Evaluation of New Bone Formation and Osseointegration Around Subperiosteal Titanium Implants with Histometry and Nanoindentation

Noel Claffey, Haitham Bashara, Peter O’Reilly, Ioannis Polyzois

Full text link: https://pubmed.ncbi.nlm.nih.gov/26394334/

Evaluation of New Bone Formation and Osseointegration Around Subperiosteal Titanium Implants with Histometry and Nanoindentation

1. Scientific Reference

• Study Title: Evaluation of New Bone Formation and Osseointegration Around Subperiosteal Titanium Implants with Histometry and Nanoindentation
• Authors: Noel Claffey, Haitham Bashara, Peter O’Reilly, Ioannis Polyzois
• Journal: The International Journal of Oral & Maxillofacial Implants
• Publication Year: 2015
• DOI: 10.11607/jomi.3647

2. Scientific Background

Subperiosteal implants were once considered a valuable solution for patients with advanced jaw atrophy but gradually fell out of routine clinical use following the widespread adoption of endosseous implant systems. Recent advances in digital imaging, CAD/CAM manufacturing, titanium biomaterials, and implant surface technologies have renewed interest in revisiting this treatment concept for challenging implant rehabilitation cases.

Unlike conventional endosseous implants, subperiosteal implants rely on a relatively thin layer of newly formed bone for biological integration. Consequently, both the quantity and the mechanical quality of this regenerated bone are critical factors influencing implant stability. This study explores these biological events using conventional histometric evaluation alongside nanoindentation, a technique capable of measuring the mechanical behavior of bone tissue at the microscopic level.

3. Study Objective

The investigators aimed to evaluate bone formation and osseointegration around roughened titanium subperiosteal implants after three months of healing. In addition, they compared two fixation approaches—direct fixation onto cortical bone versus placement within a surgically prepared bone trough—to determine whether implant positioning influenced biological integration. The study also assessed whether nanoindentation could provide meaningful information regarding the mechanical properties of newly formed peri-implant bone.

4. Methodology

This preclinical experimental investigation was conducted using ten six-month-old white rabbits. Each animal received two titanium subperiosteal implants, one in each femur. One implant was secured directly onto the cortical bone using fixation screws, while the contralateral implant was positioned within a shallow osseous trough before screw fixation.

Following a three-month healing period, the animals were sacrificed for specimen retrieval. Histometric analyses quantified bone-to-implant contact, new bone length, and newly formed bone area. Nanoindentation testing was subsequently performed to determine hardness and elastic modulus within mature cortical bone and newly formed peri-implant bone. Two rabbits died during the healing period, leaving sixteen implants available for analysis.

5. Main Findings

Subperiosteal implants placed within a prepared bone trough demonstrated consistently superior histometric outcomes compared with implants positioned directly on the cortical surface.

Average bone-to-implant contact reached 86.5% in the trough group compared with 76.5% in the conventional fixation group. Likewise, newly formed bone extended over a greater length of the implant surface (1.78 mm versus 1.50 mm), while the projected area of regenerated bone was also substantially larger (1.91 mm² versus 1.30 mm²). All reported differences were statistically significant.

Nanoindentation measurements revealed that the biomechanical characteristics of newly formed bone differed from those of established cortical bone. Both elastic modulus and hardness remained lower within regenerated bone after three months, indicating that biological integration had occurred but tissue maturation was still incomplete.

6. Clinical Interpretation

Rather than simply demonstrating new bone formation around subperiosteal implants, this investigation highlights the importance of evaluating the quality of regenerated bone. Histological evidence alone may suggest successful osseointegration, yet the nanoindentation findings indicate that newly formed bone has not reached the mechanical characteristics of mature cortical tissue after a relatively short healing interval.

From a clinical perspective, these observations are relevant because subperiosteal implant rehabilitation is generally considered in patients with limited residual bone volume, where biological support is inherently restricted. Under these conditions, maximizing both bone coverage and tissue maturation may contribute to improved long-term stability.

The comparison between fixation methods suggests that creating a shallow bone trough enhances early biological integration by increasing bone contact and bone formation around the implant framework. However, the study does not establish that this translates into superior long-term clinical performance, since functional loading and extended follow-up were not investigated.

An additional contribution of this work is the demonstration that nanoindentation may complement traditional histomorphometric evaluation by providing insight into bone tissue quality rather than quantity alone.

7. Clinical Applications

Although conducted in an animal model, the findings may inform future research on modern custom-made subperiosteal implants intended for patients presenting with severe alveolar bone atrophy.

The results support further investigation of implant stabilization techniques that encourage greater bone formation while emphasizing the importance of bone maturation before functional loading. These observations may also contribute to the ongoing development of digitally designed subperiosteal implant systems manufactured through contemporary CAD/CAM workflows.

Because the evidence originates from a preclinical study, direct clinical recommendations cannot be established based solely on these findings.

8. Level of Evidence, Limitations and Transparency

This publication represents a preclinical animal experiment and therefore provides a relatively low level of clinical evidence compared with prospective human studies or randomized clinical trials.

Several methodological limitations should be considered. The study included a limited number of experimental animals, evaluated healing after only three months, and used a rabbit femur model rather than the human maxillofacial skeleton. The authors themselves acknowledge that the healing period may not have been sufficient for complete bone maturation.

No conflicts of interest related to the study were reported by the authors.

9. Key Study Highlights

• Study design: Preclinical animal study
• Level of evidence: Preclinical experimental research
• Study population: 10 rabbits (16 implants analyzed after healing)
• Number of implants: Two subperiosteal titanium implants per animal
• Follow-up period: Three months
• Primary outcome: Histometric osseointegration and biomechanical properties of regenerated bone
• Main finding: Bone trough preparation significantly improved bone formation and bone-to-implant contact.
• Scientific conclusion: Early osseointegration was enhanced by trough placement, although newly formed bone remained mechanically inferior to mature cortical bone after three months.
• Limitations: Animal model, limited sample size, short observation period, absence of long-term functional evaluation.

10. Scientific Impact

This study contributes to the renewed scientific interest in subperiosteal implant therapy by combining conventional histometric analysis with nanoindentation-based assessment of bone quality. Rather than focusing exclusively on the amount of regenerated bone, it emphasizes that mechanical competence should also be considered when evaluating implant integration.

The investigation supports the concept that implant positioning may influence early biological healing while demonstrating the value of advanced biomechanical assessment techniques for future implant research. Although additional long-term clinical studies are required, these findings provide useful experimental data that may assist in the development of contemporary subperiosteal implant designs intended for patients with advanced bone deficiency.

11. Editorial Conclusion

This experimental study demonstrates that placing rough-surfaced titanium subperiosteal implants within a surgically prepared bone trough enhances early osseointegration and promotes greater bone formation than positioning implants directly on cortical bone. At the same time, it shows that newly regenerated bone remains mechanically immature after three months of healing. While these findings cannot be directly translated into clinical practice, they provide valuable biological evidence supporting continued research into modern subperiosteal implant concepts and advanced methods for assessing peri-implant bone quality.