人間生活文化研究 Int J Hum Cult Stud. No. 31 2021 Dental proportion chart to summarize change of mesiodistal and buccolingual crown diameters, crown module and crown index in different tooth classes 24 ［査読無し］ Dental proportion chart to summarize change of mesiodistal and buccolingual crown diameters, crown module and crown index in different tooth classes Takashi SATAKE 1,2 , Satoru YOSHIDA 3 , and Roshan PEIRIS 4 1 Institute of Human Culture Studies, Otsuma Women’s University 12 Sanban-cho, Chiyoda-ku, Tokyo 102-8357, Japan 2 Department of Nutritional Science, National Institute of Health and Nutrition 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8636, Japan 3 Department of Anatomy, Nihon University School of Dentistry at Matsudo 2-870-1, Sakaecho-Nishi, Matsudo, Chiba 271-8587, Japan 4 Department of Basic Sciences, Faculty of Dental Sciences, University of Peradeniya Peradeniya 20400, Sri Lanka Key words：Dental proportion chart, Mesiodistal crown diameter, Buccolingual crown diameter, Crown module, Crown index Abstract It is difficult to simultaneously visualize tooth size and shape changes in dental characteristics on a single chart. A chart that includes scales for mesiodistal crown diameter, buccolingual crown diameter, crown module and crown index on a single chart is proposed – the Dental Proportion Chart. The development and use of the chart are described. 1. Introduction Mesiodistal and buccolingual crown diameters are primary measurements in odontometric studies [1] [2] . The measurements are often expressed as indices (crown module and crown index, etc.) aimed at summarizing occlusal form and deriving shape variables. The crown module is the average diameter of the crown in a particular tooth, and the crown index is buccolingual crown diameter expressed as a percentage of mesiodistal crown diameter [3] . To evaluate tooth class changes of dental characteristics, charts used ordinarily include two coordinates, tooth class as the x-coordinate and a dental characteristic (mesiodistal and buccolingual crown diameters, root length, etc.) as the y-coordinate in common. If more dental characteristics need to be illustrated graphically in a single chart, an alternative chart may be necessary. In this context, a Dental Proportion Chart (DPC) was developed to evaluate tooth class changes in size and shape [4] . The DPC includes scales for size (mesiodistal and buccolingual crown diameters, crown module) and shape (crown index) on a single chart and shows both the magnitudes and proportions of the dental characteristics simultaneously. The basic concept of the DPC has already been adopted in a chart to evaluate body proportion [5] . The present paper describes the development and application of the DPC. 2. Preparation of the Dental Proportion Chart Several steps are involved in preparation of the DPC. Mesiodistal crown diameter and buccolingual crown diameter are plotted as x- and y-coordinates, respectively (Figure 1). The coordinate for the crown module is the sum of mesiodistal and buccolingual crown diameters divided by 2 (Figure 2). For example,