Is Low Income Associated with Malocclusion in Primary Dentition Among Preschoolers?

Objective: To determine the prevalence and factors associated with malocclusion in the primary dentition of preschool children in a city of Brazilian Northeast. Material and Methods: A cross-sectional study was conducted with 566 five-years-old preschool children who were enrolled in public and private preschools in the city of Teresina, Piauí, Brazil. Data were collected using a sociodemographic questionnaire administrated to parents/caregivers and clinical oral examination of the children was performed. Foster and Hamilton Index for primary teeth was used for the diagnosis of malocclusions. Descriptive analysis was carried out and Poisson regression was used to assesses the association with independent variables. Results: The prevalence of malocclusion was 51.2%. The most frequent types were Class II canines (17% and 16.8%), increased overjet (15.2%) and reduced overbite (14%). Anterior crossbite was present in 3.5% of the preschool children evaluated. There was an association between malocclusion and low family income (PR = 1.22; 95% CI = 1.01-1.47). Conclusion: The prevalence of malocclusion in the primary dentition was high and associated with a low family income.


Introduction
Malocclusion is characterized by an abnormal relationship between teeth and/or jaws, which can lead to problems with chewing, phonation and may negatively impact an individual's quality of life [1][2][3][4]. The prevalence of malocclusion in the primary dentition varies from 46.2 to 81.44% [1,[5][6][7][8]. The variability of these frequencies occurs owing to the lack of standardization of the methodologies used [8].
Changes in dental relationships present a complex and multifactorial etiology and are predominantly determined by genetic factors. However, non-nutritive sucking habits, mouth breathing, a diet with refined foods, early weaning and premature loss of primary teeth are associated with malocclusion [9][10][11]. Currently, there is no consensus regarding the influence of socioeconomic and demographic factors [1,8,12], although a greater chance of malocclusion was observed among residents of the Midwest and Northeast of Brazil [13].
Increased overjet, deep overbite, crossbite, and open bite are the most frequent types of malocclusion in the primary dentition [5]. Some occlusal changes that settle early can self-correct, such as an open bite [14], but others, such as distocclusion and crossbite, may become worse [15,16]. In studies on the incidence of malocclusion, it was observed that the presence of malocclusion in the primary dentition is a risk factor for the need for orthodontic treatment in the permanent dentition, especially in Class II canines, anterior open bite and posterior crossbite [9][10][11]. In this context, conducting orthodontic examinations in preschoolers is important so that malocclusions are diagnosed early and the etiological factors can be identified and removed when possible [9].
Epidemiological research on the prevalence and factors associated with malocclusion in the primary dentition in different populations is important for the implementation of public policies focused on health services, in order to prevent the occurrence of more severe forms of malocclusion in the permanent dentition [8,17].
The aim of the present study was to determine the prevalence and factors associated with malocclusion in the primary dentition in preschool children from a city in the Brazilian Northeast.

Sample Characteristics and Study Design
A preschool-based, cross-sectional study was conducted with a sample of 566 pairs of parents/caregivers and five-year-old-children enrolled in public and private preschools in the city of Teresina, Piauí, Brazil.
A two-stage sampling strategy selected the participants from a total population of 7,792 children in the age group. The sample was stratified according to the type (public or private) and preschool location (north, south, east and southeast) from a list provided by the Municipal Secretary of Education of Teresina-PI and the Syndicate of Private Schools of Teresina-PI. In the first stage, five preschools were randomly selected from each location and secondly, in each institution, children were drawn from school attendance lists. The sample size was calculated based on an estimated prevalence rate of malocclusion of 50%, 95% confidence interval, 5% margin of error and a correction factor of 1.6 for design effect. In addition, to minimize possible dropouts, the sample size was increased by 10%, for a total of 602 (547 + 55 = 602) preschoolers.

Eligibility Criteria
The participants included in the sample were preschoolers 5 years of age at the time of the clinical examination, with a complete primary dentition and no permanent first molars. Children with special needs, as well as systemic and non-cooperative diseases identified during the clinical examination were considered ineligible for the study.

Training and Calibration Exercise
The theoretical-practical exercises were coordinated by a specialist in Orthodontics involved firstly a discussion regarding the diagnostic criteria for malocclusion and an analysis of photographs of teeth with and without malocclusion obtained at the Dental Clinic of the Federal University of Piauí was carried out. When the examiner (one dentist) and the specialist agreed on 80% of the assessments, the second phase of the calibration was initiated. In the clinical phase, children were clinically at two-time points with a minimum interval of 15 days between the two exams. Intra-examiner agreement was calculated (Kappa = 0.82 for malocclusion).

Pilot Study
A pilot study was carried out to evaluate the research methodology, with 10% of the sample (60 children) of three preschools (two public and one private). These children were not included in the final study sample and no changes were necessary in the methodology proposed for the study.

Data Collection
Data were collected using a sociodemographic questionnaire to parents/caregivers and based on a clinical dental examination of the children. Initially, the preschools were visited and the consent of the directors to carry out the study at the institution was obtained. The parents/caregivers then received a letter through the preschools informing them that their children had been selected to participate in the study and were informed of the study's objectives. Along with it, the Free and Informed Consent Term and sociodemographic questionnaire were sent. The questionnaires were collected, and the preschool children whose parents provided the answered forms, were examined.
The sociodemographic characteristics were evaluated by means of a questionnaire, which contained information about child's gender, monthly family income (categorized based on the average income in Braziltwo minimum wages, approximately US$246,4), maternal and paternal education (in years of formal study) and history of dental trauma. School attendance was categorized based on the cutoff point of 8 years, which corresponds to the level of primary education in Brazil.
Oral examination of children was performed in classrooms at preschools in which the child was enrolled by a single examiner previously trained and calibrated, with artificial lighting (Pelicano ® table lamp  The independent variables were socioeconomic and demographic aspects such as: sex, family income, maternal and paternal education and oral clinical aspects such as: dental caries experience and history of dental trauma. A descriptive analysis was performed to characterize the study participants. Poisson regression with robust variance was used to assesses the associations between malocclusion, as a binary endpoint, and the independent variables. The magnitude of the association was determined by the crude and adjusted prevalence ratios (PR),

Results
The final sample consisted of 566 children (94.0%) and their respective parents/caregivers. On the day of the clinical examination, 17 (2.8%) children were absent, 4 (0.7%) who had a diagnosis of autism spectrum disorder did not cooperate, and 15 (2.5%) were older than 5 years of age.
The prevalence of malocclusion was 51.2%. Male children with a family income of less than 2 minimum wages whose parents had more than 8 years of formal education formed the majority of the sample (Table 1).

Discussion
In the present study, the presence of malocclusion was observed in 51.2% of the preschool children, similar to a previous study that indicated a prevalence of 46.2% in children from Belo Horizonte/MG [6].
Comparison of studies evaluating malocclusion in primary dentition is complicated due to the variety of diagnostic criteria and nomenclatures used [6]. In the present study, the Foster & Hamilton Index [18] was performed because it was recommended by other epidemiological studies [1,5,6,9,11,19]. In addition, several studies have established different ages as inclusion criteria, ranging between 2 and 6 years of age [1,[6][7][8][9]11,19], whereas in this study, the age of 5 years was selected for comparative purposes, as recommended by the World Health Organization [20]. This age group was also selected because it was used in the most recent Brazilian National Oral Health Survey (SBrasil Project) [5].
Longitudinal studies observed that the presence of malocclusion in the primary dentition is a risk factor for the need of orthodontic treatment in the permanent dentition, especially for cases involving Class II canines, anterior open bite, and posterior crossbite in the primary dentition [9][10][11]. In this context, it is important to conduct orthodontic examinations in preschoolers so that malocclusions are diagnosed early, and etiological factors identified and removed as early as possible, in order to prevent the occurrence of more severe malocclusions in the permanent dentition [9].
Class II canines and increased overjet were the most frequent malocclusions observed in this study, corroborating the findings presented by other authors [1,8]. In addition to the genetic inherit, this malocclusion is more frequent in preschool children with pacifier sucking habit [21]. Treatment of this condition can be performed in one phase (permanent dentition only) or in two phases (mixed and permanent dentitions). There are no differences in the outcome of treatment independent of the phase in which it begins, although mixed-dentition treatments reduce the incidence of dental trauma in incisors and improves children's self-esteem [15].
The reduced overbite was the third most frequent type of malocclusion, whereas anterior open bite was one of the conditions with a lower prevalence. However, other studies consider the latter type to be one of the most prevalent types of malocclusion in the preschool age group [1,5,11]. This discrepancy may be related to the age of the children evaluated (5 years) in this study since there is a proven reduction in the prevalence of sucking habits from 3 to 5 years of age because most children present spontaneous interruption behaviors (without therapeutic intervention) [22]. In addition, the occurrence of these habits may vary among populations, as they are influenced by cultural and socioeconomic differences [1,23,24].
The etiology of open bite is usually multifactorial and may be caused by growth discrepancies, alterations in the neuromuscular function of the tongue and non-nutritive sucking habits [14]. This malocclusion can be self-corrected and have a good response to interceptive orthodontic treatments. However, they are challenging when present a skeletal etiology and some cases tend to recur [25]. The early orthodontic intervention of this condition during the primary or mixed dentition phases has been supported due to the functional and esthetic benefits. Furthermore, it decreases the need for more complex treatment in the permanent dentition, although there is insufficient evidence regarding which type of treatment is more stable [25,26].
Anterior crossbite was the least frequent type of occlusion in this study, corroborating the results found in the epidemiological survey SB Brasil [5]. The etiology of this malocclusion is also multifactorial and can occur due to hereditary growth or environmental factors such as early dental loss, presence of supernumerary teeth and parafunctional habits. It can be classified as functional, dental or skeletal, with the first type being the most frequent in the primary dentition [27]. Despite the low prevalence found in previous studies, early treatment of this malocclusion should be considered first, since uncrossing of the bite allows a more harmonious growth of the bone bases, thus reducing the severity of the changes in the permanent dentition [27][28][29].
Genetic factors, deleterious oral habits and dental caries experience have been emphasized as the main determinants of malocclusion [11,30]. In the present study, history of dental caries did not show to be associated with a higher prevalence of malocclusion. There was also no association with a history of dental trauma, sex or age. A previous representative study for the Brazilian population found an association between malocclusion and gender, with a higher prevalence among female children [13].
Children belonging to families who reported a family income of less than two minimum wages presented a 22% higher prevalence of malocclusion, diverging from other studies that did not observe a statistically significant association between socioeconomic status and the presence of malocclusion [1,6,9,11].
Family income is a characteristic that may be related to access to dental services and may influence the behavior of the population, such as eating and deleterious oral habits [13]. Previous study showed that there is a higher risk of developing a Class II canine relationship, posterior crossbite and anterior open bite among children with primary dentition who have a history of poor breastfeeding [30]. In addition, the use of pacifiers and digital suction are associated with varied risks of malocclusion development, such as increased overjet, Class II canine relationship and posterior crossbite [31].
Since the etiology of malocclusion is multifactorial and has a strong genetic component, the effect of associated factors, such as family income, would have a limited benefit in cases in which the characteristics of a patient's malocclusion are mainly genetic [31]. Thus, the relationship between socioeconomic factors and dental conditions is not well established in the literature further studies are needed to confirm these findings.
In view of the possibility of preventive action in the etiology of some malocclusions, prevention of malocclusions should be prioritized in public health policies to avoid possible damage to the permanent dentition, especially in low-income populations [13]. In addition, the financial cost for the prevention of malocclusion in the primary/mixed dentition is lower than in the permanent dentition [1].
The present study presents the inherent limitations of cross-sectional studies, so that cannot be considered a cause-and-effect relationship.

Conclusion
The prevalence of malocclusion in the primary dentition was high and associated with a low family income.

Financial Support
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) -Finance Code 001.