The basic fundamental occlusion

The basic fundamental occlusion

Plan :

1. Introduction
2. Fundamentals of Occlusion:
   1. The physiological resting position 
   2. The closing path
   3. Maximum intercusp occlusion “MIO”
   4. The centered relationship “RC”
   5. Dental organization
   6. ANGLE classification
3. Static occlusion:
   1. The vertical dimension of rest “DVR”
   2. The vertical dimension of occlusion “DVO”
   3. The free space of occlusion
   4. Occlusal curves
   5. The prosthetic occlusion plane
   6. Occlusal functions
4. Dynamic occlusion
5. Recording of occlusion in partially edentulous patients
6. Conclusion 
7. Introduction

Occlusion is a static state obtained by the contact relationships between the occlusal surfaces of the dental arches regardless of the position of the mandible. 

2. Fundamentals of Occlusion 
   1. The physiological resting position: 

It is a position of the mandible, characterized by a state of complete relaxation of the muscles of the face.

2. The closing path [Fig.1]  : 

It is a path carried out from the physiological resting position (muscle relaxation) to the maximum intercusp occlusion.  

3. Maximum intercupidial occlusion OIM [Fig.2]  : 

This is a reference (stable) mandibular position.

 It is characterized by the maximum of dento-dental contacts.

This is a purely dental reference.  

4. The centered relation RC [Fig.3]  :

 The centric relation is “the reference condylar situation corresponding to a high, simultaneous bilateral condylo-disco-temporal coaptation, obtained by unforced control. 

It is repetitive in a given time and for a given body posture and recordable from a mandibular rotation movement” (National College of Occlusodontology, 2001). 

It is a joint reference.

5. Dental organization  : 

The dental arch: the proximal contacts between adjacent teeth ensure the continuity of the arch [Fig.4], these contacts are maintained by proximal bulges, the loss of teeth results in a void which causes a disorganization of the entire arch. 

Inter-arch confrontation: the maxillary arch in horizontal view is wider than the mandibular arch, so the maxillary arch circumscribes the mandibular arch [Fig.5], which gives at the level of:

• Anterior teeth: 
• Overbite: on the vertical plane, it is measured on the vestibular surface of the lower incisors on which a black pencil line is drawn following the edge of the upper central incisors. 

The distance from this line to the free edge of the lower incisors is 2 mm.[Fig.6] 

• The overjet: on the anterosuperior or sagittal plane, this is the space existing between the free edge of the upper incisors and the vestibular surface of the lower incisors and which must be 2 mm. [Fig.6]
• Posterior teeth: meshing of the upper teeth with the antagonistic lower teeth occurs in an occlusion defined according to ANGLE.

6. ANGLE classification:

ANGLE class I: Normocclusion [Fig.7]                               

The mandibular first molar is half a cusp mesial to the maxillary molar

The mandibular canine is in front of the maxillary canine

OJ= 2mm

ANGLE Class II: [Fig.8]

The mandibular first molar is distal by half a cusp relative to the maxillary molar

The mandibular canine is behind the maxillary canine

Upper OJ 2mm

ANGLE class III: [Fig.9]

The mandibular first molar is more than half a cusp mesial to the maxillary molar

The mandibular canine is much in front of the maxillary canine

OJ is zero or negative

3. Static occlusion 

To study static occlusion, we are interested in the lower level of the face, it corresponds to the distance which separates the subnasal point from the mental point.

1. The vertical dimension of DVR rest [Fig.10]: 

Characterized by the absence of interdental contact. 

It corresponds to the height of the lower level of the face when the patient’s head is in an upright position, and the activity of the elevator and depressor muscles is in balance.

2. The vertical dimension of occlusion DVO [Fig.11]:

 The height of the lower face when the teeth are in maximum intercuspation occlusion. 

The vertical dimension of occlusion is determined according to this formula: DVO = DVR –ELI (ELI: free space of inocclusion).

3. The ELI occlusion free space  [Fig.12]: 

It is the distance that separates the vertical dimension of rest from the vertical dimension of occlusion, its value is evaluated at 2-3 mm in skeletal class I.

It may vary depending on skeletal classes. 

4. The POP prosthetic occlusion plane:

It is a curved line that passes through the free edge of the upper central incisor, the tip of the canine, the cusp tips of the premolars and the mesiopalatal tip of the upper first molar; when the reference is maxillary [Fig.13].

This plane passes through the free edge of the mandibular incisors, the disto-vestibular cusps of the 2nd mandibular molar; when the reference is mandibular [Fig.13]. 

When there is loss of posterior or anterior teeth, the reference becomes the Camper plane at the posterior level and the bipupillary plane at the anterior level.

• The bipupillary plane: In a frontal orientation, the bipupillary plane is parallel to the line that passes through the patient’s pupils [Fig.14].

• Camper’s plane: in a sagittal orientation, this plane passes through the subnasal point and tragus point (point located in front of the orifice of the external auditory canal of the ear) [Fig.15]. 

3.5 Occlusal curves:

• The curve of Spee: it is a sagittal curve with superior concavity, it passes through the tip of the mandibular canine and the vestibular cusp tips of the mandibular premolars and molars [Fig.16]. 
• Wilson’s curve: this is a frontal curve with superior concavity, joining the peaks of the vestibular and palatal cusps of the two homologous teeth [Fig.17]. 

4.5 Occlusal functions:

• The shim function: 

This function ensures inter-arch and intra-arch stability, the latter being ensured by the continuity of the arch through proximal contacts.

• The centering function: 

The position of the mandible in maximum intercuspation occlusion or centric relation is transversally centered, which allows the TMJ to absorb stresses without pathogenic risk.

• Guiding function:                                                                        During a protrusion movement (the mandible moves forward) [Fig.18] and laterotrusion (the mandible moves laterally) [Fig.19], the anterior teeth (incisors and canines) guide these movements and protect the posterior teeth. 

4. Dynamic occlusion:

All movements of the mandible occur within a limit movement envelope, analyzed and recorded by Posselt.

Posselt takes the lower inter-incisal point as a reference point to record these mandibular limit movements in the vertical direction, in the sagittal direction and in the lateral direction.

1. In the vertical direction [Fig.20]: this path is carried out in 3 stages, the inter-incisal point describes a trajectory which records the opening and closing movement.

The opening movement is carried out in two stages: 

• The ^1st corresponds to a simple rotation of the condyles in the glenoid cavities, this axis of rotation is called the hinge axis.
• The 2nd corresponds to a translation of the condyles; this is the maximum opening.

The closing movement is done in one go.

2. In the antero-posterior direction [Fig.21]: this movement is carried out in close teeth in four stages:

• 1st ^stage : the teeth are in retrusion, or centric relation position.
• 2nd ^step   : the teeth slide slightly forward to reach the maximum intercuspation position.
• 3rd time: the teeth are end to end ^.
• 4th time: the teeth are protruding ^.

3. In the lateral direction [Fig.22]: the mandible performs limit movements in the lateral direction (right and left side); this is the Gothic arch.

Lateral movements take place inside the Gothic arch: the side where the movement takes place is called the working side, while the opposite side is called the non-working side.

5. Recording of occlusion in partially edentulous patients:

Two situations of toothlessness can arise:

• First situation: small extent of edentulism, this is edentulism which concerns a few teeth (1 to 4), without loss of the wedging function, in this case the reference position is the maximum intercuspation occlusion (dental reference).
• Second situation: large edentulism with loss of the wedging function, in this case the reference position is the centric relation (articular reference).

1. Prior to occlusion recording:

These are the occlusion models made in the laboratory [Fig. 23] in compliance with the production standards, and are composed of:

• A base plate made of wax (or resin; in large areas of edentulism) using positive biological indices (crest, tuberosity, hard palate, etc.) and avoiding negative indices (frenulum), this model extends anteriorly on the palatal or lingual faces of the anterior teeth at the level of the cervical 1/3 or the cingulum and posteriorly, it rests on 2/3 of the palatal or lingual faces.
• A reinforcing wire is essential if the model is made of wax, because this material can deform under continuous stress. However, if the model is made of resin, it is rigid without adding a reinforcing wire. 

The latter extends from the first upper right molar to the first left molar (from 16 to 26), and from the second lower right molar to the second lower left molar (from 36 to 46).

• One or more wax occlusion rims depending on the edentulism: the height is 1-2 mm above the cusp tips of the remaining teeth on the arch, the width will depend on that of the adjacent teeth and even that of the edentulous ridges.

In the absence of reference teeth to adjust the height of the rims: if the rim is located anteriorly, it will be adjusted parallel to the bipupillary plane and if it is located posteriorly, it will be adjusted parallel to the Camper plane.

                                                Figure 23: Occlusion model in a partially edentulous person

2. Actual recording of the occlusion:

• First situation: maximum intercuspation occlusion: easy to record: the patient is asked to gently squeeze the previously warmed rims until they regain their usual engagement.

This position is transferred to the laboratory using an articulator: to check the accuracy of this dental reference: marks are drawn in black pencil on the vestibular faces of the opposing teeth (which ensure the meshing).

Second situation: the centric relation: is recorded after adjusting the vertical dimension of occlusion according to the formula DVO = DVR – ELI, then the practitioner delicately guides the patient’s mandible in centric relation.

This step allows us to assemble the artificial teeth in the laboratory.

3. Choice of occlusal concept: 

There are three occlusal concepts during mandibular dynamics:

• Canine function or protection: the laterotrusion movement is guided only by the canine.
• Group function: The laterotrusion movement is guided by a group of teeth including the canine.
• Bilaterally balanced occlusion: all teeth act as guides.

6. Conclusion : 

Occlusion is of primary importance regardless of the type of prosthesis made; it is the key element of oral function .

The basic fundamental occlusion

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The basic fundamental occlusion