I found a very comprehensive gear info resource:
The pitch angle for a bevel gear is the angle between the pitch cone and a line normal to the shaft axis (or a radial line coming from the shaft). A bevel gear with pitch angle of 90 degrees is a normal spur gear.
The root angle is similar to the pitch angle, only it's the angle between the root of the tooth profile and a radial line from the shaft.
The root angle will be slightly higher than the pitch angle. The pitch angle for a miter gear is 45 deg, so the root angle will be slightly higher than 45 or 51 deg 33'.