DM Sheet #11 By Mohammad Al-Shantir

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DM Sheet #11 By Mohammad Al-Shantir

Post by Sura on 11/12/2011, 2:28 pm

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Sura

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تاريخ التسجيل : 2010-09-29

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Re: DM Sheet #11 By Mohammad Al-Shantir

Post by Shadi Jarrar on 23/12/2011, 7:31 pm

Dental ceramic

Last time we have talked about metal alloy and cast alloy, today we are going to talk about dental ceramic.

90-95% from our preparation either full ceramic or porcelain fused to metal crowns.

We have talked about cast alloy and we said that there is not a lot of science about it.

The CAD/CAM technique (this technique make a lot of changes in dentistry), this technique very useful for ceramic crowns…we will talk about it in 5th year.

In Jordan:

Restoration cost in avg: 20 JD

Crown cost in avg: 100 jd

The cost of crowns it’s not just come from dental lab or material cost….it’s come from our preparation.

Expectivity for our restoration 7-8 years, there is study by cheven burgs say that life time for amalgam or composite is about 5-6 years.

Crown and bridge life time (12-13) years, so we charge the patient better service, so the patient have to pay extra for that.

The patient when he/she come and want w a crown, he/she expect the high cost.

Until 1700-1800 there is no ceramics or porcelain in Europe except in royalty, the was imported it from china.

Mr. Marco polo: he tries to describe the ceramic, and he say: it’s something snow white light, it gives a sound like the sound of metal.

We talked about histological background in area in Germany 1917, china known by chinaware.

The dr start to talk about the best president in united state, and the dr said “George Washington” the best president.

French people, they talked about feildspathic porcelain.

Porcelain fused to metal: if we do a good preparation and good mechanical requirement; the life expectancy up to 15 years or more.

After 2000: zerconia age (north Italy)……zerconia: industrial diamond we cannot trim it by manual laboratory method, we should do it by with CAD/CAM technique.

Chinaware consists of:

1) Silica

2) Cowley (mainly)…الطين

3) Network modifier...feldspathic less than 10%

In dentistry we don’t need that. We care about translucency, and to have a structure that reassemble the tooth structure.

In dental ceramic there is no Cowley.

Dental ceramic:

1) Vitira silica (not crystallized)...strong part…high melting temp.

2) Network modifier

3) Net forming offside (for radioobacity)

4) Fluorescent offside.

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different t wavelength.

Feldspathic porcelain it’s the first one industrial…..70% from porcelain.

Feldspar: something either related to sodium or to potassium.






Silica either amorphous or crystalline.

Crystalline won’t give us the properties that we want; the material dull and opaque (not very glassy).

If we need strength we go to the crystalline…densely centered pure zirconia or alumina.

The other side if we want more Esthetic …so we go to feldspathic.

Bond strength: increase if there is short bond!! And if it connected all around like crystalline one.



Network modifier: For open those more (I think the dr mean the bonds).

We want to add something to metal to modify it so the melting temp for the metal will be more.



Considered for structure we classified it to types:

-Predominantly glass structure amorphous

-polycrystalline material

Another classification either use it as veneer materials, above metal or tooth structure….we use feldspathic porcelain, glass ceramic, hot press ceramic, zirconia,alumina or inceram(rare).

-impress ceramic for anterior tooth…translucency sometimes better than zirconia.

Veneers: something we put it above another structure, and that’s for more Esthetics, strength come from underlying structure.

-particulate feldceramic mainly:

Polycrystalline (alumina, zirconia)

Cast glass ceramic

Loucyte. (loucodisilicate…im not sure)

How to make ceramic?

From four types of material:

-sinitering (powder +water … we mix them, then heated to 800 degree)

-ceramming cooking (heating) the material to certain degree (more than the sinitring…..maturation for bonds) like Pyrex (heat treated glass).

Corning company –newyork it’s the first company that discover Pyrex, also it’s the first company that discover dental ceramic…”Dicope”..There are a lot of studies about dicope, we use it for 20 years but the company had stopped the production of dicope, it could last for 15 years (weak material for us).

-pressing cementring (not sure): time consuming, need very professionals ceramist (adding layer by brush), high cost, so difficult…there is easier method by wax up technique and pressing by lost wax technique like wt we do with metal.

-machining CAD (computer aided design)/CAM (computer aided manufacture)

Foley melen is the prototype of CAD/CAM….its look like ((خراطة المفاتيح.. it’s like to take take a structure and make something like it…to make structure based on known processing.

Zirconia we can’t make it by sinitering or ceramming so we go millen by CAD/CAM.

Properties: biocompatibility:

It’s an inert material (can’t do any foreign body rxn)

Glad surface: best surface for cleaning the tooth…it’s the best surface after the tooth.

Enamel very glad surface.

Bacteria cannot attach to glad porcelain surface.

Color maintenance: composite and acrylic after 5 years we may say some color change…..porcelain it must not change! Except here in Jordan (it’s May due to quality of the material or….)

It’s a brittle material; that’s due to the covalent bond; stronger in compression than the tension, its multifactorial material…it’s a layering technique so maybe we find voids.

Fracture toughness:

Zirconia>alumina>feldspathic porcelain

The dr start showing us cross section graphs…..crown consist of two layers: core and veneering porcelain …..Core with alumina or CAD/CAM there is no voids but the material that build up by dental lab (hand made) there is a propapilty to see voids by cross section.

Voids: weak that’s decrease the fracture resistance.

The main disadvantages of full ceramic crowns is……fracture……but the zirconia better there is a crack healing mechanism we will talk about zirconia next week ensha2 alah.

How to strengthen our ceramic???

By lamination, put it on the top of metal but we have to be certain from the coefficient of thermal expansion and bonding technique.

The coefficient of thermal expansion for the metal should be more than porcelain.

Lamination: porcelain outside…metal inner side.

Other more strengthening by alumina ( alumina zaget crowns)

Glass infiltration in inceram.

Problem in porcelain: its do abrasion to tooth structure (enamel) especially if the porcelain not blazed...”veneers do abrasive more”

Although the zirconia stronger than feldspathic but the feld spathic do abrasive more than zirconia.

The translucency, the highest in feldspathic.
Done by: Mohammad Al-Shanitr
Dental material no:12
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Shadi Jarrar
مشرف عام

عدد المساهمات : 997
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تاريخ التسجيل : 2009-08-28
العمر : 26
الموقع : Amman-Jordan

http://jude.my-rpg.com

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