An original hybrid gear model is introduced, which combines lumped parameter and finite elements along with a specific interface aimed at coupling mismatched discrete models. A mortar-based interface is presented, which eliminates the numerical errors induced by direct collocations between the tooth contact and gear body models. It is shown that the proposed interface can capture the instant contact conditions in the profile and lead directions for both spur and helical gears. A number of quasi-static and dynamic simulation results are presented, which illustrate the potential and practical interest of the methodology. It is observed that thin rims are more influential in the case of helical gears and that the overall dynamic tooth loads seem largely uncoupled from the local contact conditions on the teeth.