Gemination can be described as teeth ‘twinning’. In dental context, gemination refers to a developmental irregularity in which a single tooth germ divides resulting in a bifid crown on a single root, that is, two teeth develop together from a single tooth bud. The two parts of the double tooth will be exact images of each other. It is seen as a cleft crown on x-rays where the radiopaque enamel outlines the invagination."
Source : Denta Gamma
The cause(s) of gemination, which affects between 0.1% and 2.5% of the population, are unknown.
Contributing factors have been suggested to include vitamin deficiency, hormonal irregularities, infection or inflammation of areas near to the developing tooth bud, drug effects, genetic predisposition, and radiotherapy.