Testing the association between tobacco smoking, alcohol consumption, and risk of periodontitis: A Mendelian randomization study

Depression, stress-related disorders and risk for dental caries and periodontitis: A bidirectional and multivariable Mendelian randomization study

AIMS

Our Mendelian randomization (MR) analysis focused on investigating the bidirectional relationships between major depressive disorder (MDD), anxiety and stress-related disorder (ASRD), and dental caries as well as periodontitis.

MATERIALS AND METHODS

We used summary statistics from two studies: an MDD genome-wide association study (GWAS) including 135,458 cases with 344,901 controls and a Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH) GWAS based on 12,655 ASRD individuals and 19,225 controls from Denmark. GWASs on dental caries and periodontitis were based on the Gene-Lifestyle Interactions in Dental Endpoints (GLIDE) consortium. We employed different MR approaches, such as inverse-variance weighted (IVW), MR-Egger, weighted median, and MR-PRESSO, to calculate causal effects.

RESULTS

Single-variable MR analysis revealed that ASRD was potentially significantly associated with decayed, missing, and filled tooth surfaces (DMFS) (β = 0.056; 95 % CI: 0.009, 0.103; p = 0.018). Periodontitis was suggested to be causally related to increased ASRD risk (OR = 1.143, 95 % CI: 1.008, 1.298; p = 0.038). According to the multivariable MR analysis, no significant associations were detected between MDD and ASRD with dental caries and periodontitis, and vice versa.

CONCLUSIONS

ASRD demonstrated a potential association with DMFS, and periodontitis was found to potentially impact ASRD according to single-variable MR analysis. Nevertheless, no significant associations were identified between MDD, ASRD, dental caries, or periodontitis after adjusting for smoking status and education level. Hence, more robust genetic instruments are required to validate and reinforce our findings.

Role of CD86 on granulocyte in mediating the effect of Genus Roseburia on periodontitis

OBJECTIVES

This study aimed to explore the causal link between the gut microbiota and periodontitis, and to delineate and quantify the intermediary role of immune cells, so as to provide new insights into the pathogenesis, prevention and treatment of periodontitis.

MATERIALS AND METHODS

We employed a two-sample Mendelian randomization (MR) approach to analyze the genetic predictors of gut microbiota composition (covering 412 gut microbiota taxa and functions) and periodontitis (involving 4,784 cases and 272,252 controls) derived from genome-wide association study (GWAS) datasets. A subsequent two-step MR analysis was conducted to evaluate the extent to which immune cell traits (encompassing 731 immune cell characteristics) mediate the influence of gut microbiota on periodontitis risk.

RESULTS

Our analysis implicated nine gut microbiota taxa as causal factors in periodontitis susceptibility (p < 0.05). Notably, the Genus Roseburia was identified as exerting a protective effect against periodontitis, partially mediated through the upregulation of CD86 expression on granulocytes, with an 8.15% mediation effect observed.

CONCLUSIONS

Our findings establish a causal relationship between the gut microbiota and periodontitis, highlighting the protective role of Roseburia against this condition. A notable proportion of this protective effect is mediated via the upregulation of CD86 on granulocytes.

CLINICAL RELEVANCE

It can provide new ideas for the pathogenesis, prevention and treatment for periodontitis through exploring the causal link between the gut microbiota and periodontitis, and describing and quantifying the intermediary role of immune cells.

Healthy lifestyles ameliorate an increased risk of periodontitis associated with polycyclic aromatic hydrocarbons

The risk of chronic inflammatory diseases has been linked to exposure to polycyclic aromatic hydrocarbons (PAHs). However, limited data are available regarding their impact on periodontitis. This study aims to explore the association between PAHs and periodontitis while also evaluating the potential modifying effects of healthy lifestyles. We included 17,031 participants from the US National Health and Nutrition Examination Survey (NHANES, 2001-2004 and 2009-2014). A meta-analysis-based environment-wide association study (EWAS) was adopted to identify environmental chemicals for the mean probing pocket depth (PPD) and the mean attachment loss (AL). PAHs were further evaluated concerning the cross-sectional association with Mod/Sev periodontitis using multivariable logistic regression models. Moreover, healthy lifestyle scores were estimated to assess their modifying effect on the PAH-periodontitis association. EWAS analysis identified several urinary PAH metabolites as significant risk factors for the mean PPD and AL (false discovery rate <0.05, Q > 0.05). Periodontitis severity was positively associated with eight individual and total PAH concentrations. Stratifying the participants in terms of healthy lifestyle scores did not reveal any association in the healthy group. Moreover, the association weakened in never-smokers and individuals with sufficient physical activity and normal weight. PAH exposure was a risk factor for periodontitis. A healthier lifestyle was observed to offset the risk potentials of PAHs for periodontitis. Smoking cessation, physical activity, and weight loss might be recommended as a healthy lifestyle strategy for ameliorating PAH-related periodontitis.

Mendelian randomization studies of periodontitis: Understanding benefits and natural limitations in an applied context

Mendelian randomization (MR) is a flexible analytical tool that has been widely applied to strengthen causal inference in observational epidemiology and is now gaining attention in many areas including periodontal research. The interpretation of results drawn from MR is based on a series of assumptions, which can be unrealistic or difficult to meet faithfully in some settings. However, we argue that with care, this does not necessarily prevent valuable deployment of the approach. We argue that clarity of presentation as well as careful assessment of specific analytical conditions is a fundamental part of all MR analyses. To that end, awareness of its limitations should also guide the design of MR investigations and the presentation of results rather than rule out its use altogether. Notably, considerations similar to those known to be important in conventional epidemiological settings apply to MR. While MR studies are valuable in their contrast to other study limitations, the application of this technique must be carefully cross-examined. Specific considerations include possible confounders, recruitment strategy and phenotypic measurement and differential analysis properties across studies. In the case of periodontal research, current MR applications are limited by the available evidence base for genetic contributions to periodontitis; however, this sets a specific scene for the strategic use of MR and shines light on a need for greater research emphasis on the genetics of the condition and intermediaries. This article provides a perspective on the uses and inherent limitations of MR studies and the importance of adhering to basic epidemiological principles when designing them.

Prevalence of self-reported severe periodontitis: Data from the population-based CONSTANCES cohort

AIM

To assess the prevalence of severe periodontitis based on the population-based CONSTANCES cohort using a validated self-reported questionnaire.

MATERIALS AND METHODS

Individuals were selected from the adult population in France using a random sampling scheme. Analyses were restricted to those invited in 2013-2014 who completed the periodontal health questionnaire at the 2017 follow-up. The risk of severe periodontitis was assessed using the periodontal screening score (PESS) and weighting coefficients were applied to provide representative results in the general French population.

RESULTS

The study included 19,859 participants (9204 men, mean age: 52.8 ± 12.6 years). Based on a PESS ≥ 5, 7106 participants were at risk of severe periodontitis, corresponding to a weighted prevalence of 31.6% (95% confidence interval: 30.6%-32.7%). This prevalence was higher among participants aged 55 and over, those with lower socio-economic status as well as current smokers, e-cigarette users and heavy drinkers. Among individuals at risk of severe periodontitis, only 18.8% (17.3%-20.4%) thought they had gum disease, although 50.5% (48.6%-52.5%) reported that their last dental visit was less than 6 months.

CONCLUSIONS

The present survey indicates that (1) self-reported severe periodontitis is highly prevalent with marked disparities between groups in the general French adult population, and (2) periodontitis could frequently be under-diagnosed given the low awareness.

Association of lifestyle behaviors and oral health care needs: Mediating effects of inflammatory markers

OBJECTIVE

Mounting evidence indicates that modifiable risk factors such as lifestyle behaviors may be involved in the occurrence of oral diseases. However, existing research doesn't come to a unanimous consent. This study aims to evaluate the association between lifestyle behaviors and oral health care needs.

METHODS

This study used the nationally representative dataset from the National Health and Nutrition Examination Survey (NHANES) from March 2017 to 2020 pre-pandemic. Binary logistic regression analysis was used to evaluate lifestyle behavioral factors that influence oral health care needs. Mediation analysis was performed to explore the roles of inflammatory markers in the relationship between physical activities and oral problems.

RESULTS

After adjusting for covariates, multivariate analysis indicated that flossing (OR = 0.590, 95% CI, 0.510-0.682, P < 0.001), moderate alcohol consumption (per week: OR = 0.717, 95% CI, 0.588-0.873, P < 0.001; per month/year: OR = 0.794, 95% CI, 0.669-0.942, P = 0.008) and participation in recreational activities (vigorous recreational activities: OR = 0.548, 95% CI, 0.462-0.648, P < 0.001; moderate recreational activities: OR = 0.629, 95% CI, 0.549-0.721, P < 0.001) significantly reduced oral health care needs. In addition, sleep duration of 7-9 h was associated with lower oral health care needs compared to less or more sleep duration (<7 h or > 9 h) (OR = 0.851, 95% CI, 0.741-0.976, P = 0.021). Mediation analysis suggested that white blood cell (WBC) counts and high-sensitivity C-reactive protein (hs-CRP) concentrations acted significant mediating roles in the association between recreational activities and oral problems.

CONCLUSIONS

The possible beneficial effects of healthy lifestyle behaviors on oral health will guide individuals to develop good habits, thereby reducing the burden of oral diseases.

The relationship between periodontal disease and gastric cancer: A bidirectional Mendelian randomization study

BACKGROUND

Previous observational studies have suggested a possible association between periodontal disease and gastric cancer (GC); however, a causal relationship has not yet been established. This study aimed to explore the causal relationship between the 2 through a 2-sample bidirectional Mendelian randomization (MR) study.

METHODS

Genome-wide association studies (GWAS) summary statistics were obtained from publicly available GWAS and relevant databases. Two-sample bidirectional MR analysis was conducted to investigate the causal relationship between periodontal disease and GC using the inverse-variance weighted (IVW) method selected as the primary analytical approach. Cochran Q test, MR-PRESSO, MR-pleiotropy, and leave-one-out analyses were performed to assess heterogeneity, pleiotropy, and sensitivity.

RESULTS

In European ancestry, IVW analysis revealed no causal relationship between periodontal disease and GC (OR = 1.873; 95% CI [4.788e-10, 7.323e + 09]; P = .956), or between loose teeth and GC (OR = 1.064; 95% CI [0.708, 1.598]; P = .765). In East Asian ancestry, there was no causal relationship between periodontitis and GC according to IVW (OR = 0.948; 95% CI [0.886, 1.015]; P = .126). Conversely, according to the results of the IVW analysis, there was no causal relationship between GC and periodontal disease, regardless of European or East Asian ancestry. Furthermore, there was no heterogeneity or pleiotropy in the causal relationships between these variables (all P > .05), suggesting a certain level of reliability in our results.

CONCLUSION

Within the limitations of this MR study, we found no mutual causal relationship between periodontal disease and GC. This finding can prevent overtreatment by clinical physicians and alleviate the psychological burden on patients.

The effect of air pollution exposure on the risk of outpatient visits for periodontitis: a time-series study

This study aimed to determine if air pollution affected the risk of periodontitis outpatient visits. We collected the records of 56,456 periodontitis outpatient visits in Hefei, China, from January 1, 2014 to December 31, 2021. The relationship between air pollution and periodontitis outpatient visits was evaluated using distributed lag nonlinear and generalized linear models. Additional analyses were performed, stratifying the data by age, season, and sex. Subgroup analyses showed a significantly higher risk of periodontitis outpatient visits due to NO2 exposure during the warm season compared with the cold season. Moreover, O3 exposure was associated with a lower risk of periodontitis outpatient visits in the cold season. The findings suggest that NO2 exposure is associated with an increased risk of periodontitis outpatient visits, whereas O3 exposure is associated with a decreased risk of periodontitis outpatient visits. Season is found to be an effect modifier in these associations.

The Alcohol Harm Paradox in Periodontitis

Individuals of lower socioeconomic position (SEP) experience a greater rate of alcohol-related harms, yet they consume equal or lower amounts of alcohol than higher-SEP individuals. This phenomenon, called the "alcohol harm paradox" (AHP), gained attention recently, and different mechanisms have been proposed to explain it. Since both SEP and alcohol have been suggested to be associated with periodontitis risk, we conducted a secondary analysis using data from the National Health and Nutrition Examination Survey 2011 to 2012 and 2013 to 2014 cycles, aiming to examine 1) whether the association between alcohol consumption and periodontitis is modified by SEP and 2) the extent to which the effect of SEP inequalities on periodontitis is mediated by and/or interacts with alcohol consumption. We set educational attainment as the main SEP proxy and tested the poverty income ratio in subsequent sensitivity analyses. Effect measure modification analysis was employed, considering heavy drinking as exposure, and causal mediation analysis based on the potential outcome's framework decomposed the effect of SEP on periodontitis in proportions attributable to mediation and interaction. Models were fitted using binary logistic regression and adjusted for sex, ethnicity, age, body mass index, smoking status, diabetes, binge drinking, and regular preventive dental visits. The analytical sample comprised 4,057 participants. After adjusting for covariates, less educated heavy drinkers presented 175% (odds ratio, 2.75; 95% confidence interval [CI], 2.04-3.72) higher odds of periodontitis than their counterparts, and super-additive associations were found (relative excess risk due to interaction: 1.35; 95% CI, 0.49-2.20). Additionally, -69.5% (95% CI, -122.1% to -16.8%) of the effects of education on periodontitis were attributable to interaction with heavy drinking, consistent with the AHP. No contribution was found for the mechanism of mediation. Heavy drinking disproportionately impacts the occurrence of periodontitis in lower-SEP individuals. Lower-SEP individuals seem to experience differential effects of heavy drinking on periodontitis.

Alcohol and Periodontal Disease: A Narrative Review

The scientific literature dealing with alcohol and alcoholic beverages revealed that these drinks possess an adverse impact on periodontal tissues. Additionally, other principal risk factors include tobacco, smoking, poor oral hygiene, etc. It has been observed that among chronic alcoholics, there are further issues, such as mental, social, and physical effects, that promote alcoholism. These people may have weak immunity for defense against pathogenic organisms and bacteria. Thus, chances of gingival bleeding, swollen gums, bad breath, and increased bone loss are there. Different alcoholic beverages in the market cause less salivation; these beverages contain sugars that promote acid production in the oral cavity by pathogens that demineralize the enamel and damage gum and teeth. This chronic alcohol consumption can progress into different types of oral disorders, including cancer, halitosis, and caries, and is also associated with tobacco and smoking. Chronic alcohol consumption can cause alteration of the oral microbiome and increase oral pathogens, which lead to periodontal disease and an environment of inflammation created in the body due to malnutrition, diminished immunity, altered liver condition, brain damage, and gut microbiota alteration. Heavily colored alcoholic beverages produce staining on teeth and, due to less saliva, may cause other toxic effects on the periodontium. Over-dependency on alcohol leads to necrotizing lesions such as necrotizing gingivitis, necrotizing periodontitis, and necrotizing stomatitis. These pathological impairments instigate severe damage to oral structures. Therefore, proper counseling by the attending dental surgeon and related health professionals is urgently required for the patient on the basis that the individual case needs to go away from the regular heavy consumption of alcohol.

Association Between Periodontitis and Adverse Pregnancy Outcomes: Two-Sample Mendelian Randomisation Study

AIM

This Mendelian randomisation (MR) study endeavoured to delineate the causal relationship between periodontitis and adverse pregnancy outcomes (APOs), encompassing low birthweight (LBW), pre-term birth (PTB), stillbirth, miscarriage, and gestational hypertension (GH).

METHODS

Utilising genetic instruments for periodontitis (acute and chronic periodontitis) from the Genome-Wide Association Study (GWAS) database among individuals of European descent, this study explored the causal relationship with adverse pregnancy outcomes, and vice versa. The Inverse Variance Weighted (IVW) method was employed as the primary analytical approach to assess causality, with MR-Egger serving as a sensitivity analysis method.

RESULTS

The primary analytical method employed in this study, IVW, did not reveal any impact of periodontitis (acute and chronic periodontitis) on PTB, stillbirth, miscarriage, and gestational hypertension, and vice versa. Heterogeneity testing using the MR-Egger method confirmed the null causal hypothesis, with odds ratios (OR) approximating 1, and P-values exceeding 0.05. Notably, the results from the IVW analysis (OR 1.410, CI 1.039-1.915, P-value 0.028) indicate statistically significant evidence supporting a causal relationship between chronic periodontitis and LBW. However, caution is advised in interpreting the causal relationship, considering the non-significant P-values obtained from other methods.

CONCLUSION

Within the limitations of this MR study, the findings do not support the influence of periodontitis on LBW, PTB, stillbirth, miscarriage, and GH, nor vice versa.

Alcohol Exposure and Disease Associations: A Mendelian Randomization and Meta-Analysis on Weekly Consumption and Problematic Drinking

Alcohol consumption significantly impacts disease burden and has been linked to various diseases in observational studies. However, comprehensive meta-analyses using Mendelian randomization (MR) to examine drinking patterns are limited. We aimed to evaluate the health risks of alcohol use by integrating findings from MR studies. A thorough search was conducted for MR studies focused on alcohol exposure. We utilized two sets of instrumental variables-alcohol consumption and problematic alcohol use-and summary statistics from the FinnGen consortium R9 release to perform de novo MR analyses. Our meta-analysis encompassed 64 published and 151 de novo MR analyses across 76 distinct primary outcomes. Results show that a genetic predisposition to alcohol consumption, independent of smoking, significantly correlates with a decreased risk of Parkinson's disease, prostate hyperplasia, and rheumatoid arthritis. It was also associated with an increased risk of chronic pancreatitis, colorectal cancer, and head and neck cancers. Additionally, a genetic predisposition to problematic alcohol use is strongly associated with increased risks of alcoholic liver disease, cirrhosis, both acute and chronic pancreatitis, and pneumonia. Evidence from our MR study supports the notion that alcohol consumption and problematic alcohol use are causally associated with a range of diseases, predominantly by increasing the risk.

Modifiable factors for benign salivary gland neoplasms: A Mendelian randomization study

BACKGROUND

Observational studies have found associations between smoking, alcohol, radiation, body mass index (BMI), periodontitis, and the hazard of benign salivary gland neoplasms (BSGNs). Nevertheless, the etiology of BSGNs remains unclear. This study aims to assess the causal association between these modifiable factors and the BSGNs.

METHODS

Genetic instruments associated with exposures at the genome-wide significance level were selected from corresponding genome-wide association studies. The summary statistics for BSGNs were obtained from the FinnGen consortium (2445 cases and 340,054 controls). The inverse variance-weighted method was used as the primary analysis, and several sensitivity analyses were performed to test the reliability.

RESULTS

Genetically predicted higher lifetime smoking index (odds ratio [OR] = 2.10, p = 0.012) and BMI (OR = 1.58, p = 2.29 × 10-5) were associated with elevated risk of BSGNs, whereas other exposures do not. Sensitivity analyses showed consistency. The causal effect of the lifetime smoking index became more significant after adjusting for BMI (OR = 2.89, p = 0.005) and alcohol consumption (OR = 2.49, p = 0.002). A slight negative association emerged for alcohol consumption with adjustment for cigarettes per day (OR = 0.53, p = 0.034) but disappeared when adjusting for cigarettes per day and BMI.

CONCLUSION

This study supports the independent causal role of lifetime smoking index and BMI in BSGNs risk.

NHANES-based analysis of the correlation between leisure-time physical activity, serum cotinine levels and periodontitis risk

OBJECTIVE

To investigate the association of leisure-time physical activity and serum cotinine levels with the risk of periodontitis in the general population and to further analyze the interaction between leisure-time physical activity and serum cotinine levels on the risk of periodontitis.

METHODS

This was a cross-sectional study, extracting data from 9605 (56.19%) participants in the National Health and Nutrition Examination Survey (NHANES) database from 2009 to 2014, and analyzing the relationship and interaction effects of serum cotinine level, leisure time physical activity, and risk of periodontitis by weighted univariate logistic modeling; Effect sizes were determined using ratio of ratios (OR), 95% confidence intervals (95% CI).

RESULTS

5,397 (56.19%) of 9,605 participants had periodontitis; an increased risk of periodontitis was found in those in the leisure time physical activity intensity < 750 MET × min/week group (OR = 1.44, 95% CI: 1.17-1.78). Serum cotinine levels ≥ 0.05 ng/ml were associated with an increased risk of periodontitis (OR = 1.99, 95% CI: 1.69-2.33). The group with low leisure physical activity and serum cotinine levels ≥ 0.05 ng/ml had an increased risk of periodontitis compared to the group with high leisure physical activity and serum cotinine levels < 0.05 ng/ml (OR = 2.48, 95% CI: 1.88-3.27). Interaction metrics RERI = 0.90 (95% CI: 0.44-1.36) and API = 0.36 (95% CI: 0.18-0.55); CI for SI = 2.55 (95% CI: 1.03-6.28). for API 0.36.

CONCLUSION

Leisure time physical activity intensity interacted with smoking exposure on periodontitis risk and may provide the general population with the opportunity to Increasing leisure-time physical activity and smoking cessation may provide recommendations for the general population.

Exploring the causal relationship between periodontitis and gut microbiome: Unveiling the oral-gut and gut-oral axes through bidirectional Mendelian randomization

AIM

This Mendelian randomization (MR) study was performed to explore the potential bidirectional causal relationship between the gut microbiome (GM) and periodontitis.

MATERIALS AND METHODS

We used genetic instruments from the genome-wide association study of European descent for periodontitis from the GeneLifestyle Interactions in Dental Endpoints (GLIDE) consortium (17,353 cases and 28,210 controls) and the FinnGen consortium (4434 cases and 259,234 controls) to investigate the causal relationship with GM (the MiBioGen consortium, 18,340 samples), and vice versa. Several MR techniques, which include inverse variance weighting (IVW), MR-Egger, weighted median, simple mode and weighted mode approaches, were employed to investigate the causal relationship between the exposures and the outcomes. Cochran's Q-test was performed to detect heterogeneity. The MR-Egger regression intercept and MR pleiotropy residual sum and outlier test (MR-PRESSO) were conducted to test potential horizontal pleiotropy. Leave-one-out sensitivity analyses were used to assess the stabilities of single nucleotide polymorphisms (SNPs). Finally, the IVW results from the two databases were analysed using meta-analysis.

RESULTS

We confirmed three potential causal relationships between GM taxa and periodontitis at the genus level. Among them, the genera Alistipes and Holdemanella were genetically associated with an increased risk of periodontitis. In reverse, periodontitis may lead to a decreased abundance of the genus Ruminococcaceae UCG014.

CONCLUSIONS

The demonstration of a causal link between GM and periodontitis provides compelling evidence, highlighting the interconnectivity and interdependence of the gut-oral and oral-gut axes.

A Mendelian randomization study on the association of bone mineral density with periodontitis

OBJECTIVE

Observational studies indicated that individuals with osteoporosis could be at an increased risk of periodontitis. This study aimed to investigate whether there is a causal association of bone mineral density (BMD) with periodontitis using Mendelian randomization (MR).

MATERIALS AND METHODS

Summary statistics were sourced from genome-wide association study on BMD measured at different skeletal sites, including estimated heel BMD (eBMD, N = 426,824), forearm BMD (FA-BMD, N = 8143), femoral neck BMD (FN-BMD, N = 32,735), and lumbar spine BMD (LS-BMD, N = 28,498). Genetic variants of periodontitis (N = 45,563) and loose teeth (N = 461,031) were used as outcome surrogates. Inverse variance weighted meta-analysis (IVW) was adopted as main analyses. Other sensitivity MR approaches were used to boost power and account for pleiotropy.

RESULTS

IVW results suggested no evidence for a causal association of any phenotypes of BMD with periodontitis (eBMD, odds ratio [OR] = 0.984, 95% confidence interval [CI] = 0.885-1.083; FA-BMD, OR = 1.028, 95%CI = 0.864-1.193; FN-BMD, OR = 1.033, 95%CI = 0.896-1.169; LS-BMD, OR = 0.991, 95%CI =0.878-1.103; all P > 0.65). Such null associations were consistent through other sensitivity MR approaches. Similarly, no significant causal effects of BMD on loose teeth were found.

CONCLUSIONS

Within the limitation of the study, our MR estimates suggested that a decreased BMD is unlikely to substantially increase the risk of periodontitis.

Patients with periodontitis might increase the risk of urologic cancers: a bidirectional two-sample Mendelian randomization study

BACKGROUND

Numerous observational epidemiological studies have reported a bidirectional relationship between periodontitis and urological cancers. However, the causal link between these two phenotypes remains uncertain. This study aimed to examine the bidirectional causal association between periodontitis and four types of urological tumors, specifically kidney cancer (KC), prostate cancer (PC), bladder cancer (BC), and testis cancer (TC).

METHODS

Based on large-scale genome-wide association study (GWAS) data, we utilized the two-sample Mendelian randomization (MR) approach to evaluate causal relationships between periodontitis and urological cancers. Several MR methods covering various consistency assumptions were applied in this study, including contamination mixture and Robust Adjusted Profile Score to obtain robust results. Summary-level data of individuals with European ancestry were extracted from the UK Biobank, the Kaiser GERA cohorts, and the FinnGen consortium.

RESULTS

Our findings revealed significant positive genetic correlations between periodontitis and kidney cancer (OR 1.287; 95% CI 1.04, 1.594; P = 0.020). We did not find a significant association of periodontitis on prostate cancer, bladder cancer, and testis cancer. In reverse MR, no significant results were observed supporting the effect of urologic cancers on periodontitis (all P > 0.05).

CONCLUSION

Our study provides the evidence of a potential causal relationship between periodontitis and kidney cancer. However, large-scale studies are warranted to confirm and elucidate the underlying mechanisms of this association.

Inflammatory cytokines and oral lichen planus: a Mendelian randomization study

Background

Inflammatory cytokines have long been considered closely related to the development of oral lichen planus (OLP), and we further explored the causal relationship between the two by Mendelian randomization (MR) method.

Methods

We performed bidirectional MR analyses by large genome-wide association studies (GWAS). The data included a large-scale OLP dataset, as well as datasets of 41 inflammatory cytokines. All data were obtained from the University of Bristol database, which includes 41 inflammatory cytokines, and the GWAS Catalog database, which includes 91 inflammatory cytokines. OLP data were obtained from the Finngen database, which includes 6411 cases and 405770 healthy controls. We used the inverse variance weighted (IVW) method, MR-Egger method, weighted median method, simple mode method and weighted mode method to analyze the causal relationship between inflammatory cytokines and OLP, and we also combined with sensitivity analysis to further verify the robustness of the results. We performed a meta-analysis of positive or potentially positive results for the same genes to confirm the reliability of the final results.

Results

We primarily used the IVW analysis method, corrected using the Benjamin Hochberg (BH) method. When p<0.00038 (0.05/132), the results are significantly causal; when 0.00038

Conclusion

There is a causal association between OLP and some inflammatory cytokines, which may play an important role in the pathogenesis of OLP and require further attention.

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Key Words

• Mendelian randomization
• immunity
• inflammation
• inflammatory cytokines
• oral lichen planus

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MESH Headings

• Humans
• Cytokines/genetics
• Genome-Wide Association Study
• Lichen Planus, Oral/genetics
• Mendelian Randomization Analysis
• Reproducibility of Results

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Affiliation(s)

Xin Chen Department of Oral and Maxillofacial Surgery, Jiangyin People's Hospital Affiliated to Nantong University, Wuxi, Jiangsu, China
Simin Zhang Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Xiao Wu Endodontic Department, School of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, China
Yuxi Lei Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of Emergency Room, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Bing Lei Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
Zhibai Zhao Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China Department of General Dentistry, College of Stomatology, Xi’an Jiaotong University, Xi’an, Shaanxi, China

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Association between healthy lifestyle combinations and periodontitis in NHANES

BACKGROUND

Periodontitis is closely associated with chronic systemic diseases. Healthy lifestyle interventions have health-enhancing effects on chronic systemic disorders and periodontitis, but the extent to which healthy lifestyle combinations are associated with periodontitis is unclear. Therefore, this study aimed to investigate the association between periodontitis and different healthy lifestyle combinations.

METHODS

5611 participants were included from the National Health and Nutrition Examination Survey (NHANES, 2009-2014). Six healthy lifestyles factors were defined as fulfilling either: non-smoking, moderate drinking, moderate body mass index (BMI), physical activity, healthy sleep and appropriate total energy intake. Then, the adjusted logistic regression models were performed to identify the association between the periodontitis and the scoring system composed of six lifestyles (0-6 scale). Finally, different scenarios were dynamically and randomly combined to identify the optimal and personalized combination mode.

RESULTS

Higher healthy lifestyle scores were significantly associated with lower periodontitis prevalence (p < 0.05). Four lifestyle factors (smoking, drinking, BMI, and sleep) significantly varied between the periodontitis and healthy groups (p < 0.05). Smoking was considered as a strong independent risk factor for periodontitis in both former and current smokers. Results further indicated that the combination of these four lifestyles played the most essential role in determining the magnitude of periodontitis occurrence (odds ratio [OR]: 0.33; 95% confidence interval [CI]: 0.21 to 0.50). In the total population, the majority of three lifestyle combinations outperformed the two combination models, whereas the two-combination of nonsmoking-drinking (OR: 0.39; 95% CI: 0.27 to 0.58) had relatively lower periodontitis prevalence than the three-combination of healthy drinking-BMI-sleep (OR: 0.42; 95% CI: 0.26 to 0.66).

CONCLUSION

This cross-sectional study suggests that smoking, drinking, BMI, and sleep are significantly related with periodontitis and smoking is the principal risk factor related among them. This study provides various customized lifestyle combinations for periodontitis prevention.

Circulating Metabolites and Dental Traits: A Mendelian Randomization Study

It is of great importance to uncover causal biomarkers to gain insight into the pathogenesis of oral diseases and identify novel treatment targets for prevention and treatment thereof. This study aimed to systematically evaluate the causal effects of hundreds of metabolites on 10 dental traits using a 2-sample Mendelian randomization (MR) approach. Genetic variants from genome-wide association studies of 309 known metabolites were used as instrumental variables. We selected 10 dental traits, including clinical measures of dental diseases, from the Gene-Lifestyle Interactions in Dental Endpoints Consortium and self-reported oral health data from the UK Biobank. The causal relationships between metabolites and dental traits were inferred using the inverse variance-weighted approach and further controlled for horizontal pleiotropy using 5 additional MR methods. After correcting for multiple tests, 5 metabolites were identified as causal biomarkers. Genetically predicted increased levels of mannose were associated with lower risk of bleeding gums (odds ratio [OR] = 0.72; 95% confidence interval [CI], 0.61-0.85; P = 9.9 × 10-5). MR also indicated 4 metabolites on the causal pathway to dentures, with fructose (OR = 0.50; 95% CI, 0.36-0.70; P = 5.2 × 10-5) and 1-palmitoleoyl-glycerophosphocholine (OR = 0.67; 95% CI, 0.56-0.81; P = 4.8 × 10-5) as potential protective factors and glycine (OR = 1.22; 95% CI, 1.11-1.35; P = 5.6×10-5) and 1,5-anhydroglucitol (OR = 1.32; 95% CI, 1.14-1.52; P = 1.5 × 10-4) as risk factors. The causal associations were robust in various sensitivity analyses. We further observed some shared metabolites among different dental traits, implying similar biological mechanisms underlying the pathogenic processes. Finally, the pathway analysis revealed several significant metabolic pathways that may be involved in the development of dental disorders. Our study provides novel insights into the combination of metabolomics and genomics to reveal the pathogenesis of and therapeutic strategies for dental disorders. It highlighted 5 metabolites and several pathways as causal candidates, warranting further investigation.

Understanding the consequences of leisure sedentary behavior on periodontitis: A two-step, multivariate Mendelian randomization study

Background

The relationship between leisure sedentary behavior (LSB) and periodontitis risk remains unclear in terms of causality and the potential mediating effects of intermediate factors.

Materials and methods

Using the aggregate data of several large-scale genetic association studies from participants of European descent, we conducted a univariate, two-step, and multivariate Mendelian random (MR) analysis to infer the overall effect of LSB on periodontitis, and quantified the intermediary proportion of intermediary traits such as smoking.

Results

Our findings indicated that per 1-SD increase (1.87 h) in leisure screen time (LST), there was a 23 % increase in the risk of periodontitis. [odds ratios (95 % CI) = 1.23 (1.04-1.44), p = 0.013]. Smoking was found to partially mediate the overall causal effect of LST on periodontitis, with a mediation rate of 20.7 % (95 % CI: 4.9%-35.5 %). Multivariate MR analysis demonstrated that the causal effect of LST on periodontitis was weakened when adjusting for smoking, resulting in an odds ratio of 1.19 (95 % CI: 1.01-1.39, p = 0.049) for each 1 standard deviation increase in exposure.

Conclusion

The study provides evidence of a potential causal relationship between LSB characterized by LST and periodontitis, thereby further supporting the notion that reducing LSB is beneficial for health. Furthermore, it confirms the role of smoking as a mediator in this process, suggesting that inhibiting smoking behavior among individuals with long-term LSB may serve as a strategy to mitigate the risk of periodontitis.

CREB1 alleviates the apoptosis and potentiates the osteogenic differentiation of zoledronic acid-treated human periodontal ligament stem cells via up-regulating VEGF

Periodontitis represents a severe inflammatory illness in tooth supporting tissue. It has been supported that cAMP response element binding protein 1 (CREB1), a common transcription factor, extensively participates in osteogenic differentiation. Here, the current study was to look into the impacts of CREB1 on the process of periodontitis and its possible action mechanism. After human periodontal ligament stem cells (PDLSCs) were challenged with zoledronic acid (ZA), CREB1 expression was examined with RT-qPCR and western blotting. CCK-8 assay appraised cell activity. Following CREB1 elevation or/and vascular endothelial growth factor (VEGF) silencing in ZA-treated PDLSCs, CCK-8 and TUNEL assays separately estimated cell viability and apoptosis. Western blotting tested the expression of apoptosis- and osteogenic differentiation-associated proteins. ALP staining measured PDLSCs osteogenic ability and ARS staining estimated mineralized nodule formation. JASPAR predicted the potential binding of CREB1 with VEGF promoter, which was then testified by ChIP and luciferase reporter assays. RT-qPCR and western blotting tested VEGF expression. CREB1 expression was declined in ZA-exposed PDLSCs and CREB1 elevation exacerbated the viability and osteogenic differentiation while obstructed the apoptosis of PDLSCs. Additionally, CREB1 bond to VEGF promoter and transcriptionally activated VEGF expression. Further, VEGF absence partially stimulated the apoptosis while suppressed the osteogenic differentiation of CREB1-overexpressing PDLSCs treated by ZA. To be concluded, CREB1 might activate VEGF transcription to obstruct the apoptosis while contribute to the osteogenic differentiation of ZA-treated PDLSCs.

Association between periodontal disease and oral squamous cell carcinoma: a systematic review and meta-analysis

To investigate the relation between periodontal disease (PD) and oral squamous cell carcinoma (OSCC) we systematically searched records published up to August 2022. Odds ratios (OR) and relative risk (RR) with 95% confidence intervals (95% CI) were estimated to evaluate this relation, then sensitivity analysis was performed accordingly. Begg's test and Egger's test were used to detect publication bias. Out of 970 papers from several databases, 13 studies were included. Summary estimates showed that PD was positively associated with the prevalence of OSCC (OR = 3.28, 95% CI: 1.87 to 5.74), especially for severe PD (OR = 4.23, 95% CI: 2.92 to 6.13). No evident publication bias was revealed. No increased OSCC risk among patients with PD was shown according to the combined results (RR = 1.50, 95% CI: 0.93 to 2.42). Patients with OSCC exhibited significant differences in alveolar bone loss, clinical attachment loss, and bleeding on probing, when compared with controls. The systematic review and meta-analysis suggested that there was a positive association between PD and prevalence of OSCC. However, according to the current evidence, a causal relation is unclear.

Causal effects of gut microbiota on the risk of periodontitis: a two-sample Mendelian randomization study

Introduction

The oral cavity and the gut tract are interconnected, and both contain abundant natural microbiota. Gut microbiota may interact with oral flora and participate in the development of periodontitis. However, the specific role of certain gut microbiota taxa for periodontitis has not been investigated. Mendelian Randomization is an ideal method to explore causal relationships avoiding reverse causality and potential confounding factors. Thus, we conducted a two-sample Mendelian Randomization study to comprehensively reveal the potential genetic causal effect of gut microbiota on periodontitis.

Methods

SNPs strongly associated with 196 gut microbiota taxa (18,340 individuals) were selected as instrument variables, and periodontitis (17,353 periodontitis cases and 28,210 controls) was used as the outcome. The causal effect was analyzed via random effect inverse variance-weighted, weighted median, and MR-Egger. The sensitivity analyses were conducted using Cochran's Q tests, funnel plots, leave-one-out analyses, and MR-Egger intercept tests.

Results

Nine gut microbiota taxa (Prevotella 7, Lachnospiraceae UCG-008, Enterobacteriales, Pasteurellales, Enterobacteriaceae, Pasteurellaceae, Bacteroidales S24.7 group, Alistipes, and Eisenbergiella) are predicted to play a causal role in enhancing the risk of periodontitis (p< 0.05). Besides, two gut microbiota taxa (Butyricicoccus and Ruminiclostridium 6) have potentially inhibitive causal effects on the risk of periodontitis (p< 0.05). No significant estimation of heterogeneity or pleiotropy is detected.

Conclusion

Our study demonstrates the genetic causal effect of 196 gut microbiota taxa on periodontitis and provides guidance for the clinical intervention of periodontitis.

A retrospective epidemiological investigation of periodontitis risk and current smoking status based on the number of cigarettes per day and the Fagerström Test for Nicotine Dependence: a preliminary pilot study

PURPOSE

The aim of this study was to investigate the risk of periodontitis according to current smoking status based on the number of cigarettes smoked per day (CPD) and the Fagerström Test for Nicotine Dependence (FTND).

METHODS

All enrolled patients were diagnosed and classified according to the new periodontal classification scheme, and current smoking status was investigated via a self-reported questionnaire. The correlation between smoking status (CPD and FTND) and periodontitis risk (severity of periodontitis and tooth loss due to periodontal reasons) was statistically assessed using Spearman correlation coefficients. Moreover, partial correlation analyses between smoking and periodontal status were performed after adjusting for age, sex, and diabetes mellitus.

RESULTS

Overall, data from 74 men and 16 women (mean age: 48.1±10.8 years) were evaluated. The mean number of missing teeth, CPD, and FTND score were 3.5±5.2, 24.6±15.5, and 3.5±2, respectively. CPD and the FTND were significantly positively correlated with each other (r=0.741, P<0.001). CPD and the FTND were also significantly correlated with the severity of periodontitis (CPD: r=0.457, P<0.05 and FTND: r=0.326, P<0.05) and the number of missing teeth due to periodontal reasons (CPD: r=0.525, P<0.05 and FTND: r=0.480, P<0.05), respectively.

CONCLUSIONS

Within the limitations of this study, both CPD and the FTND were significantly correlated with the severity of periodontitis and the number of periodontally compromised extracted teeth.

Association between skull bone mineral density and periodontitis: Using the National Health and Nutrition Examination Survey (2011-2014)

BACKGROUND AND OBJECTIVE

Bone mineral density (BMD) and periodontitis have been the subject of many studies. However, the relationship between skull (including mandible) BMD and periodontitis has not been extensively studied. An objective of this cross-sectional study was to examine the relationship between skull BMD and periodontitis using data from the National Health and Nutrition Examination Surveys (NHANES) for 2011-2012 and 2013-2014.

MATERIALS AND METHODS

From NHANES 2011-2014, 3802 participants aged 30-59 were selected. We divided the skull BMD level into quartiles to check the distribution of variables. Periodontitis was defined by the Centers for Disease Control and Prevention (CDC) and the American Association of Periodontology (AAP) in 2012. Multivariate logical regression analysis was used to explore the independent relationship between skull BMD and periodontitis. The generalized additive model (GAM), smooth curve fitting (penalty spline) and threshold effect analysis was used to evaluate dose-response relationship between skull BMD and periodontitis and the potential nonlinear relationship between skull BMD and periodontitis. Finally, subgroup analysis and interaction test were conducted to determine the role of covariates between skull BMD and periodontitis.

RESULTS

The overall average skull BMD of 3802 participants was 2.24g/cm2, the average age was 43.94 years, and the prevalence of periodontitis was 41.03%. In the fully adjusted logistic regression model, skull BMD and periodontitis showed an independent negative correlation (OR 0.73, 95% CI 0.59-0.90, P = 0.0032) and a linear relationship. Compared with the lowest quartile array (Q1:1.22-1.98) of skull BMD, the highest quartile array(Q4: 2.47-3.79) had a significantly lower risk of periodontitis (OR 0.70,95% CI 0.56-0.87, P = 0.0014). Subgroup analysis showed a highly consistent negative correlation between skull BMD and periodontitis. In the interaction test, people with moderate poverty income ratio (1.57-3.62) and those who had more than 12 alcohol drinks in the past year had a lower risk of periodontitis.

CONCLUSIONS

This result suggested that periodontal disease can be related to low skull BMD, for those people, oral hygiene and health care should be more closely monitored. Validation of our findings will require further research.

Osteoporosis and Alveolar Bone Health in Periodontitis Niche: A Predisposing Factors-Centered Review

Periodontitis is a periodontal inflammatory condition that results from disrupted periodontal host-microbe homeostasis, manifested by the destruction of tooth-supporting structures, especially inflammatory alveolar bone loss. Osteoporosis is characterized by systemic deterioration of bone mass and microarchitecture. The roles of many systemic factors have been identified in the pathogenesis of osteoporosis, including endocrine change, metabolic disorders, health-impaired behaviors and mental stress. The prevalence rate of osteoporotic fracture is in sustained elevation in the past decades. Recent studies suggest that individuals with concomitant osteoporosis are more vulnerable to periodontal impairment. Current reviews of worse periodontal status in the context of osteoporosis are limited, mainly centering on the impacts of menopausal and diabetic osteoporosis on periodontitis. Herein, this review article makes an effort to provide a comprehensive view of the relationship between osteoporosis and periodontitis, with a focus on clarifying how those risk factors in osteoporotic populations modify the alveolar bone homeostasis in the periodontitis niche.

Appraising the causal role of smoking in multiple diseases: A systematic review and meta-analysis of Mendelian randomization studies

BACKGROUND

The causal association between cigarette smoking and several diseases remains equivocal. The purpose of this study was to appraise the causal role of smoking in a wide range of diseases by summarizing the evidence from Mendelian randomization (MR) studies.

METHODS

MR studies on genetic liability to smoking initiation or lifetime smoking (composite of smoking initiation, heaviness, duration, and cessation) in relation to circulatory system, digestive system, nervous system, musculoskeletal system, endocrine, metabolic, and eye diseases, and neoplasms published until February 15, 2022, were identified in PubMed. De novo MR analyses were performed using summary statistics data from genome-wide association studies. Meta-analysis was applied to combine study-specific estimates.

FINDINGS

Meta-analyses of findings of 29 published MR studies and 123 de novo MR analyses of 57 distinct primary outcomes showed that genetic liability to smoking (smoking initiation or lifetime smoking) was associated with increased risk of 13 circulatory system diseases, several digestive system diseases (including diverticular, gallstone, gastroesophageal reflux, and Crohn's disease, acute pancreatitis, and periodontitis), epilepsy, certain musculoskeletal system diseases (including fracture, osteoarthritis, and rheumatoid arthritis), endocrine (polycystic ovary syndrome), metabolic (type 2 diabetes) and eye diseases (including age-related macular degeneration and senile cataract) as well as cancers of the lung, head and neck, esophagus, pancreas, bladder, kidney, cervix, and ovaries, and myeloid leukemia. Smoking liability was associated with decreased risk of Parkinson's disease and prostate cancer.

INTERPRETATION

This study found robust evidence that cigarette smoking causes a wide range of diseases.

FUNDING

This work was supported by research grants from the Swedish Cancer Society (Cancerfonden), the Swedish Heart Lung Foundation (Hjärt-Lungfonden, 20210351), the Swedish Research Council for Health, Working Life and Welfare (Forte, 2018-00123), and the Swedish Research Council (Vetenskapsrådet, 2019-00977). Stephen Burgess is supported by Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (204623/Z/16/Z) and the National Institute for Health Research Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the authors and not necessarily those of the National Institute for Health Research or the Department of Health and Social Care.

Cannabis use and the risk of periodontitis: A two-sample Mendelian randomization study

AIM

This study aimed to leverage human genetic data to investigate whether cannabis use causally affects periodontitis.

MATERIALS AND METHODS

Data were obtained from summary statistics of genome-wide association studies of lifetime cannabis use (N = 184,765), cannabis use disorder (17,068 cases; 357,219 controls), and periodontitis (17,353 cases; 28,210 controls). We performed two-sample Mendelian randomization (MR) analysis using 6 genetic variants as instrumental variables for lifetime cannabis use and 11 variants as instruments for cannabis use disorder to estimate associations with periodontitis.

RESULTS

There was no evidence for an association between genetic liability for lifetime cannabis use or cannabis use disorder with periodontitis. The estimates from the primary analyses were supported in multivariable MR analysis, which considered potential pleiotropic pathways and in weak instrument analyses.

CONCLUSIONS

This study provides little evidence to support a detrimental effect of genetic liability for cannabis use on periodontal health.

Relationship between periodontitis and psoriasis: A two-sample Mendelian randomization study

AIM

Observational research suggests that periodontitis affects psoriasis. However, observational studies are prone to reverse causation and confounding, which hampers drawing causal conclusions and the effect direction. We applied the Mendelian randomization (MR) method to comprehensively assess the potential bi-directional association between periodontitis and psoriasis.

MATERIALS AND METHODS

We used genetic instruments from the largest available genome-wide association study of European descent for periodontitis (17,353 cases, 28,210 controls) to investigate the relationship with psoriasis (13,229 cases, 21,543 controls), and vice versa. Causal Analysis Using Summary Effect (CAUSE) estimates and inverse variance-weighted (IVW) MR analyses were used for the primary analysis. Robust MR approaches were used for sensitivity analyses.

RESULTS

Both univariable methods, CAUSE and IVW MR analyses, did not reveal any impact of periodontitis on psoriasis (CAUSE odds ratio [OR] = 1.00, p = 1.00; IVW OR = 1.02, p = .6247), or vice versa (CAUSE OR = 1.01, p = .5135; IVW OR = 1.00, p = .7070). The null association was corroborated by pleiotropy-robust methods with ORs close to 1 and p-values >.59. Overall, MR analyses did not suggest any effect of periodontitis on psoriasis. Similarly, there was no evidence to support an effect of psoriasis on periodontitis.

CONCLUSIONS

Within the limitations of this MR study, the outcomes supported neither periodontitis affecting psoriasis nor psoriasis affecting periodontitis.

Alcohol Intake Influences the Occurrence and Progression of Periodontitis Differently According to Sex and Country Sociodemographic Development: A Two-Stage Systematic Review

AIMS

To conduct an overview and systematic evaluation of prospective cohort studies on whether alcohol intake is associated with the incidence and progression of periodontitis.

METHODS

Nine databases were searched by two independent reviewers up to November 2021 according to prespecified eligibility criteria. Risk of Bias in Systematic Reviews and Risk of Bias in Non-Randomized Studies of Interventions were used for risk of bias assessment and certainty of evidence was assessed using the GRADE approach. Random-effects pair-wise meta-analyses were performed with data from cohort studies on the effects of higher levels of alcohol intake compared with current non-drinking to determine risk ratios (RR) and confidence intervals of periodontitis.

RESULTS

The four systematic reviews were at high risk of bias and concluded that alcohol intake is associated with periodontitis regardless of the study design. Five reports from seven cohort studies contributed to the meta-analyses and no statistically significant differences were found for higher levels of consumption regarding the risk of periodontitis, except for men from countries with low- and high-middle socio-demographic index (RR = 1.30, 95% CI: 1.13-1.46), with low certainty evidence.

CONCLUSION

Higher levels of alcohol consumption seem to be part of the causal mechanism of periodontitis when cooccurring with male sex in underdeveloped countries. No conclusion can be drawn regarding alcohol use disorders or patterns of consumption.

Causal Inference: Onward and Upward!

When announcing the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel 2021, the Royal Swedish Academy emphasized how conclusions about cause and effect can be drawn from natural experiments. But what can dental research learn from this? The economist’s toolbox provides a number of methods for causal inference from observational data such as instrumental variables, regression discontinuity designs, or difference-in-differences analyses. Although the relevance of improving causal inference in dental research has repeatedly been highlighted in recent years, dental research still seems to reveal major room for improvement in the application of such methods. First, there seems to be an absence of causal literature on key essential research questions for oral health. Second, the diversity and diffusion of causal inferential methods in the dental literature seem very limited so far. Third, while dental research has widely been promoting the use of directed acyclic graphs (DAGs) to help conceptualize causal thinking, comparably little attention seems to have been paid to choosing and applying appropriate data-analytic approaches for causal inference. Fourth, similar to other fields of medicine, confusion seems to persist within the dental research community as to the use of causal language. If dental research is to secure a robust evidence base for promoting effective oral health interventions, we argue that dental research needs to move beyond its current methodological echo chamber and embrace a radically different approach to causal inference. We call for editors, reviewers, and authors to embrace a much more critically reflective approach to causal inference.

No Genetic Causal Association Between Periodontitis and Arthritis: A Bidirectional Two-Sample Mendelian Randomization Analysis

Objectives

Periodontitis (PD) has been linked to arthritis in previous epidemiological observational studies; however, the results are inconclusive. It remains unclear whether the association between PD and arthritis is causal. The purpose of this study was to investigate the causal association of PD with arthritis, including rheumatoid arthritis (RA) and osteoarthritis (OA).

Methods

We performed a two-sample bidirectional Mendelian randomization (MR) analysis using publicly released genome-wide association studies (GWAS) statistics. The inverse-variance weighted (IVW) method was used as the primary analysis. We applied four complementary methods, including weighted median, weighted mode, MR-Egger regression and MR pleiotropy residual sum and outlier (MR-PRESSO) to detect and correct for the effect of horizontal pleiotropy.

Results

Genetically determined PD did not have a causal effect on OA (OR = 1.06, 95% CI: 0.99-1.15, P = 0.09) and RA (OR = 0.99, 95% CI: 0.87-1.13, P = 0.89). Furthermore, we did not find a significant causal effect of arthritis on PD in the reverse MR analysis. The results of MR-Egger regression, Weighted Median, and Weighted Mode methods were consistent with those of the IVW method. Horizontal pleiotropy was unlikely to distort the causal estimates according to the sensitivity analysis.

Conclusions

Our MR analysis reveals non-causal association of PD with arthritis, despite observational studies reporting an association between PD and arthritis.

Causal Associations of Obesity With Achilles Tendinopathy: A Two-Sample Mendelian Randomization Study

BACKGROUND

Achilles tendinopathy (AT) is associated with severe pain and is the cause of dysfunction and disability that are associated with significant reduction in social and economic benefits. Several potential risk factors have been proposed to be responsible for AT development; however, the results of observational epidemiological studies remain controversial, presumably because the designs of these studies are subject to residual confounding and reverse causality. Mendelian randomization (MR) can infer the causality between exposure and disease outcomes using genetic variants as instrumental variables, and identification of the causal risk factors for AT is beneficial for early intervention. Thus, we employed the MR strategy to evaluate the causal associations between previously reported risk factors (anthropometric parameters, lifestyle factors, blood biomarkers, and systemic diseases) and the risk of AT.

METHODS

Univariable MR was performed to screen for potential causal associations between the putative risk factors and AT. Bidirectional MR was used to infer reverse causality. Multivariable MR was conducted to investigate the body mass index (BMI)-independent causal effect of other obesity-related traits, such as the waist-hip ratio, on AT.

RESULTS

Univariable MR analyses with the inverse-variance weighted method indicated that the genetically predicted BMI was significantly associated with the risk of AT (P=2.0×10^-3), and the odds ratios (95% confidence intervals) is 1.44 (1.14-1.81) per 1-SD increase in BMI. For the other tested risk factors, no causality with AT was identified using any of the MR methods. Bidirectional MR suggested that AT was not causally associated with BMI, and multivariable MR indicated that other anthropometric parameters included in this study were not likely to causally associate with the risk of AT after adjusting for BMI.

CONCLUSIONS

The causal association between BMI and AT risk suggests that weight control is a promising strategy for preventing AT and alleviating the corresponding disease burden.

Understanding the consequences of educational inequalities on periodontitis: Mendelian randomization study

AIM

Higher educational attainment is associated with a lower risk of periodontitis, but the extent to which this association is causal and mediated by intermediate factors is unclear.

METHODS AND MATERIALS

Using summary data from genetic association studies from up to 1.1 million participants of European descent, univariable and multivariable Mendelian randomization analyses were performed to infer the total effect of educational attainment on periodontitis and to estimate the degree to which income, smoking, alcohol consumption, and body mass index mediate the association.

RESULTS

The odds ratio of periodontitis per one standard deviation increment in genetically predicted education was 0.78 (95% CI: 0.68-0.89). The proportions mediated of the total effect of genetically predicted education on periodontitis were 64%, 35%, 15%, and 46% for income, smoking, alcohol consumption, and body mass index, respectively.

CONCLUSIONS

Using a genetic instrumental variable approach, this study triangulated evidence from existing observational epidemiological studies and suggested that higher educational attainment lowers periodontitis risk. Measures to reduce the burden of educational disparities in periodontitis risk may tackle downstream risk factors, particularly income, smoking, and obesity.