Nose breathing and mouth breathing both bring
oxygen into the lungs but with different consequences
and different oxygen absorption levels. Dental and dental
hygiene education in the past touched only briefly on
problems associated with mouth breathing, primarily dry,
inflamed oral tissues around maxillary anterior teeth. There
is now evidence that mouth breathing has far more serious
and long-lasting implications than drying of oral tissues. A
simple five-step screening process identifies factors affecting
At the end of this program, participants will be able to:
Humans are designed to be nose breathers, but for a variety
of reasons the switch can be made to mouth breathing, with serious
consequences. The nose and mouth have different functions.
Each nostril functions independently and synergistically
to filter, warm, moisturize, dehumidify and smell the air. It’s like
having two noses in one. Breathing through the mouth provides
none of these benefits of nose breathing and a lengthy list of
adverse effects. The problems associated with mouth breathing
begin in the mouth by changing the tongue rest position, thus
changing the normal growth pattern of the palate, both maxillary
and mandibular jaws and the airway.1 Inadequate skeletal
growth leads to crowded teeth, a high-vaulted palate and abnormal
occlusion, called the Long Face Syndrome. In mouth
breathers, the tongue rests down and forward, not in the palate
as it should, leading to tongue thrust, abnormal swallowing
habits and speech problems. A significant problem with mouth
breathing is reduced oxygen absorption leading to a cascade of
sleep, stamina, energy level and ADHD problems. Dryness of
the oral and pharyngeal tissues from mouth breathing leads to
inflamed tonsils, tonsil stones, dry cough, swollen tongue, halitosis,
gingivitis and caries. Mouth breathers chew with their
mouths open, swallowing air, leading to gas, bloating, flatulence
and burping. Lips become flaccid with mouth breathing because
they don’t close regularly to provide the necessary lip seal.
- Understand physiologic differences between nasal breathing
and mouth breathing.
- Describe symptoms of mouth breathing.
- Understand the impact of mouth breathing on malocclusion.
- List the five steps in the mouth-breathing screening exam.
- Recognize the role of RDHs in preventing mouth breathing.
Dental and dental hygiene education in the past touched
only briefly on problems associated with mouth breathing, primarily
dry, inflamed oral tissues around maxillary anterior teeth.
Adding to that knowledge, there is now evidence that mouth
breathing has far more serious and long-lasting implications
than drying of oral tissues.
Many misconceptions about mouth breathing persist today.
In some circles, mouth breathing and nose breathing are thought
to be equivalent and in athletics, mouth breathing is still
assumed to be better than nose breathing. Assuming that mouth
breathing and nose breathing are no different ignores basic physiologic
facts about the exchange of oxygen and carbon dioxide.
Today professional athletic teams are being coached to train with
their mouths closed, focusing on nose breathing to increase
endurance, stamina and muscle memory. Another misconception
is assuming more oxygen is absorbed with a big inhale
through the mouth doesn’t take into consideration the fact that
oxygen is absorbed on the exhale, not the inhale. Sleep medicine
writings assume mouth breathing and sleep apnea are not connected,
which is not supported by scientific evidence. Mouth
breathing and obstructive sleep apnea (OSA) are connected.4
Dental professionals are in a perfect position to evaluate
mouth and nose breathing, check for tongue rest position and
intervene early with young children to assure normal skeletal
development and help mouth breathers of all ages become nose
breathers. Understanding the physiology of breathing and
implementing a simple five-step screening system raises awareness
of the significance of this problem and provides an opportunity
to implement far-reaching changes in patients’ lives.
Physiology of Breathing
The purpose of breathing is to deliver oxygen to the cells
of the body and to remove excess carbon dioxide. The body
requires approximately two to three percent oxygen and the
atmospheric level is 21 percent so there is no need to store oxygen.
The body’s requirement for carbon dioxide is 6.5 percent
and the atmospheric content is 0.03 percent, so the body has to
produce and store carbon dioxide in the lungs and blood.
Carbon dioxide is produced as a byproduct of exercise and
digestion of food. Carbon dioxide has several functions in the
body: facilitate release of oxygen from hemoglobin, trigger
breathing, maintain blood pH by buffering with bicarbonate or
carbonic acid and prevent smooth muscle spasms. All of these
functions are reduced or impaired in mouth breathers.
Breathing is subconscious with each inhale determined not
by the need for oxygen, but by the level of carbon dioxide in the
alveoli of the lungs and blood. As carbon dioxide builds up in
the body, the pH of the blood drops. This pH change is monitored
by chemoreceptors in blood vessels that will signal the
brain to trigger the next breath. Normal respiration follows a
gentle wave pattern with 10 to 12 breaths per minute, providing
five to six liters of air per minute. Mouth breathers often have a
respiration rate above 12 breaths per minute and those with
asthma and serious medical conditions have rates of 20 respirations
per minute or higher.
Breathing through the nose controls the amount of air taken
in and, more importantly, controls the amount of air exhaled. Oxygen is absorbed on the exhale, not on the inhale. The backpressure
created in the lungs with the slower exhale of nose
breathing compared to mouth breathing allows more time for
the lungs to transfer oxygen to the blood. The exchange of oxygen
in the blood requires the presence of carbon dioxide.
Approximately 98 percent of oxygen is carried in hemoglobin.
Carbon dioxide levels need to be at five percent in the alveoli
and arterial blood before the oxygen molecules are released from
hemoglobin to reach brain and muscle cells. Lower than five
percent carbon dioxide levels lead to an elevation in blood pH
and the oxygen “sticks” to the hemoglobin, this is the Bohr
Effect, first described in 1904 by physiologist Christian Bohr.
Nitric oxide is released in the nasal cavity and inhaled with
nose breathing. Nitric oxide increases the efficiency of oxygen
exchange. With nitric oxide, blood oxygen increases by 18 percent.
Mouth breathing bypasses the nitric oxide.
Seventy-five percent of the inhaled oxygen is exhaled.
During strenuous exercise, 25 percent of the oxygen inhaled is
exhaled. Mouth breathing to take in more air does not increase
the level of oxygen in the blood, which is already 97-98 percent
saturated. Mouth breathing with big breaths actually lowers the
carbon dioxide level in the lungs and the blood leading to lower
levels of oxygen released from the hemoglobin to body cells.
Taking in more air doesn’t deliver more oxygen to the cells of the
body. A balanced pH of the blood is achieved with proper oxygen-carbon dioxide exchange. Nasal breathing will increase oxygen
in the lungs, blood and cells. Excessive carbon dioxide loss
through mouth breathing decreases oxygen levels in the lungs,
blood and cells.
Signs of Mouth Breathing
Determining if someone is a mouth breather is not always
easy. Some people admit they always breathe through their mouth. Others believe they are nose breathers, but if you watch
them, their mouth is open most of the time. Sitting still, they
might have their mouth closed, but if they get up and walk
across the room, their mouth is open. Telltale signs of mouth
breathing are an addiction to chap stick or lip balm. An open
mouth leads to drooling, both awake and asleep, causing
chapped lips and a tendency for mouth breathers to lick their
lips frequently. Closed mouth lip seal is efficient at keeping
saliva in and air out but chronic mouth breathers find it very difficult
to hold their lips together. Mouth breathing at night
causes drooling and dries the oral tissues so the mouth, teeth,
tissue and throat are all dry upon waking. If someone wakes
with a dry mouth, he or she is likely a mouth breather at night,
which means he or she is also mouth breathing during the day.
The tongue normally rests against the palate, without touching
the teeth. With mouth breathing, the tongue drops down
and forward. It might in fact be that the down and forward
tongue position triggers mouth breathing. Mouth breathing is
impossible with the tongue resting against the palate. A simple
tool to self-test for mouth breathing is the square plastic bag
closers used on plastic bread bags. Place the square plastic chip
between the lips and have the person go about their daily activities.
If the chip falls out, they are mouth breathing.
Mouth Breathing – What Goes Wrong
Several things go wrong with mouth breathing, beginning
with oxygen/carbon dioxide exchange, the change in tongue rest
position and swallowing air. The low carbon dioxide levels associated
with mouth breathing trigger the activation of breathing
faster than usual, leading to over breathing or hyperventilation.
With less oxygen being delivered to the brain, muscles and all
the cells of the body, the body functions less than optimally.
Sleep is often disturbed and of poor quality, leaving the mouth
breather tired in the morning and feeling
fatigued mid-afternoon. Attention deficit
hyperactivity disorder (ADHD)
is also linked to mouth breathing.11 This
dryness and lack of air filtration in
mouth breathing causes enlarged and
inflamed tonsils and adenoids and
increased risk of upper respiratory tract
infections. Lower levels of carbon dioxide
cause smooth muscle spasms associated
with gastric reflux, asthma and
bedwetting. Smooth muscle is found
throughout the body in the respiratory
system, digestive system, circulatory
system, all hollow organs and all tubes
The tongue resting in the palate
provides passive pressure, stimulating
stem cells located in the palatal suture
and within the periodontal ligaments around all the teeth to direct normal palatal growth. When the
tongue rests in the palate, the teeth erupt around the tongue,
producing a healthy arch form. The lateral pressures from the
tongue counters inward forces from the buccinator muscles.
When the tongue is down and forward, the buccinator muscles
continue to push unopposed, causing the upper arch to collapse.
Children who mouth breath have an underdeveloped, narrow
maxilla with a high vault.2 They develop a retrognathic
mandible and generally have a long face. Harvold et al. surgically
blocked noses in monkeys and they all developed malocclusions
from mouth breathing.3 Mouth-breathing-related
problems of skeletal development will set children up for
obstructive sleep apnea later in life.4
It might seem logical that mouth breathing occurs because
the nose is congested, but that is not always the case. The brain
of a mouth breather thinks carbon dioxide is being lost too
quickly from the nose and stimulates the goblet cells to produce
mucous in the nose to slow the breathing.5 This creates a viscous
circle of mouth breathing triggering mucous formation, nasal
passage blocking, leading to more mouth breathing. So in fact,
mouth breathing can cause nasal congestion leading to more
In some cases, mouth breathing is caused by ankyloglossia,
or a tight lingual frenum keeping the tongue from effectively
moving in the mouth to assist in chewing and swallowing and
comfortably resting on the palate.6 Unless a frenectomy is done,
mouth breathing will continue. Ankyloglossia can be diagnosed
and treated in the first few days after birth.7 However, many
cases are ignored until significant problems have developed.
Early intervention prevents subsequent problems.8
Changing from Mouth to Nose Breathing
Bringing a person’s mouth breathing to his or her attention
starts the process of breaking the habit. Some people will change
back to nose breathing when made aware of it. To remind people
to keep their lips together, paper tape is often used by
breathing coaches. It may sound strange, but easy-to-remove
paper tape helps people experience the many benefits of nose breathing for themselves. Be sure they can breathe through their
nose before taping. Best to test this during the day before trying
it overnight while sleeping. Try the tape yourself before suggesting
it to a patient. A variety of oral appliances are available that
position the tongue to the roof of the mouth, close the lips and
encourage nose breathing.9 In many cases, the tongue might
need to be exercised since it’s been laying on the floor of the
mouth and doesn’t have the stamina to rest on the palate all day
or all night. Orofacial myofunctional exercises are important at
this stage. These exercises are essential for those receiving a
frenectomy to treat ankylosglossia. In adult cases of life-long
mouth breathing, orthodontics to expand the palate may be necessary
to make room for the tongue.10
Screening for mouth breathing is easy and takes very little
time with the five-step process. The first three steps are easily
answered with observation and questions to the patient. First,
are the lips together, second, can the person breathe through
their nose and third, where is their tongue at rest? The next two
steps require measurement, first the mouth opening and second
the mouth open with the tongue touching the roof of the
mouth. Most people can open the width of three fingers stacked
vertically. With the tongue on the roof of the mouth, they
should be able to open at least two fingers. Less than that and
there is a problem with the lingual frenum, either ankyglossia or
a tight lingual frenum. The last screening step is to measure the
maxillary cross arch distance between the bicuspids. The distance
should be equal to a standard cotton roll.
The earlier mouth breathing is recognized and converted to
nose breathing, the fewer and less serious the problems will be.
Dental hygienists are the ideal dental professionals to screen for
mouth breathing. Despite the fact that people are more often
asked to open their mouths in a dental office, checking for a
closed mouth is essential to oral and general health.
- Souki, B., Pimenta, G., et al: Prevalence of malocclusion among mouth breathing in children: do expectations
meet reality? Int J Pediatr Otorhinolaryngol 73(5):767-773, 2009.
- Malhorta, S., Pandey, R., et al: The effect of mouth breathing on dentofacial morphology of growing child.
J Indian Soc Pedo Prev Dent 30(1):27-31, 2012.
- Harvold, E., Tomer, B., Vargervik, K., Chierici, G.: Primate experiments on oral respiration. Am J
Orthod 79(4):359-372, 1981.
- Juliano, M., Machado, M., et al: Polysomnographic findings are associated with cephalometric measurements
in mouth-breathing children. J Clin Sleep Med 15(5):554-561, 2009.
- Bresolin, N., Shapiro, P., et al. Mouth breathing in allergic children: it’s relationship to dentofacial development.
Am J Orthod 83 (4):334-340, 1983.
- Olivi, G., Signore, A., Olivi, M., Genovese, M.: Lingual frenectomy: functional evaluation and new
therapeutical approach. Eur J Paediatr Dent 13: 101-106, 2012.
- Fiorotti, R., Bertolini, M, Nicola, J., Nicola, E.: Early lingual frenectomy assisted by CO2 laser helps
prevention and treatment of functional alterations caused by ankyloglossia. Int J Orofacial Myology 30:
- Suter, V., Bornstein, M.: Ankyloglossia: facts and myths in diagnosis and treatment. J Perio 80: 1204-
- Cartwright, R., et al. Snoring Control Using a New Tongue-Retaining Oral Appliance” Journal of Sleep,
Vol. 27, 2004, 412.
- Singh, G., Lipka, G.: Case Report: introducing the wireframe DNA appliance. J Am Acad Gnathol
Ortho 26(4): 8-11, 2009.
- Bonuck, K., Freeman, K., Chervin, R., Xu, L.: Sleep-disordered breathing in a population-based cohort:
behavioral outcomes at 4 and 7 years. Pediatrics 129(4): e857-e865, 2012.