Mastication : Classical Concepts

– C- USUAL CONCEPTS  –  EVOLUTION of OCCLUSION

fonct canine

 

 

Fig. C24: Usual concepts:
Intermaxlllar relationship and occlusion: In manipulated CR
Dynamic balancing from centric occlusion: In protrusion, and cuspid protection in centrifugal movement (C24), without rear contacts.
Posterior teeth? Only contacts in static occlusion, with tripodiques contacts between the molars.

The techniques of occlusal checking and adjustment, proposed by the gnathologic school, are based on the achievement of a canine protection during lateral movement, performed from a maximum interdental occlusion (M.I.O.) in centric relation (C.R.). This movement goes in the opposite orientation of the chewing cycles kinetics, where posterior teeth get closer up to touch under the effect of elevator muscles.

During protection of a canine lateral movemen, performed from a maximum interdental occlusion (M.I.O.) in centric relation (C.R.). This movement goes in the opposite orientation of the chewing cycles kinetics, where posterior teeth get closer up to touch, under the effect of elevator muscles.
Kinetics and muscular recruitment compared analysis (Fig. C3, C4) show that lateral movement, allows to take in consideration only a reduced share of the functional envelope and in reverse orientation.
In the usual procedures, chewing is not taken into account. It is thus never checked nor balanced. It is very easy to observe and understand that malocclusions and functional incoordination of the guides are frequently forgotten on the occlusal faces of the posterior teeth, and the consequences could never be assessed by the traditional techniques.
Depending of the occlusal anatomy and relationship, the difference between lateral movement and chewing function is more significant in young adults, with all of their guiding potential.
The optimum characteristics of human teeth are progressively lost by wearing, without any possibility of regeneration, with for consequence, a more or less fast flattening of occlusal anatomy, resulting in adaptive ways of functioning. They can be: group function balanced occlusion, with-non working contacts or utterly flat, whose characteristics are too diverse to be modeled, especially with only lateral movements simulation.

For instance, taking as a reference a total group function in laterality, where the contacts are placed on the same occlusal slopes either in laterality or cycle-in: they are not in the same orientation and above all cycle-out slopes are completely neglected.
The periodontal sensory inputs have a very acute discriminating ability. If a simplified, approximate and incomplete model is only used, the adaptive and avoidance ability of the CNS will go to limit the functional kinetics to adaptive cycles restricting chewing function efficiency and responsible for strain and imbalance of the recruited muscles.

Fig. C25 a,b Biocorrosion by soda (phosphoric acid); c,d biocorrosion by wine;  e anterior wear with bilateral lost of lower molars; f anterior bruxism; g anterior bruxism on too hard ceramometallic crowns...

Main consequences of these clinical observations are: the lost of occlusion, the lost of vertical dimension, the mandible in protrusion or misplacement, the frontal orientation of the cycles and/or various limited breadth, the lost of functional efficiency, Muscles strain, TMJ disorders…

These clinical situations result of the random lost specificities of the initial functioning model. They can’t be reliable references to generalize for occlusal rebuilding.

How to restore occlusion, and manducatory tract in these so miscellaneous clinical situations?

It’s the initial functioning model that must become the reference to rebuild it, with an adaptation to the present local conditions and taking into account the only remaining informations of this initial model, like the dynamic memory of occlusal faces stored in the TMJ anatomy, during the growth.

Some rebuilding protocols, like the lost of vertical dimension, partially-have yet be described. The other clinical procedures of rebuilding will be described in the following chapters.

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