In cap stage, regulating factor for cusp shape formation is present in
Enamel Knot: The cells in the center of the enamel organ are densely packed to form enamel knot.
Enamel cord: It is the vertical extension of the enamel knot.
Enamel Septum: The enamel cord extends to meet the outer enamel epithelium and form enamel septum.
Enamel Navel: It is the small depression at the point of meeting of enamel cord and outer enamel epithelium.
Enamel niche is the apparent structure created by the plane of histological sections cutting through a curved dental lamina so that mesenchyme is surrounded by the dental epithelium. It appears as a double attachment of dental lamina to the overlying epithelium.

Recent studies shows that enamel knot acts as a signaling center expressing growth factors which play an important role in determining the shape of the tooth
Dental papilla
Dental follicle
Inner enamel epithelium
Enamel knot