Occlusal equilibration
Introduction
The balance of total prostheses involves a harmonious distribution of occlusal loads in centric and eccentric occlusion. This occlusal harmony is not due to occlusal equilibration alone, but is the result of all the sessions of prosthetic treatment.
According to LEJOYEUX: “equilibration constitutes the last stage of a prosthetic design and construction, it is intended to ensure in centric relation and during all other occlusions a harmonious and lasting distribution of the occlusal load, on all the supporting tissues and their bone infrastructure”
- Definition
Occlusal equilibration corresponds to the set of technical and therapeutic means intended to promote bio-organic integration, to restore the different physiological functions, but also to preserve the integrity of the remaining tissues.
Indeed, occlusal equilibration directly addresses the occlusal surfaces of the prosthetic teeth, also contributing, thanks to the established balance, to the integration of the prosthesis within the masticatory apparatus. But indirectly, it addresses the mucosal and bony support tissues of the support surfaces of the prosthesis, as well as the muscular and articular tissues by regulating the masticatory function.
- Justification:
Even if during the functional test the occlusal contacts were optimal, equilibration is imperative for the following reasons:
- Distortions during polymerization especially if the temperature rise or cooling was sudden
- The articulator, even semi-adaptable, is never able to reproduce the entirety of masticatory physiology.
- Limitations of balancing grinding:
Grinding is in no way capable of correcting an error in the recording of the occlusion or during assembly, otherwise the occlusal relief would be removed, thus reducing masticatory efficiency.
- Material
For occlusal corrections of porcelain teeth, the material used consists of diamond tips of different shapes and granulations, green tips and Arkansas tips, rubber grinding wheels for polishing ceramic.
The markers required are fine articulating papers or dental floss, carried by Miller clamps.
For resin teeth, the correction and marking materials are identical; only the polishing systems differ, which must be adapted to the material of the tooth.
- Timeline of Occlusal Equilibration:
Lejoyeux chronologically distinguishes three equilibrations:
- Immediate balancing
- Mediate balancing
- And secondary balances
Occlusal equilibration
- Immediate balancing:
The balancing grindings are first carried out on an articulator, then in the mouth.
The upper model is placed in the articulator either using the mounting key, or, if this has not been done before polymerization, the hinge axis will be located and transferred.
The centric relation is recorded using a Tench articulation. The condylar slopes are arbitrarily programmed in a symmetrical manner.
Coronoplasty of artificial teeth:
- Law 1: Flat surfaces do not exist and cannot exist without creating an intercuspal blockage in centric occlusion and without causing horizontal or oblique components during all eccentric occlusions.
- Law 2: In the sagittal plane, all active cusps must be located in line with an embrasure or an intercuspal groove.
Elimination of premature contacts in centric relation
A red hinged sheet metal interposed between the two arches allows premature contacts to be located in centric relation. Four laws govern equilibration in centric relation:
- Law 3: The active cusps to be preserved are the upper palatal cusps and the lower vestibular cusps. They must have a spheroidal relief and never be blocked at the bottom of a fossa or an intercuspal groove.
- Law 4: The secondary value cusps that can be modified are the upper vestibular cusps and the lower lingual cusps playing no role in centric occlusion.
- Law 5: A necessary and sufficient generalized contact must exist between all the upper active cusps and the internal slopes of the lower intercuspal groove.
- Law 6: Any active cusp responsible for premature contact will only be reduced when during a diduction movement it hinders bicuspid contact on the opposite side. Otherwise, it is the fossa that will be deepened.
Other interocclusal disharmonies may exist:
- An unnoticed anterior slippage: grinding will be carried out at the expense of the upper mesial and lower distal cusp slopes MS-DI
- a lateral slip: if it is significant, it is advisable to reassemble the entire lower arch.
- Law 7: When the lateral slip is insignificant, it will be appropriate to widen the upper intercuspal groove on the side towards which the slip exists at the expense of the internal slopes of the secondary cusps and the lower groove on the opposite side.
Occlusal equilibration
- Mediate equilibrations
- Definition :
We call mediate equilibrations all interocclusal corrections that must occur between the immediate equilibration carried out on the day of insertion and the final secondary equilibration, necessarily occurring at the optimal moment when the prosthesis has completed its organic and psychological integration.
- Objective
- Gradually correct occluso-articular imbalances that may appear during the adaptation period.
- Technical
During the visit on the 2nd day :
- The patient is either satisfied: the supporting tissues are examined. The patient will be reviewed as soon as he feels pain or prosthetic instability.
- The patient complains of pain or instability: balancing will be carried out as on the day of insertion (transfer to articulator and elimination of prematurities.
- Secondary balancing
It can be undertaken when comfort is optimal, the patient is able to perform pure condylar rotation alone in the terminal axial position, and the TMJ examinations show a physiological and symmetrical position of the condyles in their glenoid cavities.
- Definition
Secondary equilibration is the term used to describe all the manipulations carried out in the office and in the laboratory, occurring at the end of the more or less long adaptation period, and intended to ensure a harmonious distribution of the occlusal load during all centric and eccentric occlusions.
- Technique:
More precise than those implemented for immediate and mediate equilibrations:
- Graphical localization and transfer of the hinge axis
- Recording and transfer of centric relation and condylar trajectories
- Coronoplasty and removal of premature contacts in RC
- Law 1: at the final stage of secondary equilibration, the necessary overhang of the secondary value cusps of the premolars and molars must be accentuated or recreated, at the expense of the external slopes of the active cusps, while imperatively respecting the contact points ensuring occlusion in RC
The second coronoplasty must obey the second law
- Law 2: Mandibular retraction is always accompanied by premature contacts between the antagonistic cusp slopes of retrusion. Correction must be carried out selectively at the expense of the mesial slopes of the upper cusps and the distal slopes of the lower cusps of secondary value. MS-DI
- Establishment of a permanent balanced harmonious sliding between the two arches during the first millimeters of propulsion. Grinding will be done at the expense of the upper distal and lower mesial slopes of the secondary cusps.
- Elimination of any cuspal interference during right and left lateralities, it must obey the following laws:
- Law 1: Grinding must always be carried out transversely on the working side and diagonally on the non-working side. It always preserves the RC contact points.
- Law 2: Grinding must respect occlusal morphology .
On the working side, it will preferably be carried out at the expense of the internal slopes of the upper vestibular and lower lingual secondary cusps.
On the non-working side: it is carried out at the expense of the mesial internal slopes of the lower active cusps or distal internal slopes of the upper active cusps, i.e. MIVI-DILS, respecting the Wilson curve
- Lapping with an abrasive paste
Occlusal equilibration
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