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Hasegawa M, Tanaka R, Zhong J, Kobayashi M, Manabe A, Shibata Y. Deciphering load attenuation mechanisms of the dentin-enamel junction: Insights from a viscoelastic constitutive model. Acta Biomater 2023; 171:193-201. [PMID: 37669711 DOI: 10.1016/j.actbio.2023.08.050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 08/03/2023] [Accepted: 08/24/2023] [Indexed: 09/07/2023]
Abstract
A considerable material discontinuity between the enamel and dentin might jeopardize the tooth's mechanical durability over time without the attenuation of the dentin-enamel junction (DEJ). However, the critical loading transmission mechanism at the DEJ remains understudied. This study aimed to define the extent and effective width of the DEJ, along with its mechanical competence. The presence of DEJ interphase layer was identified using a motif analysis based on the ion beam-transmission electron microscopy coupled with nanoindentation modulus mapping. For each region, nanoindentation load-displacement curves were recorded and mathematically analyzed using an appropriate viscoelastic constitutive model. The time-course of indenter penetration (creep) behavior of the tooth tissues can be mathematically approximated by the Kelvin-Voigt model in series, which determined the visco-contribution to the overall mechanical responses. Therefore, the elastic-plastic contribution can be distinguished from the overall mechanical responses of the tooth after subtracting the visco-contributions. During the loading period, the enamel behavior was dominated by elastic-plastic responses, while both the dentin and DEJ showed pronounced viscoelastic responses. The instantaneous modulus of the DEJ, which was measured by eliminating viscoelastic behavior from the raw load-displacement curve, was almost double that of the dentin. The DEJ was stiffer than the dentin, but it exhibited large viscoelastic motion even at the initial loading stage. This study revealed that the load attenuation competence of the DEJ, which involves extra energy expenditure, is mainly associated with its viscoelasticity. The mathematical analysis proposed here, performed on the nanoindentation creep behavior, could potentially augment the existing knowledge on hard-tissue biomechanics. STATEMENT OF SIGNIFICANCE: In this study, we undertake a rigorous mechanical characterization of the dentin-enamel junction (DEJ) using an advanced nanoindentation technique coupled with a pertinent viscoelastic constitutive model. Our approach unveils the substantial viscoelastic contribution of the DEJ during the initial indentation loading phase and offers an elaborate delineation of the DEJ interphase layer through sophisticated image analysis. These insights significantly augment our understanding of tooth durability. Importantly, our innovative mathematical analysis of creep behavior introduces a novel approach with profound implications for future research in the expansive field of hard-tissue biomechanics. The pioneering methodologies and findings presented in this work hold substantial potential to invigorate progress in biomaterials research and fuel further explorations into the functionality of biological tissues.
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Affiliation(s)
- Masataka Hasegawa
- Department of Conservative Dentistry, Division of Aesthetic Dentistry and Clinical Cariology, Showa University Graduate School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan
| | - Reina Tanaka
- Department of Biomaterials and Engineering, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
| | - Jingxiao Zhong
- School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney NSW, 2006, Australia
| | - Mikihiro Kobayashi
- 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
| | - Atsufumi Manabe
- 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
| | - Yo Shibata
- Department of Biomaterials and Engineering, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
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Desoutter A, Felbacq D, Gergely C, Varga B, Bonnet L, Etienne P, Vialla R, Cuisinier F, Salehi H, Rousseau E, Rufflé B. Properties of dentin, enamel and their junction, studied with Brillouin scattering and compared to Raman microscopy. Arch Oral Biol 2023; 152:105733. [PMID: 37247560 DOI: 10.1016/j.archoralbio.2023.105733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 05/31/2023]
Abstract
OBJECTIVE Dentin, enamel and the transition zone, called the dentin-enamel junction (DEJ), have an organization and properties that play a critical role in tooth resilience and in stopping the propagation of cracks. Understanding their chemical and micro-biomechanical properties is then of foremost importance. The aim of this study is to apply Brillouin microscopy on a complex biological structure, that is, the DEJ, and to compare these results with those obtained with Raman microscopy. DESIGN Both techniques allow noncontact measurements at the microscopic scale. Brillouin microscopy is based on the interaction between acoustic phonons and laser photons and gives a relation between the frequency shift of the scattered light and the stiffness of the sample. Raman spectra contain peaks related to specific chemical bonds. RESULTS Comparison of the Brillouin and Raman cartographies reveals correlations between mechanical and chemical properties. Indeed, the shapes of the phosphate content and stiffness curves are similar. The two spectroscopies give compatible values for the mean distance between two tubules, i.e., 4-6 µm. Moreover, for the first time, the daily cross striations of enamel could be studied, indicating a relationship between the variation in the phosphate concentration and the variation in the rigidity within the enamel prisms. CONCLUSIONS We demonstrate here the possibility of using Brillouin scattering microscopy to both study complex biological materials such as the enamel-dentin junction and visualize secondary structures. Correlations between the chemical composition and mechanical properties could help in better understanding the tissue histology.
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Affiliation(s)
- Alban Desoutter
- LBN, Univ. Montpellier, 545 avenue Professeur Jean-Louis Viala, 34193 Montpellier Cedex 5, France.
| | - Didier Felbacq
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Csilla Gergely
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Béla Varga
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Laurent Bonnet
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Pascal Etienne
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Remy Vialla
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Frédéric Cuisinier
- LBN, Univ. Montpellier, 545 avenue Professeur Jean-Louis Viala, 34193 Montpellier Cedex 5, France
| | - Hamideh Salehi
- LBN, Univ. Montpellier, 545 avenue Professeur Jean-Louis Viala, 34193 Montpellier Cedex 5, France
| | - Emmanuel Rousseau
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
| | - Benoit Rufflé
- L2C, Univ. Montpellier, CNRS, place Eugène Bataillon, 34090 Montpellier, France
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Alshahni RZ, Shimada Y, Zhou Y, Yoshiyama M, Sadr A, Sumi Y, Tagami J. Cavity adaptation of composite restorations prepared at crown and root: Optical assessment using SS-OCT. Dent Mater J 2019; 38:779-789. [PMID: 31341148 DOI: 10.4012/dmj.2018-265] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Evaluation of gap formation at the interfaces of a two-step self-etching adhesive with/without pre-etching was performed using sweptsource optical coherence tomography (SS-OCT). Round cavities were prepared in bovine incisors at the middle (MC) and cervical (CC) thirds of the crown and the cervical third of the root (CR). Clearfil SE bond was directly applied to one group (SE) and another (PA) was pretreated with K-etchant gel. Following restoration by flowable composite resin, the teeth were thermally challenged and stored for 2 months. Interfacial gaps observed in the cross-sectional OCT images were analyzed and the bottom cavities exhibited increased gaps compared to the margin and dentin-enamel junction (DEJ). The CR site had a larger gap than at MC and CC in the SE group. DEJ separation at the MC was significantly smaller than that at CC in both groups. Therefore, gap formation depends on the cavity region, location, and bonding protocol.
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Affiliation(s)
- Rima Zakzuk Alshahni
- Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University
| | - Yasushi Shimada
- Department of Operative Dentistry, Okayama University, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
| | - Yuan Zhou
- Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University
| | - Masahiro Yoshiyama
- Department of Operative Dentistry, Okayama University, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
| | - Alireza Sadr
- Department of Restorative Dentistry, University of Washington, School of Dentistry
| | - Yasunori Sumi
- Division of Oral and Dental Surgery, Department of Advanced Medicine, National Center for Geriatrics and Gerontology, National Hospital for Geriatric Medicine
| | - Junji Tagami
- Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University
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Seyedmahmoud R, Wang Y, Thiagarajan G, Gorski JP, Reed Edwards R, McGuire JD, Walker MP. Oral cancer radiotherapy affects enamel microhardness and associated indentation pattern morphology. Clin Oral Investig 2018; 22:1795-1803. [PMID: 29151196 PMCID: PMC5908727 DOI: 10.1007/s00784-017-2275-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 11/13/2017] [Indexed: 11/25/2022]
Abstract
OBJECTIVES The aim of this study is to determine the effects of in vitro and in vivo high-dose radiotherapy on microhardness and associated indentation pattern morphology of enamel. MATERIALS AND METHODS The inner, middle, and outer microhardness of enamel was evaluated using three experimental groups: control (non-radiated); in vitro irradiated; in vivo irradiated. In vitro specimens were exposed to simulated radiotherapy, and in vivo specimens were extracted teeth from oral cancer patients previously treated with radiotherapy. Indentations were measured via SEM images to calculate microhardness values and to assess the mechanomorphological properties of enamel before and after radiotherapy. RESULTS Middle and outer regions of enamel demonstrated a significant decrease in microhardness after in vitro and in vivo irradiation compared to the control group (p < 0.05). Two indentation patterns were observed: pattern A-presence of microcracks around indent periphery, which represents local dissipation of deformation energy; pattern B-clean, sharp indents. The percentage of clean microindentation patterns, compared to controls, was significantly higher following in vitro and in vivo irradiation in all enamel regions. The highest percentage of clean microindentations (65%) was observed in the in vivo irradiated group in the inner region of enamel near the dentin-enamel junction. CONCLUSIONS For the first time, this study shows that in vitro and in vivo irradiation alters enamel microhardness. Likewise, the indentation pattern differences suggest that enamel may become more brittle following in vitro and in vivo irradiation. CLINICAL RELEVANCE The mechanomorphological property changes of enamel following radiation may be a contributory component of pathologic enamel delamination following oral cancer radiotherapy.
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Affiliation(s)
- R Seyedmahmoud
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
| | - Y Wang
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA.
- Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA.
| | - G Thiagarajan
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
- Department of Civil and Mechanical Engineering, School of Computing and Engineering, University of Missouri-Kansas City, Kansas City, MO, USA
| | - J P Gorski
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
- Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
| | - R Reed Edwards
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
| | - J D McGuire
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA
| | - M P Walker
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA.
- Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, 650 East 25th St, Kansas City, MO, 64108, USA.
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