afnan ali shayma albaloushi aya al-asmar · 2019-03-29 · afnan ali shayma albaloushi __ aya...
TRANSCRIPT
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10
Afnan Ali
Shayma Albaloushi
__
Aya Al-Asmar
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-All calcium hydroxide cements, zinc eugenol and zinc phosphate
depend on micromechanical interaction with the tooth. There isn’t
any chemical adhesion. (no crosslinking with the teeth)
• It was the first cement system developed with potential for
chemical adhesion to tooth structure. Applications:
• Primarily for luting permanent restorations. -Ex: If you want to replace temporary crown with permanent crown you
should use permanent luting agent such as zinc polycarboxylate. After
adding that you can't simply remove it (like in zinc oxide eugenol) because
it adheres by chemical adhesion with tooth. To remove it you have to
break the crown. you can split the permanent crown only when using zinc
eugenol by a specific maneuver.
*All slides are included starting from slide #50.
*Sentences are underlined to facilitate
memorizing them or because the doctor
specifically mentioned them.
**A wise man once said: there are two kinds of
people, those who study sheets and those who
are lying…
We took in the last lecture about the uses of dental cements; we can use them as
varnish, liners and bases under the filling restoration +use them at endodontic treatment to stabilize
the gutta-percha + use them as luting agents to make preparation to fix crowns+ making
modification to use them as filling materials as varnish(resin) can be natural or synthetic with volatile
solvent & calcium hydroxide cement as liner, or zinc oxide eugenol and zinc phosphate.
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• As bases and liners. -We can use it as a base or as a liner below the material with deep
cavity or root canal treatment when you don’t want to fill all the
cavity with composite or amalgam, so you can use it on materials as a
base or thin as a liner WHY? Because when we have chemical
adhesion with the tooth we ensure complete closure from depth of
the cavity and that leakage will not occur from saliva, then you can
put your permanent restoration.
• Used in orthodontics for cementation of bands. -Nowadays when you put braces, the bands(brackets) stick them by
composite(resins). But in the past before inventing these bands we
used to use zinc polycarboxylate because it has special property:
adheres very well with stainless steel(brackets)
Available as:
• Powder and liquid in bottles. "we buy the material depending on
what well use it on"
-If I want to use it with a cemented crown, I need it to be fluid.
-If I want it to have a low viscosity and more fluidity to adhere to the
crown that means powder particles (crystals) are smaller & vice versa
if I want it as filling material, high viscosity so the powder particles
(crystal)are bigger.
• Capsules of proportioned powder and liquid.
- Like capsuled glass ionomer proportion means measuring and
mixing are not needed.
• Water settable polycarboxylate cements.
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Composition:
**Powder=
• Zink oxide; basic ingredient
• Magnesium oxide; principle modifier and also aids in sintering
• Stannous fluoride; increase strength, modifies setting time and
imparts anti-cariogenic properties.
-Any material that contains fluoride is anti-cariogenic.
• Oxides of bismuth and aluminum in small amounts.
-Materials that are added to substances some of them give a color,
others dilute the taste and others give radiopacity HOW? The materials
are originally radiolucent don’t appear in x-rays, so we add Barium and
other specific substances to appear in radiograph and become
radiopaque.
-It can reduce setting and work time that I need and can affect the
material's shelf life. **Liquid=
• 32% to 42% Aqueous solution of polyacrylic acid.
Water settable polycarboxylate cements:
• In these cements, the polyacid is freeze dried and its powder is
then mixed with the cement powder. Water is used as the liquid. • When the powder is mixed with water, the polyacrylic acid goes
into the solution and the reaction proceeds as described for the
conventional cements.
Phosphoric acid ➔liquid for Zinc-phosphate
Zinc oxide➔common powder for the 3 types (zinc.)
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-The only difference in composition is that it has a longer shelf life;
instead of mixing liquid polyacrylic acid with powder zinc oxide, They
make freeze drying for polyacrylic acid and ground it to make it
powder and put it with the powder in one bottle (poly acrylic acid &
Zinc oxide) then when you want to use it you should use water so
that's why they call it water settable, when you add water the poly
acrylic acid will defuse -which was freeze dried- and now the final
material is ready.
Setting reaction: • When the powder and liquid are mixed, the surface of powder
particles are attacked by the acid, releasing zinc, magnesium and
tin ions. These ions bind to the polymer chain via the carboxyl groups. They also react with carboxyl groups of adjacent
polyacid chains to form cross linked salts.
Properties: • Setting reaction is shorter compared with zinc-phosphate
cements and are less viscous in general, despite the higher initial
viscosity (pseudoplastic property). -Pseudoplastic= At the beginning it has a high viscosity, but it turns
into fluid under pressure.
• P/L for luting cement is 1.5:1 by weight. (P/L ratio 3gm:1ml)
-Material properties are affected negatively if we change the ratio.
-When the working time increases, setting time will also increase SO
it will affect the material's properties and its success or failure.
Powder (increase P/L)= working time
Liquid (decrease P/L)= working time
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-Ways to increase working time before setting happens:
1-The glass slab should be cold.
2-Materials incorporation: DON’T pour liquid on powder directly. This
will make them aggregate, and it will be hard to mix and work with.
The most suitable way is to take a small amount of powder and a
small amount of liquid and mix them in wide area to give a long
working time without affecting the properties and setting time.
• The higher the P/L ratio or higher M.W. of copolymer, the
shorter working time. • Extended working time by using cooled glass slab or by
refrigerating the powder. • Refrigeration of the liquid is not recommended ➔gelation of
polymer due the hydrogen bonding. • Shorter working time is a potential problem that can be
overcome by optimizing the amount of tartaric acid in the
material (without affecting the setting time). -One of zinc polycarboxylate disadvantages is that it has a very short
working time SO you should work very fast and put it inside the
patient's mouth before it dries. Biocompatibility:
• To soft and hard tissues ➔less irritant than zinc-phosphate
cement because: -The liquid is rapidly neutralized by the powder. The pH of
cement rises more rapidly than zinc-phosphate.
-Penetration of polyacrylic acid in dentinal tubules is less.
• Low pH 3-4 (fresh mixed cement), pH of the cement is 5-6after 24h -Zinc polycarboxylate has polyacrylic acid.
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-Zinc phosphate causes irritation because it has a low pH➔high
acidity
-Zinc polycarboxylate: has a low pH (3-4)➔high acidity➔but
neutralization occurs to it after 24h.
- Zinc phosphate causes irritation, but zinc carboxylate doesn’t WHY?
Because polyacrylic acid molecules are big so they can’t easily enter
dental tubules and reach the pulp. Therefore, its effect on the pulp is
a lot lower than zinc phosphate.
Mechanical properties:
• Compressive strength of 55-85 Mpa depending on P/L ratio if
prepared for luting (lower than zinc phosphate) • The material sets quickly and reaches 80% of its strength after 1h. -It has high compressive strength, but less than zinc phosphate and
more than zinc oxide eugenol. Therefore, we can't use zinc oxide
eugenol as a permanent luting cement because if the patient bites, a
crack will occur in the cement below the crown and break the
cementation, and it will fail in a few months.
Zinc poly carboxylate can withstand this because it has high
compressive strength higher and chemical adhesion, which enables us
to use it as a permanent luting cement.
-Sometimes it seems not good to use a temporary filling (zinc oxide
eugenol) it might fall.
For example, if I want to perform a pulp capping, and I must keep
checking on pulp for 2-3 weeks.
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If I use zinc oxide eugenol in this case it might fall. So, we use
polycarboxylate because it adheres more. Why don’t we use a
permanent filling?
Because although it has high occlusal strength, it won't be able to
withstand the load for long periods of time "a year".
Solubility:
• Solubility in water 0.1-0.6% by weight and is slightly more
soluble than zinc phosphate cement.
• It is more soluble in organic acids like lactic acid.
• Low P/L ratio results in significantly higher solubility and
disintegration in the oral cavity.
- Its solubility is better than zinc oxide eugenol. It doesn’t melt in
oral fluids like eugenol. But its solubility is less than zinc
phosphate. (that’s why we said zinc phosphate is the gold standard)
Adhesion:
• The only cement that has ability to adhere to enamel and dentin
and can be good enough to exceed the cohesive strength of cements.
• Carboxylate groups of the polymer in polyacrylic acid chelate
with the calcium in enamel and dentin, and this causes the
chemical adhesion.
• Does not adhere to gold or porcelain.
• Adhesion to stainless steel bands is excellent. Thus, it is used in
orthodontics for cementation of fixed appliances.
-For gold: use zinc phosphate cements & for porcelain: use resin cements.
-For metal: use zinc polycarboxylate cements.
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Thermal properties:
• They are good thermal insulators.
- If I have a deep cavity and I don’t want the patient to complain
about the thermal diffusion of amalgam, adding polycarboxylate
will solve the issue because of their good thermal properties.
Manipulation:
• Conditioning: the tooth structure should be clean for proper bonding.
To clean the surface 10% polyacrylic acid solution followed by rinsing
with water, or 1 to3% H2O2 may be used. Then dry and isolate.
• Proportioning; 1.5 parts of powder to 1 part of liquid by wt.
• Procedure: the powder and liquid are taken on cooled glass slab.
• The liquid is dispensed just prior to the mixing otherwise viscosity
increases. The powder is incorporated into the liquid in bulk 90%
with a cement spatula and remaining powder is added to adjust
consistency. The mix appears quite thick, but this cement will
flow readily into a thin film when seated under pressure.
• Mixing time: 30to40 seconds.
- Since it chelates with calcium, do you
think it will have a stronger adhesion with
enamel or dentin? It will have a stronger
adhesion with enamel, because enamel
has a crystallized structure and more
inorganic proportion.
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((Doesn’t cause irritation as zinc phosphate due to the large molecules))
((Because of stannous fluoride that is incorporated into the ingredients))
((that’s why we still use it))
((as plastic deformation))
((that’s why we don’t use it as a permanent restoration))
((Long setting time and short working time))
((by time with oral fluid, dissolution will occur and cause
microleakage on the surroundings of the restoration. so, saliva
enters the pulp and causes secondary caries))
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• This is a group of dental cements based on powders of alumina- silicate glass and liquids consisting of polyacrylic acid.
Composition:
• Powder: calcium fluoro-alumino silicate glass Silica 41.9%
Alumina 28.6%
Alumina fluoride 1.6%
Calcium fluoride 15.7%
Sodium fluoride 9.3%
Aluminum phosphate 3.8%
-It made a revolution in dentistry because it can make chemical
adhesion with the teeth & leaching for fluoride, so they have high anti-
bacterial properties.
-It used in all permanent restoration for primary teeth, after
endodontic treatment(deep cavities), class 5 cavity, and it's also used
in difficult cases where I can't use composite such as high caries
index. "they don’t look as good as a composite does, but they're still
better looking than zinc phosphate.
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- And with time its color matches the tooth. Cements crowns
permanently, high occlusal surfaces, used as base and liner
• The mixture of this powder (which contains silica,
alumina, sodium and aluminum fluorides…) is fused
at high temperature and the motion mass is then
shock-cooled and firmly ground to a powder.
-Types of glass ionomer:
1-powder& liquid form=used in filling, bases and luting the crown.
2-syringe form (gun form) =using capsule and mix it with
amalgamator machine, it's easier because If there is no
mixing, there won't be any voids or bubbles, and this
means the filling is stronger, its already pre-proportioned.
• Particles size 50 µm for filling and 20 µm for luting
and lining materials.
-The larger particles size the more viscous material.
• The release of ions from glass (important for setting characteristics,
the solubility, and the released of F) is a function of the type of glass
employed.
• The esthetics of these restorations depend on the refractive index
and presence of pigment in glass of powder.
-When it stays longer we can notice a change in color and a decrease
in the whiteness to become more matching with the tooth structure.
Polyacid:
• Wide range of polyacrylic acids are used with a large variety of
formulations.
Zinc phosphate
cements
is the
gold standared
Amalgamator
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• Polyacids used mostly are copolymers of acrylic and itaconic
acid or acrylic and maleic acid plus tartaric acid in water.
• The viscosity of liquid depends both upon the polyacid
concentration and its MW.
• Tartaric acid controls pH during setting process which in turn
controls the rate of dissolution of the glass.
-To prevent high irritation of pulp.
• Tartaric acid improves the handling characteristics increases
working time and shortens setting time.
• water is the most important constituent of the cement liquid as
it hydrates the reaction products. The amount of water in the
liquid is critical. Too much water results in a weak cement. Too
little water impairs the reaction and subsequent hydration. -80% of the strength of the material is formed during the first hour after
applying it on the tooth. The remaining 20% is formed after 24 hours.
-In the chemical reaction: not all the powder and liquid will mix.
We will have a core of unreactive powder particles. All the powder
and liquid that were mixed will give us the 80% strength. After 24
hours, when the core is mixed with them, we will have the 20% and
the full strength of the material.
Available as:
• 1-powder/ liquid
**Problems=
• Excessive solubility of cement in saliva coupled with slow setting
reactions.
• Obtaining correct or incorrect P/L ratio.
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• Reduced powder➔smooth creamy paste➔slower setting,
weaker cement and more susceptible to dissolution.
• 2-anhydrous cement ➔water hardening type.
• 3-capsules➔pre-proportioned, powder/liquid in capsules.
Setting reaction:
• Even after the cement has apparently set, precipitation of the
polysalts for initial set continues to occur. However, formation
of calcium salt is probably responsible for the initial set. With
time, the slower forming aluminum polysalts becomes the
dominant phase in the matrix.
• Exposure of the cement to water before the hardening reaction
is complete, leads to loss of cations and anions which leach out
form the matrix as they can be dissolved.
-glass ionomer absorbs water, and this affects the mechanical
properties of a material (they Sharply drop). Because the
dissolution of the material in the oral cavity will increase. That’s
why I should cover the filling during the initial setting time with
varnish or Vaseline and then I can manipulate and shape it.
Before dismissing the patient, I should add another layer of varnish
or Vaseline or unfilled resin, to form an insulating layer on the glass
ionomer to protect it during the initial set.
-If you add the glass ionomer too dry, the carboxylic groups and
calcium chelating won't occur. There won't be enough wettability
for chemical adhesion. That’s why you should always stick to the
correct proportions.
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Esthetics:
• They are inferior to composites. They lack translucency and
have a rough surface texture.
-You can notice translucency at incisal edge of your incisor
- We can find such translucency in the composite but not in ionomer
cement. So that's why we don’t use it as a cosmetic filling, but we can
use it in fillings near the gum "cervical area" because there is no
translucency there.
-Composites have a smooth surface unlike ionomer cement, the
smooth surface looks more esthetic and reduces dental plaque,
which is the principle cause of caries, but the rough surface that is
found in ionomer cement will be discolored more with foods and
drinks.
Biocompatibility:
• Pulp response- mild.
• The pulp reaction is greater than ZnOE cement but less than Zinc
phosphate cement
• In deep cavities, the pulp should protected by a layer of Ca(OH)2
-It has good pulp compatibility, in the past we used to put under the
glass ionomer Ca(OH)2, but now we can use the glass ionomer
The doctor skipped this slide
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directly on tooth without any barriers to benefit from all the
advantages of chemical adhesion and fluoride leaching.
Anticariogenic properties:
• Fluoride release.
• Adhesion may reduce infiltration of oral fluids. Manipulation:
• Conditioning of tooth surface.
• Proper manipulation.
• Protections of cement during setting.
• Finishing. Powder/liquid ratio: Generally 3:1 by wt
• Hand mixing: the power and liquid is dispensed just prior to mixing.
A cool and dry glass slab is preferred as it allows all the power to be
incorporated into the mix and yet maintain its plasticity. The powder is divided into 2 equal increments. The first increment is
incorporated into the liquid rapidly with the stiff spatula to produce
a homogenous milky consistency. The reminder of the powder is
then added. The mixing is done in a folding method in order to
preserve the gel structure.
-We will experience few cases of hand mixing because we use a gun
capsule that is already pre-proportioned. Rules that apply on the glass
ionomer apply on everything.
-we use cold glass slap to lengthen the working length, make mixing in
proportions between liquid and powder to give good working length.
• Mixing time: 45 second
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Protection of cement during setting:
• GIC is extremely sensitive to air and water during setting. Thus,
immediately before placement into the cavity, a pre-shaped
matrix is applied to:
1- Protect the cement from the environment during initial set.
2- Provide maximum contour so that minimal fishing is required.
• The matrix is removed after five minutes. Immediately after
removal, the cement surface is again protected with:
1- A special varnish supplied by manufacturer, or
2- An unfilled light cured resin bonding agent.
-We can also use Vaseline as an external insulating layer to protect the glass
ionomer.
protect glass ionomer.
The doctor skipped this slide
-zinc eugenol= used in temporary restorations.
-zinc phosphate= used in permanent restorations.
-zinc carboxylate= used in permanent restoration because it has
chemical adhesion, but its weaker than zinc phosphate and eugenol, so
it can't be used at high occlusal surface.
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→Glass ionomer is stronger than zinc oxide eugenol, zinc phosphate and
zinc polycarboxylate. That’s why it’s the most common material used in
cementing crowns. (even in areas with high occlusal forces)
((that’s why it is the most used material
in cementing of crowns))
((You should work carefully to ensure a higher
success rate))
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-Resin looks better than
glass ionomer so they
combined both glass
ionomer and resin to get the
advantages of both
materials.
-This eliminated the dissolution because its stronger.
- This also eliminated the long setting time.
- But its more expensive that’s why it's not very common.
The Doctor said here that this
type is not common
The doctor skipped this slide
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Anticariogenic properties:
• Consist of silane treated boro-silicate glass in a resin matrix of
BIS-GMA co-polymerized with ethylene glycol dimethacrylate
as a viscosity diluent. • Supplied as powder-liquid or paste-paste. • Chemical auto-cure, light cure or dual cure cements.
-These are the strongest cements.
- They look better.
- It doesn’t have any solubility problems because as soon as you apply it
you light cure it.
- They have good bonding with the teeth, BUT this bonding isn’t chemical.
(unlike polycarboxylate and glass ionomer).
-The bonding is micromechanical and it’s a sensitive technique
This will be further explained in the composite lecture.
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Advantages Disadvantages
-High strength & more aesthetic -Multiple steps & more expensive -Can be used with metals, laboratory composites or all ceramic restorations
-Moisture sensitive Technique (saliva, water, blood, and crevicular fluid can damage the filling)
-Excellent bond to tooth (micromechanical bond not chemical bond like polycarboxylate and glass ionomer)
-Possible post cementation sensitivity
-Insoluble -Little to no fluoride release
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