Introduction
This cross-sectional retrospective epidemiologic study assessed the relationship between exclusive breastfeeding duration and the prevalence of posterior crossbite in the deciduous dentition.
Methods
Clinical examinations were performed in 1377 Brazilian children (690 boys, 687 girls), 3 to 6 years old, from 11 public schools in São Paulo, Brazil. Based on questionnaires answered by the parents, the children were classified into 4 groups according to the duration of exclusive breastfeeding: G1, never (119 subjects); G2, less than 6 months (720 subjects); G3, 6 to 12 months (312 subjects); and G4, more than 12 months (226 subjects). The statistical analyses included the chi-square test ( P <0.05) and the odds ratio.
Results
The posterior crossbite was observed in 31.1%, 22.4%, 8.3%, and 2.2% of the children, in groups G1, G2, G3, and G4, respectively. The results showed a statistically significant relationship between exclusive breastfeeding duration and the prevalence of posterior crossbite.
Conclusions
Children who were breastfed for more than 12 months had a 20-fold lower risk for the development of posterior crossbite compared with children who were never breastfed and a 5-fold lower risk compared with those breastfed between 6 and 12 months.
Mothers’ milk is a highly nutritious food that diminishes infant mortality, helps to prevent diseases, promotes immunologic and antiallergic protection, and reduces obesity and gastrointestinal problems; it is also directly linked to the baby’s emotional and affective needs. From the oral-health viewpoint, the method and duration of infant feeding have been related to the development of severe early childhood caries. Furthermore, some authors have pointed out that breastfeeding provides the advantage of greater oral muscle exercise over bottle feeding. In 2002, based on a systematic review of the literature, the World Health Organization recommended a minimum of exclusive maternal breastfeeding up to the age of 6 months. Moreover, in orthodontics, breastfeeding might influence craniofacial growth and development, help to prevent nonnutritive sucking habits, and stimulate the harmonious functional development of the stomatognathic system.
Because alterations in occlusal development might be the result of genetic or environmental factors, various authors have studied the relationship between breastfeeding and malocclusion, but the literature is still controversial about this subject. Some authors found no relationship between breastfeeding and the development of malocclusions. Warren and Bishara, after assessing 372 children, 4 to 5 years old, found no statistically significant associations between breastfeeding duration and the prevalence of anterior open bite, posterior crossbite, and increased overjet. However, other studies have pointed out that insufficient breastfeeding duration is related to malocclusions, particularly posterior crossbites. Because this type of malocclusion develops early and rarely self-corrects, the deciduous dentition is an excellent phase to promote preventive or interceptive measures. Therefore, the purpose of this research was to analyze the relationship between exclusive breastfeeding duration and the prevalence of posterior crossbite in the deciduous dentition.
Material and methods
This cross-sectional study was done according to the Resolution Act 196/96 from the Brazilian National Committee of Health.
The sample consisted of 1377 Brazilian children (690 boys, 687 girls) in the complete deciduous dentition phase, from 3 to 6 years of age, enrolled at 11 public schools in eastern São Paulo, Brazil. Furthermore, other inclusion criteria for sample selection were no extensive carious lesions, missing teeth, dental anomalies of shape, number, structure, and eruption, as well as no history of orthodontic treatment, traumatic injuries to the craniofacial complex, or oral surgeries. These criteria were used to exclude changes in occlusal relationships that could interfere with our results.
The clinical examinationss were performed by 3 previously calibrated orthodontists (kappa: 0.89-1.00; r >0.90). The occlusal relationships were examined by direct visual inspection with the teeth in centric occlusion. Posterior crossbite was diagnosed when an inverted relationship of occlusion was observed between at least 1 posterior tooth (deciduous canine or molar) in the transverse plane. Posterior crossbite in the deciduous dentition was classified into 3 categories: bilateral, true unilateral, and unilateral with functional deviation of the mandible.
Based on questionnaires answered by the mothers, a retrospective investigation was made concerning the length of time that children were exclusively breastfed. Accordingly, children were classified into 4 groups: group 1 (G1), never breastfed (n = 119); group 2 (G2), breastfed for less than 6 months (n = 720); group 3 (G3), breastfed for 6 to 12 months (n = 312); and group 4 (G4), breastfed for more than 12 months (n = 226). Information on nonnutritive sucking habits was also requested in the questionnaires.
Statistical analyses were performed with Stata software (version 8.0, StataCorp, College Station, Tex). The Pearson chi-square test was used to verify the association between posterior crossbite prevalence and breastfeeding duration ( P <0.05). In addition, the odds ratio (OR) was used to measure the strength of the association and the relative chances of developing the investigated malocclusion.
Results
For the total sample, the results showed a posterior crossbite prevalence of 16.6%, with 2.8% of the children having bilateral crossbite, 4.4% with true unilateral crossbite, and 9.4% having functional unilateral crossbite ( Table I ). Posterior crossbite was more prevalent in older than in younger children during the deciduous dentition ( Table I ).
| Age (y) | Total sample | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 3 | 4 | 5 | 6 | |||||||
| Posterior crossbite | n | % | n | % | n | % | n | % | n | % |
| Absent | 141 | 87.6 | 415 | 85.2 | 450 | 83.3 | 142 | 75.1 | 1,148 | 83.4 |
| Bilateral | 4 | 2.5 | 11 | 2.3 | 14 | 2.6 | 10 | 5.3 | 39 | 2.8 |
| True unilateral | 7 | 4.3 | 16 | 3.3 | 29 | 5.4 | 9 | 4.8 | 61 | 4.4 |
| Functional unilateral | 9 | 5.6 | 45 | 9.2 | 47 | 8.7 | 28 | 14.8 | 129 | 9.4 |
| Total | 161 | 100.0 | 487 | 100.0 | 540 | 100.0 | 189 | 100.0 | 1,377 | 100.0 |
Table II shows that 8.6% of the children were never breastfed (G1), 52.3% were exclusively breastfed for less than 6 months (G2), and 39.1% were exclusively breastfed for more than 6 months (G3 and G4). Furthermore, the prevalence of posterior crossbite gradually decreased as breastfeeding duration increased: 31.1% for G1 and only 2.2% for G4.
| Sample | Presence of posterior crossbite | |||
|---|---|---|---|---|
| Group | n | % | n | % |
| G1 | 119 | 8.6 | 37 | 31.1 |
| G2 | 720 | 52.3 | 161 | 22.4 |
| G3 | 312 | 22.7 | 26 | 8.3 |
| G4 | 226 | 16.4 | 5 | 2.2 |
| Total | 1,377 | 100.0 | 229 | 16.6 |
There was a statistically significant relationship between exclusive breastfeeding duration and the prevalence of posterior crossbite ( Table III ) in the 6 comparisons in the 4 groups, particularly between groups G1 and G3, G1 and G4, G2 and G3, and G2 and G4 ( P = 0.0000). Therefore, children who had never been breastfed exhibited a higher prevalence of posterior crossbite compared with children who were exclusively breastfed between 6 and 12 months (OR = 4.9) and also compared with children who were breastfed for more than 12 months (OR = 19.9). Children who were breastfed for less than 6 months had a 3-fold higher risk compared with children who were exclusively breastfed between 6 and 12 months, and a 12-fold higher risk compared with children who were breastfed for more than 12 months.
| Comparison | Chi-square | P value | OR |
|---|---|---|---|
| G1/G2 | 4.31 | 0.0378 | 1.57 |
| G1/G3 | 35.67 | 0.0000 | 4.96 |
| G1/G4 | 60.63 | 0.0000 | 19.94 |
| G2/G3 | 28.84 | 0.0000 | 3.17 |
| G2/G4 | 48.21 | 0.0000 | 12.73 |
| G3/G4 | 9.03 | 0.0027 | 4.02 |
Table IV shows the distribution of posterior crossbite prevalence according to the breastfeeding period only for children with no nonnutritive sucking habits (finger or pacifier). Again, a gradual decrease in the prevalence of this malocclusion was observed as breastfeeding duration increased, particularly in groups G3 and G4, comprising children breastfed for more than 6 months. In these 2 groups, only 1 child with posterior crossbite was found, indicating a combined prevalence of 0.31%. When the chi-square test was applied in the group of children without nonnutritive sucking habits ( Table V ), statistically significant relationships were seen between exclusive breastfeeding duration and the prevalence of posterior crossbite between groups G1 and G3 ( P <0.0000) and G2 and G3 ( P <0.0003). Children who were never breastfed had a 29-fold higher risk for developing posterior crossbite compared with the children who were exclusively breastfed between 6 and 12 months. Children breastfed for less than 6 months had a 16-fold higher risk compared with children whose exclusive breastfeeding was interrupted between 6 and 12 months. For the other paired comparisons involving G4, it was not possible to estimate the OR because of a null prevalence of posterior crossbite in this group, making mathematical calculations unfeasible.
| Group | Sample | Presence of posterior crossbite |
||
|---|---|---|---|---|
| n | % | n | % | |
| G1 | 22 | 4.4 | 4 | 18.2 |
| G2 | 161 | 32.0 | 18 | 11.2 |
| G3 | 132 | 26.2 | 1 | 0.8 |
| G4 | 188 | 37.4 | 0 | 0 |
| Total | 503 | 100.0 | 23 | 4.6 |
| Comparison | Chi-square | P value | OR |
|---|---|---|---|
| G1/G2 | 0.89 | 0.3449 | — |
| G1/G3 | 18.11 | 0.0000 | 29.11 |
| G1/G4 | — | — | — |
| G2/G3 | 12.95 | 0.0003 | 16.49 |
| G2/G4 | — | — | — |
| G3/G4 | — | — | — |
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