Microstrain Patterns in Mandibular Ti-Zr Mini-Implant Overdentures: Effects of Mucosal Thickness and Implant Configuration

Background: The biomechanical behaviour of mandibular Ti-Zr mini-implant (MDI) retained overdentures is influenced by implant number, loading conditions, and mucosal thickness. This study assessed the effect of mucosal thickness and other factors on peri-implant and distal edentulous ridge microstrain values under functional loading. Methods: Eight stereolithographic mandibular models simulating D2 bone were fabricated with one, two, three, or four Ti–Zr MDIs and covered with artificial mucosa of 1.9 mm (thin) or 3.8 mm (thick). Standardized overdentures were loaded anteriorly, unilaterally, and bilaterally with forces ranging from 50 to 300 N. Strain gauges measured micro-deformation at vestibular and oral peri-implant sites and the distal edentulous ridge. Data were analyzed using MANOVA and between-subject tests, with effect sizes (η2) calculated. Results: Peri-implant microstrain decreased with increasing implant number, with single-implant overdentures reaching more than 2500 µε under anterior loading, as well as two-implant overdentures under unilateral loading; four-implant configurations remained <2000 µε. Mucosal thickness had no influence on peri-implant strains in two- and four-implant setups; however, thicker mucosa showed a very small attenuation effect in one-implant arrangements and medium effect in three-implant arrangements. Loading force and position were the dominant determinants of peri-implant strain. Distal ridge microstrain was significantly attenuated by thicker mucosa (η2 ≈ 0.449). Conclusions: Implant number, loading force and position predominantly govern peri-implant strain distribution, while thicker mucosa effectively reduces distal ridge strain beneath the overdenture. Single- or two-implant mandibular overdentures are more vulnerable to high unilateral or anterior loads, emphasizing the importance of careful implant planning and occlusal management in clinical practice.