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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

..بالتوفيق 88888لمع ا