A Study of Dental Restorations using In-Situ Ion Etching in a Scanning Electron Microscope

Abstract

A new approach to the study of the adaptation of various dental restorative materials to the cavity wall of the tooth has been developed using in-situ ion etching in a scanning electron microscope. A review of the literature concerning the restoration process and the different materials used is included and particular reference is made to amalgam and composite type restorative materials. This is followed by a discussion of the theory, techniques and applications of the sputtering process. In this work the fine beam version of the saddle field ion source has been used and experiments have shown that this source will only operate satisfactorily if the anode temperature is maintained at less than about 450°C. This has been satisfactorily achieved by water cooling the source. A novel method for measuring the sputtering yield and etching rate has been used which is essentially an ion-drilling technique in which the sputtered area has been measured in the scanning electron microscope. In the main part of this study the temperature of the restored tooth during ion bombardment has been maintained at oral temperatures using a cryogenic stage. Four types of restorations have been studied, namely amalgam, with and without the use of cavity varnish, and composite, with and without the acid etch technique. Prior to ion etching the restorations, examination of the surfaces in the microscope has shown that there was always a good adaptation between the restorative material and the enamel. However after ion etching amalgam for & hours, during which about 50 pm of amalgam was removed, gaps around the cavity of 10-20 pm were observed. On the other hand when a similar thickness of composite material was removed, gaps of only 0.5-4 pm were observed and thus it is concluded that composite materials adapt better to the cavity wall than amalgam.