Purpose: This study aimed to compare the biomechanical behavior of PEEK and Nylon in unmodified Kennedy class II restored with unilateral, tooth/implant-supported prosthesis using a three-dimensional finite element analysis (3D-FEA).

Materials and methods: A 3D-FEA model of mandibular unmodified Kennedy class II restored with unilateral, tooth/implant-supported and attachment-retained prosthesis. Premolars on the edentulous side were splinted and restored with porcelain fused to metal crowns with an OT-attachment mounted their distal surface and a distal titanium implant with a ball abutment in the 2nd molar region. Anterior and posterior retentive caps were modelled twice with (PEEK and Nylon). Oblique and vertical load was applied on each type of retentive caps. Von Misses stresses in the peri-implant bone, implants, OT-attachments and OT-connectors, ball abutments and prosthesis of each model was calculated. The numeric data were then collected, color-coded, and compared between the models.

Results: The highest stress concentration was in horizontal unsupported bar of OT-attachment followed by OT-connector at the junction of OT- attachment with splinted crowns in both Nylon and PEEK models under oblique load. Minimal stresses were in the peri-implant bone and implants in both models under both vertical and oblique load.

Conclusions: PEEK can be a valid alternative option to nylon for rehabilitation of unmodified Kennedy Class II cases with unilateral tooth/implant- supported prosthesis retained with double ball attachments. The design simulated in this study should be modified before it can be recommended for clinical use to improve occlusal support and minimize the stresses transmitted to OT-attachment and OT-connector.