prostho- sheet #5 -by Safa'a Mak7ool

بسم الله الرحمن الرحيم

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Prosthodontics

Our lecture today will be about recording of the denture’s polished and occlusal surfaces “bite registration”.

Tell now we learned how to record the fitting surface and get the master cast.
The master model is the final fitting surface for our complete denture, it’s a positive against which the negative – which is the denture- is going to be constructed.


As you know that every connection between the mandible and the cranium is made by the tempromandibular joint (TMJ).


In the slides you can see in the picture that there is no bone contacts instead there is disk in between to connect the ligaments between the cranium and the mandible .





In natural dentition  we have contact anteriorly between the teeth this is what we call “occlusion” or articulation.

In edentulous patient  we don’t have this any more so we want to reconstruct our patient’s intra oral conditions to reestablish what was there before.

There is a space between the maxilla and the mandible, if the patient opened his mouth this space will increase and if he closed it will decrease.
We have to determine which space is the appropriate for our complete denture constructing.
In which step you determine that?
In the bite registration step in which we record the polished and occlusal surfaces.

Now in fitting surface recording we have 2 models must be related to each other in a similar way that the upper and lower edentulous arches are related to each other inside the patient’s mouth.














Now the upper model might be pushed anteriorly or the space between the jaws increased or decreased what we need by bite registration step is to record the relation between maxilla and the mandible inside the patient’s mouth why do we need to record this relation??
In order to be used when we are going to relate the upper and the lower models to each other in the laboratory because the upper and lower jaws separately mean nothing.

The fitting surface is recorded during the impression making procedure while the polished and occlusal surfaces are recorded in this step “the bite registration step”.

In order to be able to record the polished and the occlusal surfaces we need a tool .
In fitting surface recording we used the tray starting with stock tray and the special one.
Another tool is used for the recording of the occlusal and polished surfaces which is the bite block.

The bite block is composed of 2 parts:
1-the base plate “the record base” which will be firm to the master model which will be fixed in the articulator. If you use the primary model to make the base plate it will not fit the master one.


The base plate must extend to the full depth and width of the sulcus because the sulcus recorded now is the final one we assume that it’s correct.


Also the base plate must be rigid, strong, perfectly fit the master model and made of a dimentional stable material , mostly we use:
Light cured acrylic material, cold cured acrylic material , or Shellac.
It also can be made by heat cured acrylic material and this will be a permanent base which means that it will be a part of the final denture, but if it was made by light cured acrylic material, cold cured acrylic material , or Shellac it will be a temporary base and will be replaced by a heat cured acrylic material.


Now on top of this base plate we will make the second part of the bite block which is:
2- occlusion “wax” rim.
Why do we choose wax? Because we can easily adjust it by add or remove and this is needed in the next clinical steps.
This occlusion rim is made according to the average dimentions that we find usually in normal population, but its not necessarily to fit your patient so the average dimentions must be the starting point from which you are gonna add, remove in order to reach your final goal.

The maxillary occlusion rim is labially inclined because the natural teeth were there but the resorption of the maxilla will cause it to retract posteriorly toward the palate.





So when we make the occlusion rim we imagine the previous position of the teeth and try to put the rim there.








What is the importance of taking the position of the natural teeth??
We have 2 points of view:
1-esthetic point of view to restore tissue support.
2-Functionally, biochemical point of view:
By this we prefer that the artificial teeth to be on the top of the crest of the ridge, not labially inclined because this is more stable when the patient bites, this is what we prefer even though we neglect biochemics for a while and we put the artificial teeth in the place of the natural ones..

We said “for a while” why?
Because later on we will find that putting the artificial teeth in the place of the natural ones is biochemically correct, how??
Your teeth are stable in their positions inside your mouth which means that the net forces acting on your teeth are zero or very close to zero.
So that the orthodontist uses a very little force “50gm” to change the position of the teeth.

So when you put the artificial teeth in the place of the natural ones the net forces acting on them will be nearly zero is that good?
Yes, because they will be very stable, when your tongue move, it will act a force on the teeth pushing them labially then the lip willl act an opposite force, the resultant force will be zero.



The complete denture is a floating object where ever you move it, it will move, we place it in a situation where the resultant forces acting on it are close to zero this will add stability to the denture.



When you put the denture in the patient’s mouth the forces acting on the anterior teeth will try to stir the denture so we always make the occlusion in a way that when the patient bites the forces concentrate posteriorly where the teeth are closer to the ridge, and the time of biting doesn’t exceed 15 min per day so most of the time the denture will be in contact with the lips ,cheeks and the tongue if they were stable this will give more stability to the denture against forces which will act for a long period of time and soft tissue support will reestablished.






There are sets of artificial teeth, every tooth is found separately not in arches because of the huge variations in the arch forms some are tapered, squared, or ovoid we determine that in the “bite registration step.







In order to start teeth setting “making the wax denture” we need:
-the fitting surface.
-knowing the form of denture arches.
-location of the occlusal plane , occlusal surface of the upper and the occlusal surface of the lower , when the patient is closing they are one they meet each other.
-the orientation of the occlusal plane :horizontal, to the left , to the right, ant.posteriorly : above or below, the best is to be horizontal.

The occlusion plane will be recorded in relation to the TMJ by a tool called the “face bow”













So we will determine the location and the orientation of the occlusal plane in relation to the upper and lower models and to the TMJ as well how?
by using the articulator : we will put the upper and lower models the occlusion plane will be relate to them.
Also the joint will be posteriorly in the articulator so you can determine the occlusion plane in relation to it , ideally this relation must be the same to the TMJ joint of the patient so that we use the face bow.

Vertical and horizontal relationships between maxillary and mandibular working casts is also needed before you start constructing your wax denture.

Recording the relation between maxilla and mandible will be very hard without a medium to transfer this relationship: this is the function of the bite blocks: acting as a link between maxilla and mandible inside the patient’s mouth and maxillary and mandibular models In the lab.

Now the models are related to each other and fixed in the articulator by mounting “plaster” between the upper member of the articulator and the plate of the upper model, and the lower member of the articulator with the plate of the lower model, the two members are related to each other by the joint of the articulator.

Determination of the arch form:
Again: after teeth extraction and resorption the ridge will retract posteriorly so we have to put the bite block and artificial teeth in the same location of natural whhhyyy???
-the support of the tissue will reestablished
-the resultant force will be close to zero this area is called the neutral zone or zone of minimal conflict , the bite block must be out in that area.

How to determine this zone?
Inside the patient’s mouth there is cheeks and tongue, in the lab you don’t have these so you make them according to avg then you adjust :
If you find that the wax extend to cheeks you have to remove
If you find that there is a space between cheeks and the block you have to add.
If you find that the upper lip is not fully supported you have to add.
If you find that the upper lip is stretched you have to remove wax.

The upper bite block is in contact with the tongue when the patient is closing his mouth but you can’t see that contact so you rely on the cheeks and the lip to adjust the wax.
For the lower u can see the contact with the tongue, cheeks and the lip.

Sometimes you find in the lower that the tongue is unable to reach its place in the lingual aspect of ant. Teeth , in this case you have to remove wax to widen the wax rim , this is the first thing you have to do , to establish the tongue place.
Once the tongue in the proper place you can see the relation with it and with cheeks.

To see the relation with cheeks don’t catch the cheek with your hand you have to see without any external force just ask the patient to open his mouth and look from the angles left and right, if the contact is equal from both sides most probably this is close to the neutral zone.

But remember: don’t start to record the relations and to adjust the wax before making sure that the tongue established its proper position then check the contact labially and lingually.

You always have to ask your patient if he feels comfortable and use a mirror during adjustment because what you prefer not necessarily be preferable for the patient.

We have an important land marks to locate the occlusion rim.
Lower: the retro molar bad is very important for the location of the wax rim horizontally and vertically .

Now the location of the occlusion rim anteriorly:
In the upper model: we have the incisive papilla
located in the labial aspect between our 2 incisors.

The distance between the center of the incisive papilla and the labial aspect of the central incisors is usually 8-10 mm, you can use this as a reference for location of the artificial bite blocks why?

When resorption occur the incisive papilla keeps its position stable, surly it will moves anteriorly in relation to the crest of the ridge but the distance between it and the labial aspect of the incisors remains stable.

So when you make your bite block, determine the center of incisive papilla then put the labial aspect of the bite block anteriorly 8-10 mm.
Tips of the canine will be 1 mm from a line extending through the center of incisive papilla.

Now you can tell the location of central incisors and canines.

After determination of arch for you have to determine the location and the orientation of the occlusal plane we have two methods to do so:
-starting with maxilla.
-starting with mandible.

The dr. prefers to make every one separately , first the occlusal plane of maxilla , then mandible when you ask the patient to close they will not occlude in each other there will be a conflict between them you have to remove this conflict according to your common sense and the criteria you are going to take.

Starting with maxilla
You have already determined the arch form, now you have to determine the occlusion “the height of the arch form”.

First, the incisal plane meaning “height of the occlusion rim anteriorly”.
at rest only 1-2 mm of the central incisors are visible, sometimes 3mm are visible and sometimes nothing is visible how to determine that?
Ask the patient to say (m) and to open his mouth the part appears from occlusion rim will appear from artificial teeth.

We usually let just 1-2mm to appear not more or less.
So incisor show 1-2 mm it shows more in young patients and females, the patients with short lips will show more, also there is a regional differences: Asians and Europeans show more but in our region it’s less.
Most of your patients will ask you not to show there ant teeth.

After determining the height of incisal plane you have to determine the orientation of it, it must be parallel to the horizon of the patient.

What determines the horizon of the patient “esthetic horizon”?
Many references : eye brows , pupils, upper lip, lower lip, and the ear lobes because they are lateral, and you have to look to all of them.

Determination the level of incisal plane:
-esthetics : we talked about them previously.
-function  speech (V, F) now when you say (F) the upper incisor will make contact with the junction between the skin and the mucosa which is called “vermilion zone” in normal cases the contact is light.

If the incisors were descended the contact will be excessive so (F) will be converted into (V).
But if the contact were lighter (V) will be converted into (F).
You have to ask your patient to say a word contains the same letter twice and concentrate on the second one because the patient may hardly say the first one properly but he will not be able to say the second properly.

Example:
Ask your patient to say “falafel” if he said:
Valavel or falavel  you have to shorten the bite block “to raise it upward”

Then ask him to say “Volvo” if he said:
Folfo or volfo you have to lower the bite block.

Determination the orientation of the occlusion plane:
We have a tool called the “fox plane” it consists of a fork like structure and 2 wings.










The fork must be put in the upper bite block inside the patient mouth.
The wings are parallel to the fork meaning they are parallel to the occlusion plane.
In frontal view the wings must be horizontal , if there is any inclination adjust the wax. These wings must be parallel to the eye pupils and the ear lobes as well. Then ask the patient to smile it must be parallel to the lips too.



Anterioposteriorly the fox plane must be parallel to a plane we call it Camper’s plane which extend from the lower aspect of the ala of the nose to the middle or superior of the tragus of the ear.







Superior border of external auditory meatus to the infraorbital margin this plane is called Frankfort plane it can be seen by radiograph or by touching.






So we have:
Fox plane the tool
Camper’s plane parallel to the upper occlusion rim
Frankfort plane horizontal.


Starting with mandible
To determinate height of the occlusion plane
The lower incisal plane is less important from esthetic point of view than the upper.

So in the mandible we look a little bit posteriorly we will concentrate on the relation between ‘modulus” which is a notch in the corner of the mouth and it’s the junction between 8 facial muscles.
Modulus is part of sphincter mechanism between it and buccal surface of the teeth to keep the polus of the food inside ur mouth preventing it from going ant.
Other sphincter from the lingual aspect is the tongue.

The modulus must be at the level of the occlusal plane if it was below the occlusal plane when it contract it will hit the lower teeth instead of being in the space between upper and lower and that will move the denture from its place.

How to use this?
Ask the patient to close his mouth and bring a blunt instrument enter it from one corner in one side then ask him to open his mouth and check if it was in the occlusion plane then this is the ideal but if it was bumped into the bite block then you have to remove wax , and if it doesn’t touch the block then you have to add wax.

In this way we determine the height anteriorly by modulus. Posteriorly the height will be 2/3 the height of the retro molar bad.

Another thing to determine the lower occlusion plane is the dorsum of the tongue.
When the patient opens his mouth the dorsum of the tongue at rest must be just above the occlusion plane.

Now you determine the occlusion plane of maxilla and mandible when you put them inside the patient mouth he will not close properly because every one was made separately to adjust there are two options:
1-the areas where there is contact remove from them
2-the areas where there is no contact add to it
Which way to choose?????

Next lecture…






Best Wishes



Done by : Safa’a Makhool
sheet #5
date of the lecture:19/10/2010