BIOMECHANICAL EVALUATION OF MANDIBULAR OVERDENTURES SUPPORTED BY MINI-IMPLANTS: A FINITE ELEMENT ANALYSIS

This paper presents the effects of using two or four mini-implants to support a mandibular overdenture for edentulous patients. The stresses on the mini-implants and the strains on the peri-implant and surrounding bone were evaluated and compared to known values of strength for the mini-implants and physiologic bone strain to potentially stimulate and maintain bone volume of the edentulous ridge. Two finite element models created were identical with the exception of the number of denture-supporting mini-implants. Both models contained modeled mucosa, cortical bone, cancellous bone, and two anterior mini-implants (approximating the position of the mandibular canine teeth). The second model also contained two posterior mini-implants (in the molar region). Clinical masticatory loading of three 70N loads bilaterally was used. The anterior mini-implants in both models showed stresses below the material's fracture threshold. In contrast, posterior mini-implants experienced stresses above the implant's yield limit, indicating that the posterior mini-implants could be at risk for failure. Strains in the peri-implant and surrounding bone around the posterior mini-implants were above the physiologic limit, indicating that this region might be at risk for bone resorption. The addition of the posterior mini-implants did not appear beneficial to maintain edentulous bone. Based on the limitations of this study, anterior mini-implants can be safely used for a mandibular overdenture whereas posterior mini-implants may not be a wise treatment option for edentulous patients due to risks of implant fracture and pathologic bone resorption. Dentists must weigh risks and benefits of using posterior mini-implants placed in the molar region.