occlusion sheet # 2 - Dania Salhab

Occlusion lecture #2
Dr.Suzan Hattar
Done by: Dania Salhab
Date of the lecture: 13.2.2011

Articulators

** What is an articulator?
An articulator is a mechanical device that is used to stimulate the mandibular movements. The principle employed here is the mechanical replication of the path of the movements of the posterior determinants and the anterior determinants.
(The posterior determinant is the condylar guidance angle and the anterior determinant is the incisal guidance angle).
As we all know, all sorts of movements can be accommodated by an articulator, but the border movements are our interest, which are considered as reproducible movements (we can repeat them again and again). These movements are important in programming the articulator because these are positions that we can always have again and again in the same position, like: centric occlusion, edge to edge and maximum opening.





** Why do we need an articulator?
We need something in the lab that resembles the patient, meaning…the casts on the articulator should exhibit the same tooth to tooth and edge to edge relationships as in the patient's mouth, so we need to stimulate the movements of the mandible on the articulator as close as possible.


** How can an articulator stimulate the clinical situation?
First step: mounting the upper cast on the articulator using the facebow in the same relationship that the upper teeth are related to the terminal hinge axis.

Second step: mounting the lower cast by interocclusal records, it is recording the occlusal surfaces of the upper casts and the occlusal of the lower cast in a certain position, it could be: -Centric interocclusal record
-Eccentric intrrocclusal record
…we will talk about them next week in details.

Third step: programming the articulator.
The aim and the benefit are to have prosthesis that is in harmony with the existing occlusal scheme and TMJ.


** What are the advantages of an articulator?
1. The articulator permits the visualization of the tooth from all aspects.
2. Using an articulator helps us to study every sector of the dental arch separately.


** What are the uses of an articulator?
…we can use it in two stages:
1. Pretreatment stage
Before doing prosthesis and putting a treatment plan, we study our case.
- Occlusal analysis and equilibration (selective grinding)…we study the occlusion, where are the points of contact and if we have any interferences or no interferences, by using an articulating paper (like carbon paper). We do all of that on the articulator because for example if we have an interference between a specific cusps and we decided to do a reduction for them inside the patient's mouth, this is an irreversible step, once we touch or remove any structure we can not get it back…so we need to do a trial on the articulator then transfer it to the patient's mouth.
- Sometimes we use an articulator in an orthodontic procedure. We need it to study our case, see how to arrange the tooth and to visualize what would look like later on.
- Wax up…for example patient has missing posterior teeth, we stimulate our final prosthesis using the wax for sort of morphology (for the patient) and for visualizing and planning what the patient needs as well as for communicating and explaining to the patient how the teeth would be.

2. Treatment stage
- Fabrication of our fixed or removable prosthesis.
- Splints for occlusal therapy (TMJ problems).


** What are the components of an articulator?
- Superior and inferior members.
- Two vertical arms.
- Mechanical fossa and mechanical condyle.
- Incisal pin (to determine the vertical dimension) and incisal table (to reproduce the incisal guidance).

… What is the anterior guidance?
It is a relationship between the upper anterior teeth and the lower anterior teeth in sliding movements.


** Classification of articulators…
We can classify the articulators according to the mechanical condyle and the mechanical fossa, into:
1- Arcon: articulating condyle…
. The condyle is attached to the lower member
. The fossa is attached to the upper member
…just like what we have in the skull… the condyl is attached to the mandible and clenoid fossa is attached to the skull. This type of articulator is used for the fixed prosthesis.
2- Non-Arcon: has the opposite.
…which on is more accurate?!


** Programming the articulator…
We have to program:
- the posterior determinants:
. Condylar angle.
. Lateral shift.
. Bennett angle.
- The anterior determinants: anterior guidance.


** What are the methods that are used to program an articulator?
1. External method: it is a pantograph tracing and usually it is used with fully adjustable articulators.
2. Internal methods: one of them is taking different introcclusal records for example, protrusive introcclusal record and lateral introcclusal record to know the condyler angle and the Bennett angle, respectively.


** What are the types of articulators?
1. Hinge articulator…
- Nonadjustable, capable only of hinge opening and closing and the only relationship that it has is centric occlusion (maximum intercuspation).
- Used with single tooth restoration when the occlusal influence is minimal.
- Inconveniences: we can not do any type of movements with this type of articulator.
- Variant form this hinge articulator is Twin stage articulator that has lower member, upper member and another functional position.
- Problems:
 It is inaccurate articulator because it doesn't have any type of movements or relationships except one.
 Its dimensions are small which means the movements are different from what is in the patient's mouth.

2. Average articulator…
- In this articulator the condylar inclination is fixed (200-300).
- Here the mounting of the upper cast is done by something called occlusal table, without the facebow.
- This articulator cannot be programmed, it is an average articulator but at least it has lateral and protrusive movements (better than hinge articulator).

3. Semi adjustable articulator…
- There are three generations.
- More accurate reproduction of the mandibular movements.
- We can change the intercondylar distance, it is not fixed (we have small, medium and large).
 First generation:
. Reproduces the condylar inclination and Bennett angle.
. Also reproduces the direction and the end point of a movement.

… What do we mean by the direction and the end point of a movement?
We know that when the mandible moves for example in a protrusive movement, the condyles will go downward and forward, this path is a curved path (because the movement is between bones) and the articulator cannot easily resemble this curved path…so it is a direction and point angle.

 Second and third generations:
. We can accommodate paths known as anatomical paths or curved paths, this can give us more accuracy than the straight lines (first generation).

4. Fully adjustable articulator…
- Reproduces all sorts of mandibular movements, border movements (inclination and paths)
- Stimulate the mandibular movements in four dimensions. (timing is the fourth)
- The intercondyler distance is completely adjustable.
- Requires a pantographic recording that trace the hole movements in order to program it on the articulator.
- Requires a kinematical facebow registration. (we will talk about it in details later on)
- It is highly expensive and time consuming.


** Some indications…
- The nonadjustable articulators (hinge and average) are for single tooth restoration.
- The semi adjustable articulators are used for fixed and removable prosthesis.
- The fully adjustable articulators are used for problems, such as:
. Missing anterior teeth
. Extensive occlusion modifications
. Complete mouth rehabilitation, for example when dentate patient comes in and we want to change all the occlusal surfaces, it is an extensive work so we need something very articulator.
. Changes in the vertical dimension
. Atypical mandibular movements
. TMJ problems

…As we go from the left to the right, we can notice the following:

[Fully adjustable>>Semi adjustable articulator>>Average articulator>>Hinge articulator]

. Diagnostic information decreases
. Occlusal information decreases
. Time and skill needed decreases
. Modification in the patient's mouth increases


…and finally,
The more accurate the articulator stimulates the occlusion relationship the more accurate the end result would be…


Hope every thing is clear…

>>The End<<