Drs. Akimoto, Becker, Persson, Baker, Roher, and O’Neal (Int J Oral Maxillofac Implants 1999;14:351-360) report an interesting dog study in an attempt to evaluate the efficacy of implanting extraction sites that are larger than the implant being placed. In dogs they created four osteotomy sites: a control with no visible space around the implant, and three experimental sites with gap sizes of 0.5mm, 1.0mm, and 1.4mm extending 6mm of the 10mm implants being placed. The tissues were closed without membranes or grafts. At twelve weeks (without function) all the sites appeared to have bony apposition to the implants.

Experimental Model	Implants at Surgury	Implants at 12 Weeks

These were experimental sites, without membranes or function. No statistical differences were found between any of the sites when the apical 4mm were compared. There was a decreasing histologic percentage of bone and height of bone as the gap size increased. In an implant in contact with a tooth, a fibrous tissue interface was noted. The results indicate that since visual bony apposition in not necessarily real, there is a need to closely evaluate implants not placed in intimate contact with bone, or contacting a tooth.

Fig. 7 One of the control implants. Bone is in direct contact with the implant up to the rim. Note good bone - to - implant contact for the entire length of the implant.	Fig. 8 Site III implant, which was placed in contact with the canine fibrous encapsulation, without any direct bone - to - implant contact. No cementum is seen on the implant surface.	Fig. 9 Site II implant. In the coronal portion, where the gap was created at the time of placement, connective tissue can be seen between the implant and bone. In the apical portion of the implant, good bone - to - implant contact is observed.