Clinical Procedures : Referential Scheme

  -D- REFERENTIAL  SCHEME

Important: The clinical analysis must precede the occlusal analysis on the articulator. It is necessary to remember that the dynamic functioning model is well represented by the patient and not by the mechanical simulator that one animates in the laboratory. It is clear that the lateroclusion movements, usually requested in voluntary execution, have been copied on the kinematics of articulators with fixed hinge axes. This does not allow the approximation of the posterior teeth observed in the mouth during mastication and makes them unfit to reproduce.

Fig. D2: The memory of the first molar anatomy, fossilized in the articular shape during growth, will allow later to rebuilt the lost occlusal anatomy. The neighboring teeth, will be incorporated progressively, to the found again, functional scheme of the first molar, including cuspid, and even anterior teeth, to rehab the half arcade. If necessary, the other half arcade will be rebuilt in the same way.

REFERENTIAL SCHEME and PROTOCOLS  (Le Gall et Lauret, 2002 ; Le Gall et Lauret, 2008, 2011)
Taking chewing function as a reference, requires significant modifications of occlusal approach.
From swallowing M.I.O., dynamic balancing is not limited to balance by subtraction cuspid guided movement laterality and protrusion. Purpose finality is the full rehabilitation of the dental limit envelope, guiding the cycles and antero-posterior incision guidances.
From simulation of functional movements, this aim is generally obtained by clinical built up technics. In case of prosthetic rebuilding, the concept of articulator must be fitted to reproduce functional movements or alternatives technics must be considered.
Evolution of our natural model is wearing and dilapidation. In these conditions, how to rebuilt occlusal surfaces of a patient, when his own anatomical references are lost ?

During the growth, the occlusal anatomy and its functional kinetics have been used as guides in the completion of the shape of the joint, and particularly its transversal size that, from 5-6 years old into adulthood, is multiplied by 2,5 (Nickel 1988). In addition to the genetic determinism, the anatomy and the articular kinetics, depends on the occlusal anatomy of teeth and on the envelope limit of motion enabled, when they are in static or dynamic contacts.
T.M.J. is the only joint in the human body, whose limit of functional envelope is made of a rigid structure: the contact of the teeth in occlusion (Mc Neill, 1993) Fig. D3.

Fig.D3: Occlusal and TMJ anatomy must be paired in an optimal way, to allow the patient to describe the limit of the envelope chewing cycles, in dental contact.

The fact that the axis of dentoalveolar inertia and arcades center of gravity passes through the maxillary and mandibular first molars in the frontal plane, show a balanced relationship of arcades certainly of functional origin (Treil and Casteist, 2000).

When the occlusal anatomy is lost, the memory of this anatomy that is fossilized in the shape of the joint will help us restore by addition the lost occlusal faces. Beginning with the first molar, because the occlusal scheme in the adult, has itself built from this tooth and also, considering his position on the arcade, the most relevant tests of restoration, must be made at this level. When the coordinated functioning of the couple TMJ and 1st molar is restored, it will serve as a reference to gradually restore the occlusal anatomy of all the neightboring teeth, including cuspids, and even anterior teeth. These tests aiming at restoring the wedging and the guidance of the occlusal surfaces are currently carried out with micro or nano composites featuring a wearing modulus similar to the one of natural enamel (Lambrechts et al, 2006). They can be thus considered as permanent restorations. On natural teeth, the addition is very often appropriate, while for fixed restorations, addition and/or subtraction must often be associated.
If occlusal relationship is not in class 1, build-up must be adapted for modify the present occlusion, in order to result in well balanced occlusal guides, harmoniously fitted with the TMJ actual kinetics.

Adjonction

Fig. D4  a: enamel treatment; b:  a compule allows easily to make composite-up; c: a micro brush soaked with adhesive allows  to easily sculpt composite cones; d view of the cones before closure.

Clinical protocols had to be changed when chewing function served as a reference. As molars fuctional occlusal interactions, related to guidance and cycle pattern, had been never before regarded under this angle, it has been necessary to propose a new terminology to describe them, because it don’t existed.
Likewise, as the occlusal anatomy is not self-repairing, and that it evolves progressively toward the lost of its initial characteristics and the destruction of the optimal functioning model, it has been necessary:to propose rebuilding technics to restore the teeth and their functioning ability,
to minimize selective grinding techniques that accelerate the loss of volume of the teeth
It has been also necessary to introduce a new terminology considering negative interferences or malocclusions, that must be balanced by addition, and not by subtraction, on the next teeth. They can concern occlusal support of swallowing as well as mastication guides.
On natural teeth, build-up is privileged.
On prostheses, build-up and alterations can be used, according to the clinical case.
The board below is a summary:

Taking mastication as a reference has needed to change the protocols. As its posterior occlusal interactions, related to guidance and cycle pattern, had never been considered before, under this angle, it has been necessary to propose a new terminology to describe them, because it don’t existed.
Likewise, as occlusal anatomy  is not self-repairing, and that it evolves  progressively toward the lost of its initial characteristics and the destruction of the optimal functioning model, it has been necessary:

  • to propose rebuilding technics to restore the functional capacity, of teeth
  • to reduce at the minimum, selective grinding procedures that worsen it.
  • it has also been necessary to introduce a new terminology considering negative interferences or malocclusions, that must be balanced by adding, without any subtraction on the next teeth. They can concern occlusal supports of swallowing as well as mastication guides.  The board below is a summary:

Fig. D5:   Infracontacts are black spots,   Infraguidances are black arrows,   Overcontacts are red spots,   Overguidances are red arrows

Indications and Clinical Practice of occlusal balancing techniques by Addition and / or Subtraction.

On natural teeth, equilibration by subtraction is prohibited, since it is assimilated to the mutilation of occlusal surfaces whose natural progressive wear is compensated by no regeneration.

The built up must be privileged to reconstruct the lost volumes by increasing the vertical dimension if necessary. With two levels of rehabilitation: 1/Minimal restoration balanced surfaces of cycles-in and cycles-out, 2/Optimal restoration of surfaces and guidance rails of the first molar couples.

Exceptions: retouching of extruded or malpositional teeth is permitted to restore optimal occlusal relationship and Wilson and Spee curves, if their ingression or orthodontic repositioning is impossible. In the presence of flattened occlusal faces, without indication of increase in VDO, the bottom of the grooves of the opposing tooth can be deepened and reprofiled, so that the tips of the cusps of the opposing tooth can be increased and vice versa if necessary . Remember that touching the tips of cusps flatten occlusal anatomy, while deepening the furrows then makes it possible to restore the anatomy opposite by increasing the cusps volume. During the verification of the closure path, a premature contact may occur which causes the mandible to deflect. It may be altered by a careful subtraction, after verifying that the arcade is not in a complete under-contact, which should be corrected by generalized additions.

In the case of fixed prostheses on natural teeth, the principles remain the same but apply with more flexibility, since occlusal retouching is possible and the return to the laboratory allows the necessary additions

When placing prostheses on implants, the initial contacts and guidances must be of very low intensity to allow the stimulation of the bone which triggers its progressive adaptation. The natural wear and tear of neighboring and antagonistic teeth gradually allows the return of well-distributed contacts between all teeth.

Clinical Practice

On the natural teeth, the control of the shape and balance of the envelope limits the chewing cycle, is optimally ensured by the mastication of a very thin colored film which allows the patient to preserve, through the film, the perception of the slightest malocclusions, while the chewing of a thicker food, even chewing gum, does not allow such a fine coordination.

The slightest guiding defect thus perceived, through this very thin film, spontaneously limits the transverse amplitude of the cycle by the activation of mechanisms of articular protection which even reduce it to a simple shear. As soon as the balance of the guidances is restored, in harmony with the ATM kinetics, the patient spontaneously describes the limiting envelope without any training. Then all the cycles with interposed foods will be located inside this envelope, without necessarily reaching its maximum limit.

Attention in implantology there is a great disparity between the discriminative capacities of the patients. Some patients have the same proprioception on the implants and on the natural teeth, but for the majority it is very reduced on the implants. They masticate on the malocclusions because they do not perceive them and the forces transmitted to the bone are then greatly amplified by the immobility of the implants.

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