Experimental investigation of the mechanical behaviour and structure of the bovine periodontal ligament

One of the key problems in dental biomechanics is the prediction of tooth mobility under functional loads. Understanding tooth displacement due to load is becoming more important as new solutions in dental restorations, prosthodontics and orthodontic treatments become increasingly more advanced. The mechanical characterization of the alveolar bone, the tooth and the periodontal ligament surrounding the root of the tooth, is necessary to predict tooth mobility. The common assumption is that the periodontal ligament acts as the major element in the stress distribution to the supporting tissues. Obtaining parameters that describe periodontal ligament mechanical behaviour is a challenging problem. Isolating the tissue for testing, the small size of the specimen, and the necessity to maintain, as much as possible, the ligament in vitro under normal physiological conditions, are all factors that contribute to the complexity of the problem. The aim of this thesis is twofold and can be subdivided into two primary objectives. The first objective is to describe its morphology, anatomy, histology and structure of the components in order to determine its geometric parameters at different length scales. The second objective is to determine its mechanical properties by identifying key parameters through shear and uniaxial tension-compression tests. Four studies are performed to describe the morphology, anatomy and histology of the periodontal ligament. First, macroscopic and microscopic measurements of the tooth, bone, and the periodontal ligament are obtained. Second, a bovine first molar system is reconstructed in three dimensions from microcomputerized tomography scans. Third, the morphology of the ligament is observed during deformation using optical microscopy. Fourth, the histology of bovine periodontium tissue is investigated. In order to characterise the mechanical behaviour of the bovine periodontal ligament, custom- designed machines and gripping devices are constructed to subject speciallyprepared tissue specimens to shear and uniaxial tension-compression experiments. Shear experiments are performed on 2 millimetre thick transverse sections, and specimens of toothligament- bone of approximately 8x5x2 millimetres for uniaxial experiments. All specimens are obtained from first molar sites of freshly slaughtered bovines. In both shear and uniaxial testing, the specimens are subjected non-destructively to preconditioning, stress-relaxation, constant strain rate, and sinusoidal loading profiles before testing to rupture. The experiments reported in this thesis elucidate geometrical and mechanical characteristics of the periodontal ligament. Concerning its geometry, a variation in collagen fibre orientation is observed in transverse sections, moreover the symmetry of the shear tests in the apicocoronal direction suggests the periodontal ligament is vertically isotropic. Uniaxial specimens, however, may be considered to be transverse isotropic. Concerning its mechanical behaviour, the periodontal ligament is nonlinear viscoelastic in that it exhibits stiffening, nonlinear elasticity, and nonlinear pseudo-plastic viscosity. The interaction between various constituents of the periodontal ligament (collagen fibres, blood vessels, interstitial fluid etc...) during deformation contribute to the observed stress-strain response of this tissue. A nonlinear viscoelastic model presented in the literature, the Power Law, adequately simulates the nonlinear behaviour of the periodontal ligament using finite element analysis

The Development and Validation of the Adolescent Sport Drug Inventory (ASDI) among Athletes from Four Continents

A significant barrier to understanding the psychosocial antecedents of doping use among adolescent athletes is the lack of valid measures. In order to address this issue, the first aim of this paper was to develop and validate the Adolescent Sport Drug Inventory (ASDI) among adolescent athletes from Asia, Europe, North America, and Oceania. The second aim was to assess the construct validity of the ASDI. As such, this paper is divided into two parts. Part 1 relates to the development of the ASDI and contains two studies: item development (Study 1) and factorial validity (Study 2). Part 2 contains information on how the psychosocial variables measured in the ASDI are associated with situational temptation, and honesty (Study 3), maturation (Study 4), stress and coping (Study 5), and coaching (Study 6). In devising the ASDI, 19 different models were examined, which culminated in a 9-factor, 43-item ASDI. Coping, mastery-approach goals, and cognitive-social maturity were associated with doping attitudes. Caring motivational climates, strong coach-athlete relationships, and positive coach behaviors were associated with athletes being less susceptible toward doping, which provides construct validity for the ASDI. The ASDI is a valid tool to assess the psychosocial factors associated with doping among adolescent athletes. This questionnaire can be used to identify athletes who are the most at risk of doping, assess how the psychosocial factors associated with doping change over time, and to monitor the impact of antidoping interventions for adolescent athletes

Call to action: a collaborative framework to better support female rugby league players

THE RISE OF WOMEN'S RUGBY LEAGUE Women's sports have seen a substantial increase in participation numbers and in their professionalism. There was a 29% increase in the number of Australian women who played rugby league in 2018 and there have been increased competition pathways for women in both Australia (ie, National Rugby League Women's (NRLW) premiership) and England (ie, Women's Super League (WSL))

Effect of mixing sequence on the curing of amine-hardened epoxy/alumina nanocomposites as assessed by optical refractometry

High performance refractometry has been proven to be a useful tool to elucidate the isothermal curing process of nanocomposites. As a model system an amine-hardening epoxy filled with non-surface-treated alumina nanoparticles was selected. The tremendous resolution of this experimental technique is used to study morphological changes within nanocomposites via the refractive index. It is shown that these morphological changes are not simply due to the curing process but also depend on the sequence of mixing the nanoparticles either first into the resin or first into the hardener. Independent of the resin/hardener composition, the type of the mixing sequence discriminates systematically between two distinct refractive index curves produced by the curing process. The difference between the two refractive index curves increases monotonically with curing time, which underlines the importance of the initial molecular environment of the nanoparticles

The workout responses of salivary-free testosterone and cortisol concentrations and their association with the subsequent competition outcomes in professional rugby league

This study assessed the responses of salivary-free testosterone (T) and cortisol (C) concentrations across selected training workouts and their association with the subsequent competition outcomes in professional rugby league. Thirteen rugby league players were assessed for salivary-free T and C concentrations across 5 training workouts performed 3-4 days before a competitive game. The game outcomes included wins and losses and game-ranked performance (1-5) based on the number of points scored, the points differential, and a coach rating. Data were pooled across the winning (n = 3) and losing (n = 2) outcomes. Pooled free T concentrations (absolute and relative changes) were significantly (p < 0.01) elevated across those workouts that preceded winning games, but not the losses, and the relative (percent) T changes were significantly (p < 0.05) higher before winning (30.9%) than before losing (3.4%). Both outcomes were associated with workout decreases in pooled free C concentrations and the relative C changes were not significantly different between wins (222.9%) and losses (225.6%). In conclusion, the free T responses to selected training workouts showed some association with subsequent winning (being elevated) and losing (no change) during a limited number of competitive games in professional rugby league. Speculatively, the free T responses to a midweek workout might provide an early sign of team readiness to compete or to recovery state, thereby providing a novel format for implementing training or management strategies to improve the competition outcomes

Influence of Nanoparticles on the Coupling Between Optical Dipoles in Epoxy-Silica Nanocomposites During Network Formation

High-performance refractometry and infrared spectroscopy are combined in order to elucidate the gelation process and the glass transition during the network formation of epoxies and epoxy-based nanocomposites. Whereas infrared spectroscopy yields the chemical conversion due to the opening of oxirane rings during the covalent network formation, high-performance refractometry is extremely sensitive to the accompanying changes of the arrangement of the molecular network. In accordance with the Lorentz-Lorenz relationship, the evolution of the refractive index seems to reflect that of the mass density during polymerization of the epoxy-based systems within the limits of a few percent. The slight deviations from the Lorentz-Lorenz relationship, which occur during the gelation of the epoxy-based systems, are attributed to long-ranged dipole-dipole interactions, which respond at optical frequencies. This point of view is supported by the fact that chemically inert silica nanoparticles embedded in the pure epoxy matrix as disturbances for these dipole-dipole interactions are able to diminish or even to suppress totally this excess contribution of the refractive index