This study identified the influence of contextual variables MHDI and proportion of dentists per inhabitant on the number of decayed teeth in Brazilian adolescents, even after adjusting for critical individual variables knowingly associated with dental caries. The presence of contextual variables among the determinants of dental caries reinforces the fact that the geographic space (territory) reflects human, social, economic, and historical relationships. It can, in fact, influence people’s living conditions and health. The context can be understood as a reflection of the conditions of its inhabitants that positively or negatively affect the living conditions of its occupants. Contextual and individual conditions are interrelated and often seem to feed back [18].
Adolescents living in cities with medium/low MHDI had, on average, 1.78 more decayed teeth than those living in cities with very high MHDI. The MHDI had already been identified as a contextual determinant of untreated caries among adolescents [22]. A previous multilevel study observed a more significant number of missing teeth among adults living in municipalities with lower MHDI [24]. This conception aligns with features found in municipalities, where worse contextual indicators and worse oral health conditions are simultaneously identified since essential aspects for maintaining dentition, such as higher education, better eating habits, greater access to information, and provision of health services are generally more available in more developed areas [19, 20]. Thus, the results of this study reinforce the finding that dental caries is a “social disease” whose unequal impact results from unavoidable individual variations and the social disparities in which they are inserted [21, 23].
The main finding of this analysis refers to the association between the number of dentists per inhabitant of the municipalities and the number of decayed teeth observed among adolescents, even after adjusting for the other blocks of variables. Adolescents living in municipalities with a higher proportion of dentists per inhabitant showed a lower mean number of decayed teeth than adolescents living in municipalities with a lower dentist per inhabitant ratio.
This finding emphasizes the importance of the availability of dental surgeons in the municipalities in adequate numbers, referring to the reflection of the need for an equitable, nationwide distribution of these professionals to ensure a more significant transfer of information and access to oral health care for the population.
The WHO recommends one dentist per 1,500 inhabitants [9]. In 2020, Brazil had a ratio of one dentist to 626 inhabitants [26, 27], exceeding the recommended by more than twice. However, our study found that the proportion of dentists per inhabitant was considerably lower in the Northern regions, with one dentist for every 2,631 inhabitants, and in the Northeast, one dentist for every 1,818, when compared to the South regions (one dentist for every 1,149 inhabitants) and Southeast (one dentist for every 1,111 inhabitants). Thus, the distribution of these professionals by Brazilian region shows great disparity, with greater concentration in the most populous and developed regions. The issue of polarized and heterogeneous distribution of dental services in the country is more related to market laws than the profile of needs [17]. This problem is repeated worldwide, with more than one million dentists duly qualified to provide oral health care. However, they are not evenly distributed and as per the populations’ needs, many of which are from the most impoverished, underprivileged regions with a higher need for this type of care, with less than one dentist for every 300,000 inhabitants [28]. Other studies also report that the proportion of dentists per inhabitant is one of the leading contextual factors associated with tooth loss [29, 30] and other oral diseases [31, 32] among adolescents. Unfortunately, despite the relevance of this variable (dentist/inhabitant ratio) in dental caries or other oral problems, this issue has not been widely explored in the scientific literature, especially considering a multilevel approach. Thus, further investigations are recommended considering this vital variable for oral health outcomes.
Regarding individual variables, a previous study found that younger adolescents had a better oral health pattern [17], which corroborates the findings of this study, possibly due to the shorter exposure time of dental elements to the oral environment. We found that black/yellow/brown/indigenous individuals had a higher mean number of decayed teeth than white individuals. Inequalities associated with dental caries related to skin color were also observed in previous studies on Brazilian adolescents [22, 33]. On the other hand, fewer decayed teeth were observed among adolescents with higher education (MR = 0.92; CI = 0.90–0.93). Higher education levels are protective factors for dental caries [22]. Adolescents with a lower household income had a higher mean number of decayed teeth than those with higher household income (MR = 1.30; CI = 1.18–1.42), evidencing the socioeconomic condition as one of the determining factors for dental caries.
Subjective oral health conditions were also associated with dental caries among adolescents. A higher mean number of decayed teeth was found among individuals who self-perceived the need for dental treatment and reported tooth and gum pain in the last six months. The conception of quality of life and general aspects of health, including oral health, has been much discussed. This relationship plays an essential role in people’s perception, characterizing a subjective factor linked to self-image, understanding of needs, and searching for dental care [34, 36].
Regarding the use of dental services, we found that the mean number of decayed teeth was higher among adolescents who had never used these services, who had used these services for more than a year, and whose reason for the visit was oral problems. Research conducted among Brazilian adolescents also found a higher likelihood of caries in adolescents who did not visit the dentist regularly or never went to the dentist [33]. The regular use of dental services possibly ensures greater access to oral health maintenance procedures, disease prevention, and early treatment. Preventive use/review of dental services is an indicator of oral health, with a higher presence of dental caries observed among individuals who used dental services due to oral problems [37]. Moreover, fewer decayed teeth were observed among adolescents who used non-public dental services than those who used the SUS. National and international studies have already identified the association between the use of dental services in the last year and less tooth loss. Adults who routinely used dental services had better oral health levels, with fewer decayed and missing teeth [24, 38]. These results show that regular access to dental services can reduce the number of decayed and missing teeth and, consequently, ensure oral health as a whole.
The results of this study are expected to be helpful for the implementation of national and regional policies by oral health care providers. Considerable progress in reducing inequalities in access and increasing the use of dental services has been observed in Brazil from 1998 to 2008 [40]. However, inequalities among social groups are still significant. Adolescents’ context and individual factors associated with dental caries reveal health disparities, highlighting the importance of eliminating inequality in accessing dental services. Oral health system managers and legislators must immediately allocate resources and reduce barriers to this end, assuring the principle of equity.
As for the limitations of this work, we should consider that it is a cross-sectional study, where causes and effects are measured simultaneously, thus hindering the inference of causality. Furthermore, secondary data were analyzed, and, consequently, some risk factors for dental caries, such as habits and lifestyle, were not evaluated since the SBBrasil 2010 did not address such characteristics. It is worth mentioning the data’s temporal limitation, collected in 2020, although they are the most recent national approach data currently available. We recognize that the descriptive results should be interpreted with some caution, as the last decade was marked by changes in the oral health policy adopted in the country, which may have impacted the prevalence of caries lesions in the population. However, we believe that the verified associations are current and relevant. Also, it is worth noting the representativeness of the investigated sample and the multilevel approach of the variables, which allowed assessing the importance of contextual and individual factors in the investigated outcome. Another strength is that the dependent variable adopted was worked on in its discrete numerical nature (without categorizations), thus allowing us to verify the impact by the mean number of decayed teeth.