he has you do ctrl r after you do the fill of the bottom, what does he mean by giving it a holding edge?
edit: this was for the tooth
The so-called holding edge is there to 'flatten out' the bottom of the tooth:
These holding edges are often necessary when using a Subdivision Surface Modifier.
JL goes into SubD in this short lesson:
https://cgcookie.mavenseed.com/lessons/subdivision-surfaces
