How tooth development (odontogenesis) creates different tooth shapes?

The shape of each tooth comes from how the enamel organ folds and where (and how many) enamel knots appear during the bell stage of tooth development. This whole process depends on signals shared between two cell types: epithelial and mesenchymal cells. The different tooth types—incisors, canines, and molars—get their unique shapes from the specific patterns of enamel knots and the size/arrangement of mesenchymal cells underneath.

Role of enamel knots

• Primary enamel knot: Shows up first in the cap stage. It sets the basic outline of the tooth. For single-cusped teeth, it marks the crown tip.
• Secondary enamel knots: Appear later, during the bell stage, in teeth with multiple cusps (like human molars). These act like “signaling hubs” that guide where the cusps grow.
• Patterning: The final look of the tooth depends on how these secondary knots are positioned. Example: in mice, knots line up straight, giving parallel cusps. In voles, they sit at angles, creating a zig-zag pattern.

Other factors that shape teeth

• Mesenchymal cells: Their size and number decide how big the tooth will be and how many cusps it can support.
• Signaling pathways: Key molecular signals like Hedgehog, Wnt, and BMP help control tooth shape by managing communication between epithelial and mesenchymal cells.
• Enamel organ folding: The crown’s shape comes from the way the inner enamel organ layer folds and grows during the bell stage.