Introduction

Amelogenesis imperfecta (AI) has been defined as a complex group of hereditary enamel defects not associated with evidence of systemic disease^1,2 affecting both primary and permanent dentitions.¹ It is a rare enamel mineralization defect described by Spokes³ in 1890 as “hereditary brown teeth” with a reported incidence of 1:14,000.⁴

Phenotypically AI is categorized into four broad groups: hypoplastic, hypomaturation, hypocalcified, and a hypomaturation-hypoplastic variety. Fifteen subtypes of AI exist phenotypically and based on modes of inheritance. This classification has been proposed by Witkop⁵ (Table 1).

Table 1. Classification of AI according to Witkop⁵ (1989).

Type I	Hypoplastic
IA	Hypoplastic, pitted autosomal dominant
IB	Hypoplastic, local autosomal dominant
IC	Hypoplastic, local autosomal recessive
ID	Hypoplastic, smooth autosomal dominant
IE	Hypoplastic, smooth X-linked dominant
IF	Hypoplastic, rough autosomal dominant
IG	Enamel agenesis, autosomal recessive
Type  II	Hypomaturation
IIA	Hypomaturation, pigmented autosomal recessive
IIB	Hypomaturation, X-linked recessive
IIC	Snow-capped teeth, autosomal dominant?
Type  III	Hypocalcified
IIIA	Autosomal dominant
IIIB	Autosomal recessive
Type IV	Hypomaturation-hypoplastic with Taurodontism
IVA	Hypomaturation-hypoplastic with taurodontism, autosomal dominant
IVB	Hypoplastic-hypomaturation with taurodontism, autosomal dominant

The types are characterized as follows:

• Type-I: Lesions may appear as pin-point to pinhead sized pits scattered across the surfaces of teeth. The distribution of lesions may be generalized or localized, and the alteration of the enamel is a result of inadequate deposition of enamel matrix.
• Type-II: Also known as the hypomaturation type is associated with abnormalities in the maturation stages of enamel formation resulting in the enamel being opaque and chalky in appearance. The enamel layer is normal in thickness but softer than normal and can be easily detached from the underlying dentin.
• Type-III: The teeth have enamel that is insufficiently mineralized and clinically appears as severely worn teeth. It results from detachment of the enamel from dentin within a short period after tooth eruption. Teeth are very sensitive to thermal changes and appear dark brown in color.
• Type-IV: AI exhibits enamel hypoplasia in combination with hypomaturation. This variety is associated with taurodontism. The most common form of AI is the autosomal dominant hypocalcified type, followed by hypomaturation, and the hypoplastic type.⁶

Other associated findings in patients with AI include delayed eruption of teeth, taurodontism, congenitally missing teeth, crown and root resorption, and pulp calcification.⁷ Radiographically the density of enamel layer is lower than normal enamel. Hypoplastic enamel shows great variation in density and it may be difficult to distinguish it radiographically from underlying dentin.

AI is caused by mutations in a variety of genes that are critical for normal enamel formation. A total of about five genes [AMELX, ENAM, KLK4, MMP20, and DLX3]^8,9 are known to be involved in enamel formation. Mutations of the amelogenin gene (AMELX) cause X-linked AI, while mutations of the enamelin (ENAM) gene causes autosomal inherited forms of AI. Other genes like Kallikrein – 4 (KLK4), MMP–20, and DLX3 genes contribute to the etiologies of some other varieties of AI which is still under investigation.

Various treatment methods or strategies were initially instituted for AI patients such as the extraction of the compromised teeth and placement of a removable prosthesis or implant supported fixed or removable prosthesis.¹⁰ However, these procedures are very invasive and have greater incidence of complications. Numerous treatment modalities have been described for rehabilitation of patients with AI.^10-17 Rehabilitation of patients with AI requires meticulous oral hygiene maintenance and patient cooperation.

This rare dental abnormality poses a major restorative challenge for the dentist. Using conservative techniques desirable esthetics can be achieved, the teeth and supporting structures preserved, and a harmonious relationship created between the occlusion and temporomandibular articulation.