This document specifies the basic formulae for the calculation of the tooth root strength of spur and helical bevel gears, zerol, spiral bevel and hypoid gears with a minimum material thickness under the tooth root of 3,5 × m<(Index)mn> and includes all influences on the tooth root strength resulting from the load transmitted by the gear and which can be assessed quantitatively. The formulae in this document are based on virtual cylindricyl gears with a tranverse contact ratio <(Index)va> < 2. This document does not apply to tooth root stresses beyond those permitted 10<(hoch)3> for load cycles, as stresses in this range could exceed the tooth's elastic limit.