Objective: The aim of the present study was the comparison of the known chronological age of the studied subjects by dental age evaluated according to the developmental stages of seven permanent teeth in the lower left dental quadrant and to determine how much the child's dental age differs from its chronological age. Methods: Radiographs of 579 patients (288 boys and 291 girls), aged 3-16 years, from the database of the Radiological Clinic of the Second Medical Faculty of Charles University and the Motol University Hospital in Prague were reviewed. The patients were examined for different indications by cone beam computed tomography (CBCT). The evaluation of the developmental stages of the teeth was performed from generated panoramic images and reconstructed three-dimensional (3D) images. The developmental stages of the teeth were evaluated by Demirjian's method for dental maturity based on seven teeth of the lower left dental quadrant (Demirjian et al. 1973). The evaluated variables were mineralization and development of the dental crown, length of the root, and closure of the apical foramen. Results: The difference between chronological and dental age was -0.16 (standard deviation (SD) 1.68, p-value 0.7) in boys and -0.10 (SD 1.65, p-value 0.27) in girls, on average. These results confirm that the method is accurate. Low SD values express the precision of the evaluation. Conclusion: Use of reconstructed 3D images makes the evaluation of the maturation of teeth more accurate in comparison to the use of generated panoramic images. The development of teeth (with exception of third molars) was complete at the age of 16 in 97.3% of the studied subjects.