Question

What does this line mean " teeth are ectomesodermal".

Answer 1

Ectoderm is one of the three primary germ layers in the very early embryo. The other two layers are the mesoderm (middle layer) and endoderm (most proximal layer), with the ectoderm as the most exterior (or distal) layer. It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma, meaning "skin."
The teeth develop from ectoderm and mesoderm: the enamel develops from ectoderm of the oral cavity, and all other tissues come from the associated mesenchyme. This is the reason teeth are ectomesodermal.