Objectives: Extraction sockets have tendency to show involution which may render implant placement difficult or impossible. Using bone substitute as filler material reduces the risk. Three different materials were compared histometrically and biomechanically at implant placement with alveoli left empty.

Methods: 67 extraction sockets (8 patients) received, randomized, either bone substitutes: BO: Bio Oss, Geistlich Pharma, Wolhusen, Switserland; COR: Bio Coral, Interpore International, Irvine, California; FIS: Fisiograft, Ghimas, Casalecchio, Italy; or were left empty. A non resorbable membrane (Cytoplast, Oraltronics, Bremen, Germany) covered extraction sites harbouring a filling material and 15 empty sites. Other extraction sites (n=24) were left uncovered. After 6 months, a trephine biopsy (inner diameter 1.7mm) was taken. The insertion torque was measured during implant placement (Osseocare^®, Nobel Biocare, Gothenburg, Sweden). After 4 (symphyseal area) to 6 (other sites) months, abutment surgery was performed and rigidity assessed by means of Periotest^® (Medizintechnik Gulden, Bensheim, Germany) measurement.

Results: Histometrically, the residual augmentation material expressed as a percentage of the biopsy was BO 18.6, COR 12.2 and FIS 7.5. The percentage of bone present was about the same for FIS, COR and reference site (30%) but 15.8 for BO. The insertion torque used during the last third of implant placement, varied between 11,4 for COR to 15 and more for the other sites although not reaching significance. The Periotest^® measurements after 6 months integration showed good rigidity for all sites with low standard deviations.

Conclusion: The slow resorption of BO placed in contact to human bone has been described previously. Thus, with this material, it is advisable to wait longer than 6 months before implant placement. Faster resorption rates and higher invasion by new bone was observed for the other two materials. Good implant rigidity was observed for all sites at abutment stage.

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