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A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods--nuts, seeds, and root vegetables--were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads. Am J Phys Anthropol 140:643-652, 2009. KEY WORDS hardness; elastic modulus; fallback foods; fracture mechanics; bite force DOI 10.1002/ajpa.21026

The expanding shark fin market has resulted in intensive global shark fishing and with 90% of teleost fish stocks over-exploited, sharks have become the most lucrative target. As predators, they have high ecological value, are sensitive to fishing pressure, and are in decline, but the secretive nature of the fin trade and difficulties obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers pay high prices with little interest in sustainability or legal trade. Thus, market demand will continue to fuel the shark hunt and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as exemplified by the case of the shortfin mako shark, and claims that sharks can be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet's aquatic ecosystems, sharks and their habitats must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for the protection of biodiversity in general is what is needed. [ABSTRACT FROM AUTHOR]

The article focuses on Caveat emptor when purchasing dental products online.

To clarify the terminology and its application in the context of materials placed in contact with tissues in living systems. Review the nature of both the biological and chemical reactions occurring in such contexts with a view to a classification of types of behaviour and thus types of material. A range of types of behaviour was identified with clear diagnostic characteristics. Materials could thus be classified accordingly, with the possibility of more than one type of behaviour being exhibited. 'Bioactivity' was concluded to depend solely on the modulation of a natural biological process, but excluding pharmaceutical action. Clarity in the characterisation and labelling of materials and their behaviours in biological systems will benefit the interpretation of the literature, the design of experiments, and future research directions. [ABSTRACT FROM AUTHOR]

Bismuth(III) oxide is included as a radio-opacifier in dental materials, including hydraulic silicate cements, the material of choice for several endodontic procedures. It has been implicated in tooth discoloration after contact with endodontic irrigants, in particular NaOCl solution, To date, there has been no work on the chemistry: all reports have been of clinical findings only. The purpose now was to report the reactions leading to colour change from Bi2O3 in contact with solutions used in routine endodontic practice. Ten-gram portions of Bi2O3 were immersed in either water, NaOH, NaCl, NaOCl or HCl solution, either in the dark or exposed to visible light, and samples retrieved at 1, 4, 12 and 24 weeks. After washing, these were exposed to either added CO2 or not, for 1 week while drying, and under the same dark or light conditions. Changes in appearance were monitored by photography and colour measurement, and chemically by X-ray diffraction and Fourier-transform infrared spectroscopy. 24-week material was studied using electron paramagnetic resonance and Raman spectroscopy; NaOCl-treated material was also examined by scanning electron microscopy. With water, NaCl and NaOH, bismuth subcarbonate was formed. With or without added carbon dioxide, discoloration occurred from pale yellow to light brown when exposed to light, and to a lesser extent in the dark, intensifying with time. In contrast, exposure to NaOCl rapidly formed a dark brown-black sodium bismuthate. With HCl, white BiOCl was formed. Bi2O3 is not at all inert in this context as is commonly believed, denying its principle of use. Previously unreported solution-mediated reaction occurs readily even in water and NaCl solution, forming new compounds that discolour. In contact with NaOCl sodium bismuthate is formed; severe darkening occurs rapidly. The reactivity is such that Bi2O3 is not indicated for dental materials and should be withdrawn from use. [ABSTRACT FROM AUTHOR]

A method proposed for determining the fracture toughness (FT) of dental materials involves a 'roller' wedging open a V-notch in a cylindrical specimen. There are a number of problems with the design of this test and its mechanical analysis, and thus with the validity of the results obtained, were it to be used. Firstly, friction is ignored in calculating the horizontal wedging force. Secondly, the test specimen does not make use of a pre-crack at the notch tip. The aim of this study was to evaluate the effects of these factors on the FT calculated. An analytical solution for the mode-I stress intensity factor (K I) of the compact tension specimen, which bears some similarities, is taken to be applicable. The mechanics of the specimen has been reanalysed, with a finite-element study of the resultant stresses, and compared with the compact-tension test. The assumed analytical solution can provide accurate estimates for K I for the V notched specimen. However, the apparent agreement is due to the fortuitous combination of an overestimated horizontal wedging force and an underestimated stress singularity at the crack tip. In any case, ignoring friction will lead to an overestimate of FT. It is concluded that the test as presented is invalid. [ABSTRACT FROM AUTHOR]

As an abundant cation in the human body, magnesium plays important roles in physiological and pathological processes. In particular, magnesium deficiency is associated with osteoporosis. Hence, Mg may be involved in the biodegradation and reconstruction of bone mineral. Previously, Mg-containing hydroxyapatite (HAp) has been synthesized as a model for bone mineral, and its properties, such as crystal size and crystallinity, have been examined. However, the effect of solution magnesium on the effective solubility of hydroxyapatite has not been studied in detail. Here, for a series of magnesium concentrations in the background solution, the mass solubility of hydroxyapatite was determined through the solid titration method at pH 3-5 and 37 °C. A general, quasilogarithmic increase in solubility was found with increasing magnesium concentration. Whether this is due to nucleation inhibition or solution complexation has yet to be ascertained, although the latter is likely on simple chemical grounds. As the direct effect of magnesium was to increase the solubility of HAp in a concentration-dependent manner, this cannot be the direct cause of osteoporosis in the event of magnesium deficiency. [ABSTRACT FROM AUTHOR]

Well-crystallized, compositionally homogeneous HA whiskers with uniform morphology and high aspect ratio were successfully prepared by hydrothermal homogeneous precipitation from aqueous solution using acetamide (AA). The product had a mean length of 116 μm and an aspect ratio of 102. The nucleation and crystal growth of such whiskers were studied by quenching the solution from various temperatures. It was found that the nuclei could be formed at about 120°C, while stable and well-grown whisker-like precipitation only occurred above 140°C. The product had the same crystallographic characteristics as normal HA crystals. No other phase than HA was detected. Compared with widely used wet chemical routes, the slow hydrolysis of AA provided a stable and continuous growth environment with a low degree of supersaturation, facilitating rapid growth of long HA whiskers directly from a hydrothermal solution, free of any interference from other phases. The whiskers showed spiral growth, with preferential c-axis orientation. [ABSTRACT FROM AUTHOR]

Carbonate is present in biological apatites (BAp) (enamel, dentine, bone, and pathological calcifications) by substitution at phosphate and hydroxide sites, tending to increase its solubility in comparison with pure hydroxyapatite (HAp). The role of solution carbonate, however, is poorly understood. Using the solid titration method, it was found that the apparent solubility of HAp increased greatly with an increase in pCO2, and was sensitively-dependent at low values. No other phase was formed at the end point except HAp, and in particular no dicalcium phosphate dihydrate (DCPD) was found. However, no carbonate was detected in the end-point solid except for a small amount at pH ∼ 7.4, pCO2 = 0.01−1.0 bar. The implications of these results need further investigation, bearing as they do on a central topic in oral chemistry. The solubility of hydroxyapatite (HAp) increases greatly with increase in pCO2 (0.01−1.0 bar), and was found to be sensitively dependent at low values, implying risks from atmospheric contamination in other studies. No carbonate was detected in end-point solid (always HAp) except for a small amount at pH ∼ 7.4. Solution complexes account for the solubility, while biological apatite must be formed under other conditions. [ABSTRACT FROM AUTHOR]

The simplistic approach to mechanical testing routinely employed in dental research does not recognize the many factors that influence the outcome, not least the non-existence of strength as a true material property. The roles of test time-scale, environmental interaction, and internal changes need evaluation. However, service conditions also involve multiple loading cycles which interact with other processes, while 'episodic' challenges are altogether outside the normal frame of testing. The case is made for testing that allows for dynamic damage-accumulation through a survival-curve approach. [ABSTRACT FROM AUTHOR]

The bioactivity of a novel composite of carbonate-containing low-crystallinity nanoparticle hydroxyapatite (HA) and a chitosan-phosphorylated chitosan polyelectrolyte complex (PEC) was evaluated in vitro and in vivo. The HA-PEC nanocomposite with complicated porous structure was prepared by a biomimetic method. An acidic chitosan (polycation) solution containing calcium and phosphate ions (6mM Ca2+, Ca/P : 1.67) was added into phosphorylated chitosan (polyanion) solution; the formation of PEC and the controlled HA crystal growth were co-organized in alkaline solution. The material was co-cultured with rat osteoblasts in vitro, and implanted into rabbit femur marrow cavities. The results indicate that the PEC-HA composite promoted osteoblast adhesion, morphology, proliferation, and differentiation in vitro; the bone tissue response to the material histologically showed that it was bioactive, as well as biodegradable. The HA-PEC composite shows promise as a bone-repair material. [ABSTRACT FROM AUTHOR]

To simulate extra‐cellular matrix, a novel three‐dimensional scaffold of polyelectrolyte complex (PEC) hydrogel as an osteoblast carrier was synthesized. First, chitosan, a natural glycosaminoglycan, was modified by phosphorylation to obtain a water‐soluble phosphorylated chitosan (P‐content: 10.7 mass%). The PEC hydrogel was then formed from equal volumes of 0.173 mass% phosphorylated chitosan in water and 1 mass% chitosan in 1% (V/V) acetic acid solution. Rat osteoblasts were seeded in the hydrogel. The PEC hydrogel had a three‐dimensional hierarchically‐porous structure and good cytobiocompatibility for osteoblasts in vitro. It is concluded that the PEC hydrogel is a promising material as an osteoblast carrier. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2007 [ABSTRACT FROM AUTHOR]