The role of ephrinB2-EphB4 signalling in bone remodelling during orthodontic tooth movement.

OBJECTIVE: The aim of this study was to investigate the role of ephrinB2-EphB4 signalling in alveolar bone remodelling on the tension side during orthodontic tooth movement (OTM). MATERIALS AND METHODS: An OTM model was established on sixty 8-week-old male Wistar rats. They were randomly divided into the experimental group and the control group. The animals in the experimental group were administrated with subcutaneous injection of EphB4 inhibitor NVP-BHG712 every other day, whereas the control group received only the vehicle. Samples containing the maxillary first molar and the surrounding bone were collected after 0, 3, 7, 14 and 21 days of tooth movement. RESULTS: EphrinB2-EphB4 signalling was actively expressed on the tension side during tooth movement. Micro-CT analysis showed the distance of tooth movement in the experimental group was significantly greater than that of the control group (P < .05) with significantly increased trabecular separation (Tb. Sp) and decreased trabecular number (Tb. N) from day 14 to day 21. The number of osteoclasts significantly increased in the experimental group compared with the control group after 3 and 7 days of tooth movement (P < .05). The expressions of alkaline phosphatase (ALP) and osteopontin (OPN) were significantly reduced by inhibition of EphB4 (P < .05). CONCLUSION: The inhibition of EphB4 suppressed bone formation and enhanced bone resorption activities on the tension side of tooth movement. The ephrinB2-EphB4 signalling might play an important role in alveolar bone remodelling during OTM.

Contribution of diabetes mellitus to periodontal inflammation during orthodontic tooth movement.

OBJECTIVE: This study aims to clarify the effects of diabetes mellitus (DM) on inflammatory profile during orthodontic tooth movement (OTM) and explore potential mechanisms. METHODS: OTM models were established in healthy (Ctrl) and DM rats for 0, 3, 7 or 14 days. The tooth movement distance and bone structural parameters were analyzed through micro-CT. The bone resorption activity and periodontal inflammation status were evaluated through histological staining. RNA sequencing was performed to detect differentially expressed genes in force loading-treated periodontal ligament fibroblasts (PDLFs) with or without high glucose. The differential expression of inflammatory genes associated with NOD-like receptor family pyrin domain containing 3 (NLRP3) between groups was tested in vitro and in vivo. RESULTS: DM caused remarkable reduction of alveolar bone height and density around the moved tooth, corresponding with the higher bone resorption activity and inflammatory scores of DM group. For force loading-treated PDLFs, high glucose induced the activation of inflammatory pathways, including NLRP3. Elevated expression of NLRP3 and cascade molecules (Caspase-1, GSDMD, and IL-1ß) were validated by RT-qPCR, Western blot, and immunohistochemistry staining. CONCLUSIONS: DM alters the inflammatory status of periodontium and affects tissue reconstruction during OTM. NLRP3 inflammasome may involve in diabetes-induced periodontal changes.

Mechanisms of sphingosine-1-phosphate (S1P) signaling on excessive stress-induced root resorption during orthodontic molar intrusion.

OBJECTIVES: The aim of this study was to investigate cementocyte mechanotransduction during excessive orthodontic intrusive force-induced root resorption and the role of S1P signaling in this process. MATERIALS AND METHODS: Fifty-four 12-week-old male Wistar rats were randomly divided into 3 groups: control group (Control), intrusive stress application group (Stress), and intrusive stress together with S1PR2-specific antagonist injection group (Stress + JTE). A rat molar intrusion model was established on animals in the Stress and the Stress + JTE groups. The animals in the Stress + JTE group received daily intraperitoneal (i.p.) injection of S1PR2 antagonist JTE-013, while the Control and Stress groups received only the vehicle. Histomorphometric, immunohistochemical, quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analyses were performed after euthanizing of the rats. RESULTS: Root resorption was promoted in the Stress group with increased volumes of resorption pits and amounts of molar intrusion compared with the Control group. The expression levels of cementogenic- and cementoclastic-related factors were affected under excessive intrusive force. Immunohistochemical staining and qRT-PCR analysis showed promoted S1P signaling activities during molar intrusion. Western blot analysis indicated decreased nuclear translocation of ß-catenin under excessive intrusive force. Through the administration of JTE-013, S1P signaling activity was suppressed and excessive intrusive force-induced root resorption was reversed. The regulation of S1P signaling could also influence the nuclear translocation of ß-catenin and the expressions of cementogenic- and cementoclastic-related factors. CONCLUSIONS: Root resorption was promoted under excessive orthodontic intrusive force due to the disruption of cementum homeostasis. S1P signaling pathway might play an important role in cementocyte mechanotransduction in this process. CLINICAL RELEVANCE: The S1P signaling might be a promising therapeutic target for novel therapeutic approaches to prevent external root resorption caused by excessive orthodontic intrusive force.

Mechanosensitive Piezo1 in Periodontal Ligament Cells Promotes Alveolar Bone Remodeling During Orthodontic Tooth Movement.

Orthodontic tooth movement (OTM) is a process depending on the remodeling of periodontal tissues surrounding the roots. Orthodontic forces trigger the conversion of mechanical stimuli into intercellular chemical signals within periodontal ligament (PDL) cells, activating alveolar bone remodeling, and thereby, initiating OTM. Recently, the mechanosensitive ion channel Piezo1 has been found to play pivotal roles in the different types of human cells by transforming external physical stimuli into intercellular chemical signals. However, the function of Piezo1 during the mechanotransduction process of PDL cells has rarely been reported. Herein, we established a rat OTM model to study the potential role of Piezo1 during the mechanotransduction process of PDL cells and investigate its effects on the tension side of alveolar bone remodeling. A total of 60 male Sprague-Dawley rats were randomly assigned into three groups: the OTM + inhibitor (INH) group, the OTM group, and the control (CON) group. Nickel-titanium orthodontic springs were applied to trigger tooth movement. Mice were sacrificed on days 0, 3, 7, and 14 after orthodontic movement for the radiographic, histological, immunohistochemical, and molecular biological analyses. Our results revealed that the Piezo1 channel was activated by orthodontic force and mainly expressed in the PDL cells during the whole tooth movement period. The activation of the Piezo1 channel was essential for maintaining the rate of orthodontic tooth movement and facilitation of new alveolar bone formation on the tension side. Reduced osteogenesis-associated transcription factors such as Runt-related transcription factor 2 (RUNX2), Osterix (OSX), and receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) ratio were examined when the function of Piezo1 was inhibited. In summary, Piezo1 plays a critical role in mediating both the osteogenesis and osteoclastic activities on the tension side during OTM.

The Role of Acid-sensing Ion Channel 3 in the Modulation of Tooth Mechanical Hyperalgesia Induced by Orthodontic Tooth Movement.

This study aimed to explore the role of acid-sensing ion channel 3 (ASIC3) in the modulation of tooth mechanical hyperalgesia induced by orthodontic tooth movement. In male Sprague-Dawley rats, closed coil springs were ligated between mandibular incisors and molars to mimic orthodontic tooth movement. Bite force was assessed to evaluate tooth mechanical hyperalgesia. The alveolar bone, trigeminal ganglia, and trigeminal nucleus caudalis underwent immunohistochemical staining and immunoblotting for ASIC3. The inferior alveolar nerves were transected to explore the interaction between the periodontal sensory endings and trigeminal ganglia. The role of ASIC3 in trigeminal ganglia was further explored with lentivirus-mediated ASIC3 ribonucleic acid interference. Results showed that ASIC3 was expressed in the periodontal Ruffini endings and expression of ASIC3 protein was elevated in periodontal tissues, trigeminal ganglia, and trigeminal nucleus caudalis, following orthodontic tooth movement. ASIC3 agonists and antagonists significantly aggravated and mitigated tooth mechanical hyperalgesia, respectively. ASIC3 expression decreased after inferior alveolar nerve transection in periodontal tissues. Both in vitro and vivo, the lentivirus vector carrying ASIC3 shRNA inhibited ASIC3 expression and relieved tooth mechanical hyperalgesia. To conclude, ASIC3 is important in the modulation of tooth mechanical hyperalgesia induced by orthodontic tooth movement. Further, the role of ASIC3 in the modulation of pain in periodontal tissues is regulated by trigeminal ganglia. An adjuvant analgesic therapy targeting ASIC3 could alleviate orthodontic movement-associated mechanical hyperalgesia in rats.