A cross‐sectional CBCT assessment of the relative position of one‐piece titanium‐zirconium mini‐implants placed for mandibular overdentures using non‐guided surgery

Abstract Objective To assess the relative position of mini‐implants to retain a mandibular overdenture, according to the surgical protocol, technical and anatomical factors. Methods Mandibular cone‐beam computed tomography (CBCT) scans were analyzed for 73 patients who received four one‐piece titanium‐zirconium mini‐implants. Drilling was performed using a 1.6 mm needle drill and a 2.2 mm Pilot Drill, according to the bone density with a surgical stent. Post‐insertion CBCT images in DICOM format were analyzed using the E‐Vol‐DX software with BAR filters. Divergence angle between implants and between implants and the overdenture path of insertion was measured using CliniView 10.2.6 software. Results Divergence between implants ranged from 0° to 22.3° (mean = 4.2; SD = 3.7) in the lateral and from 0° to 26.2° (mean = 5.3; SD = 4.1) in the frontal projections ( p < .001). Only 1 (0.2%) and 3 (0.7%) of the measurements were higher than 20° in the lateral and frontal views, respectively. The mean angulations between the implant and the path of insertion for the overdenture were 9.3° (SD = 7.5) and 4.0° (SD = 2.9) for the lateral and frontal views, respectively ( p < .001). Regression analyses showed a significant association between the divergence of implants and the frontal view projection ( p < .001), greater distance between the paired implants ( p = .017), the flapped surgical protocol ( p = .002), higher final insertion torque ( p = .011), and deeper preparation with the needle drill ( p < .001). Conclusions The mini‐implants were placed with low divergence angles and satisfactory parallelism. Factors including shorter distances between the implants, higher density bone, and a flapless surgical approach all contributed positively to improved parallelism of the mini‐implants.