Tobacco use and caries risk among adolescents – a longitudinal study in Sweden

It is generally thought that smoking and the use of smokeless tobacco may have a detrimental impact on general and oral health [1‐3]. The relationship to dental caries is however still unclear. Several studies world-wide have denominated tobacco use as a risk factor for coronal and root caries and disclosed increased caries rates in tobacco smoking young adults, adults, and elderly [4‐9]. However, a recent epidemiologic survey conducted in Sweden failed to demonstrate a relationship between tobacco use and caries in adults and elderly [10]. A recent systematic review on tobacco use and dental caries was based solely on cross-sectional studies and, as a result, the overall quality of evidence was concluded to be poor [11].

As caries is a multi-factorial disease with clear life-style, socio-economic and socio-demographic gradients, the tobacco use may be a co-variable in this complex rather than a direct etiological factor [12, 13]. We have previously presented caries risk in children and adolescents in relation to neighborhood socio-economic factors with aid of a geo-mapping tool in the Region of Halland, Sweden [14, 15]. The epidemiological data collected in this region provides an opportunity to examining the impact of tobacco use on caries risk among adolescents, with consideration to socio-economic variables by residency. Importantly, as the epidemiological data have been collected annually, we can apply a longitudinal approach.

∆DMFS differed evidently between ever and never users of tobacco (Table 1; overall p < 0.0001). Significant differences were observed in each neighborhood-level socio-economic stratum (Table 2; overall p < 0.0001). As expected, a socio-economic gradient in caries burden was evident in the study population (Table 2). Nevertheless, baseline DMFS was consistently higher among ever users, as compared with never users in neighborhoods with a similar socio-economic characteristic (Table 2). Even after controlling for baseline DMFS and sex, ∆DMFS differed highly significantly between ever and never users (Table 3; overall p < 0.0001). The pattern of more pronounced DMFS increment during adolescence among the ever users of tobacco was consistent across the strata of neighborhood-level socio-economy and baseline DMFS, although the degree of statistical evidence varied (Table 3). The change in DMFS displayed a different pattern in the most vulnerable groups (SE groups 20–29.9 and 30+, baseline DMFS > 3), indicating a weaker influence of tobacco use. On the other hand, the statistical evidence of a tobacco effect was also weaker for the individuals in the residential areas with < 10% of the families with low purchasing power, within each stratum of baseline DMFS.

To our knowledge, this report is based on the first longitudinal study addressing the impact of tobacco use on caries development among adolescents. The main finding was clear-cut; self-reported use of tobacco was significantly associated with increased incidence of dental caries over a 3 year-period, irrespective of socio-economic and geographic characteristics. Therefore, the immediate clinical implication is that the question “do you use tobacco?” is important and should be relevant to include as a component of the individual caries risk assessment. Such a comprehensive risk assessment is crucial for appropriate treatment decisions concerning prevention, non-operative and operative caries therapy [19‐21] and for determination of individual recall intervals [22]. On population level, information on the use of tobacco should be incorporated in oral health community plans.

The large size of the material, the high population coverage and the robust clinical scoring of caries were strongly enhancing the external validity of this project. The study design had still a number of limitations. The findings were based on a very crude classification of self-reported data on tobacco use, dichotomized as “ever“or “never” and the actual frequency and duration of the tobacco use was not reported. It is also likely that the true frequency of tobacco-use was somewhat under-reported, especially in the younger age-groups, due to reluctance to admit “a bad habit” in front of health professionals and sometimes parents. Furthermore, tobacco-use included both cigarette smoking and the use of smokeless tobacco (snuff) with differences in gender- and geographical pattern. Girls in urban parishes were more likely to smoke while the use of smokeless tobacco was more prevalent among rural boys (data not reported). In spite of exposure misclassification, likely to have induced bias towards the null, we were still able to demonstrate clear impact of reported tobacco use. Nevertheless, timing of exposure is an interesting aspect to investigate further. By dividing the “ever users” group into reported tobacco users at baseline (i.e., 16 years of age) and the remaining users reported tobacco use at any subsequent occasion during the follow-up (i.e., 17–19 years of age), our crude data indicate a higher mean ∆DMFS among the “baseline users” as compared with the “users commencing later” (Figure 2). Hence, the adverse effect on caries development could have been influenced by exposure time.

Another study limitation was that we were unable to control for other life-style and behavior-related factors although the adjustment for baseline DMFS and sex to some extent may have captured such obvious confounders.

The socio-economic statistics applied here were from 2010, but this was only a minor concern as the neighborhood characteristics proved to be stable over the total observation period [14]. Moreover, we considered family purchasing power as the primary indicator of neighborhood socio-economy. This indicator takes solely residing families with at least one child (≤19 years of age) into account; the elderly population was disregarded, which can be advocated. Nevertheless, family purchasing power corresponded fairly well with other alternative socio-economic indicators on the parish level, such as educational level and the proportion of immigrants [14].

Interestingly, the caries burden remained relatively unchanged over the four cohorts. On the other hand, the change in DMFS clearly depended on vulnerability (socioeconomic status), as seen in Table 3. A notable observation was that the SiC-index displayed less pronounced differences in caries incidence between tobacco-users and non-users compared with the crude mean values, considering the individuals in the neighborhoods with less favorable socio-economy (Table 2). As the distribution of caries is skewed, the SiC-index was constructed to more accurately mirror the dental health in the proportion of the population with the highest caries burden [17]. Consequently, those individuals were the adolescents with highest caries-activity and most filled surfaces at baseline, which may have limited the number of actual surfaces available for new obvious caries lesions over the study period. Bitewing radiographs were only taken on individual indications and were likely more often exposed in the high caries-group; this procedure may have enhanced the difference between the exposure groups. We also noticed that the statistical evidence of a tobacco effect was weaker for the individuals in the neighborhoods with most favorable socio-economy, within each stratum of baseline DMFS. Possible explanations could be a higher general awareness of factors associated with a healthy lifestyle or a less heavy use of tobacco products.

In conclusion, tobacco use was clearly associated with increased caries development during adolescence. Thus, this factor should be relevant to include in the clinical caries risk assessment of the individual patient as well as for community health plans dealing with oral health.