Fusion is the joining of two teeth by the pulp tissue and the dentin. The detin is the layer underneath the enamel. Enamel is the outer layer of tooth structure. This larger tooth may originate from two tooth germs. If two regular tooth germs fused, the number of teeth in the arch will be reduced by one.
Gemination is the budding of a second tooth from one tooth germ.
Accordingly, the number of teeth in the arch is normal if gemination occurs. If a deep groove is present, this tooth may be particularly susceptible to decay. Placement of a sealant would be prudent to prevent cavity formation. Distinguishing fusion and gemination can sometimes be difficult. A radiograph would be helpful in determining a diagnosis.