This is an article authored by Dr. Palmer that was published in the
Journal of Human Lactation, Volume 14, Issue 2, pp 93-98,
copyright 1998 by International Lactation Consultant Association.
Reprinted by permission of Sage Publications, Inc.
Copied and delivered electronically by permission: no further copying permitted
without the written permission of the publisher.
This article was selected by UNICEF as the
“ Breastfeeding Paper of the Month” for July, 1998.
Introduction
Conventional wisdom, supported by scientific research, advocates breastfeeding as the superior method of infant feeding. The nutritional, immunological, psychological, and general health advantages conveyed to infants have been documented for years.1 -9 Legovic, 10 listed the merits of human breast milk as compared to artificial feeds to include ideal nutritional content, better absorption, fewer food-related allergies, more favorable psychological development, better immunologic defenses, and a substantial economic advantage. There is another compelling benefit to exclusive breastfeeding: positive effects on the development of an infant’s oral cavity, including improved shaping of the hard palate resulting in proper alignment of teeth and fewer problems with malocclusions. The purpose of this commentary is to stimulate further research as well as to propose the importance of breastfeeding to developing and maintaining the physiologic integrity of the oral cavity.
Review of the Literature
Effects of Breastfeeding and Bottle Feeding on Infant Swallowing.
As lactation specialists are aware, the key to successful breastfeeding is a proper “latch-on” and swallow by the infant as described by Woolridge, 11 Escott, 12 Weber, 13 and Bosma.14 During effective latch-on, the infant draws both the nipple and some of the surrounding areolar tissue into the mouth and extends the tongue over the lower gum pad. The lips flange outward over the areolar tissue to create a good seal. Initially, suction is needed to latch on and extend the mother’s breast and nipple to the junction of the infant’s hard and soft palate. If the seal is poor, repeated additional suction will be required. So long as the seal remains intact, the infant obtains milk easily by using a peristaltic-like motion of the tongue to compress the flattened soft breast nipple against the palate. The infant must compress the areolar tissue, because the mother’s lactiferous sinuses are located in that area. The compression of the lactiferous sinus area helps to start the flow of milk forward through the multiple openings at the nipple. This peristaltic action of the infant’s tongue flattening the nipple against the hard palate moves the milk toward the throat, where the baby swallows and gains nourishment.
(Figure 1). This normal, healthy swallowing habit sets a pattern for a correct normal swallow into adulthood.
Contrasting the mechanical aspects of breastfeeding with bottle feeding, Weber13 noted that in breastfed babies the tongue action appeared to be a rolling or peristaltic motion. However, the tongue action for bottle-fed babies was more piston-like or a squeezing motion. Picard15 wrote that in order to stop the abundant flow of milk from a bottle with an artificial nipple (with a large hole in the end), the infant was forced to hold the tongue up against the hole in the nipple to prevent the formula from gushing forth. This abnormal motor activity of the tongue is referred to as a tongue thrust or a deviate swallow. Fig. 2 shows a tongue thrust and resultant open bite on an infant and two adults. It is noteworthy that the adults have not outgrown their tongue thrusts.
Weber13 also observed that when breastfed babies were not sucking or swallowing, they rested with the nipple moderately indented by the tongue, while bottle-fed babies rested with the latex teat expanded (indenting the tongue). The differences between the tongue movements and resting position of the tongue in breastfed and bottle fed babies are probably due to the properties of the latex/silicone artificial nipple. Since the manufacture of bottles and artificial nipples is not a standardized process, there may be varying effects of “bottle-feeding” on infant suck.
Effects of Breast and Bottle Feeding on Oral Cavity Development.
Muscular development. In 1959, Picard15 observed that active breastfeeding encouraged mandibular development, with a strengthening of the jaw muscles. Bosma14 concurred in 1963, suggesting that “the tongue, lower lip, and mandible move in concert to draw the nipple into the mouth and to empty it rhythmically by a series of compressions in a front-to-back sequence.” Weber13 concluded that the “stripping” movement of the tongue in breastfeeding was more important than suction in obtaining milk. Picard15 suggested that the undesirable effects of artificial nipples on infants were permanent, and that correction in later life would be extremely difficult because muscle development would be affected. The forceful breastfeeding motion encouraged mandibular development, while bottle feeding could actually hinder the formation of strong jaw muscles. Newman16 stated the early introduction of bottles could cause suckling problems.
Drane17 noted that during breastfeeding, the shape of the breast-nipple is dictated by the internal geometry of the infant’s mouth. However, an artificial teat is already formed, with a specific shape, and is made from a material stiffer than breast tissue. The piston-like action used to obtain milk from the bottle is more explosive and more powerful than the action used in breastfeeding. Therefore, greater pressure is applied to the artificial teat than is applied to the breast-nipple. This pressure is produced predominantly by the oral musculature. Koenig18 stated that during bottle-feeding, the infant produced oral suction with the oral musculature rather than with thoracic musculature. Woolridge 11 has also demonstrated that less suction is needed during breastfeeding than during bottle feeding. Forceful action causes the cheeks to draw in, putting pressure on the gums and teeth, affecting the position of teeth. This action can also cause an implosion of the oropharynx, and thereby affect the development of the oropharynx. During breastfeeding, the infant has to work the jaws and tongue in a natural physiological manner to aid in the compression of the lactiferous sinus. This action, plus normal swallowing motions, help to develop proper perioral (around the mouth and jaw) musculature.
Cranio-Facial Development and the Etiology of Malocclusions
Shepard,19 noted that the largest increments in craniofacial growth occurred within the first 4 years of life, and that craniofacial development is 90% completed by 12 years of age. The flexible and soft human breast nipple tissue is beneficial in shaping the hard palate because it flattens and broadens in response to the infant’s tongue action. As the infant uses a peristaltic-like motion to “strip” milk from the mother’s nipple/areolar area, the hard palate is gently shaped by the infant’s tongue to a rounded U-shaped configuration. A physiologically and appropriately shaped palate aligns the teeth properly and reduces the incidence of malocclusions.
In the early stages of oral cavity development, the palate is almost as malleable as softened wax. Thus, when any object is pressed against the soft bones of the palate, these bones can be molded into a narrow, unnatural shape. This eventually leads to the poor alignment of teeth, and the “V-shaped” palate found in many people with malocclusions. This dynamic also explains how the upper back teeth are pulled inward to cause a mismatch or “cross-bite.” Once a malocclusion develops, it can create a domino effect that can damage the rest of the teeth.
In 1987, Labbok and Hendershot20 published a retrospective cohort study of 9,698 children between 3 and 17 years of age. That study assessed the association between breastfeeding and malocclusion. The data demonstrated children who were breastfed for three months or less had a malocclusion rate of 32.5%. Children breastfed more than twelve months had a malocclusion rate of only 15.9%. In that study, children who were bottle fed were 1.84 times more likely to have malocclusions than children who were breastfed. Labbok and Hendershot20 concluded that each additional month of breastfeeding contributed to a decline in the malocclusion index.
Other infant habits, unrelated to feeding, may contribute to malocclusions. Studies conducted by Larsson21,22 concluded that prolonged finger sucking caused an anterior open bite, proclination and protrusion of the maxillary incisors, a lengthening of the upper arch and the anterior displacement of the maxilla. In addition, studies by Bowden,23 Melsen,24 Paunio25 and Ogaard26 found a positive association between the use of pacifiers and malocclusion. The forms of malocclusion described by these authors included crossbite, reduced arch width, lower anterior facial height, rotation of mandibular plane angle, open bite, and tongue thrust swallow.
Examination of Historical Skulls
I became interested in this subject when I noticed similarities in patterns of malocclusions, tooth defects, and the shape of the hard palates among thousands of patients seen over 27 years of private dental practice. I hypothesized that artificial nipples would negatively affect palate formation. To test this hypothesis, I began a study of ancient skulls of persons who necessarily would have been exclusively breastfed.
Historically, breastfeeding was the primary means of infant nourishment until relatively recent times. Fildes27 explains that although “glass feeding bottles with spherical bases and extended necks: with screw tops with sponges for sucking” were developed around 1770, “rubber teats did not come into general use until the mid-nineteenth century”. By comparing skulls of persons who lived before versus after the introduction of rubber teats, one can examine the impact of the artificial nipple upon formation of the oral cavity.
Larsson28 studied medieval Swedish juvenile skulls, searching for malocclusions which may have been related to a finger-sucking habit or to sucking a dummy-like object. He found the prevalence of malocclusions relatable to those habits was very low, which was consistent with reports from non-industrialized cultures.
The first collection of skulls I evaluated was preserved at the University of Kansas Medical Center in Kansas City, Kansas. These 210 skulls were believed to be old skulls from India, a culture that, until recently, predominately breastfed. Of those 210 skulls, only four (or approximately 2%) showed signs of malocclusions. One of those skulls had a genetically asymmetrical jaw, and three others had slight open bites, perhaps due to abnormal motor activity of the tongue. The skulls without malocclusions (98%) had broad hard palates with “U-shaped” arches, and proper alignment of teeth. Following the study of the original group of skulls, I reviewed an additional twenty prehistoric skulls, some dated at 70,000 years old and stored in the Anthropology Department at the University of Kansas. Those skulls also exhibited positive occlusions, minimal decay, broad hard palates, and “U-shaped” arches.
The final evaluations were of 370 skulls preserved at the Smithsonian Institution in Washington, D.C. The skulls were those of prehistoric North American Plains Indians and more contemporary American skulls dating from the 1920s to 1940s. The prehistoric skulls exhibited the same features as mentioned above, whereas significant destruction and collapse of the oral cavity were evident in the collection of the more recent skulls. Many of these more recent skulls revealed severe periodontal disease, malocclusions, missing teeth, and some dentures. This was not the case in skulls from the prehistoric periods before the invention of baby bottles, artificial nipples, and pacifiers.
Malocclusions were rarely found during the evaluation of prehistoric skulls. Figure 3 demonstrates a comparison between a prehistoric skull with a “U-shaped” arch and a modern “V-shaped” arch. The “U-shaped” arch has enough room for proper alignment. The “V-shaped” arch is associated with crowding and malalignment of the teeth.
To better understand the significance of the influence of breastfeeding on malocclusion, one must consider that, of the approximately 600 older skulls this author examined and evaluated, nearly all had perfect occlusions. All of the skulls were from populations living before the invention of the modern baby bottle or were from breastfeeding cultures, and therefore these individuals were necessarily breastfed. These skulls universally demonstrated, good occlusion, few dental caries, and well-rounded and full “U-shaped” dental arches. These features were found in far fewer of the modern skulls.
Breastfeeding and the Development of the Airway
Another problem that occurs during early oral cavity development is that of infringement on the space of the nasal cavity. When the roof of the mouth is pushed up, the floor of the nasal cavity rises as well. Since the bridge of the nose does not rise accordingly, there is a decrease in the total nasal space. This can have a dramatic effect on the individual’s breathing efficiency because the size of the nasal chamber is reduced. Kushida et al.29 have shown that a high palate and narrow arch, as described here, are good predictors of snoring and obstructive sleep apnea. Individuals with good occlusion normally have a well rounded and full “U-shaped” arch.
Conclusion
Preventing disease, in a natural way, far outweighs the alternative: treating the disease with our newest medical technologies, which can be costly and time consuming. Breastfeeding has been shown to be immunologically, emotionally and nutritionally advantageous. This paper presents another rarely reported benefit of breastfeeding: dental health.
Breastfed babies have a better chance of dental health than artificially-fed infants because of the effects of breastfeeding on the development of the oral cavity and airway. With fewer malocclusions, these children may have a reduced need for orthodontic intervention. In addition, children with the proper development of a well rounded, “U-shaped” dental arch, which is found more commonly in breastfed children, may have fewer problems with snoring and sleep apnea in later life.
Definition of Terms
Breastfeeding. Refers to exclusive breastfeeding with the mother’s nipple and areolar breast tissue entering the infant’s mouth for the purpose of nourishment.
Normal swallow. A swallow initiated with the tip of the tongue starting in the area of the maxillary anterior papilla (just behind the upper front teeth), then with a peristaltic wave-like action, the tongue presses up against the roof of the mouth, forcing the bolus of saliva or food posteriorly and finally down the throat. The tongue should not press with any force into, against, or between any teeth during a swallow.
Occlusion. The proper alignment of teeth. With proper alignment, three criteria are met in ideal occlusion (Dawson, PE: Evaluation, Diagnosis, and Treatment of Occlusal Problems. 2nd ed. St. Louis MO: Mosby, 1989): (1) All teeth touch at the same time on closing with a cusp tip point contact to a flat surface. (2) during movement of the teeth to the side, guidance comes from the cuspid (eye) tooth. Guidance is transferred to the front teeth in extreme side movements or when moving the lower jaw forward. (3) The posterior (back) teeth should not bump or drag on one another during side or forward motions.
Malocclusion. Malalignment of the teeth and failure of the bite to meet the criteria described above.
Cross-bite. A form of malocclusion in which the lower teeth are outside (to the cheek side) of the upper teeth.
Acknowledgments: This author wishes to thank Cheryl Hall Harris for assistance in organizing and developing the material, Nicole Bernshaw and Joan Gilson for their assistance, and Ann Mary Corry for procuring previously published studies supporting this research.
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Brian Palmer has been a full time family practice dentist for 27 years. He has a special interest in the treatment of snoring and obstructive sleep apnea. For over 20 years he has been observing and documenting the collapse of the oral cavity and airway.
Figure 1. “Latch-on” and peristaltic motion of the tongue during breastfeeding. Reprinted with permission from Ros Escott’s article, “Positioning, Attachment and Milk Transfer,” Breastfeeding Review, 1989, 31-37.
Figure 2. Demonstrates a tongue thrust and resultant open-bite malocclusion on a 3 1/2 year old infant and two adults. The adults have not outgrown the tongue thrust.
Figure 3. Compares a normal palate and “U-shaped” uncrowded arch of a prehistoric skull to a high palate and “V-shaped” crowded arch of a modern individual.