01/26/2011 Amelogenesis imperfect (AI)

Resident: J. Hencler
Date: 01/26/2011

Article title: Amelogenesis imperfect (AI)
Author: Crawford, Aldred, Bloch-Zupan
Journal: Orphant Journal of Rare Diseases 2007, 2:17
Type of Article: Review

Definition and Dx:
AI represents a grp of conditions, genomic in origin which, affect the structure and clinical appearance of the enamel and may be associated with morphologic or biochemical changes elsewhere in the body. AI is a developmental condition of the dental enamel characterized by hypoplasia and/or hypomineralization that shows autosomal dominant, autosomal recessive, sex linked, and sporadic inheritance patterns. Dx involves exclusion of extrinsic environmental factors, establishment of a likely inheritance pattern, and recognition of phenotype and correlation with the dates of tooth formation to exclude a chronological developmental disturbance. The prevalence in the USA has been reported to be 1:14000. AI is a genetic deisease that exists in isolation or is associated to other symptoms in syndromes. It is either related to a single gene defect or arises from a microdeletion or chromosomal defects.

Classification:
Many classifications of AI exist today. Some are based on the phenotype and others use the phenotype as the primary discriminant and the mode of inheritance as a secondary factor in dx. Recently, it has been proposed that the mode of inheritance should be the primary mode of classification, with the phenotype as the secondary discriminant.

Clinical Description:
The enamel may be hypoplastic, hypomineralized or both. The affected teeth may be discolored, sensitive or prone to disintegration either post eruption or pre-eruption (idiopatic resorption).

X-linked:
Affects male and females differently. Males express the trait fully having only a thin layer of enamel of normal color and translucency and/or yellow/brown discoloration. The phenotype may be both hypoplasia and hypomineralization. When hypoplasia is the predominant type, there may be marked sensitivity to thermal and osmotic stimuli. Females may only have vertical ridges and grooves as a result of X-chromosome inactivation.

Autosomal Dominant:
Affects one or more individuals in each generation. May be predominantly or exclusively hypoplastic, manifested by thin enamel and spacing b/t the teeth or rough, irregular pitted enamel. Some case will show hypoplasia and hypomineralization. The most severe forms of hypomineralization result in enamel that has a cheesy consistency and is easily lost.

Autosomal Recessive:
More often encountered in certain ethnic grps where intermarriage w/in the the family may be more common. This review cited Polynesian communities.

Sporadic Cases:
May represent examples of autosomal recessive or new mutations. A condition referred to as molar-incisor hypomineralization (MIH) has become prominent and affect 1 or more of the 1st perm molars. MIH is not currently classified as AI.

AI as a syndrome:
Classifications of AI have included a variant w/ taurodontism as an intrinsic feature- AI w/ taurodontism (AIT). Hertwigs root sheath is responsible for root morphology/anatomy and differentiation of the inner dental epithelial cells to ameloblasts producing enamel protiens, and is a derivative of the enamel organ. AI’s genetic basis may affect this process to cause taurodontism.

AI in syndromes:
There are strong similarieties b/t AIT and tricho-dento-osseous (TDO) syndrome which has the additions features of curly hair and skeletal changes including bone sclerosis. One molecular study has reported that AIT and TDO are genetically distinct, wheras a later paper suggested that TDO and AI hypoplastic-hypomaturation w/ taurodontism are allelic.

Differential Dx:
Questions to consider: does anyone in the family have anything like this? Are all the teeth affected in a similar manner? Is there a chronological distribution to the appearance seen? Is ther any past medical hx which may have caused sufficient metabolic disturbances to affect enamel formation? The most common differential dx is fluorosis, chronological enamel hypoplasia (may be cause by prolonged GI issues, celiac disease, and leukemia chemotherapy). MIH may also be considered.

Genetic Counseling:
The mode of inheritance and underlying genomic changes are very important in dx of AI. Any child w/ a likely dx AI should be referred to a geneticist for dx confirmation.

Treatment:
Tx during childhood has been described as a temporary phase followed by a transitory phase. In infancy, the primary dentition id protected w/ SSCs on molars and nusmile crowns on incisors. The start of the eruption of the permanent dentition at 6yo is a difficult period. Some forms of AI present w/ hypersensitive teeth or teeth that disintegrate easy and may be very difficult to restore. AI requires removal of defective enamel and depending on AI severity may require a range of tx including composites to full coverage crowns.

Assessment:
Good review of a very detailed topic. A patient w/ AI should be treated with a multidisciplinary approach due to complicated genetic basis and depending on severity of enamel defects and age of patient.