Implant-guided supracrestal alveolar bone growth using scaffolds, BMP-2, and novel scaffold-retaining device.

Abstract

To evaluate the efficacy of various scaffold systems and a Ti scaffold-retaining device with and without non-glycosylated rhBMP-2 (BMP-2) for increasing the vertical alveolar bone growth in the intra-oral mini-pig model. Forty-eight Straumann Bone Level implants with hydrophilic (SLActive) surfaces were partially embedded in mandibles of 12 adult mini-pigs with the shoulder of the implant located 3mm above the bone crest. Twenty-four implants were placed in conjunction with BMP-2 (50μg) incorporated within resorbable scaffolds. Twenty-four additional control implants were placed with scaffolds only. Scaffolds were placed around the implant and stabilized with a newly developed Ti "umbrella" scaffold retainer. Scaffolds included (i) HA-coated collagen (Healos); (ii) biphasic HA/β-TCP crystals (Straumann Bone Ceramic, SBC); and (iii) SBC crystals infused with polyethylene glycol (PEG) hydrogel. Eight test and control pairs for each scaffold group were implanted. At 9weeks, soft tissue healing was assessed and the extent of new vertical bone was evaluated with microCT and histomorphometry. microCT analysis revealed a mean of 167±47mm3 new supracrestal mineralized tissue volume formation around the test sites where BMP-2 was released from the scaffold whereas the control group (no BMP-2) showed a significantly lower mineralized tissue volume of 106±55mm3 . The SBC+BMP-2 group had the highest mineralized tissue volume of 189±36mm3 . Histomorphometry showed bone-to-implant contact of 54.5% for the test groups and 33.3% for the control groups and new vertical bone growth of 2.2±1.0 and 1.0±0.9mm, respectively. The SBC+BMP-2 group again demonstrated the best outcome (2.7±0.4mm). The qualitative scoring of soft tissue dehiscence showed that the presence of BMP-2 yielded far superior outcomes, 0.63 vs. 1.75 for all control implant sites (with scores ranging from 0, reflecting no soft dehiscence, to 4, showing a completely exposed umbrella). The release of BMP-2 from a SBC scaffold adjacent to a hydrophilic, rough Ti implant and scaffold retention umbrella consistently regenerated the greatest volume and height of new vertical bone along the length of the implant.