Amelogenesis imperfecta is a genetically diverse condition affecting dental enamel, with its patterns of inheritance classified as autosomal dominant, recessive, or X-linked. The disorder is caused by defects in genes that encode enamel matrix proteins, resulting in various forms including hypoplastic, hypomineralised, and hypomaturated enamel. Specific genetic mutations, particularly in the amel x gene, contribute to the severity of the condition, impacting the quality and appearance of the enamel across all teeth.

1. AMELOGENESIS IMPERFECTA
Makerere University
BDS 3

2. Amelogenesis imperfecta
 Is a term for a clinically and genetically heterogeneous group of conditions that affect the dental
enamel, occasionally in conjunction with other dental, oral and extraoral tissues
 Is a group of conditions caused by defects in the genes encoding enamel matrix proteins.
 Classification is complex and based on pattern of inheritance, enamel hypoplasia,
hypomineralisation or hypomaturation and appearance; smooth, rough or pitted. At least 16 forms
are recognized.
 Inheritance can be autosomal dominant, recessive or X-linked.
 However, the most common types have an autosomal inheritance and are thought to be caused by
mutations in the AMEL X gene, which codes for ameloblastin (C4), enamelin (C4) or tuftelin (Cl).
 In the case of the autosomal dominant type of amelogenesis imperfecta, the locus of the defective
gene is on chromosome 4q21 to which enamelin maps.

3.  The less common X-linked types are caused by a variety of defects in the amelogenin genes and,
confusingly
 It seems the same mutation can sometimes cause hypoplastic, hypomineralisation or
hypomaturation forms in different patients
 Genetic factors act throughout the whole duration of amelogenesis
 Characteristically therefore, all teeth are affected and defects involve the whole, or are randomly
distributed in the enamel.
 By contrast, exogenous factors affecting enamel formation (with the important exception of
fluorosis) tend to act for a relatively brief period and produce defects related to that period of
enamel formation.

4.  Dental enamel formation is divided into secretory, transition, and
maturation stages.
 During the secretory stage, enamel crystals grow primarily in length.
During the maturation stage, mineral is deposited exclusively on the
sides of the crystallites, which grow in width and thickness to coalesce
with adjacent crystals.
 The main structural proteins in forming enamel are amelogenin,
ameloblastin, and enamelin.
 During the secretory stage, enamel proteins are being secreted along
with proteases. This is a major factor in determining the composition of
the enamel matrix. Changes in this mechanism by genetic defects of
proteins or proteinases can result in the pathological changes during the
enamel formation.

6. Hypoplastic amelogenesis
imperfecta
 The main defect is in formation of the matrix.
 The enamel is randomly pitted, grooved or very thin, but hard and
translucent
 The defects tend to become stained, but the teeth are not especially
susceptible to caries unless the enamel is scanty and easily damaged.
 The main patterns of inheritance are autosomal dominant and recessive, X-
linked, and (a genetic rarity) an X-linked dominant type.
 In the last stage there is almost complete failure of enamel formation in
affected males, while in females the enamel is ridged

7. Amelogenesis imperfecta X-linked
hypoplastic form in a male. This
premolar has a cap of enamel so thin
that the shape of the tooth is virtually
that of the dentine core
.
Close-up of X-linked hypoplastic type
amelogenesis imperfecta. These teeth
from an affected female show the
typical vertical ridged pattern of normal
and abnormal enamel

8. Hypomaturation amelogenesis
imperfecta
 The enamel is normal in form on eruption but opaque, white to brownish-
yellow.
 The teeth appear similar to mottled fluoride effects.
 However, they are soft and vulnerable to attrition, though not as severely as
the hypocalcified type.
 There are several variants of hypomaturation defects such as a more severe,
autosomal dominant (type 4) of hypomaturation combined with hypoplasia.

9. Amelogenesis imperfecta,
hypomaturation types
In this form there are opaque white
flecks and patches affecting the occlusal
half of the tooth surface.
Tooth morphology is normal but there are
opaque white and discoloured
patches.

10. Hypocalcified amelogenesis
imperfecta
 Enamel matrix is formed in normal quantity but poorly
calcified.
 When newly erupted, the enamel is normal in thickness and
form, but weak and opaque or chalky in appearance.
 The teeth tend to become stained and relatively rapidly worn
away.
 The upper incisors may acquire a shouldered form due to the
chipping away of the thin, soft enamel of the incisal edge
 There are dominant and recessive patterns of inheritance

11. Amelogenesis
imperfecta,
hypocalcified type
The soft chalky enamel
was virtually of normal
thickness and form but
has chipped away during
mastication.