Effect of systemic delivery of Substance P on experimental tooth movement in rats

Nociceptor Neurons Facilitate Orthodontic Tooth Movement via Piezo2 in Mice

Multiple sensory afferents, including mechanosensitive and nociceptive nerves, are projected to the periodontium. Peptidergic afferents expressing transient receptor potential vanilloid 1 (TRPV1), a receptor for capsaicin, mediate pain caused by orthodontic forces. However, their role in orthodontic force-induced alveolar bone remodeling is poorly understood as is the contribution of mechanosensitive ion channels such as Piezo2 in nociceptive nerves. To investigate this role, we studied orthodontic tooth movement and alveolar bone remodeling using neural manipulations and genetic mouse models. Chemical ablation of TRPV1-expressing afferents localized to the trigeminal ganglia decreased orthodontic force-induced tooth movement and the number of osteoclasts in alveolar bone on the compression side. The extent of the force-induced increase in the ratio of receptor activator of nuclear factor kappa-B ligand/osteoprotegerin in the periodontium was modestly decreased in the chemical ablation group. Furthermore, chemogenetic silencing of TRPV1-lineage afferents reduced orthodontic tooth movement and the number of osteoclasts. Piezo2 was expressed in most periodontal afferents, and chemogenetic inhibition of Piezo2-expressing neurons decreased orthodontic tooth movement and the number of osteoclasts. In addition, the conditional knockout of Piezo2 in TRPV1-lineage afferents decreased orthodontic tooth movement and the number of osteoclasts. Overall, these results suggest that nociceptor neurons play critical roles in orthodontic force-induced alveolar bone remodeling and that the mechanical activation of neuronal Piezo2 in nociceptive nerves facilitates orthodontic tooth movement and associated alveolar bone remodeling.

Substance P-A neuropeptide regulator of periodontal disease pathogenesis and potential novel therapeutic entity: A narrative review

Substance P (SP), a neuropeptide primarily released by neurons, has emerged as a key player in the intricate network of factors governing periodontal inflammation, immune responses, bone metabolism, and tissue regeneration. Due to its multifaceted role, it may be explored for its potential participation in periodontal therapeutic strategies. The databases, PubMed/MEDLINE, and SCOPUS were searched for all published articles on SP, its role in inflammation, and periodontal disease. The following search terms, adapted to the specific database, were used; "substance p AND periodontal *" AND "therapeutics" and records were retrieved. All articles not pertaining to SP in periodontal health and disease were excluded from the study. The full texts of eligible articles were retrieved. Data on SP and its role in inflammation and in periodontal health, disease, and therapy were extracted and have been presented as a narrative review. SP manifests during inflammatory phase of periodontal disease and is one of the causes of bone loss. According to studies, the gingival crevicular fluid from areas with active periodontal disease and bone loss had the greatest levels of SP. These chemicals may linger long enough to trigger neurogenic inflammation and elicit pain in tissues that are vulnerable to it. SP expression during progression of periodontal disease might be a risk factor for individuals with systemic inflammatory diseases, such as chronic arthritis. However, SP may be manipulated to provide avenues for management of periodontal disease and thereby serve as therapeutic target.

Nociceptor mechanisms underlying pain and bone remodeling via orthodontic forces: toward no pain, big gain

Orthodontic forces are strongly associated with pain, the primary complaint among patients wearing orthodontic braces. Compared to other side effects of orthodontic treatment, orthodontic pain is often overlooked, with limited clinical management. Orthodontic forces lead to inflammatory responses in the periodontium, which triggers bone remodeling and eventually induces tooth movement. Mechanical forces and subsequent inflammation in the periodontium activate and sensitize periodontal nociceptors and produce orthodontic pain. Nociceptive afferents expressing transient receptor potential vanilloid subtype 1 (TRPV1) play central roles in transducing nociceptive signals, leading to transcriptional changes in the trigeminal ganglia. Nociceptive molecules, such as TRPV1, transient receptor potential ankyrin subtype 1, acid-sensing ion channel 3, and the P2X3 receptor, are believed to mediate orthodontic pain. Neuropeptides such as calcitonin gene-related peptides and substance P can also regulate orthodontic pain. While periodontal nociceptors transmit nociceptive signals to the brain, they are also known to modulate alveolar bone remodeling in periodontitis. Therefore, periodontal nociceptors and nociceptive molecules may contribute to the modulation of orthodontic tooth movement, which currently remains undetermined. Future studies are needed to better understand the fundamental mechanisms underlying neuroskeletal interactions in orthodontics to improve orthodontic treatment by developing novel methods to reduce pain and accelerate orthodontic tooth movement-thereby achieving "big gains with no pain" in clinical orthodontics.

Temporospatial Expression of Neuropeptide Substance P in Dental Pulp Stem Cells During Odontoblastic Differentiation in Vitro and Reparative Dentinogenesis in Vivo

INTRODUCTION

Substance P (SP) is a neuropeptide released from the nervous fibers in response to injury. In addition to its association with pain and reactions to anxiety and stress, SP exerts various physiological functions by binding to the neurokinin-1 receptor (NK1R). However, the expression and role of SP in reparative dentinogenesis remain elusive. Here, we explored whether SP is involved in odontoblastic differentiation during reparative dentinogenesis.

METHODS

Dental pulp stem cells (DPSCs) were isolated from healthy human dental pulp tissues and subjected to odontoblastic differentiation. The expression of SP and NK1R during odontoblastic differentiation was investigated in vitro. The effects of SP on odontoblastic differentiation of DPSCs were evaluated using alizarin red staining, alkaline phosphatase staining, and real-time polymerase chain reaction. After direct pulp capping with mineral trioxide aggregate, the expression of SP and NK1R during reparative dentin formation in rats were identified using histological and immunohistochemical staining.

RESULTS

SP and NK1R expression increased during the odontoblastic differentiation of DPSCs. SP translocated to the nucleus when DPSCs were exposed to differentiation medium. NK1R was always present in the nuclei of DPSCs and odontoblast-like cells. Additionally, we discovered that 10^-8 M SP marginally enhanced the odontoblastic differentiation of DPSCs, and that these effects could be impaired by the NK1R antagonist. Furthermore, SP and NK1R were expressed in odontoblast-like and dental pulp cells during reparative dentin formation in vivo.

CONCLUSIONS

SP contributes to odontoblastic differentiation during reparative dentin formation by binding to the NK1R.

Osteoblastic STAT3 Is Crucial for Orthodontic Force Driving Alveolar Bone Remodeling and Tooth Movement

Mechanical force is essential to shape the internal architecture and external form of the skeleton by regulating the bone remodeling process. However, the underlying mechanism of how the bone responds to mechanical force remains elusive. Here, we generated both orthodontic tooth movement (OTM) model in vivo and a cyclic stretch-loading model in vitro to investigate biomechanical regulation of the alveolar bone. In this study, signal transducer and activator of transcription 3 (STAT3) was screened as one of the mechanosensitive proteins by protein array analysis of cyclic stretch-loaded bone mesenchymal stem cells (BMSCs) and was also proven to be activated in osteoblasts in response to the mechanical force during OTM. With an inducible osteoblast linage-specific Stat3 knockout model, we found that Stat3 deletion decelerated the OTM rate and reduced orthodontic force-induced bone remodeling, as indicated by both decreased bone resorption and formation. Both genetic deletion and pharmacological inhibition of STAT3 in BMSCs directly inhibited mechanical force-induced osteoblast differentiation and impaired osteoclast formation via osteoblast-osteoclast cross-talk under mechanical force loading. According to RNA-seq analysis of Stat3-deleted BMSCs under mechanical force, matrix metalloproteinase 3 (Mmp3) was screened and predicted to be a downstream target of STAT3. The luciferase and ChIP assays identified that Stat3 could bind to the Mmp3 promotor and upregulate its transcription activity. Furthermore, STAT3-inhibitor decelerated tooth movement through inhibition of the bone resorption activity, as well as MMP3 expression. In summary, our study identified the mechanosensitive characteristics of STAT3 in osteoblasts and highlighted its critical role in force-induced bone remodeling during orthodontic tooth movement via osteoblast-osteoclast cross-talk. © 2022 American Society for Bone and Mineral Research (ASBMR).

Dronabinol inhibits alveolar bone remodeling in tooth movement of rats

INTRODUCTION

Orthodontic tooth movement is reliant on the process of bone remodeling, and a variety of medications impact the ability of teeth to move through bone. Marijuana is the most widely used recreational drug in the world, and early studies suggest the drug impacts bone remodeling as tetrahydrocannabinol binds to cannabinoid receptors which play a role in bone homeostasis. This study aimed to assess the impact of dronabinol on alveolar bone remodeling in rats with otherwise healthy tissue when subjected to orthodontic forces.

METHODS

Thirty male Sprague Dawley rats were equally allocated into 2 groups. Orthodontic appliances were placed in all animals, which consisted of a nickel-titanium coil ligated from the maxillary first molar to the central incisor. The appliance was activated to deliver a force to move teeth together. Over 21 days, daily injections of either dronabinol or the control (solvent) were given to the rats. Cephalometric analysis, histology, and bone remodeling profiles of both groups were analyzed and compared.

RESULTS

Teeth moved in both the dronabinol and control groups (P <0.05). Tooth movement in the control group followed the typical process of orthodontic tooth movement: periodontal width narrowing and bone resorption on the compression side of the tooth, with an overall decrease in the height of the alveolar bone. In contrast, the dronabinol group showed an abnormal response to tooth movement: no bone resorption on the compression side of the tooth, increased bone formation on the tension side, and the maintenance of the height of the alveolar crest. In the dronabinol group, there were also significantly more osteoclasts and osteoblasts in the alveolar bone than in the control group.

CONCLUSIONS

These results demonstrate that dronabinol attenuates orthodontic tooth movement by decreasing bone resorption, which could have implications for other bone-related recovery processes.

Intermittent parathyroid hormone improves orthodontic retention via insulin-like growth factor-1

OBJECTIVES

This study aimed to investigate the effects of intermittent parathyroid hormone (iPTH) on the stability of orthodontic retention and to explore the possible regulatory role of insulin-like growth factor-1 (IGF-1) in this process.

METHODS

Forty-eight 6-week-old male Wistar rats were adopted in this study. An orthodontic relapsing model was established to investigate the effects of iPTH on orthodontic retention. In vitro, an immortalized mouse cementoblast cell line OCCM-30 was detected by flow cytometry to study the effects of iPTH on cell proliferation and apoptosis. By application of a specific IGF-1 receptor inhibitor, the role of IGF-1 was also explored.

RESULTS

In vivo study found that daily injection of PTH significantly reduced the relapsing distance. Histological staining and ELISA assay showed faster periodontal regeneration during retention period in PTH group with increased RANKL/OPG ratio and greater amount of OCN, ALP, and IGF-1 in gingival cervical fluid (GCF). Cell experiment revealed that iPTH promoted proliferation and suppressed apoptosis of cementoblast. IGF-1 receptor inhibitor significantly restrained the anabolic effect of iPTH on OCCM-30 cells.

CONCLUSIONS

These findings suggest that iPTH could improve the stability of tooth movement by promoting periodontal regeneration. IGF-1 is essential in mediating the anabolic effects of iPTH.

Systematic review of biological therapy to accelerate orthodontic tooth movement in animals: Translational approach

OBJECTIVES

To systematically review and evaluate what is known regarding contemporary biological therapy capable of accelerating orthodontic tooth movement (OTM) in animal model.

MATERIALS AND METHODS

MedLine, Scopus, Web of Science and OpenGrey were searched without restrictions until June 2019. Following study retrieval and selection, relevant data was extracted using a standardized table. Risk of bias (RoB) assessment was performed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool.

RESULTS

Fifty-one animal studies were included. Two biological therapies were identified as capable of accelerating the OTM: chemical methods (49 studies) and gene therapy (2 studies). The main substances that increased the OTM rate were cytokines (13 studies), followed by growth factors (6 studies) and hormones (5 studies). Most studies were assessed to be at unclear or high RoB. The application protocols, measurement and reporting of outcomes varied widely and methodologies were not adequately reported.

CONCLUSIONS

Although biological therapies to accelerate OTM have been widely tested and effective in preclinical studies, the validity of the evidence is flawed to support translational of these results. There is a need for well-designed experimental studies to translate these methods for clinical field.