Healing at implants with and without primary bone contact. An experimental study in dogs.

The aim of the present investigation in the dog was to study: (i) if it was possible by the use of EREt to predictably expand the compromised alveolar ridge; (ii) if proper osseointegration also occurred at sites where the implant following installation was devoid of direct bone contact. 5 beagle dogs, about 1-year old, were included in the study. During a preparatory period, the mandibular premolars were extracted and the ridge in the edentulous regions markedly reduced. After 3 months of healing, ridge expansion surgery was performed. A partial thickness flap was raised on the buccal and lingual surfaces for the soft tissue preparation. The buccal part of the ridge was mobilised and the bone plate with its periosteum displaced in the buccal direction. In each quadrant, 2 fixture sites were prepared in the mandibular bone apical of the displaced bone plate. 2 unthreaded titanium plasma sprayed fixtures were installed in such a way that the coronal border of the fixture was flush with the level of the lingual and buccal bone plate. The "internal" distance between the mobile buccal and the non-mobile lingual bone plates was identical to the diameter of the fixtures, i.e., 3.3 mm, while the distance between the mesial and distal borders of the 2 implants and the mesial or distal bone was > 5 mm. In each quadrant, 1 additional fixture was installed in the non- reduced mesial part of the alveolar ridge (control site). 3 months after fixture installation, abutment connection was performed. Following abutment connection, a plaque control program was initiated and maintained for 4 months, at which time, the dogs were re-examined and biopsies obtained for histological examination. It was observed that bone regeneration and osseointegration may occur to titanium fixtures placed in surgically-created bone defects. The amount of bone that was in intimate contact with the fixture surface was similar in test and control sites. In addition, the periimplant mucosa at test and control implants had similar dimensions and composition in terms of junctional epithelium and connective tissue.