Neuromuscular Behavior (NMB)
1. INTRODUCTION
Young bones during their growth are subject to the influence of the musculature divided into antagonistic groups whose balance ensures both at rest and in function the morphology of the skeleton, the imbalance of this musculature results in numerous dento-facial disharmonies.
2. ANATOMICAL REMINDER OF THE ORAL CAVITY
2.1. Limits of the oral cavity
Below : the floor of the mouth formed by the mylohyoid muscle, the strap on which the tongue rests.
At the top : the palatine vault which is extended posteriorly by the soft palate or velum palate, the anterior one third of which is immobile; the mobile two posterior thirds play an important role in the functions of swallowing and phonation.
Laterally : made up of a mass of muscles: small and large zygomaticus, canine muscle, square of the chin, buccinator, risorius, masseter, temporalis, external pterygoid.
In front : the lips which are a musculo-membranous fold presenting an external or cutaneous face and an internal or mucous face; the muscular part includes the constrictor muscles (orbicularis oris) and dilators (canine, triangular of the lips) .
2.2. The Oral Cavity
2.2.1. Language
It is a muscle mass attached to the osteofibrous skeleton, a mass made up of 8 pairs of muscles plus an odd muscle.
2.2.2. Dental arches
We distinguish: the teeth, the maxillary bone (basilar bone, alveolar bone).
The arch develops between two antagonistic muscle masses;
| CHATEAU dental corridor |
Labio-jugual strap
Language
The general shape of the arches results from a balanced position of this musculature (dependent on neuro-muscular behavior) both at rest and in function .
3. NEUROMUSCULAR BALANCE
The balance of the orofacial sphere is regulated at the level of the vertical and horizontal antagonist muscle chains; the muscular activity that results takes place both in the resting position and during the various orofacial functions.
3.1. Muscle balance at rest
The muscular activity that accompanies it is low in intensity but more or less permanent in duration.
Example : the mandibular rest position must correspond to a muscular balance at the level of the lips, cheeks and tongue, this balance is conditioned by 3 elements which are at the origin of the intrinsic behavior:
- Muscle tone
- The bone base ratio
- Muscle specific character
3.1.1. Muscle tone
According to CAUHEPE it has two meanings:
At rest : this is the state of minimum lasting contraction, to which any muscle in the physiological state of apparent rest is subjected. In this case, muscular activity does not generate movement or displacement, it experiences little fatigue and consumes very little energy.
In function : Tone represents the force deployed by a muscle during the usual function it performs.
3.1.2. The resting position of the mandible
Characterized by:
- Absence of mandibular movement with apparent condition of the masticatory muscles (elevators + depressors)
- Considered as a state of balance between the different forces acting on the mandible.
3.1.3. Lip resting position
- The interlabial cleft or line is normally located 2 mm above the edge of the incisal group when the arches are half-open.
- In occlusion the lips are joined (Stomion) without contraction effort and without participation of the peripheral musculature.
3.1.4. Cheek resting position
Normally the inner face of the cheeks is located a few mm from the vestibular faces of the premolars and molars. In some patients, there is sometimes interposition at this level.
3.1.5. Tongue resting position
It should occupy the entire oral cavity, flush with the premolar joint space and its back following the palatine vault.
The tip of the tongue should be located at the level of the retro-incisive papilla.
3.2. Neuromuscular balance in function
3.2.1. Chewing
Complex act in which food is crushed.
RIX : “a set of muscles which allows the food bolus to be guided and brought precisely into the position where the teeth grind it.”
It precedes swallowing, it comes into play with the eruption of the first temporary incisors, then develops with the phenomena of teething and the transition from liquid or soft food to solid food.
Chewing cycles are the result of the successive and coordinated activity of the masticatory muscles, lips, cheeks and tongue acting to direct the food bolus between the teeth and avoid biting of the soft tissues,
Chewing: it is an opening and closing movement with anteroposterior and lateral displacement, therefore coordination of all the masticatory muscles.
3.2.2. Swallowing
It is the act by which the food bolus is propelled from the mouth to the stomach, it follows chewing.
It occurs 500 to 1200 times a day and lasts one second.
Swallowing requires to be done:
- Stopping breathing.
- The bringing together of the lips.
- The soft palate rises, the epiglottis lowers.
- The esophageal sphincter opens and then closes.
Normal swallowing occurs in three stages:
- Oral time, only voluntarily controllable.
- Pharyngeal time.
- Esophageal time.
Description of oral time : there are 3 types of swallowing:
Infant swallowing : sucking swallowing, it is characterized by:
- Interposition of the tongue between the edentulous arches.
- Tongue thrust
- Exaggerated contraction of the orbicularis oris of the lips and cheeks.
Infantile swallowing : during this:
Arcades are separated.
- The tongue does not apply to the palate, but is interposed between the arches , coming into contact with the cheeks and lips.
- The latter contract strongly to close the oral cavity and oppose the pressure of the tongue.
- The mylohyoid in turn contracts, compressing the tongue upwards and backwards and directing food toward the pharynx.
- Sometimes the contractions of the orbicularis are accompanied by those of the buccinator and the mimic muscles.
Infant swallowing is considered normal until the age of 2 to 4 years and progresses to adult swallowing around the age of 6 years.
Adult swallowing
It must be done:
- Lips together.
- Occlusion in centric relation.
- The back of the tongue in contact with the palatine vault, it hollows out into an anteroposterior groove.
- The tip of the tongue rests on the retro-incisive papilla.
- Contraction first of the temporal, then the masseter, then the external pterygoid and finally the mylohyoid.
- There is no concomitant contraction of the orbicularis oris and cheeks.
If one of these parking meters does not exist during the course of adult swallowing, we speak of; atypical swallowing , when it occurs it is accompanied by:
- Parasitic contraction of facial muscles.
- Lingual interposition.
- Suction of the lower lip,
Consequences of atypical swallowing
- Lingual interposition can result in: an anterior open bite bite if the interposition is anterior or a lateral open bite if the interposition is lateral plus an endo-alveolus
- Tongue thrust causes pro-alveolus.
3.2.3. Breathing
It allows an exchange of oxygen and carbon dioxide between the body and the surrounding environment.
During this, there is no intervention of the orofacial muscles which are at rest and in normal anatomical conditions,
The respiratory system includes:
- Rib cage and diaphragm.
- The lungs.
- The respiratory tract.
Normally inspiration and expiration are purely nasal , during the pharyngeal phase the soft palate comes into contact by its lower edge with the posterior slope of the tongue creating a posterior lock: nasal breathing
In the event of deficient posterior locking or a mechanical obstacle, mouth breathing sets in (hypertrophic adenoids, tonsils).
Consequences of mouth breathing
It may be a supplementary function to nasal breathing.
– Anterior gap è Average position of the tongue
– Mandibular progression
– Mandibular prognathism è Low position of the tongue
– Maxillary brachygnathia + maxillary retrognathia
– Dento-maxillary disharmony.
3.2.4. Phonation
Speech represents an essential act of human life ; it is what allows communication between individuals reacting in social life.
It involves the respiratory system, the lung supplied by the breath which passes through the laryngeal constriction where the sound is born.
It involves the digestive system which, through the functional mobility of the tongue and the variability of the shape of the mouth , will modulate the underlying expiratory sound production.
It is the consonants that will be important because their formation is conditioned by the muscular activity of the tongue, the veil and the lips and also by the musculature of the balance of the mandible which regulates the height of the oral cavity.
1. Linguopalatal anteriors: T – D – N – M
- T- D: result from the sudden opening of the oral canal, the tip of the tongue rests on the retro-incisive papilla.
- N – M : result from the closure of the oral canal , the tongue is applied in the same way as the T and D, the laryngeal sound flows through the nasal cavities.
2. Lateral linguo-palatals: C – H – J
The tongue rests with 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, the lips are projected forward.
3. Lower linguo-palatal: S – Z
The tip of the tongue rests on the lingual surface of the lower incisors and the lateral edges of its predorsal part on the edges of the palate at the level of the premolars.
It should be noted that in no case does the tongue rest on the upper incisors or come between the arches.
4. Brain engramming
All the motor behaviors reproducing an individual’s behavior are the result of their own experience, during early childhood (learning relationships with the external environment, maturation of functions).
The nerve impulses from the proprioceptive receptors are used to carry out the cerebral “wiring” necessary for the execution of the functions, this is what we call cerebral engrams . The reinforcement and fixation of the engram are linked to the repetition of the movements of the function or gesture, this repetition allows the gradual acquisition of an automatism, this engramming of the different functions is not really completed until around 10 years old, at this time, all the circuits necessary for the accomplishment of the oro-facial sphere are put in place.
5. Conclusion
Disruptions in the normal course of these different functions may have a more or less marked effect on the development of the jaws, the face and the position of the teeth.