The Metallography of dental amalgams

Abstract

Porosity in dental amalgam has been investigated by many workers and several explanations of the probable cause of porosity have been documented. Artefact development during preparation of amalgam specimens for metallographic examination has had scant reference in the dental literature, and therefore it is the primary concern of this thesis to elucidate some of the factors which produce porosity as an artefact on polished surfaces of amalgam specimens. The present work has shown that porosity as an artefact can be produced by the removal of phases during the polishing process and by ultrasonic cleaning of specimens between polishing stages. The ease of manipulation, adequate mechanical properties and low cost has established amalgam as the primary choice material for dental restorations. There have been many publications on amalgam failure and it has been suggested that poor cavity design, faulty amalgam manipulation, marginal failure, creep and corrosion are responsible for defective amalgam restorations. The Y2 phase is the most reactive phase of dental amalgam and the presence of this phase is believed by some authors to predispose amalgam restorations to marginal breakdown. The present work investigates the Y2 phase by describing a chemical etch to define this phase, so allowing measurement of the volume fraction of Y2 phase in a range of amalgam alloys. For in vitro corrosion studies two chemical-methods for the dissolution of the Y2 phase are described. The thesis also describes an alternative polishing and etching procedure and examines whether vibratory polishing is suitable for final polishing of amalgam specimens.