Illustration by Mathews Albert)Enamel abrasion

Abrasion is wear caused by tooth contact with nondental objects such as  chewing on fences (Figure 3A), bones, antlers, flying disks and tennis balls. What's the harm in tennis balls? They accumulate sand in the yellow web, creating a sandpaper-like effect that, when chewed, removes enamel and dentin and can expose the pulp (Figure 3B).

Figure 3A. Fence chewing resulting in loss of enamel and dentin with near pulp exposure on the distal surfaces of both mandibular canines.

Figure 3B. Tennis ball chewing resulting in excessive perpendicular wear of maxillary incisors and canines.

Enamel attrition

Attrition involves tooth wear caused by contact of a tooth with another tooth. It occurs secondary to skeletal malocclusion (the jaw lengths are abnormal) or a dental malocclusion (the jaws are of normal lengths but individual teeth are malpositioned) (Figures 4A-4I).

Figure 4A. A mandibular mesioclusion resulting in attrition caused by the maxillary second incisors.

Figure 4B. Enamel and dentin loss on the distal surfaces of the mandibular canines caused by the maxillary second incisors in the same patient as Figure 4A.

Figure 4C. The enamel and dentin defects pictured in Figure 4B restored with light-cured composite after extraction of the right and left maxillary second incisors.

Figure 4D. A left mandibular enamel canine defect caused by attrition.

Figure 4E. Light-cured composite applied to the prepared defect pictured in Figure 4D after gingivectomy.

Figure 4F. The restored tooth pictured in Figures 4D and 4E.

Figure 4G. A malpositioned left mandibular canine creating enamel loss of the maxillary canine and attached gingival loss.

Figure 4H. Enamel and gingival loss caused by the malpositioned left mandibular canine in Figure 4G.

Figure 4I. The left mandibular canine crown reduced and restored to alleviate the trauma pictured in Figure 4H. A gingivectomy was performed to treat the mucogingival defect.

Caries

Caries are areas of enamel loss that sometimes progress to include dentin and create pulp exposure. Caries are caused by demineralization from acids released during bacterial fermentation of carbohydrates. Caries are rare in dogs and cats. In dogs, they usually affect the pits in the occlusal areas of the maxillary first molars in larger-breed dogs, especially Labrador retrievers (Figures 5A-5C).

Figure 5A. A shepherd's hook explorer placed in caries.

Figures 5B and 5C. The caries removed with a round bur and the defect filled with light-cured composite before preparation for metallic crown restoration.Enamel hypoplasia

This condition occurs from an inadequate deposition of enamel matrix before the tooth emerges from the gingiva due to poor nutrition or a high temperature when the dog is between 9 and 12 weeks old. Enamel hypoplasia can affect one or several teeth and may be focal or multifocal.

The crowns of affected teeth will have areas of normal enamel next to areas of hypoplastic or missing enamel. Enamel hypoplasia does not affect deciduous teeth (Figures 6A and 6B).

Figure 6A. A left maxillary third incisor and canine affected by enamel hypoplasia. Note the deciduous canine is not affected.

Figure 6B. The left mandibular second and third incisors and canine affected by enamel hypoplasia.

In areas where enamel is not present, exposure of the underlying dentin can be painful from increased sensitivity to heat, cold and pressure, especially in younger animals. The goal of treatment is to seal the dentin tubules responsible for sensitivity with a dental bonding agent, smooth down the dental ridges that accumulate plaque and tartar with a white stone bur on a water-cooled high-speed handpiece, and restore the tooth with composite restoration. Unfortunately the composite restoration rarely lasts because of shearing forces. Repeated application of dental boding agents every six months until the dog is 2 years old allows for more dentin formation and increases the distance between outside influences and the pulp, decreasing sensitivity.

Placing metallic crowns to protect larger teeth generally creates long-term pain-free solutions. Metallic crown restoration should be considered when treating the eight larger teeth, including the canines, upper fourth premolars and lower first molars. Extraction of the affected teeth is usually not indicated as long as there is no evidence of endodontic disease (Figures 7A-7E).

Figure 7A. A left mandibular first molar affected by enamel hypoplasia.

Figure 7B. The tooth pictured in Figure 7A restored with light-cured composite before metallic crown preparation.

Figure 7C. Extensive generalized enamel hypoplasia.

Figures 7D and 7E. Metallic crowns protecting the maxillary and mandibular canines, upper fourth premolars and lower first molars of the patient pictured in Figure 7C.Enamel infraction

Enamel infractions, also called craze lines, are incomplete fractures (cracks) of the enamel without loss of tooth structure. No treatment is indicated.

Figure 8. An enamel infraction affecting the right mandibular canine.

Enamel hypomineralization

This condition occurs when there is an inadequate mineralization of enamel matrix. It can affect several or all the teeth. The crowns of affected teeth are covered by soft enamel that may flake off during ultrasonic scaling and are worn rapidly during daily chewing. Treatment is the same as that for enamel hypoplasia (Figures 9A and 9B).

Figure 9A. Enamel hypomineralization of the left mandibular canine and incisors.

Figure 9B. Enamel hypoplasia and hypomineralization.

Enamel fracture

These fractures are confined to the enamel. Because dentin is not exposed, enamel fractures are not considered painful. To protect the tooth from further damage, treatment should include smoothing any sharp enamel edges with a high-speed handpiece and applying a composite or metallic restoration (Figures 10A-10C). The enamel on cat teeth is thinner than in dogs. Because of underlying sensitivity and infection, enamel fractures in cats should be treated by extraction or root canal therapy.

Fig 10A. An enamel fracture approaching the underlying dentin in a dog.

Figure 10B. Phosphoric acid used as an etchant before applying light-cured composite.

Figure 10C. The restored canine tooth.