Carina B. Johansson

The electrochemical oxide growth behaviour on titanium in acid and alkaline electrolytes

Titanium implants have a thin oxide surface layer. The properties of this oxide layer may explain the good biocompatibility of titanium implants. Anodic oxidation results in a thickening of the oxide film, with possible improved biocompatability of anodized implants. The aim of the present study was twofold: (1) firstly, to characterize the growth behaviour of galvanostatically prepared anodic oxide films on commercially pure (c.p.) titanium and (2) secondly, to establish a better understanding of the electroche0mical growth behaviour of anodic oxide on commercially pure titanium (ASTM grade 1) after changes of the electrochemical parameters in acetic acid, phosphoric acid, calcium hydroxide, and sodium hydroxide under galvanostatic anodizing mode. The oxide thickness was measured by Ar sputter etching in Auger Electron spectroscopy (AES) and the colours were estimated by an L*a*b* system (lightness, hue and saturation) using a spectrophotometer. In the first part of our study, it was demonstrated that the interference colours were useful to identify the thickness of titanium oxide. It was also found that the anodic forming voltages with slope (dV/dt) in acid electrolytes were higher than in alkaline electrolytes. Each of the used electrolytes demonstrates an intrinsically specific growth constant (nm/V) in the range of 1.4--2.78 nm/V. In the second part of our study we found, as a general trend, that an increase of electrolyte concentration and electrolyte temperature respectively decreases the anodic forming voltage, the anodic forming rate (nm/s) and the current efficiency (nm.cm(2)/C), while an increase of the current density and the surface area ratio of the anode to cathode increase the anodic forming voltage, the anodic forming rate and the current efficiency. The effects of electrolyte concentration, electrolyte temperature, and agitation speed were explained on the basis of the model of the electrical double layer.

Aseptic loosening, not only a question of wear: A review of different theories

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

Experimental study of turned and grit-blasted screw-shaped implants with special emphasis on effects of blasting material and surface topography

In the rabbit tibia, commercially pure titanium implants blasted with 25-microns Al2O3 and TiO2 particles respectively were inserted and studied with respect to removal torque and histomorphometry. In the rabbit femur, as-machined implants and implants blasted with 75-microns Al2O3 particles were histomorphometrically compared. Before implant insertion, the differently produced surface topographies were characterized numerically and visually. The tibial implants blasted with different materials and the same sized (25 microns) blasting particles demonstrated similar results. Comparing implants blasted with 75-microns Al2O3 particles to as-machined implants, the blasted specimens exhibited a statistically significant higher bone-to-metal contact after 12 weeks in the rabbit bone.

Influence of implant diameters on the integration of screw implants: An experimental study in rabbits

The influence of diameter on the integration of titanium screw-shaped implants was studied in the rabbit tibia by means of removal torque measurements and histomorphometry. Implants 3.0, 3.75, 5.0, and 6.0 mm in diameter and 6.0 mm long were inserted through one cortical layer in the tibial metaphyses of nine rabbits and allowed to heal for 12 weeks. The implants were then unscrewed with a torque gauge, and the peak torque required to shear off the implants was recorded. The histologic analysis in undemineralized ground sections comprised (1) a gross description of the implant sites and assessments of (2) the total implant length in bone and (3) in the cortical passage, as well as (4) the thickness of the cortical bone adjacent to the implants. From the removal torque values obtained and morphometric measurements, a mean shear stress value was calculated for each implant type. The biomechanical tests showed a statistically significant increase of removal torque with increasing implant diameter. The resistance to shear seemed to be determined by the implant surface in supportive cortical bone, whereas the newly formed bone at the periosteal and endosteal surfaces did not seem to have any supportive properties after 12 weeks. It is suggested that wide diameter implants may be used clinically to increase implant stability.

Qualitative and quantitative observations of bone tissue reactions to anodised implants.

Research projects focusing on biomaterials related factors; the bulk implant material, the macro-design of the implant and the microsurface roughness are routinely being conducted at our laboratories. In this study, we have investigated the bone tissue reactions to turned commercially pure (c.p.) titanium implants with various thicknesses of the oxide films after 6 weeks of insertion in rabbit bone. The control c.p. titanium implants had an oxide thickness of 17-200 nm while the test implants revealed an oxide thickness between 600 and 1000 nm. Routine histological investigations of the tissue reactions around the implants and enzyme histochemical detections of alkaline and acid phosphatase activities demonstrated similar findings around both the control and test implants. In general, the histomorphometrical parameters (bone to implant contact and newly formed bone) revealed significant quantitative differences between the control and test implants. The test implants demonstrated a greater bone response histomorphometrically than control implants and the osteoconductivity was more pronounced around the test implant surfaces. The parameters that differed between the implant surfaces, i.e. the oxide thickness, the pore size distribution, the porosity and the crystallinity of the surface oxides may represent factors that have an influence on the histomorphometrical results indicated by a stronger bone tissue response to the test implant surfaces, with an oxide thickness of more than 600 nm.

Oxidized implants and their influence on the bone response

Surface oxide properties are regarded to be of great importance in establishing successful osseointegration of titanium implants. Despite a large number of theoretical questions on the precise role of oxide properties of titanium implants, current knowledge obtained from in vivo studies is lacking. The present study is designed to address two aspects. The first is to verify whether oxide properties of titanium implants indeed influence the in vivo bone tissue responses. The second, is to investigate what oxide properties underline such bone tissue responses. For these purposes, screw-shaped/turned implants have been prepared by electrochemical oxidation methods, resulting in a wide range of oxide properties in terms of: (i) oxide thickness ranging from 200 to 1000 nm, (ii) the surface morphology of barrier and porous oxide film structures, (iii) micro pore configuration – pore sizes<8 μm by length, about 1.27 μ2 to 2.1 μm2 by area and porosity of about 12.7–24.4%, (iv) the crystal structures of amorphous, anatase and mixtures of anatase and rutile type, (v) the chemical compositions of TiO2 and finally, (vi) surface roughness of 0.96–1.03 μm (Sa). These implant oxide properties were divided into test implant samples of Group II, III, IV and V. Control samples (Group I) were turned commercially pure titanium implants. Quantitative bone tissue responses were evaluated biomechanically by resonance frequency analysis (RFA) and removal torque (RT) test. Quantitative histomorphometric analyses and qualitative enzyme histochemical detection of alkaline (ALP) and acidic phosphatase (ACP) activities were investigated on cut and ground sections after six weeks of implant insertion in rabbit tibia. In essence, from the biomechanical and quantitative histomorphometric measurements we concluded that oxide properties of titanium implants, i.e. the oxide thickness, the microporous structure, and the crystallinity significantly influence the bone tissue response. At this stage, however, it is not clear whether oxide properties influence the bone tissue response separately or synergistically.© 2001 Kluwer Academic Publishers

Histological and histomorphometrical analyses of biopsies harvested 11 years after maxillary sinus floor augmentation with deproteinized bovine and autogenous bone

OBJECTIVE The purpose of the present study was to histologically and histomorphometrically evaluate the long-term tissue response to deproteinized bovine bone (DPBB) particles used in association with autogenous bone and to compare particle size after 6 months and 11 years, in the same patients, in order to determine possible resorption. MATERIAL AND METHODS Twenty consecutive patients (14 women and six men) with a mean age of 62 years (range 48-69 years) with severe atrophy of the posterior maxilla were included in this study. Thirty maxillary sinuses with <5 mm subantral alveolar bone were augmented with a mixture of 80% DPBB and 20% autogenous bone. Eleven years (mean 11.5 years) after augmentation, biopsies were taken from the grafted areas of the 11 patients who volunteered to participate in this new surgical intervention. The following histomorphometrical measurements were performed in these specimens: total bone area in percentage, total area of the DPBB, total area of marrow space, the degree of DPBB-bone contact (percentage of the total surface length for each particle), the length of all DPBB particles and the area of all DPBB particles. The length and the area of the particles were compared with samples harvested from the same patients at 6 months (nine samples) and pristine particles from the manufacturer. RESULTS The biopsies consisted of 44.7+/-16.9% lamellar bone, 38+/-16.9% marrow space and 17.3+/-13.2% DPBB. The degree of DPBB to bone contact was 61.5+/-34%. There were no statistically significant differences between the length and area of the particles after 11 years compared with those measured after 6 months in the same patients or to pristine particles from the manufacturer. CONCLUSION DPBB particles were found to be well integrated in lamellar bone, after sinus floor augmentation in humans, showing no significant changes in particle size after 11 years. To cite this article: Mordenfeld A, Hallman M, Johansson CB, Albrektsson T. Histological and histomorphometrical analyses of biopsies harvested 11 years after maxillary sinus floor augmentation with deproteinized bovine and autogenous bone.

The roles of surface chemistry and topography in the strength and rate of osseointegration of titanium implants in bone

The present study investigated the effects of surface chemistry and topography on the strength and rate of osseointegration of titanium implants in bone. Three groups of implants were compared: (1) machine-turned implants (turned implants), (2) machine-turned and aluminum oxide-blasted implants (blasted implants), and (3) implants that were machine-turned, aluminum oxide-blasted, and processed with the micro-arc oxidation method (Mg implants). Three and six weeks after implant insertion in rabbit tibiae, the implant osseointegration strength and rate were evaluated. Surface chemistry revealed characteristic differences of nine at.% Mg for Mg implants and 11 at.% Al for blasted implants. In terms of surface roughness, there was no difference between Mg implants and blasted implants in developed surface ratio (Sdr; p = 0.69) or summit density (Sds; p = 0.96), but Mg implants had a significantly lower arithmetic average height deviation (Sa) value than blasted implants (p = 0.007). At both 3 and 6 weeks, Mg implants demonstrated significantly higher osseointegration strength compared with turned (p = 0.0001, p = 0.0001) and blasted (p = 0.0001, p = 0.035) implants, whereas blasted implants showed significantly higher osseointegration than turned implants at 6 weeks (p = 0.02) but not at 3 weeks (p = 0.199). The present results not only support the hypothesis that biochemical bonding facilitates rapid and strong integration of implants in bone, but also provide evidence for biochemical bonding theory previously proposed by Sul.

HA particles can be released from well-fixed HA-coated stems: histopathology of biopsies from 20 hips 2-8 years after implantation.

20 hip arthroplasties with a Landos Corail Ti6Al4V stem entirely plasma-sprayed with a 155 - 35 w m thick HA coating were reoperated on after median 6 (2-8) years because of polyethylene wear (10), acetabular loosening (7), instability (2), or infection (1). We took biopsies from the proximal femurs adjacent to the well-fixed stems. Undecalcified sections were prepared and examined with a light microscope. The biopsies contained median 5 (1.3-16 ) mm metal interface with 54% HA, 32% bone, and 14% soft tissue. The median thickness of the remaining HA coating was 137 (6-380) w m, and the HA-tissue interface included 89% bone and 11% soft tissue. All HA coatings showed partial degradation and replacement by soft tissue, osteoid-like tissue, or bone. 6 hips had tissue ingrowth between HA and metal consistent with delamination. 14 hips showed bone resorptive areas containing some HA particles and large amounts of polyethylene and metal particles, partly internalized in multinucleated giant cells and macrophages. Bone resorption was associated with metal and polyethylene particles, but not with HA particles. The HA coatings were undermined, resulting in release of large flakes of HA with free access to the articulation. We believe this mechanism may be responsible for third-body wear.

Early healing of implants placed into fresh extraction sockets: an experimental study in the beagle dog. De novo bone formation

OBJECTIVES Describe the early phases of tissue integration in implants placed into fresh extraction sockets and test whether a new implant surface nano-topography (DCD nano-particles, Nanotite) promotes early osseointegration when compared with minimally rough surface implants (DAE, Osseotite). MATERIAL AND METHODS Sixteen beagle dogs received 64 test and control implants randomly installed into the distal socket of (3)P(3) and (4)P(4). Histomorphometric analysis of bone to implant contact (BIC) and bone area was performed at 4 h, 1, 2, 4 and 8 weeks. RESULTS Wound healing initiated with a coagulum that was substituted by a provisional matrix at 1 week. Bone formation started concomitant to a marked bone resorption. At 2 weeks, woven bone formation was evident and gradually remodelled into lamellar bone at 4 and 8 weeks. BIC increased similarly throughout the study in both groups with a tendency to higher percentages for the test devices at 2 and 4 weeks. The influence of the DCD nano-particles was more evident at the fourth premolar site. CONCLUSION Osseointegration occurred similarly at both implant groups, although the socket dimension appeared to influence bone healing. It is suggested that the enhanced nano-topography has a limited effect in the immediate implant surgical protocol.