The AI enamel defects are highly variable and include abnormalities that are classified as hypoplastic (defect in amount of enamel), hypomaturation (defect in final growth and maturation of enamel crystallites), and hypocalcified (defect in initial crystallite formation followed by defective growth) [5]. The enamel in both the hypomaturation and hypocalcified AI types is not mineralized to the level of normal enamel and can be described as hypomineralized. AI can be inherited as an x-linked, autosomal recessive (AR), or autosomal dominant (AD) condition.

The diagnosis and classification of AI has traditionally been based on the clinical presentation or phenotype and the inheritance pattern [6]. Although multiple gene defects responsible for causing AI have been identified since 1990, most of the AI types do not have a known molecular basis. As the molecular defects causing AI are identified, the need for a molecular based nomenclature increases. The rapid identification of multiple mutations in multiple genes has lead to the acceptance of standardized nomenclatures for reporting AI associated mutations at the genomic, cDNA and protein level [7]. The most widely accepted classification system for delineating the AI types subdivides AI into four main types based on the enamel defects and then further divides them into14 distinct subtypes based on clinical appearance (phenotype) and mode of inheritance [6].