Objectives:The aim of this study was to investigate average working lengths of Korean posterior teeth and evaluate validity of endodontic file length. Materials and Methods:The endodontic working length of the posterior teeth of 670 Korean patients were measured than each mean value and standard deviation were investigated than the frequency deviation and standard deviation per each length were calculated. Results: Among the canals of premolar, 66.5% of canal length was marked under 20 mm by endodontic working length and 95.4% could be measured under 22 mm and Among the canals of molars, 95.5% of canal length was marked under 20 mm endodontic working length . Conclusions: With the result of measurement of endodontic working length of premolars of Korean, it suggested that 23 mm endodontic file is more proper than the 21 mm and 25 mm file on the market. since these Ni-Ti files should be mounted on a handpiece and can' t apply precurvature. In clinical procedure of endodontic treatment, the time for patients to keep their mouth open is longer than in any other treatment. If the time of mouth opening increases, patient will feel discomfort and side-effects like temporo-mandibular joint disease might occur. 6,7 Using long instruments will also give difficulties during the treatment procedures for the operator too.The lengths of the endodontic instruments are designed to be based on the length of the tooth. There are several methods for measuring these lengths of the teeth. 8 There are methods like, measuring directly from extracted tooth, surveying from the radiographic films or by measuring the working length of the tooth. 9 This method of measuring working length of the tooth can be done by measuring the length of the extracted tooth, using radiographic references or by using electronic working length measuring instruments. In vivo study, the radiographs are not always reliable because they can show considerable deviations depending upon the angles of the X-ray cone. 10 The apical constriction of the the root also does not coincide with the anatomic apex. 8,11,12 It is deviated linguo-buccally or mesio-distally from the root. If the exit deviates bucco-lingually, it is very difficult to locate accurately the position of the apical foramen using only roentgenograms, even with multidirected angles. 13The electric apex locator (EAL) machine has attracted a great deal of attention because it operates on the basis of the electrical impedance rather than by a visual inspection.13 EALs help to reduce the treatment time and the radiation dose, which may be higher with conventional radiographic measurements. In addition, EALs were reported to be an accurate [14][15][16][17][18] and reproducible method as the newest third generation type and can acknowledge a root perforation.International standard follow the average tooth lengths of caucasian people. 9,19,20 Although there were reports on the average tooth length of caucasian people, few information on the differences of canal lengths between the races is available.Theref...

In recent years, the use of smartphone applications for education is increasing. Although applications are being used for various educational aspects such as exams, the study of medical educational application is lacking. This study aims to investigate the effect of educational applications on medical education by analyzing the utility of and satisfaction with educational applications for histology courses in medical schools. The researcher employed an application called "BAND" that can be used to upload and share microscopic figures taken during histology lectures. A total of 82 first-grade students from Keimyung University Medical School who participated in this study expressed satisfaction with using "BAND". A total of 68 (83%) students were satisfied with learning histology through the application, and 72 (88%) students indicated that using the application was greatly helpful for the organizational practice test and expressed overall satisfaction with the application use. This benefit was because of easy contact (29.9%), searching ability (29.9%), and memory with humorous methods by friends (20.7%). And it application is most helpful during epithelium section (20.8%) and student want to use this application for anatomy (40.3%) or microbiology (38.8%) practices. The study results imply the need for further research so that the educational application can be used in various medical education fields in the future.