Association between oral hygiene and head and neck cancer in Brazil

REV BRAS EPIDEMIOL 2020; 23: E200094 ABSTRACT: Introduction: Poor oral hygiene, regular use of mouthwash and absence of visits to the dentist could correspond to potential risk factors for the development of head and neck cancer. Objective: The objective of this study was to determine whether oral hygiene is associated with the occurrence of oral cavity and head and neck cancer in a Brazilian sample. Method: The variables of oral hygiene condition, such as toothbrushing frequency, dental loss, need and use of prosthesis, and regular visit to the dentist in a case-control study were analyzed in patients from five hospitals in the state of São Paulo, Brazil, paired by gender and age, from the multicenter project Genoma do Câncer de Cabeça e Pescoço (GENCAPO). Results: The most frequent malignancies in the 899 patients included were those of the tongue border (11.41%) and tongue base (10.92%). The multivariable statistical analysis found odds ratio values: Brushing once 0.33 (95%CI 0.25 – 0.44); Brushing twice 0.42 (95%CI 0.35 – 0.52); Flossing always 0.19 (95%CI 0.13 – 0.27); Flossing sometimes 0.19 (95%CI 0.15 – 0.24); Bleeding 2.40 (95%CI 1.40 – 4.09); Prosthesis 1.99 (95%CI 1.54 – 2.56); Visiting the dentist 0.29 (95%CI 0.22 – 0.37); Good hygiene 0.21 (95%CI 0.17 – 0.27); Regular hygiene 0.20 (95%CI 0.15 – 0.25); number of missing teeth (6 or more) 3.30 (95%CI 2.67 – 4.08). Conclusion: These data showed that, in the population studied, indicators of good hygiene such as brushing teeth and flossing were protective factors for mouth and head and neck cancer, while bleeding and many missing teeth were risk factors.


INTRODUCTION
The main etiological factor for head and neck carcinomas is tobacco, and the association between the two may be exacerbated by the consumption of alcoholic beverages 1,2 . However, as cancer is a multifactorial disease, there are other components associated with its development, such as nutritional factors 3 , inherited mutations, and immunological conditions 4 . Some viruses have carcinogenic potential, including the human papillomavirus (HPV); the effect of HPV has already been demonstrated for cervical cancer and has relevant associations with head and neck carcinomas, especially in the oropharynx 5 . Social factors and lifestyle, in addition to being risk factors, alter the prognosis of the disease 6 . Even with so many factors already known and studied, new relationships and hypotheses need to be investigated to manage the other possible etiological factors.

METHOD
The data originated from a multicenter project titled Fatores ambientais, clínicos, histopatológicos e moleculares associados ao desenvolvimento e ao prognóstico de  This investigation is in accordance with the international and national parameters of ethical investigation with human beings; the investigation protocol was submitted and approved by the Ethics Committee of the School of Dentistry of Universidade de São Paulo (FOUSP) (CAAE: 59663516.0.0000.0075; approval number: 1.731.007).
The data were stored in a database developed for GENCAPO II and can be viewed on the website http://www.gencapo2.fsp.usp.br/. The data used were collected between 2010 and 2015. The study population comprised patients with head and neck cancer whose lesions were qualified by the international classification of oncological diseases (ICD-O 3 rd Edition) and showed in (Supplement Material 1) 14 . This led to a case-control study in which participants were electronically paired using a tool developed by the GENCAPO technical team (available at http://www.gencapo.famerp.br/gencapo3/pareamento/index.php) in patient/control pairs by gender and age (five-year intervals).
Specially trained interviewers collected information on sociodemographic factors, lifestyle, and family history of cancer prior to treatment. Oral hygiene habits were collected through questionnaires with several alternatives. Bushing teeth data are presented as brushing once a day and twice a day, since we wanted to analyze whether the differences in brushing frequency could bring different results.
Conditional logistic regression was performed with bivariate analysis and with multiple analysis, standardized by the brushing frequency.
To enable statistical analysis, the STATA 13.0 ® software was used to evaluate p-values, odds ratios (OR), and confidence intervals (95%CI), with bivariate and multiple logistic regression tests; all cases were analyzed and sequentially separated into the oral cavity and other cancers. REV BRAS EPIDEMIOL 2020; 23: E200094

RESULTS
The study included 899 cases and 899 controls, paired by gender and age. Men represented 80% of the sample. The most predominant education level in both groups was incomplete primary education, 56.0% of cases and 47.0% of controls; 4.0% of cases and 11.0% of controls completed higher education. White skin color was self-reported for more than half of the cases and the controls, 58.0 and 68.0%, respectively. The distribution of other ethnic groups was also balanced, and the group that self-reported brown skin color was the second most frequent, 29.5 and 24.2% for cases and controls, respectively. The most common malignant neoplasm sites were: tongue edge (11.4%), tongue base (10.9%), and anterior floor (5.9%). Other topographic locations (50 classifications) did not reach 5.0% of the sample and they were presented in the supplementary material (Supplement Material 1). Table 1 shows the sample characterization by gender, age and the most important risk factors -consumption of tobacco and alcohol.

DISCUSSION
This study brings pooled data from 5 reference hospitals, and not as per hospital, since there were differences in the number of patients treated in each unit; they are reference hospitals in which socioeconomic conditions of the patients are similar. The Hospital da Clínicas da Faculdade de Medicina of USP accounted for most of the cases (41.60%) and the Hospital do Câncer de Barretos Fundação Pio XII, with 4.89%.
Brushing teeth was a protective measure for head and neck cancer. Patients who brushed at least once a day were less affected, and the relationship was even stronger for patients who brushed their teeth twice or more a day. In the literature search, we found controversial results with respect to the brushing frequency and its potential to prevent oral lesions 10 . Based on this information, we decided to maintain the variables "brush once" and "brush twice" and all analyses. Neoplasms in other organs are also associated with poor hygiene; for example, penile cancer has similarities to mouth cancer, e.g., mostly squamous cell carcinomas, more prevalent in developing countries, and a predominance in more vulnerable social classes, and poor local hygiene as a risk factor 15 . Cervical carcinoma, whose main risk factor is HPV, is also correlated with poor hygiene 16 .
As the oral cavity connects the external environment to the gastrointestinal system, the association between oral hygiene and pancreatic cancer and the presence of bacteria from the oral cavity in the pancreas was confirmed 17 . As oral hygiene is correlated with various types of cancer, microbiota dysregulation, and inflammation may be important and plausible factors in carcinogenesis. Furthermore, people with poor oral hygiene have higher formation of endogenous nitrosamine, a known carcinogen 18 . Thus, this set of factors may contribute to the complex mechanism of cancer. Another sustainable hypothesis is that a specific bacterium or a group of bacteria may have the ability to evade the host's response and impair innate immunity, making the environment favorable to excessive bacterial growth, promoting the conversion of the symbiotic state into the dysbiotic one 19 , generating a favorable environment through cascade events for the initiation and promotion of neoplasm 20 .
Comparing the findings of this study with those for other populations, a risk factor attributable only to the population of hospitals included in the GENCAPO project is not expressed. A Chinese study that used the same indicators, only for those who did not smoke and did not present with alcoholism, indicated that cancer patients had worse oral hygiene 21 . A study with a similar design, conducted in India, found that poor oral hygiene increased the risk of mouth cancer by 7 times (95%CI 3.7 -13.0). In this study, gingival bleeding increased the risk of mouth cancer four-fold (95%CI 2.5 -6.2), and dentist visits motivated only by pain were also correlated (OR = 3.8; 95% CI 2.4 -6.2); this interaction seemed to be more harmful when associated with smoking and/or chewing tobacco 22 . The INHANCE Consortium collected data through a multicenter project with the participation of centers in the United States, Japan, Latin America, and Europe, concluding that good hygiene is associated with a lower risk of cancer 13 . The American study Carolina Head and Neck Cancer Epidemiologic (CHANCE) showed that poor hygiene affected head and neck survival 23 .
Multicenter studies with wide population coverage have possible limitations; even though they provide primary databases, they may have some degree of inconsistency. For example, a project interviewer's manual may advise that toothless patients do not respond to questions regarding brushing frequency, use of floss, and gingival bleeding, making the number of respondents vary in these categories. Another factor that alters sample groups is that patients can choose not to answer a question.
It is expected that these patients avoid brushing, due both to the fear of manipulating an altered region and the psychological aspects inherent to the diagnosis. However, tooth loss is not a specific problem, nor does it occur abruptly 24 , except in cases of aggressive periodontitis, which is a rare disease in the population studied 25 . In addition to being more present in vulnerable populations, its decline is not consistent around the world 26 . Dental loss can then be considered a more reliable measure than hygiene, once that the brushing frequency can change as well as the brushing quality.

REFERENCES
This study showed interesting data about tooth loss that was an important factor associated to head and neck cancer, regardless of the analysis performed. Patients with many dental losses were 3 or 4 times more likely to present these neoplasms, reinforcing the theoretical model of the distribution of mouth and head and neck cancer that affects more patients in the poorest sections of society (which have limited access to dental services). It is still necessary to clarify whether there is a causal enhancement between oral diseases and cancer or only the similarity of exposure factors.
Another relevant finding was that the variables of good hygiene were used as a protective factor for head and neck cancer, even without cases of mouth, which opens the possibility for further studies to verify the cause of this correlation is in fact caused by poor hygiene deregulation of the microbite producing acetaldehyde as in chronic alcohol users or if there are other reasons such as bacterial migration 27 .
The biological plausibility of the relationship between oral hygiene and oral cancer can be explained by the fact that bacterial dysregulation and Candida albicans produce acetaldehyde, a known carcinogen in animal experiments and in vitro, due to their mutagenic effect, in clinically relevant amounts, which is why we present separate results with regard the oral cavity and other locations; then, we could try to understand if the proximity to the source of infection could have a greater causal relationship 10 .
These data showed that, in the studied population, indicators of good hygiene such as brushing teeth and flossing were protective factors for mouth and head and neck cancer, while bleeding and many missing teeth were risk factors.