Amelogenesis imperfecta

Overview

Amelogenesis imperfecta (AI) (amelogenesis - enamel formation; imperfecta - imperfect)is a group of rare, inherited disorders characterized by abnormal enamel formation. This term is restricted to those disorders of enamel development not associated with other defects of the body.

It (AI) is a disorder that affects the structure and appearance of the enamel of the teeth. This condition causes teeth to be unusually small, discolored, pitted or grooved, and prone to rapid wear and breakage. These dental problems, which vary among affected individuals, can affect both primary (baby) teeth and permanent teeth.

In this disorder, the layer of enamel is thin so that the teeth appear to be discolored, showing the color of the materials under the enamel. The teeth usually appear brown or some variant of that color.

In Clinical findings, it is usually classify AI into four main types and it is further 14 sub types are recognized, which are distinguished by their specific dental abnormalities and by their pattern of inheritance. The main types are based on enamel effects and the sub types are based on clinical appearance and mode of inheritance.

The main types are:

  • Hypoplastic (Type 1)
  • Hypomaturation (Type II)
  • Hypocalcified (Type III)
  • Hypomaturation/hypoplasia/taurodontism (Type IV)

Amelogenesis imperfecta may be inherited as an X-linked, autosomal dominant, or autosomal recessive genetic trait, depending on the type.

Symptoms

Amelogenesis imperfecta is characterized by defective or missing tooth enamel. Secondary effects of this disorder may be early tooth loss, heightened susceptibility to disease of the tissues surrounding the teeth (periodontal) such as gums, cement, ligaments, and the bone in which the tooth root rests (alveolar). Sensitivity of the teeth to hot and cold is usually increased. The dental pulp (pulpa) in the root canal is exposed in some cases, and a so-called "open bite" may occur because the upper and lower jaws do not align properly. Another complication of AI is that the unsightly teeth may cause psychological problems. With orthodontic and periodontal restoration, however, the teeth will look normal and can remain functional throughout life.

The main types of AI may be distinguished by clinical appearance, enamel thickness, appearance on x-ray negatives, and mode of inheritance.

Type I hypomaturation AI is characterized by small to normal tops (crowns) of the teeth, upper and lower teeth that do not meet showing a poor bite, and teeth that vary in color from off-white to yellow-brown. The enamel thickness varies from thin and smooth to normal, ridged or pitted.

Type II hypomaturation AI is commonly associated with an open bite and creamy to yellow-brown roughly surfaced teeth that may be tender and sore. The enamel is gernally normal in thickness but is unusually brittle. Similar to Type I hypomaturation, Type II hypomaturation AI may also be inherited as any of the autosomal dominant, autosomal recessive, or X-linked traits.

Type III hypocalcified AI is seen in patients with an open bite and creamy to yellow-brown rough enamel-surfaced teeth that may be tender and sore. These teeth usually carry substantial precipitates of stony material from the fluids of the mouth (calculi).

Type IV hypomaturation/hypoplasia/taurodontism AI usually is characterized by smaller than normal teeth, the color of which may range from white to yellow-brown, and teeth that appear to be mottled or spotted. The enamel is thinner than normal with areas that are clearly less dense (hypomineralized) and pitted. Genetically these characteristics are transmitted as autosomal dominant traits.

Causes

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.

The classification of amelogenesis imperfecta is complex, so too is the contribution of genetics to this disorder. The malfunctioning (mutations) of several genes have been identified and the sites of these genes on various chromosomes have been determined. Exactly how these genes work singly or in concert with one another remains a mystery.

  • Genes responsible for hypoplastic AI (Type I) have been tracked to gene map loci Xp22, 3-p22.1, 4q31, and Xq22-q28.
  • Genes responsible for hypomaturation AI (Type II) are tentatively assigned to the X chromosome and to locations on chromosome 19 and chromosome 11.
  • Genes responsible for hypocalcified AI (Type III) have been tracked to gene map locations 4q21, 4q21, and the X chromosome.
  • Gene responsible for hypomaturation/hypoplasia/taurodontism AI (Type IV) has been traced to a gene map locus 17q21,3-q22.

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.

Diagnosis

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 o 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. You can visit the Genetic Testing Registry to locate laboratories performing genetic testing for these genes.

Treatment

Treatment depends on the type of amelogenesis imperfecta and the type of enamel abnormality. Treatments include preventative measures, various types of crowns, as well as tooth implants or dentures in the most severe cases. Desensitizing toothpaste can prevent painful sensitivity to heat and cold. Good oral hygiene is important. Genetic counseling is recommending for families of children with amelogenesis imperfecta. The social and emotional impact of this condition should also be addressed.

Resources

  • NIH
  • Genetics Home Reference