minerals Article The Influences of Dehydration on the Mechanical Properties of Human Dentin Abu Faem Mohammad Almas Chowdhury 1,2, * , Arefin Alam 1 , MD Refat Readul Islam 1 , Monica Yamauti 1 , Mohammad Shafiqul Alam 3 , Mohammad Musfiqur Rahman 4 , Asad-Uz-Zaman 5 , Mohiuddin Ahmed 6 , Pedro Álvarez-Lloret 7 and Hidehiko Sano 1   Citation: Chowdhury, A.F.M.A.; Alam, A.; Islam, M.R.R.; Yamauti, M.; Alam, M.S.; Rahman, M.M.; Asad-Uz-Zaman; Ahmed, M.; Álvarez-Lloret, P.; Sano, H. The Influences of Dehydration on the Mechanical Properties of Human Dentin. Minerals 2021, 11, 336. https://doi.org/10.3390/min11040336 Academic Editor: Yannicke Dauphin Received: 8 March 2021 Accepted: 22 March 2021 Published: 24 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Restorative Dentistry, Graduate School of Dental Medicine, Hokkaido University, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan; arefin@den.hokudai.ac.jp (A.A.); refatrislam@den.hokudai.ac.jp (M.R.R.I.); myamauti@den.hokudai.ac.jp (M.Y.); sano@den.hokudai.ac.jp (H.S.) 2 Department of Conservative Dentistry and Endodontics, Sapporo Dental College and Hospital, Plot 24, Sector 8, Dhaka 1230, Bangladesh 3 Department of Paediatric Dentistry, Shaheed Suhrawardy Medical College, Sher-E-Bangla Nagar, Dhaka 1207, Bangladesh; shafiqulalam152@gmail.com 4 Department of Oral Anatomy and Physiology, Sapporo Dental College and Hospital, Plot 24, Sector 8, Dhaka 1230, Bangladesh; musfiq.r.b@gmail.com 5 Department of Oral Pathology and Periodontology, Sapporo Dental College and Hospital, Plot 24, Sector 8, Dhaka 1230, Bangladesh; azaman@sdch.edu.bd 6 Department of Oral and Maxillofacial Surgery, Sapporo Dental College and Hospital, Plot 24, Sector 8, Dhaka 1230, Bangladesh; mahmed@sdch.edu.bd 7 Department of Geology, Faculty of Geology, University of Oviedo, Jesús Arias de Velasco s/n, 33005 Oviedo, Spain; pedroalvarez@uniovi.es * Correspondence: chowdhuryafma@gmail.com; Tel.: +81-(0)11-706-4261 Abstract: The complex, dynamic, and hydrated microstructures of human dentin serve as the major determinant for the restorative performance of biomaterials. This study aimed to evaluate the mechanical properties of human dentin under different hydration conditions. The occlusal dentin of five third molars was exposed and cut into 1 mm 2 dentin slabs. The slabs were then polished and further cut into 1 mm 2 dentin beams and stored in distilled water. Two beams/tooth were used for testing their hardness (H) and elastic modulus (E) at 5 min (baseline), 1 h, and 24 h after dehydration (23 ◦ C and 30% RH), and also for measuring weight at following dehydration times: 0 min, 5 min, 1 h, and 24 h. Five additional molars were employed to prepare 0.4 mm 2 dentin beams (3/tooth) for determining ultimate tensile strength (UTS) at 5 min (baseline), 1 h, and 24 h post-dehydration. Statistical significance was set at α = 0.05. Dehydration time significantly affected H, E, weight-loss, and UTS of dentin (p < 0.05). H and E values showed a strongly positive and significant correlation (r > 0.5, p < 0.05). Dehydration can substantially modify the mechanical properties of dentin, leading to misinterpretation of restorative outcomes in vitro. Keywords: dentin; dehydration; hardness; elastic modulus; correlation; ultimate tensile strength 1. Introduction Human teeth are composed of three mineralized tissues: cementum, dentin, and enamel. The cementum is an avascular connective tissue involved in the attachment of teeth to the bony cavity and covers the surface of the tooth root. Enamel is a highly mineralized structure that, in a healthy condition, covers the exposed part of the tooth, forming the anatomical crown. Dentin is a hydrated mineralized tissue that forms the bulk of a human tooth. The dentin and enamel’s organization and composition construct a highly sophisticated mineral system designed to withstand specific mechanical stress types. Together with its unique hydration status, the complex structural organization of human dentin contributes to its biomechanical properties [1]. These properties, in Minerals 2021, 11, 336. https://doi.org/10.3390/min11040336 https://www.mdpi.com/journal/minerals