Abstract: PURPOSE: The modified Demirjian method was used to evaluate the development of mandibular permanent teeth in children aged 4 to 11 years old, which provided a reference for determining the clinical treatment time and formulating policies for the prevention and treatment of oral chronic diseases. METHODS: A total of 320 panoramic films from 4 to 11 years old, with 160 males and 160 females, met the inclusion criteria. The modified Demirjian scoring method was used to judge the development of 7 permanent teeth or permanent germ on the left side of the jaw, and formed the developmental score line chart and trend chart. Differences in tooth position and gender were analyzed using SPSS 25.0 software package. RESULTS: There was a certain linear relationship between the development trend of each mandibular permanent tooth and the age. The second molar had the largest slope y=0.6619x-0.8843(R²=0.99) and the first molar had the smallest slope y=0.3783x+3.8626(R²=0.9224). Mandibular tooth development had distinct differences in tooth position. The first molars developed earlier than the central incisors, but lagged behind the central incisors during the apical foramen closure stage. Canine developed earlier than the first and second premolars, and second premolars developed later than the first premolars. Female mandibular teeth developed earlier than in men, mainly in the early stages of tooth development and the whole process of canine development. CONCLUSIONS: The development of mandibular permanent teeth in children aged 4 to 11 years old has differences in tooth position and gender, so the modified Demirjian method is suitable for evaluating the development of mandibular permanent teeth in children.

Key words: Modified Demirjian method, Development of permanent teeth, Difference in tooth position, Gender difference