Table 1.
Summary of surface characterisation data (quantitative parameters) for screw-shaped implants: surface elemental composition determined by AES†, oxide thickness determined by AES depth profiling, and surface roughness measured by interference microscopy.
Fig 1.
SEM images of the implant surface.
Low-magnification images of the (A) machined and the (B) laser-modified implants. Surface microtopography of the (C) machined and the (D) laser-modified implants. High-magnification images show (E) ridges and grooves as remnants of the machining process for the machined implants and (F) a distinct nanotexture superimposed on the surface microtopography of the laser-modified implants.
Fig 2.
RFA, RTQ, load deformation and histomorphometry.
(A-B) Resonance frequency analysis (RFA) showing changes in ISQ values over time. (C) Removal torque (RTQ) at break-point. (D) Typical load deformation curves (applied load vs. angular deformation) for the machined and the laser-modified implants showing the distinctly different patterns of mechanical failure at a constant rate of 0.2°/s. (E-F) Histomorphometry. The total bone-implant contact (BIC) and the total bone area (BA) in the threads were determined along the entire length of the threaded part of the implant. The inner BIC and the inner BA were determined in the inner 1/3 of the threads of the respective implant types.
Fig 3.
Undecalcified toluidine blue-stained sections of the (A) machined and (B) laser-modified implants. Both types of implants are vertically and unicortically positioned in the tibia. The two upper threads are located in the original cortical bone (Ct.B). Endosteal bone downgrowth (white arrows) is observed, extending downwards to the level of the third/fourth thread, whereas the remaining threads are mainly located in the bone marrow (Ma) compartment. Occasionally, periosteal bone formation (black arrows) is observed, reaching up to the implant flange yet remaining below the level of the cover screw. Bone interfacing the (C, E) machined and (D, F) laser-modified implants, at the level of the upper cortical thread (C-D) and the level of the endosteal threads (E-F). For the machined implants, a separation is frequently detected (white asterisk) between bone and implant. The laser-modified surface revealed bone in direct contact. For all laser-modified implants, fracture lines (white arrowheads) were observed in the bone within the threads at short distances (typically 30–50 μm) from the implant surface and running parallel to the implant surface in the thread valley.
Fig 4.
Undecalcified toluidine blue-stained sections of the (A, C, E, G) machined and (B, D, F, H) laser-modified implants. At the bone-implant interface, morphological features of bone formation and remodelling can be clearly observed in different threads in the cortical bone and the endosteal and bone marrow compartments. (A-B) Areas of ongoing remodelling. Osteoclasts (black arrows), osteoblasts (white arrows) and osteocytes (some of which are indicated by white arrowheads) are located in areas undergoing active remodelling at the interface. Blood vessels are indicated by black arrowheads. (C-D) For both implant types, mature bone occupies the endosteal threads, consisting of densely packed osteons (black arrows), with central blood vessels, surrounded by concentric bone lamellae and mature osteocytes. (E-F) Generally, the lower three threads of both implant types are occupied by bone marrow (Ma). Islands of newly formed, immature bone (black arrows) characterised by intense toluidine blue staining and large rounded osteocytes, which indicate an early stage of bone formation, are sometimes detected in the lower threads. This type of bone appears to be formed de novo and not as an extension from the endosteum. (G-H) Some of the bone marrow threads (Ma) show condensations of haematopoietic (black arrows) as well as relatively large and lightly stained mesenchymal-like cells (white arrows) adjacent to the implant surfaces.
Table 2.
Pearson correlation analysis between different parameters of osseointegration.
The data are pooled for the machined and laser-modified implants (n = 20). The table shows the correlation coefficients, r, and the statistical significance level, p.
Table 3.
Multiple stepwise linear regression model without controlling for the confounding factors.
The data are pooled for the machined and laser-modified implants (n = 20).
Table 4.
Multiple stepwise linear regression model controlled for the confounding factors.
The data are pooled for the machined and laser-modified implants (n = 20).
Fig 5.
Backscattered electron scanning electron microscopy (BSE-SEM), Raman spectroscopy and resin cast etching.
(A-B) BSE-SEM images of the (A) machined and the (B) laser-modified implants, showing mature, remodelled, osteonal, lamellar bone filling the implant threads. Following biomechanical testing (RTQ), bone detaches from the machined implant surface, resulting in a separation at the bone-implant interface, while a fracture line appears in the bone at some distance from the laser-modified implant surface (black arrowhead). (C-E) Raman metrics evaluated at the level of the first endosteal thread (as indicated in the insert image in B); 1: valley (corresponding to the inner 1/3 of the thread), 2: flank (corresponding to the outer 2/3 of the thread), 3: outside. (F-G) The same threads (as in A-B) are visualised following resin cast etching to confirm the presence of vasculature in the vicinity of the implant surface. The osteocyte lacuno-canalicular network (Ot-LCN) communicates with Haversian canals (white arrowheads), as well as extending towards the implant surface.
Fig 6.
Osteocyte communication with the implant surface.
Direct visualisation of osteocyte (Ot) morphology adjacent to the (A-B) machined and the (C-J) laser-modified implant surfaces following resin cast etching. (A-B) Osteocytes are observed adjacent to the machined implant surface (Ti). (C-E) An osteocyte is seen in close proximity to the laser-modified surface (Ti). (F-G) Osteocyte canaliculi are attached to the surface TiO2 layer. (H-I) Osteocyte canaliculi (white arrowheads) extend approximately 6 μm to approach a globular feature within the laser-ablated part of the implant surface. (J) Osteocyte canaliculi form a vast intercommunicating network directly on the laser-modified implant surface. Scale bars in D and E = 200 nm, G = 500 nm and I = 2 μm.
Fig 7.
(A, C) HAADF-STEM and (B, D) TEM images demonstrating nanoscale interlocking of bone with the laser-modified implant surface. (A-B) Collagen fibrils are aligned parallel to the implant surface and osteocyte canaliculi are observed in close proximity to the implant surface (asterisks). (C) Osteocyte canaliculi appear to make direct contact with the implant surface (asterisks). (D) At high resolution, mineralised collagen fibrils interlock with the nanotextured surface TiO2 layer.