Beneficial effects of air inclusions on the performance of ethylene vinyl acetate (EVA) mouthguard material

Objective: To investigate the impact characteristics of an ethylene vinyl acetate (EVA) mouthguard material with regulated air inclusions, which included various air cell volumes and wall thickness between air cells. In particular, the aim was to identify the magnitude and direction of forces within the impacts. Method: EVA mouthguard material, A mm thick and with and without air inclusions, was impacted with a constant force impact pendulum with an energy of 4.4 J and a velocity of 3 m/s. Transmitted forces through the EVA material were measured using an accelerometer, which also allowed the determination of force direction and magnitude within the impacts. Results: Statistically significant reductions in the transmitted forces were observed with all the air inclusion materials when compared with EVA without air inclusions. Maximum transmitted force through one air inclusion material was reduced by 32%. Force rebound was eliminated in one material, and reduced second force impulses were observed in all the air inclusion materials. Conclusion: The regulated air inclusions improved the impact characteristics of the EVA mouthguard material, the material most commonly used in mouthguards world wide.

Effect of ethylene vinyl acetate (EVA) closed cell foam on transmitted forces in mouthguard material

Objectives: To compare transmitted forces through ethylene vinyl acetate (EVA) mouthguard material and the same EVA material with gas inclusions in the form of a closed cell foam. Method: EVA mouthguard materials with and without foam gas inclusions and 4 mm thick were impacted with a constant force from an impact pendulum. Various porosity levels in the foam materials were produced by 1%, 5%, and 10% by weight foaming agent. The forces transmitted through the EVA after energy absorption by the test materials were measured with a force sensor and compared. Results: Only minor non-significant differences in transmitted forces through the EVA with and without foam were shown. Conclusions: The inclusion of gas in the form of a closed cell foam in 4 mm thick EVA mouthguard materials did not improve the impact performance of the EVA mouthguard material.

A survey of sodium hypochlorite use by general dental practitioners and endodontists in Australia

Background: Sodium hypochlorite is used commonly as an endodontic irrigant, but there are no published reports that provide details of its use. This survey sought to determine the percentage of Australian dentists who practiced endodontics, whether they used sodium hypochlorite for irrigation, and the manner of dilution, storage and dispensing sodium hypochlorite used by both dentists and endodontists. Methods: All Australian endodontists and a stratified random sample of 200 general dentists in Australia were surveyed to address the issues identified above. Results: Almost 98 per cent of dentists surveyed performed endodontic treatment. Among endodontists, nearly 94 per cent used sodium hypochlorite for irrigation compared with just under 75 per cent of general dentists: Sodium hypochlorite use by general dentists was more common in Victoria and South Australia than in other States. An infant sanitizer (Milton or Johnson's Antibacterial Solution) was used by just over 92 per cent of general practitioners and by more than 67 per cent of endodontists. All other respondents used domestic bleach. One hundred and sixty four of the respondents (80 per cent of endodontists and over 90 per cent of general dentists) used a 1 per cent w/v solution. Ten practitioners used a 4 per cent w/v solution, five used a 2 per cent w/v solution and four used a 1.5 per cent w/v solution. Eighty per cent of the practitioners who diluted their sodium hypochlorite before use, used demineralized water for this purpose. The remainder used tap water. Only four practitioners stored sodium hypochlorite in a manner which risked light exposure and loss of available chlorine content. Conclusions: Sodium hypochlorite is commonly used as an endodontic irrigant and Australian dentists generally stored the material correctly.

Do economists ‘compose’ economics? A comparison of the creative processes of artists and economists

This is a draft for a chapter of the book version of my Ph.D thesis. The chapter addresses the following question: Are the creative processes of musical composers and academic economists essentially the same, or are there significant differences? The paper finds that there are deep similarities between the creative processes of theoretical economists and the creative processes of artists. The chapter builds a process oriented lifecycle account of creative activity, drawing on testimonial material from the arts and the sciences, and relates the model to the creative work of economists developing economic theory.

Thermal effects in the evolution of initially layered mantle material

A simplified model for anisotropic mantle convection based on a novel class of rheologies, originally developed for folding instabilities in multilayered rock (MUHLHAUS et al., 2002), is extended ¨ through the introduction of a thermal anisotropy dependent on the local layering. To examine the effect of the thermal anisotropy on the evolution of mantle material, a parallel implementation of this model was undertaken using the Escript modelling toolkit and the Finley finite-element computational kernel (DAVIES et al., 2004). For the cases studied, there appears too little if any effect. For comparative purposes, the effects of anisotropic shear viscosity and the introduced thermal anisotropy are also presented. These results contribute to the characterization of viscous anisotropic mantle convection subject to variation in thermal conductivities and shear viscosities.

Health and safety issues in contemporary dental practice

Under current workplace health and safety legislation, the owners and managers of a dental practice have a legal responsibility to provide staff with a safe working environment. In this article, the emphasis will be on four common areas of risk: posture when seated, handling scalpel blades, flooring and lighting.