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K. Rintakoski, J. Kaprio, Legal Psychoactive Substances as Risk Factors for Sleep-Related Bruxism: A Nationwide Finnish Twin Cohort Study, Alcohol and Alcoholism, Volume 48, Issue 4, July/August 2013, Pages 487–494, https://doi.org/10.1093/alcalc/agt016
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Abstract
Aims: Different psychoactive factors including alcohol, coffee and tobacco, are considered as risk factors for bruxism. Often, heavy drinking and generous intake of coffee are correlated with smoking. Interactions between these agents may confound studies. The aim was to investigate the possible independent effects of drinking alcohol and coffee consumption on the occurrence of bruxism.
Methods: Data derived from the Finnish Twin Cohort study consisting of 12,502 twin individuals (45.6% men, 54.4% women, mean age 44 years) born during the 1930–1957. The twins responded to a questionnaire sent in 1990 (response rate of 77%) consisting of 103 multiple-choice questions, seven dealing with tobacco use, four on alcohol use, one about coffee consumption and two with bruxism.
Results: Increasing alcohol intake raised the risk for weekly bruxism even when adjusted for smoking status [heavy drinking odds ratio (OR) 1.9; 95% CI 1.23–2.84, binge drinking OR 1.6; 95% CI 1.28–2.12, and passing-out due to excessive alcohol intoxication at least twice within the previous year OR 1.5; 95% CI 1.09–2.18]. The situation was similar to that for coffee consumption of more than eight cups per day (OR 1.4; 95% CI 1.01–1.98). Interaction analyses for ‘smoking with risk factors’ revealed no statistically significant interactions. Current smoking was an independent risk factor for bruxism in all models (OR 2.3–2.7).
Conclusion: Given the observed associations between alcohol drinking, binge drinking, passing-out due to excessive alcohol intake and coffee consumption, the results support our hypothesis of an independent association of both alcohol use, and coffee consumption with bruxism.
INTRODUCTION
Sleep-related movement disorder sleep bruxism (SB; AASM, 2005) is strongly related to micro-arousals from sleep and is manifested by teeth grinding and/or clenching (Macaluso et al., 1998; De Laat and Macaluso, 2002; Lavigne et al., 2003). SB is often associated with disorders of the dopaminergic system (Lobbezoo et al., 1997a, 1997b; Lavigne et al., 2001; Chen et al., 2005; Lobbezoo et al., 2006) and sleep disturbances (Ohayon et al., 2001; Lavigne et al., 2008). Risk factors associated with SB include among others alcohol and coffee consumption, smoking and nicotine dependence (Lavigne and Manzini, 2000; Ohayon et al., 2001; Lobbezoo et al., 2006; Rintakoski et al., 2010a, 2010b). However, only a few epidemiological studies about the role of legal psychoactive substances in the aetiology of bruxism exist.
Psychoactive substances affect the central nervous system and cause changes in mood, conscious behaviour and cognition (WHO, 2004). They are divided into three groups: stimulants (e.g. caffeine which act as adenosine receptor antagonists), depressants (e.g. alcohol which act as gamma-aminobutyric acid receptor agonists and NMDA receptor antagonists) and hallucinogens (e.g. LSD). However, nicotine as acetylcholine agonists acts as both stimulant and depressant depending on the dose (Henningfield et al., 2009). In our present study, we focused on two legal non-medicational psychoactive substances, coffee (caffeine and stimulant) and alcohol (ethanol and depressant). The use of medicational psychoactive substances is often a consequence of a known disease that by itself may affect SB. Furthermore, the use of illegal drugs is usually under-reported or the users are less likely to participate in surveys. Therefore, we omitted medicational and illegal psychoactive substances from the present study.
In most of the previous studies on bruxism, both caffeine (Molina et al., 2001; Ohayon et al., 2001,) and alcohol consumption (Molina et al., 2001; Ohayon et al., 2001; Bellini et al., 2011) appeared to be associated with a higher risk of bruxism. However, Hartmann et al. (1987) found no significant effect of alcohol intake on bruxism, although those authors reported a slight positive trend. Nonetheless, the number of such studies is small, and the results are partly contradictory. Previous studies have shown smoking to affect sleep-related bruxism. Among others (Lavigne et al., 1997; Molina et al., 2001; Ohayon et al., 2001; Ahlberg et al., 2004; Johansson et al., 2004; Ahlberg et al., 2005), we previously reported strong association between current smoking, the amounts smoked and nicotine dependence with sleep-related bruxism (Rintakoski et al., 2010a, 2010b). Furthermore, smoking is known to associate positively with both alcohol consumption and coffee intake (Istvan and Matarazzo, 1984; Henningfield et al., 1990; Madden and Heath, 2002). The relationship between alcohol consumption and smoking is quite strong (Grucza amd Bierut, 2006; De Leon et al., 2007). Some associations have also been found for the consumption of caffeine with alcohol use and with the use of tobacco. The relationship between coffee and smoking seems to be stronger than that of caffeine consumption and alcohol intake (Istvan and Matarazzo, 1984; Laitala et al., 2008). Hence, coffee, alcohol intake and smoking affect each other, and these mutual and possibly interacting relationships need to be taken into account when studying their individual roles in the pathogenesis of a disease.
Thus, the aim of the present study was to examine the possible roles of two legal psychoactive drugs in common use namely, caffeine and alcohol as risk factors for SB when smoking behaviour is controlled in a large population-based cohort of adult twins.
MATERIALS AND METHODS
Materials
Twin individuals (n = 12 502) responded to a questionnaire (response rate of 77%) sent in 1990 as part of the third survey of the longitudinal Finnish Twin Cohort study. The twins were born in the 1930–1957 inclusive period and were residing in Finland in 1987 as described earlier (Hublin et al., 1994; Hublin et al., 1997). The mean age of the respondents in 1990 was 44 years. An accurate and validated questionnaire method was used for the determination of zygosity (Sarna et al., 1978), which left about seven of twin pairs unclassified. This method has a misclassification probability as low as 1.7%. The validity of the questionnaire was further verified in a subsample, using 11 blood markers (Sarna et al., 1978). The ethics committee of the Department of Public Health, University of Helsinki, approved the study protocol. Subjects were informed about the study goals before they provided their informed consent.
The questionnaire that was sent in 1990 consisted of 103 multiple choice questions, of which 4 were about alcohol use, 7 about tobacco use and 22 about sleep and vigilance matters, including perceived bruxism (Hublin and Kaprio, 2003). In addition, coffee consumption habits had been sought in the two previous surveys of 1975 and 1981 (Laitala et al., 2008).
Study variables
We evaluated sleep-related bruxism with the following question: Have you experienced bruxism during night time at adulthood? The answer options were: (a) weekly, (b) monthly, (c) occasionally, (d) never and (e) I do not know. The option (d) was used as the reference category. Subjects who used option (e) in their response were excluded from the analyses leaving 10,229 twin individuals with some information about bruxism. The first three categories were combined as ‘any bruxism’ for some analyses.
Coffee consumption habits were enquired about in the 1975 and 1981 surveys and not in the 1990 survey. We used the information from 1981 for our analyses, as this was conducted chronologically closer to the 1990 survey. We assessed the coffee consumption as a continuous variable with the following question: How many cups of coffee do you drink daily? Those who did not use coffee daily were asked to answer zero. For the analyses, we divided coffee consumption into three groups: zero to three cups per day, four to eight cups per day and more than eight cups per day.
Alcohol consumption was analysed using multiple-choice questions that sought the information on weekly consumption of beer and wine and monthly consumption of spirits. We computed the answers to derive the weekly amounts of alcohol intake (Kaprio et al., 1987). The subjects were categorized into four groups according to the computation: abstainers, light drinkers (≤3 drinks per week), moderate drinkers (>3 to ≤7 drinks per week for women and >3 to ≤14 for men) and heavy drinkers (>7 for women drinks per week and >14 for men) as described elsewhere (Järvenpää et al., 2005). The frequency of alcohol consumption was enquired separately for each of the three beverage types. The five frequency of alcohol categories ranged from no use to more than 16 days per month use. We also asked about binge drinking with the following question: do you drink more than five bottles of beer at least once a month, one bottle of wine or half a bottle of spirits (or the equivalent amounts of other alcoholic beverages) on the same occasion? The answer options were (a) no or (b) yes. We also analysed the frequency of passing-out due to excessive alcohol intake within the previous year. We classified the answers into three groups: never, once and two or more times (Virta et al., 2010).
Smoking status was categorized as never, former, occasional and current (daily). These categories were used in the multinomial logistic regression analyses to adjust for smoking status (Rintakoski et al., 2010a). For further analyses performed separately for different smoking status groups, the daily and occasional smokers were grouped as all-current-smokers, whereas the ‘never’ and former-smokers were grouped as non-smokers. Information about social class was obtained by answers to the open question ‘what is your occupation, or if are not working at the moment: what was your earlier occupation? Describe it as precisely as possible.’ Social class was determined according to the Central Statistical Office of Finland's classification using occupational information (Kaprio and Koskenvuo, 1988; Broms et al., 2004; Ropponen et al., 2011; Official Statistics of Finland (OSF), 2012) and further categorized as white-collar, blue-collar and others.
Statistical methods
In most analyses, subjects were treated as individuals even though data were collected from twins sampled as twin pairs. Therefore, the individual observations within pairs could not be considered as fully independent. We corrected for this lack of statistical independnce by adjusting the models for clustering within pairs by the cluster command in Stata 11.0 (StataCorp, 2005), using a robust estimator of variance (Williams, 2000). We also studied the associations between each different risk factor and bruxism in sequence using cross-tabulations and the Pearson chi-square test of independence, corrected for clustered sampling of twins within pairs, which was expressed as an F-ratio (Rao and Scott, 1984).
Furthermore, we assessed the associations between different risk factors and bruxism using multinomial logistic regression models (Hosmer and Lemeshow, 2000) that were adjusted for age and sex (model I) and for age, sex and smoking status (model II). These models were calculated separately for coffee intake and alcohol variables, and further analyses were performed for the combinations of alcohol variables. The analyses were performed for three different bruxism outcome categories (weekly, monthly and rarely). We also calculated logistic regression models separately for all-current-smokers and non-smokers to obtain specific information about the relationship of smoking and the other risk factors with bruxism.
To determine the possible interaction between the consumption of alcohol or coffee and smoking, we calculated likelihood-ratio tests that compared the multinomial logistic regression models with and without interaction variables to reveal any possible combinations of variables that affected bruxism.
Twin pairs discordant for bruxism and the given variable were used to reveal any genetic influence that might affect the correlation between bruxism and psychoactive substances studied (caffeine and alcohol). Co-twins usually share much of the childhood environment and either all [monozygotic (MZ)] or some [dizygotic (DZ)] of the variability in their genome. Pairwise analyses were performed to determine whether the twin member with less risky behaviours than his/her co-twin had a lower risk for bruxism. The odds ratios (ORs) for the risk of bruxism in relation to psychoactive substance in discordant twin pairs were calculated using the dichotomous variable ‘any bruxism’ and compared with the ‘never bruxism’ category as the reference category. Cross tabulation and conditional logistic regression models were calculated for all discordant twin pairs, and for MZ and DZ discordant twin pairs separately.
RESULTS
Of the 12,502 twin individuals, 30% were MZ twins, 63% DZ and the zygosity of the remaining 7% were not known. The mean age of the participants was 44 (SD ± 7.79) years of which 54% were women. Information about bruxism was available for 10,229 individuals of which: 4% reported bruxism weekly, 4% monthly, 19% rarely and the rest 72% never. Frequencies of coffee and alcohol consumption, other alcohol variables and smoking were given for the weekly, monthly, rarely and never bruxism categories and are shown in Table 1.
. | n . | Weekly . | Bruxism . | Never . | |
---|---|---|---|---|---|
Monthly . | Rarely . | ||||
Sex | |||||
Men | 4754 | 4 | 5 | 21 | 70 |
Women | 5475 | 4 | 4 | 18 | 73 |
Coffee intake | |||||
0–3 cups/day | 2737 | 4 | 4 | 19 | 73 |
3.5–8 cups/day | 5924 | 4 | 4 | 20 | 72 |
>8 cups/day | 943 | 7 | 5 | 19 | 69 |
Alcohol consumptiona | |||||
Abstainer | 1430 | 3 | 2 | 16 | 79 |
Light drinker | 3656 | 4 | 4 | 18 | 74 |
Moderate drinker | 3613 | 4 | 5 | 21 | 71 |
Heavy drinker | 1485 | 7 | 7 | 23 | 64 |
Binge drinkingb | |||||
No | 7318 | 3 | 4 | 18 | 74 |
Yes | 2791 | 6 | 6 | 22 | 66 |
Passing-outc | |||||
No | 8754 | 4 | 4 | 19 | 73 |
0–1 | 646 | 6 | 6 | 22 | 67 |
<2 | 712 | 7 | 6 | 25 | 63 |
Smoking status | |||||
Never | 4704 | 3 | 3 | 16 | 77 |
Occasional | 332 | 1 | 3 | 20 | 75 |
Former smoker | 2296 | 3 | 5 | 22 | 69 |
Current smoker | 2623 | 7 | 5 | 23 | 64 |
. | n . | Weekly . | Bruxism . | Never . | |
---|---|---|---|---|---|
Monthly . | Rarely . | ||||
Sex | |||||
Men | 4754 | 4 | 5 | 21 | 70 |
Women | 5475 | 4 | 4 | 18 | 73 |
Coffee intake | |||||
0–3 cups/day | 2737 | 4 | 4 | 19 | 73 |
3.5–8 cups/day | 5924 | 4 | 4 | 20 | 72 |
>8 cups/day | 943 | 7 | 5 | 19 | 69 |
Alcohol consumptiona | |||||
Abstainer | 1430 | 3 | 2 | 16 | 79 |
Light drinker | 3656 | 4 | 4 | 18 | 74 |
Moderate drinker | 3613 | 4 | 5 | 21 | 71 |
Heavy drinker | 1485 | 7 | 7 | 23 | 64 |
Binge drinkingb | |||||
No | 7318 | 3 | 4 | 18 | 74 |
Yes | 2791 | 6 | 6 | 22 | 66 |
Passing-outc | |||||
No | 8754 | 4 | 4 | 19 | 73 |
0–1 | 646 | 6 | 6 | 22 | 67 |
<2 | 712 | 7 | 6 | 25 | 63 |
Smoking status | |||||
Never | 4704 | 3 | 3 | 16 | 77 |
Occasional | 332 | 1 | 3 | 20 | 75 |
Former smoker | 2296 | 3 | 5 | 22 | 69 |
Current smoker | 2623 | 7 | 5 | 23 | 64 |
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women), and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
. | n . | Weekly . | Bruxism . | Never . | |
---|---|---|---|---|---|
Monthly . | Rarely . | ||||
Sex | |||||
Men | 4754 | 4 | 5 | 21 | 70 |
Women | 5475 | 4 | 4 | 18 | 73 |
Coffee intake | |||||
0–3 cups/day | 2737 | 4 | 4 | 19 | 73 |
3.5–8 cups/day | 5924 | 4 | 4 | 20 | 72 |
>8 cups/day | 943 | 7 | 5 | 19 | 69 |
Alcohol consumptiona | |||||
Abstainer | 1430 | 3 | 2 | 16 | 79 |
Light drinker | 3656 | 4 | 4 | 18 | 74 |
Moderate drinker | 3613 | 4 | 5 | 21 | 71 |
Heavy drinker | 1485 | 7 | 7 | 23 | 64 |
Binge drinkingb | |||||
No | 7318 | 3 | 4 | 18 | 74 |
Yes | 2791 | 6 | 6 | 22 | 66 |
Passing-outc | |||||
No | 8754 | 4 | 4 | 19 | 73 |
0–1 | 646 | 6 | 6 | 22 | 67 |
<2 | 712 | 7 | 6 | 25 | 63 |
Smoking status | |||||
Never | 4704 | 3 | 3 | 16 | 77 |
Occasional | 332 | 1 | 3 | 20 | 75 |
Former smoker | 2296 | 3 | 5 | 22 | 69 |
Current smoker | 2623 | 7 | 5 | 23 | 64 |
. | n . | Weekly . | Bruxism . | Never . | |
---|---|---|---|---|---|
Monthly . | Rarely . | ||||
Sex | |||||
Men | 4754 | 4 | 5 | 21 | 70 |
Women | 5475 | 4 | 4 | 18 | 73 |
Coffee intake | |||||
0–3 cups/day | 2737 | 4 | 4 | 19 | 73 |
3.5–8 cups/day | 5924 | 4 | 4 | 20 | 72 |
>8 cups/day | 943 | 7 | 5 | 19 | 69 |
Alcohol consumptiona | |||||
Abstainer | 1430 | 3 | 2 | 16 | 79 |
Light drinker | 3656 | 4 | 4 | 18 | 74 |
Moderate drinker | 3613 | 4 | 5 | 21 | 71 |
Heavy drinker | 1485 | 7 | 7 | 23 | 64 |
Binge drinkingb | |||||
No | 7318 | 3 | 4 | 18 | 74 |
Yes | 2791 | 6 | 6 | 22 | 66 |
Passing-outc | |||||
No | 8754 | 4 | 4 | 19 | 73 |
0–1 | 646 | 6 | 6 | 22 | 67 |
<2 | 712 | 7 | 6 | 25 | 63 |
Smoking status | |||||
Never | 4704 | 3 | 3 | 16 | 77 |
Occasional | 332 | 1 | 3 | 20 | 75 |
Former smoker | 2296 | 3 | 5 | 22 | 69 |
Current smoker | 2623 | 7 | 5 | 23 | 64 |
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women), and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
Coffee consumption was common: 4.2% of those with information about bruxism and coffee use (n = 9604) reported no daily consumption while 10% reported consumption of more than eight cups of coffee daily. The mean daily coffee consumption was 5.3 cups for men (95% CI 5.19–5.39) and 4.9 for women (95% CI 4.78–4.94). Among those who used more than eight cups of coffee per day, 46% were current-smokers. In contrast, only 17% of those drinking at most three cups per day were current-smokers. Weekly bruxism was also less common among those consuming small amounts of coffee when compared with those who consumed large amounts of coffee (4 vs. 7%; Table 1).
Of the men with bruxism (n = 4740), 19.5% were classified as heavy drinkers, whereas only 10.3% of women (n = 5444) with bruxism could be similarly classified. Abstainers were more common among women (18.9 vs. 8.5%) than men. The mean number of alcohol drinks per day was 1.3 for men (95% CI 1.21–1.30) and 0.46 for women (95% CI 0.44–0.48) (n = 10,184 with bruxism) and the number of drinks increased with more frequent episodes of bruxism. Current smoking was less common among abstainers than among moderate or heavy drinkers as expected (10 vs. 31 and 49%, respectively). Weekly bruxism was less common among abstainers when compared with heavy drinkers (3 vs. 6.6%; Table 1).
We computed multinomial logistic regressions models for the following categories: weekly, monthly and rarely bruxism vs. never bruxism that had been adjusted for age and sex (model I), and for age, sex and smoking status (model II). The OR's, CIs and P-values for weekly bruxism are shown in Table 2. Coffee consumption of more than eight cups per day was associated with weekly bruxism regardless of smoking status (model I: OR 1.9; 95% CI 1.38–2.66; model II OR 1.4; 95% CI 1.01–1.98). Heavy drinkers had significantly a higher risk for weekly bruxism even when adjusted for smoking status (OR 1.9; 95% CI 1.23–2.84). Binge drinking was strongly associated with weekly bruxism and when alcohol consumption (four categories) was added to the same model (data not shown) both binge drinking (OR 1.8; 95% CI 1.36–2.39) and heavy drinking (OR 1.7; 95% CI 1.11–2.67) remained independent risk factors for bruxism, whereas other alcohol consumption categories were not statistically significant. However, even heavy drinking was not statistically significant when smoking status was added to the same model. Moreover, passing-out due to excessive alcohol consumption at least twice during the last year was associated with an increased risk for weekly bruxism even after adjustment for smoking status (OR 1.5; 95% CI 1.09–2.18). However, this association was no longer statistically significant when binge drinking was added to the model (data not shown) but the statistically significant association of binge drinking with weekly bruxism still held for that model (OR 1.5; 95% CI 1.17–2.01). When the overall consumption of alcohol was computed as grams of alcohol per day (log-transformed), this was significantly (P = 0.017) associated with bruxism even when adjusted for smoking status. Current smoking stayed as an independent risk factor in all models with OR's varying between 2.3 and 2.7.
. | n . | Model I . | n . | Model II . | ||||
---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 9604 | 9352 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.0 | 0.80–1.29 | 090 | 0.9 | 0.69–1.13 | 0.33 | ||
>8 cups/day | 1.9 | 1.38–2.66 | <0.001 | 1.4 | 1.01–1.98 | 0.04 | ||
Alcohol consumptiona | 10,184 | 9921 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.2 | 0.87–1.78 | 0.23 | 1.1 | 0.78–1.62 | 0.54 | ||
Moderate drinker | 1.5 | 1.06–2.19 | 0.02 | 1.2 | 0.85–1.83 | 0.25 | ||
Heavy drinker | 2.7 | 1.85–4.01 | <0.001 | 1.9 | 1.23–2.84 | 0.003 | ||
Binge drinkingb | 10,109 | 9863 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 2.2 | 1.72–2.75 | <0.001 | 1.6 | 1.28–2.12 | <0.001 | ||
Passing-outc | 10,112 | 9860 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.6 | 1.14–2.32 | 0.01 | 1.4 | 0.97–2.02 | 0.07 | ||
<2 | 2.1 | 1.50–2.90 | <0.001 | 1.5 | 1.09–2.18 | 0.01 | ||
Smoking status | 9955 | |||||||
Never | 1.0 | Reference category | ||||||
Occasional | 0.4 | 0.15–1.13 | 0.09 | |||||
Former smoker | 1.3 | 0.99–1.77 | 0.06 | |||||
Current smoker | 2.9 | 2.26–3.61 | <0.001 |
. | n . | Model I . | n . | Model II . | ||||
---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 9604 | 9352 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.0 | 0.80–1.29 | 090 | 0.9 | 0.69–1.13 | 0.33 | ||
>8 cups/day | 1.9 | 1.38–2.66 | <0.001 | 1.4 | 1.01–1.98 | 0.04 | ||
Alcohol consumptiona | 10,184 | 9921 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.2 | 0.87–1.78 | 0.23 | 1.1 | 0.78–1.62 | 0.54 | ||
Moderate drinker | 1.5 | 1.06–2.19 | 0.02 | 1.2 | 0.85–1.83 | 0.25 | ||
Heavy drinker | 2.7 | 1.85–4.01 | <0.001 | 1.9 | 1.23–2.84 | 0.003 | ||
Binge drinkingb | 10,109 | 9863 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 2.2 | 1.72–2.75 | <0.001 | 1.6 | 1.28–2.12 | <0.001 | ||
Passing-outc | 10,112 | 9860 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.6 | 1.14–2.32 | 0.01 | 1.4 | 0.97–2.02 | 0.07 | ||
<2 | 2.1 | 1.50–2.90 | <0.001 | 1.5 | 1.09–2.18 | 0.01 | ||
Smoking status | 9955 | |||||||
Never | 1.0 | Reference category | ||||||
Occasional | 0.4 | 0.15–1.13 | 0.09 | |||||
Former smoker | 1.3 | 0.99–1.77 | 0.06 | |||||
Current smoker | 2.9 | 2.26–3.61 | <0.001 |
Model I adjusted for age and sex, and model II for age, sex and smoking status.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
. | n . | Model I . | n . | Model II . | ||||
---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 9604 | 9352 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.0 | 0.80–1.29 | 090 | 0.9 | 0.69–1.13 | 0.33 | ||
>8 cups/day | 1.9 | 1.38–2.66 | <0.001 | 1.4 | 1.01–1.98 | 0.04 | ||
Alcohol consumptiona | 10,184 | 9921 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.2 | 0.87–1.78 | 0.23 | 1.1 | 0.78–1.62 | 0.54 | ||
Moderate drinker | 1.5 | 1.06–2.19 | 0.02 | 1.2 | 0.85–1.83 | 0.25 | ||
Heavy drinker | 2.7 | 1.85–4.01 | <0.001 | 1.9 | 1.23–2.84 | 0.003 | ||
Binge drinkingb | 10,109 | 9863 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 2.2 | 1.72–2.75 | <0.001 | 1.6 | 1.28–2.12 | <0.001 | ||
Passing-outc | 10,112 | 9860 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.6 | 1.14–2.32 | 0.01 | 1.4 | 0.97–2.02 | 0.07 | ||
<2 | 2.1 | 1.50–2.90 | <0.001 | 1.5 | 1.09–2.18 | 0.01 | ||
Smoking status | 9955 | |||||||
Never | 1.0 | Reference category | ||||||
Occasional | 0.4 | 0.15–1.13 | 0.09 | |||||
Former smoker | 1.3 | 0.99–1.77 | 0.06 | |||||
Current smoker | 2.9 | 2.26–3.61 | <0.001 |
. | n . | Model I . | n . | Model II . | ||||
---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 9604 | 9352 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.0 | 0.80–1.29 | 090 | 0.9 | 0.69–1.13 | 0.33 | ||
>8 cups/day | 1.9 | 1.38–2.66 | <0.001 | 1.4 | 1.01–1.98 | 0.04 | ||
Alcohol consumptiona | 10,184 | 9921 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.2 | 0.87–1.78 | 0.23 | 1.1 | 0.78–1.62 | 0.54 | ||
Moderate drinker | 1.5 | 1.06–2.19 | 0.02 | 1.2 | 0.85–1.83 | 0.25 | ||
Heavy drinker | 2.7 | 1.85–4.01 | <0.001 | 1.9 | 1.23–2.84 | 0.003 | ||
Binge drinkingb | 10,109 | 9863 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 2.2 | 1.72–2.75 | <0.001 | 1.6 | 1.28–2.12 | <0.001 | ||
Passing-outc | 10,112 | 9860 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.6 | 1.14–2.32 | 0.01 | 1.4 | 0.97–2.02 | 0.07 | ||
<2 | 2.1 | 1.50–2.90 | <0.001 | 1.5 | 1.09–2.18 | 0.01 | ||
Smoking status | 9955 | |||||||
Never | 1.0 | Reference category | ||||||
Occasional | 0.4 | 0.15–1.13 | 0.09 | |||||
Former smoker | 1.3 | 0.99–1.77 | 0.06 | |||||
Current smoker | 2.9 | 2.26–3.61 | <0.001 |
Model I adjusted for age and sex, and model II for age, sex and smoking status.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
When we also adjusted the model for social class (model III; data not shown), OR's for both heavy drinking and passing-out stayed similar to those of model II (OR 1.9; 95% CI 1.21–2.86 and 1.5; 1.09–2.19, respectively), whereas the OR for binge drinking rose to 1.7 (95% CI 1.28–2.15). However, the OR for binge drinking and alcohol consumption in model III stayed similar. Social class was not significantly associated with bruxism in our analyses.
Multinomial logistic regressions were also calculated separately for both all-current-smokers (current and occasional smokers combined) and non-smokers (never and former-smokers combined) categories (Table 3). Coffee consumption of more than eight cups per day was significantly associated with weekly bruxism in the all-current-smokers group but not in the non-smokers group. Both alcohol consumption and passing-out due to alcohol intake were not statistically significant for the all-current-smokers group but the ORs increased among the non-smokers when compared with the equivalent values for those groups in model II (all persons). Binge drinking stayed statistically significant for both groups, although the OR for non-smokers was higher than for the all-current-smokers group (2.1 vs. 1.5, respectively).
. | n . | Smoking status . | ||||||
---|---|---|---|---|---|---|---|---|
Current . | n . | Non-current . | ||||||
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 2777 | 6575 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.1 | 0.74–1.66 | 0.62 | 0.8 | 0.62–1.14 | 0.26 | ||
>8 cups/day | 2.0 | 1.25–3.22 | 0.004 | 1.1 | 0.65–1.93 | 0.68 | ||
Alcohol consumptiona | 2942 | 6979 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.0 | 0.50–2.10 | 0.95 | 1.2 | 0.76–1.81 | 0.46 | ||
Moderate drinker | 1.1 | 0.55–2.23 | 0.78 | 1.4 | 0.89–2.19 | 0.15 | ||
Heavy drinker | 1.6 | 0.78–3.24 | 0.20 | 2.5 | 1.49–4.22 | 0.001 | ||
Binge drinkingb | 2926 | 6937 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 1.5 | 1.12–2.15 | 0.01 | 2.1 | 1.43–2.97 | <0.001 | ||
Passing-outc | 2946 | 6914 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.1 | 0.67–1.86 | 0.68 | 2.0 | 1.18–3.24 | 0.01 | ||
<2 | 1.4 | 0.95–2.20 | 0.08 | 1.9 | 1.04–3.40 | 0.04 |
. | n . | Smoking status . | ||||||
---|---|---|---|---|---|---|---|---|
Current . | n . | Non-current . | ||||||
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 2777 | 6575 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.1 | 0.74–1.66 | 0.62 | 0.8 | 0.62–1.14 | 0.26 | ||
>8 cups/day | 2.0 | 1.25–3.22 | 0.004 | 1.1 | 0.65–1.93 | 0.68 | ||
Alcohol consumptiona | 2942 | 6979 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.0 | 0.50–2.10 | 0.95 | 1.2 | 0.76–1.81 | 0.46 | ||
Moderate drinker | 1.1 | 0.55–2.23 | 0.78 | 1.4 | 0.89–2.19 | 0.15 | ||
Heavy drinker | 1.6 | 0.78–3.24 | 0.20 | 2.5 | 1.49–4.22 | 0.001 | ||
Binge drinkingb | 2926 | 6937 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 1.5 | 1.12–2.15 | 0.01 | 2.1 | 1.43–2.97 | <0.001 | ||
Passing-outc | 2946 | 6914 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.1 | 0.67–1.86 | 0.68 | 2.0 | 1.18–3.24 | 0.01 | ||
<2 | 1.4 | 0.95–2.20 | 0.08 | 1.9 | 1.04–3.40 | 0.04 |
Analyses performed separately for current (current and occasional) and non-current (never and former) smokers and adjusted for age and sex.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking = drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
. | n . | Smoking status . | ||||||
---|---|---|---|---|---|---|---|---|
Current . | n . | Non-current . | ||||||
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 2777 | 6575 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.1 | 0.74–1.66 | 0.62 | 0.8 | 0.62–1.14 | 0.26 | ||
>8 cups/day | 2.0 | 1.25–3.22 | 0.004 | 1.1 | 0.65–1.93 | 0.68 | ||
Alcohol consumptiona | 2942 | 6979 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.0 | 0.50–2.10 | 0.95 | 1.2 | 0.76–1.81 | 0.46 | ||
Moderate drinker | 1.1 | 0.55–2.23 | 0.78 | 1.4 | 0.89–2.19 | 0.15 | ||
Heavy drinker | 1.6 | 0.78–3.24 | 0.20 | 2.5 | 1.49–4.22 | 0.001 | ||
Binge drinkingb | 2926 | 6937 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 1.5 | 1.12–2.15 | 0.01 | 2.1 | 1.43–2.97 | <0.001 | ||
Passing-outc | 2946 | 6914 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.1 | 0.67–1.86 | 0.68 | 2.0 | 1.18–3.24 | 0.01 | ||
<2 | 1.4 | 0.95–2.20 | 0.08 | 1.9 | 1.04–3.40 | 0.04 |
. | n . | Smoking status . | ||||||
---|---|---|---|---|---|---|---|---|
Current . | n . | Non-current . | ||||||
OR . | 95% CI . | P . | OR . | 95% CI . | P . | |||
Weekly bruxism | ||||||||
Coffee intake | 2777 | 6575 | ||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | ||||
3.5–8 cups/day | 1.1 | 0.74–1.66 | 0.62 | 0.8 | 0.62–1.14 | 0.26 | ||
>8 cups/day | 2.0 | 1.25–3.22 | 0.004 | 1.1 | 0.65–1.93 | 0.68 | ||
Alcohol consumptiona | 2942 | 6979 | ||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | ||||
Light drinker | 1.0 | 0.50–2.10 | 0.95 | 1.2 | 0.76–1.81 | 0.46 | ||
Moderate drinker | 1.1 | 0.55–2.23 | 0.78 | 1.4 | 0.89–2.19 | 0.15 | ||
Heavy drinker | 1.6 | 0.78–3.24 | 0.20 | 2.5 | 1.49–4.22 | 0.001 | ||
Binge drinkingb | 2926 | 6937 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
Yes | 1.5 | 1.12–2.15 | 0.01 | 2.1 | 1.43–2.97 | <0.001 | ||
Passing-outc | 2946 | 6914 | ||||||
No | 1.0 | Reference category | 1.0 | Reference category | ||||
0–1 | 1.1 | 0.67–1.86 | 0.68 | 2.0 | 1.18–3.24 | 0.01 | ||
<2 | 1.4 | 0.95–2.20 | 0.08 | 1.9 | 1.04–3.40 | 0.04 |
Analyses performed separately for current (current and occasional) and non-current (never and former) smokers and adjusted for age and sex.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking = drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
The analyses for the interactions between ‘smoking and alcohol consumption, smoking and binge drinking, smoking and passing-out and also smoking and coffee consumption’ revealed no statistically significant interactions for the association between either alcohol intake or coffee consumption and the occurrence of bruxism, thus, indicating independent effects of the study variables on bruxism (data not shown).
Among all twin pairs in which both twins answered the question dealing with sleep-related bruxism (n = 4862), there were 1853 pairs for whom neither twin experienced bruxism, 389 pairs for whom both twins experienced bruxism and 1077 pairs for whom only one of the twins experienced bruxism. Pairwise analyses, cross-tabulations and conditional logistic regression using the any bruxism category, indicated that within twin pairs both increasing alcohol intake and increasing coffee consumption raised the risk for any bruxism. Moreover, there were 45 discordant MZ pairs for which the twin with bruxism was the twin who also indulged in binge drinking (and the co-twin without bruxism did not binge drink). Alternatively, another 32 discordant MZ pairs for whom the twin without bruxism was the twin who reported binge drinking. Moreover, there were 18 MZ pairs for which the twin with bruxism had passed-out at least twice within the previous year, whereas the co-twin that had no bruxism had not passed-out. In contrast, four pairs of MZ twins for whom the twin without bruxism was the one who had passed-out at least twice in the previous year. The pairwise ORs for moderate and heavy alcohol consumption (OR 1.5 and 2.0, P = 0.02 and 0.001, respectively), binge drinking (OR 1.4, P = 0.01) and passing-out due to alcohol at least twice within the last year (OR 1.7, P = 0.004) were statistically significant in all discordant twin pairs. Overall, the OR's increased in all (MZ and DZ) twin pairs in association with the more risky health habits. Thus, it is suggested that the association of coffee and alcohol use with bruxism is not attributable to the confounding effects of shared genes or shared childhood environments (Table 4).
. | n . | Twins . | n . | MZ twins . | n . | DZ twins . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | OR . | 95% CI . | P . | ||||
Any bruxism | ||||||||||||
Coffee intake | 1932 | 570 | 1248 | |||||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
3.5–8 cups/day | 1.1 | 0.86–1.36 | 0.50 | 1.2 | 0.74–1.92 | 0.47 | 1.0 | 0.80–1.37 | 0.72 | |||
>8 cups/day | 1.1 | 0.76–1.64 | 0.58 | 1.3 | 0.61–2.73 | 0.50 | 1.0 | 0.63–1.63 | 0.95 | |||
Alcohol consumptiona | 2134 | 618 | 1390 | |||||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Light drinker | 1.1 | 0.81–1.55 | 0.51 | 1.1 | 0.58–2.15 | 0.73 | 1.2 | 0.81–1.77 | 0.38 | |||
Moderate drinker | 1.5 | 1.07–2.14 | 0.02 | 1.8 | 0.87–3.54 | 0.12 | 1.6 | 1.02–2.37 | 0.04 | |||
Heavy drinker | 2.0 | 1.31–2.92 | 0.001 | 2.3 | 1.02–5.15 | 0.04 | 1.9 | 1.19–3.12 | 0.01 | |||
Binge drinkingb | 2118 | 618 | 1376 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Yes | 1.4 | 1.09–1.76 | 0.01 | 1.4 | 0.89–2.21 | 0.14 | 1.4 | 1.05–1.89 | 0.02 | |||
Passing-outc | 2122 | 616 | 1378 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
0–1 | 1.4 | 0.94–2.00 | 0.11 | 1.3 | 0.62–2.56 | 0.52 | 1.6 | 0.98–2.52 | 0.06 | |||
<2 | 1.7 | 1.19–2.50 | 0.004 | 3.3 | 1.39–7.97 | 0.01 | 1.4 | 0.88–2.09 | 0.17 |
. | n . | Twins . | n . | MZ twins . | n . | DZ twins . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | OR . | 95% CI . | P . | ||||
Any bruxism | ||||||||||||
Coffee intake | 1932 | 570 | 1248 | |||||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
3.5–8 cups/day | 1.1 | 0.86–1.36 | 0.50 | 1.2 | 0.74–1.92 | 0.47 | 1.0 | 0.80–1.37 | 0.72 | |||
>8 cups/day | 1.1 | 0.76–1.64 | 0.58 | 1.3 | 0.61–2.73 | 0.50 | 1.0 | 0.63–1.63 | 0.95 | |||
Alcohol consumptiona | 2134 | 618 | 1390 | |||||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Light drinker | 1.1 | 0.81–1.55 | 0.51 | 1.1 | 0.58–2.15 | 0.73 | 1.2 | 0.81–1.77 | 0.38 | |||
Moderate drinker | 1.5 | 1.07–2.14 | 0.02 | 1.8 | 0.87–3.54 | 0.12 | 1.6 | 1.02–2.37 | 0.04 | |||
Heavy drinker | 2.0 | 1.31–2.92 | 0.001 | 2.3 | 1.02–5.15 | 0.04 | 1.9 | 1.19–3.12 | 0.01 | |||
Binge drinkingb | 2118 | 618 | 1376 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Yes | 1.4 | 1.09–1.76 | 0.01 | 1.4 | 0.89–2.21 | 0.14 | 1.4 | 1.05–1.89 | 0.02 | |||
Passing-outc | 2122 | 616 | 1378 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
0–1 | 1.4 | 0.94–2.00 | 0.11 | 1.3 | 0.62–2.56 | 0.52 | 1.6 | 0.98–2.52 | 0.06 | |||
<2 | 1.7 | 1.19–2.50 | 0.004 | 3.3 | 1.39–7.97 | 0.01 | 1.4 | 0.88–2.09 | 0.17 |
MZ = monozygotic twins, DZ = dizygotic twins.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
. | n . | Twins . | n . | MZ twins . | n . | DZ twins . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | OR . | 95% CI . | P . | ||||
Any bruxism | ||||||||||||
Coffee intake | 1932 | 570 | 1248 | |||||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
3.5–8 cups/day | 1.1 | 0.86–1.36 | 0.50 | 1.2 | 0.74–1.92 | 0.47 | 1.0 | 0.80–1.37 | 0.72 | |||
>8 cups/day | 1.1 | 0.76–1.64 | 0.58 | 1.3 | 0.61–2.73 | 0.50 | 1.0 | 0.63–1.63 | 0.95 | |||
Alcohol consumptiona | 2134 | 618 | 1390 | |||||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Light drinker | 1.1 | 0.81–1.55 | 0.51 | 1.1 | 0.58–2.15 | 0.73 | 1.2 | 0.81–1.77 | 0.38 | |||
Moderate drinker | 1.5 | 1.07–2.14 | 0.02 | 1.8 | 0.87–3.54 | 0.12 | 1.6 | 1.02–2.37 | 0.04 | |||
Heavy drinker | 2.0 | 1.31–2.92 | 0.001 | 2.3 | 1.02–5.15 | 0.04 | 1.9 | 1.19–3.12 | 0.01 | |||
Binge drinkingb | 2118 | 618 | 1376 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Yes | 1.4 | 1.09–1.76 | 0.01 | 1.4 | 0.89–2.21 | 0.14 | 1.4 | 1.05–1.89 | 0.02 | |||
Passing-outc | 2122 | 616 | 1378 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
0–1 | 1.4 | 0.94–2.00 | 0.11 | 1.3 | 0.62–2.56 | 0.52 | 1.6 | 0.98–2.52 | 0.06 | |||
<2 | 1.7 | 1.19–2.50 | 0.004 | 3.3 | 1.39–7.97 | 0.01 | 1.4 | 0.88–2.09 | 0.17 |
. | n . | Twins . | n . | MZ twins . | n . | DZ twins . | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
OR . | 95% CI . | P . | OR . | 95% CI . | P . | OR . | 95% CI . | P . | ||||
Any bruxism | ||||||||||||
Coffee intake | 1932 | 570 | 1248 | |||||||||
0–3 cups/day | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
3.5–8 cups/day | 1.1 | 0.86–1.36 | 0.50 | 1.2 | 0.74–1.92 | 0.47 | 1.0 | 0.80–1.37 | 0.72 | |||
>8 cups/day | 1.1 | 0.76–1.64 | 0.58 | 1.3 | 0.61–2.73 | 0.50 | 1.0 | 0.63–1.63 | 0.95 | |||
Alcohol consumptiona | 2134 | 618 | 1390 | |||||||||
Abstainer | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Light drinker | 1.1 | 0.81–1.55 | 0.51 | 1.1 | 0.58–2.15 | 0.73 | 1.2 | 0.81–1.77 | 0.38 | |||
Moderate drinker | 1.5 | 1.07–2.14 | 0.02 | 1.8 | 0.87–3.54 | 0.12 | 1.6 | 1.02–2.37 | 0.04 | |||
Heavy drinker | 2.0 | 1.31–2.92 | 0.001 | 2.3 | 1.02–5.15 | 0.04 | 1.9 | 1.19–3.12 | 0.01 | |||
Binge drinkingb | 2118 | 618 | 1376 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
Yes | 1.4 | 1.09–1.76 | 0.01 | 1.4 | 0.89–2.21 | 0.14 | 1.4 | 1.05–1.89 | 0.02 | |||
Passing-outc | 2122 | 616 | 1378 | |||||||||
No | 1.0 | Reference category | 1.0 | Reference category | 1.0 | Reference category | ||||||
0–1 | 1.4 | 0.94–2.00 | 0.11 | 1.3 | 0.62–2.56 | 0.52 | 1.6 | 0.98–2.52 | 0.06 | |||
<2 | 1.7 | 1.19–2.50 | 0.004 | 3.3 | 1.39–7.97 | 0.01 | 1.4 | 0.88–2.09 | 0.17 |
MZ = monozygotic twins, DZ = dizygotic twins.
aLight drinker (>0–3), moderate drinker (>3–14 men, >3–7 women) and heavy drinker (>14 men, >7 women).
bBinge drinking, i.e. drinking at least once a month more than one bottle of wine, half a bottle of spirits or the equivalent amount of other alcoholic beverages on the same occasion.
cPassing-out as a result of excessive alcohol intake.
DISCUSSION
This study provides a wide-ranging assessment of the effects that the use of two legal psychoactive substances, namely alcohol and coffee, have upon the occurrence of bruxism. The results show clear associations between alcohol consumption and coffee consumption with weekly bruxism both in the presence and in the absence of current smoking. Although multiple alcohol use patterns increase the risk for weekly bruxism, binge drinking emerged as an important independent risk factor for bruxism.
Previous studies about the association of alcohol with SB have focused on alcohol quantities per se as the measure of alcohol consumption. We are not aware of any other studies in the literature that used specific drinking patterns. Alcohol consumption is usually defined as light or moderate when the consumption is no more than 7 drinks per week, or 3 drinks per day for females and 14 per week or 4 per day for males (NIAAA, 2005). However, there is great variability in definitions of alcohol consumption (Leeman et al., 2010). In prior epidemiological studies of the associations between alcohol and bruxism, Ohayon et al. (2001) classified alcohol consumption as being zero, one to two, and at least three glasses per day. In contrast, Molina et al. (2001) and Bellini et al. (2011) measured the consumption as either yes or no, whereas Hartmann (1979) used self-reported alcohol consumption from one to four drinks per day without categorizing consumption in terms of different drinking classes. Later in their clinical study, Hartmann et al. (1987) used one to four doses of alcohol (dose P = 226 mg/kg of ethanol) given under double-blind conditions. The broad approach to the consumption and frequency patterns of alcohol use in our study allowed the effective evaluation of the effect of alcohol on bruxism. Overall consumption of alcohol is a common measure for the use of alcohol but does not provide information on the pattern of drinking. Binge drinking reflects the use of large doses of alcohol on the same occasion, and thus pre-disposes to there being toxic effects on the brain. It also might give important information about the possible role of dependence on psychoactive substances in bruxism. We did not assess actual alcohol dependence in this study, but binge drinking and passing-out due to excessive alcohol consumption are commonly found in alcohol dependence.
In an earlier study, alcohol was estimated to raise the risk for SB from 1.5 to 1.8 depending on the daily consumption rate (Ohayon et al., 2001). In general, there seems to be more alcohol consumers among ‘bruxers’ than ‘non-bruxers’ (Bellini et al., 2011). In this present study, at least moderate drinking increased the risk for weekly bruxism approximately 2-fold. However, the study by Molina et al. (2001) failed to show any significant association between bruxism and alcohol consumption. The original report by Hartmann (1979) was based on four patients and their bed partners' reports about their bruxism. Generally, patients drank between one and four drinks per day and their bed partners reported more bruxism episodes following days during which alcohol was drunk. One patient was studied using polysomnography and Hartmann reported more bruxism episodes following the day during which three drinks were imbibed when compared with the alcohol-free day. However, Hartmann (1979) only presented a case study with no further statistical analyses. Later in a double-blinded clinical trial, Hartmann et al. (1987) studied 16 patients in a sleep laboratory in which subjects were given 0 (placebo)–4 alcohol drinks to reveal possible effects of alcohol on sleep bruxism. Hartmann et al. (1987) failed to find any significant effect of acute alcohol exposure on bruxism in this setting. None of these earlier studies analysed different alcohol use patterns and any possible link with smoking. In our study, smoking decreased the effect of the use of alcohol as a risk factor when added to the same analyses, although all alcohol use patterns raised the risk for weekly bruxism. However, the effects of alcohol consumption and passing-out due to excessive alcohol intake disappeared when binge drinking was added to the same analyses, which indicated a strong effect of binge drinking as an independent risk factor for bruxism. No interactions between the use of alcohol and smoking were found, which indicated an independent mechanism of alcohol upon bruxism.
Coffee has also been associated with the increased severity of bruxism (Molina et al., 2001) and it is estimated to raise the risk for SB by 1.4 (Ohayon et al., 2001) in a study of 13,057 persons. However, Bastien et al. (1990), in their placebo-controlled study, failed to show any significant association between masseteric muscle activity and caffeine. In our study, coffee consumption of eight cups or more per day raised the risk for weekly bruxism by 1.9. Intriguingly, the OR dropped to 1.4 when smoking was added to the same model. However, we found no interaction between coffee consumption and smoking that would moderate the effect of coffee consumption on bruxism. The fact that coffee consumption was asked in previous questionnaires (1975 and 1981) may affect the results because bruxism was evaluated in 1990. However, Laitala et al. (2008) using the same data showed that the coffee consumption has been rather stable among Finnish adult population over the years.
Discordant twin pairs differed in their exposure to bruxism and this creates a unique approach to reveal whether some genetic or shared familial bias for having bruxism exist in our individual-based analyses. We performed pairwise analyses among MZ and DZ twin pairs who were discordant for bruxism, for various alcohol intake and coffee consumption. Upon comparing twin pairs discordant for bruxism, we found a trend that the twin with the more unhealthy habit (heavy alcohol or coffee use) was more often the one who also experienced weekly bruxism. The OR's of intra-pair analyses increased when the exposure to the risk factor also increased. Despite the modest statistical power of our analyses among MZ twin pairs, there seems to be a clear association that supports some causality between bruxism and alcohol consumption, binge drinking and passing-out due to excessive alcohol intake even when genetic factors and childhood environment are statistically adjusted. This finding would support the existence of a causal relationship but how such an effect is mediated still needs clarification. The association between bruxism and coffee consumption seems to be weaker than that between bruxism and alcohol.
To the best of our knowledge, no other studies about alcohol and coffee intake as risk factors for bruxism in twin pairs or twin pairs discordant for bruxism exist. Previously, we reported smoking to increase the risk for self-reported bruxism (Rintakoski et al., 2010a, 2010b). Moreover, smoking is known to associate with alcohol and coffee use. Therefore, we adjusted our models for smoking. We also analysed the possible interactions between smoking and psychoactive substances used in our study, but we found no statistically significant interactions that might make us question the independent effects of alcohol or coffee on weekly bruxism.
Data for our analyses were obtained from a unique, large-scale population-based twin cohort study of the Finnish adult population, thus data were cross-sectional. Although longitudinal analyses would be valuable, the large number of respondents in our present study strengthens our data remarkably. Moreover, our study data comprise twin individuals with a high-response rate and are, thus, very representative of the general population, which, therefore, justifies the use of a questionnaire. Furthermore, the prevalence of weekly bruxism (4.2%) in middle-aged adults in our study is in line with the existing literature in which the prevalence of often or very often occurring SB is frequently reported to be about 8% of the young adult population and decreases gradually to 3% in the elderly (Lavigne and Montplaisir, 1994; Ohayon et al., 2001). This further adds support to the representativeness of these data in respect of the general population and also the use of the self-reporting methodological approach.
SB is defined as ‘an oral parafunction characterized by grinding or clenching of the teeth during sleep that is associated with an excessive sleep arousal activity’ (AASM, 2005) and should be diagnosed with direct measurements, viz., electromyography and polysomnography (De Leeuw, 2008). The fact that information about bruxism in our study was gathered from self-reported questionnaires and not from polysomnography-based evaluation is an eminent limitation of the study because not all individuals are aware of their bruxism (e.g. those living alone). This will result in some underreporting, and also those who were suffering from less severe bruxism may also be unaware of their SB habit. However, in large population-based epidemiological studies, the difficulties with using a sleep laboratory setting include the high price, the difficulties in logistics, high requirements of sleep laboratories, in addition to the possible sleep disturbances caused by the atypical sleeping environment (Lavigne et al., 1996; Manfredini and Lobbezoo, 2010). Hence, self-reporting or interviewing is the best available method for large epidemiological surveys.
According to our analyses, the consumption of alcohol and coffee, in addition to smoking, seem to be independent risk factors each of which raises the risk for weekly bruxism significantly. The mechanism that underlies the association of SB and psychoactive substances remains unknown. However, several possibilities for the mechanism exist. First, previous studies have failed to find evidence of the role of psychosocial factors in sleep-related bruxism (Lobbezoo et al., 2006; Manfredini and Lobbezoo 2009) and our model with social class indicated no significant relevance of it in the sleep-related bruxism. Thus, although alcohol and smoking are known to associate with psychological problems and stress the role of psychoactive substances is unlikely to be mediated via common psychological problems or stress. Secondly, it is known that the dopaminergic system (both hyper- and hypo-dopaminergic states) may link to bruxism (Lobbezoo et al., 1997a, 1997b; Lavigne et al., 2001; Lobbezoo et al., 2006). Further, other neurochemicals and their possible interactions with the dopaminergic system may also affect it (Lobbezoo and Naeije, 2001; Chen et al., 2005; Lobbezoo et al., 2006). Psychoactive substances affect the central nervous system and cause changes in the functional characteristics of the transmitters or the receptors. The mechanism of action differs depending on the substance. For example, nicotine increases the levels of dopamine, whereas caffeine acts as an antagonist of the adenosine receptors that possibly interact with the dopaminergic system. Alcohol (ethanol) increases the effects of the inhibitory neurotransmitter gamma-aminobutyric acid and the amount of dopamine acting on the receptors. However, no evidence of a specific mechanism that explains the pathogenesis of bruxism exists. Nevertheless, our study supports the theory about the central regulation of SB and the presence of up- or down-regulation of certain brain function.
The present results have a significant clinical relevance as well and may improve the results of the management of the experienced problems caused by sleep-related bruxism. When dentists are aware that heavy drinking and smoking may worsen the bruxism habit, they may provide additional health advice together with other treatment to improve the outcomes. Also, the role of dentist in the provision of general health advice is increasing and it is common to offer tobacco intervention. However, the advice related to alcohol use is in many cases not as easy to offer and may feel unnatural to both dentist and patient. Therefore, it may create good opportunity to dentist to ask about potential alcohol misuse when patient is suffering with severe sleep-related bruxism, which creates an easy bridge to this rather sensitive issue. The dentist can then refer the patient to an addiction specialist if needed.
Although a large variety of factors that make individuals prone to bruxism has been studied, the aetiology of bruxism is still partly unknown. Especially, the role of psychoactive substances in the pathogenesis of bruxism is unclear. The present study shows clear associations between binge drinking, alcohol intake, passing-out due to excessive alcohol intake and also coffee consumption with that of sleep-related bruxism. Therefore, the present results support our hypothesis that the common legal psychoactive drugs of caffeine and alcohol are strongly associated with SB even when smoking is adjusted in calculations.
Funding
J.K. was supported by the Academy of Finland (265240, 263278) and the Jenny and Antti Wihuri Foundation.
Conflict of interest statement. None declared.