Journal of Periodontal Research

Article	Citations
	350
Early Cigarette Smoking Onset Increases Edentulism Risk	155
Ability of gingival crevicular fluid volume, E‐cadherin, and total antioxidant capacity levels for predicting outcomes of nonsurgical periodontal therapy for periodontitis patients	81
The association between vitamin D binding protein levels and periodontal status: A systematic review	69
The periodontal ligament, temperature‐sensitive ion channels TRPV1–4, and the mechanosensitive ion channels Piezo1 and 2: A Nobel connection	64
Soft Tissue Augmentation Around Dental Implants: Techniques, Timing, and Comparative Efficacy—A Systematic Review and Network Meta‐Analysis	62
Leptin‐deficient ob/ob mice exhibit periodontitis phenotype and altered oral microbiome	56
Periodontitis as a Model for Inflammatory Uncoupling of Bone Remodeling	52
Effect of low‐intensity pulsed ultrasound on the mineralization of force‐treated cementoblasts and orthodontically induced inflammatory root resorption via the Lamin A/C‐Yes associated protein axis	45
Artificial Intelligence in Periodontology: A Systematic Review	43
Six miRNA expressions in the saliva of smokers and non‐smokers with periodontal disease	41
Periodontal Clinical Practice: The Past, the Present, the Future	36
A Practical Guide to Evidence Synthesis: Meta‐Analysis, Network Meta‐Analysis, Meta‐Regressions and Beyond	36
Dietary patterns and periodontitis: A systematic review	36
Does Computer‐Assisted Surgery Improve the Accuracy of Immediate Implant Placement? A Systematic Review and Network Meta‐Analysis	33
3‐methyl‐1H‐indol‐1‐yl dimethylcarbamodithioate attenuates periodontitis through targeting MAPK signaling pathway‐regulated mitochondrial function	32
Genetic analysis of impaired healing responses after periodontal therapy in type 2 diabetes: Clinical and in vivo studies	31
Cover Image	31
Periodontitis causally affects the brain cortical structure: A Mendelian randomization study	30
High‐Frequency Ultrasound for Detecting Periodontal Inflammation: A Preclinical Diagnostic Accuracy Study	26
Effects of periodontal cells‐derived extracellular vesicles on mesenchymal stromal cell function	26
Glucagon‐Like Peptide 1 Receptor Agonists ( GLP ‐ 1RAs ) Improve Periodontal and Peri‐Implant Heal	26
Periodontitis and Rheumatoid Arthritis—Mechanistic Evidence	26
Metagenomic Insights Into the Subgingival Microbiome in Periodontal Health and Different Grades of Periodontitis	25
Role of ferroptosis in periodontitis: An animal study in rats	25

Periodontitis and risk of mortality in patients with chronic kidney disease: A systematic review with meta‐analysis	25
Use of ultrasound imaging for assessment of the periodontium: A systematic review	25
Artificial Intelligence in Periodontology: The Past, the Present, the Future	25
TRPV1 Promotes Periodontitis Tissue Inflammation and Oxidative Damage by Regulating STAT3 Signaling Pathway	24
	24
Differential expression of FSTL1 and its correlation with the pathological process of periodontitis	24
	24
Immunohistochemical analysis with apoptosis and autophagy markers in periodontitis and peri‐implantitis: Clinical comparative study	23
Journal of Periodontal Research—the past, the present, the future: The legacy of periodontology is here!	23
	23
Submucosal Microbiome in Peri‐Implantitis: A Comparative Metagenomic Analysis	22
Hypoxia dissociates HDAC6/FOXO1 complex and aggregates them into nucleus to regulate autophagy and osteogenic differentiation	22
	21
Gingival tissue samples from periodontitis patients demonstrate epithelial–mesenchymal transition phenotype	21
Proliferative effect of cannabidiol in human gingival fibroblasts via the mitogen‐activated extracellular signal‐regulated kinase (MEK) 1/2	21
Colitis induced by dextran sulphate sodium causes histopathological and immunological changes in the periodontal tissues of Wistar rats	21
Issue Information	20
	20
RETRACTION: I. Yamawaki, Y. Taguchi, S. Komasa, A. Tanaka, and M. Umeda, “Effects of Glucose Concentration on Osteogenic Differentiation of Type II D	20
Study on the effect of periodontitis on renal tissue in atherosclerotic mice	20
Cover Image	20
Expression profile analysis of long noncoding RNA and messenger RNA during mouse cementoblast mineralization	20
A Novel Gene DUSP8 Missense Mutation Causes Nonsyndromic Hereditary Gingival Fibromatosis by Dysre	19
Role of sodium‐dependent vitamin C transporter 2 in human periodontal ligament fibroblasts	19
Biomarker panel discriminates diabetics with and without periodontitis pre‐ and post‐therapy	19
Chronic hyperglycemia reduces the expression of intercellular adhesion molecules and increases intercellular hyperpermeability in the periodontal epithelium	19
Dipyridamole Attenuates Experimental Periodontitis by Regulating M1 Macrophage Polarization via PKA/PKG Pathways	18
Transcriptome Analysis of Porphyromonas gingivalis Lipopolysaccharide‐Induced Early Gene Expression in Human Gingival Keratinocytes	18
Cardiovascular Disease Detection in Dental Settings—Development and External Validation of a Nomogram ( PerioCARD )	18
Effects of vitamin K2 administration on guided bone regeneration in diabetic rats	18
Increased expression of angiopoietin‐like protein 4 regulates matrix metalloproteinase‐13 expression in Porphyromonas gingivalis lipopolysaccharides‐stimulated gingival fibroblasts and ligature	18
Augmented and Virtual Reality in Dental Medicine Updated: A Systematic Review and Meta‐Analysis	18
Levels of matrix metalloproteinase‐1 ( MMP ‐1), MMP ‐2, MMP	18
Artistic Realism or Clinical Evidence? Periodontitis and Pathological Tooth Migration in Caravaggio's Goliath and Medusa	17
Insulin resistance and periodontitis: Mediation by blood pressure	16
Loss of β‐catenin causes cementum hypoplasia by hampering cementogenic differentiation of Axin2‐expressing cells	16
New putative periodontopathogens and periodontal health‐associated species: A systematic review and meta‐analysis	16
Comparison of oxidative stress markers in the saliva, gingival crevicular fluid, and serum samples of pregnant women with gestational diabetes and healthy pregnant women	16
	16
Periodontitis Exacerbates Colorectal Cancer by Altering Gut Microbiota–Derived Metabolomics in Mice	16
Oxytocin alleviates periodontitis in adult rats	16
Cover Image	16
Issue Information	16
Bone Grafts: Everything You Need to Know	15
Association between Mediterranean diet and periodontitis among US adults: The mediating roles of obesity indicators	15
Issue Information	15
	15
Association between asthma and periodontitis: A case–control analysis of risk factors, related medications, and allergic responses	15
Epigenetic Regulation in the Pathogenesis of Periodontitis	15
Proanthocyanidin enhances the endogenous regeneration of alveolar bone by elevating the autophagy of PDLSCs	15

Effects of amoxicillin and metronidazole as an adjunct to scaling and root planing on glycemic control in patients with periodontitis and type 2 diabetes: A short‐term randomized controlled trial	15
Does smoking influence tryptophan metabolism in periodontal inflammation? A cross‐sectional study	15
Relationship between oral microbiota and colorectal cancer: A systematic review	15
Issue Information	15
Hepatocyte growth factor is protective in early stage but bone‐destructive in late stage of experimental periodontitis	14
The influence of different extraction indications on the morphological changes in the maxillary sinus: A retrospective cohort study	14
Inflammation Affects the Osteogenic Differentiation of Aged Periodontal Ligament Cells via NF ‐ κB	14
Hyperlipidemia impairs bone regeneration of closed bone defects and tooth extraction wounds in mice	14
Association of individual and combined exposures of 10 metals with periodontitis: Results from a large population‐based study	14
Multiomics Comparison of Proline‐Rich Peptide‐Enhanced Hyaluronic Acid Gels Versus Conventional Regenerative Materials: An Early Wound‐Healing Model	14
Effectiveness of novel oral hygiene instruction avoiding inattentional blindness using an application for unique plaque control record calculation: A randomized clinical trial	14
Extracellular Vesicles in Gingival Crevicular Fluid as Indicators of Periodontitis and Early Response to Non‐surgical Periodontal Therapy	14
Recombinant irisin enhances the extracellular matrix formation, remodeling potential, and differentiation of human periodontal ligament cells cultured in 3D	14
Effect of photobiomodulation with different wavelengths on periodontal repair in non‐hyperglycemic and hyperglycemic rats	14
Issue Information	14
Tumor Necrosis Factor Alpha‐Induced Protein 6 Suppresses Inflammation and Promotes Osteogenesis via Type H Vessels in Periodontitis	14
Accuracy of aMMP‐8 point‐of‐care test in indicating periodontal treatment outcomes in stage III/IV periodontitis: A 24‐week follow‐up study	13
Treatment Options for the Management of the Postextraction Socket: Report From the First Giuseppe Cardaropoli Foundation Consensus Conference	13
Autoimmunity and Periodontitis	13
Issue Information	13
Lipocalin 2, synthesized using a cell‐free protein synthesis system and encapsulated into liposomes, inhibits the adhesion of Porphyromonas gingivalis to human oral epithelial cells	13
Multiplexed LC‐MS/MS quantification of salivary RNA modifications in periodontitis	13
Periodontal pathogen Fusobacterium nucleatum infection accelerates hepatic steatosis in high‐fat diet‐fed ApoE	13
Porphyromonas gingivalis Translocation Along the Oral–Atrial Axis: A Microbial Contributor to Atrial Fibrosis and Atri	13
Target Trial Emulation in Observational Research—Strengths, Limitations, and Methodological Considerations	13
Melatonin promoted osteogenesis of human periodontal ligament cells by regulating mitochondrial functions through the translocase of the outer mitochondrial membrane 20	13
The effect of Porphyromonas gingivalis on the gut microbiome of mice in relation to aging	13
The Oral‐Gut Axis: Bidirectional Interactions Between Microbiome and Diseases	13
Microbiome of periodontitis and peri‐implantitis before and after therapy: Long‐read 16S rRNA gene amplicon sequencing	13
Periodontal disease and its association to endothelial dysfunction and clinical changes in limited systemic sclerosis: A case–control study	12
Risk of Bias Evaluation of Cross‐Sectional Studies: Adaptation of the Newcastle‐Ottawa Scale	12
TAM Pathway Receptor Proteins: Differential Expression in Healthy Human Masticatory Mucosa	12
Demystifying the connection between periodontal disease and chronic kidney disease – An umbrella review	12
Periodontal Prognosis: The Past, the Present, the Future	12
Cytokine responses of CD4+ T cells and NKT cells to periodontitis‐associated bacteria in individuals with or without periodontitis	12
DNA damage‐inducible transcript 3 deficiency promotes bone resorption in murine periodontitis models	12
Periodontitis and edentulism as risk indicators for mortality: Results from a prospective cohort study with 20 years of follow‐up	12
Cover Image	12
Lipotoxicity: The missing link between diabetes and periodontitis?	12
Peri‐implant crevicular fluid and serum levels of soluble ST2 in peri‐implant diseases: A pilot study	12
Selective outcome reporting bias is highly prevalent in randomized clinical trials of nonsurgical periodontal therapy	12
Development of a classification model and an immune‐related network based on ferroptosis in periodontitis	12
Platelet‐Rich Fibrins as Local Drug‐Delivery Carriers	12
Oral‐gut bacterial profiles discriminate between periodontal health and diseases	12
Issue Information	12
METTL3 promotes the osteogenic differentiation of human periodontal ligament cells by increasing YAP activity via IGF2BP1 and YTHDF1‐mediated m6	12
Treatment of periodontitis ameliorates the severity and extent of psoriasis—A randomized clinical trial	12
New Cover of the Journal of Periodontal Research—The Story Behind	12
Diagnostic Biomarkers of Periodontitis and Peri‐Implantitis: The Past, the Present, the Future	11
Limosilactobacillus reuteri ‐ Fusobacterium nucleatum Interactions Modu	11
Genetic Susceptibility to Periodontitis	11
	11
LncRNA JHDM1D‐AS1 promotes osteogenic differentiation of periodontal ligament cells by targeting miR‐532‐5p to activate IGF1R signaling	11
Comparison of Micro‐CT and Morphometric Outcomes in a Modified Experimental Rat Model of Periodontitis	11
High glucose promotes lipopolysaccharide‐induced macrophage pyroptosis through GSDME O‐GlcNAcylation	11
A Principled Framework for Mendelian Randomization in Oral Health Research	11
Enhancement of receptor‐mediated calcium responses by phenytoin through the suppression of calcium excretion in human gingival fibroblasts	11
Periodontal granulation tissue – To remove or not to remove, that is the question	11
Mobile Health to Improve Efficacy of Interdental Brushing Among Periodontitis Patients: A Randomized Clinical Trial	11
Dipotassium glycyrrhizate and hinokitiol enhance macrophage efferocytosis by regulating recognition, uptake, and metabolism of apoptotic cells in vitro	11
The impact of Resolvin E1 on bone regeneration in critical‐sized calvarial defects of rat model—A gene expression and micro‐CT analysis	11
Soft‐Tissue Integration of Dental Implants: Formation, Maintenance, and Relevance for Peri‐Implant Health	11
Prevalence and Risk Indicators of Peri‐Implant Diseases and Buccal Soft‐Tissue Dehiscence: A Cross‐Sectional Study From a University‐Based Cohort	11
Dental Implant Rehabilitation Mitigates the Increased Mortality Risk Associated With Tooth Loss: A Population‐Based Study	11
Adjunctive use of omega‐3 fatty acids in combination with low‐dose aspirin in periodontitis: Systematic review and meta‐analysis	11
EGF coating of titanium surfaces modulates cytokines in oral mucosal primary cells exposed to TNF‐α	11
Impact of Resolvin D1 on the inflammatory phenotype of periodontal ligament cell response to hypoxia	11
The role of mitochondrial dysfunction in periodontitis: From mechanisms to therapeutic strategy	11
The association between Aggregatibacter actinomycetemcomitansJP2 clone and periodontitis: A systematic review and meta‐analysis	10
Shifting Concepts in Esthetic‐Zone Implant Therapy: Reflections From a 15‐Year Institutional Registry	10
Proteomic Characterization of Grade II Furcation Defects: A Discovery‐Phase Study	10
Lip and Oral Cancer, Caries and Other Oral Conditions: Estimates From the 2021 Global Burden of Disease Study and Projections up to 2050	10
Cyclosporine A‐induced gingival overgrowth in renal transplant patients accompanied by epithelial‐to‐mesenchymal transition	10
The First 60 Years of the Journal of Periodontal Research : Celebrating the Transformation of Periodontics Into Periodontology	10
The Journey of Oral Hygiene: The Past, the Present, the Future	10
Oxidative stress‐related biomarkers in chronic periodontitis patients with or without type 2 diabetes: A systematic review and meta‐analysis	10
	10
BBR affects macrophage polarization via inhibition of NF‐κB pathway to protect against T2DM‐associated periodontitis	10
Cover Image	10
Caspase‐3 and gasdermin E mediate macrophage pyroptosis in periodontitis	10

Salivary E‐cadherin as a biomarker for diagnosis and predicting grade of periodontitis	10
Reviewers list 2023	9
Biomaterials for Reconstructive Treatment of Peri‐Implantitis	9
Risk Factors of Periodontitis: Evidence From Two‐Sample Mendelian Randomization and Meta‐Analysis	9
Issue Information	9
SIGIRR Inhibits Periodontitis‐Associated Inflammation and Promotes Regeneration by Blocking Sp1 Nuclear Translocation	9
Exosomal microRNA‐223 from neutrophil‐like cells inhibits osteogenic differentiation of PDLSCs through the cGMP‐PKG signaling pathway	9
Sclerostin deficiency effectively promotes bone morphogenetic protein‐2‐induced ectopic bone formation	9
‘ The Simpsons ’ Did It Again! Periodontitis and Tooth Loss Predict Mortality in Springfield: A Retrospective Cohort Study	9
Cannabidiol attenuates periodontal inflammation through inhibiting TLR4/NF‐κB pathway	9
Periodontal ligament cells from patients with treated stable periodontitis: Characterization and osteogenic differentiation potential	9
Geographic Influence on Subgingival Microbiota in Health and Periodontitis: A Multinational Shotgun Metagenomic Study	9
Minimally Invasive (MINST) Versus Conventional Non‐Surgical Therapy for Residual Pockets in Patients With Periodontitis: A Randomized Clinical Trial	9
Complement components C3b and C4b as potential reliable site‐specific diagnostic biomarkers for periodontitis	9
Periodontal ligament‐associated protein‐1 engages in teeth overeruption and periodontal fiber disorder following occlusal hypofunction	9
Soluble epoxide hydrolase inhibition impairs triggering receptor expressed on myeloid cells‐1 in periodontal tissue	9
Asymmetric and symmetric dimethylarginine gingival crevicular fluid levels in periodontitis	9
Regulation of RIP1‐Mediated necroptosis via necrostatin‐1 in periodontitis	9
Macrophage Efferocytosis Controls Tissue Repair via Mitochondrial Dynamics in Diabetic Periodontitis	9
The role of vitamin D in periodontal health and disease	8
Tartrate‐Resistant Acid Phosphatase‐Positive Cells: Putative Mediators of Peri‐Implant Bone Healing	8
Hydrogels in Periodontal and Craniofacial Regeneration: Current Applications and Next‐Generation Biomaterials	8
Circular RNA hsa_circ_0084054 promotes the progression of periodontitis with diabetes via the miR‐508‐3p/PTEN axis	8
Tooth mobility: The missing link?	8
Extracellular Vesicles From Dental Pulp Cells Promote Osteogenic Differentiation in Periodontal Ligament Cells	8
Nanoparticles in Periodontology and Implant Dentistry: From Mechanisms to Clinical Applications	8
Preventive effects of melatonin on periodontal tissue destruction due to psychological stress in rats with experimentally induced periodontitis	8
Timing of Re‐Evaluation After Periodontal Therapy: A Randomized Clinical Trial	8
Severe Periodontitis is Associated With Recurrent Cardiovascular Events—A 10‐Year Longitudinal Cohort Study	8
Peri‐Implant Diseases: The Past, the Present, the Future	8
Harnessing the Therapeutic Potential of Cell Secretomes and Extracellular Vesicles for Craniofacial Regenerative Applications	8
Tunnel Versus Coronally Advanced Flap for the Treatment of Localized Gingival Recessions: A Randomized Clinical Trial	8
Impaired autophagy flux by lncRNA NEAT1 is critical for inflammation factors production in human periodontal ligament stem cells with nicotine treatment	8
Diet‐derived circulating antioxidants, periodontitis and dental caries: A Mendelian randomization study	8
Association between defect morphology and healing of intrabony defects treated with minimally invasive non‐surgical therapy: A pilot exploratory analysis of two cohorts	8
Performance of three artificial intelligence (AI)‐based large language models in standardized testing; implications for AI‐assisted dental education	8
Histological Outcomes of Root Coverage Procedures: A Systematic Review With Meta‐Analysis	8
Accuracy of Freehand, Static, and Dynamic Computer‐Assisted Implant Placement: A Systematic Review and Meta‐Analysis	8
Smokeless tobacco and periodontitis: A systematic review with meta‐analysis	8
High glucose impairs human periodontal ligament cells migration through lowered microRNAs 221 and 222	8
Keratinized Mucosa Width and Incidence of Peri‐Implant Diseases: A Systematic Review With Meta‐Analysis	7
Integrative Human Genomic and Pharmacological Analyses Identify CACNB4 as a Druggable Target for Periodontitis	7
Issue Information	7
An in vitro study into three different PRF preparations for osteogenesis potential	7
Durumamide A Inhibits NLRP3 Assembly, Limiting Pro‐Inflammatory Signaling in Human Gingival Fibroblasts	7
Atypical antipsychotics olanzapine and clozapine increase bone loss in female rats with experimental periodontitis	7
Accuracy of Metabolomics in Peri‐Implant Crevicular Fluid for Diagnosis and Prognosis of Peri‐Implantitis	7
Disease recurrence during supportive therapy following peri‐implantitis treatment: A retrospective study	7
5‐FU Weakens Defensive Functions of the Junctional Epithelium	7
Hormone replacement therapy and periodontitis progression in postmenopausal women: A prospective cohort study	7
Burden of severe periodontitis and edentulism in 2021, with projections up to 2050: The Global Burden of Disease 2021 study	7
Soft‐Tissue Phenotype Modification as an Adjunct to the Treatment of Peri‐Implant Mucositis—A Quasi‐Randomized Clinical Trial	7
Issue Information	7
Micro‐needling versus acellular dermal matrix in RT1 gingival recession coverage: A randomized clinical trial	7
Molar–Incisor and Generalized Grade C Periodontitis: Distinct Microbiome–Immune Interactions Suggest Divergent Pathogenesis	7
Runx2 heterozygosity alters homeostasis of the periodontal complex	7
Welcome to the new protagonists of the Journal of Periodontal Research: Our Associate Editors and Editorial Board members!	7
Elucidation of common molecular diagnostic biomarkers between chronic periodontitis and Parkinson's disease via bioinformatics analyses	7
Effects of mechanical loading on matrix homeostasis and differentiation potential of periodontal ligament cells: A scoping review	7
Peri‐Implant Soft‐Tissue Phenotype Modification for Refractory Peri‐Implant Mucositis: A 12‐Month Prospective Clinical Study With Ultrasonographic Analysis	7
Periodontitis, Edentulism, and Risk of Metabolic Syndrome, Obesity, and Dyslipidemia: A Systematic Review With Meta‐Analyses	7
Influence of gender on periodontal outcomes: A retrospective analysis of eight randomized clinical trials	7
Effect of Connective Tissue Grafts in the Regenerative Treatment of Intrabony Defects: A Systematic Review and Meta‐Regression Analysis	7
The role of rhFGF‐2 in periodontal defect bone fill: A systematic review of the literature	6
Macrophage Phenotype Alterations in Treated Periodontitis Patients Suggest a Pro‐Inflammatory Bias	6
Variability in human tooth cementum thickness reflecting functional processes	6
Pre‐conditioning of gingival epithelial cells with sub‐apoptotic concentrations of curcumin prevents pro‐inflammatory cytokine release	6
Cover Image	6
Diet Quality as a Mediator Linking Tooth Loss and Cardiovascular Diseases in Older Adults	6
Umbelliferone reduces inflammation and ligature‐induced osteoclastic alveolar bone resorption in mice	6
	6
Issue Information	6
Viruses, Periodontitis, and Systemic Diseases	6
Local application of 0.8% hyaluronic acid gel as an adjunct to minimally invasive nonsurgical treatment of periodontal intrabony defects—A randomized clinical trial	6
Cementum and enamel surface mimicry influences soft tissue cell behavior	6
Issue Information	6
ScRNA‐seq links dental fibroblasts heterogeneity with mechanoresponsiveness	6
Characterization of oral biomarkers during early healing at augmented dental implant sites	6
Biological Responses to Biomaterials: Mechanisms and Opportunities for Enhanced Oral Tissue Regeneration	6
Periostin in the relation between periodontal disease and atherosclerotic coronary artery disease: A pilot randomized clinical study	6
Microgravity Exacerbates Periodontitis In Vivo	6
A grooved porous hydroxyapatite scaffold induces osteogenic differentiation via regulation of PKA activity by upregulating miR‐129‐5p expression	6
Limosilactobacillus reuteri supernatant attenuates inflammatory responses of human gingival fibroblasts to LPS but not to elevated glucose levels	6
Probiotics enhance alveolar bone microarchitecture, intestinal morphology and estradiol levels in osteoporotic animals	6
Porphyromonas gingivalis ‐Lipopolysaccharide Induced Gingival Fibroblasts Trained Immunity Sustains Inflammation in Periodontitis	6
Annual Incidence and Pre‐Treatment Prognostic Factors of Labial Gingival Recessions in Young Orthodontically Treated Patients	6
Periodontal Manifestations of Systemic Diseases	6
Impact of Tooth Preservation or Replacement on Diet Quality: Modified Treatment Policies Approach	6
Repercussions of Long‐Term Naproxen Administration on LPS‐Induced Periodontitis in Male Mice	6
Macrophage‐related gingival transcriptomic patterns and microbiome alterations in experimental periodontitis in nonhuman primates	6
Issue Information	6
Bidirectional associations between periodontitis and inflammatory bowel disease: A systematic review of longitudinal studies with meta‐analysis and trial sequential analysis	6
Periodontitis exacerbation during pregnancy in mice: Role of macrophage migration inhibitory factor as a key inductor	6
Periodontology: The Past, the Present, the Future	6
Preclinical Evaluation of a Poly (Lactic Acid/Caprolactone) Bilayer Membrane and a Carbonate Apatite for Periodontal Regeneration: A Canine One‐Wall Intrabony Defect Model	6