Prostho Lecture 2 Anatomy of Edentulous Ridge Done

8/3/2019 Prostho Lecture 2 Anatomy of Edentulous Ridge Done

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-Today we will talk about the anatomy of the Edentulous Ridges.

"The reading assignment for the anatomy lectures from the text book are (pg211 to

pg251)", this includes the impression procedure and the anatomy for the maxillary

and mandibular arches. The anatomy for the maxillary arch is about 6-7 pages in the

beginning of the chapter.

Last week we talked about primary impressions and pouring up the primary

impression. This week were working on making the custom trays to make thesecondary impressions .

Now whats important here is that we have

alginate impression or the impression compound for taking the primary

impression, ,and finally ending with a primary castwhich we used to make a custom

tray.


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- When we talk about the anatomy of the maxillary arch, it will be a good idea to

talk a little bit about the extra oral anatomy; not the extra oral anatomy that we used

to, such as the extra muscle for facial expression and so on. Actually, some landmarks

that we will talk about when we talk about history & examination of the patient

-now There are specific landmarks that you are very familiar with

Extra oral anatomy

Vermilion boarder

the vermilionborder of the lips; is essentially the meeting of the oral mucosa with

the skin )) vermilion= . . Vermilion borders are

important because whether the lips have support from the dentures or not,

determines whether the vermilion borders will be clear or more hidden or

straight.(meaning that the denture that I fabricate will affect how much of thevermilion boarder shows which affects estheticsso its important for me )

When the lips are supported by teeth(resting or bushed

out by teeth) the vermilion border is more clear,

however; with age or teeth extraction the lip gets

smaller.( ,

(

** You can see the upper and lower vermilion borders inthe picture.

nasiolabial groove and labiomental groove

nasio liabial groove is the line present in the area where the upper lip meets with

the cheek extending from the lateral edge of the nose to the angle of the mouth.(the

upper arrow)

Labiomental groove : is the line present at the area where the lower lip meets the

chin.(the lower arrow)

All of these specific facial features(lines) become more clear with age. If we dont

have teeth support they become even more & more exaggerated. They are signs of

age.

- Why??


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- Because we are losing essential facial support as we have no teeth. Not only welose the supportanterio-posteriorly and laterally, but also we lose the support as

the jaws become closer and more approximate to each other (we lose the support

vertically). We lose anterior facial height

" " So we have loss of facial tone.

**Some patients can do quite exaggerated facial expressions; you will be surprised

how closely jaws could be brought together when we have lost the teeth support!!

some patients could bring their lower lips above their nose.

The atrophy or resorbtion is continuous after extraction and it continues for life.

The earlier the patient extracts his teeth,the more bone resorbtion will occur so

the lessbone they will have. The resorbtion will continue through the alveolarbone to the Basel bone (from top to bottom). Until The bone isso week that it

fractures by itself.* (

)

*notice that we are talking about bone ofresidual alveolar ridge.

**Bone resorbtion means there is no support for the facial tissue because when teeth are extracted we can get some

support from residual alveolar ridge for but when the

ridge starts to resorb the whole support is lost.

Philtrum

The Philtrum is essentially a small area in the midline

in the upper lip ( ).But opposing the

philtrum we have something that is called columella.

columella

-The columella opposes the philtrum .So we have a depression in the upper lip. The

columella is essentially below the bridge of the nose,

it's the area between the nares " openings of the

nose". It's like a column, and if you follow the

columelladown there is the philtrum .


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Nasiolabial angle :

- The angle between the columella is another important feature affected by my

denture and this angle ,if there is adequate or sufficient labial support ,should be

approximately 90like the picture .

What we attempt to see is that there is an angle between them. But If the patient

loses his lip support. What will happen?

-The angle will become obtuse ( ) more than 90, the lip will lose it support.

This is important fact when we set teeth in the lab and when we do jaw

relationship record in the clinic.

We talked about specific guidelines we must

follow when we set the teeth and do jaw

relationship record, one of the main guidelines

that we look for is: this anglensio-labial

angel.

Whats the main muscle in the cheek?

It is the Buccinator (origin:pterygo-

mandibular ligament) and we have themasseter muscle(origin:zygomatic arch,insertion:angle of the mandible). We are just mentioning this because later on you willsee that it functions in the denture in an indirect way.

Those of you who have taken the lab have already heard some of the things that Im

going to talk about today. Hopefully the repetition will help you.

intra oral anatomy:

When we talked about the intra-oral anatomy of the Edentulous Arches (the

maxillary and the mandibular), we essentially divided the anatomy into two parts:

1- A part which supports the denture (the denture bearing area, the support area).2-Peripheral structures (the limiting structures around the denture).

Before talking about intra oral anatomy there are some very important terms that you

have to know to be able to understand what we are talking about :


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**denture foundation area: the surfaces of oral structures available to support adenture.*

**denture base :the part of the denture which rests on the foundation tissue and towhich teeth are attached.*

**support : the foundation area on which a dental prosthesis rests .with respect todental prostheses the resistance to displacement away from the basal tissue orunderlying structure .***Denture stability:1.the resistance of the denture to move on its tissuefoundation especially to lateral (horizontal forces) 2.a quality of a denture that

permits it to maintain a state of equilibrium in relation to its tissue foundation.*

**denture retention :1.the resistance in the movement of a denture away from itstissue foundation especially in vertical direction.2. a quality of a denture that holdsit to the tissue foundation.*

*glossary of prosthodontic terms .

^^^Good retention needs support and stability also helps in retention.we said that the object of taking the primary or secondary impression is to register the

entire surface area and the Edentulous Ridge, so that we have better support for the

denture. Its in our interest and the patients interest to cover the largest area. If I cover asmall area, and the patient chews the denture will hurt the patient in that area. The more

support I have, the greater surface area, the better and the more comfortable the patient

is.

-Now we are going to talk about some rules that we should consider when making

complete denture:

1)

* one of the most important rules in making complete denture is to cover the largest

surface area possible but not to over extend or cover areas that causes discomfort to the

patient.

2) dont over extend denture boarders into muscle or movable areas.


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So Ill cover as much as of the Edentulous Arch as I can. As I said, if I enlarge this

support area and I keep reaching the borders beyond the Edentulous Ridge Im going to

run into the tissues that move because Ive muscles.

We said that we have the Buccinator in the cheek and orbicularis oris around the

opening of the mouth and posteriorly I have the soft palate and levator and tensor veli

palatini, there are a number of muscles that attach the maxilla to the mandible into the

tongue. And in the mandibular arch I have the tongue with extrinsic and intrinsic muscles.

These tissues move and I cant extend the denture into this movement.

Extending the denture to the movable areas leads to one of two things :

1- Dislodgement and movement of the denture which is uncomfortable to the

patient. (when the over extension is large enough to cause dislodgement)

2- The denture is relatively stable so it will cause trauma( )

(if the over extension is not large enough to cause

dislodgment)

So I have a dilemma! I want to cover as much as possible but I dont want to go beyond

the normal movement. These things are important when I talk about the impression,

because as you will see the impression is taken in two stages:

secondary impression two stages:

1-Registering the boarders or the limiting structures that surrounds our denture.(Border molding on the edges of the tray as you saw in the lab).

2-Then we take an impression of the whole area. So we have the external structurearound the denture and then the denture bearing areas.

Quick review to the things that we'll be talking about today: we can take a look at the

palate, the residual ridge, the vestibule externally and the soft palate posteriorly.

Plz refer to your book (prosthodontic treatment for edentulous patients zarb-bolender)

page 215 and see figure 13-5 it contains all the anatomical land marks that are important

for you and that we are going to talk about in this lecture.

Residual alveolar ridge:


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The elevation or part of bone as you know that remains after the teeth are extracted; we

call itthe alveolar bone or the residual bone. It s shape changes after extraction with

time. And the way it resorbs or atrophies is very different from patient to patient.

The resorbtion occurs in specific directions, sometimes more resorbtion happens on the

labial than the lingual side, while other parts resorbs from the lingual more than the

labial, depending on the density of the bone and the anatomy of the bone in that area.

So The ridge can have different shapes, it can be prominent, atrophied, regular, irregular,

symmetrical or nonsymmetrical.

Maxillary tuberousities:

At each end of the residual ridge in the maxillary arch we have large prominence called

the maxillary tuberousity(designated with the squares), sometimes they are small

depending on whether they were removed during extraction.So essentially the residual ridge extends from one maxillarytuberousityto the other.

Maxillary tuberousity and supra eruption:

-The tuberousity as you can see it can be very large. If the last teeth to be extracted

are the molars sometimes with time the teeth

supra-erupt.

if I remove one tooth,

1. the teeth next to it in the same arch and


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2. the teeth opposite to it in the opposing archthey will lose the balance and drift mesially or

distally into space (the same arch) or they will go up or down supra eruptto the

opposing space(in opposing arches) eg. If I remove the lower tooth without removing

the upper tooth sometimes the upper tooth will drift and go down with the bonesurrounding it. Sometimes, if I leave posterior teeth too long, the tooth will supra-

eruptand will bring the bone with it.

Sometimes,

I end up with maxillary tuberousities that are so large that they come down and

touch the lower arch. In such cases we do surgery to reduce the amount of bone, we

have too much bone in this case.

*** (the tuberousity is too large they went for surgery the above picture)

Incisive papilla :

At the junction of the anterior part of the palate and the residual ridge you have the

incisive papilla (the circle). The incisive papilla is essentially small prominence which

over lays the exit of the naso-palatine nerve and blood vessels. Its a sensitive part, we

dont like to load it, its what we call a relief area!! We dont want pressure in this area.

If you feel the upper part of your mouth, justbehind your central incisors you will find a small

prominence, is the incisive papilla.

rugae area:

Behind the incisive papilla in the anterior part of

your mouth, we have an irregular area called rugae;

we will talk about it in more detail.

the mid palatine suture :

In the midline, at the junction between the palatine process of the maxilla and the

palatine bones we have the mid palatine suture (mid palatine raphe).

soft palate:


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If we go further behind( posteriorly) we will run into the soft palate, which has a part

of it that is movable , this information is important for us we will know why in a minute

Sulcus or vestibule :

if we go further facially, we'll end up into a pocket like structure called a vestibule

(sulcus). This is divided anteriorly and posteriorly into the labial sulcus anteriorly and thebuccal sulcus posteriorly on either side. The labial sulcus is separated from the buccal

sulcus by the buccal frenum on either side.

In the middle of the labial sulcus we have labial

frenum.

Hamular notch:

In the back, we have the (Hamular Notch)

which is a depression between the maxillary

tuberousity and the hamular process ofmedial

pterygoid plate.

** The stuctures in labial vestibule in the maxillary arch that provide support

is not significant as in the mandibular arch.

Zygoma :

Like I said we have buccal vestibule and the labial vestibule,

The buccal vestibule is divided by the Buccal Frenum- sometimes there is one

frenum or there are two frena/frenum. Posterior to the buccal frenum beneath the

vestibule you can spot a solid buccal bone (support) from the zygoma, this doesnt

usually affect the fabrication of the denture unless there is a large amount of

resorbtion in the ridge in that area

Coronoid process :

there is another landmark that we must take into consideration when making a

denture which is the coronoid process (found lateral to the maxillary tuberousity,

the coronoid process comes forward when the jaw is opened completely (this

movement must be taken into account when making the denture).

Modulus:


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Recall from your Head and Neck Anatomy Lectures the major muscles of facial

expression: The Buccinator , the orbicularis oris and mentalis. All the major

muscles of facial expression anastomose (join together) at the corner of the mouth;

this anastomosisis called the modulus.

The modulus is significant because it moves the buccal frenum with it, so when

the Buccinatorpulls the cheek back, the buccal frenum will go back and when the

orbicularis oris contracts the entire modulus comes forward .when the patient smiles

the modulus will go up.

This means when we make an impression we need to be careful in the area of the buccal

frenum, we must create a notch in the denture that allows the buccal frenum to move

freely without restriction. (

)

**Soft tissue classification:

*Special type of tissue scar tissue on the alveolar ridge

Microscopically the tissue found in the mouth on the residual ridge is a scar tissue; If

you cut yourself the tissue will heal and it will leave a scar, When we extract teeth the

tissue that remains after extraction is a scar tissue (healing tissue). It wasnt designed to

withstand the force of a denture, Its important to understand this. The Edentulous

mouth wasnt designed to support the denture. We take advantage of it to support the

denture, but the tissue and the mucosa above it arent specifically designed for denture, It

is a sensitive mucosa.

*keratinized and non-keratinized mucosa

You know that the tissue in the mouth before extraction is divided into keratinized

and non- keratinized (masticatory mucosa and lining mucosa) or specialized mucosa

(like the surface of the tongue where we have the taste bud).

If you take a look on the maxillary Edentulous Ridge, you will notice that the entirepalatal surface and the residualridge are keratinized mucosa (masticatory mucosa), it

will withstand a certain amount of friction even thought it wasnt specifically designed to

have a denture sitting on top of it.

The further out we go (sliding from palate towards the cheek), were going towards a

junction between two types of mucosa, Masticatory mucosa is an attached mucosa; its


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attached to the bone in the palate or in the residual ridge. However, when we go further

out to the vestibule, there will be a junction at which the tissue is no longer attached.

So, we have attached and un-attached tissue. We want to extend just onto the un-

attached tissue butnotbeyond it. The un-attached tissue will be lining mucosa (non-

keratinized). Friction and movement of the denture in this part of the mouth might cause

ulceration and trauma. Its not only that we want to extend to the extent of the muscle

we also want to have support from tissue that can withstand friction and force.

*sub-mucosa

Whats underneath the mucosa? We have the sub-mucosa and mucosa have squamous

epithelium, lamina propria and the sub-mucosa which has blood vessels , glandular tissue

and adipose tissue and so on (It provides support). The thickness ofthe sub-mucosavaries in different parts of the mouth, and in our case it varies in the maxillary arch, Some

parts of the arch have a thick sub-mucosa, some of them have loose sub-mucosa and some

of them have very thin area.

Depending on the thickness of sub-mucosa, we'll find that some areas are designed well

to stand stress from the denture while other areas are not! We need to relieve or avoid

them from the denture so they wont cause pain, ulceration or friction in the patients

mouth.

We already said that in the incisive papilla area we have a group of blood vessels and

nerves (a relief area). In the posterior part of the palate, we have thegreater and lesser

palatine nerves (we dontwant a heavy load in this area either). Thankfully, we have thick

sub-mucosa so itwont be a problem.

In the midline palatine raphe, the mucosa is very thin, so it's a (relief area).

Depending on the tissue and the sub-mucosa, whether it's thick or thin and depending on

other factors you will see that some areas are considered primary stress bearing areas,

or secondary stress bearing areas and some are considered relief areas(we dont want

to place force on them).

If you look closely in some mouths you will actually see a groove (depression on the

residual ridge), it indicates where the facial and lingual gingiva met after healing (like we

said its a scar tissue). The position of this groove is sometimes helpful to us when we set


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teeth just as the incisive papilla is! It does not usually change its place with resorbtion so

it's a good guideline of setting of the teeth.

What can we see behind the maxillary tuberousity (the small depression

referring to the slides? Its the hamular notch, it's a soft area with relatively thick

sub-mucosa, the only thing that you can find here are tendinous attachments for two

muscles of the soft palate which are the : levator veli palatini and tensor veli palatini.

You cant extend the denture behind this area for a specific reason, because behind

it we have a rigid tissue, it's called pterygo-mandibular raphe. It attaches to end of

the pterygoid process of the medial pterygoid plate.

***In our body when we have a prominence() of bone, If you find the bone raised

when looking at the skeleton its raised because there is tension on this area ,and it

is usually attachment of muscle or a tendon.

9) Pterygo-mandibular raphe :

Its a raphe (attachment between muscles fibers) that extends from the pterygoid

process down to the posterior part of the mandible in an area called retro molar

pad "we will talk about it next weekinshallah".

Its not there for no reason,its a junction between muscles, its an anastomosis of

two muscles, which are the Buccinator and the superior constrictor muscles,Thistension (from muscles attached there) makes the bony process (pterygoid process).

If you want to look for this process in a young child, you properly wont find it, it

wont be very clear. Just like the mastoid process, it wont be very large.

Young children dont have large sternocleidomastoid muscles. These bones tend to

be larger and more prominentas time goes on because There is tension on these

areas. So, back here we have bony process and in the end of the bony process we

have pterygo mandibular raphe. So, I cant extend beyond here because I

essentially have pterygo mandibular raphe and i cant press so much on it because

its movable and on its level lateral to it I have the thin attachment of the soft palate

muscles.

However, the (Hamular Notch) is important because it delineate the posterior part

of the denture. posterior part of the denture is very important.


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Where do we end our denture posteriorly ?

-The junction between the hard and soft palate is notthe end of the denture, I

extend my denture beyond the anatomic junction between the hard and soft palate,

justonto the soft palate.

How far in the soft palate?

Thats determined by which part of the soft palate moves. We know that the soft

palate goes up and down, it closes up the nose from the oropharynx and closes up the

mouth from the nasopharynx when we breathe or eat. This movement will end on the

soft palate not the hard palate, that means that I can take an advantage of the soft

palate to determine the end of my denture.

*** usually the junction between the movable and the unmovable parts of the soft

palate is called the vibrating line .

Because the soft palate moves when the patient

speaks or says aaaah , we take a look inside the

patient s mouth and then we can see parts of the soft

palate in this area vibrating moving up and down

,here where we want our denture to end.

*so posteriorly we end our denture on the

vibrating line that is the junction betweenmovable and non-movable parts of soft palate.

If we go posteriorly, we reach the (Hamular Notch). Its difficult to see and not

every patient has a prominenttuberousity, usually well take an instrument like a

mouth mirror or a blunt instrument and run it along the residual ridge until the

instrument drops. When it drops we know weve reached depression we want.

The vibrating line is not always visible as some of these clinical pictures. So, here we

have the imaginary vibrating line which we said is usually not on the hard palate, itsjust into the soft palate , to find it we I do one of 2 things:

defining the vibrating line:

I ask the patient to say aaaah and I look inside themouth and I see where the motion starts I take an

advantage and use a special marking pencil and I


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mark it inside the mouth to see which part of the soft palate moves and which

part of the soft palate remains stable.

And also can take an advantage of certain anatomic landmarks. We know theretwo small dots depressions in the posterior part of the palate which are

called Fovea Palatine.

The Fovea Palatine are usually located 1-2mm behind the vibrating line they can be

anterior to it but usually its behind.

When we see Fovea Palatine we mark them

and we know where the vibrating line is ,

just in front of the Fovea Palatine by 1-

2mm. we use a a marking pencil (called copia

pencil)to mark so when I put a custom tray in

the patients mouth, the line will imprint from the patients mouth onto thecustom tray . So,I can even imprint it on the primary impression if I marked it in

the mouth before I take the impression then after marking I take the impression to

imprint the line on the impression material.

Copia pencil :( ,)custom tray

And usually we take it at different stages during the fabrication of the denture. Like I

said we take advantage of these Fovea Palatine. What are Fovea Palatinehistologically??

They are essentially grooves representing mucous minor salivary gland. They dont

have that much significance in the mouth except that they provide good landmark to

find the vibrating line. (In the posterior end of the denture). You will notice that the

posterior part of the denture depends on the shape of the soft palate.

We said that the significance of knowing the limiting structures is that we dont

want the movement of the muscles to cause a displacement in the denture. We saidthat the way the denture remains inside the patient mouth is very significant, Do you

know how exactly the denture is retained inside the patient mouth?.

Where do we get denture retention from ??

1- Physical forces that keep the denture in the mouth like (adhesion and cohesion)


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Adhesion and cohesion( you dont have to memorize the definitions its just to have

an idea about their meaning )

Adhesion: the property of remaining in close proximity .*

Cohesion: the act or state of sticking together tightly .*

*from glossary of prosthodontic terms

(

)

however in the mouth, this not enough, it is there, it helps us but its not enough to

keep the denture in the patients mouth while the patient chews, speaks, shouts and

whatever . It is there, it helps but it is not significant.

** Some students said that we use some kind of glue to help the denture stay in its

position (but we dontuse adhesives to prevent the denture falling by the gravity but

it has its own indications for special cases so in most cases we dont use denture

adhesive(glue) so we dont consider it a method of retention.

2-Sometimes, we have mechanical retention.

In some mouths we have prominent bone; we can keep the denture over the

prominence but it is not possible in every mouth and we cant take an advantage in

every mouth even if its there. We said the primary method of the denture will

remain in the patients mouth according to the Physical forces.

3- atmospheric pressure (peripheral seal): (the main force that keeps denture

in place)

there is something called peripheral seal (

)a suction force, the patient places the

denture in mouth , the pressure underneath the denture is less than in the

surrounding environment so the pressure from outside keeps denture in place. If the

patient tries to remove it, the pressure will resist the movement force. So, we have

negative atmospheric pressure underneath the denture.

How can I keep the area sealed to keep the pressure ?(

...) .. we are very fortunate the limiting structures in


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the labial vestibule and a buccal vestibule are already there, I have the cheek

buccally and the lip labially.

Posteriorly, I have a problem because I dont have a muscle that comes downI dont

have anatomical seal , I have a soft palate which moves but I dont have an actual

muscle that comes down and helps the denture.

So, what we said in the lab is the vibrating line is important because I dont want to

extend the denture posteriorly to the movable parts of the soft palate but I want to

go back as far as possible in order to extend the denture onto tissues that I can press

on.

The back part; the posterior part of the denture is made so that it compresses

slightly into the tissue soft palate (

..so the back end of the denture will actually press into the tissuenot a lot it wont hurt the patient it only goes (half) mm in depth.

So, the cheeks and the lips they will come down and they will create a seal.

posteriorly, because the soft palate doesnt come down like that so what I do is that I

design the denture in away to make itpress or go up into the soft tissue.

the significance of the vibrating line is

1- it helps me go as far back as possible to make maximum coverage without going

into mobile soft palate.

2- it helps me define the area where I can press the tissue to get posterior seal.

If I end the denture on the hard palate the tissue is very thin so I cant compress it

without traumatizing the tissues so locating the vibrating line is very important

thing to create the seal it is called border orperipheral seal. It will give me retention

for the denture.

4- Physiological forces/retention(muscular control): some patients even if the

denture doesnt stay in the mouth by itself, they are able to keep the denture in their

mouth just by trapping it between the muscles ( ) Buccinatorand orbicularis oris (

) this varies

from one patient to the another. Some patients can control the denture and brace it

and other patients are unable to do that) .so we try to make the denture as

retentive as possible by itself using the other forces available without an effort from


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the patient. The Physiological forces/retention from muscle is more important

for the mandibular arch than the maxillary.

Palatal form and its effect: (softpalate)

The palatal form is different from person to person, some people are tall some

people are shorter.The soft palate is sometimes more horizontal in some patients or more vertical in

others . These positions make it easier or more difficult for us to create the posterior

seal (

)

Soft palate classification: House classification

the horizontal is class l , the vertical is class lll and class ll is the one in between ,

the most favorable is class l ~

-In general, class I represents the gentle movement, class III represents the excessive

movement, while class II lies in the middle.

Hard palate and residual ridge classification:

-the residual ridge is important but the part of the hard palate is also important.

Which shape do you think is better or more suitable to support the denture???

(remember you need a residual ridge for stability and a hard palate for support) .

the U-SHAPED palate is the bestone because you have a residual

ridge at the edges laterally to

provide some stability from sideto side.

The flatIS EXCLLENT retentionand support but there is nothing

on the sides; slight movement


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may hurt the peripheral seal no stability.

The rounded is acceptable. The V-shaped properly the poorest.

The residual ridges how they can be?

Sharp, rounded, prominent or undercut.

A nice well rounded ridge is properly the best type. rounded ridges are properly a

good supportfor the denture because they have the largest surface area so the load

is well distributed it wont cause pain at the crestof the ridge and it wont let the

denture sink into the sulcus .

*** atrophy is much faster in bone than in the soft tissue. ( )

so, when the bone resorbs , what will happen to the soft tissue??

The tissue will become loose just like someone whos very healthy they lose weightso they become thinner suddenly then the clothes will be loose. In the mouth this is

the situation. In the mouth, the bone resorbs then the soft tissue on the ridge

becomes loose in some cases, in these cases its very

important to

remove excess tissue surgically before making thedenture .

or we take our impression in a very special way to tryto record the perfect fit despite the excess tissue.

**Torus Palatinus:


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Earlier we mentioned that the mid palatine raphe is important because the

overlying tissue Is very thin, in the median

suture of the mid palatine raphe

sometimes there is a protrusion present

called: Torus Palatinus, it is basically a

bony mass very compact dense bonefound in one of every five patients (20%).

The size of these Torus differ (can be

small or very large) but the tissue

overlaying the bone is very thin, meaning that any excessive pressure on this area

will cause trauma and irritations to the patient therefore we cannot rely on this area

as a Denture support area because of patient sensitivity as well as the fact that its

not present in most patients. Attempting to remove the Tori surgically will lead to

formation of heavy scar tissue and cause irritation. there is also Tori in the

mandible usually lingual to the canine (not a tumor just a bony mass)

We only remove it in some cases when its too big and causes interference with

removal/placement of the denture.

Finally we will discuss the directions of resorption :

In different parts of the mouth the bone have different angulations.

In the upper anterior part of the mouth the teeth & the alveolar bone areslightly proclined at around 15 Degrees. (

, ),

in the upper posterior part of the mouth the molars are angled very slightlyoutward so you can see the direction is buccally (the alveolar bone of the

posterior molars follows in the same angulation),

In the lower anterior teeth & alveolar bone is angulated slightly outwards. The only exception to this rule is the lower posterior teeth which are

angulated in an inward direction (toward the tongue not toward the

cheek) because they are trying to balance out the upper teeth which are

angulated outward.

** Lower posterior teeth are the only teeth that are angulated inwards.


20/20

/

Recall from the curves of occlusion that the occlusal plane is curved. (Curve of

monson , curve of spee and the sphere of willson). When we extract a tooth the

alveolar bone beneath it will start to resorb or atrophy so it becomes shorter,

Compare the crest of the ridge before extraction and after extraction. Did it move

towards the palate or toward the cheek??

It moved towards the palate. ( ), another example: This is theresidual ridge before and after (referring to the slides) ( ridge ) . Themiddle of the ridge becomes shorter and inward (further palatal). This is the case for

all the Edentulous Ridges (Ridge & Bone) except the posterior of the mandible

mandibular posterior goes outwards and the maxillary posterior goes inwards

(they are moving opposite to each other).

You will find that the movement/resorbtion of the ridge has a significance in

making a denture and it has a significance in where we put the teeth during setting in

the lab.

In the upper arch we will put the teeth outside the Edentulous Ridgesto

compensate for the resorbtion .

In the mandible, we will try to put them further in to mimic the situation

before they were extracted.

**The lower posterior teeth are the only ones that resorb differently.

**Maxillary Arch becomes smaller

**Mandibular Arch anteriorly becomes smaller, Premolar area stays the same

& posteriorly it will become larger.

Date post:	06-Apr-2018
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Prostho Lecture 2 Anatomy of Edentulous Ridge Done

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