Influence of the indenter tip geometry and environment on the indentation modulus of enamel
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L.H. He Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, United Dental Hospital, Sydney, Surry Hills NSW 2010, Australia
T. Scho¨berl Erich Schmid Institute of Material Science, Austrian Academy of Sciences, Leoben A-8700, Austria
I. Ja¨ger Department of Material Physics, University of Leoben, Leoben A-8700, Austria
G. Dehm Erich Schmid Institute of Material Science, Austrian Academy of Sciences, Leoben A-8700, Austria; and Department of Material Physics, University of Leoben, Leoben A-8700, Austria
M.V. Swainb) Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, United Dental Hospital, Sydney, Surry Hills NSW 2010, Australia; and Biomaterials Unit, Department of Oral Sciences, School of Dentistry, University of Otago, Dunedin, New Zealand (Received 6 June 2008; accepted 16 October 2008)
The aim of the investigation was to study the influence of indenter tip geometry on the conventionally obtained indentation modulus of enamel by nanoindentation. Indentation tests on bovine enamel using three different diamond pyramidal indenters with half face angles 65.27 , 45 , and 35.26 were conducted to evaluate the indentation modulus using the Oliver–Pharr method [W.C. Oliver and G.M. Pharr, J. Mater. Res. 7, 1564 (1992)]. In addition, three different dehydration conditions were studied: wet under Hank’s balanced salt solution, laboratory dried, and vacuum dehydrated. For the Berkovich indenter (65.27 ) and 45 pyramidal indenters, there was only a small difference between indentation modulus values, whereas for the cube-corner indenter (35.26 ) a ratio of 2.4 between laboratory dry and wet samples was found. A detailed evaluation, including indentation creep and recovery as well as pileup, resulted in a reduction of this latter ratio to 1.7. This still large difference was rationalized on the basis of the different deformation mechanisms generated by indenters of different face angles. I. INTRODUCTION
Enamel, the outer cover of the tooth, is composed of about 97% by weight mineral, essentially carbonated apatite, 1% organic material, mostly protein, which is not collagen, and 2% water.1 Most of the mineral crystals are bound together in bundles called prisms or rods. Each rod is 3–6 mm in diameter. There is limited protein within the prisms “glueing” the apatite crystallites together, with more protein located at the interprism a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr_policy DOI: 10.1557/JMR.2009.0110 616
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J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 16 Mar 2015
boundaries.1 This region is often called the enamel sheath, and also consists of apatite crystals that are inclined to the axis of the rods.2 To test enamel under near in vivo conditions, in our experim
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