Abstract
Objective
This cross-sectional study aims to examine the effect of marijuana-smoking on dental caries experience and to explore the potential combined effects of tobacco and marijuana cigarette–smoking.
Methods
We used data from the 2011–2014 National Health and Nutrition Examination Survey (NHANES). We examined demographics, tobacco- and marijuana-smoking, dental examination, and dietary intake. Caries was measured as decayed, missing, filled teeth (DMFT). Data analysis included univariate, bivariate analyses, and linear regression model (LRM) to examine the association between marijuana-smoking and DMFT.
Results
Mean DMFT score was lowest for nonsmokers (8.72) and highest for current marijuana smokers (9.87) (P < .0001); however, LRM results revealed that marijuana-smoking was not associated with caries. Adjusted DMFT was the highest for current tobacco and former marijuana smokers (β estimate = 1.18; 95% CI, −0.27 to 2.62), but the relationship was not statistically significant.
Conclusions
After controlling for potential confounders, there was no significant association between marijuana-smoking and dental caries experience. However, when marijuana and tobacco were smoked concurrently, there was a notable increase in DMFT, although the difference was not statistically significant. Future research should be directed towards exploring the effects of different forms of marijuana consumption, such as edibles and drinkables, on caries development. Health promotion programmes should be aimed at educating the public regarding the combined health impacts of smoking both marijuana and tobacco, considering the potential heightened caries risk.
Key words: Marijuana, Cannabis, Caries, Smoking, Cigarettes
Introduction
Twenty-three US states have legalised recreational marijuana and its distribution, cultivation, and use by those older than 21 years.1,2 Currently, many other states are considering legalising commercial marijuana and applying the same laws and regulations as alcohol. Marijuana can be consumed by smoking it as cigarettes called joints or in water pipes, or it can be found as cannabis edibles in food or cannabis-infused drinkables. The effect of smoking marijuana can be pleasant—producing euphoria, relaxation, laughter, and increased appetite—or unpleasant—resulting in hallucination, temporary paranoia, anxiety, and fear.3 It is one of the most commonly used illicit drugs in the US, and there was a 13% increased consumption from 2011 to 2021, with almost 43% of US young adults reporting using marijuana in the past year.4 The decision to decriminalise and legalise marijuana use in the US has been somewhat controversial. Some individuals consider legalised recreational marijuana to be a new industry that will provide jobs; however, others are against this law because of the lack of clear evidence about its safety, health effects, potential addiction, and its gateway effect to other drugs. Additional research is needed to provide a solid base of its effects, both systemically and orally.
In contrast to tobacco-smoking, the mechanism of smoking marijuana involves deep, prolonged inhalation from an unfiltered cigarette, which exposes the smoker to more chemicals than tobacco. Like tobacco, chronic marijuana-smoking is also associated with various respiratory diseases including bronchitis and emphysema and may be associated with bronchogenic carcinoma and oropharyngeal cancer. Although the clinical significance is not clear, marijuana also has an immunosuppressant effect and reproductive risks.5,6
Whilst the oral effects of marijuana are not well studied, the oral effects of tobacco-smoking are well known and include increased attachment loss and gingival recession; hence, it is considered a risk factor for periodontal disease.7,8 A direct effect of cigarette-smoking on dental caries has not been well established and is controversial, with some studies concluding that smoking tobacco protects against dental caries, whilst other studies report a dose-dependent positive trend showing increasing cigarette consumption resulting in an increase in DMFT (decayed, missing, filled teeth).9
Many researchers found that marijuana users have poorer oral health, including oral lesions as leukoedema and candidiasis, oral tissue dysplasia, and periodontitis.10, 11, 12, 13 Evidence studying the effect of marijuana-smoking on dental caries is very limited. An 8-year longitudinal study examining trends in marijuana-smoking amongst Nevada adolescents and its effect on dental caries showed increased marijuana consumption from 7.4% in year 1 to 12.9% in year 8. Their results showed that the percentage mean difference (PMD) in DMFT between smokers and nonsmokers increased from 44.9% in year 1 to 51.7% in year 2, followed by a drop in year 3 to 19.8%, and then gradually increased from year 4 to year 8 to reach 33.9%. Although the authors projected future increase in DMFT, it was difficult to attribute the results to marijuana-smoking alone.14 Other studies found that marijuana causes dry mouth, a decrease in salivary secretions, a decrease in saliva PH, and increased appetite, and all these factors might contribute to a higher caries risk.15, 16, 17
The current literature has focussed on the effects of marijuana on dental tissue and periodontium, but research on the effect on dental caries is inconclusive and insufficient.18 In addition, most studies have examined the exclusive effect of marijuana, whilst most marijuana smokers also smoke tobacco cigarettes,13 so the combined effect on dental caries should be explored.
The aim of this study is to examine the effect of marijuana-smoking on dental caries experience in adults and to explore any potential combined effect when smoking both tobacco and marijuana cigarettes.
Methods
Data source
Data were obtained from the 2011–2012 and 2013–2014 National Health and Nutrition Examination Survey cycles (NHANES). NHANES is a programme of cross-sectional studies that combine questionnaires, examinations, and laboratory tests. It is a stratified, multistage, probability survey design that is conducted by the National Center for Health Statistics, which includes the civilian, noninstitutionalised population residing in the 50 states and the District of Columbia.19
Study population
Five datasets were merged in the analysis: demographics, drug use, oral health–dentition, dietary interview, and smoking–cigarette use. The total participant count after combining data from both cycles was 19,931. Our study population included 4173 adults aged 21 years and older who completed both the oral health examination and smoking questionnaire.
Dental outcome
NHANES dental variables were extracted from the oral health–dentition data. The outcome of our study was measured as DMFT. DMFT was a combination of 2 parts: (1) missing due to caries (M) and tooth with surface condition: decayed tooth (D) was considered as present if softness of the area and/or opacity adjacent to the area or white spots on smooth areas was detected or (2) filled tooth (F) was identified if a restoration, either temporary or permanent, was placed due to dental caries.19
Marijuana-smoking
The drug use questionnaire (DUQ) in NHANES was used to identify the participant's lifetime and current marijuana-smoking experience. Marijuana-smoking was classified into 3 categories: nonsmokers were those who responded that they never used marijuana; previous smokers were those who quit smoking marijuana (if the last time they smoked marijuana was months or years ago); and current smokers smoke at least 1 joint/pipe of marijuana in a day at least 1 time per month.
Tobacco-smoking
Tobacco-smoking was obtained from the smoking–cigarette use dataset. Tobacco-smoking was categorised as follows: nonsmokers were those who never smoked tobacco cigarettes (smoked fewer than 100 cigarettes in their lifetime); former smokers were those who smoked at least 100 cigarettes in their lifetime, but quit smoking (since months or years); and current smokers smoked at least 100 cigarettes in their lifetime and smoke at least 1 cigarette/day every/some days.
Variables
Demographic variables in the analysis included sex, age (in decades), race (Mexican, White, Black, and others), education (≤high school, some college, ≥college), marital status (married/with partner, divorced/widowed, single), and family income-to-poverty ratio (≤1.38, >1.38 to <3.5, and >3.5).20 Total sugar consumption was measured in grams and was assessed through 2-day total nutrients dietary interview. Mean sugar intake for the 2 days was used in the analysis (mean g/d).
Data analysis
We used prevalence to examine the distribution of the demographic variables amongst the marijuana smokers' categories. Differences amongst these categories were evaluated using Chi-square tests. We used β estimates from unadjusted and adjusted linear regression models to examine the association between marijuana-smoking and DMFT. To study the interaction between marijuana- and tobacco-smoking, we examined the relationship between marijuana usage and DMFT through linear regression modelling, stratified by the tobacco-smoking groups. The linear regression models were adjusted for sex, age, race, family income-to-poverty ratio, education level, tobacco-smoking, and mean sugar consumption. A P value < .05 was set as the threshold for statistical significance. To account for the complex, multistage sampling design in NHANES, cluster and strata commands and weights were used. All study analyses were performed using SAS version 9.4.
Results
Participants' characteristics
Almost half of US adults older than 21 years reported never smoking marijuana (49%), whilst 40% were previous marijuana smokers and 11% were current marijuana smokers. More than half of the study population (51%) reported at least some exposure to marijuana-smoking (either previous or current exposure) (Table 1).
Table 1.
Association between dental caries experience and marijuana-smoking status by sociodemographic characteristics of US adults aged 21–60 years (data from NHANES 2011–2014) (weighted %) (n = 4173).
| Nonsmokers, n = 2035 (48.7%) | Previous marijuana smokers, n = 1687 (40.4%) | Current marijuana smokers, n = 451 (10.8%) | P value | |
|---|---|---|---|---|
| Sex: | ||||
| Male | 43.9% | 52.8% | 66.0% | |
| Female | 56.1% | 47.2% | 34.0% | <.0001 |
| Age (y): | ||||
| 21–40 | 35.2% | 28.7% | 42.1% | |
| 41–50 | 35.1% | 34.3% | 30.0% | |
| 51–60 | 29.7% | 37.0% | 27.9% | <.0001 |
| Race: | ||||
| Mexican/Hispanic | 24.4% | 9.3% | 10.3% | |
| White | 52.0% | 76.9% | 67.2% | |
| Black | 12.0% | 8.7% | 19.0% | |
| Other | 11.6% | 5.1% | 3.5% | <.0001 |
| Education: | ||||
| ≤High school | 36.8% | 27.9% | 47.6% | |
| Some college | 27.0% | 32.3% | 36.4% | |
| ≥College | 36.2% | 39.8% | 16.0% | <.0001 |
| Marital status: | ||||
| Married/with partner | 75.2% | 67.6% | 55.0% | |
| Divorced/widow | 11.1% | 16.4% | 19.0% | |
| Single | 13.7% | 16.0% | 26.0% | <.0001 |
| Federal poverty level: | ||||
| ≤ 138% | 29.4% | 21.8% | 39.2% | |
| >138%, ≤350% | 31.9% | 27.4% | 36.3% | |
| >350% | 38.7% | 50.8% | 24.5% | <.0001 |
| Cigarette smoking: | ||||
| Never | 82.3% | 47.1% | 23.4% | |
| Former smoker | 10.6% | 32.2% | 24.4% | |
| Current smoker | 7.1% | 20.7% | 52.2% | <.0001 |
| Sugar intake: | ||||
| Mean g/d (SE) | 106.9 (1.8) | 111.8 (2.4) | 131.1 (4.3) | <.0001 |
| DMFT mean (SE) | 8.72 (0.18) | 9.49 (0.17) | 9.87 (0.19) | <.0001 |
DMFT, decayed, missing, filled teeth; NHANES, National Health and Nutrition Examination Survey.
Table 1 demonstrates that current marijuana smokers were more likely to be male (66%), younger (between 21 and 40 years; 42.1%), married/with partner (55%), and with low federal poverty level (FPL) (39.2%) (P < .0001). Sugar intake increased from 106.9 g/d for nonsmokers to 131.1 g/d in current marijuana smokers. In addition, current marijuana smokers were also far more likely to be current tobacco smokers. On the other hand, adults with at least a college degree were less likely to be in the current marijuana-smoking group (16%).
Previous marijuana-smoking showed a linear relationship with age, increasing from 28.7% in younger ages to 37% in older ages. White participants constituted a large percentage of the previous marijuana-smoking group (76.9%) compared to nonsmokers (52%), and they were also more likely to quit smoking tobacco (32.3%) (P < .0001).
Effect of marijuana on dental caries experience
Mean DMFT was lowest in nonsmokers (8.72), whilst the highest DMFT was in the current marijuana smokers group (9.87) (P value < .0001) (Table 1). Adjusted multiple linear regression showed no statistically significant differences for DMFT for either previous marijuana smokers or current smokers (Table 2).
Table 2.
Adjusted multiple linear regression predicting DMFT (US adults aged 21–60 years, data from NHANES 2011–2014).
| Variable | β estimates | 95% Confidence interval | P value |
|---|---|---|---|
| Marijuana-smoking: | |||
| Nonsmokers (reference) | ---- | ---- | ---- |
| Previous smokers | 0.08 | −0.28 to 0.44 | .65 |
| Current smokers | 0.31 | −0.39 to 1.01 | .37 |
| Sex: | |||
| Male | −1.08 | −1.54 to −0.62 | <.0001* |
| Female (reference) | ---- | ---- | ---- |
| Age (y): | |||
| 21–40 (reference) | ---- | ---- | ---- |
| 41–50 | 2.20 | 1.72 to 2.68 | <.0001* |
| 51-60 | 4.46 | 3.85 to 5.07 | <.0001* |
| Race: | |||
| Mexican/Hispanic | −0.015 | −0.78 to 0.48 | .63 |
| White (reference) | ---- | ---- | ---- |
| Black | −1.32 | −1.92 to −0.73 | <.0001* |
| Other | −0.56 | −1.33 to 0.19 | .14 |
| Education: | |||
| ≤High school (reference) | ---- | —— | ---- |
| Some college | 0.072 | 0.45 to 0.59 | .78 |
| ≥College | −1.18 | −1.77 to −0.58 | .0003* |
| Marital status: | |||
| Married/with partner | 0.49 | −0.12 to 1.12 | .11 |
| Divorced/widow | 0.33 | −0.27 to 0.95 | .26 |
| Single (reference) | ---- | ---- | ---- |
| Federal poverty level: | |||
| ≤138% (reference) | ---- | ---- | ---- |
| >138%, ≤ 350% | −0.45 | −1.03 to 0.12 | .11 |
| >350% | −0.15 | −0.74 to 0.43 | .59 |
| Tobacco-smoking: | |||
| Never (reference) | ---- | ---- | ---- |
| Former smoker | 0.76 | 0.31 to 1.21 | .001* |
| Current smoker | 1.11 | 0.44 to 1.78 | .001* |
| Sugar intake: | |||
| Mean g/d (SE) | 0.006 | 0.001 to 0.01 | .01* |
Statistically significant at the .05 level.
DMFT, decayed, missing, filled teeth; NHANES, National Health and Nutrition Examination Survey.
DMFT increased with older age, where people aged 41 to 50 years had double the mean DMFT scores (β estimate = 2.20; 95% CI, 1.72–2.68) and individuals aged 51 to 60 years had quadruple the DMFT scores (β estimate = 4.46; 95% CI, 3.85–5.07) compared to the younger age group. Tobacco-smoking showed a stronger relationship with DMFT than did marijuana exposure. Higher DMFT was associated with both former and current tobacco-smoking as well as with higher sugar intake (Table 2). A protective effect against caries was related to being male (β estimate = −1.08; 95% CI, −1.54 to −0.62), being Black (β estimate = −1.32; 95% CI, −1.92 to −0.73), and having a college education or higher (β estimate = −1.18; 95% CI, −1.77 to −0.58) (Table 2).
Combined effects of smoking both marijuana and tobacco cigarettes
The adjusted model found that the DMFT increase was the greatest with current tobacco/previous marijuana smokers (β estimate = 1.18; 95% CI, −0.27 to 2.62), followed by former tobacco/current marijuana smokers (β estimate = 1.02; 95% CI, −0.45 to 2.50) (Figure 1); however, no statistical difference in DMFT for marijuana smokers compared to nonsmokers, independent of the individual's tobacco exposure, was detected.
Fig. 1.
Association between marijuana smoking and decayed, missing, filled teeth (DMFT) stratified by tobacco cigarette smoking (US adults aged 21–60 years, data from NHANES 2011–2014).*
*Controlling for sex, age, race, family income to poverty ratio, education level, tobacco smoking, and mean sugar consumption.
Discussion
This study analysed the NHANES data, a nationally representative dataset, to determine the effects of marijuana-smoking on dental caries experience amongst adults. Whilst our initial, unadjusted results showed that marijuana smokers had a higher DMFT score, this correlation lost its statistical significance after controlling for sociodemographic factors and other potential confounders. Therefore, our results suggest that marijuana by itself may not increase the risk of caries. Instead, certain behaviours frequently associated with marijuana-smoking, such as increased appetite and snacking on cariogenic foods and beverages, infrequent dental visits, or poorer oral hygiene, might be the relevant risk factors.21, 22, 23
Our study results are consistent with the finding of a study conducted in Switzerland, which compared dental caries amongst 42 marijuana smokers and 43 tobacco smokers (control group). They found no significant difference in the number of decayed and filled surfaces (DFS index) between cases and controls. However, marijuana users had significantly higher decay on the smooth surfaces of the teeth (P = .0001), greater consumption of sugary foods and drinks, and less frequent daily tooth brushing and regular dental visits. Therefore, the authors speculated that it is not marijuana but the behaviours accompanying marijuana-smoking that are the main risk factors for smooth surface caries.23
The combined effect of smoking both marijuana and tobacco cigarettes together showed a higher DMFT, with the highest DMFT found amongst previous marijuana smokers and current tobacco smokers, although this relationship was not statistically significant. The exact reason that this group had the highest DMFT is unclear. Possible explanations could be the altered quantity and quality of the saliva, with some research reporting xerostomia as one of the side effects of smoking marijuana.9,10,12 Another explanation is that the previous marijuana smokers were mostly older and had higher risk of dental caries (quadruple the risk in our analysis).
Tobacco-smoking was found to increase the risk of dental caries in our study. In the literature, tobacco-smoking has an inconsistent relationship with saliva, as some studies suggest that smoking causes xerostomia, increased salivary thickness, and changes in the salivary pH, whilst other studies indicated that tobacco-smoking does not affect the saliva.9,24, 25, 26
Although our study did not find a statistically significant association between marijuana-smoking and dental caries experience, it is crucial for dentists to take into account the potential effects of the drug on clinical treatments. It is important for dental professionals to be aware of their patients’ marijuana-smoking status. In this way, dentists can expect the oral condition of the patient related to marijuana-smoking and can avoid possible interactions between marijuana and drugs used in the patient's treatment. For example, acute marijuana exposure can interact with epinephrine, producing an abnormal stress response and prolonged tachycardia.21 Confirming previous and current smoking status is a good opportunity for the dental professional to educate patients regarding the oral and systemic effects of marijuana- and tobacco-smoking and emphasise practicing good oral hygiene habits, regular dental checkups, and healthy snacking.15
Our study is a cross-sectional study; hence, the relationships do not indicate causality. Although we adjusted for multiple confounders in our analysis (eg, age, sex, race/ethnicity, federal poverty level, education, marital status, tobacco-smoking, and mean sugar intake), unmeasured confounding effects cannot be ruled out. The small number of current marijuana/current tobacco smokers is a limitation, which might provide unstable estimates for DMFT. In addition, the use of DMFT as an index has its limitations, as it does not specify the severity or the activity of the disease. Recall bias can occur when participants are asked to self-report their drug use. This can affect the reliability of the data. However, NHANES utilises various methods to minimise this bias, such as detailed questionnaires and verification steps.
However, there are several strengths in this study. Based on our knowledge, this is the first study using national data to examine the effect of marijuana-smoking on dental caries experience as well as the combined effect of smoking both marijuana and tobacco. Using NHANES data allowed us to study a large representative sample of the US population, where oral health measures and examination were conducted by licensed dentists.
Future research is required to establish causality between marijuana-smoking and oral disease. Thus, longitudinal studies with a larger sample of marijuana smokers is needed, as well as examination of dose-response effects and whether the method of marijuana consumption affects oral health differently. Future research should include other possible confounding factors such as oral hygiene measures, tooth brushing frequency, and dental visits. Studies focussing on the combined effect of smoking both marijuana and tobacco are a future direction for research. Differentiating marijuana-smoking from cannabis edibles and drinkables is another direction for future research, as these products might have a different effect on caries due to their frequent inclusion of sugar. Community programmes educating the public about the possible oral effects of smoking marijuana, especially when combined with tobacco-smoking, are recommended.
Conclusions
This study aimed to examine the potential association between marijuana-smoking and dental caries experience (DMFT) and to study the combined effect of smoking both marijuana and tobacco cigarettes. Based on our findings, within the limitations of our study, smoking marijuana was not significantly associated with DMFT after controlling for confounders. However, when smoking marijuana was combined with tobacco-smoking, a modest increase in DMFT was observed, especially amongst former marijuana and current tobacco smokers.
With marijuana legalisation expanding across the US, the number of marijuana users is increasing. Consequently, the potential synergistic effect of tobacco and marijuana, which could amplify oral health effects, is a growing concern. Health promotion programmes should be directed towards educating the public regarding the health effects of smoking both substances. Directing dental programmes towards this at-risk group is another approach to enhance awareness and implement preventive strategies.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
CRediT authorship contribution statement
Meyassara Samman: Conceptualization, Data curation, Formal analysis, Methodology, Validation, Visualization, Writing – original draft, Writing – review & editing. Thayer Scott: Conceptualization, Methodology, Project administration, Supervision, Validation, Writing – original draft, Writing – review & editing. Woosung Sohn: Conceptualization, Methodology, Project administration, Supervision, Validation, Writing – review & editing.
Conflict of interest
None disclosed.
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