Nanoindentation: Application to dental hard tissue investigations
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M.V. Swaina) Biomaterials, School of Oral Sciences, Faculty of Dentistry, University of Otago, Dunedin, New Zealand; and Biomaterials, Faculty of Dentistry, Sydney Dental Hospital, University of Sydney, Surry Hills, New South Wales 2010, Australia (Received 9 January 2006; accepted 16 May 2006)
In the last decade, most publications on the mechanical properties of dental calcified tissues were based on nanoindentation investigation. This technique has allowed a better understanding of the mechanical behavior of enamel, dentin, and cementum at a nanoscale. The indentations are normally carried out using pointed or spherical indenters. Hardness and elastic modulus are measured as a function of indenter penetration depth and from the elastic recovery upon unloading. The unique microstructure of each calcified tissue significantly contributes to the variations in the mechanical properties measured. As complex hydrated biological composites, the relative proportions of the composite components, namely, inorganic material (hydroxyapatite), organic material, and water, determines the mechanical properties of the dental hard tissues. Many pathological conditions affecting dental hard tissues cause changes in mineral levels, crystalline structures, and mechanical properties that may be probed by nanoindentation. This review focuses on relevant nanoindentation techniques and their applications to enamel, dentin, and cementum investigations.
I. INTRODUCTION
Baseline information on the physical and mechanical properties of teeth is of importance in restorative dentistry. The knowledge is essential for numerical modeling of restored teeth to understand load transfer within a tooth, which is uniquely composed of different structures with different mechanical properties, but must act as a single mechanical unit. Ideally, a restoration should not only be able to chemically bond to the tooth structure, but must also behave physically, thermodynamically, and mechanically like tooth itself in the oral environment, especially when subjected to mastication. It is anticipated that under masticatory loadings, a restoration with adequate and comparable mechanical properties to that of the adjacent tooth structure will have a longer lifetime. For example, differences in the elastic modulus of enamel and a composite-resin restoration result in differential deflections under occlusal loading and high-localized stresses at bonding interfaces, thereby
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0257 J. Mater. Res., Vol. 21, No. 8, Aug 2006
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potentially compromising these crucial regions, which may result in mechanical failures or microleakages, leading to secondary or recurrent caries. The mechanical properties of calcified tissue have been also shown to reflect the level of mineralization.1–5 Most diseases affecting dental hard tissue such as infectious dental caries, as well as other developmental and genetic pathosis, i
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