The effect of surface treatments on the adhesive bond in all-ceramic dental crowns using four-point bending and dynamic loading tests

The aim of this study was to determine the effect of sandblasting, grinding and plasma treatment on the adhesive bond strength between framework ceramic (Y-TZP) and veneering ceramic (feldspar ceramic). Therefore, four-point bending specimens (n = 180) were cut from densely sintered 3Y-TZP blanks. Subsequently, 80 of these samples received surface treatment by sandblasting and 80 samples by grinding. A reference group (20 samples) was not processed. Half of the specimens that received a surface treatment were additionally exposed to an oxygen plasma treatment. After processing, all specimens were manually veneered with feldspar ceramic and examined with a four-point bending test to evaluate the strain energy release rate G. The surface treatment parameters that achieved the highest and lowest G were transferred to real geometries of a posterior crown (n = 45). The crowns' ceramic framework was sandblasted and veneered by hand. The all-ceramic crowns were tested in a dynamic loading test and Wöhler curves were evaluated. Four-point bending samples blasted at an angle of 90° at 6 bar and a working distance of 1.5 cm without plasma treatment achieved the highest energy release rate. Samples blasted at an angle of 90° at 2 bar and a working distance of 1 cm with plasma treatment achieved the lowest energy release rate. Overall, plasma treatment did not improve bond strength. In the dynamic loading test, the group blasted with 2 bar showed the best results.

Effect of sandblasting on the surface roughness and residual stress of 3Y-TZP (zirconia)

A defined surface roughness is important for the adhesive bonding of veneering ceramic to zirconia frameworks. Thus, we investigated the effects that sandblasting has upon the surface roughness and residual stress of zirconia. So as to achieve well-defined blasting parameters and also generate highly reproducible results; a custom-made, automated sandblasting machine was constructed (based on a 3D-printer construction kit). Thirty-two samples (measuring 30 mm × 35 mm × 0.2 mm) were cut from densely sintered 3Y-TZP blanks and then ground with a 45 µm grinding disc. After undergoing regeneration firing, the samples were sandblasted with varying working parameters: blasting angle (45°, 60° and 90°); blasting pressure (2 bar, 4 bar and 6 bar); and working distance (0.5 cm, 1.0 cm and 1.5 cm). The sandblasting path was chosen so as to create samples with an even surface roughness. Changes in blasting pressure resulted in the greatest changes in the surface roughness, the highest surface roughness values were achieved with sandblastings perpendicular to the sample surface. Furthermore, a correlation was found between the mean surface roughness and the residual stress.

Ancistroguineines A and B as well as ancistrotectorine-naphthylisoquinoline alkaloids from Ancistrocladus guineënsis

The isolation of three naphthylisoquinoline alkaloids from the leaves of Ancistrocladus guineënsis is described. Their complete structures were established by spectroscopic, chiroptical and degradative methods. Thus, two hitherto unknown 5,8'-coupled naphthylisoquinoline, named ancistroguineines A and B, were isolated, constituting the first example of a pair of 3-epimeric naphthylisoquinoline alkaloids. Moreover, ancistrotectorine, a 7,3'-coupled alkaloid previously known only from the South-East Asian species Ancistrocladus tectorius, was isolated. Its absolute stereostructure was confirmed by oxidative degradation and by comparison of experimental and calculated CD spectra.