SMEAR LAYER : Introduction : Unknown and unrecognized for years, the smear layer has become a force to be reckoned with during the last decade. Most dentists know now it exists but are often puzzled as to whether or not they should cope with it. Since the smear layer has been recognized, dentist have come to realize that they must renew their acquaintance with the science of dental materials so they can understand the relationships of the products they work with to the smear layer. History : •
Boyde et al (1963) were the first to describe and demonstrate the presence of a “smear layer” on surfaces of cut enamel such a layer was readily removed with sodium hypochlorite, leading them to conclude that an organic layer containing apatite particles was deposited or smeared on the enamel surface, through functional heat generated during cutting. They believed that the heterogenous nature of enamel was the source of the smeared components.
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Provenza and Sardana (1996) evaluated means of removing debris from enamel and dentin after the use of steel burs, diamond stones and hand instruments. They reported variations in the degree to which debris was removed. Detergents were relatively ineffective, EDTA left behind a film, 0.1N hydrochloric acid was considered too destructive in its action, hydrogen peroxide appeared to be most effective.
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Nelsen and Zisman (1966) described the dynamics of cutting dental tissues and appeared to imply the existence of an altered surface layer due to elastic and plastic deformation of the tissue.
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Eick et al (1970) found that surfaces cut dry are rougher and more smeared than those in which water is used as a coolant. In the absence of coolant, smeared debris does not form a continuous layer but exists