Guided bone regeneration in calvarial critical size bony defect using a double-layer resorbable collagen membrane covering a xenograft: a histological and histomorphometric study in rats.

PURPOSE: The aim of the present study was to evaluate histologically and histomorphometrically the bone regeneration in critical size calvarial defects in rats grafted with either a deproteinized bovine bone mineral (DBBM) alone or in combination with a single or double layer of native bilayer collagen membrane (NBCM). The secondary objective was to evaluate histologically and histomorphometrically the residual DBBM in these defects. MATERIAL AND METHODS: Thirty-two Wistar rats were divided into two groups: a control group of 16 rats with two critical size calvarial defects (CSD) of 5 mm performed each on either side of the median sagittal suture, where the frontal defect remained without any filling (negative control), while the occipital defect (positive control) was filled with DBBM; and then a test group of 16 rats, with two CSD filled with DBBM and covered by either a single (SM) or a double layer (DM) of NBCM. The animals were sacrificed at 4 and 8 weeks. RESULTS: At 1 month, the histological and histomorphometric analysis showed new bone formation (NBF) in the defects that received only DBBM, DBBM+DM, and DBBM+SM (11.5, 17.3, and 22.7%, respectively), while the negative control defects showed only 0.4% of new bone formation. At 2 months, the histological and histomorphometric analysis showed NBF in the defects that received only DBBM, DBBM+DM, and DBBM+SM (16.8, 24.5, and 37%, respectively), while the negative control defects showed only 0.9% of new bone formation. The residual xenogeneic material (RXM) was higher in defects covered by SM (30.2% at 1 month and 25.3% at 2 months) or DM (32.5% at 1 month and 28.5% at 2 months) compared with defects that were not covered by membranes (15.3% at 1 month and 9.4% at 2 months). CONCLUSIONS: This study demonstrated that GBR with a xenogeneic material in rat calvarial (CSD) of 5 mm requires the application of resorbable collagen membranes in either single or double layer, and a single layer alone is sufficient to promote this regeneration.