Dental mini-implant designs to support overdentures: Development, biomechanical evaluation, and 3D digital image correlation

Custom mini-implants are needed for edentulous patients with extensive mandibular deficiencies where endosteal placement is not possible. However, the best design for these mini-implants is unclear.The purpose of this in vitro study was to develop 2 dental mini-implant designs to support mandibular overdentures and evaluate the effect of their geometries on primary stability and stress distribution.Two mini-implant designs were developed with changes in the shape, size, and arrangement of threads and chamfers. The experimental mini-implants were made of Grade V titanium alloy (Ti-6Al-4V), (Ø2.0×10 mm) and submitted to a nanoscale surface treatment. Thirty mini-implants (n=10) were placed into fresh swine bones: experimental-threaded, experimental-helical, and a commercially available product model (Intra-Lock System) as the control. The biomechanical evaluations of the experimental mini-implants were compared with those of the control in terms of primary stability, through insertion torque (IT), and with the pullout test. The analysis of stress distribution was performed by using the method of 3D digital image correlation under 250-N axial load and 100-N oblique (30-degree angled model) load. The data were analyzed by ANOVA and the Tukey HSD test (α=.05).The IT and pullout test presented a statistically significant difference for all mini-implants (P.05), with higher IT for the experimental-threaded and maximum pullout force for the control, followed by threaded (P=.001) and helical (P=.001). Regarding the 3D digital image correlation, a lower incidence of stress was found in the cervical third for all mini-implants. No statistically significant differences were found between the designs evaluated (P.05).Comparing the experimental mini-implants with the commercially available control, the experimental-threaded model presented greater primary stability, and all mini-implants showed less stress in the cervical third.