Objective: The aim of the present experiment was to analyze the temporal and spacial dynamics of GBR in a human model. Materials and Methods: Nine healthy subjects (4 women,5 men,aged 18-35 years,median 24) with no lower third molars were selected. A mucoperiosteal flap was raised distal to the second lower molar. A standardized bed was drilled in the bone and a titanium test cylinder of 3 mm diameter and 4 mm height was sunk to a depth of 2 mm. The upper end of the cylinder was then covered by an ePTFE-membrane and the flap sutured. Three cylinders were surgically harvested after 4, 6, and 9 months (mo), respectively. They were processed for non-decalcified hard tissue histology. Histomorphometrical analysis of tissue components and interface associations was performed directly in the light microscope at a magnification of 250x using an optically superimposed eyepiece test grid. Results: All surgical sites healed well and no adverse reactions were recorded. The mean fraction of regenerated mineralized bone trabeculae within the newly formed tissue amounted to 10.7% at 4 mo, to 7.9% at 6 mo and to 7.1% at 9 mo. The surface fraction of the new bone covered by osteoblasts increased from 4 mo (18.3%) to 6 mo (34.1%) and 9 mo (32.5%). In contrast, osteoid not covered by osteoblasts decreased from 32.5% at 4 mo, to 18.2% at 6 mo, and 16.0% at 9 mo. No statistically significant differences were found (Kruskal-Wallis). Remodeling of the primary woven bone scaffold into lamellar bone was observed in the more basal areas of the cylinders. Conclusions: The results of this study indicate that after 9 mo the process of formation of bone trabeculae is still ongoing. Transformation of woven into lamellar bone takes place in the absence of functional loading.

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