Sem in dental research

The versatility of scanning electron microscopy (SEM) makes it an extremely useful tool in the exciting and remarkably wide field of dental research. Dental research ranges from the study of soft and hard tissues (such as dentin, enamel, and bone) to cell culture (i.e. mineralizing bone cells) to dental materials (such as adhesives and composites, metals, and ceramics). Characterization of these materials relies to a large extent on SEM. For example, in 2009, 33% of papers in the journal of Dental Materials and 47% in Dental Materials Journal (Japan) contained information obtained with SEM. It is difficult to overestimate the importance of SEM in dental research. It is equally difficult to summarize in more than general terms the dental investigations that employ SEM in one book chapter. This chapter, therefore, is focused on certain practical aspects of the utilization of SEM in dental research with some examples based on current literature. Teeth are covered with a layer of enamel protecting the dentin which surrounds the pulp (Figure 13.1). The pulp is a living viable tissue composed of nerves and blood vessels which connect directly to the supporting bone. Biological fluid is transported from the blood supply in the bone through the dentin tubules to the dentin and creates a dynamic circulatory system between the living bone and tooth structure. A carious lesion involves breakdown of the hard tooth structure by acid-producing bacteria, many times leading to infection of the pulp and possible death of the tooth and supporting bone. A large proportion of dental research is devoted to restoration of carious lesions with dental composite. Accordingly, a number of examples in this chapter involve composite restorations, so a basic explanation of this restorative technique is presented. Preparation of a carious lesion (i.e. cavity) with dental cutting instruments creates a smear layer on top of the exposed enamel and dentin (Eick et al., 1970). The smear layer consists of collagen debris and mineral (hydroxyapatite). For proper adhesion of dental bonding agents, the smear layer and the underlying dentin should be etched with acids to remove the mineral and expose the dentin collagen network. Adhesives penetrate the network creating a hybrid layer (effectively a collagen-resin composite) and form a bond to dentin (Nakabayashi, 1982; Eick et al., 1997). Subsequently, dental composite, a mixture of resin and filler particles, is filled over the adhesive layer.