title: Understanding nature's residual strain engineering at the human dentine-enamel junction interface.
abstract: Human dental tissue is a hydrated biological mineral composite. In terms of volume and mass, a human tooth mainly consists of dentine and enamel. Human dental tissues have a hierarchical structure and versatile mechanical properties. The dentine enamel junction (DEJ) is an important biological interface that provides a durable bond between enamel and dentine that is a life-long success story: while intact and free from disease, this interface does not fail despite the harsh thermo-mechanical loading in the oral cavity. The underlying reasons for such remarkable strength and durability are still not fully clear from the structural and mechanical perspectives. One possibility is that, in an example of residual stress engineering, evolution has led to the formation of a layer of inelastic strain adjacent to the DEJ during odontogenesis (tooth formation). However, due to significant experimental and interpretational challenges, no meaningful quantification of residual stress in the vicinity of the DEJ at the appropriate spatial resolution has been reported to date. In this study, we applied a recently developed flexible and versatile method for measuring the residual elastic strain at (sub)micron-scale utilising focused ion beam (FIB) milling with digital image correlation (DIC). We report the results that span the transition from human dentine to enamel, and incorporate the material lying at and in the vicinity of the DEJ. The capability of observing the association between internal architecture and the residual elastic strain state at the micrometre scale is useful for understanding the remarkable performance of the DEJ and may help the creation of improved biomimetic materials for clinical and engineering applications.
  
  
  CONCLUSIONS
  We studied the micron-scale residual stresses that exist within human teeth, between enamel (outer tooth shell, hardest substance in the human body) and dentine (soft bone-like vascularised tooth core). The dentine-enamel junction (DEJ) is an extremely interesting example of nature's design in terms of hierarchical structuring and residual stress management. Key developments reported are systematic focused ion beam (FIB) milling and digital image correlation (DIC) micrometre scale residual strain evaluation, and the determination of principal strain direction near DEJ, correlated with internal architecture responsible for remarkable strength. This work helps understanding DEJ performance and improving biomimetic materials design for clinical and engineering applications.
authors.affiliation: Multi-Beam Laboratory for Engineering Microscopy (MBLEM), Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK. Electronic address: tan.sui@eng.ox.ac.uk.
authors.forename: Tan
authors.initials: T
authors.lastname: Sui
authors.affiliation: Multi-Beam Laboratory for Engineering Microscopy (MBLEM), Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
authors.forename: Alexander J G
authors.initials: AJG
authors.lastname: Lunt
authors.affiliation: Multi-Beam Laboratory for Engineering Microscopy (MBLEM), Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Baimpas
authors.affiliation: School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Sandholzer
authors.affiliation: Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore.
authors.forename: Tao
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore.
authors.forename: Kaiyang
authors.initials: K
authors.lastname: Zeng
authors.affiliation: School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Landini
authors.affiliation: Multi-Beam Laboratory for Engineering Microscopy (MBLEM), Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Korsunsky
mesh_terms: D003743:Dental Enamel / Q000502:physiology*; D003804:Dentin / Q000502:physiology*; D004548:Elasticity; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007477:Ions; D013314:Stress, Mechanical
chemical_list: D007477:Ions
keywords: Dentine–enamel junction (DEJ); FIB–DIC; Human dental tissue; Residual elastic strain