-B- PHYSIOLOGY of DEGLUTITION
When bolus is prepared, it’s collected on the tongue and directed toward isthmus of the gullet, to be swallowed. The teeth come early in maximum intercuspation contacts, to allow jaw stabilization. The mandible become then a support to realize first elevation of hyoid bone and then lowering (muscles elevator and depressor), and triggering of the transfer of the bolus, toward the stomach, by a peristaltic movement.
For new borns, without teeth, and old edentulous patients, the tongue placed between the arcades, allows to wedge swallowing.
Fig. B2: During the phases, buccal and pharingeal, of deglutition, the mandible remains fixed with the teeth maintained in Maximum Intercuspation Occlusion (Pameijer et al. 1970) by the bilateral recruitment of muscles masseter, temporal and pterygoid medial. It become then a support for muscle mylo-hyoid, whose contraction provokes the climbing of hyoid bone and contributes to that of the tongue. For 97% to 98% of the patients, MIO is physiologically placed ahead the Centric Relation (Posselt 1968, Joerger 2005).
The first buccal phase (Fig. B2) is the results in the combined action of mandibular elevator muscles, of intrinsic-extrinsec muscles of the tongue, facial and those of oropharynx (Menekrati 1998,Le Gall & Lauret 2008). When the buccal preparation is finished, the tip of the tongue is leaned against palate, in anterior position, and the bolus is collected on its dorsum and then directed toward isthmus of gullet to be swallowed.
Thanks to the early MIO contacts, obtained by the action of elevator muscles, the mandible becomes a support point, that allows to the muscles supra-hyoid and infra-hyoid, to raise and lower the hyoid bone. This action produces a peristaltic wave, moving the bolus towards the stomach. These occlusal contacts in maximum intercuspation (MIO) are performed, in neuromuscular balance, more than one thousand times a day (Lear et al.,1965).
In the child mouth, permanent functional stimulations resulting from numerous deglutitions, allow to progressively install during growth, of a direct anatomic correlation, between: MIO in neuro-muscular equilibrium, and articular relations during swallowing.
The part and the posture of the tongue are essential for a physiologic deglutition(Fontenelle et Woda 1993, Bonnet 1992, Bonnet 1993, Fournier 1991). In child, her mispositioning is constantly associated to dysmorphisms and disruptions of growth . The reeducation of oral functions and the early repositioning of the tongue, allow to prevent the pathological consequences, by a early reorientation of the growth (Fournier 1991, Deffez et al 1995).
A keystone of reeducation is to place at rest, the tongue in a centered position and upper ,with her tip in contact the anterior part of the palate, against the medial papilla, just backward the upper incisors. And to make then several deglutitions (Fontenelle et Woda 1993, Fournier 1991). Because it’ s the tongue natural position at the beginning of the first phase of swallowing, that allows optimal placement of the muscles recruited and a physiologic deglutition, following.
In these conditions, in an adult mouth, the functional contacts during swallowing and Maximum Intercuspation are the same. These data are individual and can’t be standardized and applied, when based on average or theoretical values.
According those data, we will describe a clinical protocol ,self-determined by the patient, more physiological and more reliable, allowing to adjust the MI in accordance to a well balanced swallowing, without performing any manipulations (Le Gall et al., 2010).
The axiographic data (Joerger 2005; Joerger et al., 2012) have shown that, occlusion deglutition is not harmonized with the articular Centric Relation (CR) – whatever the operator, the type and the strength of manipulation – but, that mandible finds a well balanced position, in a more or less anterior situation to the CR, according to each patient’s resilience capacity. We may us wonder about the relevance of manipulation technic, thesis aiming at finding the reference functional position for each patient, in a posterior CR. (Romerovski 2006).To check or find, the natural swallowing position of the mandible in an adult, two complementary procedures, already used separately since numerous years, are going to be associated in a simultaneous way (Le Gall et al., 2010):
– The technical of deprogramming , in patients with teeth, using a specific maxillary anterior jig, described by Le Guern in 1987, and used in occlusal procedures in adult, since more than 25 years, but with a procedure and design, gradually modified.
– The tongue position in the oral cavity, during deglutition, already used to reeducate children’s swallowing, in dental orthopedics.
Mandible Posture of swallowing (Le Gall et Lauret 2011)
The starting point for all of the mandibular movements is the Rest Position of the Patient. It’s a Physiologic Posture of reference, steady and repetitive,when there is not disruption of the neuromuscular tract. The closure path associated, leads to the Maximum Interdental Occlusion (MIO), that is responsible for the mandibular stabilization during swallowing (Pameijer et al., 1970, Fontenelle et Woda,1993), and for the posture of the lower third of the face. In addition, all of the chewing cycles pass through MIO.
If MIO is unstable or disrupted by an occlusal prematurity, a central adaptive mechanism is activates. The mandible shifts slightly toward a more stable position. The rest position is modified, in according with the new adaptive MIO. In this occlusion, the Rest Position of the Patient is shifted and the muscles are not in equilibrium. The postural muscle tone is not at a minimum, and the muscles are not in a symmetric neuromuscular equilibrium.
That adaptive posture can result from others causes than occlusal interferences, as by instance: teeth gradually weared and bio-corrosion, lesions articular and dental, accidental trauma, contracture of muscles, related to behavior, psychosomatic, or to central disorders(like bruxism),or to body inbalanced posture, and abnormalities in posture and dynamic of the tongue.
A simple occlusal analysis do not allows to detect these possibly mandibular misplacement, because the patient spontaneously closes in his shifted adaptive occlusion.
Several methods, of unequal relevance, have been proposed, to try again to find the physiologic rest position.
We prefer to use an anterior deprogramming device, placed on maxillary central incisors, with only a contact median opposite. It allows to suppress all of the proprioceptive information from periodontal mechanoreceptors, (Wesberg et al 1983), excepted on the jig. (objective are different from the initial jig by Lucia, 1983).Wearing this jig (Le Guern 1987) several minutes, allows to deprogram, the precise avoidances and the adaptive engrams from the CNS (Central Nervous system) related to the precise cortical representation of dental anatomy, and occlusal contacts and guidances (Netter,1991).
The cancellation of the avoiding mechanisms, and the relaxing of muscles, consecutive to the placing of the jig, allow the repositioning of the mandible in relationship with the skull, and allow then a closure, directly on the premature contact. Then it can be corrected.
The mandible displacements are provoked by the reciprocal and coordinated action of masticatory, hyoid and genioglossus muscles. They are collectively recruited in a selective way, depending on the oral functions, or voluntary movements and para-functions.
The movements of the tongue, depend on similar recruitments excepted for the tip that can be moved by the only will.
The role and effect of the tongue displacements, on the posture of the mandible, has been neglected in adult occlusion, and had not been taken into account by the jig protocol proposed by Jean Yves Le Guern.
Fig. B3: Tests to do with your own tongue, so as to well understand the repercussion of the tongue posture on the mandible positioning.
Fig. B4: The rest position and the Maximum Intercuspal Occlusion are linked together by the closure path . When the position of MIO is modified, consequently the rest position and the path of closure change also. It is the consequence of a mandible displacement resulting from traumatic or pathologic processes, or from dental wear, or bruxism and from inappropriate manipulations…
The mandible follows the movement of the tongue, in the same orientation.
To understand well the dependence of the mandible to the tongue displacements, some simple tests of placement can be easily realized.
If you make a swallowing test with the tip of the tongue leaned against the anterior median portion of palate, the closure is done directly in Maximum Interdental Occlusion. If the tongue is stuck on the teeth of a maxilla side, on right or left, the mandible moves to the side where the tongue is placed. During a swallowing test, there are only unilateral contacts on the side where the tongue is placed. In the same way, if the tip of the tongue is turned over against the soft palate, during a closure test, the mandible moves back and the contacts reported first, are situated at the back of the MIO. They are followed by a symmetric sliding (postero-anterior) of the mandible towards MIO. This is a constant and can be verified in the three planes of space.
One can deduce that inter-maxilla relationship checking , with a bad posture of the tongue, will be more or less wrong, according to the proximity or the distance of the optimum position, of her tongue.
The jig alone don’t take into account lingual posture.
The lingual posture alone do not allow the cancellation of adaptive engrams.
It’s why taking into account simultaneously protocols of anterior jig and lingual posture is complementary and necessary to find the physiologic posture of the jaw and check the balance of Maximum Intercuspation Contacts during deglutition.
Fig. B5: The keys to find the natural position of the mandible swallowing, is to associate a procedure for the cancellation of adaptive engrams , and the placement of the tongue in swallowing posture.
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