Characterization of nanoindentation-induced residual stresses in human enamel by Raman microspectroscopy |
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Authors: | Li-Hong He Elizabeth A Carter Michael V Swain |
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Institution: | (1) Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, Sydney Dental Hospital, Surry Hills, NSW, 2010, Australia;(2) Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW, 2145, Australia;(3) Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, Sydney, NSW, 2006, Australia |
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Abstract: | The objective of this research was to investigate nanoindentation-induced residual stresses in human enamel using Raman microspectroscopy
and establish if this approach can be used as a stress meter. Healthy human premolars and sintered hydroxyapatite samples
were embedded, cut, and the surfaces were polished finely with a 0.05 μm polishing paste before Berkovich and spherical indentations
were made with a force of 100 mN. Spectra were collected using a Renishaw Raman InVia reflex microscope equipped with an air-cooled
charge-coupled device (CCD) camera. Sample excitation was achieved using either an argon ion laser emitting at 514.5-nm or
a NIR diode laser emitting at 830-nm. The residual micro stresses within and surrounding the indentation impressions were
monitored by mapping the position of the ν1(PO4) band of (crystalline) hydroxyapatite. The Raman maps coincided well with the optical micrographs of the samples. Despite
the presence of a fluorescence background from the organic component of human enamel, spectra collected using 514.5-nm excitation
exhibited more significant shifts in the position of the ν1(PO4) band than spectra collected using 830-nm excitation. This implies that the former excitation may be a more appropriate excitation
for stress detection. It was concluded that Raman microspectroscopy provides a novel high-resolution and non-destructive method
for exploring the role of microstructure on the residual stress distribution within natural biocomposites.
Figure Stress maps of nanoindentation impressions on both human enamel and hydroxyapatite disk via Raman Microspectroscopy |
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Keywords: | Raman spectroscopy Stress Enamel Hydroxyapatite |
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