composite.13.5 ABNORMALITY OF TOOTH FORM
13.5.1 Abnormality of crown form
Fusion and gemination
Some cases of megadont crowns are as a result of fusion of adjacent tooth germs
(fusion), or attempts at developmental separation of a single tooth germ to produce
two separate teeth (gemination) and a variety of terms have been used for such
situations. The term 'double teeth' has been applied to cover both situations. It is
important to count the number of teeth present clinically and, with the aid of
radiographs to determine whether fusion or gemination is more likely to have
occurred. The prevalence of such abnormalities ranges from 0.5% to 1.6% of
Caucasian populations studied in the primary dentition. The permanent dentition is
less commonly affected (prevalence 0.1-0.2%). Males and females are affected
equally. A genetic basis has been suggested but not confirmed.
The clinical manifestation may vary from a minor notch on the incisal edge of an
abnormally wide incisor crown to two separate crowns with a single root. The crowns
and root may be in continuity along their entire length or may be almost separate;
some pulp intercommunication is often present. The most typical areas affected are
the anterior segments of the arches in the primary dentition, with the mandible more
commonly affected than the maxilla (807HFig. 13.13 (a) and (b)). There may be an
association with hypodontia, so that a larger than normal tooth of the primary series
together with a missing tooth in that series may represent an intermediate stage
between the presence or absence of a tooth.
Physiological root resorption of primary fused or geminated teeth may be delayed and
this may lead to delayed eruption of the permanent successors.
Treatment
When this condition affects the primary dentition no treatment per se is required. It is
important, however, to consider the possibility of abnormalities of the number and/or
form of the permanent dentition in the area. One problem which can occur is that
caries can develop at the interface between the two crown segments (808HFig. 13.14). This
can be prevented by an etch-retained restoration to fill in the defect, which will also
improve the cosmetic appearance. In the permanent dentition, the final decision on
whether to retain, extract, surgically divide or otherwise treat such teeth will depend