An alternative position for holding the facemask when bag-mask ventilating edentulous patients is described and evaluated. 49 patients with inadequate seal and air leak during two-hand positive-pressure ventilation had significantly improved ventilation as measured by reduced air leak and increased expiratory volume when the caudal end of the mask was repositioned above the lower lip while maintaining neck extension.

Face mask ventilation in edentulous patients: a comparison of mandibular groove and lower lip placement
Anesthesiology. 2010 May;112(5):1190-3