Every anthropological study of the skulls of our hunter and gatherer ancestors delivers the same findings: they all had wide jaws with all 32 teeth (yes, wisdom teeth, too!) in perfect alignment. Exceptions to this were very rare. As time has progressed, small jaws with crowded teeth have become the norm. The conveniences of modern, industrialized society have been a great force behind this.

First, a brief introduction to our jaws:

Meet your maxilla.

Our upper jaw, the maxilla, is comprised of a left and a right segment that meet in a middle junction known as the midline suture. A properly developed maxilla grows wide and forward. The maxilla grows by intramembranous growth, meaning that it builds bone from the midline as it grows. The tongue is the scaffold for appropriate growth. When muscle pressure from the tongue in the palate (the roof of the mouth) is the dominating muscle force, the maxilla develops into the perfectly sized and positioned unicorn that it is destined to be.

Meet your mandible.

Our lower jaw, the mandible, grows by appositional growth. As the mandible follows the maxilla forward, new bone is deposited at the distal, the back end, of the jaw.

Let’s start with the basics. What is the most influential factor of jaw growth? Muscle activity. The tongue, the cheeks, the lips, and the chewing muscles are all key players. Pulling and pushing in all of the right places makes perfect jaws. For these muscles to do their job and do it well, we need to have 3 things in place: proper resting oral posture, proper swallow, a lot of chewing. Let’s take a closer look at each of these, along with how modern society has fallen away from them.

When not eating or speaking, our mouth posture should be this: lips sealed, tongue on the roof of the mouth, teeth lightly touching or slightly apart. With the tongue resting on the roof of the mouth and the mouth closed, the perfect balance occurs. The light pressure from the tongue acts as the scaffold for a perfect broad U-shaped palate. There is no inward counter force from the cheeks or lips. In this posture, we are nasal breathing.

What can break this system?

• Mouth Breathing: With the mouth hanging open, the tongue is not on the roof of the mouth. The inward pressure from the cheeks trumps the complete lack of outward pressure from the tongue. With this muscle pressure imbalance, we end up with a narrow V-shaped upper jaw, rather than a wide U-shaped upper jaw.

• Non-nutritive sucking habits with a pacifier or thumb: The finger/paci takes the place of the tongue on the roof of the mouth. The combination of the sucking inward force of the cheeks and the midline upward force of the thumb/paci ends with an even more significant narrow V-shaped upper jaw.

• The growth of the mandible is also affected by poor oral posture. Appositional growth happens as the mandible follows the maxilla forward. Improper oral posture causes problems in two main ways. An open mouth posture (like with mouth breathing) keeps the mandible in a down and back position, rather than forward, so minimal growth occurs. Pouring salt on the wound- the low postured tongue often rests between the back teeth, which can allow the anterior teeth to over-erupt into an overbite. The overbite then further blocks the forward growth and development of the mandible. Double whammie!! See pic below to demonstrate the effect this can have on your profile!

• A correct swallow occurs with the tongue pushing up and sliding back on the roof of the mouth, efficiently delivering the food bolus or the drink straight down the hatch. This force of the tongue on the palate puts the perfect amount of lateral force on the left and right segments of the maxilla, encouraging intramembranous growth at the suture. A tongue that appropriately rests on the roof of the mouth is already in prime position to dominate its swallow game.
• Our method of swallow develops in our first days/months/years of life. Breastfeeding is a key player in acquiring a proper swallow. In order to express milk, the tongue must push up and back on the roof of the mouth, with nothing getting in between.
• Two examples of improper swallow are an anterior tongue thrust and a lateral tongue thrust. In both of these, the tongue is not pushing on the roof of the mouth. Rather, it pushes between the teeth to create a seal to swallow. An improper swallow has a tremendous effect on both jaw development and tooth alignment.
• Risks for developing an improper swallow are anything that gets between the tongue and the roof of the mouth. This includes a finger, a pacifier, or a bottle nipple. The incidence of improper swallow and the narrow jaws/altered tooth alignment that comes along with it has had a marked increase in correlation with the great rise in bottle feeding over the past 50 years.

• Remember the talk of our hunter/gatherer ancestors and their perfectly formed jaws in a full set of all 32 teeth in alignment? These guys and gals chewed a lot of hard raw food. Hunter/gatherer babies never experienced pureed mush. They went straight from breastfeeding to chewing (or gumming;) solid foods. This meant a lot of muscle pull on the boney jaws, developing and maintaining wide perfect arches.
• With industrialization came processing and pureeing for an early soft diet. Soft foods require minimal chewing and muscle activity. Decreased muscle pull develops smaller jaws.
• An excellent resource for early solid food introduction, to skip the mush and grow the jaws, is the Baby Led Weaning book. You can easily find it on Amazon or in any book stores that care about your jaws;).

This post just scratched the surface of some very important things. In future posts, I will dive into much of this more deeply. An important thing to note is that there are so many factors involved in development, and that not everyone will be affected in the same way by the risk factors discussed above. With rare exception, each tiny human is born with the genetic code for the same perfect jaw development as our hunter/gatherer ancestors. Epigenetics is a broad term for factors that influence how this genetic code is expressed. Mouth breathing, bottle feeding, and prolonged pacifier usage are all epigenetic factors that can change the course of development from the genetically coded set of perfect jaws to an epigenetically modified set of altered jaws. Epigenetic factors have varying effects on each person. Humans are complex creatures- risk factors can affect each person differently. This post is meant to help you begin to understand the influential factors in jaw development.

When something goes wrong, it is important to know that a derailed train can get back on the tracks. Just like physical therapy to regain proper use of a damaged limb, there are exercises in orofacial myofunctional therapy to retrain the system for appropriate swallowing, breathing, and resting oral posture. There are also a variety of appliance options that can aid in getting that train back on its tracks. Myofunctional therapy exercises, thorough examination for anatomical issues, and appropriate appliances (when necessary) can turn an altered set of jaws into a unicorn. Severe cases of poor jaw development may require corrective jaw surgery. My goal, however, is to do everything we can to naturally grow the jaws for the least invasive tooth alignment possible. Whenever we can, we try to avoid the need for surgical and complex orthodontic intervention.

Here’s to health!
~Dr. Mindy