Engineered pre-dentin with well-aligned hierarchical mineralized collagen fibril bundles promote bio-root regeneration.

Stem cell-mediated bio-root regeneration is an alternative tooth replacement strategy; however, physiologically functional bio-root regeneration with distinctive dentin structure remains challenging. In this study, the distinct arrangements of collagen fibril bundles were identified that account for hierarchical structural differences between dentin, cementum, and alveolar bone. Thus, an "engineered pre-dentin" was fabricated, which was a dentin hierarchical structure mimicking collagen (MC) scaffold, with well-aligned hierarchical mineralized collagen fibril bundles. The results revealed that it has a stronger effect on promoting biological root regeneration in nude mice and miniature pigs with dental pulp stem cell (DPSC) and periodontal ligament stem cell (PDLSC) sheets compared to hydroxyapatite tricalcium phosphate (HA/TCP). The success rate in the MC group was also higher than that in the HA/TCP group (67% and 33%, respectively). In conclusion, the hierarchical dentin-mimicking scaffold can enhance the regeneration of bio-roots, which provides a promising strategy for tooth regeneration.

Photobiomodulation suppresses allergic contact dermatitis by inhibiting T-cell activation.

BACKGROUND: Allergic contact dermatitis (ACD) is a dermal inflammatory disease caused by allergic reactions to substances that contact the skin. The hyperactivation of T cells plays an important role in its pathogenesis. Photobiomodulation (PBM) is an efficacious therapeutic approach for suppressing inflammatory diseases. OBJECTIVE: This study aimed to evaluate the potentially beneficial role of PBM in ACD models and investigate its possible mechanisms. METHODS: In this study, the ACD model of C57BL/6 mice was produced and treated with PBM, and the number of T cells was evaluated. In an in vitro study, naïve T cells were isolated and intervened with PBM. The markers of T cell activation were detected by flow cytometer. Transforming growth factor-ß (TGF-ß) and reactive oxygen species (ROS) were detected to investigate the mechanism. RESULTS: PBM effectively inhibited the inflammatory response by impeding the number of T cells in the ACD model. And in vitro studies showed that PBM could directly moderate the activation of naïve T cells and possess the capability to impede T cell activation via TGF-beta signaling pathway. CONCLUSION: Our finding elucidates the potential mechanism underlying the inhibitory effects of PBM in inflammatory diseases and furnishes a theoretical foundation for its clinical application.

Risk prediction model of impacted supernumerary tooth-associated root resorption in children based on cone-beam computed tomography analysis: a case control study.

BACKGROUND: External surface resorption is pressure-induced resorption and occurs on the external surface of the root, pressure exerted by impacted teeth, is common causes of external surface resorption. Predictive risk factors of impacted supernumerary tooth-associated root resorption (ISTARR) mentioned in this article include supernumerary teeth and patient factors. To investigate the risk factors of impacted supernumerary tooth-associated root resorption and predict the incidence of root resorption. METHODS: This restrospective study enrolled 324 patients with impacted supernumerary tooth. All Cone-Beam Computed Tomography (CBCT) data and patient information were divided into two groups (without tooth root resorption and with root resorption). CBCT images and patient information (age and gender) of 133 patients had adjacent tooth root resorption and 191 did not. seven variables were analysed using binary logistic regression. RESULTS: Individual analysis of potential risk factors showed that age, crown mesiodistal direction, root formation, and odontotheca of the impacted supernumerary tooth were associated significantly with ISTARR. Binary logistic regression showed that impacted supernumerary tooth with odontotheca (Odd Ratio = 2.926), the crown is in the middle (Odd Ratio = 1.446), located at the middle third of the adjacent tooth root (Odd Ratio = 1.614), complete root development (Odd Ratio = 1.334), and patient's age (Odd Ratio = 1.261) were significantly associated with ISTARR risk. CONCLUSIONS: The risk factors of root resorption can be detected and predicted early according to the features of supernumerary tooth and patient's age. Still, more prospective studies with larger sample size are needed to validate the result.

MicroRNA-19b exacerbates systemic sclerosis through promoting Th9 cells.

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by fibrosis of the skin and multiple vital organs, but the immunological pathogenesis of SSc remains unclear. We show here that miR-19b promotes Th9 cells that exacerbate SSc. Specifically, miR-19b and interleukin (IL)-9 increase in CD4+ T cells in experimental SSc in mice induced with bleomycin. Inhibiting miR-19b reduces Th9 cells and ameliorates the disease. Mechanistically, transforming growth factor beta (TGF-ß) plus IL-4 activates pSmad3-Ser213 and TRAF6-K63 ubiquitination by suppressing NLRC3. Activated TRAF6 sequentially promotes TGF-ß-activated kinase 1 (TAK1) and nuclear factor κB (NF-κB) p65 phosphorylation, leading to the upregulation of miR-19b. Notably, miR-19b activated Il9 gene expression by directly suppressing atypical E2F family member E2f8. In patients with SSc, higher levels of IL9 and MIR-19B correlate with worse disease progression. Our findings reveal miR-19b as a key factor in Th9 cell-mediated SSc pathogenesis and should have clinical implications for patients with SSc.

Bone morphogenetic protein 4 alleviates pulmonary fibrosis by regulating macrophages.

Fibrosis is a pathological change mainly characterized by an increase of fibrous connective tissue and decrease of parenchymal cells. Its continuous progress may lead to the destruction of organ structure and function decline. An excess of alternatively activated M2 macrophages have been considered crucial candidates in the progression of fibrosis. Bone morphogenetic proteins (BMPs), a group of multifunctional growth factors, are essential for organ development and pathophysiological process, however, the roles that BMPs play in innate immune homeostasis in the development of fibrosis and the downstream signals have not been fully explored. In the current study, we firstly found that the expression of BMP4 was significantly down-regulated in human and mouse fibrosis samples. Then we investigated the effects of BMP4 on macrophage polarization in IL-4 environment and related molecular mechanisms, and found that BMP4 caused a decrease in polarized response towards M2, reflected in the expression of the markers Fizz1, Ym1 and Arg1, together with an inhibition in Stat6 phosphorylation. This relied on the Smad1/5/8 signaling, which had a crosstalk with Stat6. Moreover, the in vivo study showed that BMP4 treatment can reduce collagen deposition and delay the development of experimental pulmonary fibrosis in mice by inhibiting M2 macrophages through adoptive transfer experiment. These findings revealed a novel role of BMP4 in regulating macrophages, offering potential strategies for treating pulmonary fibrosis.

Cardiovascular disease therapeutics via engineered oral microbiota: Applications and perspective.

Engineering bacteria are considered as a potential treatment for cardiovascular diseases and related risk factors. Oral bacteria are closely related to the occurrence and development of cardiovascular diseases, and their engineering has broad prospects and potential in the treatment of cardiovascular diseases. Oral pathogenic bacteria undergo protein and genetic engineering, including the incorporation of exogenous plasmids to yield therapeutic effects; genetically engineered oral probiotics can be harnessed to secrete cytokines and reactive oxygen species, offering novel therapeutic avenues for cardiovascular diseases.

Topical Application of Nitrate Ameliorates Skin Fibrosis by Regulating ST2+CD4+ T Cells in Systemic Sclerosis Mouse Model.

Systemic sclerosis (SSc) is characterized by intractable multiorgan fibrosis caused by vascular and immune dysfunction. Currently, effective therapeutic options for patients with SSc are limited. Nitrate, an abundant nutrient in the diet, has been demonstrated to be preventative and therapeutic for several diseases. To determine whether nitrate can slow or reverse SSc progression, topical application of nitrate delivered by dissolving microneedles was used to treat a bleomycin-induced dermal fibrosis mouse model. In this study, nitrate considerably attenuated dermal thickness, stiffness, and collagen deposition. Bulk RNA sequencing of skin revealed that Cd4 was a key hub gene in SSc nitrate therapy. In addition, bleomycin-induced cytokines and chemokines were inhibited by nitrate, and CD4+ T cells infiltration markedly declined. Il4, Il6, Il13, and Tgfb expressions in CD4+ T cells isolated from skin biopsies also significantly decreased. Mechanistically, Il1rl1, a type 2 immune response inducer, was markedly repressed in isolated CD4+ T cells and dermal tissues after nitrate treatment. Remarkably, compared with wild-type mice, mice lacking Il1rl1 showed impaired transcriptional profiles after intradermal bleomycin injection. Adoptive transfer of ST2+CD4+ T cells promoted bleomycin-induced Rag2-/- mice dermal fibrosis. Collectively, these findings demonstrate that nitrate targeting ST2+CD4+ T cells is an effective therapeutic option for SSc.

Effects of interleukin-10 treated macrophages on bone marrow mesenchymal stem cells via signal transducer and activator of transcription 3 pathway.

BACKGROUND: Alveolar bone defects caused by inflammation are an urgent issue in oral implant surgery that must be solved. Regulating the various phenotypes of macrophages to enhance the inflammatory environment can significantly affect the progression of diseases and tissue engineering repair process. AIM: To assess the influence of interleukin-10 (IL-10) on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) following their interaction with macrophages in an inflammatory environment. METHODS: IL-10 modulates the differentiation of peritoneal macrophages in Wistar rats in an inflammatory environment. In this study, we investigated its impact on the proliferation, migration, and osteogenesis of BMSCs. The expression levels of signal transducer and activator of transcription 3 (STAT3) and its activated form, phosphorylated-STAT3, were examined in IL-10-stimulated macrophages. Subsequently, a specific STAT3 signaling inhibitor was used to impede STAT3 signal activation to further investigate the role of STAT3 signaling. RESULTS: IL-10-stimulated macrophages underwent polarization to the M2 type through substitution, and these M2 macrophages actively facilitated the osteogenic differentiation of BMSCs. Mechanistically, STAT3 signaling plays a crucial role in the process by which IL-10 influences macrophages. Specifically, IL-10 stimulated the activation of the STAT3 signaling pathway and reduced the macrophage inflammatory response, as evidenced by its diminished impact on the osteogenic differentiation of BMSCs. CONCLUSION: Stimulating macrophages with IL-10 proved effective in improving the inflammatory environment and promoting the osteogenic differentiation of BMSCs. The IL-10/STAT3 signaling pathway has emerged as a key regulator in the macrophage-mediated control of BMSCs' osteogenic differentiation.

Nd:YAG water mist laser treatment for giant gestational gingival tumor: A case report.

BACKGROUND: This case of gestational gingival tumor is huge and extremely rare in clinical practice. As the growth location of this gingival tumor is in the upper anterior tooth area, it seriously affects the pregnant woman's speech and food, causing great pain to the patient. The use of Nd:YGA water mist laser to remove the gingival tumor resulted in minimal intraoperative bleeding, minimal adverse reactions, and good postoperative healing, which is worthy of clinical promotion and application. CASE SUMMARY: The patient, a pregnant woman, reported a large lump in her mouth on the first day of postpartum treatment. Based on medical history and clinical examination, the diagnosis was diagnosed as gestational gingival tumor. Postoperative pathological biopsy also confirmed this diagnosis. The use of Nd:YAG water mist laser to remove the tumor resulted in minimal intraoperative bleeding, clear surgical field of view, short surgical time, and good postoperative healing. CONCLUSION: In comparison to traditional surgery, Nd:YAG water mist laser surgery is minimally invasive, minimizes cell damage, reduces bleeding, ensures a clear field of vision, and virtually eliminates postoperative edema, carbonization, and the risk of cross infection. It has unique advantages in oral soft tissue surgery for pregnant patients. Therefore, the clinical application of Nd:YAG water mist laser for the treatment of gestational gingival tumors is an ideal choice.

Advances in the Study of Extracellular Vesicles for Bone Regeneration.

Promoting the efficiency of bone regeneration in bone loss diseases is a significant clinical challenge. Traditional therapies often fail to achieve better therapeutic outcomes and shorter treatment times. However, in recent years, extracellular vesicles (EVs) have gained significant attention due to their exceptional osteogenic function in bone regeneration and superior therapeutic effects compared to traditional cell therapy. EVs have emerged as a promising therapy for tissue defect regeneration due to their various physiological functions, such as regulating the immune response and promoting tissue repair and regeneration. Moreover, EVs have good biocompatibility, low immunogenicity, and long-term stability, and can be improved through pretreatment and other methods. Studies investigating the mechanisms by which extracellular vesicles promote bone regeneration and applying EVs from different sources using various methods to animal models of bone defects have increased. Therefore, this paper reviews the types of EVs used for bone regeneration, their sources, roles, delivery pathways, scaffold biomaterials, and applications.

Porphyromonas gingivalis aggravates colitis via a gut microbiota-linoleic acid metabolism-Th17/Treg cell balance axis.

Periodontitis is closely related to inflammatory bowel disease (IBD). An excessive and non-self-limiting immune response to the dysbiotic microbiome characterizes the two. However, the underlying mechanisms that overlap still need to be clarified. We demonstrate that the critical periodontal pathogen Porphyromonas gingivalis (Pg) aggravates intestinal inflammation and Th17/Treg cell imbalance in a gut microbiota-dependent manner. Specifically, metagenomic and metabolomic analyses shows that oral administration of Pg increases levels of the Bacteroides phylum but decreases levels of the Firmicutes, Verrucomicrobia, and Actinobacteria phyla. Nevertheless, it suppresses the linoleic acid (LA) pathway in the gut microbiota, which was the target metabolite that determines the degree of inflammation and functions as an aryl hydrocarbon receptor (AHR) ligand to suppress Th17 differentiation while promoting Treg cell differentiation via the phosphorylation of Stat1 at Ser727. Therapeutically restoring LA levels in colitis mice challenged with Pg exerts anti-colitis effects by decreasing the Th17/Treg cell ratio in an AHR-dependent manner. Our study suggests that Pg aggravates colitis via a gut microbiota-LA metabolism-Th17/Treg cell balance axis, providing a potential therapeutically modifiable target for IBD patients with periodontitis.

Fructose Potentiates Bone Loss and Marrow Adipose Tissue Accumulation by Inhibiting Adenosine 5'-Monophosphate-Activated Protein Kinase in Mesenchymal Stem Cells.

Increased fructose consumption has been elucidated to contribute to metabolic diseases. Bone is a dynamic organ that undergoes constant remodeling. However, the effects of fructose on bone health are still in dispute. Here, we identified fructose deteriorated bone mineral density while promoting the abundance of bone marrow adipose tissue. Fructose remarkably promoted the bone marrow mesenchymal stem cells' (BMMSCs) adipogenic commitment at the expense of osteogenic commitment. Fructose boosted the glycolysis of BMMSCs and inhibited phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK), which played a crucial role in bone-fat alteration. Our results suggested that fructose potentiated bone loss and marrow adipose tissue accumulation by suppressing AMPK activation in BMMSCs. Understanding fructose which affected bone metabolism was thus of primary importance in order to establish preventative measures or treatments for this condition.

Purpurolide C-based microneedle promotes macrophage-mediated diabetic wound healing via inhibiting TLR4-MD2 dimerization and MYD88 phosphorylation.

Delayed wound healing in diabetes is a global challenge, and the development of related drugs is a clinical problem to be solved. In this study, purpurolide C (PC), a small-molecule secondary metabolite of the endophytic fungus Penicillium purpurogenum, was found to promote diabetic wound healing. To investigate the key regulation targets of PC, in vitro RNA-seq, molecular docking calculations, TLR4-MD2 dimerization SDS-PAGE detection, and surface plasmon resonance (SPR) were performed, indicating that PC inhibited inflammatory macrophage activation by inhibiting both TLR4-MD2 dimerization and MYD88 phosphorylation. Tlr4 knockout in vivo attenuated the promotion effect of PC on wound healing. Furthermore, a delivery system consisting of macrophage liposome and GelMA-based microneedle patches combined with PC (PC@MLIP MN) was developed, which overcame the poor water solubility and weak skin permeability of PC, so that successfully punctured the skin and delivered PC to local tissues, and accurately regulated macrophage polarization in diabetic wound management. Overall, PC is an anti-inflammatory small molecule compound with a well-defined structure and dual-target regulation, and the PC@MLIP MN is a promising novel biomaterial for the management of diabetic wound.

Mesenchymal stem cell-derived apoptotic bodies alleviate alveolar bone destruction by regulating osteoclast differentiation and function.

Periodontitis is caused by overactive osteoclast activity that results in the loss of periodontal supporting tissue and mesenchymal stem cells (MSCs) are essential for periodontal regeneration. However, the hypoxic periodontal microenvironment during periodontitis induces the apoptosis of MSCs. Apoptotic bodies (ABs) are the major product of apoptotic cells and have been attracting increased attention as potential mediators for periodontitis treatment, thus we investigated the effects of ABs derived from MSCs on periodontitis. MSCs were derived from bone marrows of mice and were cultured under hypoxic conditions for 72 h, after which ABs were isolated from the culture supernatant using a multi-filtration system. The results demonstrate that ABs derived from MSCs inhibited osteoclast differentiation and alveolar bone resorption. miRNA array analysis showed that miR-223-3p is highly enriched in those ABs and is critical for their therapeutic effects. Targetscan and luciferase activity results confirmed that Itgb1 is targeted by miR-223-3p, which interferes with the function of osteoclasts. Additionally, DC-STAMP is a key regulator that mediates membrane infusion. ABs and pre-osteoclasts expressed high levels of DC-STAMP on their membranes, which mediates the engulfment of ABs by pre-osteoclasts. ABs with knock-down of DC-STAMP failed to be engulfed by pre-osteoclasts. Collectively, MSC-derived ABs are targeted to be engulfed by pre-osteoclasts via DC-STAMP, which rescued alveolar bone loss by transferring miR-223-3p to osteoclasts, which in turn led to the attenuation of their differentiation and bone resorption. These results suggest that MSC-derived ABs are promising therapeutic agents for the treatment of periodontitis.

MicroRNA-155 targets SOCS1 to inhibit osteoclast differentiation during orthodontic tooth movement.

BACKGROUND: MicroRNA-155 (miR-155) is a multifunctional miRNA whose expression is known to be involved in a range of physiological and pathological processes. Its association with several oral diseases has been established. However, the specific role of miR-155 in orthodontic tooth movement remains unclear. In this study, we investigated the impact of miR-155 on osteoclast differentiation and orthodontic tooth movement models, aiming to explore the underlying mechanisms. METHODS: In this experiment, we utilized various agents including miR-155 mimic, miR-155 inhibitor, as well as non-specific sequences (NC mimic & NC inhibitor) to treat murine BMMNCs. Subsequently, osteoclast induction (OC) was carried out to examine the changes in the differentiation ability of monocytes under different conditions. To assess these changes, we employed RT-PCR, Western blotting, and TRAP staining techniques. For the orthodontic tooth movement model in mice, the subjects were divided into two groups: the NaCl group (injected with saline solution) and the miR-155 inhibitor group (injected with AntagomiR-155). We observed the impact of orthodontic tooth movement using stereoscopic microscopy, micro-CT, and HE staining. Furthermore, we performed RT-PCR and Western blotting analyses on the tissues surrounding the moving teeth. Additionally, we employed TargetScan to predict potential target genes of miR-155. RESULTS: During osteoclast induction of BMMNCs, the expression of miR-155 exhibited an inverse correlation with osteoclast-related markers. Overexpression of miR-155 led to a decrease in osteoclast-related indexes, whereas underexpression of miR-155 increased those indexes. In the mouse orthodontic tooth movement model, the rate of tooth movement was enhanced following injection of the miR-155 inhibitor, leading to heightened osteoclast activity. TargetScan analysis identified SOCS1 as a target gene of miR-155. CONCLUSIONS: Our results suggest that miR-155 functions as an inhibitor of osteoclast differentiation, and it appears to regulate osteoclasts during orthodontic tooth movement. The regulatory mechanism of miR-155 in this process involves the targeting of SOCS1.

Antimicrobial peptides in treatment of Stage III Grade B periodontitis: A randomized clinical trial.

BACKGROUND: To evaluate the effects of antimicrobial peptides (AMPs) on Stage III Grade B periodontitis. METHODS: This trial abided by the principle of consistency test, approved by ethics committee and registered in clinical trials. All qualified 51 patients with Stage III Grade B periodontitis were randomly divided into three groups: SRP group, SRP with minocycline hydrochloride (Mino group) as Control groups, and SRP with AMPs (AMP group) as the Test group. Clinical examinations and subgingival plaques were monitored at baseline and at 7 and 90 days after treatment in the SRP, SRP with AMP and Mino groups. RESULTS: The AMP group (Test group) had a reduced PD (Periodontal probing depth) and an attachment gain significantly higher than SRP and Mino groups (Control groups) at day 90. The abundance of periodontal pathogens was decreased in the AMP group at 7 and 90 days compared with the SRP group and Mino group. Only the AMP group showed an increase the abundance of periodontal probiotics including Capnocytophaga, Gemella, and Lactobacillus at 7 and 90 days. CONCLUSIONS: This study shows that AMPs as an adjunct to SRP promote additional clinical and microbiological benefits in the treatment of Stage III Grade B periodontitis.

The bidirectional effect of neutrophils on periodontitis model in mice: A systematic review.

OBJECTIVE: To evaluate the regulatory role of neutrophils as the first line of host immune defense in the periodontal microenvironment of mice. METHODS: A systematic search was performed using PubMed, Web of Science, and ScienceDirect databases for articles published between 2012 and 2023. In this review, articles investigating the effect of neutrophils on alveolar bone resorption in a mouse model of periodontitis were selected and evaluated according to eligibility criteria. Important variables that may influence outcomes were analyzed. RESULTS: Eleven articles were included in this systematic review. The results showed that because of their immune defense functions, the functional homeostasis of local neutrophils is critical for periodontal health. Neutrophil deficiency aggravates alveolar bone loss. However, several studies have shown that excessive neutrophil infiltration is positively correlated with alveolar bone resorption caused by periodontitis in mice. Therefore, the homeostasis of neutrophil function needs to be considered in the treatment of periodontitis. CONCLUSIONS: Pooled analysis suggests that neutrophils play a bidirectional role in periodontal tissue remodeling in mouse periodontitis models. Therefore, targeted regulation of local neutrophil function provides a novel strategy for the treatment of periodontitis.

Macrophage-derived apoptotic bodies impair the osteogenic ability of osteoblasts in periodontitis.

OBJECTIVES: Periodontitis is induced by the imbalance between osteoblast and osteoclast activity, which leads to periodontal tissue destruction. Macrophages play a vital role in periodontitis. However, the hypoxic periodontal environment will also induce macrophage apoptosis within a short time. Apoptotic bodies (ABs) are the major products generated from apoptotic cells, but whether macrophage-derived ABs play a regulatory role as their mother cells in periodontitis remains unknown. In the present study, we aimed to investigate the effects of ABs on osteoblasts. METHOD: ABs derived from hypoxia-induced macrophages were co-cultured with osteoblasts and the impact of ABs on osteoblast differentiation in vitro was assessed. In vivo, periodontitis model was established and macrophages-derived ABs were injected into the gingival sulcus. The effects of ABs on periodontal bone resorption were determined. RESULTS: The results showed that ABs significantly inhibit osteoblast differentiation and promoted alveolar bone resorption in periodontitis. MicroRNA (miRNAs) array analysis was performed and revealed that miR-483-5p is the key miRNA in ABs. Dual luciferase reporter assays were performed and confirmed that miR-483-5p targeted Col1A1 mRNA and attenuated its expression. CONCLUSION: Macrophage-derived ABs inhibit osteoblast differentiation via the transfer of miR-483-5p, which downregulates Col1A1 expression and finally suppresses osteogenic activity.

The impacts of oral and gut microbiota on alveolar bone loss in periodontitis.

Periodontitis, a chronic infectious disease, primarily arises from infections and the invasion of periodontal pathogens. This condition is typified by alveolar bone loss resulting from host immune responses and inflammatory reactions. Periodontal pathogens trigger aberrant inflammatory reactions within periodontal tissues, thereby exacerbating the progression of periodontitis. Simultaneously, these pathogens and metabolites stimulate osteoclast differentiation, which leads to alveolar bone resorption. Moreover, a range of systemic diseases, including diabetes, postmenopausal osteoporosis, obesity and inflammatory bowel disease, can contribute to the development and progression of periodontitis. Many studies have underscored the pivotal role of gut microbiota in bone health through the gut-alveolar bone axis. The circulation may facilitate the transfer of gut pathogens or metabolites to distant alveolar bone, which in turn regulates bone homeostasis. Additionally, gut pathogens can elicit gut immune responses and direct immune cells to remote organs, potentially exacerbating periodontitis. This review summarizes the influence of oral microbiota on the development of periodontitis as well as the association between gut microbiota and periodontitis. By uncovering potential mechanisms of the gut-bone axis, this analysis provides novel insights for the targeted treatment of pathogenic bacteria in periodontitis.