Biocompatibility of Subperiosteal Dental Implants: Changes in the Expression of Osteogenesis-Related Genes in Osteoblasts Exposed to Differently Treated Titanium Surfaces

Marco Roy, Elisa Chelucci, Alessandro Corti, Lorenzo Ceccarelli, Mauro Cerea, Barbara Dorocka-Bobkowska, Alfonso Pompella, Simona Daniele

Full text link: https://pubmed.ncbi.nlm.nih.gov/38921520/

Biocompatibility of Subperiosteal Dental Implants: Changes in Osteogenesis-Related Gene Expression in Osteoblasts Exposed to Differently Treated Titanium Surfaces

1. Scientific Reference

• Study Title: Biocompatibility of Subperiosteal Dental Implants: Changes in Osteogenesis-Related Genes in Osteoblasts Exposed to Differently Treated Titanium Surfaces
• Authors: Marco Roy, Elisa Chelucci, Alessandro Corti, Lorenzo Ceccarelli, Mauro Cerea, Barbara Dorocka-Bobkowska, Alfonso Pompella, Simona Daniele
• Journal: Journal of Functional Biomaterials
• Year of Publication: 2024
• DOI: 10.3390/jfb15060146

2. Scientific Background

Severe maxillary or mandibular bone atrophy remains one of the most challenging situations in implant dentistry. Conventional endosseous implants require sufficient bone volume and density, which often necessitates bone augmentation procedures in highly resorbed jaws. While grafting techniques can restore implant sites, they may increase surgical complexity, treatment duration, cost, and the risk of complications.

The renewed interest in subperiosteal dental implants is largely driven by advances in digital dentistry, including cone-beam computed tomography (CBCT), computer-aided design and manufacturing (CAD/CAM), and additive manufacturing technologies. Unlike traditional endosseous implants, subperiosteal frameworks are positioned over the residual bone and beneath the periosteum, making them less dependent on residual bone volume.

As these devices are intended to remain in intimate contact with both bone and soft tissues, understanding the biological response to their titanium surfaces is critical. This study explored whether different titanium surface treatments can influence osteoblast behavior and promote biological processes associated with bone formation and implant integration.

3. Study Objective

The primary objective of this investigation was to assess the biological compatibility of five differently treated titanium surfaces used in the manufacturing of modern subperiosteal implants.

The researchers specifically aimed to determine whether these surface modifications could stimulate osteoblast differentiation, mineralization, and the expression of genes and proteins involved in osteogenesis while maintaining normal cellular viability.

4. Methodology

This research was conducted as an in vitro preclinical study using a primary human osteoblast cell line.

Titanium alloy (TiAl6V4, Grade 5) discs underwent five different surface treatments:

• Raw machined surface
• Acid electropolished surface
• Sand-blasted and acid-etched surface
• AlTiColor™ proprietary surface treatment
• Anodized surface

Human osteoblasts were cultured on these titanium specimens and evaluated through several biological assays. The investigators measured:

• Cell viability
• Mineralization capacity using Alizarin Red staining
• Gene expression of RUNX2, osteocalcin (OST), osterix (OSX), and alkaline phosphatase (ALP)
• Protein expression of focal adhesion kinase (FAK), N-cadherin, β-catenin, and osteocalcin
• Osteoprotegerin (OPG) release

Most osteogenic assessments were performed after seven days of mineralization culture.

5. Main Results

All titanium surfaces demonstrated favorable biological compatibility with human osteoblasts.

Cell viability remained unaffected across all tested groups, indicating that none of the evaluated surface treatments exhibited detectable cytotoxic effects under the experimental conditions.

Mineralization assays revealed enhanced calcium deposition on all titanium surfaces compared with the control condition. The most pronounced mineralization response was observed on the anodized surface (Ti-5), while Ti-1 and Ti-4 also demonstrated significantly increased calcium deposition.

Several osteogenic markers showed increased expression following exposure to titanium-treated surfaces. Elevated expression of RUNX2, osteocalcin, and osterix suggested stimulation of osteoblast differentiation and maturation pathways. The anodized surface frequently displayed the strongest biological response among the tested groups.

Protein analyses also showed increased levels of osteogenesis-related markers, including N-cadherin, β-catenin, and osteocalcin. Furthermore, all titanium surfaces promoted greater osteoprotegerin release compared with controls, suggesting activation of mechanisms involved in bone remodeling regulation.

6. Clinical Analysis

The significance of this study lies in its contribution to the biological understanding of modern subperiosteal implant systems. Historically, subperiosteal implants fell out of favor due to manufacturing limitations and adaptation challenges. The emergence of digital workflows and selective laser melting technologies has enabled the production of highly customized titanium frameworks, reopening interest in this treatment modality for patients with advanced bone loss.

The findings suggest that contemporary titanium surfaces can support cellular events associated with bone formation. Increased expression of transcription factors such as RUNX2 and osterix, together with higher osteocalcin production, indicates activation of osteogenic pathways that are generally considered favorable for bone integration processes.

From a clinical perspective, these observations may be particularly relevant for patients with severe jaw atrophy who are not ideal candidates for extensive bone grafting procedures. However, caution is essential when interpreting these results. The study evaluates cellular behavior under laboratory conditions rather than clinical outcomes. Consequently, no conclusions can be drawn regarding implant survival, long-term stability, complication rates, or clinical success in human patients.

The results should therefore be viewed as biological evidence supporting the potential compatibility of these titanium surfaces rather than definitive proof of clinical performance.

7. Clinical Applications

The findings may be relevant in several areas of advanced implant rehabilitation, including:

• Management of severe maxillary or mandibular bone atrophy
• Cases where bone grafting procedures are contraindicated or undesirable
• Full-arch implant rehabilitation in highly resorbed jaws
• Digitally planned subperiosteal implant reconstruction
• CAD/CAM-guided implant manufacturing workflows
• Personalized titanium implant frameworks produced through additive manufacturing

The study supports the biological suitability of modern titanium surface treatments used in customized subperiosteal implant fabrication, although clinical validation remains necessary.

8. Level of Evidence, Limitations and Transparency

This publication represents a preclinical in vitro investigation, which corresponds to a relatively low level of clinical evidence when compared with prospective clinical trials or systematic reviews.

Although the experimental design provides valuable insight into osteoblast behavior, laboratory findings cannot be directly translated into clinical outcomes. The study does not evaluate implant survival, patient-centered outcomes, mechanical complications, or long-term osseointegration.

Additional limitations include:

• Absence of human clinical data
• Short experimental observation periods
• Lack of long-term biological assessment
• Limited ability to predict real-world clinical performance

Regarding transparency, the study reports financial support from Eaglegrid Srl. In addition, Marco Roy and Mauro Cerea are disclosed as clinical consultants for the same company. These declarations were reported by the authors and should be considered when interpreting the findings.

9. Key Study Points

• Study Type: In vitro preclinical study
• Level of Evidence: Preclinical
• Population Studied: Primary human osteoblast cell line
• Number of Patients or Implants: Not applicable
• Follow-up Duration: Up to 7 days depending on the assay
• Primary Outcome: Expression of osteogenesis- and mineralization-related markers
• Main Finding: All tested titanium surfaces promoted osteogenic activity without negatively affecting cell viability
• Scientific Conclusion: The evaluated titanium surface treatments appear biologically compatible with osteoblast differentiation and bone-forming processes
• Key Limitations: In vitro design, absence of clinical outcomes, limited observation period

10. Scientific Impact

This study contributes important biological evidence to the growing body of research supporting the modern revival of subperiosteal implant therapy.

While advances in digital implant planning, CBCT imaging, CAD/CAM design, and additive manufacturing have transformed the technical feasibility of customized subperiosteal implants, biological validation remains essential. The present work provides mechanistic data showing that multiple titanium surface treatments can stimulate cellular pathways associated with osteogenesis and bone remodeling.

An additional contribution of the study is the direct comparison of several surface modification strategies currently used in implant manufacturing. Although all tested surfaces demonstrated favorable biological responses, the anodized surface appeared particularly effective in promoting osteoblast differentiation markers.

These findings strengthen the scientific rationale for further translational and clinical research investigating the long-term behavior of modern subperiosteal implant systems in patients with severe bone atrophy.

11. Editorial Conclusion

This preclinical study provides encouraging evidence regarding the biological compatibility of titanium surfaces used in contemporary subperiosteal dental implants. All tested surface treatments supported osteoblast viability and stimulated molecular markers associated with bone formation and mineralization. Among the evaluated surfaces, anodized titanium demonstrated particularly strong osteogenic activity. Nevertheless, the findings remain limited to laboratory conditions and should be interpreted as foundational biological data rather than proof of clinical efficacy. Further clinical investigations are required to determine whether these cellular responses translate into improved outcomes in implant rehabilitation of severely atrophic patients.