Exceptional contact elasticity of human enamel in nanoindentation test

Naofumi Shimomura; Reina Tanaka; Yo Shibata; Zhongpu Zhang; Qing Li; Jun Zhou; Wurihan; Takuma Tobe; Sachiko Ikeda; Kazuko Yoshikawa; Yukie Shimada; Takashi Miyazaki

doi:10.1016/j.dental.2018.11.005

Exceptional contact elasticity of human enamel in nanoindentation test

Dent Mater. 2019 Jan;35(1):87-97. doi: 10.1016/j.dental.2018.11.005. Epub 2018 Nov 30.

Authors

Affiliations

¹ Department of Pediatric Dentistry, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan.
² Department of Conservative Dentistry, Division of Biomaterials and Engineering, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
³ Department of Conservative Dentistry, Division of Biomaterials and Engineering, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; The University of Sydney, School of Aerospace, Mechanical and Mechatronic Engineering, NSW 2006, Australia. Electronic address: yookun@dent.showa-u.ac.jp.
⁴ The University of Sydney, School of Aerospace, Mechanical and Mechatronic Engineering, NSW 2006, Australia.
⁵ Department of Conservative Dentistry, Division of Biomaterials and Engineering, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; School of Stomatology, Hospital of Stomatology, Tianjin Medical University, 12 Observatory Road, Tianjin 300070, China.
⁶ Department of Conservative Dentistry, Division of Aesthetic Dentistry and Clinical Cariology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan.

PMID: 30502962
DOI: 10.1016/j.dental.2018.11.005

Abstract

Objective: Tooth enamel has unsurpassed hardness and stiffness among mammalian tissue structures. Such stiff materials are usually brittle, yet mature enamel can survive for a lifetime. Understanding the nanoscale origin of enamel durability is important for developing advanced load-bearing biomaterials. Here, nanoscale exceptional contact elasticity of the human tooth enamel, based on nanoindentation tests, is reported.

Methods: Spherical indenter tips with radii of 243 and 1041nm were used to determine stress-strain curves of enamel. Force-displacement curves were recorded using quasi-static loading strain rates of 0.031, 0.041, and 0.061s^-1. The storage moduli from a superimposed signal amplitude (dynamic strain at 220Hz) embedded during primary quasi-static loading and from quasi-static elastic theory were simultaneously measured. Modulus mapping was considered to be an extremely low quasi-static loading strain rate indentation test.

Results: The elastic limits were 7-9GPa and 5-6GPa for the small and large indenters, respectively. The elastic-plastic transition point and elastic modulus value increased with substantially increased quasi-static loading strain rate. The results suggested that the increase of the elastic limit during high-loading strain was associated with exceptional contact elasticity at the nanoscale of the enamel structure and the consequent extension of the contact area (i.e., a temporary pile-up response, dependent on the enamel nanocrystals and protein glue).

Significance: Structural modification at this scale effectively prevents the initiation of cracking from localized strain, thus reinforcing the bulk structure. These results may provide valuable insight for conceptualizing bio-inspired nanocomposites.

Keywords: Dynamic mechanical analysis; Enamel; Mechanical properties; Nanoindentation; Resilience; Stress–strain behavior.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Dental Enamel*
Elastic Modulus
Elasticity
Hardness
Humans
Weight-Bearing