so that a band of abnormal enamel is seen in horizontal distribution at some part on
the tooth crown. Typically this results in a groove in the enamel of affected teeth. The
term chronological hypoplasia is often used to describe such cases (837HFig. 13.31). A
knowledge of the timing of commencement of formation of the teeth will aid in
understanding the timing of such an insult.
Systemic (chronological) enamel defects
Enamel formation in utero may be affected by a wide range of maternal and foetal
conditions. These will include endocrine disturbances (hypoparathyroidism),
infections (rubella), drugs (thalidomide), nutritional deficiencies, and haematological
and metabolic disorders (Rhesus incompatibility). In such cases, the enamel covering
the incisal portions of the crowns of the primary incisors will typically be affected in
the pattern shown in 838HFig. 13.32 (a) and (b). Similar changes may be seen in pre-term,
low birth weight, infants. It is not yet clear whether this is associated with the use of
intubation for these children in the neonatal period although the latter has been
identified as a local cause affecting forming incisors only.
When there is a systemic upset or marked physiological changes occur at birth or in
the neonatal period, corresponding enamel defects may be seen in the primary
dentition. Illness in the neonatal period may also affect the tips of the first permanent
molars as these commence development at around birth.
Enamel defects may also arise as a result of acute or chronic childhood illnesses (839HFig.
13.33). This will include hypothyroidism and hypoparathyroidism, chronic renal
disease, and gastrointestinal disorders producing malabsorption, such as coeliac
disease. The use of tetracycline during pregnancy and childhood is to be avoided
because of deposition of the tetracycline in developing dental matrices, producing a
distinctive blue/grey discolouration of the teeth, sometimes in a chronologically
banded distribution (840HFig. 13.34).
In the past, exanthematous fevers caused by measles and other infections were
associated with a disturbance of normal enamel formation and a corresponding
chronological hypoplasia affecting the crowns of developing teeth. Modern medical
care has now made this uncommon, unless such changes may occur in the case of
babies and infants who develop pneumonia.
Enamel formation is also sensitive to chemical agents, such as fluoride. Excessive
intake of fluoride, either from naturally occurring sources such as drinking water with
fluoride levels over 1-2 ppm, or from over use of fluoride supplements or fluoride
toothpastes, can cause enamel mottling. In its mildest form fluorosis appears as an
opacity of the enamel. The condition is dose-dependant, with increasing intake of
fluoride being associated with more marked opacity, areas of discolouration of the
enamel as well as pitting, and more extensive hypoplastic defects (841HFig. 13.35 (a)).
Confusion between fluorosis and amelogenesis imperfecta can occur. One
distinguishing feature may be that amelogenesis imperfecta does not show a
chronological distribution and that fluorosis, depending on the timing of the excessive
intake, does. Local, fluorotic lesions may respond very well to the microabrasion
technique (842HFig. 13.35 (b)).