Trends in Oral Diseases in the U.S. Population

This article reviews trends in dental caries, periodontal disease, and tooth loss for the United States along with population dynamics and risk factors that might influence these trends going forward. Dental caries experience remains high in the primary dentition. Caries severity in permanent teeth of children has declined to historically low levels, and long-standing inequalities in untreated caries appear to be narrowing. Declines in caries severity of children's permanent teeth have stabilized at a low level, but likely will contribute to future reductions in dental caries severity in adults. The prevalence of periodontal disease is high in adults, and only a small percentage have severe forms of the disease. Countervailing trends in determinants would suggest little change in the prevalence of periodontal disease in the future, but the lack of an obvious trend over the last two decades makes projections uncertain. Tooth loss as a consequence of dental disease has declined markedly over the last half century and has been all but eliminated in high-income groups. However, notable exceptions to these favorable trends are evident. Progress in prevention policies and programs that affect disease experience appears slower than progress in meeting population-level caries treatment needs. Clearly, long-standing inequities related to political and social determinants remain for all dental diseases, and income disparities in dental disease are widening for some indicators. Growing inequalities raise ethical and public health concerns that should be prominent in discussions of dental workforce needs and strategies for the next 25 years. This article was written as part of the project "Advancing Dental Education in the 21^st Century."

Epiregulin and EGFR interactions are involved in pain processing

The EGFR belongs to the well-studied ErbB family of receptor tyrosine kinases. EGFR is activated by numerous endogenous ligands that promote cellular growth, proliferation, and tissue regeneration. In the present study, we have demonstrated a role for EGFR and its natural ligand, epiregulin (EREG), in pain processing. We show that inhibition of EGFR with clinically available compounds strongly reduced nocifensive behavior in mouse models of inflammatory and chronic pain. EREG-mediated activation of EGFR enhanced nociception through a mechanism involving the PI3K/AKT/mTOR pathway and matrix metalloproteinase-9. Moreover, EREG application potentiated capsaicin-induced calcium influx in a subset of sensory neurons. Both the EGFR and EREG genes displayed a genetic association with the development of chronic pain in several clinical cohorts of temporomandibular disorder. Thus, EGFR and EREG may be suitable therapeutic targets for persistent pain conditions.

Do Genetic Markers of Inflammation Modify the Relationship between Periodontitis and Nonalcoholic Fatty Liver Disease? Findings from the SHIP Study

An association between periodontitis and nonalcoholic fatty liver disease (NAFLD) has been reported by experimental animal and epidemiologic studies. This study investigated whether circulating levels of serum C-reactive protein (CRP) and a weighted genetic CRP score representing markers of inflammatory burden modify the association between periodontitis and NAFLD. Data came from 2,481 participants of the Study of Health in Pomerania who attended baseline examination that occurred between 1997 and 2001. Periodontitis was defined as the percentage of sites (0%, <30%, ≥30%) with probing pocket depth (PD) ≥4 mm, and NAFLD status was determined using liver ultrasound assessment. Serum CRP levels were assayed at a central laboratory, and single-nucleotide polymorphisms previously identified through genome-wide association studies as robustly associated with serum CRP were combined into a weighted genetic CRP score (wGS_CRP). Logistic regression models estimated the association between periodontitis and NAFLD within strata of serum CRP and separately within strata of the wGS_CRP. The prevalence of NAFLD was 26.4% (95% confidence interval [CI], 24.6, 28.1) while 17.8% (95% CI, 16.0-19.6) had ≥30% of sites with PD ≥4 mm. Whereas the wGS_CRP was not a modifier ( P_interaction = 0.8) on the multiplicative scale, serum CRP modified the relationship between periodontitis and NAFLD ( P_interaction = 0.01). The covariate-adjusted prevalence odds ratio of NAFLD comparing participants with ≥30% of sites with PD ≥4 mm to those with no site affected was 2.39 (95% CI, 1.32-4.31) among participants with serum CRP <1 mg/L. The corresponding estimate was 0.97 (95% CI, 0.57-1.66) for participants with serum CRP levels of 1 to 3 mg/L and 1.12 (95% CI, 0.65-1.93) for participants with serum CRP >3 mg/L. Periodontitis was positively associated with higher prevalence odds of NAFLD, and this relationship was modified by serum CRP levels.

Racial differences in periodontal disease and 10-year self-reported tooth loss among late middle-aged and older adults: the dental ARIC study

OBJECTIVE

To investigate racial differences in the associations between periodontitis and 10-year self-reported incident tooth loss in a biracial, community-based cohort of US late middle-aged and older adults.

METHODS

Subjects were 3,466 dentate men and women aged 53-74 who underwent dental examinations from 1996 to1998. In 2012-2013, telephone interviewers asked participants about tooth loss in the preceding 10 years. Separate multivariable ordinal logistic regression models were used to calculate proportional odds ratios (OR) and 95% confidence intervals (CI) as estimates of association between periodontitis and tooth loss for Whites and African-Americans (AAs).

RESULTS

The majority of participants were White (85 percent) and female (57 percent) with 23 teeth on average at enrollment. Approximately half the Whites (56 percent) and AAs (49 percent) had periodontitis. At follow-up, approximately 44 percent of AAs and 38 percent of Whites reported having lost ≥1 tooth. In multivariable models, severe periodontitis (OR = 3.03; 95% CI = 2.42-3.80) and moderate periodontitis (OR = 1.64; 95% CI= 1.39-1.94) were significant risk factors of incident tooth loss among Whites. For AAs, severe but not moderate periodontitis increased the odds of incident tooth loss (OR = 2.22; 95% CI = 1.37-3.59). In the final model, education was inversely associated with incident tooth loss among AAs, while lower income was associated with greater odds of tooth loss among Whites.

CONCLUSIONS

In this population-based cohort, there is racial heterogeneity in the association between periodontitis and tooth loss. Interventions to reduce the impact of periodontitis on tooth loss need to consider these differences.

Causal Mediation in the Development of Painful Temporomandibular Disorder

We explored causal mediation of sleep quality and perceived stress in development of painful temporomandibular disorder (TMD). Sleep quality and perceived stress were assessed at baseline and quarterly intervals thereafter in 2,737 initially TMD-free adults in the Orofacial Pain Prospective Evaluation and Risk Assessment study (OPPERA) prospective cohort study. During follow-up, incident TMD cases were classified using research diagnostic criteria. Mediation analysis was conducted using a weighted Cox proportional hazards regression model that estimated hazard ratios (HRs) and 95% confidence limits (CL) of first-onset TMD. Models determined whether: 1) poor sleep quality during follow-up mediated the effect of baseline perceived stress on first-onset TMD, and 2) perceived stress during follow-up mediated the effect of baseline poor sleep quality on first-onset TMD. In both analyses, the total effect was decomposed into natural direct and indirect effects. Poor baseline sleep quality led to heightened perceived stress that then contributed to TMD development. When the total effect of poor sleep quality (HR = 2.10, CL = 1.76, 2.50) was decomposed, 34% of its effect was mediated by perceived stress (indirect effect HR = 1.29, CL = 1.06, 1.58). The effect of perceived stress on first-onset TMD was not mediated by sleep quality. Improving sleep may avert escalation of stress, limiting effects of both factors on TMD development.

PERSPECTIVE

Causal mediation analysis highlights mechanisms by which poor sleep quality promotes development of TMD. First, poor sleep quality exerts a direct effect on pain. Second, it triggers a heightened perception of stress, which acts as an intermediate factor in the causal pathway between poor sleep quality and first-onset TMD pain.

GWAS Identifies New Loci for Painful Temporomandibular Disorder: Hispanic Community Health Study/Study of Latinos

Temporomandibular disorder (TMD) is a musculoskeletal condition characterized by pain and reduced function in the temporomandibular joint and/or associated masticatory musculature. Prevalence in the United States is 5% and twice as high among women as men. We conducted a discovery genome-wide association study (GWAS) of TMD in 10,153 participants (769 cases, 9,384 controls) of the US Hispanic Community Health Study/Study of Latinos (HCHS/SOL). The most promising single-nucleotide polymorphisms (SNPs) were tested in meta-analysis of 4 independent cohorts. One replication cohort was from the United States, and the others were from Germany, Finland, and Brazil, totaling 1,911 TMD cases and 6,903 controls. A locus near the sarcoglycan alpha ( SGCA), rs4794106, was suggestive in the discovery analysis ( P = 2.6 × 10⁶) and replicated (i.e., 1-tailed P = 0.016) in the Brazilian cohort. In the discovery cohort, sex-stratified analysis identified 2 additional genome-wide significant loci in females. One lying upstream of the relaxin/insulin-like family peptide receptor 2 ( RXP2) (chromosome 13, rs60249166, odds ratio [OR] = 0.65, P = 3.6 × 10^-8) was replicated among females in the meta-analysis (1-tailed P = 0.052). The other (chromosome 17, rs1531554, OR = 0.68, P = 2.9 × 10^-8) was replicated among females (1-tailed P = 0.002), as well as replicated in meta-analysis of both sexes (1-tailed P = 0.021). A novel locus at genome-wide level of significance (rs73460075, OR = 0.56, P = 3.8 × 10^-8) in the intron of the dystrophin gene DMD (X chromosome), and a suggestive locus on chromosome 7 (rs73271865, P = 2.9 × 10^-7) upstream of the Sp4 Transcription Factor ( SP4) gene were identified in the discovery cohort, but neither of these was replicated. The SGCA gene encodes SGCA, which is involved in the cellular structure of muscle fibers and, along with DMD, forms part of the dystrophin-glycoprotein complex. Functional annotation suggested that several of these variants reside in loci that regulate processes relevant to TMD pathobiologic processes.

Circulating Omentin-1 and Chronic Painful Temporomandibular Disorders

AIMS

To investigate the relationship between omentin-1 levels and painful temporomandibular disorders (TMD).

METHODS

In a case-control design, chronic painful TMD cases (n = 90) and TMD-free controls (n = 54) were selected from participants in the multisite OPPERA study (Orofacial Pain: Prospective Evaluation and Risk Assessment). Painful TMD case status was determined by examination using established Research Diagnostic Criteria for TMD (RDC/TMD). Levels of omentin-1 in stored blood plasma samples were measured by using an enzyme linked immunosorbent assay. Binary logistic regression was used to calculate the odds ratios (ORs) and 95% confidence limits (CLs) for the association between omentin-1 and painful TMD. Models were adjusted for study site, age, sex, and body mass index.

RESULTS

The unadjusted association between omentin-1 and chronic painful TMD was statistically nonsignificant (P = .072). Following adjustment for covariates, odds of TMD pain decreased 36% per standard deviation increase in circulating omentin-1 (adjusted OR = 0.64; 95% CL: 0.43, 0.96; P = .031).

CONCLUSION

Circulating levels of omentin-1 were significantly lower in painful TMD cases than controls, suggesting that TMD pain is mediated by inflammatory pathways.

Painful Temporomandibular Disorder: Decade of Discovery from OPPERA Studies

In 2006, the OPPERA project (Orofacial Pain: Prospective Evaluation and Risk Assessment) set out to identify risk factors for development of painful temporomandibular disorder (TMD). A decade later, this review summarizes its key findings. At 4 US study sites, OPPERA recruited and examined 3,258 community-based TMD-free adults assessing genetic and phenotypic measures of biological, psychosocial, clinical, and health status characteristics. During follow-up, 4% of participants per annum developed clinically verified TMD, although that was a "symptom iceberg" when compared with the 19% annual rate of facial pain symptoms. The most influential predictors of clinical TMD were simple checklists of comorbid health conditions and nonpainful orofacial symptoms. Self-reports of jaw parafunction were markedly stronger predictors than corresponding examiner assessments. The strongest psychosocial predictor was frequency of somatic symptoms, although not somatic reactivity. Pressure pain thresholds measured at cranial sites only weakly predicted incident TMD yet were strongly associated with chronic TMD, cross-sectionally, in OPPERA's separate case-control study. The puzzle was resolved in OPPERA's nested case-control study where repeated measures of pressure pain thresholds revealed fluctuation that coincided with TMD's onset, persistence, and recovery but did not predict its incidence. The nested case-control study likewise furnished novel evidence that deteriorating sleep quality predicted TMD incidence. Three hundred genes were investigated, implicating 6 single-nucleotide polymorphisms (SNPs) as risk factors for chronic TMD, while another 6 SNPs were associated with intermediate phenotypes for TMD. One study identified a serotonergic pathway in which multiple SNPs influenced risk of chronic TMD. Two other studies investigating gene-environment interactions found that effects of stress on pain were modified by variation in the gene encoding catechol O-methyltransferase. Lessons learned from OPPERA have verified some implicated risk factors for TMD and refuted others, redirecting our thinking. Now it is time to apply those lessons to studies investigating treatment and prevention of TMD.

Periodontal therapy and glycaemic control among individuals with type 2 diabetes: reflections from the PerioCardio study

OBJECTIVES

Diabetes mellitus and periodontal disease are highly prevalent among Indigenous Australian adults. Untreated periodontitis impacts glycaemic control in people with diabetes. The aim of this study was to report on the effect of periodontal therapy on glycaemic control among people with obesity.

METHODS

This subgroup analysis is limited to 62 participants with diabetes from the original 273 Aboriginal Australian adults enrolled into the PerioCardio study. Intervention participants received full-mouth non-surgical periodontal scaling during a single, untimed session while controls were untreated. Endpoints of interest included change in glycated haemoglobin (HbA1c), C-reactive protein (CRP) and periodontal status at 3 months post-intervention.

RESULTS

There were more females randomized to the treatment group (n = 17) than control (n = 10) while the control group had a higher overall body mass index (BMI) [mean (SD)] 33.1 (9.7 kg m^-2 ) versus 29.9 (6.0 kg m^-2 ). A greater proportion of males were followed up at 3 months compared to females, P = 0.05. Periodontal therapy did not significantly reduce HbA1c: ancova difference in means 0.22 mmol mol^-1 (95% CI -6.25 to 6.69), CRP: ancova difference in means 0.64 (95% CI -1.08, 2.37) or periodontal status at 3 months.

CONCLUSIONS

Non-surgical periodontal therapy did not significantly reduce glycated haemoglobin in participants with type 2 diabetes. Reasons are likely to be multifactorial and may be influenced by persistent periodontal inflammation at the follow-up appointments. Alternatively, the BMI of study participants may impact glycaemic control via alternative mechanisms involving the interplay between inflammation and adiposity meaning HbA1c may not be amenable to periodontal therapy in these individuals.

Systematic Review and Meta-analysis of the Association Between Exposure to Environmental Tobacco Smoke and Periodontitis Endpoints Among Nonsmokers

OBJECTIVE

A systematic review was conducted to summarize the epidemiological evidence on environmental tobacco smoke (ETS) exposure and prevalent periodontitis endpoints among nonsmokers.

METHODS

We searched PubMed, EMBASE, Web of Science, Pro-Quest dissertations, and conference proceedings of a dental research association. We included studies from which prevalence odds ratios (POR) could be extracted for periodontitis determined by examiner measurements of clinical attachment level (CAL) and/or probing pocket depth (PD) or self-report of missing teeth. Studies determined ETS exposure by self-report or biomarker (cotinine) levels.

RESULTS

For studies reporting CAL and/or PD (n = 6), associations were stronger with cotinine-measured exposure (n = 3; random effects POR [95% prediction interval] = 1.63 (0.90, 2.96)) than self-reported exposure (n = 3; random effects POR = 1.15 (0.68, 1.96)). There was no meaningful difference in summary estimate for studies reporting CAL and/or PD endpoint (n = 6; random effects POR = 1.34 (0.93, 1.94)) as opposed to tooth loss (n = 2; random effects POR = 1.33 (0.52, 3.40)).

CONCLUSIONS

There appears to be a positive association between exposure to ETS and prevalent periodontitis endpoints among nonsmokers, the magnitude of which depended mostly on the method of ETS assessment.

IMPLICATIONS

The notoriety of ETS is often discussed in terms of its associations with cancer, chronic conditions like cardiovascular diseases, and respiratory illnesses in children. However, very little attention is paid to its association with oral diseases, especially periodontitis. Periodontitis affects a large proportion of the population and is a major cause of tooth loss. This study summarized the epidemiologic association between exposure to ETS and periodontitis among nonsmokers. Although the findings are consistent with a positive association, methodological weaknesses relating to study design, assessment of ETS, periodontitis, and adjustment covariates were highlighted and recommendations for improvement in future studies provided.

Directed Acyclic Graphs for Oral Disease Research

Directed acyclic graphs (DAGs) are nonparametric graphical tools used to depict causal relations in the epidemiologic assessment of exposure-outcome associations. Although their use in dental research was first advocated in 2002, DAGs have yet to be widely adopted in this field. DAGs help identify threats to causal inference such as confounders, bias due to subject selection, and inappropriate handling of missing data. DAGs can also inform the data analysis strategy based on relations among variables depicted on it. This article uses the example of a study of temporomandibular disorders (TMDs), investigating causal effects of facial injury on subsequent risk of TMD. We illustrate how DAGs can be used to identify 1) potential confounders, 2) mediators and the consequences of attempt to estimate direct causal effects, 3) colliders and the consequences of conditioning on colliders, and 4) variables that are simultaneously mediators and confounders and the consequences of adjustment for such variables. For example, one DAG shows that statistical adjustment for the pressure pain threshold would necessarily bias the causal relation between facial injury and TMD. Finally, we discuss the usefulness of DAGs during study design, subject selection, and choosing variables to be measured in a study.

MicroRNA expression profiles differentiate chronic pain condition subtypes

Chronic pain is a significant health care problem, ineffectively treated because of its unclear etiology and heterogeneous clinical presentation. Emerging evidence demonstrates that microRNAs (miRNAs) regulate the expression of pain-relevant genes, yet little is known about their role in chronic pain. Here, we evaluate the relationship among pain, psychological characteristics, plasma cytokines, and whole blood miRNAs in 22 healthy controls (HCs); 33 subjects with chronic pelvic pain (vestibulodynia, VBD); and 23 subjects with VBD and irritable bowel syndrome (VBD + IBS). VBD subjects were similar to HCs in self-reported pain, psychological profiles, and remote bodily pain. VBD + IBS subjects reported decreased health and function; and an increase in headaches, somatization, and remote bodily pain. Furthermore, VBD subjects exhibited a balance in proinflammatory and anti-inflammatory cytokines, whereas VBD + IBS subjects failed to exhibit a compensatory increase in anti-inflammatory cytokines. VBD subjects differed from controls in expression of 10 miRNAs of predicted importance for pain and estrogen signaling. VBD + IBS subjects differed from controls in expression of 11 miRNAs of predicted importance for pain, cell physiology, and insulin signaling. miRNA expression was correlated with pain-relevant phenotypes and cytokine levels. These results suggest that miRNAs represent a valuable tool for differentiating VBD subtypes (localized pain with apparent peripheral neurosensory disruption vs widespread pain with a central sensory contribution) that may require different treatment approaches.

Mu Opioid Splice Variant MOR-1K Contributes to the Development of Opioid-Induced Hyperalgesia

BACKGROUND

A subset of the population receiving opioids for the treatment of acute and chronic clinical pain develops a paradoxical increase in pain sensitivity known as opioid-induced hyperalgesia. Given that opioid analgesics are one of few treatments available against clinical pain, it is critical to determine the key molecular mechanisms that drive opioid-induced hyperalgesia in order to reduce its prevalence. Recent evidence implicates a splice variant of the mu opioid receptor known as MOR-1K in the emergence of opioid-induced hyperalgesia. Results from human genetic association and cell signaling studies demonstrate that MOR-1K contributes to decreased opioid analgesic responses and produces increased cellular activity via Gs signaling. Here, we conducted the first study to directly test the role of MOR-1K in opioid-induced hyperalgesia.

METHODS AND RESULTS

In order to examine the role of MOR-1K in opioid-induced hyperalgesia, we first assessed pain responses to mechanical and thermal stimuli prior to, during, and following chronic morphine administration. Results show that genetically diverse mouse strains (C57BL/6J, 129S6, and CXB7/ByJ) exhibited different morphine response profiles with corresponding changes in MOR-1K gene expression patterns. The 129S6 mice exhibited an analgesic response correlating to a measured decrease in MOR-1K gene expression levels, while CXB7/ByJ mice exhibited a hyperalgesic response correlating to a measured increase in MOR-1K gene expression levels. Furthermore, knockdown of MOR-1K in CXB7/ByJ mice via chronic intrathecal siRNA administration not only prevented the development of opioid-induced hyperalgesia, but also unmasked morphine analgesia.

CONCLUSIONS

These findings suggest that MOR-1K is likely a necessary contributor to the development of opioid-induced hyperalgesia. With further research, MOR-1K could be exploited as a target for antagonists that reduce or prevent opioid-induced hyperalgesia.

Parameter estimation in Cox models with missing failure indicators and the OPPERA study

In a prospective cohort study, examining all participants for incidence of the condition of interest may be prohibitively expensive. For example, the "gold standard" for diagnosing temporomandibular disorder (TMD) is a physical examination by a trained clinician. In large studies, examining all participants in this manner is infeasible. Instead, it is common to use questionnaires to screen for incidence of TMD and perform the "gold standard" examination only on participants who screen positively. Unfortunately, some participants may leave the study before receiving the "gold standard" examination. Within the framework of survival analysis, this results in missing failure indicators. Motivated by the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study, a large cohort study of TMD, we propose a method for parameter estimation in survival models with missing failure indicators. We estimate the probability of being an incident case for those lacking a "gold standard" examination using logistic regression. These estimated probabilities are used to generate multiple imputations of case status for each missing examination that are combined with observed data in appropriate regression models. The variance introduced by the procedure is estimated using multiple imputation. The method can be used to estimate both regression coefficients in Cox proportional hazard models as well as incidence rates using Poisson regression. We simulate data with missing failure indicators and show that our method performs as well as or better than competing methods. Finally, we apply the proposed method to data from the OPPERA study.

COMT Diplotype Amplifies Effect of Stress on Risk of Temporomandibular Pain

When measured once, psychological stress predicts development of painful temporomandibular disorder (TMD). However, a single measurement fails to characterize the dynamic nature of stress over time. Moreover, effects of stress on pain likely vary according to biological susceptibility. We hypothesized that temporal escalation in stress exacerbates risk for TMD, and the effect is amplified by allelic variants in a gene, catechol-O-methyltransferase (COMT), regulating catechol neurotransmitter catabolism. We used data from the Orofacial Pain: Prospective Evaluation and Risk Assessment prospective cohort study of 2,707 community-dwelling adults with no lifetime history of TMD on enrollment. At baseline and quarterly periods thereafter, the Perceived Stress Scale (PSS) measured psychological stress. Genotyped DNA from blood samples determined COMT diplotypes. During follow-up of 0.25 to 5.2 y, 248 adults developed examiner-verified incident TMD. PSS scores at baseline were 20% greater (P < 0.001) in adults who developed incident TMD compared with TMD-free controls. Baseline PSS scores increased by 9% (P = 0.003) during follow-up in cases but remained stable in controls. This stress escalation was limited to incident cases with COMT diplotypes coding for low-activity COMT, signifying impaired catabolism of catecholamines. Cox regression models confirmed significant effects on TMD hazard of both baseline PSS (P < 0.001), modeled as a time-constant covariate, and change in PSS (P < 0.001), modeled as a time-varying covariate. Furthermore, a significant (P = 0.04) interaction of COMT diplotype and time-varying stress showed that a postbaseline increase of 1.0 standard deviation in PSS more than doubled risk of TMD incidence in subjects with low-activity COMT diplotypes (hazard ratio = 2.35; 95% confidence limits: 1.66, 3.32), an effect not found in subjects with high-activity COMT diplotypes (hazard ratio = 1.42; 95% confidence limits: 0.96, 2.09). Findings provide novel insights into dynamic effects of psychological stress on TMD pain, highlighting that effects are most pronounced in individuals whose genetic susceptibility increases responsiveness to catecholamine neurotransmitters.

The effect of lifetime fluoridation exposure on dental caries experience of younger rural adults

BACKGROUND

The aim of this study was to confirm whether the level of lifetime fluoridation exposure is associated with lower dental caries experience in younger adults (15-46 years).

METHODS

Data of the cohort born between 1960 and 1990 residing outside Australia's capital cities from the 2004-2006 Australian National Survey of Adult Oral Health were analysed. Residential history questionnaires were used to determine the percentage of each person's lifetime exposure to fluoridated water (<50%/50+%). Examiners recorded decayed, missing and filled permanent teeth (DMFT). Socio-demographic variables, periodontal risk factors, and access to dental care were included in multivariable least-squares regression models.

RESULTS

In bivariate analysis, the higher level of fluoridation category had significantly lower DMFT (mean 6.01 [SE=0.62]) than the lower level of fluoridation group (9.14 [SE=0.73] p<0.01) and lower numbers of filled teeth (4.08 [SE=0.43], 7.06 [SE=0.62], p<0.01). In multivariate analysis, the higher number of full-time equivalent dentists per 100,000 people was associated with a lower mean number of missing teeth (regression coefficient estimate=-1.75, p=0.03), and the higher level of water fluoridation with a lower mean DMFT (-2.45, p<0.01) and mean number of filled teeth (-2.52, p<0.01).

CONCLUSIONS

The higher level of lifetime fluoridation exposure was associated with substantially lower caries experience in younger rural adults, largely due to a lower number of filled teeth.

The nicotinic α6 subunit gene determines variability in chronic pain sensitivity via cross-inhibition of P2X2/3 receptors

Chronic pain is a highly prevalent and poorly managed human health problem. We used microarray-based expression genomics in 25 inbred mouse strains to identify dorsal root ganglion (DRG)-expressed genetic contributors to mechanical allodynia, a prominent symptom of chronic pain. We identified expression levels of Chrna6, which encodes the α6 subunit of the nicotinic acetylcholine receptor (nAChR), as highly associated with allodynia. We confirmed the importance of α6* (α6-containing) nAChRs by analyzing both gain- and loss-of-function mutants. We find that mechanical allodynia associated with neuropathic and inflammatory injuries is significantly altered in α6* mutants, and that α6* but not α4* nicotinic receptors are absolutely required for peripheral and/or spinal nicotine analgesia. Furthermore, we show that Chrna6's role in analgesia is at least partially due to direct interaction and cross-inhibition of α6* nAChRs with P2X2/3 receptors in DRG nociceptors. Finally, we establish the relevance of our results to humans by the observation of genetic association in patients suffering from chronic postsurgical and temporomandibular pain.

Update on Prevalence of Periodontitis in Adults in the United States: NHANES 2009 to 2012

BACKGROUND

This report describes prevalence, severity, and extent of periodontitis in the US adult population using combined data from the 2009 to 2010 and 2011 to 2012 cycles of the National Health and Nutrition Examination Survey (NHANES).

METHODS

Estimates were derived for dentate adults, aged ≥30 years, from the US civilian non-institutionalized population. Periodontitis was defined by combinations of clinical attachment loss (AL) and periodontal probing depth (PD) from six sites per tooth on all teeth, except third molars, using standard surveillance case definitions. For the first time in NHANES history, sufficient numbers of non-Hispanic Asians were sampled in 2011 to 2012 to provide reliable estimates of their periodontitis prevalence.

RESULTS

In 2009 to 2012, 46% of US adults, representing 64.7 million people, had periodontitis, with 8.9% having severe periodontitis. Overall, 3.8% of all periodontal sites (10.6% of all teeth) had PD ≥4 mm, and 19.3% of sites (37.4% teeth) had AL ≥3 mm. Periodontitis prevalence was positively associated with increasing age and was higher among males. Periodontitis prevalence was highest in Hispanics (63.5%) and non-Hispanic blacks (59.1%), followed by non-Hispanic Asian Americans (50.0%), and lowest in non-Hispanic whites (40.8%). Prevalence varied two-fold between the lowest and highest levels of socioeconomic status, whether defined by poverty or education.

CONCLUSIONS

This study confirms a high prevalence of periodontitis in US adults aged ≥30 years, with almost fifty-percent affected. The prevalence was greater in non-Hispanic Asians than non-Hispanic whites, although lower than other minorities. The distribution provides valuable information for population-based action to prevent or manage periodontitis in US adults.

Does lower lifetime fluoridation exposure explain why people outside capital cities have poor clinical oral health?

BACKGROUND

Australians outside state capital cities have greater caries experience than their counterparts in capital cities. We hypothesized that differing water fluoridation exposure was associated with this disparity.

METHODS

Data were the 2004-06 Australian National Survey of Adult Oral Health. Examiners measured participant decayed, missing and filled teeth and DMFT Index, and lifetime fluoridation exposure was quantified. Multivariable linear regression models estimated differences in caries experience between capital city residents and others, with and without adjustment for fluoridation exposure.

RESULTS

There was greater mean lifetime fluoridation exposure in state capital cities (59.1%, 95% confidence interval = 56.9, 61.4) than outside capital cities (42.3, confidence interval = 36.9, 47.6). People located outside capital city areas had differing sociodemographic characteristics and dental visiting patterns, and a higher mean DMFT (capital cities = 12.9, non-capital cities = 14.3, p = 0.02), than people from capital cities. After adjustment for sociodemographic characteristics and dental visits, DMFT of people living in capital cities was less than non-capital city residents (regression coefficient = 0.8, p = 0.01). The disparity was no longer statistically significant (regression coefficient = 0.6, p = 0.09) after additional adjustment for fluoridation exposure.

Tooth loss, periodontal disease, and cognitive decline in the Atherosclerosis Risk in Communities (ARIC) study

OBJECTIVE

The purpose of this prospective study was to investigate whether poor oral health predicted 8-year cognitive function change in predominantly late middle adults in the Atherosclerosis Risk in Communities (ARIC) study.

METHODS

Participants included a subset of ARIC participants aged 52-75 years at 1996-1998 from two study sites: Forsyth County NC and Jackson MS. All subjects completed cognitive function assessments both in 1996-1998 and 2004-2006, and the same subjects received a dental examination at the initial visit. Cognitive assessment consisted of delayed word recall (DWR), digit symbol substitution (DSS), and word fluency (WF) tests. In the analysis, cognitive function for 911 dentally screened participants was evaluated, and 558 of 785 dentate participants received comprehensive oral examinations, including periodontal probing. Measures of oral health included dental status, number of teeth, and periodontal disease classified by the biofilm-gingival interface (BGI) index. The generalized estimating equations (GEE) method was used to analyze repeated measures of cognitive scores with adjustment for socio-demographic characteristics and cardiovascular risk factors.

RESULTS

Of 911 study participants, 13.8% were edentulous. About 13% of dentally examined participants had periodontal pockets (≥ 4 mm) with severe bleeding. At the follow-up visit, DWR and WF scores were lower in edentulous compared to dentate people, whereas other oral health measures were not associated with cognitive function. Mean values declined over time for all three cognitive measures, although poor oral health conditions were not associated with greater degree of decline in cognitive function.

CONCLUSIONS

In these late middle-aged adults, complete tooth loss was significantly associated with lower cognitive performance. However, neither edentulism, number of teeth, nor periodontal disease predicted greater subsequent cognitive decline.

Epistasis between polymorphisms in COMT, ESR1, and GCH1 influences COMT enzyme activity and pain

Abnormalities in the enzymatic activity of catechol-O-methyltransferase (COMT) contribute to chronic pain conditions, such as temporomandibular disorders (TMD). Thus, we sought to determine the effects of polymorphisms in COMT and functionally related pain genes in the COMT pathway (estrogen receptor 1 [ESR1], guanosine-5-triphosphate cyclohydrolase 1 [GCH1], methylenetetrahydrofolate reductase [MTHFR]) on COMT enzymatic activity, musculoskeletal pain, and pain-related intermediate phenotypes among TMD cases and healthy control subjects. Results show that the COMT rs4680 (val(158)met) polymorphism is most strongly associated with outcome measures, such that individuals with the minor A allele (met) exhibit reduced COMT activity, increased TMD risk, and increased musculoskeletal pain. Epistatic interactions were observed between the COMT rs4680 polymorphism and polymorphisms in GCH1 and ESR1. Among individuals with the COMT met allele, those with 2 copies of the GCH1 rs10483639 minor G allele exhibit normalized COMT activity and increased mechanical pain thresholds. Among individuals with the COMT val allele, those with 2 copies of the ESR1 rs3020377 minor A allele exhibit reduced COMT activity, increased bodily pain, and poorer self-reported health. These data reveal that the GCH1 minor G allele confers a protective advantage among met carriers, whereas the ESR1 minor A allele is disadvantageous among val carriers. Furthermore, these data suggest that the ability to predict the downstream effects of genetic variation on COMT activity is critically important to understanding the molecular basis of chronic pain conditions.

Projections of U.S. Edentulism prevalence following 5 decades of decline

After decades of decline in prevalence of complete tooth loss (edentulism), the trend continues to be misinterpreted, producing flawed projections and misdirected health goals. We investigated population trends in edentulism among U.S. adults aged ≥ 15 yr by creating time-series data from 5 national cross-sectional health surveys: 1957-1958 (n ≈ 100,000 adults), 1971-1975 (n = 14,655 adults), 1988-1998 (n = 18,011 adults), 1999-2002 (n = 12,336 adults), and 2009-2012 (n = 10,522 adults). Birth cohort analysis was used to isolate age and cohort effects. Geographic and sociodemographic variation in prevalence was investigated with a sixth U.S. survey of 432,519 adults conducted in 2010. Prevalence through 2050 was projected with age-cohort regression models using Monte-Carlo simulation of prediction intervals. Across the 5-decade observation period, edentulism prevalence declined from 18.9% in 1957-1958 (95% confidence limits: 18.4%, 19.4%) to 4.9% in 2009-2012 (95% confidence limits: 4.0%, 5.8%). The most influential determinant of the decline was the passing of generations born before the 1940s, whose rate of edentulism incidence (5%-6% per decade of age) far exceeded later cohorts (1%-3% per decade of age). High-income households experienced a greater relative decline, although a smaller absolute decline, than low-income households. By 2010, edentulism was a rare condition in high-income households, and it had contracted geographically to states with disproportionately high poverty. With the passing of generations born in the mid-20th century, the rate of decline in edentulism is projected to slow, reaching 2.6% (95% prediction limits: 2.1%, 3.1%) by 2050. The continuing decline will be offset only partially by population growth and population aging such that the predicted number of edentulous people in 2050 (8.6 million; 95% prediction limits: 6.8 million, 10.3 million) will be 30% lower than the 12.2 million edentulous people in 2010.

Pressure pain thresholds fluctuate with, but do not usefully predict, the clinical course of painful temporomandibular disorder

Central sensitization elicits pain hypersensitivity and is thought to be causally implicated in painful temporomandibular disorder (TMD). This causal inference is based on cross-sectional evidence that people with TMD have greater sensitivity than controls to noxious stimuli. We tested this inference in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) prospective cohort study of 3258 adults with no lifetime history of TMD when enrolled (visit 1). During 5 years of follow-up, 1 group labeled "persistent TMD cases" (n=72) developed first-onset TMD by visit 2 that persisted ⩾ 6 months until visit 3. Another group labeled "transient TMD cases" (n=75) developed first-onset TMD at visit 2, which resolved by visit 3. Randomly sampled "controls" (n=126) remained TMD-free throughout all 3 visits. At each visit, pressure pain thresholds (PPTs) were measured by algometry at 10 cranial and bodily sites. In persistent TMD case patients, mean PPTs reduced 43 kPa (P<.0001) between visits 1 and 2 and thereafter did not change significantly. In transient TMD case patients, mean PPTs reduced 41 kPa (P<.001) between visits 1 and 2, and then increased 20 kPa (P<.001) by visit 3. These patterns were similar after excluding cranial sites symptomatic for TMD. Importantly, visit 1 PPTs had no clinically useful prognostic value in predicting first-onset TMD (odds ratio [OR]=1.07, P=.15). Among first-onset case patients, visit 2 PPTs were modest predictors of persistent TMD (OR=1.36, P=.002). In this longitudinal study, PPTs reduced when TMD developed then rebounded when TMD resolved. However, premorbid PPTs poorly predicted TMD incidence, countering the hypothesis that PPTs signify mechanisms causing first-onset TMD.