Exceptional contact elasticity of human enamel in nanoindentation test. Issue 1 (January 2019)

• Record Type: Journal Article
• Authors: Shimomura, Naofumi; Tanaka, Reina; Shibata, Yo; Zhang, Zhongpu; Li, Qing; Zhou, Jun; Wurihan, ; Tobe, Takuma; Ikeda, Sachiko; Yoshikawa, Kazuko; Shimada, Yukie; Miyazaki, Takashi
• Is Part Of: Dental materials. Volume 35:Issue 1(2019)
• Page Start: 87
• Page End: 97
• Publication Date: 2019-01
• Subjects: Enamel -- Nanoindentation -- Mechanical properties -- Stress–strain behavior -- Dynamic mechanical analysis -- Resilience; Dentistry -- Periodicals; Dental materials -- Periodicals; 617.695
• DOI: 10.1016/j.dental.2018.11.005
• Languages: English
• ISSNs: 0109-5641

Abstract

Highlights: Strain-rate-dependent contact elasticity of tooth enamel at a nanoscale level. Enhanced elastic limit based on temporary pile-up response to high strain rate. Intrinsic dynamic response related to nanoscale structural modification of enamel. Nanomechanical characterization protocol for biominerals and bio-inspired materials. 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 1041 nm 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 0.061 s −1 . The storage moduli from a superimposed signal amplitude (dynamic strain at 220 Hz) 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 7–9 GPa and 5–6 GPa 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.