This study evaluated the accuracy of Cameriere’s method based on normalized measurement of open apices of developing permanent teeth (xi) and a number of teeth with closed apices (N0) in a sample of 121 cone-beam computed tomography (CBCT) scans of children (60 males and 61 females), aged between 5 and 13 years from Krakow, Poland. Intra-class correlation coefficient on randomly selected 30 CBCT scans showed good to exceptional intra-observer, and inter-observer agreement of normalized open apices, while Kappa score showed an absolute agreement of the number of teeth with complete maturation. Dental age overestimated by 0.17 years (p = 0.120) and 0.18 years (p = 0.149) in males and females, respectively. The mean absolute errors between dental and chronological age of MAE between dental and chronological age of the complete sample were 0.73 years and 0.77 years in males and females, respectively. In conclusion, the present results support usage of Cameriere’s method for age estimation in Polish children in cases where CBCT scans are available and previously taken for a specific clinical indication and taking into account the more demanding procedure of measuring variables in a non-orthogonal projection of teeth compared to a panoramic image.