Perhaps we are talking different things here, with "tooth-angle" I mean the cut-angle of the gear itself, the angle used create to a smother load-distribution when in motion? That angle certainly generates an axial force as I tried to xplain.
As for the life-xpectancy of roller bearings, this is best evaluated by the ISO 281:1990, or its different developments;
http://www.skf.com/portal/skf/home/prod ... ink=1_0_20
The equivalent load on the bearing, as a function of axial and radial load, is xplained here;
http://www.skf.com/portal/skf/home/prod ... ink=1_0_25