Prostho 9,Teeth Setting

8/3/2019 Prostho 9,Teeth Setting

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Tooth setting

Today we will continue talking about complete denture, Tooth Setting.

Last week we started talking about selection of anterior teeth and the setting of theupper and the lower anterior teeth, today we will continue talking about selection

of teeth but we will concentrating on posterior setting, there is a difference

between the way we set the anterior teeth and the posterior teeth usually the

anterior teeth despite of the occlusal scheme or the occlusal design they are similar,

the posterior teeth can vary widely in there anatomy and the way they are set. If

you remember from the last week we talked about five concept which can give us

something called balanced occlusion or articulation, we will talking about that

today.

Now, what we try to achieve on complete denture when we compare it to natural

teeth in complete dentures, because there is no natural teeth we going to minimize

trauma in underlining supporting tooth structure and remember underlining

supporting residual mucosa and remember the mucosa was not design to with stand

the denture so what we trying to do is load the denture without irritating the

mucosa we want to maintain what's there, remember to the patient soon they

extract there is going to be continuous resorption out life so we are trying to only

reduce trauma we trying to maintain what's there.

At the same time we need to be able to allow the patient to chew to masticate and

to speak and to smile normally at the same time is providing the function without

irritating the mucosa.

we talked in lab about the differences between the natural teeth and the complete

denture occlusion the major difference we said that the fact the natural tooth in

individual is attach to the residual bone by PDL, and we also said the natural teeth

do not require balance between the right and the left side. when we have complete

denture teeth we said there a significance difference in dynamics function we look

at the occlusion we see the relationship between the upper and the lower jaw

statically in centric relation which is the zero point and we take a look at all the ec-

centric movement in the patient mouth what we want is contact between the upper

and lower arch in centric relation and to all the ec-centric motion inside the patient

mouth.

What is PDL provides us in natural teeth? It give us sensory feedback tells

the patient not to bite to hard or when to relax it tells the patient when to bite

even little harder, it provides us with the retention, stability and support and it

allows us to balance. with an edentulous mouth this is not as simple, not


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straight forward, the edentulous mucosa doesn't have the detailed sensation that

present in the PDL the patient can irritate the mucosa we don't have the

same feedback that we normally have.

What is retention? What is support? What is stability?

Retention:is essentially what keeps the denture in place, it is the forces that

prevent the denture from coming out, it is essentially perpendicular to the

residual ridge

Stability:is the lateral stability

Supportis the tissue in the bone which prevents the denture from seating in

the denture arch; so when the patient bites down the denture doesn't seat

further

How thick is the normal healthy mucosa? It is about 2mm thick.

How thick the PDL is? A round number "0.2mm"

So how much of differences do we have in terms of compressibility between

oral mucosa and the PDL? There is approximately 10 times the amount ofcompressibility there; there is much more movements under a denture than there is

under the PDL, also the PDL is a direct attachment between the tooth and the

surrounding bone, but the mucosa is not an attachment it is just there as filler

between the bone and the tissues, there is much more movement much more lack

of stability.

In general we talked about balance in ec-centric motion when we talk about the

occlusal scheme and it means the occlusal design; the way that we design theteeth, the way we arrange then in the patient's mouth. Here there is two

important concepts

The 1st one we talked about last week is balanced occlusion or articulation

or bilateral balance

The difference between the natural teeth and the denture teeth is that when we

move out natural teeth on the working side the teeth in the other side "non-

working side" will not contact, if they contact it is considered a problem it is


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called interference

There is no need for the teeth to contact on the other side, it is unhealthy

In complete denture when the patient eats "chew" on one side there is nothing

to prevent dropping the denture on the other side except the contact of the teethSo in complete dentures opposite to what we have in natural teeth we design it

so the teeth in the opposite side will contact when we chew on one side

So we need the teeth to be in contact in both sides even if we are chewing on

one of them so the side which the patient is chewing on is for chewing and

the other side is for balancing so the denture won't fall down.

In natural teeth we have a working side and a non-working side

In complete dentures we have a working side and a balancing side

- It has a different function now it is no longer a non-working side

Remember that each denture functions as if it has individual teeth"

- When I bite on one side of the denture the other side rotates

And this is the problem that I am trying to correct so usually my design is

something called balanced occlusion or articulation and 90% of what we

do in the clinic is balanced occlusion and articulation

- But there is another concept and we rarely use it; it's called the neutral

centric occlusalconcept it doesn't say we don't need balance what it says

in certain cases it is possible to give a patient the denture without creating a

balance what we are depending on is the way the patients chews instead

of teaching the patient to chew side to side we tell him to chew up and downChopping instead of chewing and these are natural chewing patterns

some patients they don't chew from side to side the point is that since there

is no movement of the patient except up and down there is no need for lateral

stability.

- The point is there is because no lateral movement in patient is just chewing up

and down there is not much need for the lateral stability , you need to know

about it even though we want the practicing and coercing university , the

scheme we normally called is bilateral balance or balance articulation , we


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deep for bilateral balance ,

- So What is the bilateral balance : the is definition , it stable simultaneous

contact of opposing upper and lower teeth in centric relation and then

nice even sliding contact from centric relation to all ec-centric othercontact .

So you have a bolus on one side , you want the teeth in contact in the other

side create balance , this is true between right and left laterally ,and true

anterio-posteriorly from petrosal ( not sure) contact when we bite something

like carrot or apple.

- We can also do it with flat teeth, do it in teeth have cusps or no cusps

Now there is something called Christian's phenomena

We know the lower jaw is attached to upper jaw through the TMJ, The TMJ

joint essentially have glenoid fossa and articulator eminence, when the patient

opens more than about 5 mm, the condyle will come down.

If a patient has teeth or they have a denture, when the patient opens his mouth

and protrude, the condyle will come down and go forward.

But the teeth are touching in the front, what happens?

Essentially we get a space between the upper and lower posterior teeth, in the

posterior part of the mouth. When the patient moves the lower jaw foreword,

because the condyle has to come down to go forward, we have space between

the posterior teeth, and the teeth contact in the front.

You see we have more than one application, I will talk about it later

It has an application doing jaw relation record, and I need you to understand

this idea because if the teeth are made completely flat, when the patient chewfrom one side to the other, or bite foreword, there is going to be space on the

non working side or the balancing side.

Because of the condyle coming down in the articulator eminence posteriorly the

jaw will separate on one side or the other depending on what they are doing.

How do we solve this problem?

So if we have flat teeth here these teeth have no cusps, they called monoplane


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teeth

The creation of the space called Christian's phenomena

, that mean if I set the teeth in such a situation, I'm going to end up with a

problem

if the patient bite in the front ,I'm going to have space in the back , when Hebite in the front is going to be force in the front ,What will happen in the back?

They will drop down or will go up in the back.

"

"

In order to create balance , called hanau who is an engineer not a dentist , he

described five factors , because he made the articulator to be able to do

balanced occlusion , theses five factors (we talked about them in the lab) arecalled :

1- the condyler guidance angle2- incisal guidance angle : how the lower incisors edge slide against the

upper incisal edge , and it is affected by how much over bite we have and

how much over jet we have , We have guidance between the anterior teeth ,

we have guidance between the TMJ center the condyle in the articular

eminence

3- Another factor which is the occlusal plane, I told you the occlusal plane is

pretty much standard for most people, we looked specific guide what is it

which is camper's plane, look for inter papillary from the anterior, and from

the posterior the ala-tragus line give us the angle.

But I told you the posterior reference for the ala-tragus line can be the

lower border of the tragus line or the middle of the tragus , that means the

angle moves up and down five to ten degree , I don't really change it but it iseffect how teeth meet in the slide against each other .

4- Then I have cusp inclination, the artificial teeth which I have are not

standard, even the teeth that we use in the university are almost universal.

But world wild if you open the ""artificial acrylic teeth or porcelain teeth

you will find these teeth come in different shapes and forms .

They come in different cuspal height: Zero degree, fifteen degree, twenty

degree, or thirty degree . Depend on how cuspal inclination you want this

cuspal inclination will affect the way the teeth touch when the patient chewsfrom side to side


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5- And finally we have the compensating curve, we said the natural dentition

we have the gentle curve in the occlusion, anterior-posterior is called the

curve of spee and laterally it is called curve of Wilson, it doesn't serve the

same function in natural teeth and complete denture. In complete denturewe called them compensating curve, why? Because like I said when the

patient bite forward we have space in the back; because of Christian's

phenomena

when the patient chew to the right we have a space in the left side, instead

of making occlusion flat we set the teeth in the curve, the curve allows the

teeth to chew on one side while the teeth on the side still in contact.

, " " The curve compensate for the space which happens on the balanced side , it tries to

keep contact between the teeth , and if you make the curve steeper it allows better

contact , if you make the carve flatter it will be more difficult to create the contact

in the opposite side

Now you can simplify this by rearranging the factors we have:

Codyle inclination, Incisal guidance, occlusal plane, Cusp inclination,Compensation curve

- You can think of it as algebraic formula, although we are not talking about

numbers here, we talking about how the factors affect each other.

This simplification is called Thaimond (not sure of the name) formula

" "

So if we take a look at Thaimond formula, you notice some factor you can

change and some factor you can't.

- So very simply can you change the condyler guidance angle? It is anatomic, I

can't go inside the jaw and start trimming the articular eminence or trimming

the condyle it is impossible "anatomically I cannot change it "

- The occlusal plane..Can I change it? I really can change it but just five to

ten degrees not a lot

""

So do not change the occlusal plane


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occlusal plane .It is standard , I have very slight variation in it , I can

modified it slightly , I cannot make it too steeper or too shallow.

- Incisal guidance: can I change the space between lower incisor teeth and upper

incisor teeth?yes I can but also within certain limit, I have to keep in mind that I have to

produce normal phonetics and esthetics, I can modified but I have to remember

when the patient speak I can't create over jet to five mm which create problem,

but I can vary it slightly,

- however I can change Cuspal inclination

"

"

- Can I change compensating curve? Yes, I can set the teeth in steeper curve or

flat curve

- So normally the things that I modify are:

1. Cusp inclination

2. The compensating curve

3. And to certain degree I change incisal guidance

Condyler inclination I can't change And the occlusal plane I can change it only into very limited fashion which

doesn't have any significant effect in the balance of the teeth

However if I change any factor, it can change all of the other things

If all of these three factors are adjusted to compensate for problems that I have

with the two unadjustable factors, I can create balance.

Now if the Condylar inclination is perpendicular (or in high angle), that will

make my work difficult WHY? Because when the patient provides his jaw

forward that will create a large space

So Patient has very steep condylar guidance angle posteriorly, his jaw will move

and he will have a very big space when he provides his jaw forward , What can I

do to compensate for this space ?


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Some of the students said that I would increase the length of the cusps; maybe I

can increase the length of the cusps 1-1.5mm, but can I close the space entirely or

completely? NO.

What else can I do? Usually I try to mirror the incisal guidance angle with the

condylar guidance angle, but if my angle like this can I make the incisor guidance

like this(doctor is explaining on his mouth !!), it helps but doesnt always solve the

problem . Is there something can I do?

And that is thecompensating curve instead of making the teeth flat I make them

curve in such matter so when the patient opens and closes it is like sliding in a

curve so I can alter these different things in the setting of the teeth to compensate

of what I am doing , so when the patient protrudes if the incisal guidance and the

condylar guidance are similar I can simply get away with altering the cuspation of

the teeth or increase the curve of the teeth ,, now all these pictures are anterior-

posterior in protrusion but the same true for the Wilson curve when I move from

the right to the left .

So if I have a steep condylar guidance angle what can I do?

I am going to end up with the space between the posterior teeth, how can I

compensate for it? Can I change the condylar guidance angle? What can I do?

I can make the teeth longer or steeper compensating curve. when might I have asteep condylar guidance angle? May be for esthetic or phonetic reasons, something

are determined by thing which I can't control.

Q: Can you explain the compensating curve??

ANS: if you take a look at this slide (O.o) these teeth are flat means; the

teeth are not set on a curve neither the curve of spee and curve of Wilson ,

this is curve of spee ,, curve of spee here is flat it is 0 degree ,,, is there any

curvature ? NO... Now when the condylar up here comes down because ofthe articular eminence this condyle has to slid down at a certain angle it is

going to create space between the teeth, now what is my problem? I can try

to close this space by placing cusp so the teeth continue to contact and

sliding each other.

The other way I can do that is by instead of keeping the teeth flat I create a

curvature .

If you take a look here at these teeth,, these teeth has a small curvature, I have a

simple curve between the upper and the lower teeth and I can suppose that it is partof a circle which is the curve of spee, the lower jaw as it moves forward because it


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is not a flat surface the curvature allows the teeth to slid against each other; it

compensate for the space..

So here we have flat teeth, we have no compensating curve and we have no cusps,

if the patient protrudes, the incisal guidance will separate and the condylar

guidance angle will separate the teeth,, how can I compensate for this ????

Essentially I have to either reduce the incisal guidance angle or am going to end up

the space between the posterior teeth ,, so usually what I do as if I want cusp teeth

and I need to change the compensating curve. "" the doctor start to draw something

at the slide"" what I have here essentially a curve it is a gentle curve not sever this

will allow the upper and lower teeth to contact even though may dont have cusps

or if you want to create cusps you can use smaller compensating curve

We said that there is different types of teeth,, different cusp inclination , companies

make teeth according to different types of designs the normal shape of teeth will

be:

1. Anatomic; it has the cusp which shape familiar with; we have the

mesiobuccal cusp, distobuccal cusp, mesiolingual cusp, distolingual cusp

for molars. Usually anatomic teeth are set in balanced occlusion or balance

articulation

2. semi anatomic instead of cusps with knife sharp cusps we have something

that looks like they almost flat the anatomy looks like it there but the shape

is might to be flatter instead of having 30-33 degree we have something it

might 12-15 degree .

3. We also have monoplane teeth which are designed so that the occlusal

surfaces are entirely flat,, when do you think you might use monoplane

teeth? Why you might use teeth without any anatomy or cusps??,monoplane teeth are teeth which essential dont have cusps going up the

occlusal plane may be sets in balance but they also can set in the

neutrocentric contact ,, the patient whom opens and close (up and down) we

dont make balance to him and there is no need to have cusps ,,

We also have a variation in the artificial type of occlusal called lingualized

occlusion, lingualized occlusion is a variation in anatomy, a gentleman

called Prayn Lang tried to promote this concept.


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The idea is that if you remember from lab where the weakest thing in the

occlusion , we said that the lower denture is weaker than the upper denture

because there is too much movements, and we said that the lower posterior

teeth are directly over the residual ridge so that we have stability ,,, the

lingualized concept of occlusion detect that be function cusps in the upper arch; the lingual cusps or the palatal cusps set in the central fossa of the lower , now

to reduce the amount of lateral instability the teeth are designed so the buccal

cusps is shorter than the palatal cusps, it looks like normal tooth but instead of

having buccal and lingual cusps that looks similar the only cusps which is very

prominent is the palatal cusps ,, so these the anatomic forms you see they have

a cusps angle , that the one in the bottom is flat you can see the cusps all at the

same height it looks like it have anatomy it might been have the semblance of

the groove but the cusps are flat and they all in the same height they look like

worn down teeth even though when you look at them " if you look at patient

wear denture" you dont really notice that the anatomy is not there "it's like an

optical illusion".

- Here we have semi-anatomical teeth it doesn't have the cusp height that we had

with anatomic, we only have a slight height we have the anatomy but not as

sharp as it was it is like a half way worn down tooth when we compare it

with the previous one

- So when one tooth is indicated and another tooth indicated? There are specific

indications or preferences for the dentist when to use one or another for

example if I have a patient who has poor neuromuscular control, this means

he can't control his teeth or cheek very well, with Parkinson's disease for

example they have constant shaking or vibration and they can't control the

denture we can't provide them with good inter-locking teeth because every

time they chew from right to left the lower denture will be unstable.

- So to allow free sliding contact without interference between the teeth we

reduce the efficiency of the function of the cusps and fossa by giving them

flatter teeth.

So it helps with a patient with poor neuromuscular control it also helps

with people with very resorbed ridges, the patient has a ridge which is almost

flat, after 15-30 yrs the residual bone completely goes away and sometimes it

becomesve and the patient has a hole instead of a ridge !!


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- So if you put a denture in such as patient's mouth how can you maintain

stability? Because every time the patient closes down on the teeth the cusps

inter-lock, anytime the patient wants to move his jaw left or right the jaws

move but the denture stays in its place! So sometimes we reduce the

efficiency of chewing by allowing sliding contact. We reduce the inter-lockingof the teeth by creating flat occlusion

- So flat ridges, flabby ridges and poor muscular control, are good indications

when needed!

Sometimes patients who have bruxism it is a good idea to make a monocentric

occlusion for them

- Also it is helpful when we have problems withjaw relationships the teeth

that you set in the lab are being set for casts having a classic class I occlusion

the upper jaw is a little bit forward but what happens if the lower jaw is

too far behind or too far forward? You will conclude that the setting of teeth in

that ideal position is impossible; sometimes we end up with something that is

called cross bite instead of having the lower teeth inside the upper teeth

toward the lingual we end up of setting the tooth in reverse >>>cross bite!

the patient is born with a larger lower jaw it will be impossible to set the

teeth in the way we learned ideally so setting it to the left or the right will be

difficult especially if the normal relationship was cusp to cusp so if I willend up with wrong setting it is easier to not have cusps at all, so that anywhere

the patient closes the teeth will meet evenly.

>>> So in the rare case where we have poor neuromuscular control, massive

resorption, bruxism, or poor skeletal relationship sometimes mono-occlusion

relationship makes setting of teeth easier even though it reduces the functional

efficiency of the patient.

The Dr. was showing examples of the teeth we had anatomic, reduced

cusp angle for semi-anatomic, if you take a look on the lingualized occlusion

will see that we have a lingual cusp but the buccal cusp is shorter

We also tend to make the lower cusps flatter so the palatal cusp doesn't

interfere it is if there is only one functional cusp on the lower occlusal

surface

This is the change in the design instead of having interdigitation upper and


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lower we have essentially we flatten the lower and have one main functional

upper cusp

And then we had non-anatomic teeth they are flat, we don't have cusps

We had a look on the anatomic tooth set up what you are doing in the lab now,

we want all the teeth to interdigitate normally, we don't have 3rd molars, and

essentially the lower teeth are half unit forward in relation to the upper teeth!

Because of the position of the canine and the smaller size of the lower anterior

teeth.

We should have good intercuspation between the upper and lower teeth;

the functional cusp of the upper sets in the central fossa of the lower and

the functional cusp of the lower sets in the central fossa of the upper, like

it does in natural teeth

Semi anatomical teeth are the same only we have a shallower cusp angle

especially when we don't need sharp compensating curves

In order to do this the angles on the articulator needs to be adjusted the way

they are in the patient's mouth; you have an average value articulator but if we

want to adjust the angles we need to use a semi adjustable or a fully adjustable

articulator, we use a semi adjustable fully adjustable are for complex fullmouth fixed rehabilitation

- The angle on your articulators is about 30 if you use the semi adjustable

articulator you can change the angulations and record it from the patient's

mouth using a protrusive record during jaw relationship records

- We mark all the guide lines on the patient's mouth for setting as we normally

do as we talked about last time, we check the occlusal plane and we start setting

teeth according to the weakest link which is the lower jaw and as yousaw in the lab we set the posterior lower teeth so that the center of the fossa

would be on the crest of the ridge even though the natural position is slightly

lingual

As we go beyond the 2nd premolar the buccal and distal cusps of the molars tend

to become higher and we talked about it in details in the lab after you set the

teeth you will end up with a curvature in the back


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- The posterior teeth do not touch so we have a compensating curve

We set the teeth according to a flat plane even though we don't let everything

touch the plane when we do balanced occlusion

After we set the upper posterior teeth it is very easy and straight forward to set

the lower posterior teeth because they fit together like Lego

As long as I have anatomy of the teeth I know where to put them for example I

know that the mesiobuccal cusp of the lower molar will be between the distal

marginal ridge of the 2nd premolar and the mesial marginal ridge of the upper

1st molar

So I close down the articulator on soft wax and the tooth will fit in place, which

is why you should have a lot more effort setting the upper more than you do on

the lower teeth

Showing a picture: (O.o) what is the problem with the setting? If the

yellow line is the center of the residual ridge the teeth were too far buccal

you should shift them more lingual if I leave it there it will create

instability and rotation in the denture

If I already set the upper posterior teeth what does this mean? If I set the

upper posterior teeth and the lower posterior teeth and I saw that the lower

teeth are buccal to the ridge what does this mean? this means that I have toreset the upper teeth that is why we don't set the upper posterior teeth until

we know where the center of the ridge is

The upper palatal cusp should be aligned with the center of the lower

residual ridge so we essentially fill in the spaces

Showing a picture: (O.o) these are mono plane occlusion the teeth don't

have cusps they are almost completely flat if you look at the surface

does it looks like I have anatomy? Yeah but it is like a worn down anatomy

{moh-tary}

So follow the same guide lines but there is major difference I usually

don't have a vertical over bite when I set mono plane teeth if I had a

vertical over bite what will happen if the patient protrudes? The posterior

teeth will separate and I will have a larger space so for mono plane teeth

{flat teeth} even if I set them on a curve for balance usually I could

have a horizontal over jet but I don't have a vertical over lap, I try to avoid

it because it creates instability I can use it for class I skeletal

relationship, if I have a large over jet I can use it for class II and if I


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have a smaller over jet I can even use it for class III when the lower jaw is

forward

If you take a look at the posterior teeth you can see that the teeth are flat

there could no curvature or I can make curvature in the plane so when thepatient slides forward there still be contact it means that I still need a

horizontal over lap on the posterior teeth to have some degree of balance

otherwise the setting of the teeth is almost identical but the fact that we don't

have interlocking between the cusps gives us some stability when the patient

moves right and left if the ridge is not giving me enough lateral support or if the

tongue and the cheek are not giving me enough support or if the occlusal

scheme requires me to shift slightly to one side or the other.

Finished... Alhamdulellah

Special thanks to my best friends Ayah M. Tareef , Nada Nammas,

Duaa Abu Hmaid for their help ^^

Documents

Prostho 9,Teeth Setting