Multifunctional Hybrid Material for Endoprosthetic Implants Based on Alumina-Toughened Zirconia Ceramics and Additively Manufactured TiNbTa Alloys

Aseptic implant loosening after a total joint replacement is partially influenced by material-specific factors when cobalt-chromium alloys are used, including osteolysis induced by wear and corrosion products and stress shielding. Here, we aim to characterize a hybrid material consisting of alumina-toughened zirconia (ATZ) ceramics and additively manufactured Ti-35Nb-6Ta (TiNbTa) alloys, which are joined by a glass solder. The structure of the joint, the static and fatigue shear strength, the influence of accelerated aging, and the cytotoxicity with human osteoblasts are characterized. Furthermore, the biomechanical properties of the functional demonstrators of a femoral component for total knee replacements are evaluated. The TiNbTa-ATZ specimens showed a homogenous joint with statistically distributed micro-pores and a slight accumulation of Al-rich compounds at the glass solder-TiNbTa interface. Shear strengths of 26.4 ± 4.2 MPa and 38.2 ± 14.4 MPa were achieved for the TiNbTa-ATZ and Ti-ATZ specimens, respectively, and they were not significantly affected by the titanium material used, nor by accelerated aging (p = 0.07). All of the specimens survived 107 cycles of shear loading to 10 MPa. Furthermore, the TiNbTa-ATZ did not impair the proliferation and metabolic activity of the human osteoblasts. Functional demonstrators made of TiNbTa-ATZ provided a maximum bearable extension-flexion moment of 40.7 ± 2.2 Nm. The biomechanical and biological properties of TiNbTa-ATZ demonstrate potential applications for endoprosthetic implants.

Fracture strength of monolithic and glass-soldered ceramic sub-components of 5-unit fixed dental prosthesis

PURPOSE

Zirconium dioxide ceramic has been successfully introduced as a framework material for fixed dental prostheses. To reduce manufacturing constraints, joining of sub-components could be a promising approach to increase the mechanical performance of long-span fixed dental prostheses. In this experimental study, the biomechanical behavior of monolithic and soldered framework specimens for fixed dental prostheses made of Y-TZP was investigated.

MATERIALS AND METHODS

Framework specimens (n  =  80) of 5-unit fixed dental prostheses made of Y-TZP were prepared and divided into 10 equal groups. The specimens were monolithic or composed of sub-components, which were joined using a silicate-based glass solder. Thereby, three joint geometries (diagonal, vertical with an occlusal cap, and dental attachment-based) were investigated. Moreover, the groups differed based on the mechanical test (static vs. dynamic) and further processing (veneered vs. unveneered). The framework specimens were cemented on alumina-based jaw models, where the canine and second molar were acting as abutments, before a point-load was applied. In addition, μCT scans and microscopic fractography was used to evaluate the quality of soldered joints and to determine the causes of fracture.

RESULTS

The determined fracture loads of the different unveneered framework specimens in static testing did not vary significantly (p  =  1). Adding a veneering layer significantly increased the mechanical strength for monolithic framework specimens from 1,196.29 ±203.79 N to 1,606.85 ±128.49 N (p  =  0.008). In case of soldered specimens with a dental attachment-based geometry the mechanical strength increased from 1,159.42 ±85.65 N to 1,249.53 ±191.55 N (p  =  1). Within the dynamic testing, no differences were observed between monolithic and soldered framework specimens. μCT scans and fractography proved that the dental attachment-based joining geometry offers the highest quality.

CONCLUSION

Using glass soldering technology, sub-components of 5-unit framework specimens made of Y-TZP could be joined with mechanical properties comparable to those of monolithic frameworks. This article is protected by copyright. All rights reserved.

New Coating Technique of Ceramic Implants with Different Glass Solder Matrices for Improved Osseointegration-Mechanical Investigations

Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the functionality of a bone implant. We investigated the application of a glass solder matrix in three configurations—consisting mainly of SiO₂, Al₂O₃, K₂O and Na₂O to TZP-A ceramic specimens. The corresponding adhesive strength and surface roughness of the coatings on ceramic specimens have been analyzed. Thereby, high adhesive strength (70.3 ± 7.9 MPa) was found for the three different coatings. The obtained roughness (R_z) amounted to 18.24 ± 2.48 µm in average, with significant differences between the glass solder configurations. Furthermore, one configuration was also tested after additional etching which did not lead to significant increase of surface roughness (19.37 ± 1.04 µm) or adhesive strength (57.2 ± 5.8 MPa). In conclusion, coating with glass solder matrix seems to be a promising surface modification technique that may enable direct insertion of ceramic implants in dental and orthopaedic surgery.

GABAB antagonists: resolution, absolute stereochemistry, and pharmacology of (R)- and (S)-phaclofen

Phaclofen, which is the phosphonic acid analogue of the GABAB agonist (RS)-3-(4-chlorophenyl)-4-aminobutyric acid (baclofen), is a GABAB antagonist. As part of our studies on the structural requirements for activation and blockade of GABAB receptors, we have resolved phaclofen using chiral chromatographic techniques. The absolute stereochemistry of (-)-(R)-phaclofen was established by X-ray crystallographic analysis. (-)-(R)-Phaclofen was shown to inhibit the binding of [3H]-(R)-baclofen to GABAB receptor sites on rat cerebellar membranes (IC50 = 76 +/- 13 microM), whereas (+)-(S)-phaclofen was inactive in this binding assay (IC50 > 1000 microM). (-)-(R)-Phaclofen (200 microM) was equipotent with (RS)-phaclofen (400 microM) in antagonizing the action of baclofen in rat cerebral cortical slices, while (+)-(S)-phaclofen (200 microM) was inactive. The structural similarity of the agonist (R)-baclofen and the antagonist (-)-(R)-phaclofen suggests that these ligands interact with the GABAB receptor sites in a similar manner. Thus, it may be concluded that the different pharmacological effects of these compounds essentially result from the different spatial and proteolytic properties of their acid groups.