TNF-α is responsible for the contribution of stromal cells to osteoclast and odontoclast formation during orthodontic tooth movement

Effect of age on orthodontic tooth movement in mice

Background/purpose

The number of middle-aged and elderly orthodontic patients is increasing due to changes in age composition. It is important to investigate the detailed mechanisms of bone remodeling in orthodontic tooth movement (OTM) in the elderly. However, there are few reports on the mechanism of tooth movement in the elderly. The purpose of the present study was to analyze OTM and osteoclastogenesis in aged mice and to elucidate the mechanism.

Materials and methods

It has been reported that tumor necrosis factor (TNF)-α plays an important role in osteoclast formation and OTM. First, 8-week-old and 78-week-old male C57BL/6J mice were subcutaneously injected with TNF-α into the calvaiae, and micro-CT, tartrate-resistant acid phosphatase (TRAP) staining, and real-time PCR were performed to evaluate osteoclast formation and bone resorption. Furthermore, osteoclastogenesis by TNF-α and receptor activator of nuclear factor-kappa B ligand (RANKL) using bone marrow cells was evaluated in vitro. Finally, a nickel-titanium closed-coil spring was attached, mesial movement of the maxillary left first molar was performed, and tooth movement distance and osteoclast formation were evaluated.

Results

Compared to 8-week-old mice, 78-week-old mice had decreased TNF-α-induced bone resorption, osteoclastogenesis, and TRAP and cathepsin K expression in the calvariae. In vitro osteoclast formation also decreased in 78-week-old mice. Furthermore, tooth movement distance and osteoclastogenesis were reduced.

Conclusion

OTM decreased in aged mice, which was shown to be caused by a decrease in osteoclastogenesis. Therefore, it was suggested that it is necessary to keep in mind that tooth movement may be suppressed when treating elderly patients.

Role of αENaC in root resorption of adjacent teeth due to entirely impacted mandibular third molars

BACKGROUND

Entirely impacted mandibular third molar (EIM3M) concerns the pathological external root resorption (ERR) of the adjacent mandibular second molar (M2M) and formation of granulation tissue between two molars. The study aimed to clarify the effect of αENaC, a mechano-sensitive molecule, to explore the mechanical mechanism in this scenario.

METHODS

The force EIM3M exerted on M2M was proved by finite element analysis. αENaC expressions were tested by real-time polymerase chain reaction (PCR), immunoblotting and immunofluorescence. Inflammatory and epithelial-mesenchymal transition (EMT)-related molecules expressions were also detected by real-time PCR. The correlation was analyzed by Spearman's correlation analysis, and receiver-operator characteristic (ROC) curve was further exhibited.

RESULTS

The force was concentrated in the ERR area. αENaC was upregulated, positively correlated with ERR degree and localized to the fibroblasts in ERR granulation tissues. Moreover, αENaC was respectively and positively associated with elevated TNF-α and N-cadherin in ERR granulation tissues. More importantly, ROC analysis verified αENaC as a novel indication of the incidence of this disease.

CONCLUSIONS

Our finding revealed the force from EIM3M causing ERR of M2M, and elucidated the expression and localization of αENaC and its positive correlation with inflammation, EMT and disease severity, suggesting a novel indication in this disease.

Osteoimmunology in Periodontitis and Orthodontic Tooth Movement

PURPOSE OF REVIEW

To review the role of the immune cells and their interaction with cells found in gingiva, periodontal ligament, and bone that leads to net bone loss in periodontitis or bone remodeling in orthodontic tooth movement.

RECENT FINDINGS

Periodontal disease is one of the most common oral diseases causing inflammation in the soft and hard tissues of the periodontium and is initiated by bacteria that induce a host response. Although the innate and adaptive immune response function cooperatively to prevent bacterial dissemination, they also play a major role in gingival inflammation and destruction of the connective tissue, periodontal ligament, and alveolar bone characteristic of periodontitis. The inflammatory response is triggered by bacteria or their products that bind to pattern recognition receptors that induce transcription factor activity to stimulate cytokine and chemokine expression. Epithelial, fibroblast/stromal, and resident leukocytes play a key role in initiating the host response and contribute to periodontal disease. Single-cell RNA-seq (scRNA-seq) experiments have added new insight into the roles of various cell types in the response to bacterial challenge. This response is modified by systemic conditions such as diabetes and smoking. In contrast to periodontitis, orthodontic tooth movement (OTM) is a sterile inflammatory response induced by mechanical force. Orthodontic force application stimulates acute inflammatory responses in the periodontal ligament and alveolar bone stimulated by cytokines and chemokines that produce bone resorption on the compression side. On the tension side, orthodontic forces induce the production of osteogenic factors, stimulating new bone formation. A number of different cell types, cytokines, and signaling/pathways are involved in this complex process. Inflammatory and mechanical force-induced bone remodeling involves bone resorption and bone formation. The interaction of leukocytes with host stromal cells and osteoblastic cells plays a key role in both initiating the inflammatory events as well as inducing a cellular cascade that results in remodeling in orthodontic tooth movement or in tissue destruction in periodontitis.

Docosahexaenoic acid inhibits TNF-α-induced osteoclast formation and orthodontic tooth movement through GPR120

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that has a range of positive impacts on human health, including anti-inflammatory effects and inhibition of osteoclast formation via G-protein-coupled receptor 120 (GPR120). Orthodontic force was reported to induce tumor necrosis factor-α (TNF-α) expression, which activates osteoclast differentiation during orthodontic tooth movement (OTM). The aim of this study was to investigate the influence of DHA on TNF-α-induced osteoclast formation and OTM in vivo. We examined osteoclast formation and bone resorption within the calvaria of both wild-type (WT) and GPR120-deficient (GPR120-KO) mice injected with phosphate-buffered saline (PBS), TNF-α, TNF-α and DHA, or DHA. DHA inhibited TNF-α-induced osteoclast formation and bone resorption in WT mice but had no effect in GPR120-KO mice. OTM experiments were performed in mouse strains with or without regular injection of DHA, and the effects of DHA on osteoclast formation in the alveolar bones during OTM were examined. DHA also suppressed OTM in WT but not GPR120-KO mice. Our data showed that DHA suppresses TNF-α-induced osteoclastogenesis and bone resorption via GPR120. TNF-α has considerable significance in OTM, and therefore, DHA may also inhibit TNF-α-induced osteoclast formation and bone resorption in OTM.

Absence of tumor necrosis factor receptor 1 inhibits osteoclast activity in apical dental resorption caused by endodontic infection in mice

INTRODUCTION

To evaluate osteoclastogenesis and dental resorption resulting from endodontic infection in wild-type (WT) and tumor necrosis factor receptor 1 genetically deficient (TNFR1 KO) mice.

METHODS

After approval by the Ethics Committee on the use of Animals, 40 mice were distributed into two experimental groups based on periods: 14 days (n=10 WT mice; n=10 TNFR1 KO mice) and 42 days (n=10 WT mice; n=10 TNFR1 KO mice). After these periods, morphometrics analysis was done using bright field and fluorescence microscopy and tartrate-resistant acid phosphatase histoenzymology to identify osteoclasts. One-way analysis of variance followed by Tukey's post-hoc test was used for the statistical analysis (a=0.05).

RESULTS

WT mice in the 42-day period had a greater resorption in the apical region distal root of the first molar than TNFR1 KO mice (p<0.05). On the other hand, TNFR1 KO mice showed a smaller number of osteoclasts on the dental surface than WT mice (p<0.05).

CONCLUSION

WT mice had more extensive bone and apical dental resorptions and a larger number of osteoclasts on the tooth surface than TNFR1 KO mice.

Immunomodulatory Activities of Periodontal Ligament Stem Cells in Orthodontic Forces-Induced Inflammatory Processes: Current Views and Future Perspectives

Orthodontic tooth movement (OTM) is induced by applying active mechanical forces, causing a local non-infectious inflammatory response in the periodontal ligament (PDL). As a prerequisite for OTM, the inflammation status is associated with increased levels of various cytokines and involves the interaction between immune cells and periodontal ligament stem cells (hPDLSCs). It is well established that hPDLSCs respond to orthodontic forces in several ways, such as by secreting multiple inflammatory factors. Another essential feature of hPDLSCs is their immunomodulatory activities, which are executed through cytokine (e.g., TNF-α and IL-1β)-induced production of various soluble immunomediators (e.g., indoleamine-2,3-dioxygenase-1, tumor necrosis factor-inducible gene 6 protein, prostaglandin E₂) and direct cell-to-cell contact (e.g., programmed cell death ligand 1, programmed cell death ligand 2). It is well known that these immunomodulatory abilities are essential for local periodontal tissue homeostasis and regeneration. So far, only a handful of studies provides first hints that hPDLSCs change immunological processes during OTM via their immunomodulatory activities. These studies demonstrate the pro-inflammatory aspect of immunomodulation by hPDLSCs. However, no studies exist which investigate cytokine and cell-to-cell contact mediated immunomodulatory activities of hPDLSCs. In this perspective article, we will discuss the potential role of the immunomodulatory potential of hPDLSCs in establishing and resolving the OTM-associated non-infectious inflammation and hence its potential impact on periodontal tissue homeostasis during OTM.

Micro-Osteoperforations Induce TNF-α Expression and Accelerate Orthodontic Tooth Movement via TNF-α-Responsive Stromal Cells

Micro-osteoperforations (MOPs) have been reported to accelerate orthodontic tooth movement (OTM), and tumor necrosis factor (TNF)-α has been reported to play a crucial role in OTM. In this report, the influence of MOPs during OTM was analyzed. We evaluated the expression of TNF-α with and without MOPs by RT-PCR analysis. A Ni-Ti closed coil spring was fixed between the maxillary left first molar and the incisors as an OTM mouse model to move the first molar in the mesial direction. MOPs were prepared on the lingual side and mesial side of the upper first molars. Furthermore, to investigate the target cell of TNF-α for osteoclast formation during OTM with MOPs in vivo, we created four types of chimeric mice in which bone marrow of wild-type (WT) or TNF receptor 1- and 2-deficient mice (KO) was transplanted into lethally irradiated WT or KO mice. The results showed that MOPs increased TNF-α expression, the distance of tooth movement and osteoclast formation significantly. Furthermore, mice with TNF-α-responsive stromal cells showed a significant increase in tooth movement and number of osteoclasts by MOPs. We conclude that MOPs increase TNF-α expression, and tooth movement is dependent on TNF-α-responsive stromal cells.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

Orthodontics Surgical Assistance (Piezosurgery®): Experimental Evidence According to Clinical Results

Orthodontic tooth movement (OTM) is based on intermitted or continuous forces applied to teeth, changing the mechanical loading of the system and arousing a cellular response that leads to bone adaptation. The traditional orthodontic movement causes a remodeling of the alveolar bone and changes in the periodontal structures that lead to tooth movement. The use of a piezoelectric instrument in orthodontic surgery has already shown great advantages. The purpose of this study is to rank the behavior of inflammatory mediators in accelerating orthodontic tooth movement. Ten patients with malocclusion underwent orthodontic surgical treatment, which included a first stage of surgically guided orthodontic movement (monocortical tooth dislocation and ligament distraction, MTDLD) to accelerate orthodontic movements. In all cases, corticotomy was performed by Piezosurgery. Bone and dental biopsy was executed to evaluate changes in the cytokines IL-1beta, TNF-alpha and IL-2 in different time intervals (1, 2, 7, 14 and 28 days). The molecular mediators are IL-1 beta, TNF-alpha and IL-2. Immediately after the surgical procedure there was a mild expression of the three molecular markers, while the assertion of IL-1 beta and TNF-alpha reached the maximum value after 24 h and 48 h, indicating a strong activation of the treated tissues. The Piezosurgery® surgical technique induces an evident stress in short times, within 24–48 h from the treatment, but it decreases significantly during the follow-up.

Tumor necrosis factor-α enhances the expression of vascular endothelial growth factor in a mouse orthodontic tooth movement model

Background/purpose

Tooth movement that is achieved using orthodontic mechanical principles relies on bone resorption which takes place on the compression side via osteoclasts. Tumor necrosis factor-α (TNF-α) has been known to affect osteoclast formation in orthodontic tooth movement (OTM). Vascular endothelial growth factor (VEGF), which is one of the mediators of angiogenesis, also plays an important role in OTM by inducing vascular permeability and chemotaxis of osteoclast precursors. Therefore, the purpose of this research was to evaluate the effect of TNF-α on VEGF expression during OTM.

Materials and methods

In order to demonstrate the effect of TNF-α on VEGF expression during OTM, a nickel titanium closed coil spring was fixed to the upper left first molar and the alveolar bone beneath the upper incisors of both wild type (WT) and TNF receptors (TNFRs) deficient mice resulting in a mesial movement of the molar for 12 days. The maxilla was removed for histological analysis and real-time RCR analysis of VEGF expression.

Results

Immunohistochemical analysis revealed that there were fewer VEGF-positive cells in the periodontal membrane on the mesial side of the distobuccal root in TNFRs-deficient mice than that in WT mice during the OTM for 12 days. Furthermore, expression of VEGF mRNA is lower level in TNFRs-deficient mice than that in WT mice.

Conclusion

Our results indicate that TNF-α plays an important role in VEGF expression during tooth movement.

Enhancement of orthodontic tooth movement and root resorption in ovariectomized mice

Background/purpose

As the number of patients with osteoporosis requiring orthodontic treatment is increasing with the aging of society, it is necessary to evaluate the relations between bone metabolism in old age and orthodontic tooth movement (OTM). However, the effects of changes in bone metabolism due to osteoporosis on OTM and root resorption are still unclear. Therefore, we investigated the effects of OTM and root resorption in a mouse ovariectomy (OVX)-induced osteoporosis model.

Materials and methods

Eight-week-old female wild-type mice underwent OVX or sham surgery (Sham) as controls. One month after treatment, a nickel titanium coil spring was used to apply a mesial force to the maxillary left first molars of OVX or Sham mice for 12 days. The distance between the maxillary first molar and the second molar changed due to OTM and osteoclast formation was evaluated. The odontoclast formation and root resorption along the root surface of the distobuccal root of the first molar was also evaluated by histological analysis and scanning electron microscopy.

Results

Distance of tooth movement and osteoclast formation were significantly increased in OVX mice compared to Sham controls. Furthermore, root resorption in the mesial surface of the distal molars induced by orthodontic force was significantly increased in OVX mice.

Conclusion

The amount of OTM was significantly increased, and the accompanying root resorption was also increased in OVX mice. Therefore, attention should be paid to the risk of root resorption associated with orthodontic treatment in patients with osteoporosis.

Effect of TNF-α on osteocyte RANKL expression during orthodontic tooth movement

Background/purpose

Orthodontic tooth movement (OTM) is facilitated by two events; bone resorption on the compression side and bone formation on the tension side simultaneously termed bone remodeling. Osteocytes play a critical role in bone remodeling during OTM, as they have been described as the critical source of nuclear factor-κB ligand (RANKL) necessary for bone remodeling during OTM. Tumor necrosis factor (TNF)-α is a cytokine that acts by amplifying RANKL expression in osteocytes. In this study, we evaluated the effects of TNF-α on RANKL expression in osteocyte during OTM.

Materials and methods

We assessed whether TNF-α influenced RANKL expression in osteocyte during orthodontic tooth movement by using wild-type (WT) and TNF receptor I and II deficient (TNFRsKO) mice. A Nickel-titanium closed coil spring was attached to the maxillary alveolar bone near the incisors and the upper left first molar, and the first molars were moved mesially in WT and TNFRsKO mice. After OTM, the number of RANKL-positive osteocytes in the alveolar bone was evaluated by immunohistochemistry.

Results

The number of RANKL-positive osteocyte in the alveolar bone significantly increased in WT mice than in TNFRsKO mice after OTM.

Conclusion

The results indicate that TNF-α induces the expression of RANKL in osteocyte during OTM.

Effects of Incretin-Related Diabetes Drugs on Bone Formation and Bone Resorption

Patients with type 2 diabetes have an increased risk of fracture compared to the general population. Glucose absorption is accelerated by incretin hormones, which induce insulin secretion from the pancreas. The level of the incretin hormone, glucagon-like peptide-1 (GLP-1), shows an immediate postprandial increase, and the circulating level of intact GLP-1 is reduced rapidly by dipeptidyl peptidase-4 (DPP-4)-mediated inactivation. Therefore, GLP-1 receptor agonists and DPP-4 inhibitors are effective in the treatment of type 2 diabetes. However, these incretin-related diabetic agents have been reported to affect bone metabolism, including bone formation and resorption. These agents enhance the expression of bone markers, and have been applied to improve bone quality and bone density. In addition, they have been reported to suppress chronic inflammation and reduce the levels of inflammatory cytokine expression. Previously, we reported that these incretin-related agents inhibited both the expression of inflammatory cytokines and inflammation-induced bone resorption. This review presents an overview of current knowledge regarding the effects of incretin-related diabetes drugs on osteoblast differentiation and bone formation as well as osteoclast differentiation and bone resorption. The mechanisms by which incretin-related diabetes drugs regulate bone formation and bone resorption are also discussed.

Immune Changes Induced by Orthodontic Forces: A Critical Review

Orthodontic tooth movement (OTM) is generated by a mechanical force that induces an aseptic inflammatory response in the periodontal tissues and a subsequent coordinated process of bone resorption and apposition. In this review, we critically summarize the current knowledge on the immune processes involved in OTM inflammation and provide a novel insight into the relationship between classical inflammation and clinical OTM phases. We found that most studies focused on the acute inflammatory process, which ignites the initial alveolar bone resorption. However, the exact mechanisms and the immune reactions involved in the following OTM phases remain obscure. Recent studies highlight the existence of a typical innate response of resident and extravasated immune cells, including granulocytes and natural killer (NK), dendritic, and γδT cells. Based on few available studies, we shed light on an active, albeit incomplete, process of resolution in the lag phase, supported by continuously elevated ratios of M1/M2 macrophage and receptor activator of nuclear factor κB ligand/osteoprotegerin ratio. This partial resolution enables tissue formation and creates the appropriate environment for a transition between the innate and adaptive arms of the immune system, essential for the tissue's return to homeostasis. Nevertheless, as the mechanical trigger persists, the resolution turns into a low-grade chronic inflammation, which underlies the next, acceleration/linear OTM phase. In this stage, the acute inflammation dampens, and a simultaneous process of bone resorption and formation occurs, driven by B and T cells of the adaptive immune arm. Excessive orthodontic forces or tooth movement in periodontally affected inflamed tissues may hamper resolution, leading to "maladaptive homeostasis" and tissue loss due to uncoupled bone resorption and formation. The review ends with a brief description of the translational studies on OTM immunomodulation. Future studies are necessary for further uncovering cellular and molecular immune targets and developing novel strategies for controlling OTM by local and sustained tuning of the inflammatory process.

Local administration of high-dose diabetes medicine exendin-4 inhibits orthodontic tooth movement in mice

OBJECTIVES

To investigate the effects of exendin-4 on orthodontic tooth movement distance, root resorption, and expression levels of osteoclast-related cytokines in a mouse model.

MATERIALS AND METHODS

A 10-g NiTi coil spring was placed between the anterior alveolar bone and upper left first molar of 8-week-old male C57BL/6 mice. Twenty microliters of exendin-4 solution (containing 0.2 μg, 4 μg, or 20 μg exendin-4) or phosphate-buffered saline (PBS) were injected on the buccal side of the upper left first molar at 2-day intervals (4 mice per group). Mice were sacrificed on day 12; silicone impressions were taken to record tooth movement distance. The left maxillae of the PBS and 20 μg exendin-4 groups were also excised for histological analysis and quantitative reverse transcription polymerase chain reaction analysis.

RESULTS

Orthodontic tooth movement distance was smaller in the 20 μg exendin-4 group than in the PBS group (P < .01). Compared with the PBS group, the 20 μg exendin-4 group showed lower osteoclast number (P < .05), odontoclast number (P < .05), and root resorption surface percentage (P < .05). Relative to maxillae with PBS injections, maxillae with 20 μg exendin-4 injections had lower receptor activator of nuclear factor kappa-B ligand (RANKL) mRNA expression (P < .05), TNF-α mRNA expression (P < .05), and RANKL/osteoprotegerin (OPG) ratio (P < .01). There were no differences in the expression of OPG mRNA.

CONCLUSIONS

Exendin-4 inhibits orthodontic tooth movement. Therefore, additional attention is needed for orthodontic patients who receive exendin-4 for diabetes treatment. GLP-1 receptor may be a treatment target for patients with severe root resorption.

γδT Cells Are Essential for Orthodontic Tooth Movement

Sustained mechanical forces applied to tissue are known to shape local immunity. In the oral mucosa, mechanical stress, either naturally induced by masticatory forces or externally via mechanical loading during orthodontic tooth movement (OTM), is translated, in part, by T cells to alveolar bone resorption. Nevertheless, despite being considered critical for OTM, depletion of CD4⁺ and CD8⁺ T cells is reported to have no impact on tooth movement, thus questioning the function of αβT cells in OTM-associated bone resorption. To further address the role of T cells in OTM, we first characterized the leukocytes residing in the periodontal ligament (PDL), the tissue of interest during OTM, and compared it to the neighboring gingiva. Unlike the gingiva, monocytes and neutrophils represent the major leukocytes of the PDL. These myeloid cells were also the main leukocytes in the PDL of germ-free mice, although at lower levels than SPF mice. T lymphocytes were more enriched in the gingiva than the PDL, yet in both tissues, the relative fraction of the γδT cells was higher than the αβ T cells. We thus sought to examine the role of γδT cells in OTM. γδT cells residing in the PDL were mainly Vγ6⁺ and produced interleukin (IL)-17A but not interferon-γ. Using Tcrd-GDL mice allowing conditional ablation of γδT cells in vivo, we demonstrate that OTM was greatly diminished in the absence of γδT cells. Further analysis revealed that ablation of γδT cells decreased early IL-17A expression, monocyte and neutrophil recruitment, and the expression of the osteoclastogenic molecule receptor activator of nuclear factor-κβ ligand. This, eventually, resulted in reduced numbers of osteoclasts in the pressure site during OTM. Collectively, our data suggest that γδT cells are essential in OTM for translating orthodontic mechanical forces to bone resorption, required for relocating the tooth in the alveolar bone.

Current Trends in In Vitro Modeling to Mimic Cellular Crosstalk in Periodontal Tissue

Clinical evidence indicates that in physiological and therapeutic conditions a continuous remodeling of the tooth root cementum and the periodontal apparatus is required to maintain tissue strength, to prevent damage, and to secure teeth anchorage. Within the tooth's surrounding tissues, tooth root cementum and the periodontal ligament are the key regulators of a functional tissue homeostasis. While the root cementum anchors the periodontal fibers to the tooth root, the periodontal ligament itself is the key regulator of tissue resorption, the remodeling process, and mechanical signal transduction. Thus, a balanced crosstalk of both tissues is mandatory for maintaining the homeostasis of this complex system. However, the mechanobiological mechanisms that shape the remodeling process and the interaction between the tissues are largely unknown. In recent years, numerous 2D and 3D in vitro models have sought to mimic the physiological and pathophysiological conditions of periodontal tissue. They have been proposed to unravel the underlying nature of the cell-cell and the cell-extracellular matrix interactions. The present review provides an overview of recent in vitro models and relevant biomaterials used to enhance the understanding of periodontal crosstalk and aims to provide a scientific basis for advanced regenerative strategies.

Inhibitory effect of baicalin on orthodontically induced inflammatory root resorption in rats

Objective

This study investigated the inhibitory effect of baicalin on orthodontically induced inflammatory root resorption in rats.

Methods

Forty-five male Wistar rats were randomly divided into three groups of 15 rats each. Fifty grams of force was used to establish an orthodontic tooth movement model. Baicalin (40 mg/kg) was locally injected into rats in the baicalin group at 3-day intervals; concurrently, normal saline was injected into rats in the negative control group. On the 21st day after orthodontic treatment, the tooth movement distance and root resorption area ratio were measured. Histomorphology changes were observed by hematoxylin and eosin staining and immunohistochemistry.

Results

There was no significant difference in tooth movement distance between groups. The root resorption area ratio was significantly lower in the baicalin group than in the negative control group. Runx-2 expression was significantly higher in the baicalin group than in the negative control group, while tumor necrosis factor (TNF)-α expression was significantly lower in the baicalin group than in the negative control group.

Conclusions

Baicalin inhibits orthodontically induced inflammatory root resorption by enhancing the expression of Runx-2 and reducing the expression of TNF-α, but does not affect tooth movement distance.