Amelogenesis imperfecta is a disorder of tooth development. This condition causes teeth to be unusually small, discolored, pitted or grooved, and prone to rapid wear and breakage. Other dental abnormalities are also possible. These defects, which vary among affected individuals, can affect both primary (baby) teeth and permanent (adult) teeth.

Researchers have described at least 14 forms of amelogenesis imperfecta. These types are distinguished by their specific dental abnormalities and by their pattern of inheritance. Additionally, amelogenesis imperfecta can occur alone without any other signs and symptoms or it can occur as part of a syndrome that affects multiple parts of the body.

In general, both the primary and permanent teeth are affected. The enamel tends to be soft and weak, and the teeth appear yellow and damage easily.

The defects associated with amelogeneis imperfecta are highly variable and include abnormalities classified as hypoplastic (defects in the amount of enamel), hypomaturation (defect in the final growth and development of the tooth enamel), and hypocalcification (defect in the initial stage of enamel formation followed by defective tooth growth). The enamel in the hypomaturation and hypocalcification types is not mineralized and is thus described as hypomineralized.

Traditionally, the diagnosis and classification of amelogenesis imperfecta is based on the clinical presentation and the mode of inheritance. There are four principal types based on the defects in the tooth enamel. These types are subdivided into 14 different subtypes based on the clinical presentation and the mode of inheritance.

Amelogenesis imperfecta is caused by mutations in the AMELX, ENAM, and MMP20 genes. These genes provide instructions for making proteins that are essential for normal tooth development. These proteins are involved in the formation of enamel, which is the hard, calcium-rich material that forms the protective outer layer of each tooth. Mutations in any of these genes alter the structure of these proteins or prevent the genes from making any protein at all. As a result, tooth enamel is abnormally thin or soft and may have a yellow or brown color. Teeth with defective enamel are weak and easily damaged.In some cases, the genetic cause of amelogenesis imperfecta can not been identified. Researchers are working to find mutations in other genes that are responsible for this disorder.

The different types of amelogenesis imperfecta can have different types of inheritance according to the gene that is altered:

The following types have autosomal dominant inheritance:

• IA
• IB
• IIIA
• IIIB
• IV

The types that are inherited in an autosomal recessive manner are:

• IC
• IF
• IG or enamel-renal syndrome type
• IH
• IJ
• IIA1
• IIA2
• IIA3
• IIA4
• IIA5
• IIA6

Type 1E is inherited in a dominant pattern linked to the X chromosome.

In autosomal dominant cases, one copy of the altered gene in each cell is sufficient to cause the disorder. Autosomal recessive inheritance means two copies of the gene in each cell have to be altered for the person to have the disease. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In most cases, males with X-linked amelogenesis imperfecta experience more severe dental abnormalities than females with this form of this condition.

A dentist can identify and diagnose amelogenesis imperfecta on the basis of the patient's family history and the signs and symptoms present in the affected individual.

Extraoral X-rays (X-rays taken outside the mouth) can reveal the presence of teeth that never erupted or that were absorbed. Intraoral X-rays (X-rays taken inside the mouth) show contrast between the enamel and dentin in cases in which mineralization is affected.

Genetic testing is available for the genes AMELX, ENAM, and MMP20.

Treatment depends on the type of amelogenesis imperfecta, the age of the affected person, and the type and severity of enamel abnormality. Treatments include preventative measures, various types of crowns, as well as tooth implants or dentures, orthodontic, peirodontal and restorative treatment. The social and emotional impact of this condition should also be addressed.