On the R-curve behavior of human tooth enamel |
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| Authors: | Devendra Bajaj Dwayne D. Arola |
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| Affiliation: | 1. Department of Mechanical Engineering, University of Maryland, Baltimore County, Baltimore, MD 21250, USA;2. Department of Endodontics, Prosthodontics, and Operative Dentistry, Baltimore College of Dental Surgery, University of Maryland, Baltimore, MD 21201, USA;1. Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, 06006 Badajoz, Spain;2. Department of Biology, Saint Michael''s College, Colchester, VT 05439, USA;3. Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;1. State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China;2. State Key Laboratory of Nonlinear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing, China;3. Department of Conservative Dentistry and Endodontics, West China College of Stomatology, Sichuan University, Chengdu 610041, China;1. Lyles School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA;2. Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA;3. Materials Science and Engineering, University of California, Riverside, CA 92521, USA |
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| Abstract: | In this study the crack growth resistance behavior and fracture toughness of human tooth enamel were quantified using incremental crack growth measures and conventional fracture mechanics. Results showed that enamel undergoes an increase in crack growth resistance (i.e. rising R-curve) with crack extension from the outer to the inner enamel, and that the rise in toughness is a function of distance from the dentin enamel junction (DEJ). The outer enamel exhibited the lowest apparent toughness (0.67 ± 0.12 MPa m0.5), and the inner enamel exhibited a rise in the growth toughness from 1.13 MPa m0.5/mm to 3.93 MPa m0.5/mm. The maximum crack growth resistance at fracture (i.e. fracture toughness (Kc)) ranged from 1.79 to 2.37 MPa m0.5. Crack growth in the inner enamel was accompanied by a host of mechanisms operating from the micro- to the nano-scale. Decussation in the inner enamel promoted crack deflection and twist, resulting in a reduction of the local stress intensity at the crack tip. In addition, extrinsic mechanisms such as bridging by unbroken ligaments of the tissue and the organic matrix promoted crack closure. Microcracking due to loosening of prisms was also identified as an active source of energy dissipation. In summary, the unique microstructure of enamel in the decussated region promotes crack growth toughness that is approximately three times that of dentin and over ten times that of bone. |
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