Biomechanical Effect of Implant Thickness and Screw Diameter on CFR-PEEK Subperiosteal Implants: A Three-Dimensional Finite Element Analysis

Eda Etik, Basak Keskin Yalcin

Full text link: https://pubmed.ncbi.nlm.nih.gov/42032041/

Biomechanical Effect of Implant Thickness and Screw Diameter on CFR-PEEK Subperiosteal Implants: A Three-Dimensional Finite Element Analysis

1. Scientific Reference

• Study Title: Biomechanical effect of implant thickness and screw diameter on CFR-PEEK subperiosteal implants: a three-dimensional finite element analysis
• Authors: Eda Etik, Basak Keskin Yalcin
• Journal: Scientific Reports
• Year: 2026
• DOI: 10.1038/s41598-026-49671-0

2. Scientific Background

The rehabilitation of patients with severe maxillary atrophy continues to represent one of the most demanding situations in implant dentistry. When conventional endosseous implants cannot be placed because of insufficient bone volume, alternative treatment strategies become necessary. Advances in digital imaging, CAD/CAM technologies, and additive manufacturing have renewed clinical interest in patient-specific subperiosteal implants, offering customized solutions for anatomically complex cases.

Alongside digital design, material selection has become an essential factor influencing implant performance. Carbon Fiber Reinforced Polyetheretherketone (CFR-PEEK) has attracted growing attention because it combines high mechanical strength with an elastic modulus closer to that of bone than conventional metallic materials. Despite these advantages, limited evidence is available regarding how implant design variables—particularly framework thickness and fixation screw diameter—affect the biomechanical behavior of customized subperiosteal implants. This study addresses that knowledge gap using three-dimensional finite element analysis to evaluate the mechanical response of different implant configurations.

3. Study Objective

The purpose of this investigation was to determine how variations in subperiosteal implant framework thickness and fixation screw diameter influence the biomechanical performance of patient-specific implants manufactured from 60% Carbon Fiber Reinforced PEEK.

Specifically, the authors compared stress distribution patterns and structural displacement across several implant configurations to assess how these design parameters affect overall mechanical stability and load transfer within the implant–bone complex.

4. Methodology

This research was designed as a preclinical in silico finite element analysis (FEA). A three-dimensional anatomical model was reconstructed from computed tomography data obtained from a patient presenting with severe maxillary atrophy (Cawood and Howell Class V). The digital reconstruction served as the basis for creating a patient-specific subperiosteal implant model.

Four implant configurations were generated by combining two framework thicknesses (1.0 mm and 1.5 mm) with two fixation screw diameters (1.5 mm and 2.0 mm). The implant framework was modeled using 60% CFR-PEEK, while fixation screws, abutments, and the metallic framework were assigned titanium material properties.

Three clinically relevant loading conditions were simulated: bilateral posterior vertical loading, unilateral posterior oblique loading, and bilateral anterior vertical loading. Outcome measures included total displacement, maximum and minimum principal stresses within the bone, and Von Mises stresses affecting the implant framework, abutments, and metallic components. Because this was a computational study, no clinical follow-up was performed.

5. Main Findings

The simulations demonstrated that implant geometry had a substantial impact on the biomechanical response of the entire implant system. Increasing the framework thickness from 1.0 mm to 1.5 mm consistently reduced overall structural displacement, indicating greater mechanical rigidity under all loading conditions. The thicker framework also lowered both tensile and compressive stresses within the surrounding maxillary bone, particularly in the posterior alveolar crest, which experienced the highest functional loads throughout the analyses.

A similar trend was observed when the fixation screw diameter was increased from 1.5 mm to 2.0 mm. Larger screws decreased stress concentrations within both the supporting bone and the subperiosteal implant by improving load distribution across the fixation interface. However, this improvement was accompanied by increased stress within the metallic framework, suggesting that part of the functional load was redistributed toward the prosthetic superstructure rather than being eliminated entirely.

Among the three loading scenarios, posterior loading generated the greatest mechanical demand, with the highest stress values consistently occurring in the posterior maxillary region. In contrast, anterior loading produced lower overall stress levels and a different distribution pattern, with stress concentrations shifting toward the piriform aperture and adjacent nasal floor. The analyses also indicated that the relatively high elastic modulus of 60% CFR-PEEK reduced stress transmission to the bone while concentrating greater mechanical loads within the implant body and metallic framework. Based on these numerical simulations, the authors concluded that all evaluated configurations fulfilled the essential biomechanical requirements for patient-specific subperiosteal implant systems, while emphasizing that these findings remain limited to finite element modeling and require experimental and clinical validation.

6. Clinical Analysis

Rather than proposing a new clinical protocol, this study provides valuable biomechanical insight into how relatively small design modifications can influence the mechanical behavior of customized subperiosteal implants. The findings highlight that implant performance depends not only on the biomaterial itself but also on the interaction between framework geometry, fixation strategy, and functional loading conditions.

Increasing framework thickness improved structural rigidity and reduced deformation under functional loads. From a biomechanical perspective, limiting implant displacement may contribute to a more favorable transfer of occlusal forces to the supporting bone. Likewise, larger fixation screws distributed mechanical loads more evenly across the bone–implant interface, decreasing stress concentrations that could otherwise develop around fixation points. Although these observations are encouraging, they should not be interpreted as evidence of superior long-term clinical outcomes, since biological healing and bone remodeling were not evaluated.

The study also illustrates an important principle in implant biomechanics: optimizing one component often shifts mechanical stresses elsewhere within the system. While thicker frameworks and larger screws reduced stress within the peri-implant bone, they simultaneously increased stress levels within the metallic framework. This redistribution emphasizes that implant design requires a balanced approach rather than focusing exclusively on minimizing bone stress.

The performance of 60% CFR-PEEK is another noteworthy aspect of this investigation. Its relatively high stiffness reduced stress transmitted to the surrounding bone while maintaining overall structural stability. However, the simulations also demonstrated that this mechanical behavior resulted in greater stress concentration within the implant framework itself. Consequently, material selection should be considered together with implant geometry rather than as an isolated design parameter.

Several limitations should be acknowledged before extrapolating these findings to clinical practice. The finite element model was derived from a single patient’s anatomy, and all materials were assumed to behave as homogeneous, isotropic, and linearly elastic. Biological variables—including bone remodeling, healing capacity, patient-specific bone quality, and long-term fatigue loading—were beyond the scope of the computational model. Accordingly, the results should be regarded as biomechanical evidence supporting future experimental and clinical investigations rather than direct clinical recommendations.

7. Clinical Applications

The findings of this study are particularly relevant for the digital planning and engineering of patient-specific subperiosteal implants intended for individuals with severe maxillary atrophy who may not be suitable candidates for conventional implant placement or advanced bone augmentation procedures.

Within a fully digital workflow integrating CT imaging, CAD/CAM design, and customized manufacturing, framework thickness and fixation screw diameter emerge as important variables that may influence implant stability and stress distribution. These data may assist engineers and clinicians during the design phase of customized implant rehabilitation by identifying geometric characteristics associated with improved biomechanical performance.

However, the study does not establish clinical guidelines or recommend a specific implant configuration. The reported findings should instead be viewed as preclinical evidence supporting further laboratory research and prospective clinical studies before these design principles can be translated into routine patient care.

8. Level of Evidence, Limitations, and Transparency

This publication is a preclinical in silico investigation based on three-dimensional finite element analysis (FEA). While this methodology is well established for evaluating biomechanical behavior under standardized conditions, it represents preclinical evidence and cannot directly predict clinical performance, implant survival, or patient-related outcomes.

Methodologically, the study benefits from a detailed patient-specific digital model reconstructed from computed tomography data, the comparison of four implant configurations, and the simulation of three clinically relevant loading conditions. The authors also performed a mesh convergence analysis to improve the numerical reliability of the finite element models before conducting the biomechanical simulations.

Several limitations should be considered when interpreting the findings. The computational model was derived from the anatomy of a single patient, limiting the generalizability of the results. Furthermore, all materials were modeled as homogeneous, isotropic, and linearly elastic, assumptions that simplify the complex mechanical behavior of living bone and surrounding tissues. Biological processes such as bone remodeling, osseointegration, tissue adaptation, and patient-specific variability were beyond the scope of the simulation. Consequently, although the study provides valuable biomechanical insights, its findings should not be interpreted as direct evidence of clinical superiority for any particular implant configuration.

The manuscript reports institutional ethical approval and informed patient consent for the use of CT imaging data. Based on the information available in the article, no conflicts of interest or financial relationships with implant manufacturers are reported.

9. Key Study Points

• Study type: Preclinical in silico finite element analysis (FEA).
• Level of evidence: Preclinical computational study.
• Population: One patient-specific digital model representing a severely atrophic maxilla (Cawood and Howell Class V).
• Number of patients: 1.
• Implant configurations: Four virtual models combining two framework thicknesses (1.0 mm and 1.5 mm) with two fixation screw diameters (1.5 mm and 2.0 mm).
• Follow-up: Not applicable.
• Primary outcome: Influence of framework thickness and screw diameter on stress distribution and structural displacement.
• Main finding: Increasing framework thickness and screw diameter reduced stress within the supporting bone and improved structural stability while increasing stress concentrations within the implant framework and metallic superstructure.
• Scientific conclusion: Framework geometry, fixation screw diameter, and CFR-PEEK stiffness significantly influence the biomechanical performance of patient-specific subperiosteal implants under simulated loading conditions.
• Main limitations: Single-patient computational model, simplified material assumptions, and absence of biological or clinical validation.

10. Scientific Impact

This study contributes meaningful biomechanical evidence to the growing body of research on patient-specific subperiosteal implants by investigating two design variables that have received comparatively limited attention: framework thickness and fixation screw diameter. Rather than focusing exclusively on material properties, the authors demonstrate that implant geometry itself plays a critical role in determining how functional forces are transmitted throughout the implant–bone complex.

The work also supports the continued exploration of 60% Carbon Fiber Reinforced PEEK (CFR-PEEK) as an alternative framework material for customized implant rehabilitation. Its mechanical behavior appears capable of reducing stress transferred to the surrounding bone while maintaining adequate structural rigidity. At the same time, the study highlights that optimizing implant biomechanics requires balancing stress distribution across all components rather than minimizing stress within a single structure.

Although the investigation does not establish clinical efficacy, it provides quantitative biomechanical data that may inform future implant design strategies. More importantly, it lays the foundation for experimental validation and prospective clinical research aimed at determining whether the favorable stress patterns observed in numerical simulations translate into improved long-term outcomes in patients undergoing rehabilitation with customized subperiosteal implants.

11. Editorial Conclusion

This preclinical finite element study demonstrates that both implant framework thickness and fixation screw diameter are key determinants of the biomechanical behavior of customized CFR-PEEK subperiosteal implants. The simulations suggest that thicker frameworks and larger fixation screws improve structural stability while reducing stress transmitted to the supporting bone, although mechanical loads become more concentrated within the implant framework itself. These findings provide valuable engineering insight for the digital design of patient-specific implants, but they should be interpreted within the limitations of computational modeling. Clinical studies remain necessary to determine whether these biomechanical advantages result in improved long-term treatment outcomes.