Research portfolio: a new in-vitro methodology for the study of microleakage of low volume shrinkage composite resin.

Abstract

Microleakage has been defined as the passage of bacteria, fluids, molecules or ions along the tooth-restoration interface (Kidd, 1976). This leakage may be clinically undetectable, but is a major factor influencing the longevity of dental restorations as it causes many severe biological effects on the restored tooth including the recurrence of caries, pulp pathology, hypersensitivity and marginal breakdown (Hersek, 2002). The investigation of microleakage is, therefore, important in the assessment of restorative materials. A variety of in vitro methods have been introduced into the study of microleakage including compressed air, neutron activation, electrochemical, fluid filtration, bacteria and the use of dyes (Karagenς, 2006; Kidd, 1976;Taylor, 1992). In addition, various techniques such as scanning electron microscopy, transmission electron microscopy and electron probe microscopic analysis have been used to image and measure leakage. However, the above specimen preparation techniques are two-dimensional in nature and do not take the whole tooth-restoration interface into account, as some sections obtained randomly are taken to measure microleakage. Over the past few years there have been efforts to investigate microleakage of restorative materials three dimensionally (Gale, 1994; Iwami, 2005; Lyroudia, 2000; Youngson, 1992). However, this methodology was also destructive as images were reconstructed from serial cross-sections of continuously ground surfaces. One of the most advanced techniques in medical imaging in recent years has been the advent of micro-computed tomography (MCT) that can achieve a spatial resolution at the micron level. Recently, the MCT Skyscan 1072 (MCT 1072) has been introduced into dentistry for the study of many subjects including dental materials, dental morphology and dental implants (Bergmans, 2001; Park, 2005; De Santis, 2005). De Santis et al (2005) first used MCT to study microleakage and although these workers introduced a non-destructive method, the model they chose had some weaknesses. From the clinical perspective only flat dentine surfaces were studied rather than definite cavities, as in the clinical situation. Furthermore, no three-dimensional quantitative and qualitative analyses were undertaken. In considering various methods that have been used to study microleakage, the technology of MCT would appear to offer significant advantages over two-dimensional methods involving sectioning of specimens. In order to image microleakage using MCT, an x-ray contrast dye solution is needed. It has been reported that a silver nitrate solution has been the only metal solution that is able to express the microleakage of restorative materials (Besnault, 2003; Taylor, 1992; Taylor, 1993; Tsatsas, 2005). Filtek Silorane (3M ESPE) has been recently introduced into the market and is considered as a low volume shrinkage composite resin. Very little microleakage research has been done for this new material. It is from this fundamental basis that the project evolved, with firstly, the need to explore the potential of using MCT scanning of composite resin restorations and secondly, to develop a suitable study model that can be used effectively with the MCT 1072. Thirdly, qualitative and quantitative microleakage patterns of Filtek Silorane are studied non-destructively and three-dimensionally. As an introduction to this investigation it is necessary to review the adverse effects of microleakage on the restored teeth. In addition, aetiologies and dynamic processes of microleakage will be considered. Furthermore, the current methodologies with their main advantages and disadvantages will be discussed. Having discussed the current thinking on microleakage, there will be a further discussion of x-ray contrast dye solutions and MCT 1072. There will be also an overview of the new version of composite resin namely, Silorane. Finally, the factors that can influence the results of microleakage studies will be reviewed.