Plap-1 lineage tracing and single-cell transcriptomics reveal cellular dynamics in the periodontal ligament.

Periodontal tissue supports teeth in the alveolar bone socket via fibrous attachment of the periodontal ligament (PDL). The PDL contains periodontal fibroblasts and stem/progenitor cells, collectively known as PDL cells (PDLCs), on top of osteoblasts and cementoblasts on the surface of alveolar bone and cementum, respectively. However, the characteristics and lineage hierarchy of each cell type remain poorly defined. This study identified periodontal ligament associated protein-1 (Plap-1) as a PDL-specific extracellular matrix protein. We generated knock-in mice expressing CreERT2 and GFP specifically in Plap-1-positive PDLCs. Genetic lineage tracing confirmed the long-standing hypothesis that PDLCs differentiate into osteoblasts and cementoblasts. A PDL single-cell atlas defined cementoblasts and osteoblasts as Plap-1-Ibsp+Sparcl1+ and Plap-1-Ibsp+Col11a2+, respectively. Other populations, such as Nes+ mural cells, S100B+ Schwann cells, and other non-stromal cells, were also identified. RNA velocity analysis suggested that a Plap-1highLy6a+ cell population was the source of PDLCs. Lineage tracing of Plap-1+ PDLCs during periodontal injury showed periodontal tissue regeneration by PDLCs. Our study defines diverse cell populations in PDL and clarifies the role of PDLCs in periodontal tissue homeostasis and repair.

Lipase-a single-nucleotide polymorphism rs143793106 is associated with increased risk of aggressive periodontitis by negative influence on the cytodifferentiation of human periodontal ligament cells.

BACKGROUND AND OBJECTIVE: Aggressive periodontitis (AgP) is characterized by general health and rapid destruction of periodontal tissue. The familial aggregation of this disease highlights the involvement of genetic factors in its pathogeny. We conducted a genome-wide association study (GWAS) to identify AgP-related genes in a Japanese population, and the lipid metabolism-related gene, lipase-a, lysosomal acid type (LIPA), was suggested as an AgP candidate gene. However, there is no report about the expression and function(s) of LIPA in periodontal tissue. Hence, we studied the involvement of how LIPA and its single-nucleotide polymorphism (SNP) rs143793106 in AgP by functional analyses of LIPA and its SNP in human periodontal ligament (HPDL) cells. MATERIALS AND METHODS: GWAS was performed using the genome database of Japanese AgP patients, and the GWAS result was confirmed using Sanger sequencing. We examined the mRNA expression level of LIPA and the protein expression level of the encoded protein lysosomal acid lipase (LAL) in periodontium-composing cells using conventional and real-time polymerase chain reaction (PCR) and western blotting, respectively. Lentiviral vectors expressing LIPA wild-type (LIPA WT) and LIPA SNP rs143793106 (LIPA mut) were transfected into HPDL cells. Western blotting was performed to confirm the transfection. LAL activity of transfected HPDL cells was determined using the lysosomal acid lipase activity assay. Transfected HPDL cells were cultured in mineralization medium. During the cytodifferentiation of transfected HPDL cells, mRNA expression of calcification-related genes, alkaline phosphatase (ALPase) activity and calcified nodule formation were assessed using real-time PCR, ALPase assay, and alizarin red staining, respectively. RESULTS: The GWAS study identified 11 AgP-related candidate genes, including LIPA SNP rs143793106. The minor allele frequency of LIPA SNP rs143793106 in AgP patients was higher than that in healthy subjects. LIPA mRNA and LAL protein were expressed in HPDL cells; furthermore, they upregulated the cytodifferentiation of HPDL cells. LAL activity was lower in LIPA SNP-transfected HPDL cells during cytodifferentiation than that in LIPA WT-transfected HPDL cells. In addition, ALPase activity, calcified nodule formation, and calcification-related gene expression levels were lower during cytodifferentiation in LIPA SNP-transfected HPDL cells than those in LIPA WT-transfected HPDL cells. CONCLUSION: LIPA, identified as an AgP-related gene in a Japanese population, is expressed in HPDL cells and is involved in regulating cytodifferentiation of HPDL cells. LIPA SNP rs143793106 suppressed cytodifferentiation of HPDL cells by decreasing LAL activity, thereby contributing to the development of AgP.

CD40-CD40 ligand interaction between periodontal ligament cells and cementoblasts enhances periodontal tissue remodeling in response to mechanical stress.

OBJECTIVE: We analyzed the localization and expression of Cluster of differentiation 40 ligand (CD40L) in murine periodontal tissue applied with the orthodontic force to determine the CD40L-expressing cells under mechanical stress. Furthermore, we investigated whether CD40-CD40L interaction played an important role in transducing mechanical stress between periodontal ligament (PDL) cells and cementoblasts and remodeling the periodontal tissue for its homeostasis. BACKGROUND: PDL is a complex tissue that contains heterogeneous cell populations and is constantly exposed to mechanical stress, such as occlusal force. CD40 is expressed on PDL cells and upregulated under mechanical stress. However, whether its ligand, CD40L, is upregulated in periodontal tissue in response to mechanical stress, and which functions the CD40-CD40L interaction induces by converting the force to biological functions between the cement-PDL complex, are not fully understood. METHODS: The orthodontic treatment was applied to the first molars at the left side of the upper maxillae of mice using a nickel-titanium closed-coil spring. Immunohistochemistry was performed to analyze the localization of CD40L in the periodontal tissue under the orthodontic force. Human cementoblasts (HCEM) and human PDL cells were stretched in vitro and analyzed CD40L and CD40 protein expression using flow cytometry. A GFP-expressing CD40L plasmid vector was transfected into HCEM (CD40L-HCEM). CD40L-HCEM was co-cultured with human PDL cells with higher alkaline phosphatase (ALP) activity (hPDS) or lower ALP (hPDF). After co-culturing, cell viability and proliferation were analyzed by propidium iodide (PI) staining and bromodeoxyuridine (BrdU) assay. Furthermore, the mRNA expression of cytodifferentiation- and extracellular matrix (ECM)-related genes was analyzed by real-time PCR. RESULTS: Immunohistochemistry demonstrated that CD40L was induced on the cells present at the cementum surface in periodontal tissue at the tension side under the orthodontic treatment in mice. The flow cytometry showed that the in vitro-stretching force upregulated CD40L protein expression on HCEM and CD40 protein expression on human PDL cells. Co-culturing CD40L-HCEM with hPDF enhanced cell viability and proliferation but did not alter the gene expression related to cytodifferentiation and ECM. In contrast, co-culturing CD40L-HCEM with hPDS upregulated cytodifferentiation- and ECM-related genes but did not affect cell viability and proliferation. CONCLUSION: We revealed that in response to a stretching force, CD40L expression was induced on cementoblasts. CD40L on cementoblasts may interact with CD40 on heterogeneous PDL cells at the necessary time and location, inducing cell viability, proliferation, and cytodifferentiation, maintaining periodontal tissue remodeling and homeostasis.

Chronic hyperglycemia reduces the expression of intercellular adhesion molecules and increases intercellular hyperpermeability in the periodontal epithelium.

BACKGROUND/AIMS: Hyperglycemia in diabetes is closely associated with periodontal disease progression. This study aimed to investigate the effect of hyperglycemia on the barrier function of gingival epithelial cells as a cause of hyperglycemia-exacerbated periodontitis in diabetes mellitus. METHODS: The abnormal expression of adhesion molecules in gingival epithelium in diabetes was compared between db/db and control mice. To study the effects of hyperglycemia on interepithelial cell permeability, the mRNA and protein expressions of adhesion molecules were investigated using a human gingival epithelial cell line (epi 4 cells) in the presence of either 5.5 mM glucose (NG) or 30 mM glucose (HG). Immunocytochemical and histological analyses were performed. We also studied HG-related intracellular signaling to assess abnormal adhesion molecule expression in the cultured epi 4 cells. RESULTS: The results of the proteomic analysis implied the abnormal regulation of cell-cell adhesion, and mRNA and protein expression assessments revealed the significant downregulation of Claudin1 expression in the gingival tissues of db/db mice (p < .05 vs control). Similarly, the mRNA and protein expressions of adhesion molecules were lower in epi 4 cells cultured under HG conditions than in those cultured under NG conditions (p < .05). Three-dimensional culture and transmission electron microscopy revealed reduced thickness of the epithelial cell layers with no flattened apical cells and heterogeneously arranged intercellular spaces among adjacent epi 4 cells under the HG. These results were consistent with the increased permeability of epi 4 cells under the HG relative to that of cells under the NG. This abnormal expression of intercellular adhesion molecules under the HG was related to the increased expression of receptors for advanced glycation end products (AGEs) and oxidative stress relative to that seen under the NG, along with stimulation of ERK1/2 phosphorylation in epi 4 cells. CONCLUSIONS: High glucose-induced impairment of intercellular adhesion molecule expression in gingival epithelial cells was related to the intercellular permeability of gingival cells, representing a possible link to hyperglycemia-related AGE signaling, oxidative stress, and ERK1/2 activation.

Mice Lacking PLAP-1/Asporin Show Alteration of Periodontal Ligament Structures and Acceleration of Bone Loss in Periodontitis.

Periodontal ligament-associated protein 1 (PLAP-1), also known as Asporin, is an extracellular matrix protein expressed in the periodontal ligament and plays a crucial role in periodontal tissue homeostasis. Our previous research demonstrated that PLAP-1 may inhibit TLR2/4-mediated inflammatory responses, thereby exerting a protective function against periodontitis. However, the precise roles of PLAP-1 in the periodontal ligament (PDL) and its relationship to periodontitis have not been fully explored. In this study, we employed PLAP-1 knockout mice to investigate its roles and contributions to PDL tissue and function in a ligature-induced periodontitis model. Mandibular bone samples were collected from 10-week-old male C57BL/6 (WT) and PLAP-1 knockout (KO) mice. These samples were analyzed through micro-computed tomography (µCT) scanning, hematoxylin and eosin (HE) staining, picrosirius red staining, and fluorescence immunostaining using antibodies targeting extracellular matrix proteins. Additionally, the structure of the PDL collagen fibrils was examined using transmission electron microscopy (TEM). We also conducted tooth extraction and ligature-induced periodontitis models using both wild-type and PLAP-1 KO mice. PLAP-1 KO mice did not exhibit any changes in alveolar bone resorption up to the age of 10 weeks, but they did display an enlarged PDL space, as confirmed by µCT and histological analyses. Fluorescence immunostaining revealed increased expression of extracellular matrix proteins, including Col3, BGN, and DCN, in the PDL tissues of PLAP-1 KO mice. TEM analysis demonstrated an increase in collagen diameter within the PDL of PLAP-1 KO mice. In line with these findings, the maximum stress required for tooth extraction was significantly lower in PLAP-1 KO mice in the tooth extraction model compared to WT mice (13.89 N ± 1.34 and 16.51 N ± 1.31, respectively). In the ligature-induced periodontitis model, PLAP-1 knockout resulted in highly severe alveolar bone resorption, with a higher number of collagen fiber bundle tears and significantly more osteoclasts in the periodontium. Our results demonstrate that mice lacking PLAP-1/Asporin show alteration of periodontal ligament structures and acceleration of bone loss in periodontitis. This underscores the significant role of PLAP-1 in maintaining collagen fibrils in the PDL and suggests the potential of PLAP-1 as a therapeutic target for periodontal diseases.

The effect of aging on the nanostructure of murine alveolar bone and dentin.

INTRODUCTION: Alveolar bone, dentin, and cementum provide a striking example of structurally different collagen-based mineralized tissues separated only by periodontal ligament. While alveolar bone is strongly remodeled, this does not hold for dentin and cementum. However, additional dentin can be deposited on the inner surface of the pulp chamber also in older age. By investigating alveolar bone and molar of mice, the aim of our study is to detect changes in the mineral nanostructure with aging. MATERIALS AND METHODS: Buccal-lingual sections of the mandible and first molar from C57BL/6 mice of three different age groups (young 5 weeks, adult 22 weeks and old 23 months) were characterized using synchrotron small and wide-angle X-ray scattering. Local average thickness and length of the apatite particles were mapped with several line scans covering the alveolar bone and the tooth. RESULTS: In alveolar bone, a spatial gradient was seen to develop with age with the thickest and longest particles in the distal part of the bone. The mineral particles in dentin were found to be become thicker, but then decrease of average length from adult to old animals. The mineral particle characteristics of dentin close to the pulp chamber were not only different to the rest of the tooth, but also when comparing the different age groups and even between individual animals in the same age group. CONCLUSIONS: These results indicated that mineral particle characteristics were found to evolve differently between molar and alveolar bone as a function of age.

Effects of oxidative stress-induced increases in Zn2+ concentrations in human gingival epithelial cells.

BACKGROUND AND OBJECTIVE: Previous studies have reported that oxidative stress increases intracellular Zn2+ concentrations and induces cytotoxicity. However, no studies have investigated whether oxidative stress induces such changes in periodontal tissue cells. In the present study, we investigated the effect of oxidative stress on intracellular Zn2+ concentration in periodontium constituent cells and its potential relationship with periodontal disease. METHODS: We analyzed changes in intracellular Zn2+ concentrations in human gingival epithelial (epi4) cells treated with hydrogen peroxide (H2 O2 ). The fluorescent probes FluoZin-3 AM and CellTracker Green CMFDA were used to detect intracellular Zn2+ and thiol groups, respectively. Western blot analyses, luciferase reporter assays, and real-time polymerase chain reaction (PCR) analyses were performed to examine the effect of intracellular Zn2+ on epi4 cells. RESULTS: H2 O2 treatment increased intracellular concentrations of Zn2+ in epi4 cells by facilitating the movement of Zn2+ from cellular nonprotein thiols to the cytoplasm and promoting cell membrane permeability to Zn2+ . Furthermore, H2 O2 -induced increases in intracellular Zn2+ activated the p38 cAMP response element-binding protein/mitogen-activated protein kinase (p38 CREB/MAPK) cascade, upregulated nuclear factor kappa B (NF-κB) DNA binding, and increased the expression of inflammatory cytokines and matrix metallopeptidase-9 (MMP-9). CONCLUSION: Increases in intracellular Zn2+ induced by oxidative stress activate signaling pathways involved in inflammation, potentially contributing to the progression of periodontal disease.

Aromatase inhibitor anastrozole modifies cellular functions in gingival fibroblasts and endothelial cells: possible periodontal complications of aromatase inhibitor treatment.

BACKGROUND: Recent studies have shown that treatment with aromatase inhibitors contributes to an increased prevalence of periodontitis. OBJECTIVE: In this study, we assessed effects of the aromatase inhibitor anastrozole on cellular function of human gingival fibroblasts (HGFs) and endothelial cells. METHODS: Expression levels of collagen, extracellular matrix (ECM) proteins, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) were examined in HGFs exposed to anastrozole. Furthermore, inflammatory responses in HGFs cultured with anastrozole were evaluated in the presence of Porphyromonas gingivalis lipopolysaccharide. We also evaluated the vascular permeability and vascular endothelial (VE)-cadherin expression of endothelial cells exposed to anastrozole. RESULTS: Anastrozole enhanced expression levels of collagen, ECM proteins, TIMPs, and inflammatory cytokines in HGFs, as well as vascular permeability of endothelial cells. In addition, anastrozole reduced expression levels of MMPs in HGFs and VE-cadherin in endothelial cells. CONCLUSION: These results suggest that anastrozole modulates various cellular functions in HGFs and endothelial cells.

Long-term exposure to cigarette smoke influences characteristics in human gingival fibroblasts.

BACKGROUND: Periodontal disease is a chronic inflammatory disease caused by periodontopathic bacteria accumulated in the gingival sulcus and periodontal pocket. Cigarette smoking is a well-established risk factor for periodontal disease, and periodontal tissues in smokers are chronically exposed to cigarette smoke on a long-term basis. OBJECTIVE: In this study, we investigated the effects of long-term exposure to nicotine or cigarette smoke condensate (CSC) on cellular functions of human gingival fibroblasts (HGFs). METHODS: In vitro-maintained HGFs were divided into two groups. The HGFs of the short-term and the long-term culture groups were cultured for 4 and 25 days, respectively, in the presence or absence of nicotine, which is one of the main components of cigarette smoke, or CSC. The cellular proliferation and migration capacities of HGFs exposed to nicotine or CSC were evaluated by WST-1 and wound healing assays. The effects of exposure to nicotine or CSC on the expression of various extracellular matrix (ECM) components, inflammatory cytokines, and senescence-related genes were examined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. The cellular senescence of HGFs exposed to nicotine or CSC was detected by the senescence-associated ß-galactosidase (SA-ß-gal) assay. To explore the senescence-associated microRNA (miRNA), we extracted miRNA from the HGFs and the expression profiles were examined by miRNA array. RESULTS: In short-term culture, no significant changes were observed. Long-term exposure of HGFs to nicotine or CSC significantly suppressed their cellular proliferation and migration and upregulated type Ⅰ collagen, type Ⅲ collagen, interleukin (IL)-6, IL-8, p16, p21, and p53 mRNA expression, and IL-6 and IL-8 protein expression. Furthermore, long-term nicotine or CSC exposure significantly increased the percentage of SA-ß-gal-positive HGFs. In addition, long-term nicotine or CSC exposure reduced miR-29b and miR-199a expression to less than 50% of that in the unstimulated HGFs. CONCLUSION: These data suggest that long-term smoking habits may reduce wound healing ability, modulate ECM protein homeostasis, stimulate the inflammatory response, and accelerate cellular senescence in HGFs, and consequently accelerate the progression of periodontal diseases.

Will implants with a fixed dental prosthesis in the molar region enhance the longevity of teeth adjacent to distal free-end edentulous spaces?

OBJECTIVES: Clinical evidence demonstrating the effectiveness of implants in preventing tooth loss is limited because of the many risk factors involved in tooth loss. This retrospective cohort study investigated whether an implant in the molar region of a distal free-end edentulous space affects the loss of the most distal tooth after 6 years, adjusting for other risk factors associated with tooth loss using propensity score matching analysis. MATERIAL AND METHODS: A total of 571 subjects and 1,085 teeth adjacent to a distal free-end edentulous space were evaluated. At baseline, the 1,085 teeth were divided into two groups according to the presence or absence of a molar implant with a fixed dental prosthesis in the distal free-end edentulous space. Propensity score matching analysis was used to reduce the effects of bias by matching teeth with and without implants according to similar background factors at baseline. The adjusted variables were age group, occlusal support status, Kennedy classification, tooth position, tooth type, restoration status, dental caries, periodontal pocket depth, and condition of the opposing tooth. RESULTS: A total of 56 teeth (28 associated with a molar implant; 28 with no implant) were enrolled according to propensity score matching. Fisher's exact test showed that a molar implant significantly protected the tooth adjacent to the distal free-end edentulous space (p = .01). CONCLUSIONS: Within the limitations of this retrospective cohort study, it was found that implants in free-end edentulous spaces may be beneficial in extending the longevity of adjacent teeth. Further research will be necessary to confirm this finding.

Association of periodontal disease with atherosclerosis in 70-year-old Japanese older adults.

Periodontal disease and arteriosclerotic disease are greatly affected by aging. In this study, the association of conventional risk factors and periodontal disease with atherosclerosis was longitudinally examined in Japanese older adults. Subjects in this study were 490 community-dwelling septuagenarians (69-71 years) randomly recruited from the Basic Resident Registry of urban or rural areas in Japan. At the baseline examination, all subjects underwent socioeconomic and medical interviews; medical examinations, including examinations for carotid atherosclerosis, hypertension, diabetes mellitus, and dyslipidemia; and conventional dental examinations, including a tooth count and measurement of probing pocket depth (PPD). After 3 years, 182 septuagenarians who had no atherosclerosis at the baseline examination were registered and received the same examination as at the baseline. In the re-examination conducted 3 years after the baseline survey, 131 (72.0%) of the 182 participants who had no atherosclerosis at the baseline examination were diagnosed with carotid atherosclerosis. Adjusting and analyzing the mutual relationships of the conventional risk factors for atherosclerosis by multiple logistic regression analysis for the 171 septuagenarians with a full set of data, the proportion of teeth with PPD ≥ 4 mm was independently related to the prevalence of atherosclerosis (odds ratio: 1.029, P < 0.022). This longitudinal study of Japanese older adults suggests that periodontal disease is associated with the onset/progression of atherosclerosis. Maintaining a healthy periodontal condition may be an important factor in preventing the development and progression of atherosclerosis.

A cross-sectional study of relationships between periodontal disease and general health: The Hitachi Oral Healthcare Survey.

BACKGROUND: This cross-sectional study performed to clarify the relationship between periodontal disease and non-communicable diseases (NCDs), such as obesity, diabetes mellitus, impaired glucose tolerance (IGT), chronic obstructive pulmonary disease (COPD), and atherosclerotic cardiovascular disease (ASCVD) by introducing dental examinations into the annual health examinations conducted by Japanese companies, and to highlights the importance of a medical system that connects dental and medical professionals. METHODS: A total of 1.022 Hitachi Ltd. employees were enrolled in this cross-sectional study. We examined correlations and odds ratios (ORs) between the dental and overall health of employees using stratification and multiple logistic regression analyses based on the periodontal health indicators, general health indicators, and occlusal force. RESULTS: The adjusted OR of PPD for obesity (OR, 1.42; 95% confidence interval [CI], 1.09-1.84; p = 0.009), IGT (OR, 1.48; 95% CI, 1.00-2.20; p = 0.049), and COPD (OR, 1.38; 95% CI, 1.02-1.88; p = 0.038) significantly differed. The adjusted OR of body mass index (OR, 1.28; 95% CI 1.15-1.42; p < 0.001), haemoglobin A1C (HbA1c) (OR, 4.34; 95% CI, 1.89-9.98; p < 0.001), fasting blood glucose (FBG) levels (OR, 1.08; 95% CI 1.04-1.11; p < 0.001), postbronchodilator forced expiratory volume in one second/forced vital capacity ratio (%FEV1) (OR, 0.95; 95% CI 0.91-1.00; p = 0.031) and smoking (OR, 2.32; 95% CI 1.62-3.33; p < 0.001) for severe periodontal disease also significantly differed. Occlusal force was significantly reduced in employees aged 50-59 years compared to those aged 40-49 years. Both PPD, HbA1c, FBG levels were significantly associated with occlusal force among employees with moderate/severe periodontitis. PPD was significantly associated with occlusal force among employees with and moderate COPD, and ASCVD. %FEV1 was significantly associated with occlusal force among employees with IGT. CONCLUSIONS: This cross-sectional study revealed mutual relationships among periodontal disease, NCDs, and occlusal force on Japanese corporate workers. We demonstrated that a comprehensive, regional healthcare system centred on annual integrated dental and physical health examinations in the workplace will benefit employees and positively impact corporate health insurance.

Fibroblast growth factor-2 inhibits CD40-mediated periodontal inflammation.

Fibroblast growth factor-2 (FGF-2) stimulates periodontal regeneration by a broad spectrum of effects on periodontal ligament (PDL) cells, such as proliferation, migration, and production of extracellular matrix. A critical factor in the success of periodontal regeneration is the rapid resolution of inflammatory responses in the tissue. We explored an anti-inflammatory effect of FGF-2 during periodontal regeneration and healing. We found that FGF-2 on mouse periodontal ligament cells (MPDL22) markedly downregulated CD40 expression, a key player of inflammation. In addition, FGF-2 inhibited CD40 signaling by the non-canonical nuclear factor-kappa B2 (NFκB2) pathway, resulting in decreased production of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), which have the potential to recruit immune cells to inflamed sites. Furthermore, in vivo treatment of FGF-2 enhanced healing of skin wounds by counteracting the CD40-mediated inflammation. These results reveal that FGF-2 has an important function as a negative regulator of inflammation during periodontal regeneration and healing.

Identification of genetic risk factors of aggressive periodontitis using genomewide association studies in association with those of chronic periodontitis.

To identify the genetic risk factors for aggressive periodontitis (AgP), it is important to understand the progression and pathogenesis of AgP. The purpose of this review was to summarize the genetic risk factors for AgP identified through a case-control genomewide association study (GWAS) and replication study. The initial studies to identify novel AgP risk factors were potentially biased because they relied on previous studies. To overcome this kind of issue, an unbiased GWAS strategy was introduced to identify genetic risk factors for various diseases. Currently, three genes glycosyltransferase 6 domain containing 1 (GLT6D1), defensin α1 and α3 (DEFA1A3), and sialic acid-binding Ig-like lectin 5 (SIGLEC5) that reach the threshold for genomewide significance have been identified as genetic risk factors for AgP through a case-control GWAS.

Dental plaque-induced gingival conditions.

OBJECTIVE: This review proposes revisions to the current classification system for gingival diseases and provides a rationale for how it differs from the 1999 classification system. IMPORTANCE: Gingival inflammation in response to bacterial plaque accumulation (microbial biofilms) is considered the key risk factor for the onset of periodontitis. Thus, control of gingival inflammation is essential for the primary prevention of periodontitis. FINDINGS: The clinical characteristics common to dental plaque-induced inflammatory gingival conditions include: a) clinical signs and symptoms of inflammation that are confined to the gingiva: b) reversibility of the inflammation by removing or disrupting the biofilm; c) the presence of a high bacterial plaque burden to initiate the inflammation; d) systemic modifying factors (e.g., hormones, systemic disorders, drugs) which can alter the severity of the plaque-induced inflammation and; e) stable (i.e., non-changing) attachment levels on a periodontium which may or may not have experienced a loss of attachment or alveolar bone. The simplified taxonomy of gingival conditions includes: 1) introduction of the term "incipient gingivitis;" 2) a description of the extent and severity of gingival inflammation; 3) a description of the extent and severity of gingival enlargement and; 4) a reduction of categories in the dental plaque-induced gingival disease taxonomy. CONCLUSIONS: Dental plaque-induced gingival inflammation is modified by various systemic and oral factors. The appropriate intervention is crucial for the prevention of periodontitis.

Periodontal health and gingival diseases and conditions on an intact and a reduced periodontium: Consensus report of workgroup 1 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions.

Periodontal health is defined by absence of clinically detectable inflammation. There is a biological level of immune surveillance that is consistent with clinical gingival health and homeostasis. Clinical gingival health may be found in a periodontium that is intact, i.e. without clinical attachment loss or bone loss, and on a reduced periodontium in either a non-periodontitis patient (e.g. in patients with some form of gingival recession or following crown lengthening surgery) or in a patient with a history of periodontitis who is currently periodontally stable. Clinical gingival health can be restored following treatment of gingivitis and periodontitis. However, the treated and stable periodontitis patient with current gingival health remains at increased risk of recurrent periodontitis, and accordingly, must be closely monitored. Two broad categories of gingival diseases include non-dental plaque biofilm-induced gingival diseases and dental plaque-induced gingivitis. Non-dental plaque biofilm-induced gingival diseases include a variety of conditions that are not caused by plaque and usually do not resolve following plaque removal. Such lesions may be manifestations of a systemic condition or may be localized to the oral cavity. Dental plaque-induced gingivitis has a variety of clinical signs and symptoms, and both local predisposing factors and systemic modifying factors can affect its extent, severity, and progression. Dental plaque-induced gingivitis may arise on an intact periodontium or on a reduced periodontium in either a non-periodontitis patient or in a currently stable "periodontitis patient" i.e. successfully treated, in whom clinical inflammation has been eliminated (or substantially reduced). A periodontitis patient with gingival inflammation remains a periodontitis patient (Figure 1), and comprehensive risk assessment and management are imperative to ensure early prevention and/or treatment of recurrent/progressive periodontitis. Precision dental medicine defines a patient-centered approach to care, and therefore, creates differences in the way in which a "case" of gingival health or gingivitis is defined for clinical practice as opposed to epidemiologically in population prevalence surveys. Thus, case definitions of gingival health and gingivitis are presented for both purposes. While gingival health and gingivitis have many clinical features, case definitions are primarily predicated on presence or absence of bleeding on probing. Here we classify gingival health and gingival diseases/conditions, along with a summary table of diagnostic features for defining health and gingivitis in various clinical situations.

Regulation of CONIFERALDEHYDE 5-HYDROXYLASE expression to modulate cell wall lignin structure in rice.

MAIN CONCLUSION: Regulation of a gene encoding coniferaldehyde 5-hydroxylase leads to substantial alterations in lignin structure in rice cell walls, identifying a promising genetic engineering target for improving grass biomass utilization. The aromatic composition of lignin greatly affects utilization characteristics of lignocellulosic biomass and, therefore, has been one of the primary targets of cell wall engineering studies. Limited information is, however, available regarding lignin modifications in monocotyledonous grasses, despite the fact that grass lignocelluloses have a great potential for feedstocks of biofuel production and various biorefinery applications. Here, we report that manipulation of a gene encoding coniferaldehyde 5-hydroxylase (CAld5H, or ferulate 5-hydroxylase, F5H) leads to substantial alterations in syringyl (S)/guaiacyl (G) lignin aromatic composition in rice (Oryza sativa), a major model grass and commercially important crop. Among three CAld5H genes identified in rice, OsCAld5H1 (CYP84A5) appeared to be predominantly expressed in lignin-producing rice vegetative tissues. Down-regulation of OsCAld5H1 produced altered lignins largely enriched in G units, whereas up-regulation of OsCAld5H1 resulted in lignins enriched in S units, as revealed by a series of wet-chemical and NMR structural analyses. Our data collectively demonstrate that OsCAld5H1 expression is a major factor controlling S/G lignin composition in rice cell walls. Given that S/G lignin composition affects various biomass properties, we contemplate that manipulation of CAld5H gene expression represents a promising strategy to upgrade grass biomass for biorefinery applications.

FGF-2 promotes initial osseointegration and enhances stability of implants with low primary stability.

OBJECTIVES: The aim of this study was to examine the effect of basic fibroblast growth factor (FGF-2) on osseointegration of dental implants with low primary stability in a beagle dog model. MATERIALS AND METHODS: Customized titanium implants that were designed to have low contact with the existing bone were installed into the edentulous mandible of beagle dogs. To degrade the primary stability of the implants, the diameters of the bone sockets exceeded the implant diameters. FGF-2 (0.3%) plus vehicle (hydroxypropyl cellulose) or vehicle alone was topically applied to the sockets in the FGF-2 and control groups, respectively. In Study 1, the new bone area and length of new bone-to-implant contact (BIC) were evaluated at 4, 8, and 12 weeks after installation using histomorphometry and scanning electron microscopy. In Study 2, the implant stability quotient (ISQ) values were sequentially measured for 16 weeks using an Osstell system. RESULTS: The histomorphometric analysis revealed that the new bone area and length of BIC in the FGF-2 group were significantly larger than those in the control group at 4 weeks. Electron microscopic observation showed intimate contact between the mature lamellar bone and the implant surfaces, osseointegration, in both groups. The ISQ values in the FGF-2 group were significantly increased from 6 to 16 weeks compared with those in the control group. CONCLUSIONS: Taken together, our study demonstrates that FGF-2 promoted new bone formation around the dental implants and subsequent osseointegration, resulting in promotion of stability of implants with low primary stability.

The nanostructure of murine alveolar bone and its changes due to type 2 diabetes.

Alveolar bone - the bony ridge containing the tooth sockets - stands out by its remodeling activity where bone is being formed and resorbed at a much higher rate than in any other bony tissue. Teeth that are anchored in the jaw through the periodontal ligament exert very large localized loads during mastication that could lead to a unique adaptation of the collagen/mineral structure in the bone. Our aim was to characterize the nanostructure of alveolar bone and to determine the influence of diabetes on structural characteristics of the mineralized matrix. Using small- and wide-angle X-ray scattering (SAXS/WAXS), we studied a spontaneous diabetic mouse model (KK+) and its corresponding healthy controls (KK-) (n=6) to determine the size and mutual alignment of the mineral nanoparticles embedded in the collagen matrix. On cross-sections (buccal-lingual) of the first molar multiple line scans with a spatial resolution of 30µm were performed on each sample, from the lingual to the buccal side of the mandible. Mineral particle thickness and length are decreasing towards the tooth in both buccal and lingual sides of alveolar bone. While mineral particles are well aligned with the long axis of the tooth on the buccal side, they are in a quarter of the measurements oriented along two preferred directions on the lingual side. These nanostructural differences can be interpreted as the result of an asymmetric loading during mastication, leading to a tilting of the tooth in its socket. In diabetic mice particle thicknesses are smaller compared to control animals.

Proinflammatory M1 Macrophages Inhibit RANKL-Induced Osteoclastogenesis.

In response to a defined panel of stimuli, immature macrophages can be classified into two major phenotypes: proinflammatory (M1) and anti-inflammatory (M2). Although both phenotypes have been implicated in several chronic inflammatory diseases, their direct role in bone resorption remains unclear. The present study investigated the possible effects of M1 and M2 macrophages on RANKL-induced osteoclastogenesis. In osteoclastogenesis assays using RAW264.7 cells or bone marrow cells as osteoclast precursors, addition of M1 macrophages significantly suppressed RANKL-induced osteoclastogenesis compared to nonstimulated conditions (M0), addition of M2 macrophages, or no macrophage addition (P < 0.05), suggesting that M1 macrophages can downregulate osteoclastogenesis. This effect was maintained when direct contact between M1 and osteoclast precursors was interrupted by cell culture insertion, indicating engagement of soluble factors released from M1. M1 macrophages developed from interferon gamma (IFN-γ) knockout (IFN-γ-KO) mice lost the ability to downregulate osteoclastogenesis. Antibody-based neutralization of interleukin-12 (IL-12), but not IL-10, produced by M1 macrophages also abrogated M1-mediated downregulation of osteoclastogenesis. Real-time PCR analyses showed that IFN-γ suppressed gene expression of NFATc1, a master regulator of osteoclastogenesis, whereas IL-12 increased the apoptosis of osteoclasts, suggesting molecular mechanisms underlying the possible roles of IFN-γ or IL-12 in M1-mediated inhibition of osteoclastogenesis. These findings were confirmed in an in vivo ligature-induced mouse periodontitis model in which adoptive transfer of M1 macrophages showed a significantly lower level of bone loss and less tartrate-resistant acid phosphatase (TRAP)-positive cell induction than M0 or M2 macrophage transfer. In conclusion, by its secretion of IFN-γ and IL-12, M1, but not M0 or M2, was demonstrated to inhibit osteoclastogenesis.