Background: The use of xenogenous bone blocks (XBB) as an alternative to autogenous bone blocks (ABB) has considerably increased in oral implantology. Nevertheless, there is little information on the histological findings of these grafts to date.
Aim: To compare histomorphometrically the graft remodeling process of ABB and XBB used for mandibular onlay grafting.
Material and Methods: Nine adult male New Zealand white rabbits (3.5-4Kg) were used in this split mouth randomized study. The control side of the mandible was subjected to onlay iliac crest grafting (ABB) and test side received xenogenous (XBB) bone graft (Heket Biomaterials, Vicenza, Italy), with 10 mm diameter x 3 mm height dimension. Both sides were covered with a collagen membrane (Heket Biomaterials, Vicenza, Italy). At 07, 20 and 60 days post-operatively, 03 animals were sacrificed in order to obtain bone biopsies. Paraffin sections were stained in Hematoxylin-Eosin and Masson´s Trichrome for histomorphometric assessment. The percentage of residual graft and new bone was evaluated through a counting point procedure in which a lattice of about 0.4 x  0.6 mm, with squares of 50 micrometers in dimensions, was superposed over the slides at a magnification of x200. ANOVA and the t test were performed for statistical analysis.
Results: New bone formation could not be observed at 07 days for both ABB and XBB groups. At 20 and 60 days, no statistical differences were found between intra-group (time) and inter-group (grafts) analyses.  Residual xenograft was significantly resorbed between 07 and 20 days. At 60 days, inter-group analysis showed more residual autograft in comparison to residual xenograft.
Conclusion: These data indicate that ABB and XBB showed similar amount of new bone formation over time. The percentage of residual iliac graft and xenograft tended to decrease for both groups, with more remaining bone at 60 days for ABB.  

This study was support by Sao Paulo Research Support Foundation (FAPESP).

Histomorphometric study on onlay xenograft remodeling. Preliminary results in rabbits.