Newborn Oral Development

Infants perform a series of complex oral movements to obtain sufficient nutriment from their mother's breast to meet daily nutritional requirements and to support rapid growth, especially during the first few months of life. Suckling is a dynamic process, as the infant is continually adjusting to a changing anatomy. The act of suckling is far more than simply obtaining food. The infant's earliest autonomous functions are focused about his mouth and pharynx area. The infant's mouth is the cockpit of his awareness and is the principal site of interaction with his environment.

In the embryo, facial and pharyngeal regions develop from neural-crest cells at about the time of neural-tube closure. Further development is due to tissue differentiation from the endoderm, which later forms the digestive tract. During gestation, the fetus is able to swallow fluid as early as 11 weeks (Miller, 1982) and has a suckle reflex at 24 weeks (Herbst, 1981). Older studies reported that the rooting response and the link between suckling and swallowing was not established until 32 weeks (Amiel-Tison, 1967; Bu'Lock, Woolridge, & Baum, 1990) and not well coordinated until 37 weeks (Bu'Lock, Woolridge, & Baum, 1990). However, in a study of Swedish preterm infants (Nyqvist, Sjo-den, & Ewald, 1999), efficient rooting, areolar grasp and latching on at the breast were observed at 28 weeks—much earlier than previously thought.

At birth, the infant's mouth is vertically short in comparison with that of the adult. There is so little room that when the newborn's mouth is closed, the tongue is in lateral contact with the gums and with the roof of the mouth. There are other proportional differences in size and shape between the infant and the adult skull (Figures 3-12 and 3-13). The infant's lower jaw (mandible) is small and somewhat receded. Whereas the adult's hard palate is deeply arched and situated on a higher plane relative to the base of the skull, the infant's is short, wide, and only slightly arched at birth. Corrugated transverse folds (rugae) on the hard palate assist the newborn in holding the breast during suckling.

Because the infant's tongue fills the small oral cavity, the extent and the direction of tongue movement is limited. Taste buds on the tongue (mostly on the tongue tip) are present at birth, but the newborn has an increased suckling response only to sweet taste. The entire surface of the tongue is within the oral cavity. The infant's lips are well adapted to effect an airtight closure around the breast. The lips are partially everted so that the oral mucosa presents slightly externally; they have tiny swellings on the inner surface (eminences of the

FIGURE 3-12. Midsagittal section of cranial and oral anatomy of an adult while swallowing.

Breastfeeding Breast Anatomy

FIGURE 3-13. Midsagittal section of cranial and oral anatomy of an infant while swallowing.

FIGURE 3-12. Midsagittal section of cranial and oral anatomy of an adult while swallowing.

FIGURE 3-13. Midsagittal section of cranial and oral anatomy of an infant while swallowing.

pars villosa) that facilitate holding the breast and areola in place.

The largest increments in craniofacial growth occur during the first 4 years of life. During the first year after birth, the lower jaw grows downward, creating a larger intraoral space. Active breastfeeding encourages mandibular development and strengthens the jaw muscles. The tongue also gradually descends. By the fourth or fifth year of age, the tongue is attached directly to the epiglottis of the larynx. The frenulum is a fold of mucous membrane midline on the undersurface of the tongue that helps to anchor the tongue to the floor of the mouth. If the frenulum is too short to allow freedom of tongue movement or is placed too far forward to permit tongue extension upward or forward, it can interfere with an infant's ability to suckle (Notestine, 1990).

The infant's epiglottis lies just below the soft palate, unlike the adult's, as seen in Figure 3-13. This makes it possible for food to move laterally on the outside of the epiglottis and to pass directly into the esophagus. The epiglottis plays an important role by closing off the pathway to the lungs when the infant swallows. Such closure ensures that the milk will travel into the esophagus rather than into the trachea. Relative to an adult larynx, the infant larynx is much higher in the oral cavity and occupies a larger space. It is short and funnel-shaped. As fluid passes through the mouth, the larynx elevates so that fluid can move easily into the pharynx. Because the larynx is high and elevated during swallowing, it depends much less on the action of the epiglottis and on closure of the vocal folds to protect the airway. The shape of the pharynx gradually changes as the child grows. At birth, the pharynx curves very gradually downward to join the oral cavity. This curvature would prevent articulate speech even if the necessary central nervous system linkage were present. By puberty, the posterior walls of the nasal and oral segments join almost at a right angle.

The infant has pads of fat on both cheeks to assist with suckling. Each pad is a circumscribed layer of fat enclosed within its own capsule of fibrous connective tissue. It lies between the buccinator and masseter muscles. It is thought that buccal fat pads provide stability for suckling and reduce the likelihood of collapsing of the cheeks and buccinator muscles between the gums. When babies suck their own tongues, the degree of negative pressure is such that drawing in of the cheeks occurs, creat ing a characteristic dimpling. Collapsing of the cheeks is more likely in a premature baby who lacks the layer of fat (including that in the cheeks) that gives full term infants their characteristic plump facial appearance.

The shape and softness of the human breast is beneficial to shaping the hard palate into a round U-shaped configuration because it broadens and flattens in response to the infant's tongue movements. Compared with the V shape associated with bottle-fed children, the broad and wide palate of a breastfed child is physiologically ideal because it aligns teeth properly and most likely reduces the incidence of malocclusions (Palmer, 1998).

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