Distraction Osteogenesis in Irradiated Rabbit Mandibles With Adjunctive Hyperbaric Oxygen Therapy

Comparative Analysis of Bone Regeneration According to Particle Type and Barrier Membrane for Octacalcium Phosphate Grafted into Rabbit Calvarial Defects

This animal study was aimed to evaluate the efficacy of new bone formation and volume maintenance according to the particle type and the collagen membrane function for grafted octacalcium phosphate (OCP) in rabbit calvarial defects. The synthetic bone substitutes were prepared in powder form with 90% OCP and granular form with 76% OCP, respectively. The calvarial defects were divided into four groups according to the particle type and the membrane application. All specimens were acquired 2 weeks (n = 5) and 8 weeks (n = 5) after surgery. According to the micro-CT results, the new bone volume increased at 2 weeks in the 76% OCP groups compared to the 90% OCP groups, and the bone volume ratio was significantly lower in the 90% OCP group after 2 weeks. The histomorphometric analysis results indicated that the new bone area and its ratio in all experimental groups were increased at 8 weeks except for the group with 90% OCP without a membrane. Furthermore, the residual bone graft area and its ratio in the 90% OCP groups were decreased at 8 weeks. In conclusion, all types of OCP could be applied as biocompatible bone graft materials regardless of its density and membrane application. Neither the OCP concentration nor the membrane application had a significant effect on new bone formation in the defect area, but the higher the OCP concentration, the less graft volume maintenance was needed.

External devices increasing bone quality in animals: A systematic review

Background: Osteoporosis can reduce bone quality and increase the risk of fractures. In addition to pharmacological approaches, physical activity, and implanted devices, external devices can also be detected in the literature as a technique to strengthen bones. This type of intervention arises to be particularly promising because it minimizes the invasiveness of therapy. Methods: A systematic review of the technologies involved in such devices was carried out to identify the most fruitful ones in improving bone quality. This review, according to the PRISMA Statement, focuses on studies involving animals, and excludes pharmaceutical approaches. Findings: The animal models and devices used, their settings, interventions, outcomes measured, and consequent effect on bone quality are reported for each detected technology. Ultrasound and laser arose to be the most studied technologies in the literature, even if they have yet to be proved to have a significant effect on bone quality. Interpretation: External devices for bone quality improvement offer a non-invasive approach that causes minimum discomfort to the patient. This review aimed to detect which technologies reported in the literature significantly affect bone quality. The results showed that several technologies are currently used to improve bone quality. However, each study measures different outcomes and uses different measurement methods, device settings, and interventions. This lack of standardization and the reduced number of articles found do not allow for proper quantitative comparisons.

Overview of Physical and Pharmacological Therapy in Enhancing Bone Regeneration Formation During Distraction Osteogenesis

Distraction osteogenesis (DO) is a kind of bone regeneration technology. The principle is to incise the cortical bone and apply continuous and stable distraction force to the fractured end of the cortical bone, thereby promoting the proliferation of osteoblastic cells in the tension microenvironment and stimulating new bone formation. However, the long consolidation course of DO presumably lead to several complications such as infection, fracture, scar formation, delayed union and malunion. Therefore, it is of clinical significance to reduce the long treatment duration. The current treatment strategy to promote osteogenesis in DO includes gene, growth factor, stem-cell, physical and pharmacological therapies. Among these methods, pharmacological and physical therapies are considered as safe, economical, convenience and effective. Recently, several physical and pharmacological therapies have been demonstrated with a decent ability to enhance bone regeneration during DO. In this review, we have comprehensively summarized the latest evidence for physical (Photonic, Waves, Gas, Mechanical, Electrical and Electromagnetic stimulation) and pharmacological (Bisphosphonates, Hormone, Metal compounds, Biologics, Chinese medicine, etc) therapies in DO. These evidences will bring novel and significant information for the bone healing during DO in the future.

Validation of a rabbit model of irradiated bone healing: preliminary report

Introduction: External radiotherapy can lead to severe bone alteration. The aim of this pilot study was to validate a model for assessment of postextractional bone healing in the irradiated rabbit mandible. Material and method: The radiation protocol consisted of 5 sessions delivering 8.5 Gy each. Surgery was performed immediately after completion of radiotherapy. Sacrifices were performed from Day 0 to Day 42. Results: The bone mineral density and the trabecular number were decreased after radiotherapy whereas trabecular separation increased. The main differences between irradiated and non-irradiated rabbits were observed at Day 28 and 42. Discussion: Radiation seems to cause a delay in bone healing. It decreases bone quality and bone mineral density. Five sessions seem to be a valuable compromise between tissues effect and feasibility of the experiment. Conclusion: This model seems to be valuable for evaluating postextractional bone healing in the irradiated rabbit mandible.

Comprehensive Treatment of Facial Deformity Due to Radiotherapy in Rhabdomyosarcoma Patients: Distraction Osteogenesis and Free Flaps Surgical Technique

Radiotherapy is essential for achieving and maintaining local control in head and neck rhabdomyosarcoma patients. However, radiotherapy may cause outgrowth disturbances of facial bone and soft tissue, resulting in facial asymmetry.Several studies have shown that the management of irradiated bones still remains challenging. The possibility of obtaining functional and aesthetic results when managing facial deformities due to radiation therapy with distraction osteogenesis combined with free flaps reconstruction is not common and not well documented in recent literature.In this report, we present the long-term results of distraction osteogenesis and soft tissue reconstruction via microvascular free flap to correct the facial hypoplasia of a young patient who underwent radiation therapy for rhabdomyosarcoma.This is the first presentation of 26 years long-term results in a patient who also underwent free flaps reconstruction as ancillary surgery for esthetic good results.

Synergistic effects of HBO and PRP improve bone regeneration with autologous bone grafting

Bone defects remain a challenge for patients and orthopaedic surgeons. Autologous transfer of cancellous bone grafts remains the standard of care. However, in recent years various osteoinductive substitute materials, such as platelet rich plasma (PRP) and hyperbaric oxygen therapy (HBO) have been shown to improve bone healing. This study evaluates the effects of a combined application of PRP and HBO with autologous bone grafting in an animal model. In 48 New Zealand White rabbits bone defects at the radius were filled with autologous bone harvested at the iliac crest. This was combined with application of autologous PRP and/or HBO treatment for the duration of this study. After 3 and 6 weeks histomorphometric, immunohistochemical and radiologic evaluations were performed. All animals tolerated the treatment well. Improved bone regeneration was shown in all groups at 6 weeks compared to 3 weeks. Additional application of PRP and HBO resulted in an increase in new bone formation and increased neovascularization at 3 and 6 weeks. There was no statistical significant difference between PRP and HBO application in these regards. A combinatory use of PRP and HBO resulted in an increased bone regeneration and neovascularization compared to all other groups. This study provides evidence for an improvement of bone regeneration with the combinatory application of PRP and HBO to autologous cancellous bone grafts in a model of weight bearing bone defects in rabbits. Also synergistic effects of these two measures on angiogenesis were evident.

Propolis accelerates the consolidation phase in distraction osteogenesis

We evaluated the effect of propolis on new bone formation after distraction osteogenesis (DO). This study examined 3 groups: control group, P100, and P200. Rabbits underwent DO of the left mandible after an osteotomy between the first molar and the mental foramen. Bone mineral content and bone mineral density were evaluated using dual-energy x-ray absorption 1 and 4 weeks after the procedure. The volume of connective tissue and new bone and the number of capillaries were measured using stereologic analysis after the subjects were killed. Dual-energy x-ray absorption showed that the bone mineral content and bone mineral density were higher in the groups treated with propolis by week 4, and these parameters were higher in the P200 group. Stereologic analysis showed no significant differences in connective tissue volume and number of capillaries among the groups. New bone volume was lowest in the P200 group. We concluded that propolis accelerates bone formation and may shorten the consolidation phase with DO.

Hyperbaric oxygen therapy improves angiogenesis and bone formation in critical sized diaphyseal defects

Besides the use of autologous bone grafting several osteoconductive and osteoinductive methods have been reported to improve bone healing. However, persistent non-union occurs in a considerable number of cases and compromised angiogenesis is suspected to impede bone regeneration. Hyperbaric oxygen therapy (HBO) improves angiogenesis. This study evaluates the effects of HBO on bone defects treated with autologous bone grafting in a bone defect model in rabbits. Twenty-four New-Zealand White Rabbits were subjected to a unilateral critical sized diaphyseal radius bone defect and treated with autologous cancellous bone transplantation. The study groups were exposed to an additional HBO treatment regimen. Bone regeneration was evaluated radiologically and histologically at 3 and 6 weeks, angiogenesis was assessed by immunohistochemistry at three and six weeks. The additional administration of HBO resulted in a significantly increased new bone formation and angiogenesis compared to the sole treatment with autologous bone grafting. These results were apparent after three and six weeks of treatment. The addition of HBO therapy to autologous bone grafts leads to significantly improved bone regeneration. The increase in angiogenesis observed could play a crucial role for the results observed.

Measurement of Elastic Modulus and Vickers Hardness of Surround Bone Implant Using Dynamic Microindentation - Parameters Definition

The clinical performance of dental implants is strongly defined by biomechanical principles. The aim of this study was to quantify the Vicker's hardness (VHN) and elastic modulus (E) surround bone to dental implant in different regions, and to discuss the parameters of dynamic microindantion test. Ten cylindrical implants with morse taper interface (Titamax CM, Neodent; 3.5 mm diameter and 7 mm a height) were inserted in rabbit tibia. The mechanical properties were analyzed using microhardness dynamic indenter with 200 mN load and 15 s penetration time. Seven continuous indentations were made distancing 0.08 mm between each other perpendicularly to the implant-bone interface towards the external surface, at the limit of low (Lp) and high implant profile (Hp). Data were analyzed by Student's t-test (a=0.05) to compare the E and VHN values obtained on both regions. Mean and standard deviation of E (GPa) were: Lp. 16.6 ± 1.7, Hp. 17.0 ± 2.5 and VHN (N/mm2): Lp. 12.6 ± 40.8, Hp. 120.1 ± 43.7. No statistical difference was found between bone mechanical properties of high and low profile of the surround bone to implant, demonstrating that the bone characterization homogeneously is pertinent. Dynamic microindantion method proved to be highly useful in the characterization of the individual peri-implant bone tissue.

Transplantation of human dental pulp stem cells: enhance bone consolidation in mandibular distraction osteogenesis

PURPOSE

The main aim of the present study was to evaluate the capacity of stem cells from human exfoliated deciduous teeth (SHED) to enhance mandibular distraction osteogenesis (DO) in rabbits.

MATERIALS AND METHODS

A randomized controlled trial was conducted. Eighteen skeletally immature New Zealand white rabbits were divided into 2 groups, with 9 in the control group and 9 in the SHED group. The SHED were isolated, expanded, and characterized. Six million cells were transplanted into the distracted area during the osteotomy period. After a 4-day latency period, a total of 6 mm was distracted for 6 days. The newly formed bone was analyzed radiologically, histologically, and histomorphometrically at 2, 4, and 6 weeks postoperatively. Nonparametric analysis of variance (Kruskal-Wallis test) was used for data analysis, and P < .05 was considered statistically significant.

RESULTS

The cell lineage was positive for the 2 mesenchymal stem cell markers tested (CD105 and CD166). More mature bone in the SHED transplanted group was observed radiographically and histologically. Histomorphologically, the percentage of newly formed bone after 2, 4, and 6 weeks was 18.41% and 41.53%, 31.68% and 59.78%, and 52.34% and 65.24% in the control and SHED groups, respectively. The difference between the groups was statistically significant (P = .012). The bone union and stage of bone maturity scores were significantly different between the control and SHED groups (P = .006 and P = .011, respectively).

CONCLUSIONS

Our findings suggest that SHED can serve as an additional cell resource for DO enhancement in rabbits and might be a promising model for the reconstruction of large mandibular defects in human oral maxillofacial surgery.

The rabbit as experimental model for research in implant dentistry and related tissue regeneration

The use of rabbits for experimental research has a long historical tradition. The aim of this review consists in outlining the use of the rabbit for research in implant dentistry and related tissue regeneration. Rabbits appear as a first-hand choice for fundamental implant design studies because of their size, easy handling, short life span, and economical aspects in purchasing and sustaining. In the following, the various anatomical sites in the rabbit will be summarized to provide an overview of current possibilities and limitations of this model for bone research in oral implantology.

Distraction osteogenesis in the dog mandible under 60-Gy irradiation

OBJECTIVE

The objective of this study was to explore the probability of distraction osteogenesis (DO) in the irradiated dog mandible after 60-Gy irradiation.

STUDY DESIGN

Fourteen Chinese dogs were randomly divided into 2 groups. Twelve dogs received a preoperative unilateral irradiation from (60)Co (group R) in the mandible with a total dose of 24.8 Gy in four 6.2-Gy fractions (biologically equivalent to 60 Gy/25 fractions). The other 2 dogs without irradiation served as the control (group C). Bilateral corticotomies were made 6 months after completion of irradiation. Bone distraction was activated at a rate of 0.5 mm twice daily for 10 days after a 1-week latency period, followed by a consolidation phase of 8 weeks. The inferior alveolar nerve (IAN) underwent electrophysiologic analysis. Dog mandibles were subsequently subjected to histologic and radiographic analysis.

RESULTS

All the animals had successful distractions. After 8 weeks of consolidation, no difference was found between the percentage area of new bone in both groups. New bone was more mature and organized in group C than in group R. The action potential of IAN showed corresponding alternation during the irradiation and distraction process.

CONCLUSIONS

Based on this study it seems that DO may be feasible in dog mandible under 60-Gy irradiation. Further research is indicated.

A hyperbaric oxygen chamber for animal experimental purposes

Facilities for hyperbaric oxygen therapy that are suitable for animal experimental research are scarce. In this paper, the authors introduce a hyperbaric oxygen chamber that was developed specifically for animal experimental purposes. The hyperbaric oxygen chamber was designed to meet a number of criteria regarding safety and ease of use. The hyperbaric oxygen chamber conforms to 97/23/EC (Pressure Equipment Directive), Conformity Assessment Module G Product Group 1. It provides easy access, and can be run in manual mode, semi-automatic mode and full-automatic mode. Sensors for pressure level, oxygen level, temperature, humidity and carbon dioxide level allow full control. This state-of-the-art hyperbaric oxygen chamber for animal experimental purposes permits the investigation of the biological mechanisms through which hyperbaric oxygen therapy acts at a fundamental level.

Quantitative histomorphometric assessment of regenerate cellularity and bone quality in mandibular distraction osteogenesis after radiation therapy

BACKGROUND

The use of mandibular distraction osteogenesis (MDO) for tissue replacement after oncologic resection in head and neck cancer could have immense therapeutic ramifications. We have previously demonstrated significantly decreased mechanical and microdensitomeric metrics of our MDO regenerate after 36-Gy radiation. Quantitative histomorphometry, a third metric, would permit objective investigation of the effects of radiation on tissue and cellular composition. Our hypothesis is that radiation-induced cellular depletion and diminution in function impair optimal bone regeneration.

METHODS

Five rats received radiation to the left mandible; 5 received none. All animals underwent surgical placement of external fixators, creation of mandibular osteotomies, distraction to a 5.1-mm gap width, and consolidation. Point counting and color thresholding were performed.

RESULTS

There was a significant increase in empty lacunae and a corresponding diminution in osteocytes after radiation. Whereas the volume fraction of mineralized, mature bone was not different, that of nonmineralized, immature osteoid was significantly increased in the radiated group compared with that in the nonradiated group.

CONCLUSIONS

Our findings confirm our prior 2 metrics. Actually, all 3 diverse metrics--microdensitometry, biomechanical analysis, and histomorphometry--corroborate our hypothesis of cellular depletion and diminution of function as the potential mechanism of radiation-induced attenuation in the distracted regenerate. Furthermore, our findings of tissue and cellular changes in the irradiated regenerate elucidate the pathophysiology of decreased bone quality when amalgamated with our previous results. Therapeutic agents may now be introduced, and their effects on the irradiated regenerate critically measured, so that MDO may be used as a viable reconstructive option in patients with head and neck cancer.

Amount of bone lengthening affects blood flow recovery and bone mineralization after distraction osteogenesis in a canine cleft palate model

OBJECTIVES

Distraction osteogenesis has been applied to the craniofacial region. To reduce the cleft width of patients with cleft lip and palate, alveolar bones are distracted toward the cleft. However, no reports have described limitations to the amount of lengthening that can be achieved by distraction osteogenesis in this area. Therefore, we investigated the healing process following different extents of distraction osteogenesis using a canine cleft palate model.

METHODS

A 10-mm bone defect was made in the palates. A bony segment including the canine was prepared and translocated into the defect area at a rate of 1 mm/d for 6 or 10 days, resulting in two groups (6- and 10-mm groups). Canine pulpal blood flow was monitored for 100 days with Doppler flowmetry. Then, the animals were sacrificed and the regenerated bone area was evaluated radiologically and histologically. Statistical significance was confirmed with the Mann-Whitney rank test.

RESULTS

Pulpal blood flow in the 6-mm group recovered to original levels earlier than in the 10-mm group. Cortical bone density in the regenerated bone, measured by peripheral quantitative computed tomography, was significantly greater in the 6-mm group than in the 10-mm group. The amount of regenerated bone in histologic sections was also significantly greater in the 6-mm group.

CONCLUSION

We clearly showed that healing progress depends on the extent of distraction osteogenesis, highlighting the importance of limited distraction osteogenesis in the alveolar area.

The Effects of Hyperbaric Oxygen on Tooth Movement into the Regenerated Area after Distraction Osteogenesis

Objective

To analyze the effect of hyperbaric oxygen on newly formed bone in distracted areas surrounding the root of a moving tooth by histological and radiological analysis. It was hypothesized that the application of hyperbaric oxygen to a tooth moving into the distracted area would accelerate ossification and vascularization of newly formed bone in the distracted space.

Design

Ten dogs were used. After creating a 10-mm-long bone defect, a bony segment was prepared and translocated into the defect area at a rate of 1 mm/d for 10 days. Following the distraction period, tooth movement was started and the dogs were divided into two groups. The HBO group received hyperbaric oxygen; whereas, the control group did not. At 150 days after tooth movement, the distracted area around the moving tooth was evaluated radiologically and histologically. Differences between groups were confirmed by a Mann-Whitney U test.

Results

Trabecular bone density and cortical and subcortical bone areas measured by peripheral quantitative computed tomography in the HBO group were significantly higher than those in the control group. Histological observations revealed regenerated bone and blood vessels formation in the tension site of the moving tooth in the HBO group. The regenerated bone structure measured by bone histomorphometry was larger and more active in bone formation in the HBO group than in the control group.

Conclusions

Applying hyperbaric oxygen to tooth movement into a distracted area appears to accelerate ossification and vascularization of regenerated bone in the that area.

Addition of mesenchymal stem cells to the scaffold of platelet-rich plasma is beneficial for the reduction of the consolidation period in mandibular distraction osteogenesis

PURPOSE

Platelet-rich plasma (PRP) is a wonderful scaffold to induce osteogenesis. In this study, we investigated whether the combination of mesenchymal stem cells (MSC) with PRP has advantages over PRP for the reduction of consolidation period in mandibular distraction osteogenesis.

MATERIALS AND METHODS

After osteotomy, an external distraction device was fixed in both mandibles of 38 rabbits. After a 5-day latency period, a total of 6.3 mm was distracted for 6 days. PRP gel with or without MSC was injected into the distracted area on day 1 of the consolidation period. Healing tissues were analyzed histologically, radiologically, and mechanically on weeks 1, 2, 3, and 4 after consolidation.

RESULTS

In week 1, the MSC/PRP group was 34%, 20%, 21%, and 32% higher than the PRP group in the result of histomorphometry, radiodensity ratio of new bone/host bone and new bone/adjacent tooth, and microhardness test, respectively. Consolidation period was reduced by 6.6 and 5.1 days at 80% and 90% new bone/host bone ratio through regression analysis, respectively.

CONCLUSION

The addition of MSC in PRP scaffold significantly (P < .05) increased new bone formation, mineralization, and mechanical property compared to the PRP-only group. These results indicate that the combination therapy of MSC and PRP is more effective for reducing the consolidation period of distraction.

Hyperbaric oxygen: therapy for patients with maxillofacial implants?

Osseointegration was an innovative treatment in dentistry during the last 3 decades. The success of osseointegration is related to factors such as material biocompatibility, adequate quality of bone tissue that allows implantation, surgical technique, and macrostructure and microstructure of implant. The osseointegrated implants are successfully applied in dental clinic including oral and facial rehabilitations mainly for patients submitted to mutilating surgeries. However, patients submitted to radiation therapy present risks to treatment with implants owing to adverse effects on bone tissue. Nowadays, the literature suggests different therapies to improve the success of osseointegration such as hyperbaric oxygen therapy that aims to prepare bone and adjacent tissues to receive the implant. Therefore, the purpose of this study was to present a literature review concerning indications, contraindications, successes, and difficulties with hyperbaric oxygen therapy associated to maxillofacial implants.

Alteration in volumetric bone mineralization density gradation patterns in mandibular distraction osteogenesis following radiation therapy

BACKGROUND

The use of mandibular distraction osteogenesis for tissue replacement after oncologic resection or for deformations secondary to radiotherapy could have immense therapeutic ramifications. Radiotherapy, however, drastically impairs bone healing, potentially precluding the use of mandibular distraction osteogenesis as a durable reconstructive option. The authors have previously demonstrated significantly decreased mechanical and histologic metrics of the mandibular distraction osteogenesis regenerate after 36 Gy. The authors' goal is to now investigate the effect of these same radiation dosages on bone densitometrics using micro-computed tomographic scanning.

METHODS

Six Sprague-Dawley rats received 36-Gy fractionated radiotherapy sessions to the left mandible; six received none. All animals had external fixators placed, creation of osteotomies, distraction, and consolidation. Mandibles were scanned with micro-computed tomographic scanning. Volumetric density and microdensitometric measurements were analyzed.

RESULTS

There was a significant difference in volumetric bone mineralization patterns in irradiated animals. Bone volume fraction and bone mineral density, however, demonstrated no significant differences.

CONCLUSIONS

The authors discovered a significant increase of low mineralized, immature bone and a significant decrease of highly mineralized, mature bone in the irradiated regenerate. These findings corroborate the authors' hypothesis that radiation induces a diminution in cell function, impairing optimal bone regeneration. Overall densitometrics, however, were unchanged according to micro-computed tomographic measurements, despite documented significant changes in biomechanical and histologic metrics. An optimal radiation dose must now be sought that demonstrates a higher degree of reproducible degradation, but not irreversible destruction, in all three outcomes. Such an approach will allow formulation of therapeutic interventions designed to enhance mandibular distraction osteogenesis so that it may be used as a viable reconstructive option.

Effects of recombinant human erythropoietin on mandibular distraction osteogenesis

PURPOSE

To evaluate the effects of subcutaneous administration of recombinant human erythropoietin (rHuEPO) on regeneration formation and quality during mandibular distraction osteogenesis.

MATERIALS AND METHODS

Sixteen adult male New Zealand rabbits were used in this study. Ethical approval was obtained from the Animal Research Institute of Selcuk University, Konya, Turkey. Subjects were randomly divided into 2 groups. Distraction osteogenesis (DO) was performed with a custom-made distractor on the left mandibles of rabbits. In the experimental group, 4 doses of 150 IU/kg rHuEPO were administered at 48-hour intervals. The first dose was given immediately after surgery. Control subjects received 0.5 mL/kg isotonic solution in the same manner. After 2 days of latency, mandibles were distracted 1 mm/day at 12-hour intervals for 5 days. A 5-mm lengthening was achieved. All animals were sacrificed after 30 days of consolidation. Afterward, samples were prepared for histomorphometric evaluation of newly formed bone area.

RESULTS

The number of osteoblasts and blood vessels was significantly higher, whereas the number of osteoclasts was significantly lower, in the experimental group than in the control group (P < .05). In the experimental group, the area of new bone formation was greater than in the control group (P < .05). Moreover, fibroblast and collagen numbers per unit area were higher in the experimental group. However, this finding was not statistically significant (P > .05).

CONCLUSION

The subcutaneous administration of rHuEPO improves the rate and quality of bone-healing during distraction osteogenesis. However, the short-term favorable effects of rHuEPO in this study should be extended with long-term investigations before clinical application.

Effects of hyperbaric oxygen on proliferation and differentiation of osteoblasts from human alveolar bone

In view of the controversy of the clinical use of hyperbaric oxygen (HBO) treatment to stimulate fracture healing and bone regeneration, we have analyzed the effects of daily exposure to HBO on the proliferation and differentiation of human osteoblasts in vitro. HBO stimulated proliferation when osteoblasts were cultured in 10% fetal calf serum (FCS), whereas an inhibitory effect of HBO was observed when cultures were supplemented with 2% FCS. On the other hand, HBO enhanced biomineralization with an increase in bone nodule formation, calcium deposition, and alkaline phosphatase activity, whereas no cytotoxic effect was detected using a lactate dehydrogenase activity assay. The data suggest that the exposure of osteoblasts to HBO enhances differentiation toward the osteogenic phenotype, providing cellular evidence of the potential application of HBO in fracture healing and bone regeneration.