Custom-made Subperiosteal Implants: A Finite Element Analysis on Monoblock and Dual Implant Systems in Atrophic Maxilla

Custom-made Subperiosteal Implants: A Finite Element Analysis on Monoblock and Dual Implant Systems in Atrophic Maxilla

1. Bibliographic Reference

• Study Title: Custom-made Subperiosteal Implants: A Finite Element Analysis on Monoblock and Dual Implant Systems in Atrophic Maxilla
• Authors: Mustafa Ayhan, Abdulkadir Burak Cankaya
• Journal: International Journal of Medical Sciences
• Year of Publication: 2023
• Volume: 20(13)
• Pages: 1755–1762
• DOI: 10.7150/ijms.89411

2. Scientific Background

The rehabilitation of patients with severe maxillary atrophy remains one of the most challenging situations in contemporary implant dentistry. Conventional endosseous implants require sufficient bone volume and density to achieve primary stability and long-term osseointegration. In cases of advanced bone resorption, clinicians often rely on extensive augmentation procedures, including autogenous bone grafting or iliac crest grafts.

Although these reconstructive approaches can be effective, they are associated with increased morbidity, longer treatment times, higher costs, and greater patient discomfort. Alternative solutions such as zygomatic implants have been proposed; however, they may involve specific anatomical and surgical complications.

Advances in digital imaging, CAD/CAM technologies, and additive manufacturing have renewed interest in patient-specific subperiosteal implants. These custom-designed frameworks are manufactured to fit the residual anatomy precisely and may offer a viable alternative for patients with insufficient bone volume who are not suitable candidates for conventional implant therapy.

3. Study Objective

The primary objective of this study was to evaluate and compare the biomechanical behavior of two custom-made subperiosteal implant concepts designed for the rehabilitation of severely atrophic maxillae:

• A monoblock implant covering the entire maxillary arch.
• A dual implant system consisting of two independent mirror-image frameworks covering the right and left maxillary halves separately.

Using Finite Element Analysis (FEA), the authors investigated:

• Stress distribution within the implant structures.
• Residual stress transferred to the maxillary bone.
• Implant displacement under functional loading.
• Stress concentration at the abutment level.

The study also assessed the influence of implant thickness and fixation screw diameter on biomechanical performance.

4. Materials and Methods

Study Design

This was a preclinical experimental investigation based on three-dimensional finite element analysis.

Patient Selection

Between 2018 and 2021, 49 patients presenting with insufficient bone volume for conventional implant therapy were evaluated for custom-made subperiosteal implant treatment.

After excluding individuals with:

• uncontrolled systemic conditions;
• bisphosphonate therapy;
• a history of cleft lip and palate;
• active smoking habits;

11 patients remained eligible and were included in the digital modeling process. All participants were older than 60 years.

Model Development

Computed tomography (CT) scans from the 11 patients were processed using 3D Slicer software to generate an average anatomical model of a severely atrophic maxilla.

Two implant configurations were subsequently designed:

• A monoblock framework covering the entire maxilla.
• A dual implant configuration consisting of two independent implants.

Eight implant variations were created according to:

• implant thicknesses of 1.0 mm and 1.5 mm;
• fixation screw diameters of 1.5 mm and 2.0 mm.

All implant models were fabricated virtually using Ti-6Al-4V titanium alloy properties.

Loading Conditions

The simulated masticatory forces included:

• 150 N vertical loads applied bilaterally in the posterior regions;
• 50 N vertical load applied in the anterior region.

Each implant was secured through seven fixation points representing surgical fixation screws.

Stress calculations were performed using:

• the Von Mises criterion for implant structures;
• Piola–Kirchhoff stress tensors for bone analysis.

Implant displacement and abutment stress values were also evaluated.

5. Main Results

Implant Stress Distribution

All calculated stress values remained substantially below the yield strength of Ti-6Al-4V titanium alloy, indicating a negligible risk of plastic deformation under the simulated loading conditions.

For monoblock implants:

• Maximum Von Mises stress: 206 MPa (M5 model).
• Minimum Von Mises stress: 131 MPa (M2 model).

For dual implant systems:

• Maximum Von Mises stress: 178 MPa (M7 model).
• Minimum Von Mises stress: 124 MPa (M4 model).

Overall, dual implant configurations generated lower stress concentrations within the implant structure than monoblock designs.

Stress Distribution Pattern

The highest stress concentrations were consistently located in the zygomatic extension regions of the implants, regardless of implant design.

These findings indicate that lateral anchorage areas play a critical role in load transmission throughout the framework.

Residual Bone Stress

The highest residual stress within the maxillary bone was observed in the M6 model.

The lowest residual stress values were identified in models M1 and M3, reaching approximately 12 MPa.

Unlike implant stress patterns, thin monoblock implants demonstrated a more homogeneous load distribution to the surrounding bone and generated lower residual bone stress values.

Conversely, larger fixation screws and thicker implant structures tended to increase stress transfer to the maxillary bone.

Implant Displacement

Maximum displacement values remained below:

0.21 mm

The greatest displacement occurred in posterior regions.

Monoblock implants generally demonstrated slightly greater displacement than dual implant systems.

Implants with a thickness of 1.0 mm exhibited more displacement than 1.5 mm designs; however, the differences were considered clinically negligible.

Abutment Stress

Stress values at the prosthetic abutments remained low:

• Lowest value: 15.7 MPa (M2).
• Highest value: 18.1 MPa (M4).

These levels were significantly below the material’s mechanical limits, suggesting a low risk of prosthetic component failure under static loading conditions.

6. Clinical Analysis

The findings highlight distinct biomechanical characteristics between monoblock and dual implant concepts.

Dual implant systems demonstrated lower internal stress values, suggesting a potentially lower risk of long-term structural fatigue. The separation of the framework into two independent components appears to facilitate more efficient stress absorption and load redistribution.

Conversely, monoblock implants generated lower residual stress within the supporting maxillary bone due to a more homogeneous load distribution pattern. This characteristic may be beneficial in preserving surrounding bone structures and reducing localized overload.

The authors also suggest that the greater displacement observed in monoblock implants may contribute to force absorption and improve biomechanical behavior during immediate loading protocols.

Importantly, the study identified screw diameter and fixation strategy as factors that may exert a greater influence on bone stress than implant design itself.

7. Clinical Applications

The results may be particularly relevant in:

• severely atrophic maxillae;
• fully edentulous patients with inadequate bone volume;
• patients unwilling or unable to undergo bone grafting procedures;
• CAD/CAM-guided full-arch implant rehabilitation;
• immediate loading protocols;
• custom-made subperiosteal implant treatment planning.

The study supports the use of personalized subperiosteal implants as a potential alternative for complex maxillary rehabilitation cases where conventional implant placement is not feasible.

8. Level of Evidence, Limitations and Transparency

This publication represents a preclinical biomechanical investigation based on finite element simulation.

Several limitations should be acknowledged:

• absence of prospective clinical validation;
• reliance on static loading conditions;
• inability to reproduce biological bone remodeling processes;
• simplified assumptions regarding bone–implant interactions;
• relatively small patient sample used to create the anatomical reference model.

The authors reported no competing interests.

9. Key Study Highlights

• Study Type: Finite Element Analysis (FEA)
• Level of Evidence: Preclinical biomechanical study
• Patients Included: 11
• Clinical Indication: Severe maxillary atrophy
• Implant Designs: Monoblock and dual custom-made subperiosteal implants
• Material: Ti-6Al-4V titanium alloy
• Applied Loads: 50 N anteriorly, 150 N posteriorly
• Maximum Von Mises Stress: 206 MPa
• Maximum Implant Displacement: < 0.21 mm
• Lowest Residual Bone Stress: 12 MPa
• Main Finding: Dual implants reduced implant stress, whereas monoblock implants generated lower residual stress within the supporting bone.

10. Scientific Impact

This study contributes valuable biomechanical data to the growing body of literature concerning custom-made subperiosteal implants for the rehabilitation of severely resorbed maxillae.

By comparing monoblock and dual implant concepts, the authors provide insight into how implant geometry, thickness, and fixation strategies influence mechanical behavior under functional loading.

The findings support further development of patient-specific implant frameworks and may contribute to optimizing future implant designs intended for complex atrophic cases.

The study also emphasizes the critical role of fixation screw selection, which may have a greater impact on bone loading than the implant design itself.

11. Editorial Conclusion

This finite element analysis demonstrates that custom-made subperiosteal implants are biomechanically capable of supporting functional loading in severely atrophic maxillae. Dual implant systems showed lower internal implant stress and displacement values, whereas monoblock frameworks provided a more uniform distribution of forces to the supporting bone. These findings suggest that each design offers specific biomechanical advantages depending on the clinical objective. Although promising, these results require confirmation through long-term clinical studies evaluating implant survival, biological response, and patient-centered outcomes.