Correlation of implant position and crestal bone loss in 2-implant mandibular overdentures with immediate loading protocols: A prospective clinical study

STATEMENT OF PROBLEM: The 2-implant mandibular overdenture (2IMO) is a popular treatment for patients with an edentulous mandible, but information on the effect of the optimum implant position on the peri-implant crestal bone level with immediate loading protocols is lacking.

PURPOSE: The purpose of this prospective clinical study was to evaluate correlations between different implant positions and crestal bone loss and between interimplant distance and the crestal bone loss in patients with 2IMOs with immediate loading protocols at 1-year follow-up.

MATERIAL AND METHODS: A total of 24 participants (13 men, 11 women, mean ±standard deviation age 63.25 ±10.76 years) were treated with 2IMOs (48 Ti-Zr implants) by a single operator between August 2015 and October 2020. The implant diameters (3.3 mm or 4.1 mm) and lengths (10 mm or 12 mm) were selected based on the crestal bone width, and the implants were placed, if possible, in the canine regions. Implant positions and interimplant distance (mm) were measured intraorally with dividers. Prefabricated mandibular dentures were immediately loaded with the LOCATOR-attachments by using a direct intraoral pickup procedure. Crestal bone-level changes were measured with a software program on the mesial and distal sides of each implant from periapical radiographs made with a paralleling technique (at baseline and 1-year follow-up). The measurement values were normalized. The Spearman rho correlation test and paired samples t tests were used for data analysis (α=.05).

RESULTS: The mean ±standard deviation position of the implants from the midline was 8.78 ±2.25 mm (9.00 ±2.22 mm right side, 8.56 ±2.31 mm left side), and the mean interimplant distance was 16.94 ±4.03 mm. At 1-year follow-up, the mean ±standard deviation crestal bone loss was 0.50 ±0.47 mm (n=48) (0.57 ±0.65 mm mesial, 0.43 ±0.53 mm distal). The mean ±standard deviation crestal bone loss was 0.46 ±0.4 mm with Ø3.3-mm implants (n=42) and 0.9 ±0.8 mm with Ø4.1-mm implants (n=6) (P=.005). Implant positions were negatively correlated (rs=-0.37) with the crestal bone loss, and the correlation was significant (P=.009). Interimplant distances were also negatively correlated with crestal bone loss (rs=-0.60; P=.002). Bone loss on the mesial side was positively correlated with that on the distal side rs=0.20; however, the correlation was not significant (P=.16).

CONCLUSIONS: A weak and negative correlation was found between the implant position from the midline and the crestal bone loss and also between the interimplant distance and crestal bone loss in patients provided with 2IMOs with immediate loading protocols.