How many rabbits have you seen with crooked teeth? How about bears or dogs? Why are humans the only mammals with crooked teeth?

An orofacial myofunctional disorder, or OMD, describes abnormal lip, jaw, or tongue positions during rest, swallowing, or speech. There are many distinct points at which a child or adult’s system may experience a breakdown, leading to subsequent events known as craniofacial sequences. Allowing these events to persist without intervention may ultimately lead to an OMD.

An OMD can be caused by airway obstruction (such as sinus infections, enlarged tonsils, allergies), structural dysmorphology (such as craniofacial differences, restricted oral frenula), and/or idiosyncratic behaviors (such as sucking or chewing habits).

Human teeth get crooked. Palatal expanders and braces may fix the problem, but how do they become crooked in the first place? At rest, your tongue tip should be on the roof of your mouth, also called the alveolar ridge; your lips should be closed, and there should be about 1 millimeter of space between your back molars. There are three reasons why a child’s tongue may lie at the bottom of the mouth: to maximize the airway, soft tissue obstruction (for example, a lip or tongue tie), or there were airway or soft tissue obstructions that were fixed, but the child is continuing the habit. There are many more reasons why an adult’s tongue may lie at the bottom of the mouth, including the aforementioned reasons.

A palatal expander is used to widen a narrow palate. When the tongue tip lies on the alveolar ridge, it counteracts the pressure of the cheeks, which would otherwise push the upper jaw in, narrow the palate, and cause dental issues (like crooked teeth). Thus, the tongue tip is our body’s natural palatal expander. Neglecting to utilize our natural mechanism results in a narrowed palate, leading to complications such as dental misalignments. Employing our tongue tip comes at no cost and is a more economical approach compared to using a palatal expander! Additionally, the lips act as natural braces for the teeth. Again, this is more economical than braces.

As I mentioned, OMDs are caused by a sequence of events. Imagine a row of dominoes being knocked down, one right after another. If we don’t stop them, they will continue to fall. Let’s take a look at some examples.

Consider a child who develops airway obstruction secondary to allergies. This obstruction causes the child to open their jaw to maximize the airway. The jaw opening causes the tongue’s position to lower and move forward. Because the tongue tip is no longer lying on the roof of the mouth, the hard palate narrows. When the hard palate narrows, the teeth no longer have enough room, causing dental changes, including malocclusions. It doesn’t stop here, though. Due to the shifted tongue posture and narrower palate, articulation will be affected. Likely, this child will have an articulation disorder. Mouth breathing due to sinus tissue swelling (rhinitis) and impaired nose function can lead to sleep-disordered breathing.

Next, let’s consider a child with a low resting posture due to consistent thumb sucking. The tongue descends and moves forward, initiating the cycle again. In this case, thumb-sucking can transition into tongue-thrusting. Because the tongue remains under the thumb for extended periods, once the thumb is removed from the mouth, the tongue continues the back-and-forth motion. This child will end up with bottom teeth leaning medially and upper teeth leaning distally, resulting in an open bite.

Now, let’s examine an adult who is morbidly obese. Daily activities are a struggle, leading the adult to breathe through their mouth all day. Consequently, the tongue falls low, triggering the domino effect once again.

Lastly, let’s consider two different adults who never had allergies or any of the aforementioned issues. One receives dentures, and the other gets a bite plate. What happens to the resting tongue posture? It can no longer be at the alveolar ridge because the appliances are slippery, causing the tongue to rest at the bottom of the mouth. Consequently, the jaw must open wider to accommodate the tongue. Inefficient breathing leads to mouth breathing, which likely occurs during both day and night. The domino effect is set in motion.

Recall the initial question about why humans are the only mammals with crooked teeth. Simply put, we are the only mammals altering our eating habits, breathing patterns, and sleep positions. By addressing these areas, we can prevent the domino effect of misaligned teeth, sleep-disordered breathing, articulation disorders, and more.

Stephanie Jeret is a speech pathologist.