Interaction between enamel, porcelain and a gold alloy: an in vitro wear study.

Abstract

In dental practice, wear of the natural dentition is commonly seen in patients of all ages. It can have a mild effect on teeth, or be severe enough to affect patients’ quality of life. Although different indirect restorative materials such as gold alloy or porcelain have been used for many years to restore excessively worn teeth, the procedures are generally complex and challenging to the dentists as well as costly and time-consuming for the patients. A good restorative material should be aesthetic, durable and not be abrasive to the opposing dentition. Gold has been reported to be “enamel-friendly”, but the colour makes it un-aesthetic. On the contrary, porcelain is aesthetic, biocompatible, durable and has become a popular choice for both clinicians and patients. However, previous studies have shown that some of the porcelain systems can be abrasive to the opposing natural enamel. The use of such abrasive porcelain systems would therefore be harmful to a patient’s dentition in the long term. Four porcelain systems and a gold alloy have been selected for this study: - a veneering porcelain normally used in porcelain bonded to metal restorations (PBM-veneering porcelain). - a leucite-reinforced glass ceramic used for veneering (LR-veneering ceramic). - a leucite-reinforced pressable ceramic (LR-pressable ceramic). - a machinable ceramic. - a type III gold alloy (gold). The aims of the study were to determine the wear rates of the selected porcelains and opposing enamel under controlled conditions which simulated two clinical conditions: - heavy attrition at near neutral pH (pH 6.1). - heavy attrition with gastric regurgitation (pH 1.2). In addition, preliminary studies on the wear of zirconia and enamel were conducted. In this study, electro-mechanical tooth wear machines were used to simulate wear. Wear volume loss was measured by scanning specimens with 3D profilometers and evaluating the data using a purpose-written software. The surface micromorphology of wear facets was also observed by scanning electron microscopy (SEM). As a result of this analysis a more detailed investigation of the machinable ceramic was undertaken. The results revealed that at pH 6.1, while enamel wear caused by the PBM-veneering porcelain, LR-veneering ceramic, machinable ceramic and gold alloy were not significantly different to the control group in which enamel specimens were worn against each other, significantly increased enamel wear was associated with the LR-pressable. Although enamel wear rates increased dramatically in conditions simulating attrition combined with gastric regurgitation, the gold alloy did not wear the opposing enamel more than the enamel controls. In addition, in this study the machinable ceramic became porous under acidic conditions. The findings presented in this thesis have implications for selection of porcelain for specific clinical cases. Although the findings should be cautiously extrapolated to in vivo conditions, they contribute to the understanding of new porcelain materials in terms of wear and erosion. In addition, results from preliminary experiments with zirconia will provide data to inform the development of protocols for future research.