Introduction

• Enamel is an inert, 96% inorganic substance which covers the crown of teeth. It is formed by hydroxyapatite crystals (Ca5 (PO4)3(OH)).
• Enamel is embryologically derived from ectodermal cells which form the enamel organ.
• Ameloblasts are the cells which form enamel and are present towards the end of the bell stage of tooth development. These cells secrete the enamel matrix which form hydroxyapatite crystals whithin enamel rods (mineralization stage). The crystals then grow in size (maturation phase).
• Once the tooth erupts, the ameloblasts no longer function, thus enamel can only be produced during tooth development. It cannot be repaired or regenerated in the mature animal.
• Enamel is the hardest, densest structure in the body.
• However, it is still subject to attack by external agents which may result in enamel defects, eg discoloration/staining, infractions  , abrasions  , attrition  , or bacterial plaque which results in caries Teeth: caries.
• Enamel hypoplasia (EH   ), is a developmental anomaly of the enamel (thin enamel of normal density/calcification).
• Enamel hypocalcification (EHC)  , is poorly mineralized enamel during development resulting in thin, easily worn enamel.
• Disturbance of morphogenic development of enamel - enameloma (enamel pearls) and odontoma.
• Dens invaginatus (dens in dente)  is a developmental problem where the top of the tooth bud folds in on itself, forming additonal layers of enamel, dentin and pulp tissue within the tooth.
• Amelogenesis imperfecta describes a hereditary reduction in the amount of enamel matrix laid down due to malfunction of enamel proteins. The enamel is discolored and chips away easily resulting in excessive wear.
• Congenital ectodermal defects may combine deformed teeth with partial or total baldness, eg Chinese Crested dogs .
• Acquired enamel defects are more common and may occur during enamel development, such as canine distemper virus infection . Depending on the point in time the infection occurs, different teeth will be affected as well as their roots. Trauma can also affect developing enamel, such as facial trauma, or iatrogenic (extraction attempts of deciduous teeth can affect the developing permanent tooth bud)  .
• Exposure to certain chemicals during tooth development can also affect enamel. Excessive fluoride intake results in fluorosis causing opaque, white patches in a mottled enamel.
• Tetracycline Tetracycline compounds can cause intrinsic dental staining of a yellow, to orange/grey color as the drug is bound to tissue undergoing calcification.

Pathogenesis

Etiology

• Trauma or infection during the developmental stage of enamel production. Ameloblasts present during the late bell stage secrete an enamel matrix. Hydroxyapatite crystals are laid down within enamel rods (mineralization phase) and then increase in size (maturation phase) to become tightly packed within the rod. If these cells are damaged, enamel will not be properly formed.
• Amelogenesis imperfecta: malfunction of enamel proteins due to defective genes, which means normal tooth development cannot occur. A genetic link has been demonstrated in Standard Poodles in Sweden. Enamel is not properly formed, so is discolored, and is soft.

Predisposing factors

General

• Genetic trait (amelogenesis imperfecta, in combination with other ectodermal defects (Chinese Crested dog  ) Dental disease: congenital.
• Fluorosis.
• Trauma.

Pathophysiology

Odontoma

• Abnormal neoplastic development of fully developed enamel, dentine, cementum and pulp at aberrant site (hamartoma=normal tissue in abnormal site).

Enameloma

• Abnormal morphogenic development of enamel may leave enamel pearls on root structure which means the periodontal ligament does not attach well to tooth. This results in a long junctional epithelium allowing plaque accumulation which may accelerate periodontal inflammation/disease.

Enamel hypoplasia or hypocalcification

• Accelerated wear compared to normal teeth, possible tooth root infection or tooth fracture.

Dens invaginatus

• Infolding of enamel into developing tooth bud may allow subsequent exposure of pulp tissue to the oral environment, resulting in pulpitis, and eventual necrosis. This can lead to tooth root abscessation.

Timecourse

• Many enamel problems will be identified in the young dog.

Diagnosis

Treatment

Prevention

Outcomes