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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]

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]

Abstract The paper entitled " A United States shark fin ban would undermine sustainable shark fisheries " (D.S. Shiffman & R.E. Hueter, Marine Policy 85 (2017) 138–140) argues that The Shark Fin Trade Elimination Act of 2017 (HR 1456) and its companion bill in the Senate (S 793), now before Congress in the United States of America, would be counterproductive. We demonstrate that the figures used in support of this claim are inappropriately selected, misinterpreted or incorrect, and that therefore the argument cannot stand. In the face of the extreme depletion of shark numbers globally, the paper fails to give an accurate or objective assessment of the situation. [ABSTRACT FROM AUTHOR]

• Failure to check statistical significance leads to errors, especially with respect to physical boundary conditions. • C Appropriate use of regression yields better predictions. • Boundary condition checking is essential for fitted functions accidental matching of prediction with expectation is misleading. • Detailed analysis has provided a rational prediction and revealed potential problems with literature data. [Display omitted] The use of fitted functions without reference to boundary conditions, physical implications, or the statistical contribution of all terms is dangerous. A crystallographic example of such errors is considered (ABiO 3), problems identified, and a better approach suggested. [ABSTRACT FROM AUTHOR]

Objective Bleaching ( alias whitening) is increasingly the chosen means of modifying the appearance of teeth for cosmetic reasons. Behbehani et al. (2012) acquired the largest known data set for the effects of bleaching over time (300 patients for ∼1 year), but the analysis then was rather superficial and did not exploit the full depth of information available in it. Methods Data collected by Behbehani et al. (2012) were re-analysed to explore in detail the variation in outcome between patients and over time. Results There is a distinct regression in shade scale value with time, taking something over 1 year to approach stability. There appears to be an intrinsic shade that cannot be altered, at around 1 unit (0.5M1 on the Vita 3D bleached shade guide). Some patients (11/300 at 1 year) appear to be worse-off after treatment, especially those with lighter starting shades, while many get no real benefit, with a change ≤2 units. Significance The effects of bleaching are often transient, but the reversion to a darker shade than the original may be due to the cumulative damage done to the organic matrix of enamel. The ethics of the treatment are questioned, as are over-the-counter products and whitening toothpastes. It might be appropriate to suggest to a patient that there is no point unless the shade is darker than some (Vita) shade value, say ∼1M2, but in any case informed consent is in need of improvement. All observations of the effects of bleaching ought to be made on timescales longer than 1 year to be meaningful. [ABSTRACT FROM AUTHOR]

Abstract: Failure mode under Hertzian indentation and the behavior on immersion in water of bis-GMA-based composites with HA whiskers or nanoscopic HA powder as filler were evaluated. Failure load decreased with increase in filler loading, but the decrease was smaller for whiskers, which showed a different failure mode both macroscopically and microscopically. Particle-filled composites failed mainly by radial cracking and cone cracking, with some plastic deformation at low filler loading, with fracture into irregular segments. For whisker-filled materials, crack propagation was inhibited by the well-dispersed whiskers by the usual toughening mechanisms; cone cracking was the dominant failure mode, at higher loads than for the powder, and fracture was incomplete. The filler reduced both water-uptake and elution of soluble materials, as expected, but both were lower for the whisker-filled material. Such composites might form the basis of viable materials for dental load-bearing restorations and other applications. [Copyright &y& Elsevier]

Abstract: Hydrothermal homogeneous precipitation combines the best characteristics of the hydrothermal and homogeneous precipitation methods, and allows long and uniform hydroxyapatite (HA) whiskers, with a high aspect ratio and high crystallinity, to be obtained. Their morphology and structural characteristics depend on the initial Ca/P ratio (iCa/P) and pH (ipH), as well as the initial calcium concentration (i[Ca]). Variation in these values had no effect on constitution, which was crystallographically indistinguishable from HA. Ca/P ratio steadily improved with increases in both ipH and iCa/P, but was independent of i[Ca]. Uniform whiskers were obtained at high iCa/P and low ipH, or at high ipH and low iCa/P. Whiskers with a mean length of 96–140μm and an aspect ratio of 96–136 were obtained at ipH=2–3 and iCa/P=1.67–2. At a low ipH and low iCa/P, irregular plate-like particles and branch-like whiskers were formed, while a high ipH favoured the formation of lath-like HA at high iCa/P. Preferred growth along the c-axis was more intense at higher iCa/P and ipH as well as at low i[Ca]. However, under these conditions, the crystal growth habit was also changed, showing preferred growth along both the c- and a-axes. The increase in whisker width over the general value obtained was abrupt at low i[Ca] and high iCa/P. [Copyright &y& Elsevier]

Abstract: Strontium (Sr) plays a special role in bone remodelling, being associated with both the stimulation of bone formation and a reduction in bone resorption. Thus, the modification of biomaterials by partial or full substitution by Sr is expected to increase both bioactivity and biocompatibility. However, such effects have to be studied individually. Although no phase transition was found in Sr-substituted hydroxyapatite (Sr–HA), Sr-containing calcium silicate (Sr–CS) or Sr-containing borosilicate (Sr–BS), their biological performance was substantially affected by changes in the physico-chemical properties and Sr content of the materials. Three distinct outcomes were found for the presence of Sr: (1) increased HA solubility; (2) no significant effect on the degradation rate of CS; (3) apparent inhibition of the otherwise rapid degradation of BS. In each case the released Sr affected osteoblast proliferation and alkaline phosphatase activity, with clear evidence that an optimum Sr dose exists. Such chemical and biological variations must be disentangled for the behaviour to be properly understood and materials design to be advanced. [Copyright &y& Elsevier]

Abstract: The ability to trigger the formation of apatite from a supersaturated solution has been widely used to imply the bioactivity of an implant in vivo. However, the method itself may provide at best incomplete information, primarily because it is determined only by solution supersaturation, irrespective of biological processes. Bone regeneration is triggered mainly by the vitality of osteoblasts, and regulated by the expression of growth factors such as oestrogen, parathyroid hormone and bone morphogenetic proteins, while ions or other species released from an implant may affect the expression of such growth factors, and so bone resorption or formation. The misinterpretation of the outcome of such tests must result in misunderstanding of the true effects and behaviour of materials intended for use in embedded biological contexts. Thus, the underlying and motivating hypothesis needs to be carefully reconsidered, along with the results of all work founded on the concept. It would seem that it is only viable to test using osteoblasts, whether in vivo or in vitro. [ABSTRACT FROM AUTHOR]

Abstract: Currently-available HA particle-reinforced composites are not suitable for use in large stress-bearing restorations and biomedical substitution due to low strength and poor durability. HA is the most promising because of good biocompatibility and bioactivity, and since reinforcement efficacy is greatly affected by length and aspect ratio, the preparation of long HA whiskers could be important for biomedical applications. Acetamide, formamide, and carbonyl diamide were tested as precipitation agents to modify crystal growth habit. The morphology and composition of the whiskers showed a sensitive dependence on the additive used. Carbonyl diamide and formamide led to contaminated HA; crystals were needle-like but contained carbonate or formate, respectively. In comparison, acetamide showed a low hydrolysis rate under hydrothermal conditions, giving rise to a rapid growth of HA crystals at a low supersaturation. Furthermore, the hydrolysis products of AA affected neither the composition nor the growth habit of the HA. [Copyright &y& Elsevier]

Abstract: Objective: To design a protocol for the determination of the flexural modulus of elasticity of wire with high accuracy and precision. Methods: Cantilever bending was used at long span and low loads, using a laser displacement sensor. Various wires were tested for proof-of-concept: stainless steel, Elgiloy, Wiptam and a gold alloy, with primary attention being paid to the source and magnitude of errors. Results: The moduli of elasticity were determined with a median relative error of ∼0.15%, with a worst case of 0.56%, taking into account all measurement errors. The precision was such as to permit distinctions between the values for the wires of different thermomechanical history. Significance: The determination of the elastic modulus of wires may be made with good precision using cantilever bending providing attention is given to all sources of error. These results represent the most reliable measures of modulus of elasticity of orthodontic archwires to date. [Copyright &y& Elsevier]

Abstract: Long and uniform HA whiskers with high crystallinity, controlled morphology and high aspect ratio were successfully synthesized by hydrothermal homogeneous precipitation using acetamide. Compared with the additive urea, which is commonly used to raise the pH to drive nucleation and growth of HA crystals, acetamide has a low hydrolysis rate under the required hydrothermal conditions. This allows better and easier control, giving rise to rapid growth of whiskers at a low supersaturation. Whisker length and width were in turn determined by solution conditions, including the concentration of Ca and PO4. Whiskers had a mean length of 60–116μm and an aspect ratio of 68–103 for starting solutions containing 42–84mmolL−1 Ca and 25–50mmolL−1 PO4 with a fixed Ca/P ratio of 1.67. Such whiskers are favourable for their improved bone bonding and bioactivity, as well as their mechanical properties. Whiskers were slightly Ca-deficient with Ca/P=1.60–1.65, with the preferred direction of growth along the c-axis. Variation of acetamide concentration did not affect the constitution, the crystallinity or the crystal growth habit. [Copyright &y& Elsevier]

Abstract: Objective: To examine the low-cycle fatigue (LCF) behaviour of NiTi rotary endodontic instruments in aqueous sodium hypochlorite solution. Methods: Four brands of NiTi rotary instrument (n =179) were subjected to a rotational-bending fatigue test at a rate of 250rpm until fracture, the instrument being immersed in 1.2% sodium hypochlorite solution. The surface strain amplitude, calculated from the curvature (from a pre-test photograph) and diameter of the fracture cross-section (from SEM photomicrograph) was plotted against the total number of revolutions to failure. An apparent fatigue-ductility exponent was determined from a regression line fitted to the LCF lives for each brand of instrument. All detached fragments were examined fractographically for crack initiation and the extent of crack extension into the cross-section. The values were compared using one-way analysis of variance (ANOVA) or χ 2, where appropriate, at α =0.05. Results: A linear strain-life relationship was obtained for all groups; the apparent fatigue-ductility exponent was similar between various brands (ANOVA, P >0.05), but not for the number of crack origins (χ 2, P <0.05). There was an inverse, linear relationship between the square root of the extension of the fatigue-crack and the strain amplitude. Significance: NiTi rotary instruments fatigued in hypochlorite shows a strain-life relationship with low-cycle and high-cycle fatigue regions. The LCF behaviour is not affected by the cross-sectional shape of the instrument. There appears to be a critical extent of crack propagation for various surface strain amplitudes leading to final, catastrophic fracture of the instrument. [Copyright &y& Elsevier]

Abstract: This study examined the low-cycle fatigue (LCF) behavior of a nickel-titanium (NiTi) engine-file under various environmental conditions. One brand of NiTi instrument was subjected to rotational-bending fatigue in air, deionized water, sodium hypochlorite, or silicone oil. The curvature of each instrument, diameter of the fracture cross-section, and the number of rotations to failure were determined. The strain-life relationship in the LCF region was examined by using one-way analysis of variance, and the number of crack origins with χ2, for differences between groups. The results showed a linear relationship, on logarithmic scales, between the LCF life and the surface strain amplitude; regression line slopes were significantly different between noncorrosive (air, silicone oil) and corrosive (water, hypochlorite) environments (P < .05), as well as number of crack origins (P < .05). Hypochlorite was more detrimental to fatigue life than water. In conclusion, environmental conditions significantly affect the LCF behavior of NiTi rotary instruments. Fatigue testing of NiTi engine-files should be in a service-like environment. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to compare the low-cycle fatigue (LCF) behavior of electropolished and nonelectropolished nickel-titanium (NiTi) instruments of the same design in hypochlorite. Forty-five electropolished and 62 nonelectropolished NiTi engine files were subjected to rotational bending at various curvatures in 1.2% hypochlorite solution. Number of revolutions to failure, crack-initiation sites, extent of slow crack extension into the fracture cross-section, and surface-strain amplitude were noted. A linear relationship was found between LCF life and surface-strain amplitude for both groups, with no discernible difference between the two (p > 0.05). No electropolished instrument showed more than one crack origin, significantly fewer than for the nonelectropolished instruments (p < 0.05). The square root of crack extension and strain amplitude were inversely related. Although surface smoothness is enhanced by electropolishing, this did not protect the instrument from LCF failure. [Copyright &y& Elsevier]

Abstract: The aim of the present study was to establish a mathematical model to characterize the flexural behavior of nickel-titanium (NiTi) rotary instruments. The bending behavior of ProFile (0.06 and 0.04 tapers), K-3 (0.06 taper), Quantec (0.04 taper) with tip size of ISO 25, was assessed by pressing the tip of the static rotary file against a smooth, freely movable, glass surface. The deflected instrument was photographed digitally, and the deflection path was digitized in software, to which data a function was fitted that best described the bending behavior of the instrument. It was found that all instruments deflected in a manner closely resembling a negative exponential function: . The present approach indicated that the analytical difficulties of handling the complex cross-section in tapering spirals in beam-bending theory may be circumvented by a practical and elementary curve-fitting method. [Copyright &y& Elsevier]

Objective Miniature magnets are used in dentistry, principally for the retention of prosthetic devices. The relationship between force and separation of a magnet and its keeper, or, equivalently, two such magnets, has been neither defined theoretically nor described practically in any detail suitable for these applications. The present paper addresses this lacuna. Methods A magnet is considered as a conglomeration of magnetic poles distributed over a surface or a solid in three-dimensional space, with the interaction of poles governed by the Coulomb law. This leads to a suite of mathematical models. These models are analysed for their description of the relationship between the force and the separation of two magnets. Results It is shown that at a large distance of separation, an inverse power law must apply. The power is necessarily integer and at least two. All possibilities are exhausted. Complementarily, under reasonable assumptions, it is shown that at a small distance of separation, the force remains finite. Significance The outcome is in accordance with practical experience, and at odds with the use of simple conceptual models. Consequences relevant to the usage of magnets in dentistry are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Objective: It had previously been shown that the inverse-square law does not apply to the force–distance relationship in the case of a long, thin magnet with one end in close proximity to its image in a permeable plane when simple point-like poles are assumed. Treating the system instead as having a ‘polar disc’, arising from an assumed bundle of dipoles, led to a double integral that could only be evaluated numerically, and a relationship that still did not match observed behavior. Using an elaborate ‘stretched’ exponential polynomial to represent the position of an ‘elastic’ polar disc resulted in a fair representation of the physical response, but this was essentially merely the fitting of an arbitrary function. The present purpose was therefore to find an explicit formula for the force–distance relationship in the polar-disc problem and assess its fit to the previously obtained experimental data. Methods: Starting from Coulomb''s law a corrected integral formula for the force–distance relationship was derived. The integral in this formula was evaluated explicitly using rescaling, changes of order of integration, reduction by symmetry, and change of variables. The resulting formula was then fitted to data that had been obtained for the force exerted by eighty-five rod-shaped magnets (Alnico V, 3mm diameter, 170mm long) perpendicular to a large steel plate, as a function of distance, at small separations (<5mm). Subsequently, the fit of alternative functions was explored. Results: An explicit formula in terms of elliptic integrals was obtained for the polar-disc problem. Despite the greater fidelity, this too was found not to fit the observed physical behavior. Given that failure, nevertheless a simple formula that conforms closely and parsimoniously to the actual magnet data was found. A key feature remains the marked departure from inverse-square behavior. Significance: The failure of the explicit formula to fit the data indicates an inadequate model of the physical system. Nonetheless it constitutes a useful tool for quantifying the force–distance relationship on the premise of polar discs. Given these insights, it may now be possible to address the original motivating problem of the behavior of real dental magnets. [Copyright &y& Elsevier]

Thermal treatment is one of the common methods used in the recovery of biological apatite from bones and teeth. However, the effect of this on its physicochemical and biological properties has not yet been given full consideration. As a simplified research model with characteristics assumed to be similar to biological apatite, carbonated hydroxyapatite was used to study the effect of thermal treatment on its physicochemical properties. Carbonated hydroxyapatite was prepared and heated at 600–1000 °C. The morphology, chemical composition, crystal characteristics, functional groups and solubility of the as-prepared and heated samples were determined. Crystal growth and aggregation were observed for materials heated at 800 °C and above. With increase of heating temperature, carbonate and water content decreased, while the crystallinity increased. The solubility of as-prepared material and those heated at 600 and 700 °C was higher than the reference curve for hydroxyapatite, while that of the rest overlapped the latter. Such changes indicate that the preparation approaches involving high temperature may not be appropriate for the recovery of ‘biological’ apatite; and that the importance of carbonate to the apparent solubility of calcium phosphate must be taken into account in all such work. [ABSTRACT FROM AUTHOR]

Abstract: The solubility of hydroxyapatite (HA) is critical in fields such as medicine, dentistry and geochemistry. Previously, it had been found that it was apparently slightly increased with 1mmol/L excess phosphate present. This study was to determine the solubility of HA over the pH range 3.3–5.4 with a series of concentrations of such ‘excess’ phosphate with solid titration (ST), and to identify the precipitate formed at equilibrium with SEM, TEM, EDX, FTIR and XRD. For [PO4]XS=0–0.3mmol/L, results followed closely the already-reported ST ‘low’ solubility isotherm. At [PO4]XS=0.5mmol/L, the solubility surface switched abruptly to a ‘high’ position that could not be reconciled with either the ‘low’ isotherm or conventional calculations. Thus, HA solubility is critically dependent on the presence of excess phosphate. Such excess may account for the discrepancy between ST and excess-solid results, although the crystallographic explanation is as yet lacking. [Copyright &y& Elsevier]

Abstract: Geometric, electronic and elastic properties of three intermetallic systems, including starting alloy (Ag3Sn) and two reaction product phases (Ag2Hg3 and Sn8Hg), are characterized by state-of-the-art density functional theory (DFT) experiments. The traditional mean-field approach failed for Sn8Hg (γ2-phase) due to inaccurate description of site occupancy, remedied through the use of supercells. Results were in quantitative agreement with experiment for all phases, within 3.2% and 2.7% for unit cell parameters and Young modulus (of elasticity), respectively. An efficient procedure is presented which may lead to the rational design of novel filling materials for such service, prior to physical trials being initiated. [Copyright &y& Elsevier]