Fig. 2.

Schematic of tooth development process. a The continual lamina is present in diphyodonts and monophyodonts. The rudimental successional dental lamina cannot develop into a tooth under normal conditions, whereas the successional lamina forms the second dentition in diphyodonts. The dotted arrow indicates that a few parts of the tooth developmental process are omitted. B: buccal; L: lingual; M: mesial; D: distal; M1: first molar; M2: second molar; M3: third molar. b Different tooth types are classified according to the clinical crown-to-root ratio and the self-renewal ability after eruption. c Cell behaviour during early tooth development. Yellow cells form the suprabasal cells (light yellow) via asymmetric division; orange cells undergo vertical expansion. Grey–blue mesenchymal cells condense around the epithelium. d Top view of the migration of Fgf8⁺ epithelium in the lower jaw