Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth

ABSTRACT Objective: To determine the prevalence of malocclusion and its association with the early loss of deciduous teeth and other factors in children in the mixed dentition phase, aged six to eight years, enrolled in public schools in southern Brazil. Methods: A cross-sectional study was conducted with a representative sample of 528 children from municipal public schools in 2009. Data collection involved a clinical examination for the determination of early tooth loss, dental caries, tongue pressure and malocclusion (outcome), as well as the administration of a questionnaire. Poisson regression analysis with robust variance was used to model the association between malocclusion and the independent variables. Results: The prevalence of malocclusion and early tooth loss was 69.1% and 21.8%, respectively. In the raw data analysis, malocclusion was associated with age, early tooth loss, dental caries and tongue pressure. After the adjustment, the likelihood of malocclusion was greater among children older than eight years, those who exerted tongue pressure on the teeth and those with early tooth loss. The likelihood of malocclusion was 24% greater among children with early tooth loss, compared to those without tooth loss. Conclusion: The early loss of deciduous teeth was associated with the occurrence of malocclusion in the children studied.


INTRODUCTION
Regardless of the developmental stage of the dentition, researchers are unanimous in declaring that the prevalence of malocclusion is higher than normal occlusion, in different populations. [1][2][3][4] Due to the high prevalence and impact on quality of life, malocclusions are considered a global public health problem. 5,6 Epidemiological studies demonstrated that the frequent occurrence of malocclusion is related to its multifactorial etiology, with the combined influence of genetic and environmental factors. 2,3,7,8 The early loss of deciduous teeth, especially molars, is one of the etiological factors of malocclusions. 9,10 Although traumatic dental injury can lead to tooth loss, dental caries continue to be the major cause. [11][12][13][14] The transition from the deciduous to the permanent dentition is a complex phenomenon in which deciduous teeth play an important role. The early loss of these teeth can cause the migration of adjacent teeth, leading to a reduction or even the complete closure of the space destined for the eruption of the successor permanent teeth, and affecting the chronology of the eruption process. 9,15 Although the understanding of the mixed dentition and the repercussion of early tooth loss is important to the planning of preventive and interceptive measures, few Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 5 studies in the literature have evaluated this phase. The diagnosis and early treatment of occlusal abnormalities in any phase of the dentition favor adequate growth and development, reduce the cost, time and severity of orthodontic treatment, and favor planning in the public health area. 16 The following hypotheses were tested in the present study: A) the prevalence of malocclusion is high in the mixed dentition phase; and B) there is an association between malocclusion and the early loss of deciduous teeth in the mixed dentition phase.
Therefore, the aim of this study was to determine the prevalence of malocclusion and the association with the early loss of deciduous teeth and other factors in children in the mixed dentition phase, aged six to eight years, enrolled in public schools in the municipality of Florianópolis, Santa Catarina, Brazil.

An observational cross-sectional study was conducted between
March and July 2009, with a representative sample of children in the mixed dentition phase, aged six to eight years, enrolled in public schools in the municipality of Florianópolis, Santa Catarina, Brazil.
Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 6 The estimated population of the city in the period was approximately 408 thousand residents, with 23,974 children aged five to nine years. The sample size was determined using a sampling procedure considering a total of 7,636 students from 32 public schools distributed among the five regions of interest (northern, southern, eastern, western and central).
Cluster sampling was performed. The primary sampling unit was public schools in the municipality, and 24 of the 32 schools distributed in the five administrative regions of Florianópolis were randomly selected (by lots), considering the proportion of the population that attended each school. In the northern, southern and eastern regions, one class was randomly selected from each school to ensure that students from all grades would be selected in each region. In the western and central regions, all students in all grades were selected.
This procedure resulted in a sample of 528 children in the target age range enrolled in 24 municipal public schools.
The inclusion criteria were: enrollment in a primary school in the municipal public school system in the first semester of 2009, age six to eight years, being in the mixed dentition phase and not wearing an orthodontic appliance. Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 8 overbite (> 3 mm) and dental crowding. 19 Tooth loss was classified as premature when a deciduous tooth was extracted at least one year prior to the eruption of the successor permanent tooth. 19 This information was obtained from the parents/ caregivers. Caries experience was evaluated using the mean value of the Decayed, Missing and Filled Teeth (DMFT) index.
Flat dental mirrors, a community periodontal index (CPI) probe and natural and artificial light 17 were used to evaluate all dental surfaces. Tongue interposition was investigated by the observation of water swallowing (without touching the participant) and checking for tongue projection and the participation of the perioral musculature, such as contraction of the lips and the mental muscle. 18 Lip interposition was assessed by observing the child. 18 The data were analyzed using SPSS for Windows version 15.0.
Descriptive statistics involved calculation of the distribution of relative frequencies, to identify the percentage of prematurely lost deciduous teeth and malocclusion categories, and obtain prevalence rates for the other variables of interest. The chisquare test was used to determine associations between the variables investigated and child's sex. Raw and adjusted Poisson analyses were performed, with the determination of prevalence ratios (PR) and respective 95% confidence intervals (CI). In the adjusted model, malocclusion was the dependent variable, and the independent variables were sex (female or male), age (six, Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 9 seven or eight years), early tooth loss (no/yes), dental caries (no/yes), nail biting habit (no/yes), thumb sucking (no/yes), lip pressure (no/yes) and tongue pressure (no/yes). The forward selection process was used for the determination of variables to be incorporated into the model, for which the inclusion criterion was a p-value < 0.25 in the raw analysis (Wald test).
The significance level was set to 5% for all statistical tests.
Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 10 Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 11 Early tooth loss was not significantly associated with the types of Angle malocclusion (p = 0.139). with the outcome in the adjusted analysis (Table 3).
Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 12 Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 13 Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth

DISCUSSION
In the present study, the prevalence of malocclusion in the mixed dentition was high and was associated with the early loss of deciduous teeth. These findings are in agreement with data described in previous studies reporting a high frequency of malocclusion in this phase. 16,21 Moreover, the early loss of deciduous teeth causes harm that can extend to the permanent dentition and affect the development of bone and muscle tissues of the face, thereby contributing to the establishment and/or aggravation of malocclusion, as well as causing problems related to speaking, chewing, aesthetics, psychological aspects and the appearance of deleterious oral habits. 9,10,22,23 These findings can be used to guide decision making by the dentists, and can contribute to public health measures, especially those targeting more vulnerable populations, with a low socioeconomic status, as in the sample of the present study.
An association was found between the ages of seven and eight years and a greater prevalence of malocclusion. According to previous studies, early tooth loss at younger ages leads to a greater reduction in the perimeter of the dental arch. 24 In the present study, there was no record of when tooth loss occurred, and the Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 15 Dental caries were found in less than half of the children, and no longer presented a significant association with malocclusion in the adjusted analysis. A cross-sectional study conducted with 646 Chinese children aged 6 to 13 years found an association between caries and malocclusion. 25 Another study involving 1,601 children aged 12 to 14 years found a 63.8% prevalence rate of malocclusion, and the association with caries experience was confirmed in the multivariate analysis. 26 It is important to point out that the DMFT index used in the present study to measure dental caries does not distinguish between a small, slightly Fadel MAV, Santos BZ, Antoniazzi RP, Koerich L, Bosco VL, Locks A Prevalence of malocclusion in public school students in the mixed dentition phase and its association with early loss of deciduous teeth 16 It is also necessary to consider that the consequences of early deciduous tooth loss are influenced by many factors, such as the age at which the loss occurred, potential facial and dental growth, and the occurrence of deleterious oral habits. 11 Tooth movement depends on the eruption space, time and route, intercuspation and age at the time of tooth extraction. 24 Thus, the management of the space after early tooth loss plays an important role in preventive and interceptive orthodontics. 24 The use of space maintainers in the developing dentition can help prevent the loss of length and width in the dental arch, especially in cases of early loss of the deciduous molars.

CONCLUSION
More than half of the evaluated children exhibited malocclusion, which was associated with the early loss of deciduous teeth, even after the adjustment for the independent variables.