Jürgen Geis-Gerstorfer

Potential of chemically modified hydrophilic surface characteristics to support tissue integration of titanium dental implants

In the past, several modifications of specific surface properties such as topography, structure, chemistry, surface charge, and wettability have been investigated to predictably improve the osseointegration of titanium implants. The aim of the present review was to evaluate, based on the currently available evidence, the impact of hydrophilic surface modifications of titanium for dental implants. A surface treatment was performed to produce hydroxylated/hydrated titanium surfaces with identical microstructure to either acid-etched, or sand-blasted, large grit and acid-etched substrates, but with hydrophilic character. Preliminary in vitro studies have indicated that the specific properties noted for hydrophilic titanium surfaces have a significant influence on cell differentiation and growth factor production. Animal experiments have pointed out that hydrophilic surfaces improve early stages of soft tissue and hard tissue integration of either nonsubmerged or submerged titanium implants. This data was also corroborated by the results from preliminary clinical studies. In conclusion, the present review has pointed to a potential of hydrophilic surface modifications to support tissue integration of titanium dental implants.

The Roles of Titanium Surface Micro/Nanotopography and Wettability on the Differential Response of Human Osteoblast Lineage Cells

Surface micro- and nanostructural modifications of dental and orthopedic implants have shown promising in vitro, in vivo and clinical results. Surface wettability has also been suggested to play an important role in osteoblast differentiation and osseointegration. However, the available techniques to measure surface wettability are not reliable on clinically relevant, rough surfaces. Furthermore, how the differentiation state of osteoblast lineage cells impacts their response to micro/nanostructured surfaces, and the role of wettability on this response, remain unclear. In the current study, surface wettability analyses (optical sessile drop analysis, environmental scanning electron microscopic analysis and the Wilhelmy technique) indicated hydrophobic static responses for deposited water droplets on microrough and micro/nanostructured specimens, while hydrophilic responses were observed with dynamic analyses of micro/nanostructured specimens. The maturation and local factor production of human immature osteoblast-like MG63 cells was synergistically influenced by nanostructures superimposed onto microrough titanium (Ti) surfaces. In contrast, human mesenchymal stem cells cultured on micro/nanostructured surfaces in the absence of exogenous soluble factors exhibited less robust osteoblastic differentiation and local factor production compared to cultures on unmodified microroughened Ti. Our results support previous observations using Ti6Al4V surfaces showing that recognition of surface nanostructures and subsequent cell response is dependent on the differentiation state of osteoblast lineage cells. The results also indicate that this effect may be partly modulated by surface wettability. These findings support the conclusion that the successful osseointegration of an implant depends on contributions from osteoblast lineage cells at different stages of osteoblast commitment.

Investigation of cell reactions to microstructured implant surfaces

Abstract Surface topography is one of the key parameters influencing cellular reactions towards artificial materials. Surfaces with defined microstructures may be useful for enhancement of the stable anchorage of transcutaneous implants in connective tissue or for prevention of epithelial downgrowth and subsequent exfoliation. Cell reactions of keratinocytes and fibroblasts were investigated on microstructured titanium experimental surfaces with alternating grooves and ridges in the range between 1–20 μm width and 0.4–2.0 μm depth. While fibroblasts displayed oriented cell growth on the structured surfaces, human keratinocytes failed to show orientation or enhanced number of focal contacts on structures in the 2–10 μm width range. In that respect, an influence of surface structure on initial cell adhesion could not be proven. The influence of a “bioactive” fibronectin (Fn) coating on adhesion and spreading of fibroblasts was tested on smooth and structured titanium model implant surfaces. Cell spreading was enhanced significantly by the fibronectin coating. Under mechanical shear stress conditions which simulated stresses during insertion of dental implants, the stimulating effects of Fn were lost on smooth surfaces due to abrasion of the coating, while complete abrasion was prevented by microstructured surfaces. The combination of microstructures with “bioactive” coatings may be used to trigger specific cell responses in areas of the implant surface with different functionality. Adhesion and growth of different cell types on microstructured surfaces was investigated by a modified technique at the electron microscopy (EM) level. The approach allows the detection of adhesion molecules in the different membrane domains by immunocytochemical gold labelling techniques. Preliminary results with this new technique suggest that vinculin is localized in the grooves rather than on the ridges in our model system.

In vitro corrosion behavior of four Ni−Cr dental alloys in lactic acid and sodium chloride solutions

Abstract This investigation was carried out to study the in vitro corrosion behavior of 4 nickelchromium alloys in different lactic acid and sodium chloride solutions. Electrochemical techniques like potentiodynamic potential curves and potential time curves were used to analyse the characteristics of these alloys. Substance loss was measured analytically (AAS) to determine kind and quantity of dealloying elements. The results reveal that Ni−Cr alloys currently used in dentistry show a broad spectrum of corrosion resistance (depending on their chemical composition), the best being equal to those of precious alloys, while the worst had up to a thousand times greater substance loss and showed high corrosion currents in the potential area of physiological interest. Ni−Cr alloys containing too small amounts of chromium and molybdenum yielded the worst results and showed a susceptibility to pitting corrosion.

Studies on the influence of BE content on the corrosion behavior and mechanical properties of Ni-25Cr-10Mo alloys

The influence of Be content on the corrosion behavior and strength of dental alloys was examined using experimental Ni-25Cr-10Mo-xBe alloys with graduated Be contents of 0, 0.6, 1.1, 1.6, and 2.1 wt.%. It became evident that the corrosion resistance is reduced even by a 0.6 wt.% Be content. Strength increases by 51% with increasing Be content, while ductility is reduced by 84%. The results revealed that, from the stand-point of corrosion resistance, Be-free Ni-Cr-Mo alloys should be preferred in clinical use.

Structural characterization of nanocrystalline hydroxyapatite and adhesion of pre-osteoblast cells

Nanocrystalline hydroxyapatite (Nano HA), a prototype of minerals of bones and teeth, attracts increasing interest in medicine and dentistry. Different parameters for synthesis and post-treatment were investigated to determine their effects on crystallinity of nano HA, and in vitro cell responses to nano HA were studied. XRD and TEM analyses indicate that the crystallinity of nano HA synthesized by a chemical method was within the range of 15–50 nm, which is adapted to natural minerals of hard tissues. Increasing the ageing temperature significantly increased the crystallinity of nano HA, while lengthening the ageing time or varying the post-ageing drying process did not have any influence on its crystallinity. Nano HA annealed between 300 and 900 °C showed a small increase in crystallinity with increasing annealing temperature due to the long-range ordering effect. Cell attachment and spreading on nano HA were lower than those on pure titanium, and decreased as the crystallinity of nano HA increased. However, cells on nano HA demonstrated well-developed filopodia and lamelliopodia, which facilitate migration of the cells on it. This may benefit osteogenesis at the interface between bone and nano HA in vivo.

Comparison of different in vitro tests for biocompatibility screening of Mg alloys.

Standard cell culture tests according to ISO 10993 have only limited value for the biocompatibility screening of degradable biomaterials such as Mg alloys. The correlation between in vitro and in vivo results is poor. Standard cytotoxicity tests mimic the clinical situation to only a limited extent, since in vivo proteins and macromolecules in the blood and interstitial liquid will influence the corrosion behaviour and, hence, biocompatibility of Mg alloys to a significant extent. We therefore developed a modified cytotoxicity test simulating the in vivo conditions by use of bovine serum as the extraction vehicle instead of the cell culture medium routinely used in standard cytotoxicity testing according to ISO 10993-5. The modified extraction test was applied to eight experimental Mg alloys. Cytotoxicity was assayed by inhibition of cell metabolic activity (XTT test). When extraction of the alloy samples was performed in serum instead of cell culture medium the metabolic activity was significantly less inhibited for six of the eight alloys. The reduction in apparent cytotoxicity under serum extraction conditions was most pronounced for MgZn1 (109% relative metabolic activity with serum extracts vs. 26% in Dulbeccos modified Eagles medium (DMEM)), for MgY4 (103% in serum vs. 32% in DMEM) and for MgAl3Zn1 (84% vs. 17%), resulting in a completely different cytotoxicity ranking of the tested materials when serum extraction was used. We suppose that this test system has the potential to enhance the predictability of in vivo corrosion behaviour and biocompatibility of Mg-based materials for biodegradable medical devices.

Influence of surface treatment on the wear of solid zirconia.

Abstract Objective. Recently there has been talk of the use of full-contour solid zirconia crowns or bridge restorations with no porcelain overlay. This could be a useful solution for patients with bruxism or limited interocclusal space. However, the hardness of zirconia could affect the opposite natural dentition. The aim of this in-vitro study was to investigate the role of surface treatments on the wear of a zirconia material and its antagonist. Materials and methods. Fifty plates (10 × 10 × 1 mm) made of zirconia (LavaMulti™ ZrO2, 3M ESPE), divided into five equal groups, were sandblasted and ground under standardized conditions with a fine-grit diamond bur (Komet Brasseler, Germany) to simulate clinical conditions. Group (a) was only fired, (b) was fired and sandblasted, (c) only ground, (d) was ground and additionally polished (EVE Ceramic Polishing-Set, Pforzheim) and (e) was ground and glazed. Wear behavior was measured with a pin-on-disk apparatus ABREX against 6 mm steatite balls as antagonists (45°, 5 N load, 5000 cycles, water). The amount of wear was determined topographically using a 3-D profilometer (Concept 3D, Mahr, Germany) by measuring the height loss of the antagonist and the depth of wear Pt of the zirconia. Results. In groups (a), (b), (c) and (d) the wear value Pt could not be determined (<1 μm). Wear values of the antagonists (steatite balls) revealed a similar outcome in contact with (b), (c) and (e) in the range of 81–85 μm, whereas (e) was more abrasive but not significantly. A noticeable difference in the wear of the antagonist showed group (d) to have the smallest value. Conclusion. Polished zirconia seems to have the lowest wear on the antagonists, in contrast with the other kinds of surface treatment.

Effect of Heterogenic Surfaces on Contact Angle Hysteresis: Dynamic Contact Angle Analysis in Material Sciences

Recently, the author successfully applied the classic Wilhelmy balance method and the dynamic contact angle analysis (DCA) on initial interfacial reactions of surface-modified biomaterials. In this study, the authors present further results which underline the potential of these methods to yield time-resolved data of ionic and protein interfacial reactions. In contrast to many spectroscopic methods, an on-line method, which works time-resolved and without disturbing the interface, would be important in the process-engineered quality control. This is underlined by the fact, that many biomedical material surfaces currently are pre-biofunctionalized before their application in order to increase their biocompatibility and bifunctionality. The above-outlined statement of the problems involves many disciplines. In this approach, it is highlighted and discussed on the background of current research on biomaterials.

Cell reactions to microstructured implant surfaces

Cells are capable of reacting to a variety of differently patterned substrates. A number of hypotheses have already emerged to explain cell orientation and directed migration. It seems likely that no single hypothesis is able to explain in detail the behavior of cells that produce contact guidance. Understanding the mechanisms that influence the behavior of cells on microstructured surfaces could help to optimize the surface of future implants. A processing scheme has been developed for fabricating accurately structured Araldite replicas with titanium coating serving as implant imitates suitable for cross-sectioning. Using electron microscopy and immunogold labeling it could be shown that focal contacts of human gingival fibroblasts are formed at the walls and even at the bottom of grooves as narrow as 2 µm and as deep as 2.5 µm.