prostho sheet # 7

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prostho sheet # 7

Post by Shadi Jarrar on 16/11/2010, 2:54 pm

بسم الله الرحمن الرحيم

_____________________________________ ?mbr2tlwe1dohuqg

Tuesday, November 02, 2010
بسم الله الرحمن الرحيم

In the last lecture we talked about :
 determination of arch form to determine the occlusion form
 vertical dimension and issue factors depending on which we determine the vertical dimension
final step : determining the maxillo-mandibular relation on bite registration . so we want to determine the record between maxillae and mandible at desired vertical dimension at occlusion .
Hint  vertical dimension :” a vertical measurement of the face between any two arbitrarily selected points that are conveniently located one above and one below the mouth , usually in the midline .” (CCDT)

Horizontal component determination :
this relation between maxillae and mandible in edentulous is bone-bone relation , because we do not have any teeth to know the relation .
centric relation : 1- the most posterior relation of the mandible to the maxillae at the established vertical dimension.
2- anatomically; the relation of the mandible to the maxillae when the condyles are in their most posterior-superior unstrained position in the glenoid fossae , bone to bone relation , from which unstrained lateral movement can be made at the occluding vertical relation . so the centric relation is a designation of a horizontal relation , and it is recorded between upper and lower bite blocks .

The importance of centric relation : the only movement the patient can repeat , where as he is unable to repeat any jaw position in the same way due to loosening of tactile sense . If the centric relation is recorded improperly , the completed dentures will not function correctly in the mouth .

Centric occlusion : is the relation of opposing occlusal surfaces that provides the maximum planned contact and/or intercuspation .or in other way “ relation between teeth at centric relation .
Normal person has centric occlusion with few points of interference that make contact ; like once you close your mouth the upper sevens come in contact with opposing teeth = this is your centric occlusion , the the mandible will deviate to achieve maximum intercuspation .
In our complete denture , maximum intercuspation same as centric occlusion .
What do we mean (even or planned contact ) ?
When the patient closes the upper and lower jaw simultenasly right and left side close with each other , so if you ask your patient which side is higher right or left ? he must answer you : they are the same , so there is even contact between upper and lower jaws .

Importance of even contact :
1- during final centric relation record , lab step can be done by:
 creating V notches in upper jaw in the bite registration at first molar .
 In lower bite block : we put the material that will enter in V notches , this material
can be made of : - zinco-oxide eugenol
- wax or any kind of material .
2- important in relation to mucosal compressibility dye do applying forces to make the jaws at even contact due to flexible tissues .
3- to stabilize the mandible during mastication , how ? if there is initial contact between the jaws at right side for example , then the patient will search to create contact in the left side so shifting the mandible , means you are not at centric relation .

How you can achieve even contact in the lap procedure :
Slight softening of the surface of the wax , then ask the patient to close in most physiological retruded position to get centric relation and at the same time centric occlusion (even contact ) .
How you ask your patient to get centric relation :
You will not ask the patient : put your mandible in most physiological retruded position , he will not understand you . instead , you ask him indirectly by :
1- you till him to move the mandible backward
2- or protrude the upper jaw .
3- or close on your molars
finally , you will obtain the centric relation .

Relation between centric relation and centric occlusion : centric occlusion should exist when the mandible is in centric relation to the maxillae. .

Information you can get from bite blocks :
1- mid line determination .
2- canine line at ala of the nose . The distance between tips of two canines = width of anterior teeth
3- high lip line
4- low lip line is already determined by incisal edge .
Distance between incisal edge and high lip line = length of the teeth . by this point and distance between tip of canines , we do selection for artificial teeth . so that you can sit the artificial teeth in balanced occlusion , by understanding the factors that will govern the articulation and occlusion .

Model – bite block relation :
It is very important that model must sit on the bite block properly
Cases :
1- during mounting , the bite block does not completely sit on the model = error in your bite registration .
2- model must sit on the bite block properly 100%. Within the patient’s mouth you may add wax , the biting on the added wax , so compression of the mucosa , the added wax will sit . However on the model ,the bite blocks will not sit completely due to lack of compressibility .
At the end , your concern is relation between two models ; how the are related to each other on the articulator by fixation of this relation through bite blocks .

Face bow record :
Another record that we record by bite blocks .
By this record we take the relation between upper arch and TMJ . we need the bite blocks to transfer the relation .
How ? the material on the bite fork of face bow will enter through the V-notches on the upper bite blocks . then we do mounting of upper model on the articulator according to this record . in the same meaning : we make mounting plate made of plaster upon the model to fix the relation between the model and TMJ through the bite fork .
Our wish from this step :
Relation of upper model with condyles of the articulator = relation of upper jaw with condyles of TMJ in the patient’s mouth .
(importance for this will be discussed later on ) .

Protrusive record
Or extrinsic record , another record that we record by bite blocks .
This record means : when the patient bites the mandible must be protruded not retruded . During this movement , there is no contact , a space is created between upper and lower jaw , which is triangular in shape due to:
- overlapping between upper and lower anterior teeth
- mandible moves downward
- movement from centric position to protrusion position , this triangular space called “ Christenson’s phenomena”
Explanation : how this space occurs and why :
During protrusion of the mandible “moving the mandible forward” , then TMJ inclined downward due to bony prominence at the articulation with cranium , this inclination will push the mandible away from maxillae then the space occurs .
This space has relation with condylar guidance angle .
Condylar guidance angle : is the angle produced between Frankfort plane and condyle inclination .

Hint Frankfort plane : is a theoretical plane which passes through the center of rotation of the mandible ( condyles) and the inferior border of the bony orbit .

How we record the protrusive record in the patient’s mouth ?
We can know this by putting basoplastic material like silicon between upper and lower bite blocks ,and when the patient moves the mandible forward , the material will have the same shape of the space . after setting of the material , then the material has wedge – shape . the width of the wedge related to to the condylar guidance .

Artificial teeth selection :
Anterior teeth selection

1- length of the teeth , by height of smile line
2- width of anterior teeth , by distance between two canine lines .
3- color of the teeth , related to complexion of the patient.
4- shape of the teeth .
5- material used

You have to consult the patient to determine the esthetic factors ( color , size and shape ) , because if you do any thing without asking your patient if he wants that or not since the dentist and the patient have the same level of understanding of esthetic factors , then your treatment becomes failure at the end . failure means ; if the patient wears the denture or not .
However , another factors like balance , occlusion etc can not be understood by the patient and you do not have to explain them to the patient , you just have to instruct or guide the patient to obtain such factors .

Details of the esthetic factors :
1- color of the teeth .
It has three components :
A- Hue: what is the color , orange yellow ,red etc .
B- Chroma : the concentration of the color in the tooth
C- Value : the most important one , lightness of the color

Ex : you have two teeth , they may have the same hue on gray scale , and the same value “ lightness” but on real life , one is gray and the other one is red due to different in concentration of red color “chroma” is different .
Hue and chroma , you can decide them as dentist but the value you must ask your patient
This can be done by pair comparison method :
Means  you show the patient two extreme shades one light and a dark one
 ask the patient to point to the preferred color
 eliminate the other and bring another in the preferred half of the shade guide
 ask the patient to make another selection , eliminate ,add, let him select until reaching to final decision .

The factors that may help you in determination the color of the teeth :
1- if the patient has an old picture for himself , it will give you an idea about the original color of the teeth as well as shape and size .
2- old denture , so we have base line , comparison between the old denture and the new one .
old denture:
a- patient likes the old denture but the teeth are attrition . all what you do just correction of attrition .
b- patient does not like the old denture.
c- patient says : “the color of the old teeth is dark” and when you look to the shade grade you find that color is the lightest , so patient wants unrealistic teeth , you have to discuss this with him .
Extracted teeth help you in determination the size and shape of the original teeth , but they will not help you to know the original color that changes once the tooth is extracted from the patient’s mouth .
Hue at the neck of the tooth is highest , and it is reflected by the dentin because the enamel is translucent . Tooth looks blue at incisal edge . the blue color has the shortest wave length and it highly mobile in the object , as a result it has higher percentage to interfere and return within the object . on the other hand red color has longer wave length , it has smooth pathway in the object . on the teeth what we see is reflected color which is in this case the blue color .
Central incisors are the lightest teeth , so we choose the shade of them at beginning then the color of the remaining tooth will be graduated by the manufactures.
Posterior teeth are lighter than canines , hue at canines is the highest because of the thickest layer of dentin found in the canine .
Final judgment at try in , when you put the teeth against the lips and moisten tooth before selection , because this might change the way the teeth will look , patient might change his selection. You must take in your consideration lightness in the clinic , clothes that patient wears , and ladies should not put any make up . because all previous factors affect on the color of teeth how they look in the patient’s mouth .
There are another factors may play role in the color determination :
Color of the skin and different society with different esthetics concern.
‘any mistake in choosing the anterior teeth , the dentures look artificial .

2- shape of the anterior teeth
basic shapes of the face :
1- square , so the teeth have to be square.
2- Tapered , same thing the teeth have to be tapered narrower at the neck and wider at the incisal edge .
3- Ovoid , between square and tapered , teeth have to be ovoid .
The shape of the central incisors have the same shape of the edentulous upper arch .
The shape of the central incisors has the same shape of the face ( leon Williams classification ) .
However there is no scientific evidence .

3- Size of the teeth
Criteria for selection of size of the teeth :
It has two components : length and width .
 length
Upper centrals overlap the ridge by 2-3mm cervically and show below the upper lip by 1.5-3mm according to age
or the length is dictated by the difference between the high and low lip lines .

 Width
 intercanine distance . width of upper 6 anterior teeth between the tips of canine = the width of the nose
 width of the central incisor tooth = 1/16th the bi-zygomatic width of the face
“there are another criteria were not mentioned in the lecture , please return to the slides “

“ YOU should discuss the esthetics factors with your patient , and use all available tools that may help you to know the original shape and size of the teeth, like extracted tooth , pictures etc”

4- material
artificial teeth made of : :
a- acrylic
b- porcelain

details :
a- acrylic :
- cheaper than acrylic
- made of plastic
- problems in acrylic teeth :
1- attrition with time
2- changing in the color .
these problems can be solved by : building up of layers of acrylic ; the outer layer in relation to inner layer harder, and more cross linking . less layer must be cross linking because crossing makes the bond between the denture and base is less
3- acrylic teeth have more natural look
4- more resistance to discoloration due to cross linking in the outer most layers .
5- thermal expansion of acrylic is same as the denture base
6- they break in small pieces
7- when the teeth come in contact , the sound is more assuring .

b-porcelain :
-they come in form of powder , the shape of powder is determined then setting in form of layers occurs in the oven by connecting the particles together .
- problem of porcelain :
1- it does not bind to the denture base very well , because they are different material . to solve this problem : there must be mechanical retention can be created by :
- pins in the anterior teeth
- holes in the posterior teeth , in which the porcelain enters to get mechanical retention .
“there is no chemical bonds “
3- different thermal of expansion between porcelain and denture base , then traces line or cracks occur between teeth and denture base . so discoloration of the denture base it self .
4- they may fracture .
5- the teeth when come in contact , they give alarming sound .

 some patients have limited space between upper and lower arch , so you have to make attrition in the teeth to reach the limited space :
1- acrylic teeth : mechanical retention is maintained
2- porcelain : attrition will move the pins .
they may fracture .

If the patient has opposing teeth :
a- if there are natural teeth with bridges , and bridges are made of porcelain , so you go with porcelain in choosing the artificial teeth .
b- if the opposing teeth are natural without bridges , we do not prefer porcelain because it is very hard and it will abrade even the natural teeth .

 some times we choose the teeth so that posterior teeth are porcelain and anterior teeth are acrylic teeth , but the opposite is contraindicated , because the acrylic posterior teeth abrade then contact is only anteriorly , the resorption of anterior ridges ; which must be maintained since the posterior ridges are stronger than anterior ridges.
In Jordan , we use acrylic teeth and the problem is attrition with time as we said , but after period of time say 5 years ,you have to change the denture , so it is not a big deal .

Posterior teeth size:
 Width of the posterior teeth in the denture must be less than natural teeth for two reasons : 1- to give more stability to the denture , to give more area for movement of the soft tissues like tongue , lips and cheeks .
2-to reduce the masticatory load / masticatory cycle . so that less applied forces on the denture , because the soft tissues are not designed to carry the masticatory load . so reducing the force on the incisal edges to reduce the chance of resorption .

length of the posterior teeth ;
Where we stop setting of the posterior teeth . usually we start with canine line and stop at the inclination of the mandible ;at rahmus of the mandible . at the inclination of the mandible we don’t set the teeth , because this will make the denture to shunt or moves when ever the patient bites on the teeth that are located on the inclination .
We can do that “stop setting of the teeth at inclination” by
- some times we don’t set a premolar , so we have only 3 posterior teeth . or even mo move a molar
- reduce the width of the teeth mesio-distally . but you must take in your consideration the width of the first pre molar same as canine ,from esthetics point of view .

 Classifications of the teeth according to occlusion :
1- monoplane “ flat”
2- anatomical teeth , with cusps , fossae and grooves exactly as natural teeth
3- semi-anatomical , they have the anatomy of the natural teeth but cusp angle is less .

Details :
1- Monoplane , masticatory efficiency might be less .
You choose this if the patient is old , you are not sure about centric relation and if ridges are severely absorbed. If the patient has an old denture with monoplane occlusion , so you must maintain the original situation . but if the old denture was anatomical teeth then it changes to flat , but he is complaining of masticatory efficiency, you choose the semi-anatomical teeth , don’t choose the anatomical teeth

2- anatomical teeth , problem is : the will impose lateral forces because there are vertical forces acting on the inclined plane , so denture will move
but if you make the teeth flat occlusal surface , no vertical forces on the ridge so the mandible will moves right and left he has freedom in the movement , but at this situation where ever the patient bites the denture set in its location .

so you choose the monoplane or flat occlusion plane if the patient :
- is old
- he can not coordinate his movement properly
- or he can not center the bite properly .

your choice is anatomical teeth
if he is young , and he prefers to have good masticatory efficiency, or his old denture was with anatomical teeth and he is satisfied with this .

Also determining the occlusal form depends on your skills , if you want to choose cusp teeth you must have more skills and more sophisticated equipments :
- semi adjustable articulator ,it is a kind of articulator designed to be adjusted so that the articulator movement simulate the jaw movements of the patient . the word simulate is used because the the condylar paths have a fixed contour which can not be altered and the distance between the condyles cannot be varied .
- face bow record
- extrinsic record ; protrusive record
- lateral check bites .

cusp teeth or anatomical teeth , the patient becomes a vertical chewers “imagine the lion during chewing, it does not have lateral movements” . this condition can be seen in the patients who have class 3 malocclusion ; mandible is forward in relation to maxillae , no lateral movements due to great interferences between the opposing teeth.

That’s all for this lecture , please study the lecture carefully in coordination with the slide , because not all information are mentioned in the lecture .

و آخر دعوانا أن الحمد لله رب العالمين
و كل عام و نحن لله أقرب و أمتنا الإسلامية و العربية بألف خير
إعداد : أمانـــي إسماعيــل الربابعة

من عنده بستان في صدره من الإيمان و الذكر ولديه حديقة في ذهنه من العلم و التجارب فلا يأسف على ما فاته من الدنيا .
أصبح يونس في قاع البحر في ظلمات ثلاث فأرسل رسالة عاجلة فيها اعتراف بالاقتراف ، و اعتذار عن التقصير ، فجاء الغوث كالبرق لأن البرقية صادقة .
Shadi Jarrar
مشرف عام

عدد المساهمات : 997
النشاط : 12
تاريخ التسجيل : 2009-08-28
العمر : 27
الموقع : Amman-Jordan

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