Ultrahigh toughness zirconia ceramics.

The attainment of both high strength and toughness is the ultimate goal for most structural materials. Although ceramic material has been considered for use as a structural material due to its high strength and good chemical stability, it suffers from the limitation of low toughness. For instance, although Y2O3-stabilized tetragonal ZrO2 polycrystals (Y-TZPs) exhibit remarkable toughness among ceramics due to their phase transformation toughening mechanism, this toughness is still much weaker than that of metals. Here, we report Y-TZP-based ceramic materials with toughnesses exceeding 20 MPa m1/2, which is comparable to those of metals, while maintaining strengths over 1,200 MPa. The superior mechanical properties are realized by reducing the phase stability of tetragonal zirconia by tailoring the microstructure and chemistry of the Y-TZP. The proposed ceramic materials can further advance the design and application of ceramic-based structural materials.

61Ni synchrotron radiation-based Mössbauer spectroscopy of nickel-based nanoparticles with hexagonal structure.

We measured the synchrotron-radiation (SR)-based Mössbauer spectra of Ni-based nanoparticles with a hexagonal structure that were synthesised by chemical reduction. To obtain Mössbauer spectra of the nanoparticles without (61)Ni enrichment, we developed a measurement system for (61)Ni SR-based Mössbauer absorption spectroscopy without X-ray windows between the (61)Ni84V16 standard energy alloy and detector. The counting rate of the (61)Ni nuclear resonant scattering in the system was enhanced by the detection of internal conversion electrons and the close proximity between the energy standard and the detector. The spectrum measured at 4 K revealed the internal magnetic field of the nanoparticles was 3.4 ± 0.9 T, corresponding to a Ni atomic magnetic moment of 0.3 Bohr magneton. This differs from the value of Ni3C and the theoretically predicted value of hexagonal-close-packed (hcp)-Ni and suggested the nanoparticle possessed intermediate carbon content between hcp-Ni and Ni3C of approximately 10 atomic % of Ni. The improved (61)Ni Mössbauer absorption measurement system is also applicable to various Ni materials without (61)Ni enrichment, such as Ni hydride nanoparticles.

o-Carborane as an electron-transfer mediator in electrocatalytic reduction.

Electron transfer behavior of 1,2-diphenyl-o-carborane was investigated by cyclic voltammetry (CV). In the presence of 1,2-dibromo-1,2-diphenylethane, a significant catalytic current was observed. The macroscale electrocatalytic reduction of the dibromide using a catalytic amount (1 mol%) of the carborane mediator afforded the desired trans-stilbene in excellent yield.

Electrochemical hydroxylation of organoboron compounds.

Cathodic hydroxylation of organoboron compounds was successfully performed under an oxygen atmosphere, producing the corresponding phenol derivatives with high selectivity and efficiency.

Effects of root morphology on stress distribution at the root apex.

It is thought that the stress concentration at the root apex caused by orthodontic force induces root resorption. The purpose of this study was to investigate stress distribution at the root in cases of deviated root shapes using finite element models (FEMs). To clarify this, five three-dimensional FEMs divided by deviated root shape (normal, short, blunt, bent root apex, pipette shape) were constructed and, experimental orthodontic forces, applied in a vertical (intrusive) and horizontal (lingual) direction to the tooth axis. In the short-root model, significant stress was concentrated at the middle of the root. The blunt-shaped root model showed no significant stress concentration at the root. In the models with a bent or pipette-shaped root, significant stress was concentrated at the root apex. During orthodontic force application, stress concentration was observed in the root of the models with short, bent, and pipette-shaped roots, indicating that attention must be paid to root shape during orthodontic treatment.

The effect of occlusal alteration and masticatory imbalance on the cervical spine.

The characteristics of mandibular lateral displacement include lateral inclination of the occlusal plane and the differences between the right and left masticatory muscles. The aims of this investigation were to compare the mandibular stress distribution and displacement of the cervical spine using three-dimensional finite element models (3D FEM) to simulate masticatory movements and to clarify the association between morphological and functional characteristics and head posture. A symmetrical standard model was produced (model-A). Model-B had higher masticatory muscle strength on the left side, model-C had symmetrical masticatory muscle strength but the occlusal plane was inclined upwards towards the right and model-D had the occlusal plane inclined upwards towards the right with higher masticatory muscle strength on the left side. Model-A showed a completely symmetrical stress distribution pattern, while in model-B there was an uneven distribution in the mandible with higher stress on the left side. In addition, the stress distribution in the cervical spine was asymmetrical, showing displacement to the right. Model-C showed a similar mandibular tendency to model-B but the opposite tendency in the cervical spine. In model-D, the mandibular stress distribution was markedly asymmetrical, but almost symmetrical in the cervical spine with markedly decreased lateral displacement. These results suggest that lateral inclination of the occlusal plane and imbalance between the right and left masticatory muscles antagonistically act on displacement of the cervical spine, i.e. the morphological and functional characteristics in patients with mandibular lateral displacement may play a compensatory role in posture control.

Stresses on the cervical column associated with vertical occlusal alteration.

The biomechanical effects on cervical vertebral columns (C1-C7) during mastication were calculated using a three-dimensional (3D) finite element method. To verify the biomechanical influences of vertical occlusal alteration to the cervical column, three finite element models (FEM) showing a normal (model A), a steep (model B), and a flat occlusal plane (model C) were constructed. The occlusal stress distribution showed various patterns for the three models; the stress extended to the anterior area as the occlusal plane became steeper. The plots of the stresses on the mid sagittal section of the cervical columns showed different patterns for the three models; the stress converged at the odontoid process in models A and B, whereas the stresses at C7 in model B tended to decrease compared with model A. Concentrated stress was observed at C5 in model C, supporting the hypothesis that vertical occlusal alteration could influence stress distribution in the cervical columns.