Objectives

To evaluate the association between malocclusion characteristics in the mixed dentition stage, breastfeeding, and past nonnutritive sucking habits in school-age children.

Materials and Methods

A total of 547 school children in the mixed dentition, in the age range between 7 and 13 years, were evaluated by means of questionnaire and clinical examination. Binomial and multinomial logistic regression models were used to evaluate the associations between breastfeeding and finger and pacifier sucking habits, the malocclusion characteristics of posterior crossbite, and excessive or deficient overjet and overbite.

Results

Individuals who had nonnutritive sucking habits had 2.16 times greater chance of having anterior open bite (odds ratio [OR] 2.16; 95% confidence interval [CI], 1.07–4.33) and 2.39 times greater chance of having posterior crossbite (OR 2.39; 95% CI, 1.56–5.49). Children who were exclusively breastfed up to at least 6 months of age had a higher frequency of normality for overjet and overbite and the lowest posterior crossbite index. However, in adjusted analysis, breastfeeding showed no association with malocclusion characteristics in the mixed dentition stage.

Conclusions

Breastfeeding was not associated with the presence of malocclusion in the mixed dentition, whereas past nonnutritive sucking habits were associated with the occurrence of malocclusion.

From the time they are born, babies receive neuromuscular stimuli that induce the development of the stomatognathic system, which may favor or harm the correct arrangement of the orofacial structures. These stimuli may arise from nutritive sucking, either during breastfeeding or with artificial induction via a feeding bottle or by nonnutritive sucking, such as finger or pacifier sucking habits. Breastfeeding for a period of up to 1 year of age constitutes a protective factor against the development of malocclusion in the primary dentition.1  However, for children breastfed during that period, the introduction of deleterious habits can act as a modulator of growth and development of the structures.2 

Nutritive and nonnutritive sucking habits affect not only the anatomy of the stomatognathic system but also its function. Breastfeeding promotes stimuli to the structures responsible for mastication and swallowing1,3  as well as for nasal breathing.4  During breastfeeding, the tongue assumes an elevated position in the direction of the incisive papilla to enable sucking with more intense and forceful movements, and the lip sealing around the nipple and areola favors the nasal breathing mode.4  In contrast, deleterious habits favor inadequate positioning of the structures, such as a low position of the tongue in the floor of the mouth,5  resulting in deficient transverse maxillary growth, favoring a deficit in respiratory function.

The influence of breastfeeding and nonnutritive sucking habits on the development of occlusion and of the stomatognathic system in the primary dentition has been extensively investigated, and positive associations have been found.13,59  However, their influence on the continuity of craniofacial growth is still being questioned, as few previous studies10  have evaluated these factors in the mixed dentition stage. The aim of this study was to evaluate whether there was an association between malocclusion characteristics and nutritive and nonnutritive sucking habits in school-age children in the mixed dentition stage. The conceptual hypotheses were that (1) breastfeeding protects children from the development of malocclusion and (2) and that nonnutritional sucking habits predispose them to the development of malocclusion.

Study Design and Sample

The research was conducted by means of an epidemiological survey with a cross-sectional approach in the city of Santa Maria, Rio Grande do Sul, Brazil, in 2015. Before data collection, the research was approved by the Research Ethics Committee of the Federal University of Santa Maria under protocol No. 08105512.0000.5346. Previous studies considering this same database were published previously.11,12 

In the year of data collection, the municipality had an estimated population of 261,031, of whom 30,216 (11.57%) were enrolled in primary schools and 10,569 (34.97%) were enrolled in 26 primary schools in the state network. Nine schools in the state network were selected, according to the different administrative regions and size of the school. Based on the list of pupils enrolled, children between 7 and 13 years of age were invited to participate in the study, totaling 1550 children. However, only 948 children received consent from their legal guardians to participate (response rate of 61.2%). Of these, the following were excluded: those who did not have a permanent first molar (n = 42), those who were in the primary (n = 2) or permanent (n = 73) dentition stages, those who had premature loss of teeth (n = 2), those with a history of orthodontic (n = 43) or speech language (n = 22) treatment, and those who had cognitive limitations (n = 3). The other children were excluded because they did not appear in school on the days when the evaluations were performed (n = 165), were transferred to another school during the research period (n = 43), or refused to undergo the clinical examinations (n = 6). Therefore, the final sample for this study consisted of 547 children.

To calculate the sample size, we considered a standard error of 5%, confidence level of 95%, and prevalence of malocclusion of 27.5% in the group exposed (breastfeeding for less than 12 months) and 8.6% in the nonexposed group (breastfeeding for longer than 12 months).5  The ratio of nonexposed to exposed subjects was 2:1, with a statistical power of 90%. Considering a design effect of 1.6 and adding 30% for possible losses/refusals, the minimum sample size was estimated at 395 children.

Data Collection

Data collection was performed from April to December 2015. The team was composed of five examiners, all previously trained to use the questionnaires and calibrated for the clinical exams. Four dentists performed the orthodontic measurements. The examiners were calibrated by examining 30 randomly selected children and reassessing after 15 days. The inter- and intraexaminer agreement values were higher than 0.70 for all orthodontic measures.

The examinations were performed face to face, under natural light, with the patient's jaw in occlusion to evaluate the three planes of interarch relationships based on the Foster and Hamilton Index13: (1) transverse: unilateral or bilateral posterior crossbite (present/or absent); (2) sagittal: overjet (increased or diminished/anterior crossbite); and (3) vertical: overbite (deep or diminished/anterior open bite).

Posterior crossbite was recorded when at least one maxillary posterior tooth occluded in a palatal position to the buccal cusp of the opposing mandibular tooth. Overjet and overbite measurements were performed using a WHO probe (Millennium, Golgran, São Caetano do Sul, SP, Brazil), with measurements given in millimeters.1316  For overjet and overbite, measurements between 0.5 and 3.5 mm were considered adequate; measurements ≥4 mm were considered accentuated, and measurements ≤0 mm were considered diminished, showing evidence of anterior crossbite or anterior open bite.14 

A single speech-language therapist (L.C.B.; Kappa > 0.70) used an evaluation form composed of data extracted from the Orofacial Protocol with Scores (AMIOFE) to evaluate the positioning of the tongue and respiratory mode. The position of the tongue was evaluated during rest and during the speech evaluation and was classified as normal (contained in the oral cavity = 0) or altered (interposed to the dental arches with the following subclassifications: adaptation, dysfunction, or excessive protrusion = 1). The respiratory mode of the participants was verified through spontaneous observation of the patient and classified as nasal, mouth, or oronasal (0 = normal or 1 = oral/oronasal). Sleep disorder was evaluated through a questionnaire sent to the parents about the child's sleep: snoring, drooling on the pillow, waking up to drink water, agitated sleep, mouth open while sleeping (0 = absent and 1= present). To measure intraexaminer reproducibility, 30 children were evaluated at school and reassessed after 1 week. The Kappa value for this assessment exceeded 0.70 for all measures.

The behavioral variables were collected by means of a structured questionnaire, as done in previous studies.17,18  Data on the presence of nonnutritional feeding habits were collected, dichotomized into 0 = absence or 1 = presence of habit, and analyzed. Data on the introduction of a feeding bottle were evaluated based on the when the child began to use the feeding bottle, categorized into 0 = did not use, 1 = before the age of 6 months, and 2 = after the age of 6 months. Breastfeeding data were evaluated based on the duration in months and with reference to the fact of having been exclusive. For analysis, the variable was categorized into 0 = exclusive up to 6 months, 1 = not exclusive (breastfeeding and bottle feeding), and 2 = did not breastfeed.

The demographic and socioeconomic variables were collected by means of a semistructured questionnaire and included the following data: sex (female or male), skin color (White or non-White), and mother's educational level (<8 years or ≥8 years = complete primary schooling).

Statistical Analysis

The data were analyzed by means of STATA version 14.0 statistical software (2014, StataCorp, College Station, Tex, USA). Three outcomes were considered: (1) overjet (adequate/anterior crossbite/accentuated), (2) overbite (adequate/anterior open bite/deep), and posterior crossbite (present/absent). Descriptive analysis of the demographic, socioeconomic, behavioral, and clinical characteristics of the sample was performed.

Binomial and multinomial logistic regression models were used to evaluate the association between the characteristics of the sample, according to the outcomes of posterior crossbite, overjet, and overbite, respectively. The main predictors and adjustment variables were selected according to the previous literature regarding malocclusion.310  The predictive variables that showed a P value of P ≤ .20 in the nonadjusted analysis were included in the adjusted model. The results are presented as odds ratio (OR) and a respective 95% confidence interval (95% CI). The level of significance was considered to be 0.05. The analyses were first conducted considering the sample design in clusters. When testing the empty model, no context variability was observed in the outcomes (P > .05); therefore, it was justifiable not to use multilevel analysis.

From the 547 children evaluated, 57.8% received exclusive breastfeeding up to 6 months of age or older, and 67.6% of the individuals had at least some type of malocclusion, with deep overbite being the most prevalent type in the sample (46.6%). Other demographic, socioeconomic, behavioral, and clinical characteristic distributions are expressed in Table 1.

Table 1.

Distribution of the Sample According to Demographic, Socioeconomic, Behavioral, and Clinical Characteristics (N = 547)a

Distribution of the Sample According to Demographic, Socioeconomic, Behavioral, and Clinical Characteristics (N = 547)a
Distribution of the Sample According to Demographic, Socioeconomic, Behavioral, and Clinical Characteristics (N = 547)a

Table 2 shows the distribution of the characteristics of the sample with the different types of malocclusion characteristics evaluated. Children who were exclusively breastfed up to 6 months of age had a higher frequency of normality for overjet and overbite and the lowest posterior crossbite indexes.

Table 2.

Distribution of Sample Characteristics According to the Presence of Different Malocclusion Characteristics

Distribution of Sample Characteristics According to the Presence of Different Malocclusion Characteristics
Distribution of Sample Characteristics According to the Presence of Different Malocclusion Characteristics

Adjusted and unadjusted analysis among predictive variables for overjet outcome are presented in Table 3, overbite in Table 4, and posterior crossbite in Table 5.

Table 3.

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overjet Outcome, Determined With the Use of Multinomial Logistic Regression

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overjet Outcome, Determined With the Use of Multinomial Logistic Regression
Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overjet Outcome, Determined With the Use of Multinomial Logistic Regression
Table 4.

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overbite Outcome, Determined With the Use of Multinomial Logistic Regression

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overbite Outcome, Determined With the Use of Multinomial Logistic Regression
Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Overbite Outcome, Determined With the Use of Multinomial Logistic Regression
Table 5.

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Posterior Crossbite Outcome, Determined With the Use of Multinomial Logistic Regression

Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Posterior Crossbite Outcome, Determined With the Use of Multinomial Logistic Regression
Adjusted and Unadjusted Analysis Among Predictive Variables With Regard to Posterior Crossbite Outcome, Determined With the Use of Multinomial Logistic Regression

The findings of this survey partially confirmed the conceptual hypothesis, because the presence of nonnutritive sucking habits was associated with a higher prevalence of anterior open bite and posterior crossbite but not with the presence of altered overjet. In addition, exclusive breastfeeding was not significantly associated with the occurrence of malocclusion in this stage of dentition. This finding was in agreement with that of Abreu et al.,19  who conducted a systematic review and stated that there was no association between breastfeeding and the occurrence of malocclusion in the mixed and permanent dentition. However, it was in disagreement with Limeira et al.,20  who conducted a cross-sectional study and found that the prevalence of posterior crossbite gradually decreased as the duration of exclusive breastfeeding increased.

Most children were exclusively breastfed up to 6 months of age. The mothers' degree of enlightenment and socioeconomic level are believed to have contributed to this, possibly because the majority of the mothers had at least 8 years of formal education. Heck et al. found a positive association between maternal education and breastfeeding.21  In nonadjusted analysis, children who were exclusively breastfed up to 6 months of age had a higher frequency of normality for overjet and overbite and the lowest posterior crossbite indexes. However, when the variables were adjusted, this effect disappeared. It may be hypothesized that this happened because, when deleterious habits were introduced, it was no longer possible to perceive the positive effect of breastfeeding on occlusion.

The presence of past nonnutritive sucking habits was associated with a higher prevalence of anterior open bite and posterior crossbite. This was in agreement with previous studies, which found an association between nonnutritive sucking habits and anterior open bite5,18,22  and posterior crossbite.5,18,23 

The adjusted analysis showed that the altered position of the tongue was associated with anterior open bite. In addition, children with the oronasal respiratory mode had a two times higher prevalence of overjet, which is in agreement with previous literature.18  It has been known that there is a relationship between stomatognathic system anatomy, which includes dental occlusion, and its physiology represented by mastication, swallowing, speech, and breathing.24  Therefore, exposure of a child to a nonnutritive sucking habit is capable of triggering a cascade of alterations in the system, depending on the intensity, duration, and frequency of the habit.25 

Non-White children had a higher prevalence of anterior crossbite when compared with White children. When the variable skin color was dichotomized, Asian and Black children were included in the non-White category. It is known that Africans have a high prevalence of negative overjet26  and that Class III malocclusions are more prevalent among Asians,15,26  which could have been reflected in the expression of anterior crossbite.

Children of the male sex had a higher prevalence of accentuated overbite. A previous study found a higher prevalence of malocclusion characteristics in the male sex,27  and Class II was also more associated with this sex.28  In addition, children from 9 to 13 years of age had a higher prevalence of deep overbite when compared with children from 7 to 8 years old. A previous study14  found similar results, pointing out that increases in age and time of exposure to etiological factors may be predisposing factors for this malocclusion. An altered position of the tongue appeared to be a factor of protection against deep overbite, as this increased the risk of anterior open bite, as shown in the present study.

There was a high prevalence of malocclusion characteristics in the mixed dentition, as deep overbite was present in 46.6% and increased overjet in 28% of the children in the current study. A previous study found a prevalence of 30.6% of deep overbite and 26.9% of increased overjet.18 

This study evaluated children in the mixed dentition phase, a phase somewhat neglected in epidemiological studies because of the dental changes inherent in this period, which makes it difficult to establish a standard index for occlusal evaluation. However, it is a phase that encompasses a great portion of childhood and constitutes a prime period for the interception of malocclusion and therefore deserves to be studied further.

Some strengths of this study include the technique of sample selection and the use of a sample that was representative of the population. The exclusion criteria applied led to significant loss of the initial sample invited to participate in the study. However, the minimum number suggested by the sample power calculation was exceeded. In addition, the evaluations were made by a collaboration between professionals in the areas of orthodontics and orofacial function, considering that the human body is complex and works successfully because of interrelationships among different systems; many scientific studies lack teamwork among different professional areas.

This study has some limitations, such as the use of a questionnaire sent to the families for data collection, with questions that referred to past issues such as breastfeeding, the introduction of bottle feeding, and nonnutritive sucking habits. The parents might possibly have been unable to provide accurate answers, causing a memory bias. In addition, in a cross-sectional study, it is only possible to establish associations between the predictors and the outcomes, but no causal relations could be determined. In this sense, it is suggested that longitudinal studies should be conducted.

The recommendation of exclusive breastfeeding up to 6 months29  to be continued up to 2 years of age is unquestionable because of its nutritional and immunological benefits and for development of the stomatognathic system.30  However, the role of deleterious habits on the development of malocclusion characteristics in the mixed dentition stage was evident in this study, as growth and development are complex and multifactorial parts of the process. Therefore, it is important for public health managers to encourage good habits and behaviors related to oral health, by discouraging deleterious habits and encouraging exclusive breastfeeding.

  • Breastfeeding was not associated with the development of malocclusion, whereas past nonnutritive sucking habits were associated with the occurrence of malocclusion in mixed dentition.

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Author notes

a

Postgraduate Student, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.

b

Graduate Student, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.

c

Speech-Language Therapist, Hospital de Clínicas de Porto Alegre, Porto Alegre, RS, Brazil.

d

Professor, Department of Stomatology, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.