Fig. 1

A representative case:A Preoperative radiograph of a necrotic, immature teeth with an open apex of an 8-year-old girl. B Radiograph directly after the treatment to check the coronal MTA plug. C Postoperative radiograph after 10-month follow-up period showing disappearance of periapical radiolucency, apical closure and distal sign of resorption at the coronal third of the root. Selected landmarks (α, β, μ) on the preoperative (D) and postoperative radiograph (E) to adapt the postoperative radiograph and set the scale (x,y). F The corrected postoperative radiograph after using TurboReg plug-in application of ImageJ. G The measurement of the preoperative radiograph. H The measurement of the postoperative radiograph. The length (l) increased from 12.71 mm to 13.51 mm, the root thickness (r) increased from 6.12 mm to 6.27 mm and the pulp space (p) increased from 3.29 mm to 3.38 mm. The size of the apical diameter (a) decreased from 3.24 mm to 2.09 mm