Technology and Health Care 22 (2014) 785–793 785 DOI 10.3233/THC-140852 IOS Press Nanomechanical characterization of exfoliated and retained deciduous incisors Muhammad Sohail Zafar a,∗ and Naseer Ahmed b a College of Dentistry, Taibah University, Madinah Al Munawwarah, Saudi Arabia b Department of Mechanical Engineering, Faculty of Engineering, CECOS University of IT and Emerging Sciences, Peshawar, KPK, Pakistan Received 27 May 2014 Accepted 17 July 2014 Abstract. OBJECTIVES: The anisotropic natures of dental tissues result in variable properties from one point to the other within the same tooth. The aim of this study was to analyze deciduous incisors enamel and dentin for elastic modulus and hardness. In addition, retained deciduous incisors were assessed to compare properties with exfoliated teeth. METHODS: Deciduous mandibular incisors either exfoliated at physiological age or retained were included in this study. Samples were prepared by dissecting teeth in transverse sections and surfaces under investigation were prepared and polished for nanoindentation. Nanoindentation was performed at multiple sites using Hysitron [TI 725 Ubi] testing instrument. Data analysis was performed using SPSS software (version 20) to calculate absolute hardness and elastic modulus. The statistical significance was calculated using the t-test. RESULTS: The hardness of human deciduous incisor varies between 0.01–7 GPa. The highest value of hardness was observed for the incisal edge (5.09 ± 0.64 GPa) followed by mid-surface enamel and cervical enamel. The hardness of mantle dentin was (0.56 ± 0.19 GPa) and the inner dentin was (0.34 ± 0.12 GPa). CONCLUSIONS: The average hardness of primary teeth enamel is lower than permanent teeth enamel. The hardness of retained teeth enamel is greater than exfoliated teeth however lower than permanent teeth enamel of the equivalent region. Keywords: Nanoindentation, primary teeth, incisors, elastic modulus 1. Introduction Teeth are most vital body organs needed to perform important functions such as mastication of food, speech and aesthetics [1]. Structurally, teeth are composed of hard tissues such as enamel, dentin and cementum that work as a single functional unit to withstand a variety of forces of mastication (up to ∼ 700 N) [2]. There are two sets of natural teeth; (1) primary or deciduous teeth and (2) secondary or per- manent teeth. The primary teeth start appearing from the age of six months and have their functional role until the age of 12 years either alone (until 6 years) or alongside the permanent dentition (6–12 years in the mixed dentition period). The primary dentition performs physiological functions such as mastication, skeletal growth, space maintenance and assisting eruption of permanent teeth hence their significance must not be underestimated [1,3]. * Corresponding author: Muhammad Sohail Zafar, College of Dentistry, Taibah University, Madinah Al Munawwarah, Saudi Arabia. Tel.: +966 507544691; E-mail: drsohail_78@hotmail.com. 0928-7329/14/$27.50 c  2014 – IOS Press and the authors. All rights reserved