size (and shape). Teeth which are obviously larger than normal are referred to as
megadont or macrodont whereas teeth which are smaller than normal are termed
microdont. Crown size is often related to root size, so teeth with large crowns often
have large (broad) roots, teeth with small crowns tend to have small (slender) roots.
Microdontia can be associated with hypodontia as in the example of X-linked
hypohidrotic ectodermal dysplasia, where a heterozygous female might have one
missing lateral incisor and a peg-shaped crown of the contralateral maxillary lateral
incisor (794HFig. 13.7).
Megadont teeth
Megadont maxillary incisors can occurs as a result of fusion of adjacent tooth germs
or as a result of an attempt at separation of a single tooth germ to form two separate
teeth. It is important in these circumstances to count the number of teeth to determine
which of these possibilities has occurred, as this will influence treatment planning.
The permanent maxillary central incisors are most often affected (795HFig. 13.8) followed
by the mandibular second premolars. Isolated megadontia has been estimated to occur
in approximately 1% of patients in the permanent dentition. The condition may be
symmetrical. Generalized megadontia has been reported in association with pituitary
gigantism, in unilateral facial hyperplasia and in hereditary gingival fibromatosis.
Microdontia
Microdont primary teeth are uncommon, with a reported prevalence of 0.2-0.5%. In
the permanent dentition the prevalence is approximately 2.5% for individual teeth,
with generalized microdontia occurring in approximately 0.2% of individuals.
Females are more often affected than males, with the maxillary lateral incisor being
most commonly affected, having a peg-shaped or conical crown. (796HFig. 13.9). As noted
in the previous section (13.2), there is an association between microdontia and
hypodontia.
797H
Fig. 13.7 Hypodontia concurrent with
microdontia.