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Objective: The objective of this study was to estimate the area fraction of different ratios of Bio-Oss((R)) and bone, prior to grafting in an in vitro model to demonstrate a histomorphometric baseline.

Methods: Bio-Oss((R)) particles were mixed with autogenous bone from pig jaw in three different ratios (50:50, 80:20 and 100:0) and packed in rice paper in a standardized procedure. Histomorphometric analyses were performed in 25 specimens and 74 regions of interest. The area percentage of Bio-Oss((R)), bone, and non-mineralized tissue (NMT) were calculated. Results were reported as mean values and 95% confidence interval (CI).

Results: The mean area fraction of Bio-Oss((R)) was 20.6% (CI: 18.2-23) in the 50:50 mixture, 33.6% (CI: 29.7-37.6) in the 80:20 mixture, and 43.4% (CI: 40.5-46.3) in the 100:0 mixture. The mean area fraction of NMT was 60.5% (CI: 57.9-63.1) in the 50:50 mixture, 59.6% (CI: 56.4-62.7) in the 80:20 mixture, and 56.6% (CI: 53.7-59.5) in the 100:0 mixture. The mean area fraction of bone was 18.9% (CI: 16.9-20.9) in the 50:50 mixture and 6.8% (CI: 5-8.6) in the 80:20 mixture.

Conclusion: There is a great difference in the clinically estimated percentage and the histomorphometrically evaluated percentage of Bio-Oss((R)) at baseline, prior to grafting. The area fraction of different tissues presented in this study may be beneficial as guidance for histomorphometrical baseline calculations when different mixtures of Bio-Oss((R)) and autogenous bone are used as grafting materials.