Your baby's jaw bones

The shapes of human jawbones (that is, the mandible and maxilla) are predominantly determined by our genes. However, bottle-feeding in infancy affects orthodontic development, sometimes resulting in a crossbite at the back. This finding about bottle feeding's possible effect does not mean that breastfeeding problems result in abnormal orofacial development, though, the way you often hear.

The lower jaw (or mandible)

Your baby's lower jaw contains a raised gum which will, in time, hold your baby's teeth as they erupt through. In the meantime, the jaw and gum support the lower half of your baby's face and give that lovely little mouth and chin its unique shape and definition.

A baby's lower jawbone is often quite delicate in proportion to the rest of his face, though this proportion changes with growth. Small chins are on the spectrum of normal anatomic diversity in early life.

A true retrognathia (which is a congenitally abnormal smallness of the lower jaw) results from abnormal and deficient growth of the mandible, and often occurs in the context of other congenital abnormalities. Today, many normal little baby mandibles are unhelpfully and incorrectly diagnosed as 'retrognathia'. A true, medical retrognathia can cause airway compromise and obstructive sleep apnoea.

The upper jaw (or maxilla)

The upper jawbone contains the upper gum and shapes the middle of your baby's face, including by supporting the nose. Your baby's lower jaw or mandible is hinged to the upper jaw at the temporomandibular joint.

These days, many breastfeeding support professionals tell their clients that restricted oral connective tissues will compromise maxillary development. Unfortunately, the association between bottle-feeding and compromised maxillary development is widely misunderstood.

1. Firstly, you might hear that your baby's oral connective tissue tightness is restricting her tongue movement. This is only the case if your baby has a classic (and anterior) tongue-tie - and even then, lots of babies with what seems to be a classic tongue-tie breastfeed without causing any problems. You can find out about tongue-tie starting here.

2. Then you might hear that because of restricted tongue movement which began in the womb, your baby has developed a high-arched palate or 'bell' palate, because the tongue was unable to press up against the palate during its development, to broaden it. This theory lacks biological plausibility because it misunderstands

   • The mechanisms of bony development in infants

   • Where and how the mid-tongue touches the palate during suck and swallow, explained below.

3. Finally, you might hear that if you don't proceed with bodywork or frenotomy, your baby is at risk of compromised maxillary and orthodontic development, which will affect not only your child's bite later on, but also the development of his nasal passages, resulting in snoring and sleep apnoea and broken nights. Again, this misunderstands developmental mechanisms.

These three claims arise out of pathologising belief systems, which are not scientific. You will see as we look closer at the mechanisms of sucking, below, why it is not possible for your baby's tongue to shape orofacial development.

Your baby's cheeks

Your baby's sturdy little cheeks are plump with fat pads and muscles such as the buccinator muscles. These form a fleshy wall on either side of your baby's oral cavity.

Inside baby's mouth, the buccinator muscles act as warm, firm cushions on either side of the tongue. The buccinator muscles don't directly affect the nipple and breast tissue that is drawn up inside your baby's mouth during breastfeeding, but they do prevent your baby's cheeks collapsing in when a vacuum is generated.

Your baby's hard and soft palate

Sometimes when your baby cries or yawns, or if you are allowing your little one to suck on your finger, you'll notice your baby's hard palate. The hard palate is bone covered by a mucosal lining which secretes saliva and mucous.

The fron two-thirds of the hard palate is made up of two processes or plates which extend from and are part of your baby's upper jawbone or maxilla. The back one-third of the hard palate is made up of two little stand-alone bones.

Some health profesionals like to diagnose babies' palates as high and narrow when the baby has a breastfeeding problem. You might also be told your baby's hard palate is broad and flat. But hard palate shapes occur on a spectrum of normal diversity. Normal, as you already know, is a highly diverse condition in babies!

A more narrow faced or fine-featured person, such as myself, is likely have a higher palate. A broad-faced person is likely to have a broad and flatter palate. I don't ever comment upon the shape and height of a baby's palate when I'm performing an oromotor assessment, since any comment I make about palate shape is a subjective assessment which lacks meaningful objective measures, and doesn't help parents and their babies. Trying to compare your baby's palate shape with other baby palate shapes doesn't change anything about the way we deal with breastfeeding challenges!

The hard palate is hinged to the fleshy plate of the soft palate at the junction of the hard and soft palate. The soft palate ends in the teardrop of the uvula, which you might sometimes see at the back of your baby's mouth when she yawns or cries. Your doctor will check your baby's hard and soft palates for clefts and other abnormalities using a tongue depressor to visualise the margin of your baby's soft palate and uvula.

It doesn’t make sense to think that an (undefinable and anatomically invisible) floor-of-mouth fascial tightness interferes with maxillary development. Although this has become a popular theory, which is wrongly communicated to parents as a fact, it's a theory which doesn't make sense to developmental anatomists.

Selected references

Montserrat B-C, Bellot-Arcis C, Montiel-Company J-M, Almerich-Silla J-M, Catala-Pizarro M. Does breastfeeding have a long-term positive effect on dental occlusion? J Clin Exp Dent. 2019;11(10):e947-951.

Limeira AB, Aguiar CM, Bezerra N, Camara AC. Association between breast-feeding duration and posterior crossbites. Journal of Dentition in Childhood. 2014;2014(81):122-127.