Gemination occurs during tooth development when a single tooth germ invaginates, resulting in an incomplete formation of two teeth that appear joined on a single root. It most commonly affects deciduous mandibular incisors and permanent maxillary incisors. Radiographs show a cleft in the crown and enlarged or partially divided pulp chamber within a single root. Treatment involves restoring and reshaping the crown, periodic filing to reduce the width, and eventually preparing a final crown.