Single Versus Double Implants in a Narrowed Mandibular Molar Space: A Finite Element Analysis

After molar loss, tipping of the adjacent teeth and extrusion of the opposing tooth often leave a mesiodistal space too narrow for a conventional implant. This study compared stress in the implant components and peri-implant bone among single- and double-implant configurations of different diameters in such a space. A mandibular model was constructed by computer-aided design; ridge resorption and mesial tipping of the second molar left a 13.6 mm mesiodistal space and a 7.5 mm crestal ridge width. Four configurations were modeled: 4.8 mm single (M1), 4.1 mm single (M2), 3.3 + 3.3 mm double (M3), and 4.1 + 3.3 mm double (M4). Vertical (150 N) and oblique (300 N at 45°) loads were applied; von Mises stress in the components and maximum and minimum principal stresses in bone were recorded. Oblique loading raised stress in every structure; because the oblique load was twice the vertical load, part of this increase reflects the higher force rather than loading direction alone, and direction-related increases (normalized per unit load) ranged from approximately 2- to 9-fold across components and bone. Under vertical loading, M1 gave the lowest implant body, abutment, and screw stresses (31.0, 36.7, and 16.1 MPa). Under oblique loading, M4 lowered implant body and abutment stress, whereas M1 retained the lowest screw (192.0 MPa) and configuration-level bone stresses (31.2 and 7.2 MPa). Because screw preload was not modeled, screw-stress comparisons should be interpreted as relative mechanical demand rather than as predictors of loosening or fracture risk. No configuration minimized stress in every structure. Implant diameter, site, component, and loading condition should be weighed together.