Malocclusion and social vulnerability : a representative study with adolescents from Belo Horizonte , Brazil

Malocclusion is public health problem because of its high prevalence, treatment possibility, and impact on the individual’s quality of life. This article aims to determining the prevalence of malocclusion in adolescents and to test its association with social vulnerability. A representative transversal study was performed with 1612 adolescents aged between 11 and 14 years old who came from public and private schools in Belo Horizonte, Brazil. The adolescents were examined by three calibrated examiners for diagnosis of malocclusion, using the Dental Aesthetic Index. The Social Vulnerability Index from Belo Horizonte was used to determine the degree of social vulnerability from adolescents. The data were analyzed using Poisson regression with robust variance (p<0,05). Most adolescents presented absence/minor malocclusion (68.7%). Dental crowding was diagnosed in 51.9% from the sample, diastema in 23.7%, anterior open bite in 7.6 %. Malocclusion was associated with social vulnerability (PR=1.25;95% CI=1.01-1.55). Dental crowding was the most prevalent type of malocclusion. The more socially vulnerable adolescents had worse indicators of malocclusion.


Introduction
Despite the possibility of treatment, malocclusion is considered a public health problem due to its high prevalence and the extent to which it affects the quality of life of affected individuals [1][2][3][4][5][6][7] .A Brazilian population-based study conducted in 2010 showed that 38.8% of 12-year-old adolescents suffered from malocclusion 7 .Tooth crowding and spacing, as well as marked horizontal overjet, are the types of malocclusion that most affect individuals in the 9 to 14year age group 1,8 .
In general, individuals with low socioeconomic status suffer greater degrees of oral problems 9,10 .Previous studies have shown that adolescents from low-income families whose parents have a lower level of schooling have a higher prevalence of malocclusion 6,11,12 .However, this association remains controversial, as some studies have not identified this relationship 1,13,14 .
A Brazilian study evaluated the association between malocclusion in 12-year-old childrenand individual and contextual factors and found that individuals from sanitation districts with worse conditions of basic sanitation, housing, family income and schooling had a higher prevalence of malocclusion 12 .A nationwide Brazil-based study showed that 12-year-old children living in cities where more families were dependent on government social benefits, which had a lower gross domestic product, and which performed worse in terms of population health care, had higher prevalences of malocclusion 6 .It is essential to use local indexes that assess the social vulnerability of the population through the influence of neighborhoods and access to basic services such as health, transport and general living conditions when considering the most prevalent oral disorders, such as malocclusion 11 .However, studies that analyze the influence of environment and access to infrastructure on the occurrence of malocclusion are scarce.
The identification and early treatment of individuals with malocclusion is important in terms of public health performance, as it directly affects the cost of treatment, with preventive and interceptive orthodontic practices improving occlusion during pre-adolescence and adolescence 15,16 .In this scenario, there is a need for studies thathelp to identify the relationship between malocclusion and conditions of social vulnerability.The use of the Social Vulnerability Index (SVI), an instrument developed and applied specifically for the city of Belo Horizonte, Brazil, contributes to a better understanding of the in-fluence of environment and access to infrastructure on the occurrence of health/disease indicators.The SVI measures the vulnerability of the population of the city through five dimensions of citizenship, addressing access to housing, basic infrastructure, schooling, income, work, legal support, health, food security and social security 17 .Therefore, the objective of the present study was to evaluate the prevalence and severity of malocclusion and its association with the social vulnerability to which adolescents aged 11 to 14 years in the city of Belo Horizonte are exposed.

Methods
The present study was carried out in the city of Belo Horizonte, the capital of the state of Minas Gerais, Brazil.Belo Horizonte has a population of 2,375,151 inhabitants, and is divided into nine administrative regions 18 .The Human Development Index (HDI) of the cityis 0.810, putting it in 20th position in the HDI ranking of Brazilian municipal districts 19 .According to the Instituto de Pesquisa Econômica Aplicada(the Institute of Applied Economic Research) (IPEA), the social vulnerability index of Belo Horizonte is 0.276.This value indicates that the city has conditions of social vulnerability that are similar to those in the state of Minas Gerais (0.282), and better than those in Brazil (0.326) 20 .

Calculation and selection of sample
The sample size was calculated based on a margin of error of 3, a confidence level of 95.0% and a prevalence of 62.6%, found in a previous study conducted in Belo Horizonte with adolescents from 10 to 14 years of age 1 .To improve precision, a correction factor of 1.4 was applied, as the multi-stage sampling method was used instead of simple random sampling 21 .According to the calculation, the minimum sample size was estimated as 1408 subjects.A further 20.0%(n=1690) was added to compensate for possible losses.
Adolescents between 11 and 14 years of age, representing all adolescents from the city of Belo Horizonte, were randomly selected from a population enrolled in 456 public and private schools in 2009.Initially, a public and a private school were drawn from each of the nine administrative districts (Barreiro, Center-South, East, West, Northeast, Northwest, North, Pampulha and Venda Nova) (Table 1).Next, a classroom was selected randomly in each of the schools.
A letter was sent to the parents or guardians of the adolescents selected, explaining the objective, importance and methods of the study.Only adolescents whose parents/guardians signed a Free and Informed Consent Form participated in the study, in accordance with the ethical requirements for research involving humans (Resolution 466/12 ofthe National Health Council/ Ministry of Health).

Dependent variable
The clinical criteria to determine the prevalence of malocclusion (dependent variable) were taken from the Dental Aesthetic Index (DAI) 22,23 .The DAI includes the evaluation of the following conditions: absent incisors, canines and premolars; crowding in incisor region; spacing in incisor region; diastema; largestupper anterior irregularity; largest lower anterior irregularity; anterior maxillary overjet; anterior mandibular overjet; vertical anterior open bite; and antero-posterior molar relation.Following clinical evaluation, the values were calculated using a specific equation 22 .

Calibration exercise
The clinical exams were performed by three calibrated dentists, who participated in training and calibration exercises based on the criteria proposed by the DAI.Training was performed using plaster models, with the objective of studying the main clinical characteristics of each condition.Forty-four adolescents who were not included in the study population were examined by each of the three dentists separately to determine inter-examiner agreement.After one month, ten children were reexamined to calculate intra-examiner agreement.The kappa values were 0.84 for inter-examiner agreement and 0.90 for intra-examiner agreement.

Pilot study
A pilot study was conducted with a sample of 66 adolescents who did not participate in the main study.The objective of the pilot study was to test methods such as clinical examination and questionnaire application, as well as to prepare examiners.There was no need for changes in the study methodology following the pilot study.

Data collection
The adolescents were examined in their own school, in pre-determined order, during class time.Artificial lighting (Petzl Zoom head lamp, Petzl America, Clearfield, UT, USA) and the examiners used appropriate personal protective equipment.Disposable mouth mirrors (PRIS-MA®, São Paulo, Brazil) and sterilized WHO probes (OMS-621 Trindade, Campo Mourão, Pará, Brazil) were used for the intra-oral clinical exams.

Social vulnerability
The Social Vulnerability Index (SVI) of Belo Horizonte was used to classify social vulnerability.The SVI is a locally-based social indicator, developed and applied specifically for the city of Belo Horizonte.It is used to measure the vulnerability to social exclusion of the resident population in each of the 81 planning units of the city, through five "Dimensions of Citizenship": Environmental -access to housing and basic infrastructure; Cultural -access to schooling; Economic -access to income and work; Legal -access to legal support; and Survival Security -access to health, food security and social security 24 .The SVI determines the extent to which the population of each city planning unit is vulnerable to social exclusion.SVI values are classified into five groups, ranging from Class I, which comprises the most socially vulnerable families to Class V, who are the least socially vulnerable families 25 .As adolescents usually reside near their schools and study in social settings similar to their homes, school districts were used for this classification.The SVI was dichotomized as high social vulnerability (Classes I and II) and low social vulnerability (Classes III, IV and V).

Data analysis
Statistical analysis was performed using theStatistical Package for the Social Sciences (SPSS for Windows, version 22.0, SPSS Inc., Chicago, IL, USA).Data analysis included descriptive statistics (frequency distribution and cross-tabulation) and Poisson regression with robust bivariate and multivariate variance, to observe the association between malocclusion and the independent variables of social vulnerability, gender and age.The level of significance was set at 5%.

Results
The sample of the present study consisted of 1612 adolescents, 940 (58.3%) of whom were female, representing adolescents aged 11 to 14 years residing in Belo Horizonte, Brazil.Due to the high response rate (95.4%), the sample size was slightly larger than the minimum size estimated by the sample calculation (n = 1408).The majority of these adolescents were from regions of high social vulnerability (67.5%) and had absent/minor malocclusion (68.7%) (Table 2).
Table 3 shows the distribution of the clinical criteria that make up the DAI.Tooth crowding was the most prevalent type of malocclusion in the sample (51.9%), with the presence of only one crowded segment (29.3%) more common than two crowded segments (22.6%).Anterior spacing in only one segment was found in 21.4% of adolescents, while diastema was present in 23.7% of the sample.
The result of bivariate analysis showed that only social vulnerability was associated with malocclusion, and this result was confirmed by multivariate analysis, adjusted by gender.Adolescents from regions of high social vulnerability were more likely to present malocclusion (PR = 1,163, CI = 1.006-1.344)than those from low vulnerability regions (Table 4).

Discussion
The present study demonstrated the association between the social vulnerability to which adolescents from Belo Horizonte are exposed and the presence of malocclusion, and corroborated some findings from literature, even though other methods to measure socioeconomic conditions were used in such studies 6,12,[26][27][28] .
A previous study published with data from the national oral health survey conducted in Brazil in 2010, evaluating 12-year-old children, found that the severity of malocclusions increased as family income decreased 6 .A study conducted in Turkey with children aged 9 to 18 yearsshowed that the higher the level of schooling of parents, the greater their perception of the dental aesthetics of their children 26 .However, findings in literature about this association remain controversial 13,14,[29][30][31][32] .Studies conducted with Brazilian children aged 3 to 5 years and 5 to 12 years did not identify a relationship between socioeconomic conditions and the presence of malocclusion 13,14 .Another study carried out in Belo Horizonte, Brazil with children aged from 10 to 14 years did not find an association between the educational level of parents and the normative need for orthodontic treatment in children 1 .
The differences in results found in literature can be explained by the fact that each population has its own social and economic particularities.Additionally, the differences in the indexes that assess socioeconomic status in studies from literature on this subject make it difficult to compare results.Although no systematic review of works that study the association between malocclusion and socioeconomic conditionswas found, a review published in 2012 on the association between socioeconomic indicators and dental caries showed that there is a great diversity in the indices used.The socioeconomic indicators described by this review include levels of schooling, literacy rate, school attendance, socioeconomic status, socioeconomic trajectory, inequality in relation to municipal income, social class, family income, per capita income, government benefits, satisfaction with income, occupation, unemploy-ment rate, and community indices such as the Gini Coefficient 33 .
The socioeconomic condition of the individual is one of the determinants for the use of dental services.Literature demonstrates that social vulnerability influences the ability of parents to provide access to adequate care, which affects the health status of their children 34 .A previous study conducted in Brazil stated that among the most vulnerable individuals, the number of people withoutdental care is 16 times higher than in higher income groups 35 .
In a review of literature on synthetic indexes of social vulnerability, 23 Brazilian and international indexes were identified.These indexes addressed factors related to the social determinants of health, including quality of life of individuals and families, life course and interaction with the social environment.Indexes of social vulnerability aim to identify and analyze a certain social reality, with the purpose of providing efficient management according to the development needs of each population.The use and interpretation of vulnerability indexes allows a more effective targeting of actions and programs aimed at meeting decision-making demands in public spheres 24 .
The index used in this study was the SVI, developed for the city of Belo Horizonte, which allows the identification of the regions of the city where the population is more or less vulnerable to social exclusion.It is a composite indicator, based on data from the Demographic Census, that considers the characteristics of population groups that inhabit census tracts 24 .This indicator is an instrument used to measure a section of reality, in a rapid, abbreviated, efficient, objective manner, allowing its use as an intervention aid.By transforming perceived reality into numbers, such indicators help with the understanding of such reality.In addition, the SVI makes it possible to identify in which aspects the population is most vulnerable, as it measures five dimensions of citizenship 11,17 .Therefore, the SVI has been used as one of the many ways to understand local realities in order to guide public policies and prioritize the allocation of resources 36 .However, the development of a social indicator is complex, as it must group similar constructs together in the same index, and be based on an adequate theoretical model.These limitations can result in indexes that fail to reflect the complexity of issues involving social vulnerability, and thus blur important factors 24 .
The most prevalent types of malocclusion in this study were tooth crowding, tooth spacing and marked overjet.These results were obtained from studies carried out in Brazil 1,8 .Tooth crowding and marked overjet can represent a social disadvantage, as these aesthetic changes interfere negatively with the psychological well-being and social interaction of adolescents, with facial esthetics representing an important determinant in interrelations between individuals 1,37,38 .
As a cross-sectional study is a section in time, the present work does not allow us to establish causal relationships between malocclusion and social vulnerability.However, the conduction of a representative population-based study allows the health condition of the population to be registered with external validity and the possibility of extrapolating the results to all adolescents aged 11 to 14 years old from Belo Horizonte.
Highly socially vulnerable adolescents tend to have a greater prevalence of malocclusion, as was confirmed by the present study.This social inequality observed in the occurrence of malocclusion is also reflected in the deficiency of public sector healthcare in terms of orthodontic treatment and the early evaluation of malocclusion 39 .Public health studies related to the prevalence of malocclusions provide important epidemiological data that allow the evaluation of the type and distribution of the occlusal characteristics of a given population, assessing the need for treat- ment.These data can help direct public health programs that tackle orthodontic needs in a more active manner, aiming to reduce prevalence through diagnosis and early treatment 40,41 .

Collaborations
LP Martins carried out the analysis and interpretation of the data, the writing of the article and approved the version to be published; JM Bittencourt performed the analysis and interpretation of the data, the writing of the article and approved the version to be published; CB Bendo worked on the concept, the design, the analysis and interpretation of the data, the writing of the article and approved the version to be published; MP Vale worked on the concept, design and approved the final version to be published; SM Paiva worked on the concept, the design, the writing of the article and approved the final version to be published.

Table 1 .
Distribution of sample of adolescents, in absolute and proportional values, by administrative district and school type, Belo Horizonte, Brazil (n = 1.612).

Table 2 .
Distribution of sample of adolescents, in absolute and proportional values, by dependent and independent variables, Belo Horizonte, Brazil (n = 1.612).

Table 3 .
Distribution of sample of adolescents, in absolute and proportional values, by DAI criteria, Belo Horizonte, Brazil (n = 1.612).

Table 4 .
Bivariate and multivariate Poisson regression model explaining the influence of the independent variables on malocclusion, Belo Horizonte, Brazil (n = 1.612).: Poisson regression model with robust variance.* P value for bivariate analysis; ** P value for multivariate analysis.Age was not included in the final model due to p > 0.20. Notes