In the present study, dental caries and its risk indicators were assessed among domestic waste employees with the main focus on the evaluation of the effect of direct occupational contact with domestic solid waste. The results showed that the DMFT index and its components were not associated with direct contact with domestic waste, but were associated with older age, lower income and education, no previous instruction for self–performed oral hygiene, and no daily flossing. Therefore, the original hypothesis was not confirmed.
Significantly higher mean DMFT, MT, and FT were observed in the present group of non–collectors than in collectors, while the mean DT was similar between groups. Furthermore, the regression analysis did not show any association between exposure to solid waste and dental caries. Therefore, direct occupational contact with domestic solid waste was not associated with dental caries. However, waste collectors are exposed daily to a variety of occupational hazards, including infectious pathogens, that can enter the host through direct contact with waste or inhalation, resulting in a wide range of other health effects (Zolnikov et al. 2018; Kuijer et al. 2010; Ivens et al. 1998; Andrade et al. 2017; Brina et al. 2018; Da Silva et al. 2018). The exposition to virus, fungi and bacteria from the domestic waste may cause a dysbiosis of the oral microbiome, driving the polymicrobial communities towards pathogenicity with a particular emphasis on cariogenic biofilm development, which will be able to produce acid and cause the demineralization of the tooth surface. However, the adherence of present workers to the use of personal protective equipment as a preventive measure to reduce exposure to harmful substances might have avoided this effect. In particular, continuous training of workers is required to make them aware of occupational risks and the importance of work safety. Waste collectors must also adhere to good personal hygiene, especially before eating and when leaving the workplace, so that microorganisms and harmful chemicals are unable to be absorbed inside the body or transmitted to other environments or people. By contrast, a significant association has been reported between dental caries and occupation in the cement industry (Bozyk and Owczarek 1990), petrochemical industry (Duffy 1996; Werckmeister and Ruppe 1990), agriculture (Blignaut and Grobler 1992), and in particular, in the food industry where the occurrence of dental caries in bakery workers was sufficient to characterize it as an occupational disease (Sonnamend et al. 1991).
The worse dental status of the non–collector group was due to their higher FT and MT. It could be suggested that the non–collector group had greater access to dental treatment, but this was not based on a preventive approach but on tooth restorations and extractions after the progression of dental caries, and perhaps the progression of periodontal disease. It can also be assumed that due to the low income and educational levels of the whole group of workers, most did not seek dental care periodically, and when they did, restorations and extractions were required. A preventive program associated with oral rehabilitation is required to improve the oral health of this population. However, the DMFT of the whole sample and the groups of collectors and non–collectors were within the low and moderate grade of caries prevalence as indicators of oral health (Petersen and Baez 2013). These values were also lower than the rates from the latest Brazilian nationwide oral health survey (Ministry of Health of Brazil 2011) that found a DMFT index of around 16 in people aged between 35 and 44 years, and also lower than that in workers in the textile industry (Cavalcanti et al. 2017), supermarket chains (Batista et al. 2013), and building construction (Tomita et al. 2005), who had a DMFT score of over 11. The current findings are consistent with the results of a study involving employees monitored by an inter–company Occupational Health Service in France, where the DMFT score was approximately 9 (Catteau 2013). Conversely, cross–sectional studies reported DMFT scores lower than 5.5 among workers from different sectors, such as green marble mining and industrial workers (Dagli et al. 2008; Ahlberg et al. 1996). The difference in prevalence in these studies is likely associated with the difference in exposure to risk factors among populations, as dental caries is a multifactorial disease with various factors involved in its pathogenesis, including the presence of fermentable sugars and cariogenic microbial microorganisms, and host and environmental factors (Rathe and Sapra 2020), as well as access to dental caries.
A theoretical model of dental caries, involving contextual, social and biological factors, has been outlined by Holst et al (2001), focused on the understanding of caries and its variations in populations. The theoretical framework directs attention to health effects of collective phenomena that cannot be reduced to individual attributes, as dental caries are a result of biological processes on tooth surfaces and of processes in the environment. Accordingly, the environmental process is a combined result of behavioral, contextual and societal factors, which in a series of steps ultimately influence the way dental caries develop. The occurrence of caries is thus an outcome of complex processes in the oral cavity and of behaviors of individuals and societies. Even though the association between occupational exposure to domestic solid waste was not significant, the present results fit in this theoretical framework, with associations with older age, lower income and education, daily flossing and previous oral hygiene instructions being significant. In workers from other sectors, DMFT was associated with older age (Cavalcanti et al. 2017; Batista et al. 2013; Tomita et al. 2005). This suggests that oral health problems accumulate over the years and that older individuals were not exposed to preventive care. Similar to other health conditions, lower education levels had a negative effect on tooth loss, consistent with other studies (Cavalcanti et al. 2017; Batista et al. 2013; Tomita et al. 2005; Mahdi et al. 2016; Zaitsu et al. 2017), which suggests that tooth extraction was common among these workers, probably due to the limited access to early and regular dental care, favoring the evolution of dental caries and tooth loss. Furthermore, a higher dental caries rate was associated with a lack of oral hygiene instruction and no daily flossing, and a higher filling rate was associated with higher monthly income and not using dental floss daily. This was likely due to the fact that a higher income increased access to preventive and restorative treatment, as well as dental hygiene products (Cosa et al. 2012; Molarius et al. 2014; Wamala et al. 2006).
This study has a few limitations. The analysis of a convenience sample in a single company and performing a clinical examination at their workplace may lead to poor representation of the at–risk population. For this reason, other waste collection companies should be studied in the future. In addition, due to performing the clinical examination at their workplace, subjects with negative self–perception of their oral health may refuse to participate to avoid personal exposure. However, the analysis was performed with an adequate sample size and a power of 0.8 for the DMFT values in a one–sided test with an alpha of 0.05. Moreover, this cross–sectional study simultaneously measured exposure and health outcomes; therefore, it is not possible to draw conclusions on the cause–effect relationship. Therefore, longitudinal studies should be planned to establish a temporal relationship between these variables.
The results of this study may be used to plan an oral health program for this population, which may affect general health and psychosocial development and even reduce absenteeism from work. The oral health program should be based on preventive care, focusing on education and instructions for self–performed oral hygiene and prosthetic rehabilitation of edentulism. Furthermore, at the moment, it is possible that the domestic waste is infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which may pose additional risks to domestic waste collectors and the environment (Mol and Caldas 2020). In particular, the spread of the coronavirus may be increased by inadequate waste management.