Mandibular bone characteristics, drilling protocols, and final insertion torque for titanium‐zirconium mini‐implants for overdentures: A cross‐sectional analysis

Abstract

Objective: The aim of this study was to assess the final insertion torque values achieved using site-specific drilling protocols for a novel mini implant system for removable complete overdentures. Anatomical and technical factors influencing final insertion torque were recorded and analyzed.Material and Methods: Participants were randomized to two surgical protocol groups (flapped or flapless) and all received four mini implants (Straumann ® mini implant system; Straumann AG) in the anterior mandible, using a 1.6 mm needle drill and a 2.2 mm pilot drill for the implant bed site preparation. The final insertion torque was recorded as the main outcome variable during surgery. Bone type, radiographical bone density, ridge form, implant length, and the drilling protocol were considered as independent variables. Descriptive statistics, generalized estimating equations (GEE) regression, and heatmap charts were used for data analyses.Results: A total of 296 mini implants were placed in 74 patients (mean age = 64.1 ± 8.0; 64.9% female) using flapless (n = 37) or flapped (n = 37) surgeries. Mean final insertion torque was 55.8 ± 18.4 Ncm (10.5% > 35 Ncm, 48.9% between 35 and 65 Ncm, and 40.6% > 65 Ncm). The needle drill was used in only 43.9% of the implant bed sites. Higher final torque values were observed for higher bone densities (bone type I > II > III, and D1-D2 > D3-D4), highly resorbed ridge forms (5-6 > 3-4), flapped surgeries, and male patients. However, regression models showed that the likelihood of achieving optimal insertion torque (≥35 and ≤65 Ncm) was higher for females (OR = 2.14; 95%CI = 1.14-4.01; p = 0.018), ridge forms 3-4 (OR = 2.87; 95%CI = 1.05-7.85; p = 0.040), and flapless surgeries (OR = 1.96; 95% CI = 1.09-3.51; p = 0.024).Conclusions: Sufficient primary stability for immediate loading was achieved for the majority of the mini implants placed. Surgical implant bed preparation should be sitespecific to achieve optimal primary stability for immediate loading while avoiding excessive insertion torque.

Implant survival/success and peri‐implant outcomes of titanium‐zirconium mini implants for mandibular overdentures: Results from a 1‐year randomized clinical trial

“…Therefore, due to their narrow diameter and sharp apical taper, mini implants may be exposed to a higher fracture risk than standard implants. In addition, since adequate torque had to be achieved during insertion, and extreme insertion torque values may occur in high‐density bone sites, there is a risk of reaching high torque values that exceed the implant body fracture resistance (Leles et al, 2023). Moreover, anatomical factors may also increase the risk of apical fracture during insertion, which demands the identification of potentially dangerous areas predisposing to implant breakage that may affect optimal insertion torque and implant stability.…”

“…A detailed description of all stages of the study has been previously published elsewhere (Leles et al, 2022; Leles et al, 2023). A summary of the methods concerning patient selection, surgery planning, and surgical procedures, as well as the peri‐implant assessments and study outcomes, is described as follows.…”

“…The drilling protocol was slightly modified according to specific features of the implant bone site. The mini implants were inserted to achieve a minimum of 35 Ncm final insertion torque, independent of the randomized implant loading protocol (immediate or delayed) (Leles et al, 2023). In the case of a patient assigned to the immediate loading group and any mini‐implants not achieving the minimum 35 Ncm torque, delayed loading was performed.…”

“…A detailed description of all stages of the study has been previously published elsewhere (Leles et al, 2022;Leles et al, 2023).…”

“…These findings suggested that the surgical and loading protocols may affect post‐operative symptoms and short‐term patient‐perceived outcomes. However, surgical and loading protocol combinations may not affect implant survival and success when implant bed preparation and soft tissue are appropriately managed and sufficient primary stability is achieved for immediate loading (Leles et al, 2022; Leles et al, 2023).…”