Periodontal disease and atherosclerosis from the viewpoint of the relationship between community periodontal index of treatment needs and brachial-ankle pulse wave velocity

Oral inflammatory load predicts vascular function in a young adult population: a pilot study

Background

The periodontium is a highly vascularized area of the mouth, and periodontitis initiates negative functional and structural changes in the vasculature. However, mild oral inflammation, including levels experienced by many apparently healthy individuals, has an unclear impact on cardiovascular function. The purpose of this pilot study is to investigate the effects of objectively measured whole mouth oral inflammatory load (OIL) on vascular function in apparently healthy individuals.

Methods

In this cross-sectional and correlational analysis, we recruited 28 young (18-30 years) and systemically healthy participants (16 male, 12 female). Using oral neutrophil counts, a validated measure for OIL, we collected participant's mouth rinse samples and quantified OIL. Blood pressure, arterial stiffness (pulse-wave velocity) and endothelial function (brachial artery flow-mediated dilation) were also measured.

Results

Only oral neutrophil count significantly predicted flow-mediated dilation % (p = 0.04; R2 = 0.16, β = - 1.05) and those with OIL levels associated with >2.5 × 105 neutrophil counts (n = 8) had a lower flow-mediated dilation % (6.0 ± 2.3%) than those with counts associated with gingival health with less than 2.5 × 105 neutrophil counts (10.0 ± 5.2%, p = 0.05). There were no significant predictors for arterial stiffness.

Conclusion

We found that OIL was a predictor of reduced flow-mediated dilation. An impairment in flow-mediated dilation is an indicator of future possible risk of cardiovascular disease-one of the leading causes of death in North America. Therefore, this study provides evidence for the importance of oral health and that OIL may impact endothelial function.

Association between periodontitis and pulse wave velocity: a systematic review and meta-analysis

OBJECTIVES

Severe periodontitis has been associated with endothelial dysfunction and arterial stiffness. The present study aimed to provide a critical appraisal and a meta-analysis of the literature investigating pulse wave velocity (PWV) in patients with and without severe periodontitis and to assess whether treatments influence PWV.

MATERIALS AND METHODS

English literature was searched on multiple databases up to April 2020 by two independent reviewers. Studies comparing PWV between patients with and without severe periodontitis or assessing the impact of periodontal treatments on PWV were searched and retrieved. Pool data analyses with random effect models were performed. The risk of bias was assessed using Newcastle-Ottawa Scale and RoB2 tools.

RESULTS

Seventeen studies were selected. Of these, 10 were used for the meta-analysis. Twelve were cross-sectional studies and 5 interventional studies, including 3176 patients, of whom 1894 had severe periodontitis and 1282 were considered as the controls (without severe periodontitis). Based on carotid-femoral PWV measurement, patients with severe periodontitis (n = 309) have a significantly higher PVW than patients with non-severe periodontitis (n = 213), with a mean difference of 0.84 m/s (95% CI 0.50-1.18; p < 0.0001; I² = 5%). Similarly, carotid-radial or brachial-ankle PWV values were significantly higher in patients with severe periodontitis. Results concerning the effect of non-surgical periodontal therapy were not conclusive. Overall, 9 studies (53%) were classified at a low risk of bias.

CONCLUSIONS

The present study demonstrates that patients with severe periodontitis have higher PWV compared to patients with non-severe periodontitis.

CLINICAL SIGNIFICANCE

Severe periodontitis is associated with arterial stiffness, supporting the mutual involvement of dentists and physicians.

Agrimonia pilosa Ledeb Root Extract: Anti-Inflammatory Activities of the Medicinal Herb in LPS-Induced Inflammation

Inflammation regulation is essential for maintaining healthy functions and normal homeostasis of the body. Porphyromonas gingivalis (P. gingivalis) is a gram-negative anaerobic bacterium and a major pathogen that causes oral inflammation and other systemic inflammations. This study aims to examine the anti-inflammatory effects of Agrimonia pilosa Ledeb root extracts (APL-ME) in Porphyromonas gingivalis LPS-induced RAW 264.7 cells and find anti-inflammatory effect compounds of APL-ME. The anti-inflammatory effects of APL-ME were evaluated anti-oxidant activity, cell viability, nitrite concentration, pro-inflammatory cytokines (interleukin-1[Formula: see text], interleukin-6, tumor necrosis factor (TNF)-[Formula: see text], and anti-inflammatory cytokine (interleukin-10 (IL-10)). Also, Inflammation related genes and proteins, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS), expression were decreased by APL-ME and mitogen-activated protein kinase (MAPK) signaling proteins expression was regulated by APL-ME. Liquid chromatography-mass spectrometer (LC/MS)-MS analysis results indicated that several components were detected in APL-ME. Our study indicated that APL-ME suppressed nitrite concentrations, pro-inflammatory cytokines such as IL-1[Formula: see text], IL-6 and TNF-[Formula: see text] in P. gingivalis LPS induced RAW 264.7 cells. However, IL-10 expression was increased by ALP-ME. In addition, protein expressions of COX-2 and iNOS were inhibited APL-ME extracts dose-dependently. According to these results, APL-ME has anti-inflammatory effects in P. gingivalis LPS induced RAW 264.7 cells.

Impact of anti-infective periodontal therapy on parameters of vascular health

AIM

This study assessed the impact of anti-infective periodontal therapy on the status of vascular health.

MATERIALS AND METHODS

Periodontal and vascular health of 55 patients with severe untreated chronic periodontitis was evaluated before and 12 months after anti-infective periodontal therapy. Observed parameters were bleeding on probing (BoP), pocket probing depth (PPD), periodontal inflamed surface area index (PISA), pulse wave velocity (PWV), augmentation index (AIx), central pulse pressure (PPao) and peripheral systolic pressure (RRsys).

RESULTS

ΔPISA (baseline-12 months) correlated with ΔPWV (τ 0.21; p < .03), ΔAIx (τ 0.29; p < .002) and ΔPPao (τ 0.23; p < .02). ΔBoP% (baseline-12 months) correlated with ΔPWV (τ 0.18; p < .05) and ΔAIx (τ 0.25; p < .01), while mean ΔPPD (baseline-12 months) correlated with ΔPWV (τ 0.24; p < .01) and ΔAIx (τ 0.21; p < .03). Grouping patients evenly into three groups based on tertiles of BoP resolution after 12 months revealed a significant decrease in the observed PWV median value by -0.6 m/s (p < .04) in the best response tertile (ΔBoP ≥ 88%). In the worst response tertile (ΔBoP ≤ 66%), by contrast, significant increase in PPao (+10.5 mmHg; p < .02) and AIx (+5.5; p < .02) was observed.

CONCLUSION

Efficacious resolution of periodontal inflammation may beneficially impact on vascular health.

Effects of periodontal treatment on carotid intima-media thickness in patients with lifestyle-related diseases: Japanese prospective multicentre observational study

Atherosclerosis, a chronic inflammatory disease in arterial blood vessels, is one of the major causes of death in worldwide. Meanwhile, periodontal disease is a chronic inflammatory disease caused by infection with periodontal pathogens such as P. gingivalis (Porphyromonas gingivalis). Several studies have reported association between periodontal infection and atherosclerosis, but direct investigation about the effects of periodontal treatment on atherosclerosis has not been reported. We have planned Japanese local clinics to determine the relationship between periodontal disease and atherosclerosis under collaborative with medical and dental care. A prospective, multicentre, observational study was conducted including 38 medical patients with lifestyle-related diseases in the stable period under consultation at participating medical clinics and 92 periodontal patients not undergoing medical treatment but who were consulting at participating dental clinics. Systemic and periodontal examinations were performed before and after periodontal treatment. At baseline, LDL-C (low-density lipoprotein cholesterol) levels and percentage (%) of mobile teeth were positively related to plasma IgG (immunoglobulin) antibody titer against P. gingivalis with multivariate analysis. Corresponding to improvements in periodontal clinical parameters after treatment, right and left max IMT (maximum intima-media thickness) levels were decreased significantly after treatment (SPT-S: start of supportive periodontal therapy, SPT-1y: at 1 year under SPT, and SPT-3y: at 3 years under SPT). The present study has clarified our previous univariate analysis results, wherein P. gingivalis infection was positively associated with progression of atherosclerosis. Thus, routine screening using plasma IgG antibody titer against P. gingivalis and periodontal treatment under collaborative with medical and dental care may prevent cardiovascular accidents caused by atherosclerosis.

Periodontitis and arterial stiffness: a systematic review and meta-analysis

INTRODUCTION AND AIMS

Patients with periodontitis have a higher risk of cardiovascular diseases, although a causal relationship between these conditions remains unclear. Arterial stiffness is considered a marker of arteriosclerosis and a risk factor for cardiovascular diseases. A systematic review of the literature on clinical studies using pulse wave velocity (PWV) to assess arterial stiffness in patients with periodontitis was carried out to answer the following questions: (i) Do patients with periodontitis have impaired arterial stiffness compared to non-periodontal diseased subjects? (ii) Is periodontal treatment effective as a means to improve arterial stiffness in patients with periodontitis?

LITERATURE REVIEW

Literature search was done on different databases up to September 2014. All clinical studies (excluding case reports) using PWV in patients with periodontitis were retrieved for a full-text evaluation. A total of 10 studies were included. Patients with periodontitis have increased arterial stiffness compared to controls (PWV mean difference 0.85 m/s; 95% confidence interval: 0.53-1.16; p<0.00001). The only two interventional studies showed contradictory results on the effects of periodontal treatment on PWV.

CONCLUSION

Patients with periodontitis appear to have higher values of PWV compared to controls. The effect of periodontal treatment on arterial stiffness remains unclear.

Arterial stiffness in periodontitis patients and controls. A case–control and pilot intervention study

Increased arterial stiffness (AS) is an important indicator for atherosclerotic cardiovascular disease (ACVD). Epidemiologically, periodontitis and ACVD are associated. Therefore, we aimed to investigate AS in periodontitis patients and controls. In addition, we explored the effect of periodontal therapy on AS in a sub-group of cases. Pulse-wave velocity (PWV), a non-invasive chair-side function test for AS, was measured in periodontitis patients (n=57; mean age 46.6 years) and compared with a reference group (n=48; mean age 45.5 years). In addition, 45 cases (mean age 46.9 years) were 6 months followed after periodontal treatment, to explore a possible effect on arterial function. Periodontitis patients showed a significantly increased PWV compared with the reference group (8.01±0.20 vs. 7.36±0.22 m s(-1) respectively; P=0.029) and this remained significant after adjustments for ACVD risk factors (P=0.019). After periodontal therapy, no significant reduction in PWV was seen (8.00±1.8 to 7.82±1.6 m s(-1); P=0.13), but systolic blood pressure (SBP) was significantly reduced (119.8±14.6 to 116.9±15.1 mm Hg; P=0.040). It can be concluded that periodontitis is associated with increased AS. This confirms with a new parameter the association of periodontitis with ACVD. Although periodontal treatment did not lower AS significantly, a modest reduction of SBP after 6 months was observed.

The Infection Hypothesis Revisited: Oral Infection and Cardiovascular Disease

Background. The pathophysiology of cardiovascular disease (CVD) includes inflammation in the development of atherosclerosis and thrombosis. Increasing evidence supports oral infections, and in particular the common periodontal disease, to be associated with CVD development. Periodontal infection is present in populations worldwide and in the moderate to mild form in about 35% of populations according to the World Health Organization. Objective. This review of the literature aims to present cross evidence from medical research disciplines that explore how oral infections can contribute to increase the risk for CVDs and how treatment of oral infections can reduce the risk for CVDs. Design. Review article. Results. Long-term exposure to active nontreated infections of the oral cavity presents an opportunity for bacteria, bacterial products, and viruses to enter the circulation. Toxic bacterial products enter the circulation, affecting atherosclerosis, causing platelet adhesiveness that results in clot formation, and establishing cardiac vegetation. Pathological observations have identified oral bacteria in heart valves, aortic aneurysms, and arterial walls. Clinical intervention studies on periodontal disease reduce the risk level of serological predictors for CVDs. Conclusions. This paper presents evidence across medical research disciplines for oral infections to be considered as one of the risk factors for CVDs.

Effect of periodontal therapy on arterial structure and function among aboriginal australians: a randomized, controlled trial

Observational studies and nonrandomized trials support an association between periodontal disease and atherosclerotic vascular disease. Both diseases occur frequently in Aboriginal Australians. We hypothesized that nonsurgical periodontal therapy would improve measures of arterial function and structure that are subclinical indicators of atherosclerotic vascular disease. This parallel-group, randomized, open label clinical trial enrolled 273 Aboriginal Australians aged ≥18 years with periodontitis. Intervention participants received full-mouth periodontal scaling during a single visit, whereas controls received no treatment. Prespecified primary end points measured 12-month change in carotid intima-media thickness, an indicator of arterial structure, and 3- and 12-month change in pulse wave velocity, an indicator of arterial function. ANCOVA used complete case data to evaluate treatment group differences. End points could be calculated for 169 participants with follow-up data at 3 months and 168 participants at 12 months. Intima-media thickness decreased significantly after 12 months in the intervention group (mean reduction=-0.023 [95% confidence interval {CI}, -0.038 to -0.008] mm) but not in the control group (mean increase=0.002 [95% CI, -0.017 to 0.022] mm). The difference in intima-media thickness change between treatment groups was statistically significant (-0.026 [95% CI, -0.048 to -0.003] mm; P=0.03). In contrast, there were no significant differences between treatment groups in pulse wave velocity at 3 months (mean difference, 0.06 [95% CI, -0.17 to 0.29] m/s; P=0.594) or 12 months (mean difference, 0.21 [95% CI, -0.01 to 0.43] m/s; P=0.062). Periodontal therapy reduced subclinical arterial thickness but not function in Aboriginal Australians with periodontal disease, suggesting periodontal disease and atherosclerosis are significantly associated.

Carvedilol decrease IL-1β and TNF-α, inhibits MMP-2, MMP-9, COX-2, and RANKL expression, and up-regulates OPG in a rat model of periodontitis

Periodontal diseases are initiated primarily by Gram-negative, tooth-associated microbial biofilms that elicit a host response that causes osseous and soft tissue destruction. Carvedilol is a β-blocker used as a multifunctional neurohormonal antagonist that has been shown to act not only as an anti-oxidant but also as an anti-inflammatory drug. This study evaluated whether Carvedilol exerted a protective role against ligature-induced periodontitis in a rat model and defined how Carvedilol affected metalloproteinases and RANKL/RANK/OPG expression in the context of bone remodeling. Rats were randomly divided into 5 groups (n = 10/group): (1) non-ligated (NL), (2) ligature-only (LO), and (3) ligature plus Carvedilol (1, 5 or 10 mg/kg daily for 10 days). Periodontal tissue was analyzed for histopathlogy and using immunohistochemical analysis characterized the expression profiles of MMP-2, MMP-9, COX-2, and RANKL/RANK/OPG and determined the presence of IL-1β, IL-10 and TNF-α, myeloperoxidase (MPO), malonaldehyde (MDA) and, glutathione (GSH). MPO activity in the group with periodontal disease was significantly increased compared to the control group (p<0.05). Rats treated with 10 mg/kg Carvedilol presented with significantly reduced MPO and MDA concentrations (p<0.05) in addition to presenting with reduced levels of the pro-inflammatory cytokines IL-1 β and TNF-α (p<0.05). IL-10 levels in Carvedilol-treated rats remained unaltered. Immunohistochemical analysis demonstrated reduced expression of MMP-2, MMP-9, RANK, RANKL, COX-2, and OPG in rats treated with 10 mg/kg Carvedilol. This study demonstrated that Carvedilol affected bone formation/destruction and anti-inflammatory activity in a rat model of periodontitis.

Association of periodontitis with carotid artery intima-media thickness and arterial stiffness in community-dwelling people in Japan: the Nagasaki Islands study

OBJECTIVE

Recent studies have suggested an association between periodontitis and atherosclerosis; however, the relationship between periodontal status and arterial alterations should be clarified. The purpose of this study was to examine associations between periodontal status and carotid intima-media thickness (cIMT) and arterial stiffness using the cardio-ankle vascular index (CAVI) in community dwellers.

METHODS

A community-based cross-sectional study of 1053 subjects ≥40 years with 10 teeth or more was conducted in Goto, Japan from 2008 to 2010.

RESULTS

In a multiple linear regression analysis adjusted for age, sex, number of present teeth, and other confounders, each 1-mm increase in mean periodontal pocket depth corresponded to a 0.02-mm increase in maximal cIMT (β = 0.018; P = 0.049) and also to a 0.1 increase in mean CAVI (β = 0.133; P = 0.040). In addition, each 1-mm increase in the mean periodontal attachment loss corresponded to a 0.01-mm increase in maximal cIMT (β = 0.013; P = 0.040). A multiple logistic regression analysis revealed that each 1-mm increase in mean periodontal pocket depth was associated with an increased risk of a maximal cIMT >1 mm (adjusted odds ratio [OR], 1.430; 95% confidence interval [CI], 1.067-1.918; P = 0.017) and mean CAVI of ≥8 (OR, 1.323; 95% CI, 1.003-1.743; P = 0.047). Furthermore, each 1-mm increase in mean periodontal attachment loss was associated with an increased risk of a maximal cIMT >1 mm (OR, 1.251; 95% CI, 1.032-1.516; P = 0.022).

CONCLUSION

A linear, dose-dependent relationship was found between periodontal pocket depth, cIMT, and arterial stiffness.

Tenomodulin expression in the periodontal ligament enhances cellular adhesion

Tenomodulin (Tnmd) is a type II transmembrane protein characteristically expressed in dense connective tissues such as tendons and ligaments. Its expression in the periodontal ligament (PDL) has also been demonstrated, though the timing and function remain unclear. We investigated the expression of Tnmd during murine tooth eruption and explored its biological functions in vitro. Tnmd expression was related to the time of eruption when occlusal force was transferred to the teeth and surrounding tissues. Tnmd overexpression enhanced cell adhesion in NIH3T3 and human PDL cells. In addition, Tnmd-knockout fibroblasts showed decreased cell adhesion. In the extracellular portions of Tnmd, the BRICHOS domain or CS region was found to be responsible for Tnmd-mediated enhancement of cell adhesion. These results suggest that Tnmd acts on the maturation or maintenance of the PDL by positively regulating cell adhesion via its BRICHOS domain.

Longitudinal displacement of the carotid wall and cardiovascular risk factors: associations with aging, adiposity, blood pressure and periodontal disease independent of cross-sectional distensibility and intima-media thickness

The recently discovered longitudinal displacement of the common carotid arterial wall (i.e., the motion along the same plane as the blood flow), may be associated with incident cardiovascular events and represents a novel and relevant clinical information. At present, there have only been a few studies that have been conducted to investigate this longitudinal movement. We propose here a method to assess noninvasively the wall bi-dimensional (two-dimensional [2-D], cross-sectional and longitudinal) motion and present an original approach that combines a robust speckle tracking scheme to guidance by minimal path contours segmentation. Our method is well suited to large clinical population studies as it does not necessitate strong imaging prerequisites. The aim of this study is to describe the association between the longitudinal displacement of the carotid arterial wall and cardiovascular risk factors, among which periodontal disease. Some 126 Indigenous Australians with periodontal disease, an emerging risk factor, and 27 healthy age- and sex-matched non-indigenous control subjects had high-resolution ultrasound scans of the common carotid artery. Carotid intima-media thickness and arterial wall 2-D motion were then assessed using our method in ultrasound B-mode sequences. Carotid longitudinal displacement was markedly lower in the periodontal disease group than the control group (geometric mean (IQR): 0.15 mm (0.13) vs. 0.42 mm (0.30), respectively; p < 0.0001), independent of cardiovascular risk factors, cross-sectional distensibility and carotid intima-media thickness (p < 0.0001). A multivariable model indicated that the strongest correlates of carotid longitudinal displacement in adults with periodontal disease were age (β-coefficient = -.235, p = .03), waist (β-coefficient = -.357, p = 0.001), and pulse pressure (β-coefficient = .175, p = 0.07), independent of other cardiovascular risk factors, cross-sectional distensibility and pulse wave velocity. Carotid longitudinal displacement, estimated with our approach, is impaired in the periodontal disease group, independent of established cardiovascular risk factors and other noninvasive measures of arterial stiffness, and may represent an important marker of cardiovascular risk.

Periodontal disease severity and urinary albumin excretion in middle-aged hypertensive patients

To address whether periodontal disease indexes are associated with urinary albumin-to-creatinine ratio (UACR) in conditions of high and low systemic inflammation as reflected by levels of high-sensitivity C-reactive protein (hs-CRP) in untreated hypertensive patients, we studied 242 hypertensive patients 51 ± 9 years old (24-hour systolic/diastolic blood pressure [BP] 132 ± 10/83 ± 8 mm Hg) with varying severity of periodontal disease evaluated by 3 periodontal disease indexes (PDIs) (i.e., mean clinical loss of attachment, maximum probe depth, and gingival bleeding index). Patients underwent BP measurements, echocardiography, and periodontal examination, and from fasting blood samples we assessed metabolic profile and hs-CRP. From 2 nonconsecutive overnight spot urine samples we evaluated UACR. With respect to median hs-CRP and UACR levels (1.67 mg/L and 10 mg/g, respectively), the total population was divided into patients with low-UACR/low-hs-CRP (n = 65), low-UACR/high-hs-CRP (n = 63), high-UACR/low-hs-CRP (n = 51), and high-UACR/high-hs-CRP (n = 63). PDIs differed among the 4 groups, and those with high UACR had significantly higher 24-hour systolic BP compared to those with low UACR. UACR was determined by all periodontal disease indexes, hs-CRP, and the interaction of each periodontal disease index with hs-CRP. In addition, mean clinical loss of attachment was the strongest determinant of the high-UACR/high-hs-CRP pattern among all studied periodontal disease indexes. In conclusion, in untreated middle-aged hypertensive patients, periodontal disease indexes and hs-CRP have a synergistic effect on UACR levels independently of the underlying hemodynamic load.

Cardiovascular disease and periodontitis: an update on the associations and risk

BACKGROUND

Associations between periodontitis and cardiovascular diseases have been recognized.

MATERIAL AND METHODS

New literature since the last European Workshop on Periodontology has been reviewed.

RESULTS

The lack of reliable epidemiological data on disease prevalence makes an assessment of the associations and risks between periodontitis and cardiovascular diseases difficult. Two recent meta-analysis reports have identified associations between periodontitis and cardiovascular diseases (odds ratios: 1.1-2.2). Different surrogate markers for both disease entities, including serum biomarkers, have been investigated. Brachial artery flow-mediated dilatation, and carotid intima media thickness have in some studies been linked to periodontitis. Studies are needed to confirm early results of improvements of such surrogate markers following periodontal therapy. While intensive periodontal therapy may enhance inflammatory responses and impair vascular functions, studies are needed to assess the outcome of periodontal therapies in subjects with confirmed cardiovascular conditions. Tooth eradication may also reduce the systemic inflammatory burden of individuals with severe periodontitis. The role of confounders remain unclear.

CONCLUSIONS

Periodontitis may contribute to cardiovascular disease and stroke in susceptible subjects. Properly powered longitudinal case-control and intervention trials are needed to identify how periodontitis and periodontal interventions may have an impact on cardiovascular diseases.

Association between vitamin D receptor gene haplotypes and chronic periodontitis among Japanese men

BACKGROUND

The vitamin D receptor (VDR) is involved in a variety of biological processes, such as bone metabolism and modulation of the immune response. Recent findings suggest that the pathway involving bone mineral density-mediated effects is important for the development of periodontitis, but their effects of combined VDR gene polymorphisms have not been confirmed on periodontitis. We assessed the relationship between ApaI, BsmI, and FokI VDR polymorphisms and the risk of severe chronic periodontitis among Japanese adult men.

MATERIALS AND METHODS

In a cross-sectional study, we examined 97 unrelated healthy Japanese men (mean age: 45.6 years, range: 22-59). A clinical examination was performed at a worksite health checkup, and information was obtained using a self-reported questionnaire. DNA was extracted from whole blood, and the VDR ApaI, BsmI, and FokI polymorphisms were genotyped using polymerase chain reaction.

RESULTS

F-carriers of FokI VDR polymorphisms were less likely to develop severe chronic periodontitis than non-F-carriers (p = 0.09). The ApaI and BsmI VDR polymorphisms did not show significant differences in the alleles or genotypes between the subjects with or without severe chronic periodontitis. The haplotype analysis of the three combined VDR polymorphisms revealed that the Abf homozygote had a notably higher prevalence of severe chronic periodontitis than the others, and adjustments for age, smoking status, number of teeth present, and prevalence of diabetes did not change this association (OR = 7.5; 95% CI = 1.6-34.4; p = 0.01).

CONCLUSION

The VDR haplotype constructed from the ApaI, BsmI, and FokI polymorphisms is related to the risk of severe chronic periodontitis in Japanese men.