2022, Vol. 26 ›› Issue (22): 3492-3497

Finite element biomechanical analysis of various bone mineral densities on edentulous mandibular four-implant-supported overdentures fixed using Locator attachments

Wang Yuan1, 2, 3, Zhang Yang1, 2, 3   

Abstract: BACKGROUND: The four-implant-supported overdenture is a commonly used treatment for the edentulous mandibular patient, while the bone mineral density affects the biomechanical outcome, the stability of the implant-supported prostheses, and the health of surrounding tissue, thus influences the long-term therapeutic effect.
OBJECTIVE: To evaluate the influence of bone mineral density on stress distribution of edentulous mandibular four-implant-supported overdentures via Locator attachments through a three-dimensional finite element analysis.
METHODS: Four edentulous mandibular male patients without systemic disease, who had worn four-implant-supported overdentures via Locator attachments, were selected to establish three-dimensional finite element models. Four edentulous mandible models (M1, M2, M3, and M4) made of four different bone types (type 1, 2, 3, and 4, corresponding to the order of cancellous bone whose modulus of elasticity is 9.5, 5.5, 1.6, 0.69 GPa) and embedded with four implants in the interforaminal region were established based on cone beam computerized tomography data. The mandibles were restored using four-implant-supported overdentures via Locator attachments. After 3 forces (F1, F2, and F3) of 120 N magnitudes from various directions applied on the right lower first molar, the von Mises stresses on the cortical and cancellous bones and the implants were determined.  
RESULTS AND CONCLUSION: (1) For the cortical bone or the cancellous bone, stress concentrations were found on the peri-implant area of models (M1, M2, M3, and M4), particularly on the loading side in all the models. The maximum von Mises stress increased progressively for the cortical bone and implants, but decreased progressively for the cancellous bone from type 1 (M1) to type 4 (M4) bones under three loading conditions. (2) For the implant, stress concentrations were found at the necks of implants and at the contact zones between implants and the Locator abutments, especially on the loading side. The highest maximum von Mises stress was found on M4, while the lowest maximum von Mises stress was found on M1. (3) Results indicate that compact bones (types 1 and 2) are the most suitable bones for edentulous mandibular implant-supported overdentures. Poor bone mineral density (type 4 bone) may increase the risk of biological and mechanical failures.
Key words: bone mineral density, stress distribution, edentulous mandible, implant-supported overdenture, three-dimensional finite element analysis, Locator attachments