To assess the implant position (IP), the interradicular septum width (ISW) and radiographic bone to implant contact (BIC), when simulating an immediate implant placement in first and second mandibular molars.

75 patients (150 sites) were studied using cone beam computed tomography scans (CBCT) and computer aided design software. Implants were placed in a prosthetically driven position; subsequently, IP and BIC were digitally calculated. Linear ISW was also analyzed at 2, 4 and 6mm apically to the highest septal bony peak.

Multiple linear regressions were performed to assess relationships between BIC and the different predictive variables. Additionally, the receiver operating characteristics (ROC) curve was used to create a model for BIC based on the ISW at 2mm.

BIC in implants replacing first molars was the highest at the septal (S) position when compared to those in septal-mesial (S–M) position (p-value 0.001). As for the second molar, the highest percentage of BIC was recorded at the septal (S) position, followed by those in S–M and mesial (M) positions (p<0.001).

According to the proposed classification, clinician must consider the ISW and IP when placing immediate implant in the first and second mandibular molar sites. When tackling first molars, S position is predominant, while S–M position is the most common in the second molars. ISW at 2mm should be at least respectively 2mm and 2.5mm at the first and second molar sites to achieve 50% of BIC.