Role of osteoclasts in oral homeostasis and jawbone diseases

Menopause-Associated Changes in Mandibular Bone Microarchitecture Are Site-Specific

BACKGROUND

There are conflicting reports on the effects of decreased estrogen levels on mandibular bone microarchitecture. Whether these effects are consistent throughout the mandible is unclear and may have important implications for treatment planning.

PURPOSE

The goal of this study was to evaluate trabecular and cortical bone microstructure in the mandibular condyle and the mandibular basal bone and compare these sites between premenopausal and postmenopausal women.

STUDY DESIGN, SETTING, SAMPLE

Participants were recruited for a cross-sectional cohort study at Columbia University Irving Medical Center. Each participant had cone-beam computed tomography taken of their mandibular condyles and the basal bone. Exclusion criteria for the population included a) current chemotherapy or immunotherapy; b) history of bisphosphonate or other osteoporosis therapy; and c) currently pregnant, nursing, or on hormonal birth control.

INDEPENDENT VARIABLE

The predictor variables are menopausal status (before or after menopause) and mandibular region of interest (condyle/basal bone).

MAIN OUTCOME VARIABLE

Parameters of interest included the following indicators of bone quality: trabecular bone volume fraction, trabecular thickness, trabecular number, trabecular separation, cortical bone volume fraction, cortical thickness, and cortical porosity.

COVARIATES

Covariates included demographic variables such as age, estrogen levels, and ethnicity.

ANALYSES

Quantitative microstructure analyses were conducted on cone-beam computed tomography images, and differences between groups for continuous measures (including age) were assessed with an unpaired t-test, and demographic variables were assessed by χ2. Statistical significance was recorded at P < .05.

RESULTS

The premenopausal and postmenopausal groups each had 31 participants, with the following average age: premenopausal = 43.9 ± 6.9 versus postmenopausal = 57.5 ± 7.6 years old; P < .001, and estrogen levels: premenopausal = 91.77 ± 80.13 pg/ml versus postmenopausal = 41.44 ± 61.62 pg/ml; P < .01). Postmenopausal women had significantly greater condylar trabecular separation (0.61 ± 0.18 vs 0.47 ± 0.11 mm; P < .001) and lower trabecular number (1.03 ± 0.18 vs 1.21 ± 0.19 mm-1; P < .001) compared to premenopausal women. There were no significant differences in the basal bone microarchitectural parameters between the menopausal groups.

CONCLUSION AND RELEVANCE

Menopause is associated with mandibular condylar trabecular bone loss but has minimal effects on the mandibular basal bone. This may have important ramifications for treatment planning in advanced-age individuals.

Transferrin receptor 2 mitigates periodontitis-driven alveolar bone loss

Periodontitis is associated with significant alveolar bone loss. Patients with iron overload suffer more frequently from periodontitis, however, the underlying mechanisms remain largely elusive. Here, we investigated the role of transferrin receptor 2 (Tfr2), one of the main regulators of iron homeostasis, in the pathogenesis of periodontitis and the dental phenotype under basal conditions in mice. As Tfr2 suppresses osteoclastogenesis, we hypothesized that deficiency of Tfr2 may exacerbate periodontitis-induced bone loss. Mice lacking Tfr2 (Tfr2-/- ) and wild-type (Tfr2+/+ ) littermates were challenged with experimental periodontitis. Mandibles and maxillae were collected for microcomputed tomography and histology analyses. Osteoclast cultures from Tfr2+/+ and Tfr2-/- mice were established and analyzed for differentiation efficiency, by performing messenger RNA expression and protein signaling pathways. After 8 days, Tfr2-deficient mice revealed a more severe course of periodontitis paralleled by higher immune cell infiltration and a higher histological inflammation index than Tfr2+/+ mice. Moreover, Tfr2-deficient mice lost more alveolar bone compared to Tfr2+/+ littermates, an effect that was only partially iron-dependent. Histological analysis revealed a higher number of osteoclasts in the alveolar bone of Tfr2-deficient mice. In line, Tfr2-deficient osteoclastic differentiation ex vivo was faster and more efficient as reflected by a higher number of osteoclasts, a higher expression of osteoclast markers, and an increased resorptive activity. Mechanistically, Tfr2-deficient osteoclasts showed a higher p38-MAPK signaling and inhibition of p38-MAPK signaling in Tfr2-deficient cells reverted osteoclast formation to Tfr2+/+ levels. Taken together, our data indicate that Tfr2 modulates the inflammatory response in periodontitis thereby mitigating effects on alveolar bone loss.

Breastfeeding Duration Is Associated with the Risk of Tooth Loss, Chewing Difficulty, and Undernutrition among Older Korean Women: Results of the Korea National Health and Nutrition Examination Survey (KNHANES) 2013-2015

We investigated whether older Korean women with prolonged breastfeeding duration have an increased risk of tooth loss, chewing difficulty, or undernutrition, as well as whether tooth loss and chewing difficulty mediate the association between breastfeeding duration and undernutrition risk. This study included 1666 women aged ≥65 years from the 2013-2015 Korea National Health and Nutrition Examination Survey who breastfed after delivery. The number of teeth and chewing ability were investigated based on the status of individual teeth and a self-report questionnaire, respectively. Dietary intake was estimated using the 24 h recall method. Compared with women who breastfed for 1-18 months, the odds ratios for tooth loss were 1.16 (95% confidence interval [CI] = 0.69-1.94), 1.79 (95% CI = 1.08-2.94), and 1.86 (95% CI = 1.16-2.97) among women who breastfed for 19-36, 37-72, and ≥73 months, respectively (p for trend = 0.004). Similar results were obtained for chewing difficulty and undernutrition. Furthermore, tooth loss and chewing difficulty partially mediated the association between breastfeeding duration and undernutrition risk. In conclusion, older Korean women who breastfed for longer periods are more likely to experience tooth loss, chewing difficulty, and undernutrition, which are particularly severe among women who breastfed for ≥37 months. The association between breastfeeding duration and undernutrition risk is mediated by tooth loss and chewing difficulty.

Influence of age and gender on alveolar bone healing post tooth extraction in 129 Sv mice: a microtomographic, histological, and biochemical characterization

OBJECTIVES

To analyze the effect of biological sex and aging on craniofacial bone features in 129 Sv mice and their influence on dental socket healing post tooth extraction.

MATERIALS AND METHODS

A total of 52 129 Sv mice were used, of which 28 were young (3-4 months) and 24 were aged (17-18 months), equally distributed according to biological sex. After an upper right incisor extraction, mice specimens were collected at 7, 14, and 21-days post-surgery for microtomographic (microCT) and comprehensive histological analysis. Mandible, skull bones, and maxillae at 21 days were analyzed by microCT, while blood plasma samples were collected for the detection of key bone turnover markers (P1NP and CTX-1) by enzyme-linked immunosorbent (ELISA) assay.

RESULTS

Aged females depicted significantly decreased mineralized bone content in alveolar sockets in comparison to young females and aged males at day 7, and aged males at day 14. Mandible RCA and Ma.AR of aged females were also significantly decreased in comparison with young females. Histological evaluation revealed that all alveolar sockets healed at 21 days with inflammation resolution and deposition of new bone. Immunohistochemistry for TRAP revealed increased area density for osteoclasts in alveolar sockets of aged females when compared to young females at 21 days. While a significant increase in CTX-1 levels was detected in blood plasma of aged females when compared to young females, P1NP levels did not significantly change between young and older females. No significant changes were observed for males.

CONCLUSIONS

Age and gender can significantly affect craniofacial bones of 129 Sv mice, especially maxilla and mandible in females. Considering the altered bone resorption parameters and delayed alveolar bone healing in older females, careful deliberation is necessary during development of pre-clinical models for craniofacial research.

CLINICAL RELEVANCE

Aging can be a contributing factor to slower bone healing in craniofacial bones. However, there are no sufficient experimental studies that have addressed this phenomenon along with biological sex taken into consideration.

Advanced Hydrogel systems for mandibular reconstruction

Mandibular defect becomes a prevalent maxillofacial disease resulting in mandibular dysfunctions and huge psychological burdens to the patients. Considering the routine presence of oral contaminations and aesthetic restoration of facial structures, the current clinical treatments are however limited, incapable to reconstruct the structural integrity and regeneration, spurring the need for cost-effective mandibular tissue engineering. Hydrogel systems possess great merit for mandibular reconstruction with precise involvement of cells and bioactive factors. In this review, current clinical treatments and distinct mode(s) of mandible formation and pathological resorption are summarized, followed by a review of hydrogel-related mandibular tissue engineering, and an update on the advanced fabrication of hydrogels with improved mechanical property, antibacterial ability, injectable form, and 3D bioprinted hydrogel constructs. The exploration of advanced hydrogel systems will lay down a solid foundation for a bright future with more biocompatible, effective, and personalized treatment in mandibular reconstruction.

Carbonic Anhydrase II Activators in Osteopetrosis Treatment: A Review

Osteopetrosis is a rare hereditary illness generated by failure in osteoclasts resulting in elevated bone densities. Patients with osteopetrosis possess several complications, like dental caries, earlier teeth loss, delayed eruption, malformed crowns and roots, and lamina dura thickening. Since deficiency of carbonic anhydrase II is a major cause behind osteopetrosis, carbonic anhydrase II activators have a large number of applications in osteopetrosis treatment. There is a lack of a comprehensive review on osteopetrosis, pathogenesis of dental abnormalities, and the role of carbonic anhydrase II activators in osteopetrosis treatment. To address this research gap, the authros perfomed a comprehensive review on osteopetrosis and its types, pathogenesis of dental abnormalities, and the role of carbonic anhydrase II activators in osteopetrosis treatment. A brief introduction to the pathogenesis of dental abnormalities and regeneration is provided in this survey. A discussion of types of osteopetrosis depending on genetic inheritance, such as autosomal dominant, autosomal recessive, and X-linked inheritance osteopetrosis, is presented in this survey. The paper also focuses on the importance of carbonic anhydrase II activators as a potential drug therapy for dental osteopetrosis. In addition, a brief note on the role of azole and fluconazole in treating osteopetrosis is given. Finally, future directions involving gene therapy for dental osteopetrosis are described.

A Comprehensive Review on Drug Therapies and Nanomaterials used in Orthodontic Treatment

Orthodontic treatment typically requires an extended duration of 1-2 years to complete the treatment. Accelerating the rate of tooth movement during orthodontic treatment is essential for shortening the overall treatment duration. After the completion of orthodontic treatment, a prominent concern arises in the form of orthodontic relapse, where the teeth tend to revert to their original positions. This issue affects approximately 60% of the global population, underscoring the importance of implementing effective measures to address orthodontic relapse. An approach in this regard involves the targeted administration of herbal and synthetic drugs applied directly to the specific area of interest to facilitate tooth movement and prevent orthodontic relapse. Apart from this, researchers are investigating the feasibility of utilizing different types of nanoparticles to improve the process of orthodontic tooth movement. In recent years, there has been a noticeable increase in the number of studies examining the effects of various drugs on orthodontics. However, the currently available literature does not provide significant evidence relating to orthodontic tooth movement. In this review, the authors provide valuable information about the drugs and nanomaterials that are capable of further enhancing the rate of orthodontic tooth movement and reducing the risk of orthodontic relapse. However, a notable hurdle remains, i.e., there is no marketed formulation available that can enhance orthodontic tooth movement and reduce treatment time. Therefore, researchers should try herbal-synthetic approaches to achieve a synergistic effect that can enhance orthodontic tooth movement. In this nutshell, there is an urgent need to develop a non-invasive, patient-compliant, and cost-effective formulation that will provide quality treatment and ultimately reduce the treatment time. Another critical issue is orthodontic relapse, which can be addressed by employing drugs that slow down osteoclastogenesis, thereby preventing tooth movement after treatment. Nevertheless, extensive research is still required to overcome this challenge in the future.

Effect of Taraxaci Herba on Bone Loss in an OVX-Induced Model through the Regulation of Osteoclast Differentiation

Bone is a dynamic tissue that maintains homeostasis with a balance of osteoclasts for bone resorption and osteoblasts for bone formation. Women are deficient in estrogen after menopause, which promotes bone resorption due to excessive activity of osteoclasts, leading to osteoporosis. TH (also known as dandelion) is native to warm regions and has traditionally been used to treat gynecological diseases and inflammation. Menopause is a major cause of osteoporosis as it causes abnormal activity of osteoclasts, and various studies have shown that anti-inflammatory drugs have the potential to treat osteoporosis. We analyzed the effect of TH on osteoclast differentiation and the relevant mechanisms using RANKL. After administration of TH in a menopause-like rat model in which ovariectomy of the was rats carried out, changes in bone microstructure were analyzed via micro-CT, and the antiosteoporosis effect of TH was verified by a histological analysis. In addition, the pharmacological effects of TH in an animal model of osteoporosis were compared and analyzed with osteoporosis medications (17β-estradiol (E₂) and alendronate (ALN)). TH significantly inhibited the initial osteoclast differentiation via the NFATc1/c-Fos mechanism. In addition, bone density in the femur of osteoporotic rats was increased, and the expression of osteoclast-related factors in the serum and tissues was controlled. The results of this study provide objective evidence of the inhibitory effect of TH on osteoclastogenesis and OVX-induced bone loss.

Roles of osteoclasts in alveolar bone remodeling

Osteoclasts are large multinucleated cells from hematopoietic origin and are responsible for bone resorption. A balance between osteoclastic bone resorption and osteoblastic bone formation is critical to maintain bone homeostasis. The alveolar bone, also called the alveolar process, is the part of the jawbone that holds the teeth and supports oral functions. It differs from other skeletal bones in several aspects: its embryonic cellular origin, the form of ossification, and the presence of teeth and periodontal tissues; hence, understanding the unique characteristic of the alveolar bone remodeling is important to maintain oral homeostasis. Excessive osteoclastic bone resorption is one of the prominent features of bone diseases in the jaw such as periodontitis. Therefore, inhibiting osteoclast formation and bone resorptive process has been the target of therapeutic intervention. Understanding the mechanisms of osteoclastic bone resorption is critical for the effective treatment of bone diseases in the jaw. In this review, we discuss basic principles of alveolar bone remodeling with a specific focus on the osteoclastic bone resorptive process and its unique functions in the alveolar bone. Lastly, we provide perspectives on osteoclast-targeted therapies and regenerative approaches associated with bone diseases in the jaw.

Rubbing-Assisted Approach for Fabricating Oriented Nanobiomaterials

The highly-oriented structures in biological tissues play an important role in determining the functions of the tissues. In order to artificially fabricate oriented nanostructures similar to biological tissues, it is necessary to understand the oriented mechanism and invent the techniques for controlling the oriented structure of nanobiomaterials. In this review, the oriented structures in biological tissues were reviewed and the techniques for producing highly-oriented nanobiomaterials by imitating the oriented organic/inorganic nanocomposite mechanism of the biological tissues were summarized. In particular, we introduce a fabrication technology for the highly-oriented structure of nanobiomaterials on the surface of a rubbed polyimide film that has physicochemical anisotropy in order to further form the highly-oriented organic/inorganic nanocomposite structures based on interface interaction. This is an effective technology to fabricate one-directional nanobiomaterials by a biomimetic process, indicating the potential for wide application in the biomedical field.

The Therapeutic Potential of Secreted Factors from Dental Pulp Stem Cells for Various Diseases

An alternative source of mesenchymal stem cells has recently been discovered: dental pulp stem cells (DPSCs), including deciduous teeth, which can thus comprise potential tools for regenerative medicine. DPSCs derive from the neural crest and are normally implicated in dentin homeostasis. The clinical application of mesenchymal stem cells (MSCs) involving DPSCs contains various limitations, such as high cost, low safety, and cell handling issues, as well as invasive sample collection procedures. Although MSCs implantation offers favorable outcomes on specific diseases, implanted MSCs cannot survive for a long period. It is thus considered that their mediated mechanism of action involves paracrine effects. It has been recently reported that secreted molecules in DPSCs-conditioned media (DPSC-CM) contain various trophic factors and cytokines and that DPSC-CM are effective in models of various diseases. In the current study, we focus on the characteristics of DPSC-CM and their therapeutic potential against various disorders.

Effects of high-dose all-trans retinoic acid on longitudinal bone growth of young rats

OBJECTIVE

The signaling axis consisting of GH-IGF1-IGFBP3 is the primary signal taht acts prepubertally to influence height development. Growth plate thinning and even premature closure have been reported in children with tumors treated with retinoid chemotherapy, resulting in long bone dysplasia. Growth failure may occur despite received GH treatment, but the reason is unknown. This study investigate the effect of high-dose all-trans retinoic acid (ATRA) on the development of long bones in growing SD rats.

METHODS

A total of 20 three-week-old male SD rats were randomly divided into a control group and an experimental group (n = 10). Rats were treated by gavage with or without high-dose ATRA for 10 days. The body weights of the rats were recorded daily. At the end of the experiment, we measured the length of nose-tail and tibia, stained the tibia and liver for pathological tissue and RT-PCR reaction, and measured the levels of serum GH, IGF1 and IGFBP3, and so on.

RESULTS

Compared with controls, experimental rats exhibited reduced body weight and shortened nasal-tail and radial tibial length. Cyp26b1 enzyme activity in the liver was elevated, and histopathological staining revealed that the cartilaginous epiphyseal plate was narrowed, the medullary cavity of trabecular bone was sparse, the number of trabecular bones was decreased, trabecular separation was increased, bone marrow mineralization was enhanced, osteoclastic activity was increased, and circulating GH-IGF1-IGFBP3 levels were decreased. However, RT-PCR reaction results of localized proximal tibiae showed upregulation of IGF1 and downregulation of IGFBP3.

CONCLUSIONS

High-dose ATRA intake over a short period of time can reduce GH-IGF1-IGFBP3 levels, affect cartilage and bone homeostasis, and inhibit bone growth in developing animals.

Irradiation affects the structural, cellular and molecular components of jawbones

PURPOSE

Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area.

CONCLUSIONS

The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.