Bone tissue formation adjacent to implants placed in fresh extraction sockets: an experimental study in dogs

OBJECTIVE: To study the healing of marginal defects that occurred at implants placed in a healed ridge or in fresh extraction sockets. MATERIAL AND METHODS: Six dogs were used. The right side of the mandible was used in the first part of the study. The first, second premolars and first molars were extracted. After 3 months of healing the bone was prepared for implant installation in these premolar and molar sites. The marginal 5 mm of each recipient site was widened with a conical drill. Following implant installation a gap of varying dimension occurred around the titanium rod (artificial defect (A) sites). At this interval the third and fourth premolars were extracted and implants were installed in the distal socket of the two teeth (natural defect (N) sites). The flaps were sutured to allow non-submerged healing. After 2 months, the procedures were repeated in the left side. Two months later the animals were euthanized, and biopsies were obtained and prepared for histological examination. RESULTS: The length of the zone of de novo'bone-to-implant contact' in the defect region was longer at the A sites than at the N sites both at the 2- and the 4-month interval. Further, while after 4 months of healing the marginal bone crest at the A sites was located close to the abutment/fixture junction, at the N sites a marked reduction of the height of the bone crest was documented. Hence, most A site defects became completely resolved whereas healing of the N site defects was incomplete. CONCLUSION: The process of bone modeling and remodeling at an implant placed in a fresh extraction socket differs from the resolution of marginal defects that may occur following implant installation in a healed ridge.