Abdulwahab S. Almusallam

Mechanisms and causes of wear in tooth enamel: implications for hominin diets

The wear of teeth is a major factor limiting mammalian lifespans in the wild. One method of describing worn surfaces, dental microwear texture analysis, has proved powerful for reconstructing the diets of extinct vertebrates, but has yielded unexpected results in early hominins. In particular, although australopiths exhibit derived craniodental features interpreted as adaptations for eating hard foods, most do not exhibit microwear signals indicative of this diet. However, no experiments have yet demonstrated the fundamental mechanisms and causes of this wear. Here, we report nanowear experiments where individual dust particles, phytoliths and enamel chips were slid across a flat enamel surface. Microwear features produced were influenced strongly by interacting mechanical properties and particle geometry. Quartz dust was a rigid abrasive, capable of fracturing and removing enamel pieces. By contrast, phytoliths and enamel chips deformed during sliding, forming U-shaped grooves or flat troughs in enamel, without tissue loss. Other plant tissues seem too soft to mark enamel, acting as particle transporters. We conclude that dust has overwhelming importance as a wear agent and that dietary signals preserved in dental microwear are indirect. Nanowear studies should resolve controversies over adaptive trends in mammals like enamel thickening or hypsodonty that delay functional dental loss.

The Feeding Biomechanics and Dietary Ecology of Paranthropus boisei

The African Plio‐Pleistocene hominins known as australopiths evolved derived craniodental features frequently interpreted as adaptations for feeding on either hard, or compliant/tough foods. Among australopiths, Paranthropus boisei is the most robust form, exhibiting traits traditionally hypothesized to produce high bite forces efficiently and strengthen the face against feeding stresses. However, recent mechanical analyses imply that P. boisei may not have been an efficient producer of bite force and that robust morphology in primates is not necessarily strong. Here we use an engineering method, finite element analysis, to show that the facial skeleton of P. boisei is structurally strong, exhibits a strain pattern different from that in chimpanzees (Pan troglodytes) and Australopithecus africanus, and efficiently produces high bite force. It has been suggested that P. boisei consumed a diet of compliant/tough foods like grass blades and sedge pith. However, the blunt occlusal topography of this and other species suggests that australopiths are adapted to consume hard foods, perhaps including grass and sedge seeds. A consideration of evolutionary trends in morphology relating to feeding mechanics suggests that food processing behaviors in gracile australopiths evidently were disrupted by environmental change, perhaps contributing to the eventual evolution of Homo and Paranthropus. Anat Rec, 298:145–167, 2015.

The Role of Dust, Grit and Phytoliths in Tooth Wear

The threat of wear to dental enamel from hard particles of silica or silicates may have exerted great selective pressure on mammals. Increasing the hardness of enamel helps to forestall this, but capacity for variation is small because the tissue is almost entirely composed of hydroxyapatite. Hard though it is, enamel also displays considerable toughness, which is important in setting the sharpness of particles (defined as an attack angle) necessary to wear it. Added to the threat from environmental silica(tes) are phytoliths, particles of opaline silica embedded in plant tissues. We show here that phytoliths have very different properties to grit and dust and are unlikely to wear enamel. However, phytoliths would tend to fracture between teeth under similar conditions, so resembling natural agents of wear. In this context, we suggest that phytoliths could represent an example of mimicry, forming an example of a feeding deterrent operating by deceit.

Equilibrium, Kinetic, and Thermodynamic Studies on the Biosorption of Selenium (IV) Ions onto Ganoderma Lucidum Biomass

The capacity of Ganoderma lucidum biomass for biosorption of selenium (IV) ions from aqueous solution was studied in a batch mode. In this study the effects of operating parameters such as solution pH, adsorbent dosage, initial metal concentration, contact time, and temperature were investigated. The adsorption capacity of G. lucidum was found to be 126.99 mg g−1. The biosorption follows pseudo-first order kinetics and the isotherms fit well to both Langmuir and Freundlich isotherm models. Isotherms have been used to determine thermodynamic parameters of the process, that is, free energy, enthalpy, and entropy changes. Furthermore, the biosorbent was characterized by scanning electron microscopy and FT-IR analysis. FT-IR analysis of fungal biomass shows the presence of amino, carboxyl, hydroxyl, and carbonyl groups, which were responsible for the biosorption of selenium(IV) ions. The results indicated that the biomass of G. lucidum is an efficient biosorbent for the removal of selenium (IV) ions from aqueous solutions.

Aggregation Behavior of Titanium Dioxide Nanoparticles in Aqueous Environments

We report on the stability of titanium dioxide nanoparticles suspended in various aqueous solutions with and without the presence of a model organic contaminant—salicylic acid. The stability of the suspended nanoparticles was revealed by measuring the isoelectric point by means of zetapotential scans and measuring the growth kinetics of the hydrodynamic particle size by means of dynamic light scattering (DLS) under different pH conditions. Aggregated nanoparticle sizes were also examined using atomic force microscopy. It was found that salicylic acid had a dramatic impact on the aggregation behavior of TiO2 nanoparticles, suggesting that salicylic acid adsorbs to TiO2 nanoparticles surfaces.

Delayed Aggregation of Asphaltenes in the Presence of Alcohols by Dynamic Light Scattering

Structure of an n-heptane asphaltene obtained from atmospheric residue of crude oil has been analyzed using ultraviolet, infrared, and nuclear magnetic resonance (1H and 13C) spectroscopy and elemental analysis. The molecular weight of asphaltene was deduced by GPC (M n 3372 g · mole−1). Asphaltene exhibited H/C ratio of 0.905 and high sulfur content, being of thioether, thiophene rings or other C-S-C structures. Detailed ultravioletspectra of asphaltene recognized its construction as sets of fused aromatic rings, with each set having an average of three rings, thus, deducing a model structure. The onset point and aggregation behavior of asphaltene have been studied in the presence of alcohols(n-C6OH, n-C7OH, n-C8OH and n-C10OH) versus n-heptane, n-hexane and n-pentane as precipitating agents. The aggregation study has been carried out using dynamic light scattering. N-heptanol and n-hexanol showed the most delaying influence for the asphaltene aggregation versus n-heptane, n-hexane and n-pentane, respectively. Similarly, the aggregation behavior explored by dynamic light scattering showed that the use of n-hexanol and n-heptanol results in aggregate sizes that were smaller than those obtained when using n-octanol and n-decanol.

Tooth wear: A response to “Scratching the surface: A critique of Lucas et al. (2013)'s conclusion that phytoliths do not abrade enamel” [J. Hum. Evol. 74 (2014) 130–133]

a Department of Bioclinical Sciences, Faculty of Dentistry, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait b Department of Restorative Sciences, Faculty of Dentistry, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait c Department of Mechanical Engineering, College of Engineering and Petroleum, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait d Department of Chemical Engineering, College of Engineering and Petroleum, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait e Plant Foods in Hominin Dietary Ecology Group, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany f Nanotechnology Research Facility, College of Engineering and Petroleum, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait g Department of Anthropology, Washington University in St. Louis, St. Louis, MO 63130, USA h Max Planck Weizmann Center for Integrative Archeology and Anthropology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany i School of Construction Management and Engineering, University of Reading, Whiteknights, P.O. Box 219, Reading RG6 6AW, UK

Dental abrasion as a cutting process.

A mammalian tooth is abraded when a sliding contact between a particle and the tooth surface leads to an immediate loss of tooth tissue. Over time, these contacts can lead to wear serious enough to impair the oral processing of food. Both anatomical and physiological mechanisms have evolved in mammals to try to prevent wear, indicating its evolutionary importance, but it is still an established survival threat. Here we consider that many wear marks result from a cutting action whereby the contacting tip(s) of such wear particles acts akin to a tool tip. Recent theoretical developments show that it is possible to estimate the toughness of abraded materials via cutting tests. Here, we report experiments intended to establish the wear resistance of enamel in terms of its toughness and how friction varies. Imaging via atomic force microscopy (AFM) was used to assess the damage involved. Damage ranged from pure plastic deformation to fracture with and without lateral microcracks. Grooves cut with a Berkovich diamond were the most consistent, suggesting that the toughness of enamel in cutting is 244 J m−2, which is very high. Friction was higher in the presence of a polyphenolic compound, indicating that this could increase wear potential.

The modified constrained volume model predictions in shearing flow at nonunity viscosity ratio values

In this paper, the modified constrained volume model, which describes the evolution of anisotropy of immiscible polymer blends, composed of Newtonian components, was examined during shearing motion (steady and oscillatory) at various viscosity ratio values. We found that the linear correction to the rate of deformation tensor causes the droplet to change its volume at viscosity ratio values lower than unity, and to cause premature tumbling at viscosity ratio values larger than unity, in a case where retraction, breakup, and coalescence modules of the model were turned off. The use of Eshelby tensor, together with a closure to relate anisotropy to the Eshelby concentration tensor, mostly solved the problem. The model’s predictions are then shown at various capillary number values and at various viscosity ratio values. Comparison of model predictions to single droplet data at nonunity viscosity ratio value showed good agreement. Finally, model predictions of first normal stress difference during startup of steady shear are compared to experimental rheological results for immiscible polymer blends that are available in literature. Good predictions can be achieved by the introduction of a new switch function that controls the retraction and breakup modules. The model’s predictions at large amplitude oscillatory shear were examined. It was found that linear corrections to the velocity gradient tensor can be used for strains up to 100 %. For larger strain values, the Eshelby concentration tensor must be used.

Evidence that metallic proxies are unsuitable for assessing the mechanics of microwear formation and a new theory of the meaning of microwear

Mammalian tooth wear research reveals contrasting patterns seemingly linked to diet: irregularly pitted enamel surfaces, possibly from consuming hard seeds, versus roughly aligned linearly grooved surfaces, associated with eating tough leaves. These patterns are important for assigning diet to fossils, including hominins. However, experiments establishing conditions necessary for such damage challenge this paradigm. Lucas et al. (Lucas et al. 2013 J. R. Soc. Interface 10, 20120923. (doi:10.1098/rsif.2012.0923)) slid natural objects against enamel, concluding anything less hard than enamel would rub, not abrade, its surface (producing no immediate wear). This category includes all organic plant matter. Particles harder than enamel, with sufficiently angular surfaces, could abrade it immediately, prerequisites that silica/silicate particles alone possess. Xia et al. (Xia, Zheng, Huang, Tian, Chen, Zhou, Ungar, Qian. 2015 Proc. Natl Acad. Sci. USA 112, 10 669–10 672. (doi:10.1073/pnas.1509491112)) countered with experiments using brass and aluminium balls. Their bulk hardness was lower than enamel, but the latter was abraded. We examined the ball exteriors to address this discrepancy. The aluminium was surfaced by a thin rough oxide layer harder than enamel. Brass surfaces were smoother, but work hardening during manufacture gave them comparable or higher hardness than enamel. We conclude that Xia et al.s results are actually predicted by the mechanical model of Lucas et al. To explain wear patterns, we present a new model of textural formation, based on particle properties and presence/absence of silica(tes).