Pilot GWAS of caries in African-Americans shows genetic heterogeneity

BACKGROUND

Dental caries is the most common chronic disease in the US and disproportionately affects racial/ethnic minorities. Caries is heritable, and though genetic heterogeneity exists between ancestries for a substantial portion of loci associated with complex disease, a genome-wide association study (GWAS) of caries specifically in African Americans has not been performed previously.

METHODS

We performed exploratory GWAS of dental caries in 109 African American adults (age > 18) and 96 children (age 3-12) from the Center for Oral Health Research in Appalachia (COHRA1 cohort). Caries phenotypes (DMFS, DMFT, dft, and dfs indices) assessed by dental exams were tested for association with 5 million genotyped or imputed single nucleotide polymorphisms (SNPs), separately in the two age groups. The GWAS was performed using linear regression with adjustment for age, sex, and two principal components of ancestry. A maximum of 1 million adaptive permutations were run to determine empirical significance.

RESULTS

No loci met the threshold for genome-wide significance, though some of the strongest signals were near genes previously implicated in caries such as antimicrobial peptide DEFB1 (rs2515501; p = 4.54 × 10- 6) and TUFT1 (rs11805632; p = 5.15 × 10- 6). Effect estimates of lead SNPs at suggestive loci were compared between African Americans and Caucasians (adults N = 918; children N = 983). Significant (p < 5 × 10- 8) genetic heterogeneity for caries risk was found between racial groups for 50% of the suggestive loci in children, and 12-18% of the suggestive loci in adults.

CONCLUSIONS

The genetic heterogeneity results suggest that there may be differences in the contributions of genetic variants to caries across racial groups, and highlight the critical need for the inclusion of minorities in subsequent and larger genetic studies of caries in order to meet the goals of precision medicine and to reduce oral health disparities.

Fear of Pain Mediates the Association between MC1R Genotype and Dental Fear

Fear of pain is experienced in acute and chronic pain populations, as well as in the general population, and it affects numerous aspects of the orofacial pain experience, including pain intensity, pain-related disability, and pain behavior (e.g., avoidance). A related but separate construct-dental fear-is also experienced in the general population, and it influences dental treatment-seeking behavior and oral and systemic health. Minimal work has addressed the role of genetics in the etiologies of fear of pain and dental fear. Limited available data suggest that variants of the melanocortin 1 receptor (MC1R) gene may predict greater levels of dental fear. The MC1R gene also may be etiologically important for fear of pain. This study aimed to replicate the finding that MC1R variant status predicts dental fear and to determine, for the first time, whether MC1R variant status predicts fear of pain. Participants were 817 Caucasian participants (62.5% female; mean ± SD age: 34.7 ± 8.7 y) taking part in a cross-sectional project that identified determinants of oral diseases at the community, family, and individual levels. Participants were genotyped for single-nucleotide polymorphisms on MC1R and completed self-report measures of fear of pain and dental fear. Presence of MC1R variant alleles predicted higher levels of dental fear and fear of pain. Importantly, fear of pain mediated the relation between MC1R variant status and dental fear (B = 1.60, 95% confidence interval: 0.281 to 3.056). MC1R variants may influence orofacial pain perception and, in turn, predispose individuals to develop fears about pain. Such fears influence the pain experience and associated pain behaviors, as well as fears about dental treatment. This study provides support for genetic contributions to the development/maintenance of fear of pain and dental fear, and it offers directions for future research to identify potential targets for intervention in the treatment of fear of pain and dental fear.

Bayesian Analysis of the Association between Family-Level Factors and Siblings' Dental Caries

We conducted a Bayesian analysis of the association between family-level socioeconomic status and smoking and the prevalence of dental caries among siblings (children from infant to 14 y) among children living in rural and urban Northern Appalachia using data from the Center for Oral Health Research in Appalachia (COHRA). The observed proportion of siblings sharing caries was significantly different from predicted assuming siblings' caries status was independent. Using a Bayesian hierarchical model, we found the inclusion of a household factor significantly improved the goodness of fit. Other findings showed an inverse association between parental education and siblings' caries and a positive association between households with smokers and siblings' caries. Our study strengthens existing evidence suggesting that increased parental education and decreased parental cigarette smoking are associated with reduced childhood caries in the household. Our results also demonstrate the value of a Bayesian approach, which allows us to include household as a random effect, thereby providing more accurate estimates than obtained using generalized linear mixed models.

Genetic Association of MPPED2 and ACTN2 with Dental Caries

The first genome-wide association study of dental caries focused on primary teeth in children aged 3 to 12 yr and nominated several novel genes: ACTN2, EDARADD, EPHA7, LPO, MPPED2, MTR, and ZMPSTE24. Here we interrogated 156 single-nucleotide polymorphisms (SNPs) within these candidate genes for evidence of association with dental caries experience in 13 race- and age-stratified samples from 6 independent studies (n = 3600). Analysis was performed separately for each sample, and results were combined across samples via meta-analysis. MPPED2 was significantly associated with caries via meta-analysis across the 5 childhood samples, with 4 SNPs showing significant associations after gene-wise adjustment for multiple comparisons (p < .0026). These results corroborate the previous genome-wide association study, although the functional role of MPPED2 in caries etiology remains unknown. ACTN2 also showed significant association via meta-analysis across childhood samples (p = .0014). Moreover, in adults, genetic association was observed for ACTN2 SNPs in individual samples (p < .0025), but no single SNP was significant via meta-analysis across all 8 adult samples. Given its compelling biological role in organizing ameloblasts during amelogenesis, this study strengthens the hypothesis that ACTN2 influences caries risk. Results for the other candidate genes neither proved nor precluded their associations with dental caries.

Subantimicrobial dose doxycycline as an adjunct to scaling and root planing: post-treatment effects

BACKGROUND/OBJECTIVE

Subantimicrobial dose doxycycline (SDD 20 mg bid) plus scaling and root planing (SRP) significantly improved clinical attachment level (CAL) and reduced probing depth (PD) compared with placebo plus SRP in a double-blind, placebo-controlled, multicenter study of patients with adult periodontitis (AP). In a study conducted as a follow-up, the post-treatment effects of SDD were assessed in patients who completed the SRP study.

METHODS

The SRP study was a 9-month, active-treatment study and the follow-up was a 3-month, no-treatment study. In the SRP study, tooth sites in qualifying quadrants were scaled and root planed and patients were randomized to receive twice daily SDD 20 mg or placebo. In the follow-up, patients received no study drug; investigators and patients remained blinded to the previous treatment group assignments. Efficacy measures included the change in CAL and PD from baseline values determined at the start of the SRP study in tooth sites stratified by baseline PD (i.e., 0-3 mm, 4-6 mm, > or =7 mm). Safety was evaluated using adverse event data and the results of clinical laboratory tests, oral pathology examinations, and microbiological assessments.

RESULTS

Within each disease stratum, the incremental improvements in PD and CAL demonstrated in the SDD group over 9 months of active treatment were maintained through 3 additional months of no treatment. Treatment cessation did not result in an accelerated regression of periodontal health. No differences in the incidence of adverse events (including those related to infection) or laboratory or microbiological parameters were noted between the SDD group and the placebo group.

CONCLUSIONS

The administration of SDD 20 mg bid for a period of up to 9 months is not associated with rebound effects or delayed or negative after-effects for a 3-month period after cessation of therapy.

Treatment with subantimicrobial dose doxycycline improves the efficacy of scaling and root planing in patients with adult periodontitis

BACKGROUND

In a previous study, subantimicrobial dose doxycycline (SDD) significantly improved clinical parameters associated with periodontal health in patients with adult periodontitis (AP) when used as an adjunct to a maintenance schedule of supragingival scaling and dental prophylaxis. In this double-blind, placebo-controlled, parallel-group, multicenter study, the efficacy and safety of SDD were evaluated in conjunction with scaling and root planing (SRP) in patients with AP.

METHODS

Patients (n = 190) received SRP at the baseline visit and were randomized to receive either SDD 20 mg bid or placebo bid for 9 months. Efficacy parameters included the per-patient mean changes in clinical attachment level (CAL) and probing depth (PD) from baseline, the per-patient percentages of tooth sites with attachment loss (AL) > or = 2 mm and > or = 3 mm from baseline, and the per-patient percentage of tooth sites with bleeding on probing. Prior to analysis, tooth sites were stratified by the degree of disease severity evident at baseline

RESULTS

In tooth sites with mild to moderate disease and severe disease (n = 183, intent-to-treat population), improvements in CAL and PD were significantly greater with adjunctive SDD than with adjunctive placebo at 3, 6, and 9 months (all P <0.05). In tooth sites with severe disease, the per-patient percentage of sites with AL > or = 2 mm from baseline to month 9 was significantly lower with adjunctive SDD than with adjunctive placebo (P<0.05). Improvements in clinical outcomes occurred without detrimental shifts in the normal periodontal flora or the acquisition of doxycycline resistance or multiantibiotic resistance. SDD was well tolerated, with a low incidence of discontinuations due to adverse events.

CONCLUSIONS

The adjunctive use of SDD with SRP is more effective than SRP alone and may represent a new approach in the long-term management of AP.

Long-term sub-antimicrobial doxycycline (Periostat) as adjunctive management in adult periodontitis: effects on subgingival bacterial population dynamics

Previous trials had indicated that various schedules of sub-antimicrobial doxycycline significantly reduced gingival crevicular fluid (GCF) collagenase activity in adult patients with periodontitis with no evidence of emergent tetracycline-resistant (Tcr) marker oral flora. The purpose of this nine-month study was to expand these observations, emphasizing newer microbial diagnostic methods. Subgingival paper point samples were obtained at baseline (BL), 3, 6, and 9 months. Four subject treatment groups in a double-blind design were evaluated by mechanical scaling and root planing (SRP) and/or 20 mg doxycycline BID (Periostat). Thirty-eight patients entered the study at baseline (BL). Dark-field microscopy on 260 samples showed that morphotype distribution was independent of treatment schedule. Culture analysis of the 3 most prevalent isolates recovered showed that Streptococcus and Prevotella species accounted for approximately 85% of the 724 cultures. There did not appear to be any overgrowth or replacement by opportunistic oral flora. Of 658 susceptibility patterns evaluated by Etest, the MIC50/90 and mode MIC showed stable patterns, independent of treatment group. Our findings were different from those of previously published reports, but may be partly explained by the lack of universally standardized methods in oral microbiology and interpretive criteria for susceptibility testing.

Tramadol hydrochloride: analgesic efficacy compared with codeine, aspirin with codeine, and placebo after dental extraction

Tramadol hydrochloride is a novel, centrally acting analgesic with two complementary mechanisms of action: opioid and aminergic. Relative to codeine, tramadol has similar analgesic properties but may have fewer constipating, euphoric, and respiratory depressant effects. A two-center randomized double-blind controlled clinical trial was performed to assess the analgesic efficacy and reported side effects of tramadol 100 mg, tramadol 50 mg, codeine 60 mg, aspirin (ASA) 650 mg with codeine 60 mg, and placebo. Using a third molar extraction pain model, 200 healthy subjects were enrolled in a 6-hour evaluation after a single dose of drug. Of the 200 patients enrolled, seven provided incomplete efficacy data or discontinued prematurely and one was lost to follow-up. Using standard measures of analgesia, including total pain relief score (TOTPAR), maximum pain relief score (MaxPAR), sum of pain intensity difference scores (SPID), peak pain intensity difference (Peak PID), remedication, and global evaluations, all active treatments were found to be numerically superior to placebo. ASA/codeine was found to be statistically superior to placebo for all measures of efficacy. Tramadol 100 mg was statistically superior to placebo for TOTPAR, SPID, and time of remedication, whereas tramadol 50 mg was statistically superior to placebo onlyfor remedication time. Codeine was not found to be statistically superior to placebo for any efficacy measure. A greater TOTPAR response compared with all other active measures was seen for ASA/codeine during the first 3 hours of study. The 6-hour TOTPAR scores for the tramadol groups and ASA/ codeine group were not significantly different. Gastrointestinal side effects (nausea, dysphagia, vomiting) were reported more frequently with tramadol 100 mg, ASA/ codeine, and codeine 60 mg than with placebo.

The "cyclic" regimen of low-dose doxycycline for adult periodontitis: a preliminary study

Specially-formulated low-dose doxycycline (LDD) regimens have been found to reduce collagenase activity in the gingival tissues and crevicular fluid (GCF) of adult periodontitis subjects in short-term studies. In the current, double-blind, placebo-controlled study, adult periodontitis patients were administered for 6 months a "cyclical" regimen of either LDD or placebo capsules; and various clinical parameters of periodontal disease severity, and both collagenase activity and degradation of the serum protein, alpha 1-PI, in the GCF were measured at different time periods. No significant differences between the LDD- and placebo-treated groups were observed for plaque index and gingival index. However, attachment levels, probing depth, and GCF collagenase activity and alpha 1-PI degradation were all beneficially and significantly (P < 0.05) affected by the drug regimen. We propose: 1) that LDD inhibits tissue destruction in the absence of either antimicrobial or significant anti-inflammatory efficacy; and 2) that long-term LDD could be a useful adjunct to instrumentation therapy in the management of the adult periodontitis patient.

A clinical trial of long-acting local anesthetics for periodontal surgery

The efficacy of long-acting local anesthetics for anesthesia during periodontal surgery and for analgesia during the immediate postoperative period was evaluated. The rationale for using long-acting local anesthetics such as etidocaine and bupivacaine is that they can provide surgical anesthesia and, because of their long duration, prevent discomfort that may occur for 4-6 hours postoperatively. Two clinical trials were performed. The first enrolled patients requiring bilateral periodontal surgery. Using a matched pair design and double-blind randomized study conditions, 2% lidocaine 1/100,000 epinephrine was compared with 1.5% etidocaine 1/200,000 epinephrine for periodontal surgery. The time until complete recovery and the time until pain onset were found to be longer for the etidocaine surgeries. Postoperative pain appeared more severe, and the need for oral analgesics was greater for the lidocaine surgeries. Surgeons' rating of surgical bleeding was significantly greater for the etidocaine procedures. When matched bilateral surgeries were not available, a second double-blind randomized parallel trial was performed that compared 1.5% etidocaine 1/200,000 epinephrine to 0.5% bupivacaine 1/200,000 epinephrine. No significant differences were seen in the quality of anesthesia, degree of bleeding, or postoperative pain between these two long-acting anesthetics.

Effect of linolenyl alcohol on the in-vitro growth of the oral bacterium Streptococcus mutans

The effect of primary aliphatic alcohols of varying chain length and degree of unsaturation on bacterial growth was assessed, using Strep. mutans BHT as the main test organism. Unsaturated alcohols, linoleyl and linolenyl, effectively inhibited bacterial growth. Of the saturated alcohols, only lauryl and myristyl alcohols inhibited the growth of Strep. mutans BHT, but at concentrations much higher than those required for the unsaturated alcohols. All Gram-positive organisms tested were sensitive to linolenyl alcohol. Gram-negative bacteria did not exhibit the sensitivity. Linoleic and linolenic acid were inactive as antibacterial agents at the same concentration as the related alcohol. Repeated exposure of Strep. mutans BHT to linolenyl alcohol produced no change in the sensitivity of the organism to the alcohol. Significant amounts of linolenyl alcohol were found in bacteria grown in the presence of this lipid for 24 h but linolenic acid was not detected. Thus the primary polyunsaturated aliphatic alcohols, particularly linolenyl alcohol, could be effective antibacterial agents for the prevention of dental caries and periodontal disease.