Higher Fracture Force Research Articles

The Effect of Restoration Thickness on the Fracture Resistance of 5 mol% Yttria-Containing Zirconia Crowns.

To determine what thickness of 5 mol% yttria zirconia (5Y-Z) translucent crowns cemented with different cements and surface treatments would have equivalent fracture resistance as 3 mol% yttria (3Y-Z) crowns. The study included 0.8 mm, 1.0 mm, and 1.2 mm thickness 5Y-Z (Katana UTML) crowns and 0.5 and 1.0 mm thickness 3Y-Z (Katana HT) crowns as controls. The 5Y-Z crowns were divided among three treatment subgroups (n = 10/subgroup): (1) cemented using RMGIC (Rely X Luting Cement), (2) alumina particle-abraded then luted with the same cement, (3) alumina particle-abraded and cemented using a resin cement (Panavia SA Cement Universal). The 3Y-Z controls were alumina particle-abraded then cemented with RMGIC. The specimens were then loaded in compression at 30° until failure. All 5Y-Z crowns (regardless of thickness or surface treatment) had a similar to or higher fracture force than the 0.5 mm 3Y-Z crowns. Only the 1.2 mm 5Y-Z crowns with resin cement showed significantly similar fracture force to the 1 mm 3Y-Z crowns. In order to achieve a similar fracture resistance to 0.5 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns may be as thin as 0.8 mm. To achieve a similar fracture resistance to 1.0 mm 3Y-Z crowns cemented with RMGIC, 5Y-Z crowns must be 1.2 mm and bonded with resin cement.

Effect of fracture properties of gels on tongue pressure during different phases of squeezing and swallowing.

To provide appropriate foods for elderly people with eating difficulties, it is necessary to take account of the ability of compensatory mastication such as tongue squeezing. However, the biomechanics of tongue squeezing is still unclear. The aim of present study is to investigate the effect of the initial mechanical properties of gels on the change in tongue pressure production during squeezing and swallowing. As test sample, nine kinds of gels with three fracture force and three fracture strain were prepared. Tongue pressure during squeezing and swallowing gels was measured by using an ultra-thin tongue pressure sensor with five measuring points attached on the hard palate in seven healthy participants, and analyzed at four phases; Initial squeeze, Middle squeeze, Last squeeze, and Swallowing. The maximal magnitude of tongue pressure was increased for gels with higher fracture force at most measuring points and was decreased for gels with higher fracture strain at some measuring points on the median line during Initial and Middle squeezing. However, no influence by fracture force and strain was found in magnitude during Last squeezing and Swallowing. The duration of tongue pressure increased for gels with higher force at most measuring points during Middle squeezing, although no influence by strain was found during each phase. The results clearly show how the initial fracture properties of gels influence on tongue pressure production during each phase of food oral processing, which clarified one aspect of squeezing with tongue, as the compensatory mastication.

Assessment of fracture force of CAD-CAM-fabricated overlay restorations using deep marginal elevation technique.

ABSTRACT Purpose To evaluate the fracture force of CAD-CAM-fabricated overlay restorations (Feld spathic cerec blocks) and hybrid ceramic material (VITA Enamic) using deep marginal elevation technique (DME). Materials and methods Twenty overlay restorations were constructed in this study. The samples were divided into two main groups according to the ceramic material (n=10). The type of ceramics that was used is (feld spathic for group I and vita enamic for group II). a ceramic material which was used (10 samples each):- The first group : feld spathic cerec blocks cemented by RelyX Ultimate Clicker resin cement. The second group: VITA ENAMIC hybrid ceramic overlays cemented by RelyX Ultimate Clicker resin cement. Each main group was subdivided into two subgroups for each type of the ceramic material according to the fracture force (n=5), One of them without deep marginal elevation and the other with a deep marginal elevation (DME) till the cemento-enamel junction (CEJ). Results Between the two materials There was a significant difference between the feld spathic and vita enamic materials in with and without deep marginal elevation technique . Conclusion VITA Enamic material has higher fracture force than feld spathic material in samples with deep marginal elevation. Feld spathic material has higher fracture force than vita enamic material in samples without (DME).

Plasticity of biometrical and mechanical properties of Echinocardium cordatum spines according to environment

We investigated the plasticity of spines of the burrowing heart urchin Echinocardium cordatum inhabiting sandy beaches. This urchin has very specialized spines which play specific roles in feeding and locomotion. Biometrical and mechanical properties of the spine skeleton of individuals from a wave-exposed intertidal site and a protected subtidal site (Brittany, France) were compared and related to sediment grain size, food supply and urchin small-scale distribution and burrowing depth. The intertidal site was characterized by coarser sand; the urchins were more scattered and more deeply buried than in the subtidal site. Intertidal urchins were bigger than subtidal urchins but showed similar resource allocation. Spines of intertidal urchins were longer than those of subtidal urchins, their architecture was reinforced and they presented a higher fracture force and stiffness. These spine differences would be essentially due to passive plasticity, but could also be adaptative at a certain extent.

Fracture Properties and Microstructure of Low-Moisture Starch Probes

Different microstructures were induced in thin rectangular sheets of a pregelatinized starch gel by drying in an air oven at 5 different temperatures (range 65–105°C) and by freeze drying. As drying temperature increased, air-dried probes (ADP) varied from thin, dense, and transparent to thick, cellular, and translucent, and the presence of larger air cells became more evident. Freeze-dried probes (FDP) were porous, white, and exhibited minimal shrinkage. Most samples exhibited a brittle-type fracture pattern in the range 0.0 < aw < 0.75. FDP had much higher fracture force (FF, three-point bending test) than ADP. FF increased sharply between aw 0.44 and 0.65 for ADP but not for FDP. Light and environmental electron scanning microscopy (ESEM) were used to study the morphology and microstructure of dried probes (thickness and air cells). This work suggests that drying conditions and the microstructural features derived thereof have a larger influence on fracture properties of the starchy material than the glass transition temperature.

High-intensity exercise of short duration alters bovine bone density and shape.

The ability of short-duration high-intensity exercise to stimulate bone formation in confinement was investigated using immature Holstein bull calves as a model. Eighteen bull calves, 8 wk of age, were assigned to one of three treatment groups: 1) group-housed (GR, which served as a control), 2) confined with no exercise (CF), or 3) confined with exercise (EX). The exercise protocol consisted of running 50 m on a concrete surface once daily, 5 d/wk. Confined calves remained stalled for the 42-d duration of the trial. Blood samples were taken to analyze concentrations of osteocalcin and deoxypyridinoline, markers of bone formation and resorption. At the completion of the trial, calves were humanely killed, and both forelegs were collected. The fused third and fourth metacarpal bone was scanned using computed tomography for determination of cross-sectional geometry and bone mineral density. Three-point bending tests to failure were performed on metacarpal bones. The exercise protocol resulted in the formation of a rounder bone in EX as well as in increased dorsal cortex thickness compared with those in the GR and CF. The exercised calves had a significantly smaller medullary cavity than CF and GR (P < 0.01) and a larger percentage of cortical bone area than CF (P < 0.01). Dorsal, palmar, and total bone mineral density was greater in EX than in CF (P < 0.05), and palmar and total bone mineral densities were greater (P < 0.05) in EX than in GR. There was a trend for the bones of EX to have a higher fracture force than CF (P < 0.10). Osteocalcin concentrations normalized from d 0 were higher in EX than CF (P < 0.05). Therefore, the exercise protocol altered bone shape and seemed to increase bone formation comparison with the stalled and group-housed calves.

Would Diamond Nanorods Be Stronger than Fullerene Nanotubes?

On the basis of literature ab initio data, we show that diamond nanorods would have a brittle fracture force and a zero strain stiffness that exceeds carbon nanotubes for radii greater than about 1-3 nm, depending on the orientation of the diamond nanorod. The energetic stability of diamond nanorods is predicted by molecular modeling to be comparable to single-walled carbon nanotubes. It is concluded that diamond nanorods represent an important and viable target structure for synthesis. With its exceedingly high bulk modulus and hardness, diamond has historically been considered the strongest material. Recently, however, it has been claimed based on both theory and experiment that carbon nanotubes are both stiffer and stronger along their axis than diamond. A problem with this claim is that it is difficult to make a fair comparison between these two representatives from the macro- and nanoscales unless some additional assumptions about their structure are made, for example an effective “thickness” of a sheet of carbon atoms comprising a nanotube. In this paper the mechanical properties of single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs) are compared to the predicted properties of an equivalent nanoscopic-scale diamond structure, namely a diamond nanorod (DNR). Our general analysis suggests that while a SWNT will have a higher strength-to-weight ratio, above a critical radius between about 1 and 3 nm (depending on the DNR structure) the force needed for brittle fracture of a DNR exceeds that of a SWNT. This higher fracture force, which at the nanoscopic scale is a less ambiguous property than fracture stress, results from the larger load-bearing crosssectional area of DNRs compared to SWNTs at the same diameter. Similarly, the calculations show that the zero strain stiffness of DNRs will exceed that of SWNTs for radii greater than about 1 nm. Experimental loading of SWNTs in ropes has yielded estimates for the tensile Young’s modulus that range from 320 GPa to 1.47 TPa, 1 and breaking strengths that range from 13 to 52 GPa (a strain of up to almost 6%), 1 values that