Evaluation of fracture strength and marginal adaptation of different substructure materials in hybrid prostheses

Objective: This in vitro study aimed to compare different framework materials preferred in implant-supported hybrid prostheses in terms of marginal fit, fracture resistance, and fracture type. Method: A partial hybrid prosthesis substructure in the form of prepared teeth was designed on two implants placed in the edentulous lower jaw model using the All-on-Four technique. A total of 40 samples were divided into four groups: polyetheretherketone (PEEK), zirconia (Zr), fiber-reinforced composite (FRC), and chromium-cobalt (Cr-Co) (n=10). The Cr-Co frameworks were produced using the selective laser sintering (SLS) method. The PEEK, Zr, and FRC frameworks were produced using a CAD/CAM system and bonded to titanium abutments with resin cement. All frameworks were secured by screwing them into resin models prepared using a 3D printing method. Marginal fit conditions were evaluated using a stereomicroscope. Fracture strength was measured using a universal testing machine under static loading, and fracture types were classified. Data were analyzed using SPSS 23.0 software (p<0,05). Results: There was a statistically significant difference between the groups in terms of fracture resistance (p<0,0001). The lowest average value was obtained in the FRC group (1354,41 ± 116,50 N), while the highest was obtained in the Zr group (2922,44 ± 296,22 N). In the vertical fit evaluation, the average misfit of the Cr-Co group (60,96 ± 27,36 µm) was found to be significantly higher than the other three groups (p<0,0001); while the lowest value was observed in the FRC group (28,61 ± 10,03 µm). In terms of passive fit, the lowest average was measured in the PEEK group (54,39 ± 26,25 µm), and the highest in the Cr-Co group (137,03 ± 98,41 µm), and the difference was found to be statistically significant (p<0,0001). No significant relationship was found between marginal fit and fracture resistance (p>0,05). Conclusion: The fact that all materials demonstrate clinically acceptable marginal fit and sufficient fracture resistance shows that different substructure options are interchangeable in implant-supported hybrid prostheses. Key words: implant-supported hybrid prosthesis, hybrid prosthesis substructure materials, marginal fit, fracture resistance, prosthetic complications