Biomechanical context and clinical challenges

The long-term success of an implant-supported rehabilitation relies on the rigorous management of mechanical stresses transmitted to the peri-implant bone and prosthetic components. While titanium remains the standard, the rise of zirconia implants and the introduction of polymer materials such as PEKK are modifying the biomechanical balance of the bone-implant interface. The practitioner faces a complex trade-off: should priority be given to the rigidity of cobalt-chrome (Co-Cr) or zirconia frameworks, or should the resilience of PEKK be chosen, particularly in prosthetic designs with extensions?

The specific objective of this study was to evaluate, through 3D finite element analysis (FEA), the stress distribution exerted on the implant, the prosthetic system, and the peri-implant tissues. Based on an edentulous maxilla model reconstructed by CT scan, twelve configurations were tested. The study compares titanium and zirconia implants associated with three types of frameworks (Co-Cr, PEKK, zirconia) under two designs (with or without cantilever). The researchers tested the hypothesis that material stiffness and the presence of a cantilever significantly influence peak stresses (Von Mises) at the level of the posterior abutments and the trabecular bone under an oblique load of 200 N.

Methodology of the finite element study

This in silico study is based on a three-dimensional finite element analysis (FEA). Researchers modeled an edentulous maxilla from computed tomography (CT) data to develop 12 experimental models simulating various clinical configurations.

The protocol evaluated the interaction of three variable parameters:

• Implant materials: Comparison between titanium and zirconia.
• Infrastructure materials: Use of three distinct materials, Cobalt-Chrome (Co-Cr), PEKK (polyetherketoneketone) and zirconia (Y-TZP).
• Prosthetic design: Comparison between prostheses with and without extension (cantilever).

The experiment consisted of applying a static oblique load of 200 N, oriented at a 45° angle in a palato-vestibular direction, at the central fossa of the first molar. The analyses focused on the distribution of Von Mises stresses and principal stresses exerted on the implant, the abutment, the prosthetic screw, the framework, and the peri-implant bone. This approach allows for the precise quantification of force distribution and mechanical stress concentration zones within each component of the implant-prosthetic system.

Analysis of constraints: predominance of design and material

Finite Element Analysis (FEA) reveals significant stress variations across the 12 tested configurations. The highest peak Von Mises stress was recorded at 378.388 MPa in the model combining a zirconia implant and a PEKK framework with a cantilever.

Comparison of infrastructures and displacements

The choice of framework material directly influences biomechanical stability. Compared to Cobalt-Chrome (Co-Cr) and zirconium, the use of PEKK generated:

• Systematically higher Von Mises stresses.
• Greater prosthetic displacement under an oblique load of 200 N.

Impact of the extension (Cantilever)

The presence of a cantilever acted as a stress amplifier for all tested materials. Stress concentration areas are primarily located at the posterior abutments and the peri-implant bone. In the dental practice, this observation highlights the increased risk of local overload when using extensions.

Major clinical finding: in models with PEKK infrastructure and cantilever, stress values in the trabecular bone exceeded the physiological threshold, signaling a potential risk for long-term bone stability.

Zirconia vs Titanium

L'étude montre que les implants en zircone affichent des niveaux de contraintes supérieurs à ceux des implants en titane. Toutefois, les auteurs notent que ces valeurs sont restées dans des limites de sécurité mécaniques acceptables.

Clinical analysis of stress distribution

The results of this finite element analysis (FEA) study highlight the critical importance of structural rigidity in implant prosthetic design. The use of PEKK, while attractive for its shock-absorbing properties, shows clear biomechanical limitations when combined with a cantilever. The model combining a zirconia implant and a PEKK framework with a cantilever generated the highest stresses (378.388 MPa), even exceeding the acceptable physiological threshold for trabecular bone. This observation suggests an increased risk of peri-implant bone resorption and prosthetic system instability in this specific configuration.

Limitations and perspective

This study is based on a 3D numerical simulation subjected to an oblique static load of 200 N at 45°. Although rigorous, it does not reproduce the dynamic complexity of the oral environment, such as long-term material fatigue or the influence of biological bone remodeling. However, the data confirm that while zirconia implants undergo higher stresses than titanium ones, they remain within acceptable safety limits, validating their clinical viability subject to an optimized prosthetic design.

Implications for daily practice

The choice of materials must be dictated by the prosthesis configuration. Rigid frameworks made of Cobalt-Chrome (Co-Cr) or zirconium offer a much more balanced stress distribution than PEKK, particularly in areas with high occlusal load. The absence of a cantilever remains the golden rule to preserve the integrity of the peri-implant bone and minimize the risks of failure of the healing screws or abutments.

Summary of biomechanical results

This finite element analysis (FEA) reveals that the combination of a zirconia implant with a PEKK framework and a cantilever generates the highest stresses (378.388 MPa). While zirconia consistently induces more stress than titanium, it remains within safe limits, whereas the use of rigid materials and the absence of extension minimize the risks of peri-implant bone overload.

In concrete terms, for the practitioner:

• Prioritize rigidity: Opt for Co-Cr or zirconia frameworks rather than PEKK to reduce bone stress and prosthetic displacement, particularly on zirconia implants.
• Eliminate cantilevers: Avoid prosthetic extensions that push trabecular bone stress beyond the physiological threshold, increasing the risk of posterior resorption.
• Zirconia safety: You can use zirconia implants with confidence, as despite their superior rigidity, they maintain clinically acceptable stress distribution provided there is a balanced prosthetic design.

Technical lexicon of the study

Finite Element Analysis (FEA): Numerical simulation method used to model biomechanical behavior and quantify stress distribution within complex bone-implant-prosthesis structures.

Von Mises stress: Mathematical formula used to calculate the overall stress experienced by a ductile material in order to predict its risk of deformation or failure under multidirectional loads.

PEKK (Polyetherketoneketone): High-performance thermoplastic polymer used for prosthetic frameworks, characterized by lower stiffness than metals, resulting in greater flexibility under clinical load.

Cantilever (Extension): Prosthetic design featuring an overhanging part beyond the last implant abutment, increasing the lever arm and stress concentration on the supporting structures.

Y-TZP Zirconia: Yttria-stabilized tetragonal zirconia polycrystals, a ceramic material used for implants and frameworks, featuring high biocompatibility and a modulus of elasticity superior to that of titanium.

Trabecular Bone: Internal bone tissue with a porous structure (cancellous) whose physiological tolerance threshold to mechanical stress was specifically evaluated in this study to avoid resorption risks.

Oblique Static Load: 200 N force applied at 45° in the central fossa of the first molar to simulate masticatory stresses during biomechanical analysis.

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