Abstract
Background. Breastfeeding has multiple nutritional, immunological and psychological benefits, as well as a positive influence on the development of the stomatognathic system.
Objectives. The present study attempted to determine the relationship between the duration of breastfeeding and the development of non-nutritive habits, and transversal and vertical occlusal alterations in preschool children.
Material and methods. This cross-sectional study involved 155 preschoolers aged 2–5 years from 3 public schools in Lima, Peru. The sample was divided into 2 groups with regard to the duration of breastfeeding: group A (n = 50) included infants that had been breastfed for up to 6 months; and group B (n = 105) included infants that had been breastfed for 6–12 months. Two trained and calibrated dentists evaluated each group, and clinically determined the presence or absence of transversal or vertical occlusal alterations. Likewise, the children’s parents or caregivers were consulted to determine the development of non-nutritive habits.
Results. A significant association was found between breastfeeding duration and the development of the oral breathing habit; groups A and B showed a prevalence of 30.0% and 16.2%, respectively (p = 0.048). Likewise, breastfeeding duration affected the appearance of oral breathing (OR (odds ratio) = 0.84; 95% CI (confidence interval): 0.74–0.96; p = 0.011). Furthermore, the use of a bottle for more than 24 months significantly influenced the appearance of oral habits (OR = 3.55; 95% CI: 1.20–10.55; p = 0.022) and open bite (OR = 12.12; 95% CI: 1.16–126.31; p = 0.037).
Conclusions. Breastfeeding duration of 6–12 months was shown to be a protective factor in preventing the appearance of oral breathing. Posterior crossbite (PCB), open bite and deep bite seemed not to be influenced by breastfeeding duration. However, the use of a bottle for more than 24 months significantly influenced the appearance of anterior open bite.
Keywords: habits, breastfeeding, dental occlusion
Introduction
Breastfeeding is the first step in promoting the general health of both babies and their mothers.1 Breastfeeding has multiple nutritional, immunological and psychological benefits, as well as a positive influence on the development of the stomatognathic system.2, 3, 4, 5, 6, 7, 8, 9, 10, 11 The World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) recommend an early start for breastfeeding (within the first hour of life), exclusive breastfeeding for the first 6 months of life, and continued breastfeeding for up to 24 months or more in order to achieve optimal growth, development and health.12, 13, 14, 15, 16, 17, 18
Breast milk is best for babies because of its immunomodulatory effects and protection against early infections. Early infections are major risk factors for asthma and allergic diseases; protection through breastfeeding may be a pathway that shields against allergic diseases.19
Breastfeeding reinforces the physiological nasal breathing of newborns during and after feeding, as they must forcefully close their mouth to suck properly.20 It is considered a nutritive sucking habit, since it feeds the infant. Contrarily, introducing bottle-feeding early in the infant’s life triggers rapid satiety and does not involve as much of a sucking effort. This leads the newborn to satisfy its suction desire through non-nutritive suction – sucking on objects that do not provide food, such as fingers, pacifiers or toys.21, 22
Sucking fingers and/or pacifiers are the most common non-nutritive sucking habits among infants. The early introduction of a pacifier and/or a feeding bottle may confuse the newborn’s sucking reflex, resulting in premature weaning. Non-nutritive habits can cause different alterations of dental occlusion depending on their frequency, intensity and duration. Dental occlusion alterations are developmental disorders that occur in the dentofacial structure, comprising the jaw, tongue and facial muscles.5 The baby’s sucking during breastfeeding stimulates the balance between the internal and external restraining forces of the facial musculature. This allows the appropriate development of the stomatognathic system and the adequate growth of the craniofacial complex, which can play an important role in preventing occlusal disorders in the child’s primary dentition.3, 5, 7, 23, 24, 25
Breastfeeding has been reported to protect against occlusal alterations in the primary dentition. Some studies report protection against occlusal alterations after 6 months of breastfeeding, and other emphasize the need for longer periods of breastfeeding for greater benefits.3, 5, 15, 26, 27 However, only 40% of infants worldwide are exclusively breastfed for the first 6 months.27 This average reduces to 37% in low- and middle-income countries.28 It is known that when a baby is weaned after receiving breastfeeding, if a bottle is offered as a substitute, and used for a long time and at high frequency, it can overshadow the benefits of breastfeeding. Well-designed studies make it possible to identify whether prolonged breastfeeding is a protective factor against the appearance of harmful habits, or transversal and vertical occlusal alternations. They allow us to know the consistency of the results in a specific association. Given this context, the main purpose of the present study was to determine the association between the duration of breastfeeding and the development of non-nutritive habits, and transversal and vertical occlusal alterations in children aged 2–5 years from Lima, Peru.
Material and methods
This study was approved by the Ethics Committee at the School of Dentistry of the Scientific University of the South (Universidad Científica del Sur), Lima, Peru (No. of approval: 000444). The parents or legal guardians of the children signed the informed consent forms prior to participation in the study.
The sample was composed of 155 children aged 2–5 years, of both genders, from 3 public schools in Lima, Peru. They were distributed into 2 groups based on the duration of breastfeeding: group A (n = 50) included children that had been breastfed for 0–6 months; and group B (n = 105) included children that had been breastfed for more than 6 months and up to 1 year.
Children with systemic diseases, uncooperative, with morphological alterations, not breastfed from birth, with tooth decay injuries that covered more than 50% of the tooth surface, or whose parents did not provide consent to their participation were excluded.
Non-nutritive habits, and transversal and vertical occlusal alterations were clinically evaluated by 2 previously trained and calibrated examiners.
Evaluation of non-nutritive habits
Digital sucking was evaluated through the presence or absence of a digital callus on at least 1 finger, validated with the child’s caregiver’s response to the survey, and the presence of some type of characteristic related to sucking in the oral cavity, such as disturbances in the arch form, wrinkled, chapped or blistered fingers, ulceration or corn formation, etc.
Labial sucking was determined through clinical observations. It was considered as present in the children who unconsciously sucked their lips during the evaluation process, presenting a constantly moisturized lower lip. The observations were corroborated by the child’s caregiver’s response to the survey.
To assess atypical swallowing, children were asked to swallow their saliva. Then, they were asked to eat crackers. Thus, liquid and food swallowing were observed. The following criteria were checked: effortless lip sealing; lingual interposition; movement of the head or other parts of the body; tension of the mentalis muscle; tension of the orbicularis oris muscle; leakage of food; and noise. Children were considered to swallow atypically when they met at least 3 of these criteria.
Oral breathing was assessed through the child’s caregiver’s response to the survey on whether the child snored or drooled at night. Furthermore, 7 clinical criteria were also taken into account: presence of eye shiners; characteristics of the nostrils; dry lips; underdeveloped maxillary bone due to the lack of maxillary sinus development; lip incompetence; palate type; and anterior open bite, as well as a breathing test that consisted in positioning a mouth mirror over the child’s nostrils. Oral breathing was considered present when a child met at least 5 of these criteria.
Also, the children’s parents or caregivers were asked to fill in a questionnaire; it included questions about the child and the mother, the type and duration of breastfeeding, the use of a bottle and the duration of bottle-feeding, the presence of habits such as digital or labial sucking, atypical swallowing, the type of breathing (either nasal or oral), snoring, and drooling.
Evaluation of transversal occlusal alterations
Posterior crossbite (PCB) was clinically evaluated; it is considered present when the vestibular surfaces of the upper molars fit behind the vestibular surfaces of the lower molars. It can be unilateral if no midline shift exists, but in general, PCB is bilateral. Likewise, 2 types were considered for the diagnosis of a complete PCB – buccal, when the upper jaw completely covered the lower jaw, or lingual, when the lower jaw completely covered the upper jaw.
Evaluation of vertical occlusal alterations
Open bite was clinically evaluated by measuring the distance between the incisal edges of the maxillary and mandibular central incisors. The end-to-end incisor relationship or the negative overbite condition were considered open bite.
Deep bite was clinically evaluated by measuring the coverage percentage of the upper central incisor on the vestibular surface of the lower central incisor; deep bite was considered present when the coverage was more than 30%.
Study error
All evaluations were performed again for all variables by the same examiner after a 10-day interval. The intra-examiner concordance was evaluated with the kappa coefficient, achieving values greater than 0.9 for all the outcome variables.
Statistical analysis
Statistical analysis was performed using IBM SPSS Statistics for Windows, v. 25.0 (IBM Corp., Armonk, USA). The χ2 test was used to analyze the possible associations between breastfeeding duration and the presence of non-nutritive habits or occlusal alterations. Subsequently, logistic regression analysis was performed to identify the presence of risk factors with regard to the outcome variables. The duration of breastfeeding (in months), the duration of bottle use (in months), gender, age, the parents’ educational level, and the number of children in the family were considered predictor variables. The overfit method was used. At first, a primary regression considering all predictor variables was performed. Then, a final regression selecting only the variables with a p-value <0.25 was performed. The significance level was set at p < 0.05 for all tests.
Results
The gender distribution is shown in Table 1. Breastfeeding duration was significantly associated with oral breathing (p = 0.048); the possible oral breathing was lesser in children that had been breastfed for more than 6 months (Table 2). No other statistically significant associations were found (Table 1, Table 2, Table 3).
The logistic regressions showed that the use of a bottle for more than 24 months significantly influenced the appearance of non-nutritive habits (OR (odds ratio) = 3.55; 95% CI (confidence interval): 1.20–10.55; p = 0.022) (Table 4). Breastfeeding duration (OR = 0.84; 95% CI: 0.74–0.96; p = 0.011) and gender (OR = 0.22; 95% CI: 0.07–0.69; p = 0.009) significantly affected the development of oral breathing (Table 5). The probability of the occurrence of the oral breathing habit was greater in the case of shorter breastfeeding duration and in girls (Table 5).
Regarding occlusal alterations, the use of a bottle for more than 24 months significantly influenced the appearance of anterior open bite (OR = 12.12; 95% CI: 1.16–126.31; p = 0.037). Furthermore, boys were found to be less likely to have anterior open bite (OR = 0.27; 95% CI: 0.08–0.99; p = 0.048). Older preschool children appeared to be less likely to present PCB (OR = 0.10; 95% CI: 0.02–0.54; p = 0.007). Finally, the youngest children in the family presented a decreased likelihood of having deep bite (OR = 0.45; 95% CI: 0.26–0.77; p = 0.003) (Table 6).
Discussion
There are few studies regarding the minimum duration of breastfeeding that protects newborns against the development of non-nutritive habits or dental occlusion alterations, and they report varied results.28, 29, 30 Previous systematic reviews generally found a protective effect of breastfeeding on allergic outcomes, although many studies had methodological limitations.20 Although breastfeeding is reported to protect against lower respiratory tract infections during infancy, such protection has not been clearly demonstrated for asthma.26 Children who are breastfed generally adopt nasal breathing due to the hermetic mouth seal during sucking, thus reducing their susceptibility to allergies; consequently, they develop fewer non-nutritive habits and fewer occlusal alterations.19 To confirm this relationship, more studies are needed. In this regard, this study sought to determine the association between breastfeeding duration, the development of non-nutritive habits, and transversal and vertical occlusal alterations in children aged 2–5 years from Lima, Peru. The aim was to demonstrate whether prolonged exclusive breastfeeding for more than 6 months acts as a protective factor against the development of non-nutritive sucking habits or occlusal alterations. For this purpose, data collected through questionnaires and clinical assessments was analyzed.
The findings of this study reinforce the notion that a longer breastfeeding period may lead to a decrease in the occurrence of some non-nutritive habits, specifically oral breathing, and more consistency about this association is now available. The group that had been breastfed for more than 6 months had a significantly smaller percentage of children with oral breathing (16.2%) (Table 2). In addition, the regression results showed that breastfeeding duration was a protective factor against this habit (Table 5). To understand how breastfeeding duration works as a protective factor against oral breathing, it should be noted that during breastfeeding, babies adopt nasal breathing due to the hermetic mouth seal which occurs during suction, reinforcing nasal respiration during feeding. During suction, children open, protrude, close, and retrude their jaws, developing the entire muscular system of masseter, temporal and pterygoid muscles. Additionally, the temporomandibular joint is stimulated during breastfeeding and the anteroposterior growth of the mandibular body is expected. Conversely, during bottle-feeding, the tongue is positioned lower and further back, and the lips are separated; therefore, the tongue propulsion is weaker. Furthermore, pterygoid muscles and masseters are used less, because, due to the lingual depression at the time the baby carries out the passage of the food, they cannot be synchronized with respiration, thus increasing the probability of oral breathing.31, 32 Breastfeeding promotes nasal respiration due to suction, and this results in the adequate craniofacial development and prevents respiratory infections.33, 34
Breastfeeding is promoted for its multiple benefits, both nutritional and psychological. There is consensus among different institutions and organizations that in order to guarantee its benefits, breastfeeding should be the exclusive source of feeding for a baby for 6 months or more in low- and middle-income countries.7, 14, 22 Our findings reinforce these recommendations and the role of breastfeeding with regard to oral breathing.
Furthermore, exclusive breastfeeding is strongly and inversely associated with the frequency, intensity and duration of the use of a bottle, which can lead to occlusal alterations. The use of baby bottles is extremely popular for several reasons. One very important reason is that many mothers go to work and cannot breastfeed their children. The prolonged use of a bottle could be associated with the lack of knowledge of parents about its harmful effects and how it can influence occlusal alterations in children. We found that the use of a bottle for more than 24 months significantly influenced the appearance of open bite (Table 6). Furthermore, we found that the duration of bottle-feeding was a risk factor with regard to the appearance of oral habits (Table 4). Hence, bottle use should be avoided. Contrarily, the duration of breastfeeding was not related to the occurrence of transversal or vertical occlusal alterations (Table 6). However, we identified some factors that affected the outcome variables, for instance, boys were found to be less likely to have anterior open bite (OR = 0.27; 95% CI: 0.08–0.99; p = 0.048), older preschool children appeared to be less likely to present PCB (OR = 0.10; 95% CI: 0.02–0.54; p = 0.007) and the youngest children in the family presented a decreased likelihood of having deep bite (OR = 0.45; 95% CI: 0.26–0.77; p = 0.003) (Table 6). Although these predictor variables showed an influence on the appearance of various types of malocclusion, we must remember that they can be accompanied by several environmental factors, and that a genetic factor should always be taken into account.
As this was a meticulous study, we found some challenges when carrying it out, especially when collecting essential information from the parents and/or guardians. Further research with larger populations is needed for more general conclusions. Even though both groups had different sample sizes and the size of group A was considerable (50 participants), so the results should not have been affected, yet other studies with different samples might corroborate the results of the present study.
Our findings are relevant to the promotion of public health, pediatric dentistry and orthodontics. Clinicians should be aware of the benefits of prolonged exclusive breastfeeding. Therefore, they can educate laypeople on the correct practice of exclusive breastfeeding to obtain all of its benefits. Finally, the results of this study allow us to conclude that preschool children who have prolonged breastfeeding have a lower probability of presenting oral breathing. In addition, the prolonged use of a baby bottle can produce occlusal alterations and lead to the presence of anterior open bite in children.
Conclusions
Breastfeeding duration of 6–12 months was shown to be a protective factor in preventing the appearance of oral breathing. Posterior crossbite, open bite and deep bite seemed not to be influenced by breastfeeding duration. However, the use of a bottle for more than 24 months significantly influenced the appearance of anterior open bite.
Ethics approval and consent to participate
This study was approved by the Ethics Committee at the School of Dentistry of the Scientific University of the South (Universidad Científica del Sur), Lima, Peru (No. of approval: 000444). The parents or legal guardians of the children signed the informed consent forms prior to participation in the study.
Data availability
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Consent for publication
Not applicable.