ORO-FACIAL FUNCTIONS

The orofacial sphere constitutes the seat of different vital and social functions whose development influences the balance and development of the stomatognathic apparatus.

Among them, swallowing, ventilation, chewing and phonation which are coordinated functions that appear in intrauterine life.

It is therefore important in dentofacial orthopedics to carry out a functional study because any functional anomaly encountered is the cause of numerous bone and alveolo-dental dysmorphoses, inevitably having repercussions on the development of the facial mass and consequently influencing the appearance and aesthetics of our patients.

1. Swallowing  

Swallowing is the act by which the contents of the mouth are propelled from the mouth to the stomach. It follows chewing. It occurs 500 to 1200 times/day and lasts 1 second. To do this, it requires:

• stopping breathing 
• the rapprochement of the lips 
• The soft palate rises
• the epiglottis lowers 
• The esophageal sphincter opens and then closes  

It is the first coordinated function that appears in intrauterine life. 

 Depending on the position of the bolus, there are 3 stages of swallowing: oral, pharyngeal and esophageal. Only the oral stage interests us, it is clearly distinguished from the other stages because swallowing can be stopped voluntarily at any time during this stage and therefore can be modified. 

• Oral time: During this time:

• The orbicularis oris closes
• The food bolus is located between the tongue and the front part of the palate.
• All movement is stopped while the posterior temporal stabilizes the mandible.
• The pharyngeal and esophageal times: are involuntary (reflexes) there is a 

• Lowering of the epiglottis
• Closure of the tracheal glottis
• Opening of the esophageal sphincter
• A peristaltic or pharyngeal wave
• The descent of the food bolus
• Esophageal peristaltic wave with closure of the esophageal orifice behind the passage of the bolus.

2. The different types of swallowing

Three main types of swallowing have been identified:

• Fetal swallowing
• Infant (newborn) sucking and swallowing
• The swallowing “arch in contact” of the toothed child will also be that of the adult and this by “substitution”.

2. Ventilation  

It is the set of mechanisms which allows the exchange of gases between the external environment and the internal environment of living organisms.

2.  Anatomical reminder of the respiratory system:

The respiratory system is anatomically composed of the following organs:

• upper airway (extrathoracic)

• nose and nasal passages
• mouth
• pharynx (aerodigestive crossroads)
• larynx (throat)
• lower airway ( intrathoracic ) 

• extra pulmonary: trachea 
• intrapulmonary  :
  • bronchi 
  • Bronchioles 
  • pulmonary alveoli

• The nasal passages fulfill two essential roles, associated but distinct: They carry respiratory air to the nasopharynx, and they convey odorous particles to the olfactory organ.
• The play of these different parts of the respiratory system is dependent on the central nervous system (CNS). 

3. Physiology of nasal breathing:

Normal breathing is done by inspiration and expiration which are purely nasal. During the pharyngeal phase, the velum comes into contact by its lower edge with the posterior slope of the tongue, creating a posterior lock. 

Normally, during physiological breathing, the orofacial muscles never intervene, they are at rest and in normal anatomical conditions

4. VENTILATION MECHANISM

Air reaches the lungs through the upper airways. It enters through the nostrils , where it will be filtered, warmed and humidified. Then it will reach the pharynx which it follows to the larynx.

• The nasal valves will control the airflow 
• The vestibule which follows the nostril orifice will slow down the air flow.

• The vestibulonasal slit (posterior limit of the vestibule), it ensures the regulation of the quantity of air inspired.
•  the inspired air collides with the different turbinates causing the creation of vortices, these vortices will stimulate the development of the maxillary sinuses.
• A small part of this current reaches the cribriform plate of the ethmoid where it is used for olfaction
• Then the airflow passes through the choanae, reaches the ceiling of the cavum, then towards the trachea

3. Chewing 

Mastication is the first step of digestion in most mammals, it is accomplished through rhythmic mandibular movements in the three spatial directions that allow the fragmentation and crushing of food between the dental arches associated with coordinated movements of the tongue, cheeks and lips that ensure the transport, formation and control of the food bolus.

• According to Rix, it is a play of all the muscles which allows the food bolus to be guided and brought precisely into the position where the teeth grind it.

3.1. MATURATION OF MASTICATION

True chewing develops after the development of temporary teeth during the establishment of the first occlusal keys, with periodontal afferents playing an essential role in this learning.

This maturation is rapid and the masticatory type is stable and well coordinated around 4 or 5 years for some authors or during the occlusion of the first molars.

2. TYPES OF CHEWING

Depending on the position of the food between the arches, three modes of chewing are distinguished:

• unilateral alternating chewing, the most frequent and most physiological: the food is crushed on one side only (working side) but with a more or less regular alternation depending on the cycles;
• strict or dominant unilateral chewing: the working side is almost always the same;
• bilateral chewing: the food is crushed simultaneously on both sides.

3. Physiology of chewing:

The masticatory cycle is defined by the movement of the incisive point (PII); During chewing, the mandible performs rhythmic movements in the 3 planes of space within the limit positions. and each time the lower PII returns to its starting position, the mandible performs a masticatory cycle. The cycles follow one another until the preparation of the food bolus.

The shape of the masticatory cycles varies from one individual to another and in the same subject from one cycle to another because the food can be crushed depending on the masticatory mode:

• On one side only, with regular alternation from left to right on the working side “alternating unilateral chewing” which is more frequent (80% of cases) according to POSSELT. 
• On one side, always the same “unilateral chewing” (12%). 
• Simultaneously on both sides “bilateral chewing” (8%).

4. phonation 

Phonation is a function for the purpose of communication. It requires the participation of several anatomical units, allowing first the inspiration, then the expiration of air more or less modulated, resulting in the formation of phonemes. It is the muscles of the oral-pharyngeal cavity that allow this expired air to be transformed into audible and understandable sounds.

It is a very complex phenomenon that involves the lungs , the pharyngolarynx , the supraglottic cavities , the nasal cavities and the oral cavity producing vowels and consonants.

2. Mechanism of phonation 

Phonation involves a plurality of physiological mechanisms successively affecting the larynx, the acoustic cavities (pharyngeal, buccal and nasal); it involves:

• The respiratory system  : The lung provides the breath which travels through the laryngeal constriction where the sound is born.
• The digestive system which, through the functional mobility of the tongue and the variability of the shape of the mouth, will shape the underlying expiratory sound production. First, a subglottic air pressure is required, provided by the expiratory muscles; therefore, the muscles not only of the thorax but also of the abdomen and diaphragm are involved; then, rhythmic variations of this air pressure are required at audible frequencies, as it passes through the laryngeal slit. Thus, a primary glottic sound is given birth, this glottic air acquires pharyngo-buccal and nasal qualities through constrictions made in various ways to produce the articulation of the sounds emitted by the larynx. 

Note  :  In singing  : the laryngeal passages predominate.

                             In the spoken voice  : it is the articular behaviors which predominate.

4.1. Vowels 

Vowel formation consists of giving a vocalic character to the laryngeal sound. Classically, vowels are determined by the shape of the opening of the labial cleft, the arches are separated, the tongue resting on the floor, its tip is in contact with the lower incisors without pressure.

3. The consonants 

The formation of consonants is conditioned by the oral effectors mainly by the muscular activity of the tongue, the soft palate, the lips and by the musculature which regulates the position of the mandible. There are several categories of consonants:

• Explosive consonants: This is a sudden opening of the pharyngo-buccal auricle, either in its posterior position or in its anterior region, causing a sort of explosion of expired air. 
• Continuous consonants  : This is a continuous flow of exhaled air slowed down at various levels and in various ways.
• Voiced consonants  : they require a concomitant vibration of the vocal cords for their articulation.

• Voiceless consonants  : they do not require concomitant vibration of the vocal cords for their articulation.
• Nasal consonants  : they result from communication between the nasopharynx and the oropharynx.

NB: During normal phonation, the tongue never comes into contact with the teeth, it always remains inside the cavity.

The anterior linguo-palatals: TDN  

The T and D result from the sudden opening of the oral canal, the tip of the tongue rests on the retro-incisive papilla, the lateral edges against the lateral walls. The D requires pharyngeal vibration, T does not.

The N requires closure of the oral canal, the tongue is applied in an almost identical manner for the T and the D, the pharyngeal sound flows through the nasal cavities.

Lateral linguo-palatals: CH-J

They result from the continuous passage of air through a median canal between the palatine vault and the tongue, the tongue rests by its lateral edges against the lateral walls of the palatine vault with its tip in a posterior position towards the middle part of the vault but not applied against it, J requires a laryngeal vibration.

Linguo-dental: SZ

S and Z result from the passage of air in a median canal between the anterior part of the palatine vault and the lateral edges of the tongue curved into a gutter applied against the lateral walls of the vault, its tip coming to rest against the lower incisors without exerting excessive pressure.

Z requires laryngeal vibration and S does not.

The time for articulation of a phoneme is 1/10 of a second, during which time the perioral muscles exert much less pressure than during swallowing, hence the lesser importance of anomalies in the support of the oral musculature for phonation than for swallowing.

The labio-dental: FV

 The lower lip touches the free edge of the upper incisors without pressure. 

Bilabials: BP

They result from the sudden opening of the labial orifice, not requiring laryngeal vibration for P and requiring it for B. The M actually results from a closure of the labial orifice during which the primary laryngeal sound passes through the nasal fossae.

5. The mimic 

It involves all the skin and lingual muscles in the expression of thought or feeling through gesture, and the play of physiognomy orienting the external facial aspect.

In ODF; It is the mimicry specific to the labio-jugal muscles which is the most important, morphogenetic action of the arches. The shape and the relationships of the alveolo-dental arches are conditioned by the modeling action of the muscles. 

A strong tendency of the alveolar processes to tilt so as to compensate for all or part of the skeletal anomalies.

The balance between the tongue, lips and cheeks is physiological. The direction of growth of the alveolar processes is objectified by the dental axes, which will allow the determination of the different positions.

ORO-FACIAL FUNCTIONS

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ORO-FACIAL FUNCTIONS