Low-intensity ultrasound accelerates mandibular implant bone integration in dogs with mandibular osteoradionecrosis

The Progress in Reconstruction of Mandibular Defect Caused by Osteoradionecrosis

Osteoradionecrosis (ORN) is described as a disease with exposed, nonviable bone that fails to heal spontaneously or by means of conservative treatment after radiotherapy in at least 3 months. Though traditional theories in the early stage including hypoxic-hypocellular-hypovascular and fibro-atrophic in addition to new findings such as ferroptosis were put forward to explain the mechanisms of the osteoradionecrosis, the etiology of ORN is still unclear. With the high rate of occurrence in the head and neck area, especially in the mandible, this disease can disrupt the shape and function of the irradiated area, leading to a clinical presentation ranging from stable small areas of asymptomatic exposed bone to severe progressive necrosis. In severe cases, patients may experience pain, xerostomia, dysphagia, facial fistulas, and even a jaw defect. Consequently, sequence therapy and sometimes extensive surgery and reconstructions are needed to manage these sequelae. Treatment options may include pain medication, antibiotics, the removal of sequesters, hyperbaric oxygen therapy, segmental resection of the mandible, and free flap reconstruction. Microanastomosed free-flaps are considered to be promising choice for ORN reconstruction in recent researches, and new methods including three-dimensional (3-D) printing, pentoxifylline, and amifostine are used nowadays in trying increase the success rates and improve quality of the reconstruction. This review summarizes the main research progress in osteoradionecrosis and reconstruction treatment of osteoradionecrosis with mandibular defect.

Medication-related osteonecrosis and osteoradionecrosis of the jaws: Update and current management

Medication related osteonecrosis of the jaws (MRONJ) and osteoradionecrosis of the jaws (ORNJ) are two different diseases of quite similar appearance. MRONJ is mainly due to antiresorptive or antiangiogenic drug therapy and ORNJ to radiotherapy. The present work aimed at presenting and comparing the current knowledge on MRONJ and ORNJ. They both present as an exposure of necrotic bone and differ in some clinical or radiological characteristics, clinical course and mostly in treatment. They share similar risk factors. A tooth extraction is more frequently found as a triggering factor in MRONJ. The frequency of a maxillary localisation seems higher for MRONJ. On computed tomographic images, a periosteal reaction seems characteristic of MRONJ. More frequent pathological fractures seem to occur in ORNJ. It is mandatory, for ORNJ diagnosis, to exclude a residual or recurrent tumour using histological examination. Both MRONJ and ORNJ are challenging to treat and cannot be managed similarly. For both, it would still be worth to optimise awareness within the medical community, patients' oral hygiene and dental cares to improve their prevention and make their incidences decrease. Conservative therapy is more frequently achieved for MRONJ than ORNJ and surgical resection is more often performed for ORNJ. For both diseases, the last treatment possible in refractory cases is a surgical extensive resection with free flap reconstruction. A MRONJ classification is widely used today, whereas no consensus exists to date for ORNJ classification. We propose a classification that could play this role.

Low-Intensity Pulsed Ultrasound Modulates RhoA/ROCK Signaling of Rat Mandibular Bone Marrow Mesenchymal Stem Cells to Rescue Their Damaged Cytoskeletal Organization and Cell Biological Function Induced by Radiation

Osteoradionecrosis of the jaw (ORNJ) is an infrequent yet potentially devastating complication of head and neck radiation therapy. Low-intensity pulsed ultrasound (LIPUS) has been widely accepted as a promising method for the successful management of ORNJ, but the mechanism remains unclear. In this study, the effects of LIPUS on cytoskeletal reorganization, cell viability, and osteogenic differentiation capacity of rat mandible-derived bone marrow mesenchymal stem cells (M-BMMSCs) induced by radiation were determined by immunofluorescence staining, CCK-8 cell proliferation assay, quantification of alkaline phosphatase (ALP) activity, alizarin red staining, and real-time RT-PCR, respectively. Moreover, the involvement of the RhoA/ROCK signaling pathway underlying this process was investigated via western blot analysis. We found that radiation induced significant damage to the cytoskeleton, cell viability, and osteogenic differentiation capacity of M-BMMSCs and downregulated their expression of RhoA, ROCK, and vinculin while increasing FAK expression. LIPUS treatment effectively rescued the disordered cytoskeleton and redistributed vinculin. Furthermore, the cell viability and osteogenic differentiation capacity were also significantly recovered. More importantly, it could reverse the aberrant expression of the key molecules induced by radiation. Inhibition of RhoA/ROCK signaling remarkably aggravated the inhibitory effect of radiation and attenuated the therapeutic effect of LIPUS. In the light of these findings, the RhoA/ROCK signaling pathway might be a promising target for modifying the therapeutic effect of LIPUS on osteoradionecrosis.

Long-term implant failure in patients treated for oral cancer by external radiotherapy: a retrospective monocentric study

Introduction: The placement of dental implants in irradiated bone has allowed functional rehabilitation for many oral cancer patients. Nonetheless, there is only few data about implant failure in irradiated tissues and their consequences. This retrospective study aims to highlight the rate and circumstances of implant failure. Material and method: Patients treated with external radiotherapy for oral carcinoma and who received dental implants were included. Patients reconstructed with free bone flaps were excluded. Results: Eighteen patients were included. Forty implants were placed between 2004 and 2007, 8 failed, of whom one osteoradionecrosis was observed. Time interval between radiotherapy and implantation was 44.6 (6–182) months. Mean dose was 51.8 (50–66) Gy. Discussion: In the series, the implant failure rate is 20%, which corroborates the literature's data. Failures occur more often for doses over 50 Gy. The placement of dental implant in irradiated bone leads to soft tissue complications but also increases the risk of osteoradionecrosis. The recent reimbursement of dental implants in oral cancer patients by the National Social Health system will probably increase the indications. Multidisciplinary staffs should be aware of benefit/risk ratio for each patient.

The bone regenerative capacity of canine mesenchymal stem cells is regulated by site-specific multilineage differentiation

OBJECTIVES

Mesenchymal stem cells (MSCs) offer a promising therapy in dentistry because of their multipotent properties. Selecting donor MSCs is crucial because Beagle dogs (canines) commonly used in preclinical studies have shown variable outcomes, and it is unclear whether canine MSCs (cMSCs) are skeletal site specific. This study tested whether jaw and long bone cMSCs have disparate in vitro and in vivo multilineage differentiation capabilities.

STUDY DESIGN

Primary cMSCs were isolated from the mandible (M-cMSCs) and femur (F-cMSCs) of four healthy Beagle dogs. The femur served as the non-oral control. Clonogenic and proliferative abilities were assessed. In vitro osteogenic, chondrogenic, adipogenic, and neural multilineage differentiation were correlated with in vivo bone regeneration and potential for clinical applications.

RESULTS

M-cMSCs displayed two-fold increase in clonogenic and proliferative capacities relative to F-cMSCs (P = .006). M-cMSCs in vitro osteogenesis based on alkaline phosphatase (P = .04), bone sialoprotein (P = .05), and osteocalcin (P = .03), as well as adipogenesis (P = .007) and chondrogenesis (P = .009), were relatively higher and correlated with enhanced M-cMSC bone regenerative capacity. Neural expression markers, nestin and βIII-tubulin, were not significantly different.

CONCLUSIONS

The enhanced differentiation and bone regenerative capacity of mandible MSCs may make them favorable donor graft materials for site-specific jaw bone regeneration.

The role of myofibroblasts in the development of osteoradionecrosis in a newly established rabbit model

This study aimed to establish a proper animal model of osteoradionecrosis of jaws (ORNJ) and to observe preliminarily the characteristics of myofibroblasts, the key effector cell of fibrosis, in ORNJ. Rabbit mandibles were irradiated at three different doses based on a human equivalent radiation schedule, and examined by gross manifestation, single-photon emission computed tomography (SPECT), micro-computed tomography, sequential fluorochrome labeling, and histology. Immunohistochemistry staining of α-SMA was applied to detect the existence of myofibroblasts. The exposed necrotic bone, which is the main indication of ORNJ, started to be observed at all rabbits at 9 Gy. With the radiation dose increasing, the microarchitecture of the irradiated mandibles was more destroyed, the metabolism and mineralization of the irradiated mandibles diminished, the osteocytes number decreased, and more mature bones were substituted by fibrosis in the irradiated mandibles. In addition, as the radiation dose increased, the myofibroblast number increased and collected around the separated sequestrum, which indicated that myofibroblasts might relate to the pathogenesis of ORNJ. In summary, a clinically translational ORNJ model was successfully established in our study, and the role of myofibroblasts in the pathogenesis of ORNJ is described for the first time.

Prevention of osteoradionecrosis of the jaws by low-intensity ultrasound in the dog model

The prevention of osteoradionecrosis of the jaws (ORNJ) is very important because of the current absence of effective therapies for this disease. The aim of this study was to determine whether low-intensity ultrasound has a preventive effect on ORNJ. Sixty healthy adult dogs were divided randomly into three groups: group A (radiotherapy alone), group B (radiotherapy followed by low-intensity ultrasound treatment), and a control group. The development of ORNJ was assessed and the rate of occurrence of ORNJ was compared between groups A and B. Micro-computed tomography, haematoxylin-eosin staining, and immunofluorescence were used to evaluate the microstructure of the mandible and changes in microvascular density in all groups. All animals in group A and group B (ultrasound applied for 30 days) developed ORNJ. Alveolar bone density was 609.48±53.77HU in group A and 829.65±81.46HU in group B (P=0.008). The trabecular bone volume fraction, bone surface area/bone volume ratio, trabecular thickness, and trabecular number were all lower in group A than in group B (P=0.037, P=0.022, P=0.017, and P=0.034, respectively). Haematoxylin-eosin staining showed that the Haversian canals in the osteons had expanded significantly in group A, with collagen fibres losing their circular orientation; group B tended to show typical osteons. The microvascular density in group A was decreased. In conclusion, the use of low-intensity ultrasound in the dog appears not to prevent the incidence of ORNJ, however it does somewhat improve vascularity and bone quality at the microscopic level, which contribute to ORNJ healing.

Ultrasound Stimulation of Different Dental Stem Cell Populations: Role of Mitogen-activated Protein Kinase Signaling

INTRODUCTION

Mesenchymal stem cells (MSCs) from dental tissues may respond to low-intensity pulsed ultrasound (LIPUS) treatment, potentially providing a therapeutic approach to promoting dental tissue regeneration. This work aimed to compare LIPUS effects on the proliferation and MAPK signaling in MSCs from rodent dental pulp stem cells (DPSCs) compared with MSCs from periodontal ligament stem cells (PDLSCs) and bone marrow stem cells (BMSCs).

METHODS

Isolated MSCs were treated with 1-MHz LIPUS at an intensity of 250 or 750 mW/cm2 for 5 or 20 minutes. Cell proliferation was evaluated by 5-bromo-2-deoxyuridine (BrdU) staining after 24 hours of culture following a single LIPUS treatment. Specific ELISAs were used to determine the total and activated p38, ERK1/2, and JNK MAPK signaling proteins up to 4 hours after treatment. Selective MAPK inhibitors PD98059 (ERK1/2), SB203580 (p38), and SP600125 (JNK) were used to determine the role of activation of the particular MAPK pathways.

RESULTS

The proliferation of all MSC types was significantly increased after LIPUS treatment. LIPUS at a 750-mW/cm2 dose induced the greatest effects on DPSCs. BMSC proliferation was stimulated in equal measures by both intensities, whereas 250 mW/cm2 LIPUS exposure exerted maximum effects on PDLSCs. ERK1/2 was activated immediately in DPSCs after treatment. Concomitantly, DPSC proliferation was specifically modulated by ERK1/2 inhibition, whereas p38 and JNK inhibition exerted no effects. In BMSCs, JNK MAPK signaling was LIPUS activated, and the increase in proliferation was blocked by specific inhibition of the JNK pathway. In PDLSCs, JNK MAPK signaling was activated immediately after LIPUS, whereas p-p38 MAPK increased significantly in these cells 4 hours after exposure. Correspondingly, JNK and p38 inhibition modulated LIPUS-stimulated PDLSC proliferation.

CONCLUSIONS

LIPUS promoted MSC proliferation in an intensity and cell-specific dependent manner via activation of distinct MAPK pathways.

Effect of low-intensity pulsed ultrasound on posterolateral lumbar fusion of rabbit

OBJECTIVE

To observe the effect of low-intensity pulsed ultrasound in the posterolateral lumbar fusion of rabbit.

METHODS

A total of 48 New Zealand white rabbits were randomly divided into the observation group and control group, including the autogenous iliac observation group, artificial bone observation group, artificial bone control group and autogenous iliac control group according to the different bone grafting. The posterolateral lumbar fusion of rabbits in each group was analyzed and compared.

RESULTS

After 4 weeks of treatment using the low-intensity pulsed ultrasound, the fusion in the bone grafting area of observation group was good. There was the relatively dense fusion area between the right transverse process and artificial bone. The left transverse process had been completely fused, with the clear bone trabecula through the fusion area. There was no significant fusion sign in the control group. According to the fusion comparison between two groups, the fusion rate of the observation group was 83.3% and it was significantly higher than the one of the control group (37.5%). Results of the comparison were statistically significant (P<0.05). The number of chondrocytes and the increase in the relative gray-scale in the fusion area of the iliac observation group were significantly higher than ones of the iliac control group (P<0.05). The number of chondrocytes and the increase in the relative gray-scale in the fusion area of the artificial bone observation group were significantly higher than ones of the artificial bone control group (P<0.05). The expression of IL-1, IL-6 and IL-17 4 weeks after the treatment of the observation group was significantly lower than the one of the control group, with the statistical significance (P<0.05). It indicated that the treatment of low-intensity pulsed ultrasound could reduce the expression level of inflammatory factors.

CONCLUSIONS

The low-intensity pulsed ultrasound can significantly increase the bone grafting fusion rate of the rabbit's posterolateral lumbar fusion. The possible mechanism is that it promotes the lumbar posterolateral endochondral ossification and reduces the inflammatory reaction.