Occlusion in joint prosthesis
Compliance with the principle of “centering, wedging, guiding” simply but precisely defines occlusal relationships inducing facilitated mandibular stability (wedging) and globally symmetrical functions (centering) and not locked (guiding).
- Definitions:
- Occlusion:
It is the clash of the dental arches in a static state and during the functioning of the masticatory apparatus.
- Adaptation:
We could say that adaptation is a set of compensatory mechanisms that allow us to assume functions when anatomical conditions are no longer ideal. Disorders that are compensated for can at one point or another lead to symptoms.
The therapy implemented will always aim to bring the patient back into optimal occlusal conditions, in harmony with the articular and muscular components in order to place as little strain as possible on the adaptation mechanisms.
- Functional occlusion:
- centering with, most often, a very slight anteposition in relation to the centric relation, without transverse mandibular deflection (decentering).
Occlusal contacts in centric relation, called premature, are symmetrical, rather on the premolars;
- wedging: the mandible is stabilized by the confrontation of four or five antagonistic multicuspid pairs, well distributed; the stabilization is sagittal (one tooth/two teeth occlusion) and transverse (contact in opposition) (FIG. 2 to 4);
- symmetrical guidance without posterior interference, without anterior locking.
Figures 1 a and b The dental class I ratio is a guarantee of alignment, provided that the ratio is of the one tooth/two teeth type (a), and not one tooth/one tooth (b).
Figure 2 Stability in the frontal plane is linked to the presence of opposing contacts on a vestibular slope and on a lingual slope
Figures 3 a and b Stability in the frontal plane involves the fitting of the large maxillary cusp (mesiolingual of the maxillary first molar) into the large fossa (central of the mandibular first molar) (a), which is impossible if the axis of the maxillary molar is vertical (b).
Figure 4
Occlusal stability involves a double opposition: a transverse opposition (vestibular versus lingual side) and a sagittal opposition (mesial versus distal side)
- Functional malocclusion:
This adaptive occlusal relationship actually corresponds to a malocclusion established most often gradually, well compensated, which will remain generally stable over time, with slight structural anomalies (wear, migrations, recessions) but whose balance can be fragile. The decision for extensive occlusal treatment must be justified by solid arguments.
- Pathogenic malocclusion:
It is a natural or iatrogenic occlusion, presenting anomalies beyond the subject’s adaptation potential (without reduction of its functions) and which can contribute to, trigger or maintain structural or dysfunctional disorders (pathofunction). There are structural damages (teeth, ATM, bones), recurrent neuromuscular disorders. The border between functional malocclusion and pathogenic malocclusion remains individual.
In fact, the essential criterion for the decision for immediate occlusal intervention is not whether the malocclusion is slightly or moderately pathogenic, but whether it can be corrected with simple, effective and stable means .
- Choice of static reference occlusion in joint prosthesis:
Before any prosthetic rehabilitation, the clinician is faced with the choice of this reference position with two possibilities: OIM or centric relation. We choose:
*The patient’s occlusion: this “tooth-dictated” occlusion (fig. 1) is the maximum intercuspation occlusion if it is functional , and the prosthetic treatment must then preserve it (if the fixed reconstruction does not touch the wedging teeth)
This position should be favored in daily clinical practice: easy to materialize and record if it has the characteristics of a physiological reference position
- RC: If the OIM is non-functional and cannot be maintained, another physiological position “dictated by the joints” will then be the centric relation. The prosthetic treatment will then have to create a new OIM, functional in this mandibular position.
The OIM dictates the mandibular position by a maximum of stabilizing and harmoniously distributed contact in a position close to the sagittally centric relation and without transverse differential.
- the DV: the vertical dimension of occlusion is ensured by the alignment of the arches in static occlusion obtained essentially by posterior contacts
- If, after inspection, the DVO proves satisfactory, everything must be done to preserve it during rehabilitation. The preservation and restoration of this DVO involves a phase of making temporary prostheses. Then, when recording the intermaxillary relationship (OIM or ORC), the preservation of the DVO is ensured according to the type of edentulism:
- either by the existence of sufficient dental contacts in OIM;
- either in the absence of sufficient dental contacts, by the conservation of one or more temporary prostheses which act as a stop, associated with the use of a table
occlusal wax recording at the preparation level
- In the presence of a disturbed DVO:
(excessive generalized occlusal abrasions, collapses or loss of posterior wedging, etc.), we hesitate between integrating a prosthesis into the existing occlusal pattern and the overall reconstruction of the abraded dentition.
If rehabilitation of the entire abraded dentition cannot be achieved and only a few prostheses are envisaged, they will then have to be integrated into the patient’s occlusal scheme, and monitoring of the evolution of wear will be established.
In extreme cases and/or those requiring numerous restorations, the overall restoration of occlusal morphologies must be considered. This restoration involves an increase in the DVO which, to be well tolerated, must leave sufficient free space for inocclusion at rest, a
absence of dental contact during phonation and not disrupting the masticatory function. After a 3-month active temporization period (period punctuated by tests), the usual prosthesis can then be made to this new DVO.
- Static recording of occlusion in joint prosthesis:
- Recording materials: criteria:
-Faithful recording of the reference position: position which can be difficult to maintain over a long period
-stabilized on the supports, (prefabricated plates which will support the material).
– Must not oppose any constraint to closing (physiological reflexes)
-So it should not be perceived by the patient
-preservation of deformation details after recording (visco-plastic behavior and low viscosity).
– In the laboratory: precision, reproducibility and resistance. (dimensional stability, surface precision and rigidity). On the other hand, good creep resistance.
Materials meeting these criteria more or less rigorously can be waxes, recording pastes with chemical setting such as eugenate, resins, or silicones crosslinking by addition
Waxes:
-If the coefficient of thermal expansion is high (significant dimensional stability and rigidity), but fragility with risk of fracture during assembly in an articulator.
A low coefficient of thermal expansion (low dimensional stability and rigidity), but less brittle and more pleasant to work with due to their plasticity
-The use of waxes is complex (heating water so that the wax is malleable)
-The working time is important, the setting time in the mouth however can be more or less controlled
– High viscosity
waxes used alone are often to be avoided. On the other hand, they constitute excellent support bases for other waxes reinforced with metal particles such as Aluwax® or for
cements based on zinc oxide eugenol which will provide them with the qualities they lack.
Zinc oxide oeugenol pastes:
- Most often used on a hard wax base such as Moyco® to correct wax deformations.
- Viscoelastic properties: good
-Accuracy: correct (hydrophilic).
-Dimensional stability: exceptional (less than 0.1%)
- Creep resistance is sufficient,
-Fragile behavior
-Working time is sufficient for the operator, and setting time in the mouth is relatively quick (one to three minutes).
-Occlusion recordings made using hard wax plates relined with ZOE have shown their effectiveness.
Thermoplastic materials:
like Kerr Stents®:
- The use of this material is similar to waxes (heating to make it plastic).
Acrylic resins:
Self-polymerizing: Duralay® resin:
-Precision
-Rigidity: good
-Easy to use
- Low dimensional stability
-Fragility
- Long setting time
Silicones:
- very low viscosity (the patient feels almost nothing when closing, which avoids unwanted movements).
-The setting time in the mouth is very fast (from 30 seconds to 1 minute for most silicones)
- Dimensional stability (less than 0.2%)
-Accuracy is very good to within 2μm in general and depending on the manufacturer.
-Rigidity is increased (less fragile which allows easier mounting on an articulator)
- The working time varies around 30 to 45 seconds which is sufficient for the operator.
- Recording techniques:
- sectoral registration: allows the IOM to be registered exclusively
🡪Occlusal bite
This is a simultaneous recording with an elastic material of the static relationships of the preparations with the occlusal anatomy of the antagonist teeth. To be valid, it must present clear perforations (clear contacts) or thinnings (pseudo-contacts).
hemi-arch molding, is molded and allows to obtain the antagonistic hemi-arch.
🡪Vestibular key: only allows repositioning
🡪Occlusal impressions using Triple Tray® sectoral impression trays: to be avoided
🡪 FGP: (functional generated path):
This involves recording the kinematics of the cusp trajectories antagonistic to the preparations with sectoral impressions, and the use of a particular three-branch occluder
- Global registration: These techniques consist of manual repositioning without interposition of material or with a bite registration material.
🡪 Manual repositioning without interposition of material:
It requires two casts with a sufficient number and favorable distribution of intact teeth allowing the casts to be reliably repositioned, thanks to dental contacts, on the
simulator. Only the OIM can be recorded using this technique.
🡪Repositioning with an occlusion registration material: (wax, resin, elastic material, occlusion model, relined or not with a fluid material) allows recording either the OIM or the centric relation.
- In the context of OIM registration, one can use:
- a material placed exclusively on the preparation(s) (occlusal recording table, wax, resin) to record occlusal contact with the opposing teeth, the other unprepared teeth establishing occlusal contacts.
- a material placed on both prepared and unprepared teeth:
In this case, it must present, at the level of the dental contacts, clear perforations or thinning, without deformations;
- an occlusion model, which must have ridges in slight contact with the opposing teeth and also allowing dental contacts to be established on the intact opposing teeth during recording
- In the context of centric relation (CR) recording,
- a fitted wax plate which must never have perforations
- an occlusion model which must have slightly raised rims in order to avoid any dental contact on the intact residual teeth during recording.
- Choice of dynamic occlusal concept: anterior guidance:
-In protrusion:
*Sliding of 6 teeth / 8 teeth
*Extensive anterior contact
*Posterior disocclusion
-In laterotrusion: canine function “gnathologist concept” whose characteristics:
*This concept is indicated whenever the periodontal support of the canine is resistant;
- Laterality is exclusively supported by the canine.
- Contactless non-working
-In laterotrusion: group function:
- This concept is indicated when: the incisal coverage is weak, canine support weakened and the periodontal context requires a good distribution of occlusal forces
*function group on the working side: The mandibular teeth slide laterally on the mesio-internal sides of the maxillary vestibular cusps of the PM, 1st M, and in addition, the palatal surface of the canine.
Sometimes a slippage even working incisors. Absence of contact on the non-working side
- Dynamic occlusal registration in joint prosthesis:
🡪 Recording of previous guidance:
On the incisal table, within a recording material (loaded resin) by simulating the movements through the sliding of the models relative to each other.
🡪 Reproduction:
The reproduction and then the reliable simulation of mandibular movements requires the use of an articulator and cannot be achieved on a simple occluder.
The articulators allow the mobilization of the casts, by guiding the movements within an envelope of movements (propulsion, diduction).
- Conclusion :
The recording of the occlusion depends on: the technique, the materials, but also the impression and the laboratory manipulations.
Occlusion in joint prosthesis
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