Sixteen patients with horizontal deficiencies in the posterior mandible were treated with "the Open Membrane Technique" (OMT). Dense PTFE membranes covering an allograft biomaterial were used without any attempt to passivate the flap. Flap closure with an open wound (membrane exposure) was monitored weekly for up to 6w at the time of membrane removal. At implant placement, soft and hard tissue gains were assessed clinically and radiographically. Bone cores were harvested for histological analysis from the implant preparation sites