A. Harrison

An in vitro investigation into the wear effects of selected restorative materials on enamel

Abrasive wear testing of five restorative materials was carried out with human enamel as the opposing surface using a wear machine specifically designed to simulate the masticatory cycle. The results showed that enamel demonstrated good abrasion resistance against amalgam and microfine composite and moderate abrasion resistance against gold. Conventional composite produced marked destruction of enamel and the greatest amount of enamel wear was produced by porcelain. The ranking order compared favourably with results from in vivo studies.

The effect of the addition of surface treated chopped and continuous poly (methyl methacrylate) fibres on some properties of acrylic resin

Poly (methyl methacrylate), the material most commonly used in the construction of dentures, is not without limitations particularly in terms of mechanical strength, such as flexural and fatigue strength. The Dental Practice Board for England statistics show that many dentures fail as a result of fracture. This study investigated the self-reinforcement of acrylic resin through the addition of surface treated poly (methyl methacrylate) fibres in chopped and continuous form. The effect of the addition of fibres on transverse and impact strengths was investigated. The addition of surface treated chopped or continuous fibres to acrylic resin did not improve the transverse or impact strengths. The addition of surface treated poly (methyl methacrylate), in the present form, to acrylic resin cannot be recommended as a method of reinforcement.

An assessment of the ability of dental undergraduates to choose artificial teeth which are appropriate for the age and sex of the denture wearer: a pilot study

One of the main objectives in selecting and arranging artificial teeth is to produce prostheses which defy detection. With an appropriate degree of clinical experience and expertise it should be a relatively straightforward procedure to select a suitable artificial tooth mould. However, for the relatively inexperienced dental undergraduate it can be a challenging process. The aim of this study was to assess the ability of dental undergraduates to select artificial teeth which are appropriate for the age and sex of the denture wearer. One hundred and fifty dental undergraduates aged 18-35 were asked to complete a questionnaire to assess their attitudes towards artificial tooth selection and asked to correctly identify six artificial tooth arrangements according to age and sex. The results showed that a large percentage of dental undergraduates at Bristol experience difficulty in selecting artificial teeth which are appropriate for the age and sex of the denture wearer. There is a need for improved training and guidance on artificial tooth selection and arrangement.

Reline materials--handle with care? An investigation into the effect of varying the powder/liquid ratio on some properties of auto-polymerising acrylic resin materials.

Introduction The fit of the denture base to the alveolar ridge progressively declines with alveolar ridge resorption. Once a denture becomes ill-fitting there are two main treatment options: to construct a new denture or to restore the fit of the existing denture. A denture may be relined as a laboratory procedure or at the chairside in the dental clinic. The chairside reline technique involves the direct application of auto-polymerising acrylic resin materials to the prepared denture base and the material is allowed to polymerise in the patients mouth. The reline materials are generally supplied as a powder and a liquid. Clinicians and laboratory dental staff do not always follow manufacturers’ recommended guidelines and the tendency can be simply to add varying quantities of powder and liquid until the desired consistency is achieved. This method however may have deleterious effects on the properties of the resultant material. Materials and method The aim of the study was to investigate the effect of varying the powder/liquid ratio on some properties of three auto-polymerising acrylic resin reline materials. The properties investigated were the flow characteristics in terms of the manipulation and setting time and the hardness. Four powder and liquid ratios were chosen. Results and conclusions For all the materials studied, a clinically useful lengthening of the manipulation time can be achieved by increasing the amount of liquid added to the powder. However, this is perhaps offset by the fact that it is associated with a corresponding increase in the setting time and resultant increase in clinical chair-side time. There were significant differences in surface hardness when the powder/liquid ratio was altered.