In clinical practice, core materials can be exposed after adjustments are made to previously-luted all-ceramic restorations. The purpose of this study was to evaluate the surface roughness of five different dental ceramic core materials after grinding and polishing. Five different ceramic core materials, Vita In-Ceram Alumina, Vita In-Ceram Zirconia, IPS Empress 2, Procera AllCeram, and Denzir were evaluated. Vita Mark II was used as a reference material. The surface roughness, Ra value (mum), was registered using a profilometer. The measurements were made before and after grinding with diamond rotary cutting instruments and after polishing with the Sof-Lex system. The surface of representative specimens was evaluated qualitatively using scanning electron microscopy (SEM). Results were statistically analysed using analysis of variance (anova) supplemented with Scheffè's and Bonferroni multiple-comparison tests. Before grinding, Procera AllCeram and Denzir had the smoothest surfaces, while IPS Empress 2 had the coarsest. After grinding, all materials except IPS Empress 2 became coarser. Polishing with Sof-Lex provided no significant (P > 0.05) differences between Denzir, Vita Mark II and IPS Empress 2 or between Procera AllCeram and In-Ceram Zirconia. There were no significant differences (P > 0.05) either between the ground and the polished Procera AllCeram or In-Ceram Alumina specimens. Polishing of Denzir, IPS Empress 2 and In-Ceram Zirconia made the surfaces smoother compared with the state after grinding, whereas the polishing effect on Procera AllCeram and In-Ceram Alumina was ineffective. The findings of the SEM evaluation were consistent with the profilometer readings.

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The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.

The purpose of this study is to evaluate functionalized multiwalled carbon nanotubes (fMWCNTs) as a potential coating material for dental zirconia from a biological perspective: its effect on cell proliferation, viability, morphology, and the attachment of an osteoblast-like cell. Osteoblast-like (Saos-2) cells were seeded on uncoated and fMWCNT-coated zirconia discs and in culture dishes that served as controls. The seeding density was 104 cells/cm2, and the cells were cultured for 6 days. Cell viability, proliferation and attachment of the Saos-2 cells were studied. The results showed that Saos-2 cells were well attached to both the uncoated and the fMWCNT-coated zirconia discs. Cell viability and proliferation on the fMWCNT-coated zirconia discs were almost the same as for the control discs. Better cell attachment was seen on the fMWCNT-coated than on the uncoated zirconia discs. In conclusion, fMWCNTs seem to be a promising coating material for zirconia-based ceramic surfaces to increase the roughness and thereby enhance the osseointegration of zirconia implants.

In this study, a numerical approach to the fracture behavior in a three-unit zirconia-based fixed partial denture (FPD) framework was made under mechanical loading using a newly developed three-dimensional (3D) numerical modeling code. All the materials studied were treated heterogeneously and Weibull distribution law was applied to describe the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized to judge whether the material was in an elastic or failed state. For validation, the fracture pattern obtained from the numerical modeling was compared with a laboratory test; they largely correlated with each other. Similar fracture initiation sites were detected both in the numerical simulation and in an earlier fractographic analysis. The numerical simulation applied in this study clearly described the stress distribution and fracture process of zirconia-based FPD frameworks, information that could not be gained from the laboratory tests alone. Thus, the newly developed 3D numerical modeling code seems to be an efficient tool for prediction of the fracture process in ceramic FPD frameworks.

Aim:The aim of the present study was to evaluate the shear bond strength of zirconia, stabilised with 5% yttria, luted to enamel and to evaluate the fracture pattern at loss of retention. Methods: A total of 53 test specimen were manufactured from two partially stabilised zirconia materials, Zirkonzahn Prettau Anterior (ZPA) (n ¼ 16) and Whitepeaks CopraSmile Symphony 5 layer (WCS) (n ¼ 18), and a lithium disilicate (Ivoclar e.Max Press) (n ¼ 19) acting as control. All test specimens were cemented to human enamel with Variolink Esthetic DC and then subjected to a shear bond strength test. Fracture and surface analysis were performed using light and scanning electron microscope. Results: No significant differences in shear bond strength were detected when analysing the three groups. Dividing them according to the fracture pattern significant difference in shear bond strength between the two zirconia groups could be seen analysing test bodies with failure of adhesion to the test body, but not to enamel. The ZPA had higher shear bond strength (23.68 MPa) than WCS (13.00 MPa). No significant differences were seen compared to the control group (19.02 MPa).Conclusion: Partially stabilised zirconia shows potential as a material to be used where macro mechanical bonding is not possible, although this study does not reveal how or if the bonding deteriorates over time. ARTICLE HISTORY

Zirconia is known for its high strength but lacking translucency. Recently, a new type of high translucent zirconia, 5 mol% yttria partially stabilized zirconia (5Y-PSZ), with a larger fraction of cubic zirconia phase has become commercially available. However, the resistance to aging of these commercially available zirconia materials is not yet fully established. Purpose: The aim of the present study was to analyze the effects of artificial aging on surface roughness, transparency, phase transformation and biaxial flexural strength of two 5Y-PSZ products, DD cubeX 2 and Prettau Anterior. Materials and methods: The artificial aging was performed in an autoclave under 2 bars of pressure at 134 C for 10 hours, which is estimated to correspond to 30-40 years in vivo. Artificial aging for 10 hours had no significant effect on surface roughness, transparency, or phase transformation for either of the tested materials. Results: DD cubeX 2 had higher mean flexural strength than Prettau Anterior both before and after artificial aging for 10 hours (p < .05). DD cubeX 2 showed, however, a significant reduction in flexural strength after artificial aging (p < .05), whereas Prettau Anterior showed a slight increase in flexural strength after artificial aging but not at a significant level. Conclusion: Within the limitation of the present study, both DD cubeX 2 and Prettau Anterior seems to be relatively resistant to aging. However, a wider range of measured flexural strength indicated that Prettau Anterior probably is a less stable material than DD cubeX 2 , which also means that the flexural strength of DD cubeX 2 could be more predictable.

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