DM Sheet #9 By Aseel Al-badayneh

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DM Sheet #9 By Aseel Al-badayneh

Post by Sura on 8/12/2011, 2:28 am

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Sura

عدد المساهمات : 484
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تاريخ التسجيل : 2010-09-29

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Re: DM Sheet #9 By Aseel Al-badayneh

Post by Shadi Jarrar on 23/12/2011, 7:37 pm

بسم الله الرحمن الرحيم
The First 7 minutes was about the exam questions
Now about metal alloys, and casting alloy that we talked about with dr Nadia in general view , but with dr rabab3a we will talk about fixed prostho- dontic as crowns and bridge , about metal alloys proprieties, face diagram , and the classification of casting alloys .
- When to use alloys and not to use pure metal??
- What does alloy mean??
- Why do we use alloy instead of pure metal??
-what are the proprieties for materials used in dentistry?
- 1. Bio compatible “non toxic” Toxic mean irritation, necrosis (liqufactive ), others.
- you should know that the first part of bio compatible is non toxic , but also no adverse effect is another part , even the color effect is part of bio compatible .
- if the material is toxic , so its non bio compatible at all , but not all non bio compatible material cause toxic it may cause body reaction" not toxic response "
Example: nickel in crown and bridge not bio compatible by 0.01 especially women 10 times more than men.
2- Not expensive: until the seventies, gold had been used, because it was cheap but nowadays 1 gram of gold about 40 JD according to3yar 21/24/18.
So we need some thing affordable to our patients but
Minimum price that we can charge in Nfabh Dentists is 80 JD s/ each crown if it makes from base metal alloys .
* some one ask about the cause of dental failure and doctor say it not due to martial proprieties but due to techniques failure because all our material tested .
3-easy to fabricate: in crowns and bridge its not easy to fabricate.
4- durable.
5- Have at least 50% mechanical prosperities .
6- strong enough.
7- Compatibility with over laying structures that in most cases will be ceramic. “Important “.
So not all alloys can be use with ceramic.
- 80 % of dentist working in crown and bridge are porcelain fused metal crowns (or) ceramometal crown and bridge work.
* when we talked about bonding , we talked about malarial " monophore " and its rule in The fifties to increase bonding strength of the material .
"Coefficient of thermal expansion for metal alloys suitable for porcelain, this concept done by 2 scientists " enistin one of the scientist
"
* Utile now, the bonding between different alloys and ceramic, one of the most durable bonding we have.
* If our clinical technique is good so delaminating or fracture or are negligible.
* some time you see broken porcelain and the underlying metal with expose to you and this what called de lamination due to technique problem rather than materials one except when titanium was discovered as metal used in crown and bridge work , they discover that titanium not bond to ceramic in good way .
* the materials classified to 3 categories :
1- metals / metal alloys .
2- ceramics:
is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling.wikipedia
3- polymer based on repetition of carbon bonds between monomer units and this mean the polymer is organic material so the main bond in polymers are " covalent bond " , and in ceramic its also covalent by silica interaction with different particles .
*IN metals its different story , the main bond is ionic bond , that the electrons are loosely held in such as molecules or atoms and this affect conductivity ( electrical conductivity and the thermal one ) and in the same time all metals are opaque , so aesthetic with ceramo metal crowns are not as equal as natural one , for this reason we go away from porcelain fused metal in anterior teeth , because we need more natural appearance , another thing is flashing or shiny propriety that we don’t need so for example we do amalgam polishing to not get shiny in side patient mouth .
* The doctor asks about the advantages of metal shiny in clinical situation?? The students answer but not clear what they said in record.
* Again the electrons are loosely held, we are talking about “metals own structure”
* Above atoms and molecules level as we have polymer unit which is "monomer”, in metals the crystals consider the main component above atomic level of metals .
* if crystals size are small , so more aesthetic .
* 14 different type of crystals : : body centered cubic " most common use " hexagonal , and face cubic . – example on each type use in dentistry its important in exam
jgelder@okway.okstate.edu "I found this site useful"
- the doctor shows pics about different types one is hexagonal , the second is body centered , the last is face centered …we based on atoms position if its out side cubic then its face type but if its inside cubic its body cubic.
* the metals we use its strength are 10 times the strength measured in lab if they packed well and in the way we see in picture but due to dislocation that happen in metals " when crystals growth or (?) so deformation and spaces either interstitial or as dislocation .
The doctor shows pic …. Space between crystals, so not equal distance between crystals , and the strength will be reduced .
* in some cases our patient suffer from broken bridge " due to metal dislocation .
* some one ask if the formation not happen so are we get dislocation ??
The doctor says no , the crystals will from , but any procedures we do , have Impurities , and this Impurities not allow for crystals to grow in one direction but the crystals will grow around Impurities , and because the metal alloys formed by melting and when boiling start each groups of crystals well get together , and between these group distance not have pure material 100 % .
* so gold 3yar 24 not 100 % pure we have some Impurities , and gold 3yar 21 has 75 % pure gold . so we always think how to increase metal strength .
* high % of our patients need at least one crown or more,
if the population count is 7 milliar so we need at least 7 million crowns , and bcz elder need crown more than young , and
crowns failure per year are 1-2%
* after 22 year , we will lose 25 % of our crowns so the failure percentage is low(1-2%) but its impact is high , so we try to increase the strength of the material .
* in the world ,,, from the deformation we lost 3-4 milliars .
{{Harding, Placipitation, cold working, drying filing}}} to increase metals strength .
Drying file: to control crystals size the the crystals growth should be slow and to reduce dislocation and spaced as we can .
Cold working: while the metals getting boiling we try to get precipitation Harding but after the material get hard and cold down what we can do is annealing that mean heat treatment , but cold treatment as wrought alloys we do amiability ductility ( wires ) .
- another example of cold treatment is endo file by twisting or bending .
- the student ask about how does cold working improve strength ?? how can we get drying filing ??
Drs talked : about freezing idea and how can we freeze material rapidly and by add some type of material to let crystals size smaller
* another student ask How cold working improve strength although of internal stress during bending , so in ortho we heat wire for 2-3 minute to get rid of internal stresses .
* the dr answers : ortho wire are already been done , and cold working , and for example if want to do wrought wire any dislocation present will be dissipation ( 37:52) so for that ( not clear in record but the doctor says in next lecture will explain this point ) .SORRY
Alloys : 3 different type
Solid solution , inter metallic compound as amalgam ,lactic mixture(?)
Now solid solution mean completely nested when heated to melting point then colded we can't separate them ( physical process without chemical reaction )
Intermetalic compound react as non organic compound reaction as gamma phase in amalgam was react with SG(chemical reaction )
* what is the gamma phase ??
* in solid solution the main goal reach that the range melting point higher than melting point for metals and we say range melting point because we can't separate metal from metal , and so they melt in temperature higher than both metals and also the corrosion resistance will be higher .
As example of solid solution t is stainless steel but when (??) involvement the corrosion resistance will be less .
*lactic mixture :harder and stronger than other materials but they are brittle and having special melting point and we mix in specific amount .
AS the crystals size are smaller ,the better mechanical properties so one of the methods to increase metals strength is dying filing .
*what yield tensile mean ?yield tensile differ than ultimate tensile .
*all materials during solidification will be shrink except one material which is water so aqua marine species will not die and skiing sport will beJagain about solidification shrinkage rather than water ,when we do alloy or crown preparation and take impression ,the most important thing is to get accurate detail and size
_In our practice we do wax up for the tooth of assize similar to the tooth then metal will replace this wax and get solidification so if shrinkage happen the metal will not fit the tooth ,so we need to compensate for solidification shrinkage by some methods while cooling at room temperature and while still in liquid phase and this related to use investment materials that have some thing called hydroscopic expansion for investment materials by widening the mold that material get in .
Another method to face solidification shrinkage by melt the wax up and inject the melting metal and this technique called casting .
*we talked about corrosion in amalgam and we will go again to corrosion
*metal alloys cause allergy
*silver and copper cause discoloration
*in American dental association we have high noble alloy ,noble alloy, base metal alloy and this related to the prices of metals .
-high noble alloys contain at least 40%by weight gold and 60%of noble metal alloy
-example of noble alloy are gold ,apron
-example of high noble alloy are palladium .platinum
-so palladium= .platinum=gold in cost
-noble alloy contain at least25%of noble metal alloy or metal base alloy .
*another classification “creptic “……normal fusing alloy, high fusing alloy that we raise temperature so when we put porcelain no dimensional change occur involving both palladium platinum ,palladium silver ,high palladium ,base metal alloy .
-base metal alloy either nickel chromium ,cobalt chromium .
As you know the sheet not enough for exam L


Good luckJ
Done by: Aseel AL-Badaineh
Dental material # 9 for DR Rabab3a
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Shadi Jarrar
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عدد المساهمات : 997
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تاريخ التسجيل : 2009-08-28
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الموقع : Amman-Jordan

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Re: DM Sheet #9 By Aseel Al-badayneh

Post by Sura on 5/1/2012, 1:32 am

correctio by
Aseel Al-badaineh


correction for my sheet dental material #9
page number 1:why to use alloy instead of pure metal ?bcz alloys have good physical,biological proprieties and long term use
page number 5:how to improve strength ?
1-alloying
2-precipation hardening
3-grain re fining
4-cold working
page number 6:type of alloy (solid solution ,inter metallic ,eutic mixture
page number 6:yeild strength:stress require to permanently deform alloy ~.1-.2%
page number 6:an example of solid solution is stainless steel that
with iron alloy the the corrosion resistance will increase but with gold
alloy will decrease
page number 7:type of corrosion are
1-dry
2-wet
* generalized
*localized (pitting corrosion, inter granular corrosion,crevice corrosion )
Im really sorry about this mistakes :)
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Sura

عدد المساهمات : 484
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تاريخ التسجيل : 2010-09-29

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