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Effects of different combinations of fused primary teeth on eruption of the permanent successors.

PURPOSE
The fusion of primary teeth may be associated with the absence of 1 of the 2 permanent successors. Moreover, even if both successors erupt, developmental disturbances such as microdontia or delayed tooth formation may occur. The purpose of this study was to elucidate the effects of different combinations of fused primary teeth on the eruption of permanent successors.


METHODS
One hundred ninety-seven children with 247 fused primary teeth were examined. Combinations of primary teeth involved in the fusion were identified, and the effects of these different combinations on the presence, morphology, and eruption of the permanent successors were determined.


RESULTS
Three types of fusion in the primary teeth were identified: (1) between the maxillary central and lateral incisors (UCI/LI); (2) between the mandibular central and lateral incisors (LCI/LI); and (3) between the mandibular lateral incisor and canine (LLI/C). The results revealed an absence of the successional lateral incisor in 65% of UCI/LI cases and 74% of LLI/C cases, whereas only 16% of LCI/LI cases resulted in a missing successor.


CONCLUSIONS
Fused primary teeth are highly correlated with the absence of permanent teeth, and the prevalence depends on the combination of fused primary teeth.