Tooth Form: Normally the teeth are defined as involutes generated by either a pinion rolled along the pitch line or by a conjugate rack with flat sided teeth. Unlike round gears the resulting tooth forms can be quite different. An elliptical unilobe should not have obvious changes but a bilobe with a K greater than 2 generated with the pinion method will have undercut teeth on the ends and internal teeth on the sides. The same gear generated with the rack method usually won't have the end teeth undercut and will have external teeth on the sides. In addition to pitch and pressure angle we can specify the root filet radius and tip relief. Tip relief can reduce wear and noise under high tooth loads.
Gear Loads: The tooth load is the sum of the work load plus the dynamic load due to acceleration of inertias. Because of compliance etc. the dynamic load may be difficult calculated. Tooth failure can be from a variety of causes. Generaly the teeth should be run at a load where the Hertz stress is under the endurance limit