Mechanical evaluation of bone formation by Escherichia coli-derived rhBMP-2/ACS in beagle dogs

Abstract

Objective In the present study, we performed a mechanical evaluation to determine whether new bone similar to the host bone can be formed following guided bone regeneration (GBR) with O-BMP(Escherichia coli-derived rhBMP-2/ACS). Materials and methods Saddle type defects, each having a diameter of 10 mm x 6 mm, were formed on 4 locations on the mandibles of 8 male beagle dogs. For each dog, a bone graft was placed on each site at random using O-BMP, Infuse, A-OSS, or ACS only. After 3 months(12 weeks), bone formation near the areas where the procedure was performed was inspected visually and radiographically, after which the implants were placed (TSII SA Φ 5.0x6mm (Osstem)). During the implantation, a trephine drill (Φ3.7/Φ4.5) was used to obtain bone specimens for compression testing to be performed later, while insertion torque and ISQ were measured. The upper prosthesis was inserted at 3 months after the implantation (cylindrical resin block as a single unit), at which time ISQ was measured again. The bone specimens obtained during the implantation were compressed by 1 mm/min to measure the compression yield strength (0.2% offset). Result In all experimental groups, definitive new bone formation noticeable by visual inspection or radiography occurred at 12 weeks post-GBR. The experimental results were analyzed using a nonparametric test (Kruskal-Wallis test). During implantation, at 3-months post-GBR, the torque values for O-BMP, Infuse, A-OSS, and ACS were all within the recommended implantation value range (10–40 N). Most of the experimental groups, including O-BMP, showed mean ISQ values ≥ 70 during the implantation, and outstanding initial fixation power of the fixture was observed in all groups. At 3 months post-implantation, most of the experimental groups showed mean ISQ values ≥ 70 during the insertion of the upper prosthesis. Moreover, the highest compression yield strength value in the bone specimen was found in the group administered O-BMP. Conclusion O-BMP exhibited the capability to form new bone similar to the host bone. It was equivalent to other currently used methods.