During which stage does cap-to-bell cusp patterning begin?

• A. Cap-to-bell transition.
• B. Initiation stage.
• C. Root formation.
• D. Maturation stage.

Answer: (A)

Cusp patterning is set up during morphogenesis as the enamel organ shifts from a cap shape to a bell shape. In this transition, signaling centers inside the enamel organ, especially the primary enamel knot, direct where cusps will form and start to define the crown’s cusp pattern. This is why cusp patterning begins at the cap-to-bell transition: the crown is taking on its distinctive cuspal layout, and the pattern is established as the organ morphs into the bell stage. It isn’t during initiation, root formation, or maturation, which occur at different times relative to crown morphogenesis.