Bone tissue reaction around implants placed in a compromised jaw

The present experiment was carried out to examine bone tissue alterations t hat occurred around implants at which the marginal level of bone support at fixture installation was different at buccal and lingual surfaces. 8 beagl e dogs were randomly divided into one test group and one control group. The mandibular premolars in the left side of the mandible (P1, P2, P3, P4) wer e extracted. In the 4 dogs of the test group, the buccal bone plate in the mandibular premolar region was removed to establish a bone defect that was about 25 mm long, about 5-6 mm high, and about 4 mm wide. In the 4 dogs of the control group, no bone resection was performed. 8 months after tooth ex traction, 3 fixtures (Astra Tech AB, Molndal, Sweden;TiO-blast; 8x3.5 mm) w ere installed in each dog. In the 4 dogs of the test group, the implants we re positioned in the defect sites in such a way that (i) mechanical stabili ty was achieved and (ii) their lingual surfaces were entirely invested in b one. At the buccal and approximal surfaces of the fixtures, however, the un threaded portion (2 mm) and the 3 marginal threads remained exposed. In the control group, all implants were following installation entirely surrounde d by bone tissue. After a healing period of 3 months, abutment connection w as performed and a plaque control program initiated. 4 months later, the do gs were sacrificed. The mandibles were removed and placed in a fixative. Ea ch implant region was dissected, the tissue samples were dehydrated, embedd ed, sectioned in a bucco-lingual plane and used for light microscopic exami nation. The findings demonstrated that osseointegration occurred at implant s, placed in a chronic defect with large discrepancies between the buccal a nd lingual bone. During the process of healing and function, however, marke d modeling and remodeling of the bone tissue took place. Thus, at the bucca l surface, some bone regrowth and osseointegration occurred while at the li ngual wall, there was a substantial resorption of the marginal bone and an enhanced number of bone multicellular units. Concomitant with the bone tiss ue alterations described, there was some recession of the peri-implant muco sa.