Amelogenesis imperfecta (AI) is a congenital disorder which presents with a rare abnormal formation of the enamel or external layer of the crown of teeth, unrelated to any systemic or generalized conditions. Enamel is composed mostly of mineral, that is formed and regulated by the proteins in it. Amelogenesis imperfecta is due to the malfunction of the proteins in the enamel (ameloblastin, enamelin, tuftelin and amelogenin) as a result of abnormal enamel formation via amelogenesis.People with amelogenesis imperfecta may have teeth with abnormal color: yellow, brown or grey; this disorder can affect any number of teeth of both dentitions. Enamel hypoplasia manifests in a variety of ways depending on the type of AI an individual has (see below), with pitting and plane-form defects common. The teeth have a higher risk for dental cavities and are hypersensitive to temperature changes as well as rapid attrition, excessive calculus deposition, and gingival hyperplasia. The earliest known case of AI is in an extinct hominid species called Paranthropus robustus, with over a third of individuals displaying this condition. Genetics
Several gene expression is needed for enamel formation where the relevant matrix proteins & proteinases are transcribed for regular crystal growth & enamel mineralization.Mutations in the AMELX, ENAM, MMP20, KLK-4, FAM83H, WDR72, C4orf26, SLC24A4 LAMB3 and ITGB6 genes have been found to cause amelogenesis imperfecta (non-syndromic form). AMELX and ENAM encode extracellular matrix proteins of the developing tooth enamel and KLK-4 and MMP20 encode proteases that help degrade organic matter from the enamel matrix during the maturation stage of amelogenesis.
Enamel is very thin but hard & translucent, and may have random pits & grooves. Condition is of autosomal dominant, autosomal recessive, or x-linked pattern. Enamel differs in appearance from dentine radiographically as normal functional enamel. Type 2 - Hypomaturation
Enamel has sound thickness, with a pitted appearance. It is less hard compared to normal enamel, and are prone to rapid wear, although not as intense as Type 3 AI. Condition is of autosomal dominant, autosomal recessive, or x-linked pattern. Enamel appears to be comparable to dentine in its radiodensity on radiographs. Type 3 - Hypocalcified
Enamel defect due to malfunction of enamel calcification, therefore enamel is of normal thickness but is extremely brittle, with an opaque/chalky presentation. Teeth are prone to staining and rapid wear, exposing dentine. Condition is of autosomal dominant and autosomal recessive pattern. Enamel appears less radioopaque compared to dentine on radiographs. Type 4 - Hypomature hypoplastic enamel with taurodontism
Enamel has a variation in appearance, with mixed features from Type 1 and Type 2 AI. All Type 4 AI has taurodontism in common. Condition is of autosomal dominant pattern. Other common features may include an anterior open bite, taurodontism, sensitivity of teeth.Differential diagnosis would include dental fluorosis, molar-incisor hypomineralization, chronological disorders of tooth development. Treatment
Preventive and restorative dental care is very important as well as considerations for esthetic issues since the crown are yellow from exposure of dentin due to enamel loss.