First combined electron backscatter diffraction and transmission electron microscopy study of grain boundary structure of deformed quartzite

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.

Adhesion of porcelain to three-dimensionally printed and soft milled cobalt chromium

PURPOSE

To investigate the adhesion strength and bonding interface of layered porcelain to powdered cobalt-chromium (CoCr) processed by two different computer-aided manufacturing methods.

METHODS

Sixteen specimens were manufactured from each of Three-dimensionally -printed/laser-sintered (LS) CoCr and milled pre-sintered (SM) CoCr. The specimens were layered with porcelain and 4-point bending was carried out. Nanoindentation was used to calculate changes in elastic modulus and hardness before and after porcelain firing along with adhesion energy. Fracture surface and microstructural changes were examined before and after porcelain firing observed using scanning electron microscopy.

RESULTS

The adhesion energy of the LS specimens bonded porcelain were higher than the SM specimens (P<0.05). Analysis of the fracture surfaces showed a predominantly adhesive mode of failure. Elastic-modulus and hardness of the CoCr specimens increased post porcelain firing. Examination using electron-backscatter diffraction (EBSD) showed a fine grain structure for both manufacturing methods. Significant localized changes in the crystal structure post firing were only observed at the surface of the SM specimens.

CONCLUSIONS

Both manufacturing methods showed regular microstructures prior to porcelain firing. Laser-sintered CoCr had stronger bonding to porcelain than milled pre-sintered CoCr and was also more stable microstructurally post-ceramic firing. However, both manufacturing methods were deemed to have satisfactory adhesion strength to porcelain. It was also found that increased hardness of CoCr had an inverse relationship with bonding strength. High strength porcelain bonding and stability following multiple ceramic firings indicate suitability for use of these CoCr materials with implant or tooth supported long-span frameworks.

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.