enamel knot secondary enamel knot 2015-10-01T10:25:22Z BTO:0005793 BrendaTissueOBO Marion The primary enamel knot forms at the tip of the bud during the cap stage of tooth development. This primary enamel knot is removed by apoptosis. Later, secondary enamel knots appear that regulate the formation of the future cusps of the teeth.