Objectives: The aim of the present experiment was to test if a jaw region exhibiting type IV bone can successfully be established as a model situation to study GBR. Methods: The maxillary third incisors were extracted bilaterally in five adult beagle dogs. Buccal bone was surgically removed in order to achieve a defect with loss of the buccal plate. Ten implants (Paragon Implant Company, USA) (diameter 3.75 mm, length 10 mm) made of grade IV commercially pure titanium with a machined and acid etched surface were placed. Two treatment modalities were randomly allocated to the two sites in each dog: titanium grid alone (Howmedica Leibinger, Germany) ("Ti"); and Guidor Matrix Barrier® (Guidor, Sweden) supported by a titanium grid ("Ti+GD"). Primary wound closure was obtained. Four months later, the animals were sacrificed. Results: Histomorphometric analysis of non-decalcified sections revealed the volume of newly formed bone within the area of regeneration to be around 50% in both groups (Ti+GD 46.1%, Ti 52.1%). Values for vertical bone growth reached 62.3% for the Ti+GD group and 70.7% for the Ti group without a significant difference (Wilcoxon signed rank test). The height of bone in direct implant contact related to the defect depth showed no significant difference with mean values of 27.8% for the Ti+GD group and 10.7% for the Ti group. Whereas area densities of the regenerated bone in the magnitude of 50 to 70% were formed, the area densities within the preexisting bone were only between 35 and 60% (regenerated vs. preexisting bone: a < 0.05). The amount of bone to implant contact within the preexisting bone was significantly higher (Ti+GD 70.2%, Ti 41.8%) compared to the regenerated area (Ti+GD 30.3%, Ti 7.5%). Conclusion: Successful bone regeneration by GBR occurred around implants placed into type IV bone immediately following tooth extraction.

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