prostho sheet # 13 - Safa2 Mak7ool + Eman Al-momani

Bite Registration For Partially Edentulous Cases


Our lecture today is going to be about bite registration for partially edentulous cases, and we will talk about flasking and finishing of the partial denture as well, which is basically the same as that for the complete in which we are going to produce the acrylic part of the denture.

Review of the steps of RPD construction:

-start with history examination.
-take the primary impression.
-the primary model will be produced.
-survey the primary model.
-design your RPD frame work.
-do mouth preparation.
-take the secondary impression.



-now the master model will be produced,,, this model is going to be blocked out and duplicated to produce the refractory model on which we are going to wax up our frame work.

-investment of the refractory model.
-then we retrieve our casting mostly sprwes.
-fitting of the frame work on the master model.


-go for the metal try in step:
The patient will come to your clinic, u have the frame work on the master cast, you put it in the patient’s mouth and make sure it fits properly, with the metal try in step there are other things can be done:
One of them is making the altered cast technique , the other is taking the bite “bite registration”.






Now how to take the bite?
In complete denture the bite was taken by upper and lower bite blocks
These bite blocks are used to fill the space between the two arches -since there are no teeth- u need something to record this gap according to our desired vertical dimension of occlusion.
The horizontal relations will be recorded according to centric relation which is an orthopedic position between the maxilla and the mandible.
Now according to the vertical and horizontal relations you mount the upper and lower casts on the articulator then you start setting of the teeth try in step  finishing  insertion post insertion steps….

In partially edentulous cases:
Not always we have the same space as in complete edentulous cases,
There may be lower partial denture opposing natural dentition, in this case the patient still has a bite i.e. still has an intercuspal position.

This position could be strongly protected as in fully dentate patient the maximum intercuspal position is very obvious and very strong that you ignore the centric relation position.
So if that patient needs a bridge for example, will u bring him back to the centric relation?
No, it’s not logical to do so…
And as you know in about 90% of patients the centric relation is a little bit backward when compared to maximum inter cuspation.

As the number of the remaining inter cuspating posterior teeth increases, the tendency to record our bite in maximum intercuspal position increases, and we will not even try to find the centric relation.

In some cases the number of the remaining posteriors is not sufficient to tell you where the maximum intercuspal position is, in those cases you bring the patient back to the centric relation.

Example:
In a case, there was only one pair of upper and lower posterior teeth remaining, is it logical to do your prosthesis in that maximum intercuspal position for only that one pair of upper and lower posterior teeth??
Most probably NO, you will bring the patient back to centric relation.. rearrange the occlusion and make your prosthesis in centric relation.

So recording the bite and sitting of artificial teeth later on,, in centric relation or in maximum intercuspal position depend on two factors:
1- the number of the remaining inter cuspating posterior teeth.
2- The presence of symptoms i.e. TMJ disorder.
If the patient is symptom free: you can proceed with max. intercuspal position.
If the patient has symptoms: then he is not ready for any prosthetic treatment , you have to resolve the problem first then you proceed with prosthetic treatment according to the accepted position.

After the metal try in step we put the upper and the lower models on the articulator and we start sitting of artificial teeth.

Another try-in appointment is needed to make sure that every thing is fine, the relations were properly recorded , the patient is satisfied with the prosthesis before proceed to the next irreversible step which is :
Flasking of the wax denture in which we replace the wax with heat cured acrylic material that will be fixed to the metal frame work.
In this step we use the master model ( which we didn’t use to make the frame work we made it on the refractory model) .

With flasking the master model will be destroyed and you will not be able to make a clinical remount unless you have a model on which the prosthesis is ,, so what to do?
In this case you need to take a pick-up impression by which you take an impression to the partial denture inside the patient’s mouth.

In flasking:
In the first pour there should be no undercuts but the teeth and the frame work is full with undercuts, to avoid this you have to cover all the teeth and the frame work with the first pour “plaster of Paris”.
Then we proceed with the second and third pour  put the flask in a dewaxer or in a hot water bath to remove the wax , the teeth will be in the lower member fixed to the second pour,  pack the acryl  curing finishing.



Steps for establishing a satisfactory occlusal relationship (For any partially edentulous cases whether fixed or removable) :

1-start with analysis of existing occlusion (which will give you some clues about what problems u may have) this includes examination of muscles and TMJ etc.. most of the patients are symptoms free, i.e. they don’t have TMJ disorder they may have some signs! The difference between signs and symptoms is:
Sign something you find and think it’s abnormal like clicking for example.
Symptom more serious , pain for example!

We treat the patient who has symptoms not signs mostly the treatment is minimal, superficial and not invasive.

In this step you will find difference between centric relation and max. intercuspal position but AGAIN:
If the max intercuspal position is strongly protected with posterior teeth in occlusion we have to accept it.

Examples!:
*Patient with upper and lower Kennedy class IV is there a point to make prosthesis according to centric relation?
No, you already have the posteriors inter cuspating so why to use the centric relation!

*Patient with upper Kennedy class IV and lower Kennedy class I, centric relation or max. intercuspal position??
Premolars may be found or there may not be any contact posteriorly , in both cases bring the patient back to centric relation..

*If the patient was symptomatic and you find the solution to relieve those symptoms by bringing him back to centric relation then choose the centric relation.

2-Do correction for occlusal disharmonies if u decide that they have to be corrected.
Like in patient has only upper and lower premolars in contact (upper class IV lower class I) if I feel there is a big deviation between max. intercuspal position (which is protected by only 2 teeth) and the centric relation: I may choose bring him back to centric relation, so the inter cuspation between the 2 premolars must be corrected either by selective grinding or by crowning if excessive correction is needed.

3-Record the centric relation (if u decide that the prosthesis will be constructed according to it) or record the max. intercuspal position.

4-record the eccentric jaw relations, you need them to make the occlusion in harmony not only in one position but also when the patient moves his mandible to the left or the right.

These eccentric relations are going to be used indirectly by programming the articulator first according to them then by moving it in a correct way to adjust those relations, but they are never used directly inside the patient’s mouth.
Other ways to record the eccentric relations:
-functional eccentric occlusion recording
-functional generated path technique which we are going to talk about it specifically here because it’s applied to partially edentulous cases more than in complete edentulous)

5-After we record the relations and we set our artificial teeth according to them and we process our prosthesis finally we insert it and we correct any occlusal discrepancies left between the upper and lower arches.

Occlusal adjustment is a very important step either you will make clinical remount or direct adjustment intra orally.


Sources of errors in occlusion:
1- change in the status of TMJ,
Examples: a patient has anterior displacement in the condyle and the disk is more backward than normal you took a bite then after a week the disk and the condyle return back to their normal position, in this case the centric relation you took in the first time is more backward than the normal one so it will not represent the case and the teeth will not be in even contact.

Or an inflammation in the joint will cause the condyle to move away from the fossa, after a period of time the inflammation will disappear and you will find a premature contact posteriorly on that side when you try to insert your prosthesis.

So as a rule: symptomatic patients should not be treated with any prosthetic treatment yet, until they resolve.



2-Improper maxillo-mandibular relationship , how can this happen?
-cooperation of the patient is missing
-the dentist is not well experienced
-the material has some deficiencies that appear when you mount the cast on the articulator.
-errors in the articulator, as when you mount your cast according to certain measurements then someone use the articulator and change the measurements u set previously and you start setting the teeth in different relation than you used in mounting .

3-Ill fitting base plates:
The base plates that we use to take the bite whether in complete or partial denture are not fitting the jaws properly , when you take the relation with ill fitting base plate there must be error in occlusion recording.
This is one of the reasons why in partially edentulous cases we take the bite with the metal try in step, how?
Because if the base plate is fixed to the metal frame work it will be much more stable inside the patient’s mouth than being soft tissue born.
So the presence of the frame work will give more stability to the base plate and the chances to have a correct maxillo-mandibular relationships will be more than in complete denture.

4-Faliure to use the face bow with subsequently to change the vertical dimension of occlusion.
We talked about the clinical remount, now in any record of centric relation, the contact between the upper and lower teeth must be soft ,how?
If you are recording the centric relation by wax, then the contact between all the teeth must be on the wax , if there was any contact between the teeth then deviation of the mandible will occur and that will lead wrong recording of centric relation.

So in clinical remount when you want to record the centric relation another time you ask the patient to open his mouth a little bit more than the time of the first recording of the centric relation, then mount the upper and lower dentures in the articulator and remove the pin to see the interferences , so the vertical dimension of occlusion now is different than that of the first recording of the centric relation.



The closure of the mandible in relation to the maxilla is always accompanied by forward movement of the mandible.
Now how much the mandible is backward and downward from the condyle this determines how much it will move forward during closing!!

So if you didn’t take a face bow record , the position of the arches in relation to the condyle will be wrong.


5-Every thing on the articulator is correct, but the setting of the artificial teeth is wrong i.e. no even contact between upper and lower.

6-If you set the teeth properly and at the time of try-in every thing was good , but in the flasking step you didn’t close the flask completely, this will lead to elevated vertical dimension of occlusion.

7-using too much pressure to close the flask this may cause a problem but not that much.

8-warpage of the denture due to over heating during polishing.

9- Shrinkage of the acryl during flasking but this shrinkage is restricted i.e. shrinkage will occur but the acryl still inside the mold. So it’s not free to shrink in the way it wants so the distortion will be minimal .
But this shrinkage will be accompanied by the remaining residual stresses with in the acrylic material.
If during finishing of the acryl it become over heated it will pass above the glass transition temperature and the residual stresses will exhibit as distortion of the denture there.

10- unavoidable changes in the denture base material itself.
This should not be a major source of error in partial denture even the shrinkage in partial denture is more restricted than in complete because the acryl is fixed to the metal.


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Done by: Safa’a Makhool
Date of the lec: 10/5/2011
Prostho # 13 , PART 1

Ummm... this is part 1 by safaa...

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