The prosthetic occlusion plane

The prosthetic occlusion plane

The plan 

Introduction 

1. Definition.
2. Roles: functional and mechanical.
3. Importance of PO orientation.

1. Basic requirements.
2. The five factors of HANAU.
3. Imperatives that the PO orientation must obey.
4.  Search for the position and orientation of the PO
          1- anterior component.
              a- aesthetic vocation.
              b- phonetic vocation.

2- posterior component.
           a- laboratory determination
Orientation of the PO relative to the crests
Orientation of the PO relative to the facial mass
           b- physiological design
Piezographic technique
Paterson technique
           c- anatomical design
– Parallelism of the POP to the Camper plane. 

– Cephalometric search of the position of the PO.

Conclusion.

Introduction :

In PAC, occlusion corresponds to the control of the intensity, direction, and distribution of functional forces exerted on the prosthetic support surface so that the various physiological functions are restored, tissue integrity is maintained, and stabilization and retention of the prosthesis are confirmed.

This general conception of occlusion involves taking into account a static component and a dynamic component.[1]

1. Definitions:

The definitions of the occlusal plane are both numerous and relatively divergent. Indeed, they call upon:

– maxillary references – The occlusal plane passes through the free edge of the maxillary central incisors and the disto-palatal lacuspid of the first molars.

– mandibular references – According to Gysi, the occlusal plane passes through the free edge of the lower incisors and through the disto-vestibular cusp of the mandibular second molars.

– inter-arch references – The occlusal plane is a virtual plane passing through the middle of the inter-incisal overlap and the middle of the overlap of the first molars[1].

The prosthetic occlusal plane is called the ideal plane according to which the two artificial arches must meet so that the following are simultaneously ensured: respect for the integrity of the support surfaces, restoration of aesthetics, restoration of all functions.[3]

The PO as defined in complete prosthesis is not strictly speaking a “plane” in the geometric sense of the term, since it has three curvatures:

• A sagittal curvature: the compensation curve or the curve of Spee;
• Two frontal curvatures: 

• One posterior to the level of the PM and the molars or Wilson curves,
• The other anterior which is the curvature of the incisor-canine block.[3]

The prosthetic occlusion plane

2. Roles:

The occlusal plane plays both a functional and mechanical role.

1. Functional role:

At the anterior level, the occlusal plane contributes to the restoration of aesthetics and phonetics. At the posterior level, it participates more or less directly in aesthetics but, above all, it contributes to mastication. 

Due to its orientation, it improves or reduces the patient’s masticatory power, because a change in the inclination of ± 5 degrees compared to a plane oriented parallel to the tragus-nasal wing line is accompanied by a decrease in the intensity of the pressures applied. 

In addition, due to its level, it directly participates in the kinematics of the food bolus.

2. Mechanical role:

The occlusal plane transmits functional forces to the bearing surfaces, which helps to stabilize the prosthesis, as long as the occlusal plane and the maxillary and mandibular bearing surfaces are parallel to each other. On the other hand, any lack of parallelism between the occlusal plane and the bearing surfaces results in prosthetic instability.[1]

It also ensures the integrity of the support surfaces.[2]

3. Importance of correct orientation of the occlusal plane:
4. Basic requirements:

There are two basic requirements for developing the occlusion of a complete prosthesis:

• Adaptation of the prosthesis to a pre-existing neuromuscular physiological system without playing an additional disruptive role;
• The static and dynamic balance of prostheses which is essentially based on the balanced articulation.

2. The five factors of HANAU:

The principles of this harmony were established by Hanau, for whom perfect agreement must exist between five factors, on the one hand on the articulator, on the other hand in the mouth.

• The inclination of the condylar trajectory in the vertical plane (condylar slope) and in the frontal plane (Bennett angle);
• The inclination of the incisal trajectory which is determined on the articulator by the orientation of the incisal housing, and in the mouth, by the slope of the lingual face of the upper incisors;
• The PO tilt;
• The Spee curve;
• The height and angle of the cusps of the prosthetic teeth.

The relationships of these five factors are reciprocal, three of them are determined by the practitioner:

• The inclination of the condylar trajectory,
• The position and orientation of the occlusal plane,
• The height and angulation of the cusps of the selected teeth.

The angulation of the cusps of the prosthetic teeth should be equal to the difference between the angle that defines the condylar slope and the angulation of the occlusal plane. [3]

4. What are the imperatives that the orientation of POP must obey:

These are successively:

• Respect general factors such as gender, age, constitutional type;
• Restore aesthetics;
• Ensure correct emission of all phonemes;
• Ensure the permanence of the stability of removable prostheses on the support surfaces both in centric occlusion and during all eccentric occlusions;
• To be located at the geometric locus of maximum pressures with optimal comfort for the masticatory muscles, i.e. at right angles, with the resultant of the forces developed during mastication;
• Be located at the physiological level between the tongue and the cheeks so that the transfer of the food bolus takes place alternately and without difficulty from the jugal cavity to the lingual cavity;
• Finally, respect the patient’s hereditary or somatic characteristics: such as intermaxillary malrelations, macroglossia, etc. [2]

The prosthetic occlusion plane

5. Finding the position and orientation of the PO:

This consists of finding, in relation to the facial mass and the rest of the skull, the position of the components of the occlusal plane:

• Anterior component,
• Posterior components.

The anterior component of the occlusal plane:

Its vocation is twofold: aesthetic and phonetic.

Aesthetic vocation: we must focus on finding, at the anterior level, a shape of contour of the occlusion rim which is correct in the vertical and sagittal plane. [3]

The upper model is in the mouth, the lips are at rest. The volume is assessed first ^; it should not be too large and erase the filterable gutter or the nasolabial folds, nor insufficient and accentuate the depressions under the wings of the nose. When the upper lip has regained its harmonious appearance, it will be important to determine the optimal value of the visible part of the occlusion model.

A white component will be used and is preferable to a brown component because it encourages us to leave more of the free edge visible. [2]

The occlusion rim should extend beyond the upper lip at rest by a value of 2 mm. This rule is not absolutely imperative, since it depends on the shape and tone of the upper lip, as well as the constitutional type of the individual.[3]

The free edge will then be set parallel to the bipupilary line. In the case of asymmetry of the line of sight, a compromise solution along a plane parallel to the bisector plane will be adopted.[2]

Phonetic vocation: a phonetic test will allow to considerably refine the position of the anterior teeth in the sagittal and vertical direction: during the emission of the labio-dentals, “FE, VE, EF”, the limit between the dry and wet zone of the lower lip must correspond to the incisal edge of the upper incisors. To obtain a good result; this limit between the dry and wet zone of the lower lip will be materialized using a dermographic pencil. The occlusion rim will be modified by adding or removing wax. [3]

The posterior components of the PO:

Many techniques are proposed to determine the position of the posterior components of the occlusal plane.

• Laboratory determination  : this aims to obtain the mechanical balance of the prostheses.
• Orientation of the PO relative to the ridges:

*For Bonwill, Cummer, the occlusal plane must be located at an equal distance between the two crests, so that the occlusal forces are distributed equally between the maxillary and mandibular crests.

*For Briscoll, it should be tilted from back to front and from bottom to top, in order to produce an upward and backward thrust on the maxilla, and decrease the lever arm on the mandibular prosthesis.

*For Gysi, the PO must follow the curve of the mandibular crest so that the masticatory forces are always perpendicular to this crest.

Sears describes an occlusal plane located as close as possible to the most resorbed ridge.

• Orientation of the PO relative to the facial mass:

WADSWORTH technique:

Pankey Mann and Shuler’s “Broadrick Occlusal Plane Analyser” technique.

The prosthetic occlusion plane

• Physiological design of the PO position  :

For proponents of this view, the occlusal plane must be positioned and oriented optimally to accommodate the physiology of chewing, swallowing and phonation.

• Piezographic technique  : the recording of the prosthetic corridor, which exists in the mandible, between the labio-jugal and lingual muscle masses, reveals on the lingual side a groove corresponding to the imprint of lingual movements. If we admit that there is a memory of lingual position after edentulation, the most convex part of the tongue should correspond to the occlusal plane. therefore, the concavity in the piezographic material would correspond to this occlusal plane.
• Paterson technique  : the physiological recording of the orientation of the occlusal plane will be carried out by the patient. The two models made and adjusted to the vertical dimension of occlusion in centric relation. The upper model is hollowed out to a height of two mm in the part corresponding to the pm and molars. The part thus removed is replaced by a plaster-carborundum mixture in equal parts. The models are put back in the mouth of the patient who is asked to perform lateral and mandibular propulsion movements, which will modify, by abrasion, the upper and lower models. After this lapping, the occlusal surfaces will be in dynamic and mechanical equilibrium and will allow assembly without the use of an articulator.

A variation of this technique can be used by placing tin foil over the wax occlusal rims.[3]

Anatomical design of the position of the occlusal plane:

The occlusal plane has a perfectly defined position relative to a certain number of craniofacial landmarks, the aim is to find, in the completely edentulous, a position of the occlusal plane as close as possible to that of the occlusal plane of the toothed individual. To do this, we will refer to a certain number of planes at the level of the facial massif and find a position of the occlusal plane.[3]

Reference planes  : for Comper, the occlusal plane is parallel to the plane passing through the anterior nasal spine and the center of the external auditory canals.

For some schools, the reference plane adopted is the Frankfurt plane passing through the upper edge of the external auditory canal and through the lower orbital rim in its most inclined position.

*For Andresen, it is tangent to the wing of the nose and passing through the middle of each tragus. (very close to that of Comper).

*For Gysi and Ackerman, it is slightly modified in its posterior landmarks which become the base of the tragus or external auditory canal. For Swenson, the posterior landmark is the upper edge of the tragus. 

*According to LEJOYEUX n the Camper plane is never parallel to the occlusal plane. It constitutes an easy solution which for a long time prohibited a more physiological approach to the prosthetic occlusal plane[2]. It remains no less true that this parallelization technique can give an interesting first approach to a more precise position of the occlusal plane.[3]

*For Mac Collum, the reference plane is an analysis plane determined by the two suborbital points and by the hinge axis.

For others, the reference plane is the mandibular plane or plane tangent to the basilar edge.[3]

• Parallelism of the prosthetic occlusal plane to the Camper plane:

From a technical point of view, the Camper plane is materialized by a strip of adhesive tape or a thread stretched between the subnasal point and the middle of the tragus, and the posterior segment is made parallel to this plane, this is facilitated by the use of the Fox rule.

According to a study by N’DINDIN AC, N’DINDIN- GUINAN BA ., GUINAN JC, LESCHER J. (contribution of teleradiography in determining the referential occlusion plane in the totally edentulous) on a number of totally edentulous patients, fitted for about two months and visibly satisfied with their prostheses both in terms of phonation and in terms of aesthetics and mastication, piezographs and profile radiographs are performed. It should be noted that these recordings are not used to develop the prosthesis and that they are purely experimental. Their only purpose is to allow the determination of the piezographic occlusion plane.

They conclude that the CAMPER plane is not an acceptable reference. The angle it makes with the piezographic plane is inconstant (significant standard deviation). The probability of finding this angle in a correct interval for an individual or a population average is low.

This work, after many others, underlines the little interest in this traditional reference. Therefore, if we want a physiological orientation of the occlusion plane, the parallelization of the rim of the model and the CAMPER plane is to be rejected.

At the end of this study, the following clinical proposals can be made:

– If a piezography is performed, it provides the physiological orientation of the occlusal plane without going through teleradiography. It is a safe and fairly simple way to obtain a functional orientation of the occlusal plane.

– If a piezography and a teleradiography are carried out, the piezographic plan confirms the RICKETTS plan given by the teleradiography and a verification is possible using the facial plan.

– If neither piezography nor teleradiography is carried out, then laboratory adjustment of the model in relation to the COOPERMANN plan is a good approach.[4]

The prosthetic occlusion plane

• Cephalometric search of the PO position:

The technique is broken down into three distinct steps. It allows for individual research into the orientation and position of the occlusal plane in relation to the craniofacial mass.

1. Preparation of occlusal models: The models are adjusted to the patient’s vertical dimension at centric relation without regard to the posterior position of the occlusal plane.

Lead balls will be placed at the interincisal point, anterior component of the occlusal plane. Similarly, lead balls are placed at the subnasal point and the middle of the tragus, components of the Comper plane, held in place with adhesive tape.

2. Teleradiography and cephalometric analysis: the patient, having both models in his mouth, undergoes a profile teleradiography of the skull.

From this teleradiography, a cephalometric analysis is carried out in order to find the posterior component of the occlusal plane.

by Ricketts’ technique the point X _i is located. This point X _i is constituted by the point of intersection of the diagonals of a rectangle determined in the following way:

R ₁  : the most inclined point of the anterior part of the ascending branch, through which a parallel to the Frankfurt plane is passed;

R ₂  : the steepest point of the sigmoid notch through which we pass a perpendicular to the first line passing through R ₁ .

R ₃  : the steepest point of the posterior part of the ascending branch through which a parallel is passed to the line passing through R ₁ .

R ₄  : symmetrical to R ₁ at the anterior level of the mandibular angle.

The anterior component of the occlusal plane will have been transferred to the teleradiograph using the lead ball placed at the interincisal point. 

By joining this anterior component to point X _i , the posterior component, we will obtain the patient’s prosthetic occlusion plane.

3. Transfer of the cephalometric prosthetic occlusion plane to the patient: by lowering a parallel to the Comper plane, to the cephalometric occlusion plane, an angle between these two planes will be obtained. To obtain an occlusion model in accordance with this new plane, it is necessary to transfer this angulation to the level of the upper model.

This transfer is performed using the occlusal plane angulator. This angulator is composed of a base resembling that of the Fox rule which will be applied to the upper occlusion model. Laterally, this base carries two extra-oral vertical terminals which carry a movable ruler, graduated in degrees and parallel to the base when at 0°. The angle which was calculated on the teleradiography and which separates the occlusal plane from the Comper plane is displayed on the horizontal rulers.

By transferring the occlusion plane angulator thus adjusted to the patient, the intraoral part being applied to the upper occlusion model, between the vertical ruler and the Camper plane a certain angle will be observed. By modifying the posterior part of the occlusion wax the ruler will be made parallel to the Camper plane. Thus the occlusion plane determined by cephalometric analysis will have been transferred in its position and orientation to the occlusion model. The lower model will then be readjusted to the correct vertical occlusion dimension in centric relation.

Mandibular model  : in a second stage, the restoration of all functions, and more particularly that of mastication, will be sought by using the lower occlusion model. This alone can determine the mastication plane at its most physiological level, in relation to all the muscles of the oral cavity and at a right angle to the resultant of the forces exerted by the elevator muscles. For this condition to be met, the posterior segments of the lower ridge must be parallel to the lower crest, end behind at the level of the upper third of the retromolar trigone and in front under the corner of the lips. It becomes possible, in this technique, to search in the frontal plane for its ideal level located slightly below the convexity of the buccinator and the marginal edges of the tongue. In the case of mandibular retrognathia , it will be appropriate to place it clearly below the level of the tongue.

In the case of prognathism, it is located above the level of the tongue.

The prosthetic occlusion plane

Conclusion :

The POP, by its orientation and location, must restore aesthetics, phonation and chewing. It also plays an important role in the stabilization of prostheses. 

Its location must be sought using the most reliable technique. 

References:

1. Hue O, Bertreche M. Complete prosthesis. Paris QI.2004.
2. Lejoyeux J. Complete prosthesis. 4th edition. Paris: Maloine 1986.
3. Sanguiolo R, Mariani P, Michel F, Sanchez M. bimaxillary total edentulism. Paris: Julien Prela; 1980.
4. N’dindinAc, N’dindin BA, Guinan JC, Lescher J. Contribution of teleradiography in the determination of the reference occlusal plane in the totally edentulous. 2000.

The prosthetic occlusal planeThe prosthetic occlusal plane

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The prosthetic occlusion plane