Biomechanical Analysis of Mandibular Implant-Supported Overdentures With Different Retention Materials

PURPOSE: The aim of this study is to evaluate the biomechanical effects of different modulus of elasticity retentive materials (titanium [Ti]; polyetheretherketone [PEEK] and polyetherketoneketone [PEKK]) on mandibular implant-supported overdentures. METHODS: A finite element model of a mandibular 2-implant overdenture was constructed. Attachment housings were simulated in Ti, PEEK or PEKK, paired with retentive inserts of nylon, PEEK or PEKK. Three occlusal loading conditions were simulated: a 100 N vertical load on the left first molar (centric occlusion), a 100 N oblique load on the same site (lateral occlusion), and a 100 N vertical load on the bilateral mandibular central incisors (50 N per tooth, protrusive occlusion). The stress distribution across all structures of the implant-supported overdenture and the denture displacement were analysed. RESULTS: (1) The Ti-housing/PEKK-insert configuration produced the lowest denture base stress and displacement but the highest stress on implants, abutments, and peri-implant bone, (2) Under all 3 loading conditions, bone tissue stress predominantly concentrated in the cortical bone near the implant cervix; implant stress mainly focused on its internal region connected to the abutment; denture stress primarily accumulated at the contact area between the tissue-facing surface of the denture base and the attachment housing, (3) In intergroup comparisons, oblique loading conditions showed the highest stress values for the implant, abutment, peri-implant bone tissue and denture base. CONCLUSION: Nylon, PEEK and PEKK are all viable retentive insert materials. Nylon is preferable for reducing stress on implants and bone, whereas PEEK or PEKK inserts better enhance prosthetic stability and reduce denture base fracture risk.