Is one dental mini-implant biomechanically appropriate for the retention of a mandibular overdenture? A comparison with Morse taper and external hexagon platforms.

Abstract Statement of problem Limited information is available to clinicians on the use of dental mini-implants (MI) as opposed to standard-diameter implants (SDIs) for the stabilization of implant-retained mandibular overdentures (MOs). Purpose The purpose of this in vitro and finite element analysis study was to analyze and compare the biomechanical behavior of MOs with either 1 or 2 implants with external hexagon (EH), Morse taper (MT) SDIs, and MIs. Material and methods Thirty photoelastic models (n=30) of each group (n=5) of SDIs (EH-1, EH-2, MT-1, MT-2) and MI (MI-1, MI-2) were fabricated for posterior, peri-implant, and total maximum shear stress evaluation by quantitative photoelastic analysis. One specimen of each group was further used to create the 6 computational models to be analyzed by finite element analysis. The maximum von Mises values and stress maps were plotted for each ductile component. Two types of load were applied to the overdenture: a150-N load bilaterally and simultaneously on the first molar and a 100-N load on the incisal edge of the central incisors at a 30-degree angle. The data were subjected to the 2-way ANOVA test and the Tukey honestly significant difference test (α=.05). Results The EH-2 and MT-2 showed the lowest posterior (P .05). Regardless of the loading area, the MI-1 and MI-2 groups showed the lowest von Mises stress values. However, for implant housing, the MI-1 group, under incisor loading, presented greater stress, followed by MT-1, EH-1, EH-2, MI-2, and MT-2. The attachment was the most overloaded structure, with high values under incisor loading, especially for the groups with 2 implants (MT-2, EH-2) as compared with the other models. Conclusions Biomechanically, regardless of the implant number, MI is a promising rehabilitation method with similar peri-implant shear stress and lower von Mises stress on the implant when compared with SDIs for MOs.