Primary ridge augmentation with collagenated xenogenic block bone substitute in combination with collagen membrane and rhBMP-2: a pilot histological investigation

Objective The aim of this pilot study was to test whether a porcine collagenated bone substitute block (PCBB) and collagen membrane (CM) loaded with bone morphogenetic protein-2 (BMP-2) used for horizontal ridge augmentation differ from PCBB and CM without BMP-2 regarding the osseointegration of the grafting material and the maintenance of the ridge contour. Material and methods Two semi-saddle bone defects were created in each side of the mandible of six dogs. The defects were randomly allocated to receive one of the following treatments: bone augmentation using (1) PCBB, (2) PCBB loaded with BMP-2 (PCBB-BMP2), (3) PCBB + CM and (4) PCBB + CM loaded with BMP-2 (PCBB + CM-BMP2). After 12 weeks, one titanium implant was inserted into every site. After 8 weeks, one central histological section of each site was prepared. Histomorphometrical assessments were performed evaluating the augmented area (AA), the area of new bone (NB) (primary outcome), residual bone substitute (BS) and non-mineralized tissue (NMT) within AA in mm2. In addition, the most coronal and the most buccal localizations of new bone and residual bone substitute, and the most coronal bone-to-implant contact were measured in mm. Results Clinically, all PCBB were firmly integrated and permitted implant placement. All the implants osseointegrated and exhibited complete hard-tissue coverage of the buccal surface. Bone ingrowth always reached the central portions of PCBB. AA measured 10.4 ± 4.2 mm2 for PCBB, 11.8 ± 2.8 mm2 for PCBB-BMP2, 9.8 ± 2.9 mm2 for PCBB + CM and 8.5 ± 2.2 mm2 for PCBB + CM-BMP2. Only the difference between PCBB-BMP2 and PCBB + CM-BMP2 was statistically significant (P = 0.031). NB reached 2.3 ± 1.3 mm2 for PCBB, 2 ± 0.5 mm2 for PCBB-BMP2, 2.7 ± 1.2 mm2 for PCBB + CM and 1.8 ± 0.7 mm2 for PCBB + CM-BMP2. There were no statistically significant differences regarding NB, the most coronal and the most buccal localizations of new bone, residual bone substitute and bone-to-implant contact (P > 0.05). Conclusions The addition of BMP-2 to PCBB or CM used for horizontal ridge augmentation did not render a statistically significant improvement in the maintenance of the augmented ridge contour and the new bone formation. PCBB with and without CM showed pronounced bone ingrowth and capacity to maintain the augmented ridge contour. In all the regions previously augmented with PCBB, the implants successfully integrated and presented with complete hard-tissue coverage.