The association between individual and contextual factors and functional dentition status among adults in Rio Grande do Sul State , Brazil : a multilevel study

Functional dentition plays an important role in maintaining masticatory function, which is closely related to the number of teeth present in the mouth. The objective of this study was to investigate the association between individual and contextual factors and functional dentition (defined as the presence of at least 20 teeth) in Brazilian adults. This was a multilevel cross-sectional population-based study with a two-level structure and a total sample of 10,407 adults from 84 municipalities (counties). The exposures at both levels were demographic, socioeconomic, and oral health treatment-related. Multivariate analyses showed that higher prevalence rates of functional dentition were associated (p < 0.01) with municipalities having higher mean income and fluoridated water supply and with individuals living in urban areas, younger adults, males, those with more schooling and higher income, those that reported having visited the dentist in the previous 12 months, and those with access to information on prevention. The findings suggest that research on tooth loss and functional dentition should take different socioeconomic factors into account. Tooth Loss; Oral Health; Socioeconomic Factors Introduction Tooth loss is one of the main public health problems affecting the adult population worldwide 1. This situation directly and indirectly influences the individual’s overall health. Compromised masticatory function affects quality of diet, increasing the risk of various health problems like cardiovascular diseases, physical disabilities and even death 2,3. Edentulous individuals show lower consumption of important macro and micronutrients as compared to those with functional dentition 4,5. For example, edentulism without rehabilitation with prostheses has been associated with reduced intake of carbohydrates, vitamins, and minerals 4. Obesity 3 and malnutrition 5 have also been linked to tooth loss. There are various causes of tooth loss, the main ones being dental caries and periodontal disease. Other factors include access to dental services, health system organization, and oral health care 6,7. Higher tooth loss rates have been associated with unfavorable socioeconomic conditions 8,9. Functional dentition plays an important role in maintaining masticatory function, which is closely related to the number of teeth present in the mouth 10,11,12. According to this concept, maintenance of functionality requires a minimum of 20 teeth well distributed in the upper and lower dental arches. In 1992, the World Health Organization (WHO) declared the lifetime retenARTIGO ARTICLE Koltermann AP et al. 174 Cad. Saúde Pública, Rio de Janeiro, 27(1):173-182, jan, 2011 tion of functional and aesthetic natural dentition with no fewer than 20 teeth and without requiring dental prostheses as one of the goals of oral health practices 13. According to data from the latest Brazilian nationwide oral health survey (SB Brasil: Oral Health Conditions in the Brazilian Population), the estimated prevalence of functional dentition, namely the presence of 20 or more teeth in the mouth, was 54% (95%CI: 53-55) in the 35 to 44year age bracket. Similar results were reported in the Southern geographic region of the country (55%, 95%CI: 53-57) 14. Factors associated with dental loss, and thus with the loss of functional dentition, are relatively well established at the individual level. Edentulous persons usually have lower incomes and less schooling, less access to services, and poor self-rated oral health 15. However, it has been argued that explanations based purely on individual data are insufficient and fail to capture important determinant of health and disease, the characteristics of groups and contexts to which the individuals belong 16,17. The literature is thus limited on the influence of contextual aspects on oral health in individuals and groups 18. According to a recent study of 2,680 Australian adults in 60 neighborhoods, residence in neighborhoods with better socioeconomic conditions attenuated the risk of dental loss associated with low individual income 19. The current study’s aim was to investigate the association between individual and contextual factors in the functional dentition of adults in the State of Rio Grande do Sul, Brazil.

The association between individual and contextual factors and functional dentition status among adults in Rio Grande do Sul State, Brazil: a multilevel study A associação entre aspectos individuais e contextuais na dentição funcional de adultos do Rio Grande do Sul, Brasil: um estudo multinível Introduction Tooth loss is one of the main public health problems affecting the adult population worldwide 1 .This situation directly and indirectly influences the individual's overall health.Compromised masticatory function affects quality of diet, increasing the risk of various health problems like cardiovascular diseases, physical disabilities and even death 2,3 .Edentulous individuals show lower consumption of important macro and micronutrients as compared to those with functional dentition 4,5 .For example, edentulism without rehabilitation with prostheses has been associated with reduced intake of carbohydrates, vitamins, and minerals 4 .Obesity 3 and malnutrition 5 have also been linked to tooth loss.
There are various causes of tooth loss, the main ones being dental caries and periodontal disease.Other factors include access to dental services, health system organization, and oral health care 6,7 .Higher tooth loss rates have been associated with unfavorable socioeconomic conditions 8,9 .
Functional dentition plays an important role in maintaining masticatory function, which is closely related to the number of teeth present in the mouth 10,11,12 .According to this concept, maintenance of functionality requires a minimum of 20 teeth well distributed in the upper and lower dental arches.In 1992, the World Health Organization (WHO) declared the lifetime reten-Cad.Saúde Pública, Rio de Janeiro, 27(1):173-182, jan, 2011 tion of functional and aesthetic natural dentition with no fewer than 20 teeth and without requiring dental prostheses as one of the goals of oral health practices 13 .
According to data from the latest Brazilian nationwide oral health survey (SB Brasil: Oral Health Conditions in the Brazilian Population), the estimated prevalence of functional dentition, namely the presence of 20 or more teeth in the mouth, was 54% (95%CI: 53-55) in the 35 to 44year age bracket.Similar results were reported in the Southern geographic region of the country (55%, 95%CI: 53-57) 14 .
Factors associated with dental loss, and thus with the loss of functional dentition, are relatively well established at the individual level.Edentulous persons usually have lower incomes and less schooling, less access to services, and poor self-rated oral health 15 .However, it has been argued that explanations based purely on individual data are insufficient and fail to capture important determinant of health and disease, the characteristics of groups and contexts to which the individuals belong 16,17 .The literature is thus limited on the influence of contextual aspects on oral health in individuals and groups 18 .According to a recent study of 2,680 Australian adults in 60 neighborhoods, residence in neighborhoods with better socioeconomic conditions attenuated the risk of dental loss associated with low individual income 19 ..At the contextual level, secondary data were used from the participating municipalities.

Methodology
To determine the number of municipalities comprising the sample, a simple random sample was calculated with a 95% confidence interval (95%CI) and a sampling error of ten percentage points.A total of 95 municipalities, pre-stratified by population size and region of the State, were invited to participate in the study.The number of individuals was calculated using the population according to IBGE data with 1996 as the base year, a 95% confidence interval, sample error of four percentage points, and 76.2% caries rate at 12 years of age 21 .It was estimated that a total of 40,923 persons would be needed in the different age brackets and 16,316 persons 35-44 years of age.Dentists were trained and calibrated to conduct the clinical examination, and structured interviews were held with the participants 20 .
The study outcome was defined as the presence of 20 or more teeth in the oral cavity (code 1) or fewer than 20 teeth (code 0), with the former called functional dentition 22 .Exposure variables at the individual level were demographic (gender, skin color, and age), socioeconomic (income and schooling), and dental services-related: visit to the dentist in the previous 12 months, place of care, and information on preventive dental health measures.
The demographic variable "skin color" was self-reported and classified as white, black, brown, and other.Analysis of the age variable considered two age groups, namely individuals 35-39 and 40-44 years of age.The variables used to characterize socioeconomic status at the individual level were collected in discrete form (family income in Reais and years of schooling) and categorized in the highest 25%, intermediate 50%, and 25% lowest scores.Thus, the monthly income variable was re-coded as low (R$ 0.00-R$ 279.00), medium (R$ 280.00-R$ 800.00), and high (≥ R$ 801.00), and the schooling variable as low (0-4 years of schooling), medium (5-8 years), and high (≥ 9 years).
Four categories were used for place of treatment: public, private, other, and none (no history of dental treatment).The variables for visits to the dentist in the previous 12 months and receiving preventive information on oral health were analyzed dichotomously, with having visited a dentist in the previous 12 months and having preventive information as the respective reference codes.
Data at the contextual level were representative of the municipalities (counties) that participated in the oral health survey.The secondary databases used were the Population Census, 2000 23 , the United Nations Development Program (UNDP) 24 , and the Brazilian Federal Board of Dentistry (CFO.http://www.cfo.org.br/estatística/default.cfm,accessed on 13/June/2007).
The IBGE is the official government agency in charge of conducting the national population census in Brazil.Its database was used for the contextual variables on income and schooling 23 .Like the individual socioeconomic variables, the contextual variables were categorized as the highest 25% of scores, the intermediate 50%, and the lowest 25%.This strategy aimed to better emphasize the influence of socioeconomic factors, on the oral health of adults by comparing the extreme values for each variable.The strategy also sought to relate the data to the context in which the study was performed, since it used the data distribution itself to define the categories.In other words, an individual or municipality could only be classified as having high or low socioeconomic status in comparison to other individuals or municipalities in Rio Grande do Sul.Income referred to the mean monthly income of the heads of permanent private households per municipality and was thus analyzed as low (income ≤ R$ 425.00), medium (R$ 426.00 to R$ 635.00), and high (≥ R$ 636.00).The schooling variable was evaluated as years of schooling in the following categories: low (≤ 3.8), medium (3.9-5.1), and high (≥ 5.2 years of schooling).
The aim of the UNDP is to fight poverty, adopting a comprehensive strategy that takes each country's specificities into account, to promote democratic governance, provide support for public policy implementation, and foster integrated local development 24 .The UNDP database was used for the Gini index (low ≤ 0.48, medium 0.49 to 0.56, and high ≥ 0.57), which measures the degree of inequality among individuals according to per capita household income.It varies from 0, when there is no inequality, that is, all individuals' income is the same, to 1, when inequality is maximum; and the human development index or HDI (low ≤ 0.752; medium, from 0.753 to 0.814; and high ≥ 0. 815), as an indicator of quality that is not limited only to the economic dimension in the evaluation of a population's living conditions, but also considers social and intellectual aspects.These dimensions also have the same importance in the index, which varies from 0 (worst) to 1 (best).These data are for the year 2000.
In its official website, the Brazilian National Board of Dentistry (CFO) provides nationwide data on Brazilian dentists (http://www.cfo.org.br/estatística/default.cfm, accessed on 13/ June/2007).This study used data for the number of dentists working in each city included in the study for the years 2002 and 2003, and this variable was analyzed as the total population in each municipality divided by the number of dentists (1,000-10,000 inhabitants/dentist, ≥ 10,001 inhabitants/dentist, and no dentist).The study also analyzed the place of residence (urban versus rural) and time since implementation of fluoridation in the public water supply (≥ 10 years, 5-9 years, < 5 years), both of which variables came from the national oral health survey.
Data analysis used Stata 9.0 (Stata Corp., College Station, USA) and MLwiN 2.0 (Centre for Multilevel Modeling, Bristol, UK).Descriptive analyses were performed to verify the frequency of the clinical and non-clinical variables.Since the outcome was dichotomous, the chi-square test was used for the bivariate analysis and multilevel logistic regression.Fixed-effects random models were estimated using the second-order PQL method.The aim of this analysis was to estimate the odds ratios (OR) for functional dentition (≥ 20 teeth present) and the 95%CI.
The multivariate analysis followed a theoretical model of determination (Figure 1) and was conducted as follows: first, the contextual variables were adjusted for each other.Next, adjustment was performed for the individual demographic variables and finally for the individual health-system variables.The variables at each level were adjusted for each other and only variables with p < 0.01 were maintained for the next level.Thus, all the variables in the respective level were entered into the model, removing those with the lowest significance one by one.This strategy aimed to minimize type 1 errors due to the fact that this was a large sample and with high power to detect associations.Likewise, associations between the outcome and the exposures were considered significant at the 1% level (p < 0.01) and without intersecting the 95%CI.
The project SB/RS -Oral Health Conditions in Rio Grande do Sul State was approved by the National Council on Research Ethics (document 581/2000, July 21, 2000).All the participants signed a free and informed consent form 20 .

Results
Of the 95 selected municipalities, 11 (12%) did not participate in the study.As for the individuals, 218 (2.1%) were excluded because they lacked information on functional dentition.The data analysis thus included 10,407 adults from 84 municipalities 19 .
As for individual factors, the crude analysis showed higher functional dentition rates in younger persons, males, those with more schooling and higher income, those who had visited the dentist in the previous 12 months, and those who had received information on prevention (Table 1).As for contextual factors, the highest functional dentition rates were in municipalities with higher income, higher schooling, higher HDI, more than ten years of fluoridation, and place of residence in urban areas (Table 2).

Discussion
This study aimed to assess the association between individual and contextual factors in the functional dentition rate.Individuals living in urban areas and in municipalities with better socioeconomic standards and a longer history of fluoridation in the public water supply showed higher functional dentition rates.The current study agrees with previous studies in Brazil, reporting an association between unfavorable local socioeconomic conditions and high tooth loss rates 8,28,29 , and thus lower functional dentition rates.What are the possible explanations for this finding?The most plausible explanation is that municipalities with better physical and social characteristics like transportation, community integration, and health services infrastructure can be expected to facilitate access to health-related services and activities 27 .Thus, municipalities with better socioeconomic conditions provide better opportunities for persons to preserve their teeth, especially through greater availability and access to dental services 19 .Another possibility is that some characteristics of municipalities with higher mean per capita income may attenuate the risks associated with unfavorable individual socioeconomic status 19 .In Brazil, the analysis of data from the National Household Sample Survey showed that the proportion of adults that had never visited the dentist was 16 times higher in the group consisting of the poorest 20% of the population as compared to the wealthiest 20% 7 .In addition, it had been argued previously that individual health behaviors cannot be understood without taking into consideration the characteristics and processes occurring in both the immediate and wider setting.For example, a person's diet, which has a strong influence on his or her oral health, is influenced not only by personal tastes or perceptions, but also by the local social context, for example when healthy foods are more accessible in areas with better socioeconomic conditions 28,29 .Likewise, socioeconomically privileged areas could have better access to information, due to greater social capital and lower levels of violence and stress, which would influence health-related behaviors 19,30,31,32 .Another important factor in the prevention of oral diseases is fluoridation of the public water supply, considered one of the ten most relevant public health measures in the 20 th century 33 .This measure has been the focus of numerous studies, and has been recommended by the WHO as an important factor for offsetting oral health inequalities in public health 34 .Water supply fluoridation is capable of reducing prevalence and incidence of dental caries in various age groups, decreasing treatment costs for oral diseases and reducing the inequalities between groups with distinct socioeconomic conditions 35,36,37 .Analyzing data from adults in Rio Grande do Sul State, the current study showed a positive association between higher functional dentition rates and longer exposure to fluoridated water supply.
As for geographic location, the study shows that individuals living in rural areas show a higher risk of lacking functional dentition.The same situation has been found in other studies on Brazilian adults 8,38 .This situation may result from the infrastructure distribution, to the disadvantage of individuals living in rural areas with less access to fluoridated water supply and dental services.
As for individual socioeconomic factors, the current study corroborates the common findings in the Brazilian and international literature.Higher tooth loss rates have been associated with low income, low schooling, and low socioeconomic status 8,25,38,39,40,41,42,43,44,45 .Individuals with unfavorable socioeconomic status generally have fewer teeth in their mouths due to limited access to dental services and the option for extractions rather than more conservative dental treatment 7,43 .
The high functional dentition rate among men corroborates other Brazilian studies with similar findings 2,25,38 .The hypotheses for explaining this phenomenon could include the higher caries rate among adolescent girls as opposed to boys and the greater use of dental services by women as compared to men, both of which factors favor early tooth loss, especially due to the option for tooth extraction rather than conservative treatment among socioeconomically disadvantaged groups 2,26,38 .
Some limitations are inherent to the study.Given its cross-sectional design, the study was limited to the identification of associations rather than causal relations.In addition, the presence of residual bias cannot be ruled out.The presence of other contextual factors, inherent to the municipalities studied and not contem-plated in the analysis, should be investigated in greater depth.Furthermore, the national survey lacked sampling weights, and thus the study in Rio Grande do Sul does not allow population inferences as to the prevalence of some outcomes and age groups 46 .Thus, the functional dentition rate presented in the current study may not be precise.However, this fact probably did not interfere in the associations reported here.
In general, the presence of functional dentition is influenced by both collective and individual factors.Therefore, studies on functional dentition and tooth loss should take the different levels of social structure into account.It is hoped that the study will contribute to the identification of priority municipalities and groups of individuals for the formulation and implementation of public policies in oral health based on the principles of the Unified National Health System (SUS), aimed at improving the population's quality of life.

Figure 1 Theoretical
Figure 1 Theoretical model for factors associated with functional dentition (≥ 20 teeth present) in adults.

Table 3
Odds ratios (OR) for functional dentition (≥ 20 teeth present, crude and adjusted) adjusted for contextual and individual variables in adults in Rio Grande do SulState, Brazil, 2002-2003 (n = 10,407).