Single-cell sequencing decodes the secrets of the RAP phenomenon of corticotomy.

Introduction: Corticotomy-assisted tooth movement is commonly performed in clinics, however, its time-limited efficacy and the fear of surgery among patients significantly limit its clinical application. Hence, researchers have investigated non-invasive methods to accelerate tooth movement. However, the molecular mechanisms underlying corticotomy-assisted tooth movement are not fully understood. Methods: Micro-CT and TRAP stain were used to tooth movement and bone resorption. Single-cell RNA sequencing was used to study the transcriptome heterogeneity of macrophages after corticotomy. Transmission electron microscopy and iron ion detection was used to evaluate ferroptosis and iron metabolism. In addition, we carried out immunohistochemistry, quantitative real-time and flow cytometry verify the effect of iron on macrophage polarization. Results: Single-cell RNA sequencing of digested alveolar bone identified a significant increase in iron metabolism-related genes post-corticotomy. Macrophages play a central role in this field. Following the dimensionality reduction of macrophages, we revealed a new developmental state via pseudotime analysis post-corticotomy. SCENIC analysis revealed that Atf3 is a key transcription factor influencing this new state. We found that Atf3+ macrophages were closely associated with osteoclasts. Moreover, cell chat revealed an increase in cellular communication between Atf3+ macrophages and other cell types after corticotomy. Discussion: These findings suggested that Atf3+ macrophages might play a key role in corticotomy-accelerated tooth movement, thus providing potential targets for drug development.

DNA damage-inducible transcript 3 deficiency promotes bone resorption in murine periodontitis models.

BACKGROUND AND OBJECTIVE: Periodontitis is a multifactorial inflammatory disease that leads to the destruction of supporting structures of the teeth. DNA damage-inducible transcript 3 (DDIT3) plays crucial roles in cell survival and differentiation. DDIT3 regulates bone mass and osteoclastogenesis in femur. However, the role of DDIT3 in periodontitis has not been elucidated. This research aimed to explore the role and mechanisms of DDIT3 in periodontitis. METHODS: DDIT3 gene knockout (KO) mice were generated using a CRISPR/Cas9 system. Experimental periodontitis models were established to explore the role of DDIT3 in periodontitis. The expression of DDIT3 in periodontal tissues was detected by quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC). The alveolar bone phenotypes were observed by micro-CT and stereomicroscopy. The inflammation levels and osteoclast activity were examined by histological staining, immunostaining, and qRT-PCR. Bone marrow-derived macrophages (BMMs) were isolated to confirm the effects of DDIT3 on osteoclast formation and function in vitro. RESULTS: The increased expression of DDIT3 in murine inflamed periodontal tissues was detected. DDIT3 knockout aggravated alveolar bone loss and enhanced expression levels of inflammatory cytokines in murine periodontitis models. Increased osteoclast formation and higher expression levels of osteoclast-specific markers were observed in the inflamed periodontal tissues of KO mice. In vitro, DDIT3 deficiency promoted the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts and the bone resorption activity of mature osteoclasts. CONCLUSIONS: Our results demonstrate that DDIT3 deletion aggravated alveolar bone loss in experimental periodontitis through enhanced inflammatory reactions and osteoclastogenesis. The anti-inflammation and the inhibition of bone loss by DDIT3 in murine periodontitis provides a potential novel therapeutic strategy for periodontitis.

Deferoxamine Reduces Inflammation and Osteoclastogenesis in Avulsed Teeth.

Replacement and inflammatory resorption are serious complications associated with the delayed replantation of avulsed teeth. In this study, we aimed to assess whether deferoxamine (DFO) can suppress inflammation and osteoclastogenesis in vitro and attenuate inflammation and bone resorption in a replanted rat tooth model. Cell viability and inflammation were evaluated in RAW264.7 cells. Osteoclastogenesis was confirmed by tartrate-resistant acid phosphatase staining, reactive oxygen species (ROS) measurement, and quantitative reverse transcriptase-polymerase chain reaction in teeth exposed to different concentrations of DFO. In vivo, molars of 31 six-week-old male Sprague-Dawley rats were extracted and stored in saline (n = 10) or DFO solution (n = 21) before replantation. Micro-computed tomography (micro-CT) imaging and histological analysis were performed to evaluate inflammation and root and alveolar bone resorption. DFO downregulated the genes related to inflammation and osteoclastogenesis. DFO also reduced ROS production and regulated specific pathways. Furthermore, the results of the micro-CT and histological analyses provided evidence of the decrease in inflammation and hard tissue resorption in the DFO group. Overall, these results suggest that DFO reduces inflammation and osteoclastogenesis in a tooth replantation model, and thus, it has to be further investigated as a root surface treatment option for an avulsed tooth.

Local administration of ReveromycinA ointment suppressed alveolar bone loss in mice.

ReveromycinA (RMA) was developed and is a unique agent for inhibiting osteoclast activity. In a previous study, we experimentally induced periodontal disease in a high-turnover osteoporosis osteoprotegerin-knockout mice (OPG KO) model and found that intraperitoneal administration of RMA inhibited alveolar bone resorption. We prepared a novel RMA-containing ointment for topical non-invasive administration in the oral cavity, in preparation for possible future clinical application. And we investigated whether this ointment can inhibit alveolar bone resorption in an experimental mouse model of periodontal disease. We examined wild-type (WT) and OPG KO mice ligated with wire around contact points on the left first and second molars to cause food impaction and induce experimental periodontal disease. RMA was administered three times a day. Using micro-computed tomography, we measured the volume of alveolar bone loss and also performed histological analysis. Our findings showed that localized administration of RMA containing ointment resulted in suppressed alveolar bone resorption, reduced osteoclast count, and lower immunostaining scores of inflammation sites compared with controls in both OPG KO and WT mice. Localized application of the specific osteoclast suppressor RMA in ointment form in the oral cavity could be a novel treatment for periodontitis that inhibits alveolar bone resorption locally.

Indigenous Microbiota Protects against Inflammation-Induced Osteonecrosis.

Medication-related osteonecrosis of the jaw (MRONJ) is a rare intraoral lesion that occurs in patients undergoing long-term and/or high-dose therapy with nitrogen-containing bisphosphonates, a RANKL inhibitor, antiangiogenic agents, or mTOR inhibitors. The presence of pathogenic bacteria is highly associated with advanced stages of MRONJ lesions; however, the exact role of indigenous microbes in MRONJ development is unknown. Here, we report that the normal oral flora in mice protects against inflammation-induced osteonecrosis. In mice that developed osteonecrosis following tooth extraction, there was increased bacterial infiltration when compared with healed controls. Antibiotic-mediated oral dysbiosis led to a local inhibition of bone resorption in the presence of ligature-induced periodontitis (LIP). There was no significant difference in empty lacunae, necrotic bone formation, osteoclast number, and surface area in antibiotic-treated as compared with conventionally colonized mice following extraction of healthy teeth after zoledronic acid infusions. However, extraction of LIP teeth led to increased empty lacunae, necrotic bone, and osteoclast surface area in antibiotic- and zoledronic acid-treated mice as compared with conventionally colonized mice. Our findings suggest that the presence of the indigenous microbiota protects against LIP-induced osteonecrosis.

Compressive force-induced autophagy in periodontal ligament cells downregulates osteoclastogenesis during tooth movement.

BACKGROUND: Autophagy has recently emerged as a protective mechanism in response to compressive force and an important process in maintenance of bone homeostasis. It appears to be involved in the degradation of osteoclasts, osteoblasts, and osteocytes. The aim of this study was to investigate the role of compressive force-induced autophagy in periodontal ligament (PDL) cells in regulating osteoclastogenesis of orthodontic tooth movement (OTM). METHODS: An OTM model and compressive force on PDL cells were employed to investigate the expression of autophagy markers in vivo and in vitro, respectively. Autophagosomes and autolysosomes were observed in PDL cells by transmission electron microscope (TEM) and autophagy LC3 double labelling. 3-Methyladenine (3-MA) and rapamycin were respectively used to inhibit and promote autophagy, and the effect of autophagy on osteoclastogenesis was explored via microcomputed tomography, hematoxylin and eosin (H&E) staining, histochemistry of titrate-resistant acid phosphatase, and real-time polymerase chain reaction (RT-PCR) in vivo. Receptor activator of nuclear factor-kappa B ligand/osteoprotegerin (RANKL/OPG) was investigated by RT-PCR and ELISA in vitro. RESULTS: Orthodontic force-induced autophagy was prominent on the pressured side of PDL tissues. Administration of 3-MA downregulated bone density and upregulated osteoclasts, while rapamycin had reverse results in OTM. The autophagy activity increased initially then decreased in PDL cells during compressive force application and responded to light force. In PDL cells, administration of 3-MA upregulated while rapamycin downregulated the RANKL/OPG ratio. CONCLUSION: Autophagy is activated by compressive force in PDL cells. Besides, it could modulate OTM by negatively regulating osteoclastogenesis and keep bone homeostasis via RANKL/OPG signaling.

Clodronate-Loaded Liposome Treatment Has Site-Specific Skeletal Effects.

Ineffective oral wound healing is detrimental to patients' oral health-related quality of life. Delineating the cellular mechanisms involved in optimal healing will elicit better approaches to treating patients with compromised healing. Osteal macrophages have recently emerged as important positive regulators of bone turnover. The contributions of macrophages to long bone healing have been studied, but their role in oral osseous wound healing following tooth extraction is less clear. Clodronate-loaded liposomes were used as a tool to deplete macrophages in C57BL/6J mice and assess oral osseous bone fill after extraction. In addition to macrophage ablation, osteoclast ablation occurred. Interestingly, depletion of macrophages and osteoclasts via clodronate treatment had differential effects based on skeletal location. In the nonwounded tibiae, clodronate treatment significantly increased CD68+ cells and decreased F4/80+ cells in the marrow, which correlated with increased trabecular bone volume fraction after 7 and 14 d. Serum formation and resorptive markers P1NP and TRAcP 5b were decreased as were tibial TRAP+ osteoclasts. In healing extraction sockets, clodronate treatment increased extraction socket trabecular bone thickness at 14 d, which correlated with decreased TRAP+ osteoclasts and F4/80+ macrophages. Conversely, nonwounded maxillary interseptal bone was unaffected by clodronate treatment. Furthermore, the increase in extraction socket bone fill with clodronate was less than the large increase in trabecular bone observed in a nonwounded long bone. These data suggest a temporal and spatial specificity in the roles of macrophages and osteoclasts in normal turnover and healing.

Clinico-radiographic evaluation of 1% alendronate gel as an adjunct and smart blood derivative platelet rich fibrin in grade II furcation defects.

BACKGROUND: The treatment of molar furcation involvement is unpredictable due to the complex anatomy and poor access for instrumentation. Previous studies have reported successful regeneration with endogenous regenerative material such as platelet rich fibrin (PRF) and bisphosphonates as alendronate (ALN). Hence, the present study was aimed to evaluate clinically and radiographically the efficacy of 1% ALN gel in combination with PRF (PRF+ALN) and PRF alone in the treatment of grade II furcation defects. METHODS: A split mouth study with 40 bilateral furcation defects was randomly divided into PRF group and PRF+ALN group. Bone defect volume was the primary outcome evaluated at the end of 6 months with CBCT while the secondary outcomes being changes in clinical parameters including Probing pocket depth (PPD), Clinical attachment level (CAL) and Horizontal probing depth (HPD) recorded at baseline, 3 and 6 months. RESULTS: The mean reduction in PPD, CAL and HPD was 1.85 ± 0.59 mm, 1.9 ± 0.64 mm and 1.7 ± 0.73 mm respectively for PRF group and 2.85 ± 0.88 mm, 3.05 ± 0.98 mm and 2.3 ± 0.73 mm respectively for PRF+ ALN group (p < 0.05). At the end of 6 months, mean reduction in bone defect volume for PRF and PRF+ ALN group was 8.65 ± 3.84 mm3 and 11.98 ± 4.13 mm3 respectively. CONCLUSION: PRF+ ALN treated defects exhibited better clinical and radiographic outcomes suggestive of enhanced periodontal regeneration when compared to PRF alone treated sites.

Zoledronate Impairs Socket Healing after Extraction of Teeth with Experimental Periodontitis.

Osteonecrosis of the jaws (ONJ) is a rare but severe complication of antiresorptive medications, such as bisphosphonates, used in the treatment of bone malignancy or osteoporosis. Tooth extraction and dental disease have been strongly associated with ONJ development. Here, we investigated molecular and cellular markers of socket healing after extraction of healthy or teeth with experimental periodontitis (EP) in Wistar-Han rats treated with zoledronic acid (ZA). We included 4 experimental groups: vehicle-treated animals with extraction of healthy teeth or teeth with ligature-induced EP and ZA-treated animals with extraction of healthy teeth or teeth with EP. Animals were pretreated with vehicle or ZA for a week, and EP was induced. Four weeks later, the second maxillary molars were extracted; sockets were allowed to heal for 4 wk; animals were euthanized; and maxillae were isolated. Radiographically, extraction sockets in groups 1, 2, and 3 demonstrated normal healing. Contrary incomplete socket healing was noted after extraction of teeth with EP in ZA-treated rats of group 4. Histologically, persistent inflammation and extensive osteonecrosis were seen in group 4. Disorganization of the collagen network, collagen type III predominance, and lack of collagen fiber insertion in the necrotic bone were associated with impaired socket healing. Cells positive for MMP-9, MMP-13, and α-SMA expression were present at the areas of epithelial invagination and adjacent to osteonecrotic bone. Importantly, human biopsies from patients with ONJ showed similar findings. Our data emphasize the importance of dental disease and tooth extraction in ONJ pathogenesis and help delineate an altered profile in wound-healing markers during ONJ development.