Inherited condition that affects the enamel of the teeth, making them soft and thin. The teeth are easily damaged and appear discolored because the dentin is visible through the thin enamel.
The reported incidence (all types combined) varies widely between 0.1 and 4 in 1,000 live births.
Can be autosomal dominant, autosomal recessive, or X-linked. To date, more than 20 genes have been confirmed to be candidates in AI with the ones most commonly involved being AMELX (Amelogenin on chromosome Xp22.2), ENAM (Enamelin), AMBN (Ameloblastin), AMTN (Amelotin, all three on chromosome 4q13.3), MMP20 (Matrix Metalloproteinase 20 on chromosome 11q22.2), KLK4 (Kallikrein-related Peptidase 4 on chromosome 19q13.41), and FAM83H (Family with Sequence Similarity 83, Member H on chromosome 8q24.3), which accounts for more AI cases than any other single gene and is the first-known gene encoding an intracellular protein that is associated with AI. Isolated sporadic cases have also been described.
AI describes a heterogeneous disorder characterized by an inherited developmental defect of enamel that affects both the primary and the secondary dentition. In AI the enamel is abnormally thin and/or soft, pitted, with insufficient protection resulting in poor aesthetics secondary to teeth discoloration (yellowish to black) and premature teeth decay and loss, but also pain and social issues. Enamel is produced by ameloblasts, which are lost (primarily to apoptosis) upon tooth eruption. Therefore, enamel cannot be regenerated or repaired after eruption. Mature enamel is the hardest and highest mineralized tissue in the human body and consists almost exclusively of crystals of substituted calcium hydroxyapatite in a complex structure of interlaced prisms and interprismatic matrix. Numerous classifications for AI have been proposed. One commonly used classification is predominantly based on the phenotype:
Type I: Hypoplastic AI (enamel is mineralized and hard, appears translucent, but is of reduced thickness or completely absent and results in pitting and grooves)
Type II: Hypomaturation AI (enamel is of normal thickness, but incomplete removal of the interprismatic protein from the enamel matrix leads to brittle and soft enamel with a mottled appearance)
Type III: Hypocalcified AI (enamel is of normal thickness, but insufficient deposition of calcium ions into the developing enamel leads to structurally weak and soft enamel with a chalky or opaque appearance)
Type IV: Hypomaturation-hypoplastic AI with taurodontism (a combination of Type I and II with taurodontism, which describes an abnormally shaped molar with an enlarged body and pulp chamber and the floor of the pulp chamber and furcation of the root is moved apically (ie, deeper toward the bone), which results in a shorter root that is less embedded into the alveolus.
(Type II and III are sometimes summarized as hypomineralized AI where the enamel is of full thickness, but abnormally weak).