Is titanium-zirconium alloy a better alternative to pure titanium for oral implant? Composition, mechanical properties, and microstructure analysis.

INTRODUCTION: Titanium (Ti) is widely accepted as a biomaterial for orthopaedic and dental implants, primarily due to its capacity to integrate directly into the bone and its superior corrosion resistance. It has been suggested that titanium-zirconium alloy (TiZr), with 13-17% of zirconium, has better mechanical properties than pure Ti, but there are very few published studies assessing the suitability of TiZr for high-load- bearing implants. This study aimed to compare the mechanical properties and microstructures of TiZr and commercially pure titanium (Ti). METHODOLOGY: Pure Ti and TiZr alloy discs were prepared and subjected to characterisation by nanoindentation, electron dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). RESULTS: The TiZr alloy was found to have significantly lower elastic modulus value (p < 0.0001) and greater hardness than Ti (p < 0.05). The EDS results confirmed the presence of Zr (13-17%) in the TiZr alloy, with XRD and EBSD images showing microstructure with the alpha phase similar to commercially available Ti. CONCLUSION: The lower elastic modulus, higher hardness, presence of alpha phase, and the finer grain size of the TiZr alloy make it more suitable for high-load-bearing implants compared to commercially available Ti and is likely to encourage a positive biological response.

Porcelain bonding to novel Co-Cr alloys: Influence of interfacial reactions on phase stability, plasticity and adhesion.

OBJECTIVE: The objective of the present study was to determine the hardness and adhesion strength at the porcelain to alloy interface. METHODS: 15 bi-layer porcelain veneered Co-Cr specimens of each alloy group [cast, powder metallurgy (PM), CAD/CAM(CC)] were manufactured. 12 bi-layered specimens were tested using four-point bend strain energy release rate adhesion test. One before and after porcelain firing specimen of each alloy group were nano-indented at the bulk and metal-porcelain interface to determine the mechanical properties. Electron backscatter diffraction was used to determine the microstructure and phase of the indented areas. RESULTS: The results obtained from the four-point bend strain energy release rate test indicated highest adhesion energy of 92.15J/m2 observed in the CC produced Co-Cr alloy. This was followed by the PM alloy with an adhesion energy of 62.24J/m2 and cast alloy with an adhesion energy of 42.83J/m2. All comparisons of adhesion energy between the three alloys were found to be statistically significant (p<.05). Nano-indentation test indicated higher hardness values of 4.6-6.1GPa at the metal-porcelain interface compared to the bulk, which had hardness values of 3.1-3.9GPa. SIGNIFICANCE: The adhesion of the alloy to porcelain was found to be inversely related to the hardness of the interfacial layer at the alloy surface. Lower interfacial hardness was found to be accompanied with higher adhesion energy due to the additional plastic energy consumed during crack propagation along the more ductile interface region of the alloy.

Comparison of the microstructure and phase stability of as-cast, CAD/CAM and powder metallurgy manufactured Co-Cr dental alloys.

OBJECTIVE: The objective of this study was to identify the different microstructures produced by CC, PM and as-cast techniques for Co-Cr alloys and their phase stability following porcelain firings. METHODS: Three bi-layer porcelain veneered Co-Cr specimens and one monolithic Co-Cr specimen of each alloy group [cast, powder metallurgy (PM), CAD/CAM (CC)] were manufactured and analyzed using electron backscatter diffraction (EBSD), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Specimens were treated to incremental numbers of porcelain firings (control 0, 5, 15) with crystallographic data, grain size and chemical composition subsequently obtained and analyzed. RESULTS: EBSD datasets of the cast alloy indicated large grains >200 µm whereas PM and CC alloy consisted of mean arithmetic grain sizes of 29.6 µm and 19.2 µm respectively. XRD and EBSD results both indicated the highest increase in hcp content (>13vol%) for cast Co-Cr alloy after treatment with porcelain firing while PM and CC indicated <2vol% hcp content. A fine grain interfacial layer developed on all surfaces of the alloy after porcelain firing. The depth of this layer increased with porcelain firings for as-cast and PM but no significant increase (p>.05) was observed in CC. EDS line scans indicated an increase in Cr content at the alloy surface after porcelain firing treatment for all three alloys. SIGNIFICANCE: PM and CC produced alloy had superior fcc phase stability after porcelain firings compared to a traditional cast alloy. It is recommended that PM and CC alloys be used for porcelain-fused-to-metal restorations.

Influence of a tungsten metal conditioner on the adhesion and residual stress of porcelain bonded to cobalt-chromium alloy.

STATEMENT OF PROBLEM: Cobalt-chromium (CoCr) metal ceramic restorations are known to be more susceptible to cracking and interfacial failures. This is partially related to their high potential for oxidation compared with restorations made with high noble alloys. One approach that may improve their compatibility is the use of bonding agents. PURPOSE: The purpose of this study was to investigate the influence of a tungsten metal conditioner on the adhesion and residual stress of porcelain bonded to a cobalt-chromium alloy. MATERIAL AND METHODS: Eighty-one metal-porcelain bilayered specimens were manufactured and tested with a 4-point bend for adhesion and with Vickers indentation for residual stress determination. The strain energy release rate for adhesion energy and indentation residual stress was evaluated for specimens layered with and without tungsten (W) metal conditioner. Subsequent scanning electron microscopy and energy dispersive spectrometry were performed to identify fracture behavior and chemical and phase compositions. RESULTS: The average strain energy release rate of the specimen group tested without the W metal conditioner was significantly higher (P<.05) (44.70 J/m(2)) than that of the group with the W metal conditioner (28.65 J/m(2)). The average residual stress of the specimen group with (0.1 MPa) and without (1.61 MPa) the W metal conditioner did not differ significantly. Scanning electron microscopy and energy dispersive spectrometry analysis enabled the modes of failure to be determined and indicated the mechanisms by which the W metal conditioner influenced the bond. CONCLUSIONS: The W metal conditioner used in this study significantly lowered the strain energy release rate of the porcelain-cobalt-chromium interface and did not have a significant influence on the residual stress state of the porcelain.

Effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.

OBJECTIVE: To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain. METHODS: The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior. RESULTS: The strain energy release rate for debonding of the VM9 specimens were significantly higher (p<0.05) compared to the Zirox specimens across all test groups. Increasing autoclave cycles lowered the strain energy release rate significantly (p<0.05) from 18.67 J/m(2) (control) to the lowest of 12.79 J/m(2) (cycle 10) for only the VM9 specimens. SEM analyses showed predominant cohesive fracture within the porcelain for all cycle groups. XRD analysis of the substrate prior to veneering confirmed a tetragonal to monoclinic phase transformation with increasing the number of autoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20). SIGNIFICANCE: Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal.

Bang! Month-scale eruption triggering at Santorini volcano.

The time lag between intrusion of fresh, hot magma and an ensuing eruption is of critical importance in both understanding the triggering and mitigating the consequences of volcanic eruptions. This work looks at material erupted during 1925-28 at the Nea Kameni volcanic center in Santorini, Greece, to determine this time scale. By exploiting Fe-Mg diffusion in olivine crystals, we constrained the intrusion-to-eruption time lag to between 3 and 10 weeks. These techniques have potential application at many volcanic centers; previously erupted material can be used to calibrate records of the short-time scale processes common to many volcanic centers.

Morphological analyses of minute crystals by using stereo-photogrammetric scanning electron microscopy and electron back-scattered diffraction.

We present a new method for the morphological analyses of minute faceted crystals by combining stereo-photogrammetric analysis of scanning electron microscope images and electron back-scattered diffraction. Two scanning electron microscope images of the same crystal, recorded at different tilt angles of the specimen stage, are used to determine the orientations of crystal edges in a specimen-fixed coordinate system. The edge orientations are converted to the indices [uvw] in the crystal system using the crystal orientation determined by electron back-scattered diffraction analysis. The Miller indices of crystal facets are derived from the indices of the edges surrounding the facets. The method is applicable to very small crystal facets. The angular error, as derived from tests using a calcite crystal of known morphology, is a few degrees. To demonstrate the applicability of the method, the morphology of boehmite (gamma-AlOOH) precipitated from solution during the dissolution of anorthite was analyzed. The micrometre-sized boehmite crystals are surrounded by two {010} basal facets and eight equivalent side facets that can be indexed equally well as {323}, {434} or {545}. We suggest that these side facets are in fact {111}, the morphology having been modified slightly (by a few degrees) by a small extension associated with opening along (010) microcleavage planes. Tiny {140} facets are also commonly observed.