Precision in mandibular implant overdentures

Aim: Selection of prosthetic attachment height and implant number can influence the supporting structures of implant mandibular overdentures (IMOs), including peri-implant tissue and prosthetic components. This study evaluated the biomechanical effects of single IMO (SIMO) or two IMO (TIMO) systems with different stud transmucosal heights (2, 3, or 4 mm) on cortical bone, mucosal tissue, implants, and prosthetic elements. Methods: Twelve three-dimensional finite element models were created using McNeel Rhinoceros 3D v7.0®, representing scenarios with 2 mm (SIMO-2mm, TIMO-2mm), 3 mm (SIMO-3mm, TIMO-3mm), and 4 mm (SIMO-4mm, TIMO-4mm) heights. Simulations included 100 N oblique loading (30º) on lower central incisors and 150 N axial loading on the first molars. Von Mises stress (implant, housing, stud), maximum and minimal principal stress (bone, tissue, prosthesis, nylon), and displacement were analyzed through numerical data and color-coded images. Results: Oblique loading resulted in higher stress, particularly in SIMO-4mm and TIMO-4mm. Nylon inserts in SIMO configurations experienced high compressive stress, especially in SIMO-4mm. TIMO configurations under oblique loading caused critical stress in peri-implant bone. Prosthetic tensile stress and displacement were greatest in SIMO-4mm under anterior loading. High transmucosal heights increased stress on housing, attachment, and prosthesis, particularly in systems with thin soft tissue. Conclusion: SIMO and TIMO rehabilitations under oblique loading showed high stress in ductile structures, with significant implications for SIMO-4mm due to stress concentration in nylon, prosthesis base, and displacement. Elevated transmucosal heights should be used cautiously in cases of limited soft tissue thickness.