"齿顶圆角半径" can be translated as "addendum radius of curvature" or more commonly and precisely in mechanical engineering contexts as "radius at the tooth tip fillet" or simply "tooth tip fillet radius".
"Addendum radius of curvature" emphasizes the curvature aspect at the addendum (top part) of the tooth.
"Radius at the tooth tip fillet" or "tooth tip fillet radius" directly describes the radius of the rounded corner (fillet) at the top of the gear tooth, which is a more straightforward and commonly used expression in the field.
Among these, "tooth tip fillet radius" is perhaps the most intuitive and widely recognized term.