Surface topography of implants drives bone anchorage

摘要

Introduction: Titanium (Ti) is widely used as a dental implant material. We, and others, have shown that implant surface topography, especially at the nano-scale, plays a significant role in promoting bony healing. However, we have generally superimposed discrete calcium phosphate (CaP) nanocrystals (DCD), on Ti surfaces, to create a nanotopographic complexity. This begs the question; Is it the topography, or CaP chemistry that is responsible for the improved implant performance. Thus, we report here the comparative performance of nano-Ti surfaces created within the surface Ti oxide surface with those functionalized with CaP crystals, using a bone anchorage test. Materials and Methods: 380 Custom-made commercially pure titanium implants with machined surfaces were made and split into 6 groups: (A) Machined (B) A+DCD (C) A+NaOH (D) C+SBF immersion (E) C+H2O immersion (F) A+anodized. Group D was prepared to add Ca2+ ions to the complex NaOH surface. Each surface was examined by both scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). All implants were sterilized using 25kGy y-irradiation. The implants were placed into the femora of male Wistar rats, which were sacrificed after 14,28,56,98, or 140 days. The femora were harvested and then trimmed to the width of the implant, leaving the implant in between two bony arches. The force required to disrupt the model was measured with an Instron™. Data was collected and compiled using the statistical software "R". P values ＜0.05 were considered significant. Results: SEM of all implant groups showed a relatively smooth surface with some micro-scale features at low magnification. At higher magnification, Group B had approximately 50% coverage of DCD, Groups C-E had a complex interconnected nanoporous structure with pore sizes up to 110 nm. Group F implants were covered with nanotubes of approximately 100nm diameter. XPS confirmed an increase in Ca on the surface of Group D (2.98%) as compared to Group C (0.66%) due to the SBF treatment. Disruption forces were seen to increase with time for all, but Groups A and B of which the disruption forces were significantly smaller than all other groups. Significant differences were found between all group pairs, with exceptions of C/F, and D/E at 28 days. Discussion: At all time points, the disruption forces for Groups A and B were near zero, indicating little bony anchorage to these surfaces. On the contrary Groups C and F showed significantly increased disruption forces (C = 16.8 × B at 28 days), indicating that the Ti surface oxide nanofeatures were having a profound effect, without the addition of a CaP phase. Interestingly, when this complex oxide surface was functionalized with Ca2+ ions (Group D) the disruption force decreased: However, this was also the case in Group E, which suggested that immersion in an aqueous solution had weakened the surface oxide structure. Conclusion: Bone anchorage results from implant surface topographical complexity rather than CaP chemistry.