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Harder and Stiffer Bone Osseointegrated to Roughened Titanium

The Jane and Jerry Weintraub Center for Reconstructive Biotechnology, Division of Advanced Prosthodontics, Biomaterials and Hospital Dentistry, UCLA School of Dentistry, 10833 Le Conte Avenue (B3-087 CHS), Box 951668, Los Angeles, CA 90095-1668, USA

View larger version (65K): [in a new window]   Figure 1. Images for experimental protocol. (A) T-shaped titanium implants having an inner chamber prepared with machined surface (bottom) or acid-etched surface (top). (B) Schematic description of implant site. (C) Schematic diagram of the preparation of the osseointegration interface specimen. The gray area indicates bone, and thick line represents where the implant was in place. We harvested the femoral area specimens, including the implant, by cutting at both ends of the implant, and the implant and bone tissue were then carefully separated. Nano-indentation was performed in the lower half of the bone tissue separated from the implant (*). (D) A photo of the osseointegrated bone interface separated from the implant as described in (C). Bar = 1 mm. (E) Schematic diagram of the preparation of the peri-implant bone. Rat femoral area specimens, including the titanium implant, were cut and ground to expose the cross-section of the implant chamber. The gray area indicates bone, and the solid black area represents the implant. Nano-indentation was performed in the lower half of the bone tissue formed inside the inner chamber along the implant surface (*). (F) A photo of the ground surface of the peri-implant bone, prepared as described in panel (E). (G) An optical microscope image of a dent made on copper by a preliminary nano-indentation with a fixed depth of 2 µm, depicting a precise reproduction of the tip of the Berkovich indenter. The well-defined three-sided pyramidal imprint is observed. Bar is 10 µm. (H) An optical microscope image showing the remaining three-sided pyramidal imprint (triangle) of 500-nm-depth nano-indentation applied on the osseointegration interface. Bar is 1 µm.

View larger version (26K): [in a new window]   Figure 2. Load-depth curves obtained by nano-indentation of (A) the untreated trabecular bone, (B) untreated cortical bone, (C) the week 4 osseointegration interface to the machined titanium, and (D) the week 4 osseointegration interface to the acid-etched titanium. The indentation continued to the fixed depth of 500 nm with a loading rate of 10 mN/min. Note that the maximum load required to reach the 500-nm depth varied greatly among the specimens tested. (E) Biomechanical properties (hardness and elastic modulus) of week 2 post-surgery tissues at the osseointegration interface and peri-implant bone, along with the untreated trabecular and cortical bone tissues. Data are shown as the mean ± SD (n = 6). Results from a Bonferroni multiple-comparison test are indicated. Levels of statistical significance: *p < 0.05, **p < 0.01, and ***p < 0.001. (F) Biomechanical properties (hardness and elastic modulus) of week 4 post-surgery tissues. Data are shown as the mean ± SD (n = 6). *p < 0.05, **p < 0.01, and ***p < 0.001. (G) Biomechanical property comparisons of the trabecular and cortical bone between the untreated and osteotomized areas. The tissue samples were harvested 4 wks after osteotomy.

View larger version (119K): [in a new window]   Figure 3. Morphology and elemental composition of retrieved bone-implant interface. Scanning electron microscopic (SEM) images of the week-2- and -4-retrieved machined implant surfaces (A,C) and acid-etched implant surfaces (B,D). Magnified images (E-J) were obtained from the circled areas of e-j in panels A-D, respectively. Bar = 1 mm for panels A-D, 100 µm for panels E-J. (K-P) Energy-dispersive spectroscopic (EDX) elemental analysis of the retrieved implant surfaces for Ti, Ca, P, and S elements. The spectra K, L, and M were obtained from the images E, F, and I, respectively, and the spectra N, O, and P were from the images G, H, and J.

View larger version (33K): [in a new window]   Figure 4. Three-dimensional (3-D) bone morphology and morphometry of osseointegrated bone. (A) A microCT image of the detached tissue from the machined implant at week 4 post-implantation, depicting the trabecular architecture of newly formed bone tissue. (B) A microCT image of the prepared tissue specimen for nano-indentation. The tissue was separated from the week 4 machined implant, embedded in epoxy, and polished as described in the text. The flattened and smoothened bone surface is seen at the lower half of the tissue, where the nano-indentation was perfomed. Magnified microCT images of the tissue separated from the machined surface (C) and acid-etched surface (D). The volume of interest (VOI) for these 2 images was set at 300 µm x 300 µm x 100 µm. (E) Quantitative assessment of 3-D parameters performed in the VOI of 300 µm x 300 µm x 100 µm. Data are shown as the mean ± SD (n = 6). Statistical significance, *p < 0.01. (F) Bone morphometry performed in the VOI of 100 µm x 100 µm x 100 µm. Data are shown as the mean ± SD (n = 6).