What limits our ability to grow enamel rods?
Chandra's Textbook of Dental and Oral Histology and Embryology with MCQs p40-42 explains the complexity of enamel, and provides diagrams and images of real enamel.

What I didn't know before was that the hydroxyapatite is in the form of very small crystallites packed inside the key-like structure of the rods. The rods are packed together with a cement-like material. The rods themselves are segmented.

This small design and lack of vital parts suggest to me that bioglasses like Novamin would at least not recreate the natural enamel structure.

What isn't so easy to guess is whether crystallites from the components of the bioglass are formed on the existing crystallites, and if so, whether this can continue indefinitely, and with what qualities.