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 i t was possible by the use of EREt to predictably expand the compromise d alveolar ridge; (ii) if proper osseointegration also occurred at sit es 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 a nd the ridge in the edentulous regions markedly reduced. After 3 month s of healing, ridge expansion surgery was performed. A partial thickne ss flap was raised on the buccal and lingual surfaces for the soft tis sue preparation. The buccal part of the ridge was mobilised and the bo ne plate with its periosteum displaced in the buccal direction. In eac h quadrant, 2 fixture sites were prepared in the mandibular bone apica l of the displaced bone plate. 2 unthreaded titanium plasma sprayed fi xtures were installed in such a way that the coronal border of the fix ture was flush with the level of the lingual and buccal bone plate. Th e ''internal'' distance between the mobile buccal and the non-mobile l ingual 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 quadr ant, 1 additional fixture was installed in the non- reduced mesial par t of the alveolar ridge (control site). 3 months after fixture install ation, abutment connection was performed. Following abutment connectio n, a plaque control program was initiated and maintained for 4 months, at which time, the dogs were re-examined and biopsies obtained for hi stological examination. It was observed that bone regeneration and oss eointegration may occur to titanium fixtures placed in surgically-crea ted bone defects. The amount of bone that was in intimate contact with the fixture surface was similar in test and control sites. In additio n, the periimplant mucosa at test and control implants had similar dim ensions and composition in terms of junctional epithelium and connecti ve tissue.