This study evaluated the Graduated Radiographic-Surgical Guide (GRSG) accuracy to insert mini-implant in the interradicular septum. Additionally, a Risk Index (RI) was determined to predict surgical risk. Fifty-three titanium mini-implants were placed in the buccal interradicular septum of the posterior maxillary and/or mandibular region. The GRSG was used to insert mini-implants in a centralized position regarding adjacent tooth roots. Fifty-three post-surgical radiographs were used to measure GRSG accuracy in obtaining the mini-implant centralized position in the septum. Afterwards, the GRSG inaccuracy degree was related to the septum width and the mini-implant diameter to calculate the Risk Index (RI). The link established between the radiographic and surgical procedures propitiated a small GRSG inaccuracy degree of 0.13mm, allowing an accurate prediction of the final mini-implant positioning in the interradicular septum, which contributed to a low surgical risk (RI<1).