# The Use of a 3D Image Comparison Program for Dental Identification
## 1 Introduction  
The usefulness of dental identification is currently being demonstrated [1]. Dental identification using dental findings involves matching the information of a body obtained by a dentist in a post-mortem examination room with information on the missing person from a dental clinic, which is finally authenticated by the police [2]. Specifically, police confirm the identity of the missing person by comparing the dental chart prepared from the information obtained from a visual examination of the body's mouth, which includes intraoral photography and dental X-rays obtained at a morgue, with the antemortem dental information record provided by a dental clinic. DNA identification is an effective means of identification, but it is difficult to obtain antemortem samples when a person's home is destroyed in a major disaster [2; 3]. On the other hand, dental information is considered useful because it is likely to be preserved if a family dentist's office is not lost in a disaster, which can then be used to confirm a patient's identity [2; 3]. In fact, following the 11 March 2011 earthquake and tsunami in Japan, dental information has been used to identify individuals in more than 1000 cases, about seven times more than DNA analysis and three times more than fingerprint identification [1; 4]. However, the dental charts used in conventional methods are complicated, and the antemortem dental information records being compared, which are submitted by dental institutions and dental associations in the area, differ in the level of detail provided by themedical professionals who prepared the records. The process of making a dental chart from the information on a cadaver takes a long time, as it requires review by several people after the oral conditions are accurately reproduced on the chart [5]. In addition, rigor mortis and foreign bodies in a mouth may make it difficult to open the mouth and, thus, to directly view the oral cavity [5; 6]. Moreover, if the dental clinic itself has disappeared, it may be difficult to prepare documentation before death [5; 6; 7; 8]. If the information on a large number of bodies needs to be collected in the event of a major disaster, current methods must rely on human tactics, as it is impossible to collect sufficient information due to the decomposition of bodies. In fact, during the Great East Japan Earthquake, 2000 dentists and more than 30,000 police officers were involved in identification work alone [1; 2; 4]. Another problem is that a dental chart is not always a decisive factor in identification, for example, in cases where there are many healthy teeth and few characteristic treatment marks [5; 6; 7; 8]. One solution to these problems is the use of digital technology with image comparison programs. The authors believe that it is a good idea to use digital technology to streamline the identification of unidentified persons. Since the dentition may be partially lost in a high-energy disaster, such as an airplane crash or large-scale natural disaster, the ability to identify the same model even from partial dentition information is very useful for identification. In addition, the recent popularity of portable intraoral scanners has made the acquisition of 3D data practical, even in disaster areas [9]. Furthermore, in disaster areas, if intraoral 3D data of a person can be obtained, identification can be performed anywhere and anytime, which would greatly improve work efficiency. In the advancement of dental care, digital technology not only improves dental technology but also changes the workflow of dental care and digitizes various pieces of patient information obtained in clinical practice. This digitized patient information can be processed by software, and various types of data can be integrated and used [10; 11; 12; 13; 14]. Among them, an optical impression taken with an intraoral scanner enables the output of maxillofacial morphology, including the dentition, into STL data, a standard format, and the creation of accurate three-dimensional reconstructive scan data [9].