Effect of minor amounts of ß-calcium pyrophosphate and hydroxyapatite on the physico-chemical properties and osteoclastic resorption of ß-tricalcium phosphate cylinders.

ß-Tricalcium Phosphate (ß-TCP), one of the most used bone graft substitutes, may contain up to 5 wt% foreign phase according to standards. Typical foreign phases include ß-calcium pyrophosphate (ß-CPP) and hydroxyapatite (HA). Currently, the effect of small amounts of impurities on ß-TCP resorption is unknown. This is surprising since pyrophosphate is a very potent osteoclast inhibitor. The main aim of this study was to assess the effect of small ß-CPP fractions (<1 wt%) on the in vitro osteoclastic resorption of ß-TCP. A minor aim was to examine the effect of ß-CPP and HA impurities on the physico-chemical properties of ß-TCP powders and sintered cylinders. Twenty-six batches of ß-TCP powder were produced with a Ca/P molar ratio varying between 1.440 and 1.550. Fifteen were further processed to obtain dense and polished ß-TCP cylinders. Finally, six of them, with a Ca/P molar ratio varying between 1.496 (1 wt% ß-CPP) and 1.502 (1 wt% HA), were incubated in the presence of osteoclasts. Resorption was quantified by white-light interferometry. Osteoclastic resorption was significantly inhibited by ß-CPP fraction in a linear manner. The presence of 1% ß-CPP reduced ß-TCP resorption by 40%, which underlines the importance of controlling ß-CPP content when assessing ß-TCP biological performance.

[The chemical solubility and stability of low-melting dental porcelains]. / Chemische Löslichkeit und Festigkeit von niedrigschmelzenden Dentalporzellanen.

The aim of this investigation was to study the chemical solubility of 3 new low-fusing ceramics (Duceram-LFC, Duceragold and Vita Omega 800) in comparison with a conventional PFM-ceramic (Vita Omega) together with different surface treatments. Additionally, the three-point flexure strengths were measured. Although the test conditions were very stringent in comparison to the standard solubility test, all ceramics comply with ISO/DIS 6872 specifications, and are thus deemed to be well tolerated in the oral environment. Vita Omega demonstrated the lowest chemical solubility. Mechanical polishing of the surfaces of LFC and Duceragold ceramics produced lower solubility results as compared to glazing. Vita Omega and Omega 800 behaved contrarily. After repeated hydrolysis testings Ducera-LFC demonstrated the highest disintegration resistance. The three-point flexure strengths of low-fusing ceramics were generally higher than that of the conventional PFM-ceramic. As opposed to the other ceramic materials tested, the flexure strength of Duceram-LFC increased significantly after hydrolysis testing.

[Clinical study of zirconium oxide bridges in the posterior segments fabricated with the DCM system]. / Klinische Studie von Zirkonoxidbrücken im Seitenzahngebiet hergestellt mit dem DCM-System.

Today's dental reconstructive therapeutic concepts require restoration of high esthetic quality and excellent biocompatibility. Full ceramic reconstructions accomplish these requirements but only for anterior teeth and premolars. For all-ceramic bridges the mechanical strength was insufficient to withstand the posterior chewing forces. Frequently the interdental connectors cracked, and the only way to prevent these fractures was to overconture the connectors to a size of approx. 16 mm2. The high-tech ceramic zirconia is a potential alternative for three-to five-unit full ceramic bridges in the functionally loaded posterior segments. Experimental zirconia bridges which were fabricated using the DCM system (Direct Ceramic Machining System at the ETH Zurich, were tested in vitro. The frameworks were digitally enlarged by 20% and were easily milled from a presintered yet porous zirconia blank. After the milling process, the framework was densely sintered and shrank to its original size. Due to these positive in-vitro results a clinical investigation was started. 22 veneered zirconia bridges were luted; 19 molars and 25 premolars were prepared. The connectors, max. 7 mm2, of all these bridges, have been functionally loaded by antagonists. After a mean observation time of 385 days (307 days to 488 days), all 22 bridges did not show any cracks in the framework or in the veneering porcelain. The patients commented particularly on the low heat conduction rate of zirconia. The only endodontic problem which occurred could not be directly connected to the type of bridge framework. The reliability of zirconia bridges in this investigation was connected to the DCM-Process. No statement about other zirconia-systems can be made on the results of this study.

Moisture based three-dimensional printing of calcium phosphate structures for scaffold engineering.

Powder based three-dimensional printing (3DP) allows great versatility in material and geometry. These characteristics make 3DP an interesting method for the production of tissue engineering scaffolds. However, 3DP has major limitations, such as limited resolution and accuracy, hence preventing the widespread application of this method within scaffold engineering [corrected].In order to reduce these limitations deeper understanding of the complex interactions between powder, binder and roller during 3DP is needed. In the past a lot of effort has been invested to optimize the powder properties for 3DP for a certain layer thickness. Using a powder optimized for an 88 µm layer thickness, this study systematically quantifies the surface roughness and geometrical accuracy in printed specimens and assesses their variation upon changes of different critical parameters such as the moisture application time (0, 5, 10 and 20s), layer thickness (44 and 88 µm) and the number of specimens printed per batch (6 and 12). A best surface roughness value of 25 µm was measured with a moisture application time (using a custom made moisture application device mounted on a linear stage carrying the print head) of 5s and a layer thickness of 44 µm. Geometrical accuracy was generally higher for the 88 µm thick layer, due to a less critical powder bed stability. Moisture application enabled 3DP of a 44 µm thick layer and improved the accuracy even for a powder initially optimized for 88 µm. Moreover, recycling of the humidified powder was not only possible but, in terms of reactivity, even beneficial. In conclusion, moisture-based 3DP is a promising approach for high resolution 3DP of scaffolds.