Tricalcium Silicate-based Endodontic Cements - Modifications in Mixing Liquids and Additives

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來自 The University of Hong Kong 的課程

Materials in Oral Health

148 個評分

The University of Hong Kong

Materials in Oral Health

148 個評分

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從本節課中

Modern Composites and Cements

An Introduction to Dental Cements5:06

Introduction to Glass Ionomer Cements (GIC) and Resin-modified Glass Ionomer Cements (RMGIC)4:06

Tricalcium Silicate-based Endodontic Cements - Properties and Modifications5:17

Tricalcium Silicate-based Endodontic Cements - Radiopacifier2:49

Tricalcium Silicate-based Endodontic Cements - Modifications in Mixing Liquids and Additives7:01

Tricalcium Silicate-based Endodontic Cements - Hydraulic Properties and Bioactivities3:26

與講師見面

Jukka Pekka Matinlinna
Professor in Dental Materials Science, Head of Unit
Faculty of Dentistry, The University of Hong Kong
James Kit Hon Tsoi
Assistant Professor in Dental Materials Science, Assistant Dean of Electives and Experiential Learning
Faculty of Dentistry, The University of Hong Kong

The next topic to be discussed is

another modification which is in the mixing liquid.

The first generation materials were supplied in sessions,

which had the powder,

which was made up of the cement and the radiopacifier, and a mixing liquid.

The mixing liquid is usually water.

With the second generation materials,

the mixing liquid has been modified.

In the premixed, there is no mixing liquid.

Such materials are supplied in syringes,

such as sealers and pastes, and they have no mixing liquid.

They are applied in the canal.

Anywhere there is like the root-end,

or perforation repair, and they rely on the moisture, or blood

that is present inside the area where they are placed

for hydration to work here.

This can be slightly problematic

because if the area has been dried

and there is not enough liquid,

there is a risk that the material will not hydrate.

And if the material will not hydrate,

there will be no calcium hydroxide formed.

If no calcium hydroxide is formed,

the material properties will obviously change.

Usually, water is used as a mixing liquid.

To the water, an accelerator like calcium chloride

can be added and also a superplasticizer.

The calcium chloride has the effect

of accelerating the material hyrdation.

And by accelerating the material hydration,

the setting time will be reduced.

If a superplasticizer is added,

less water for the same consistency can be used.

In this way, if the water is reduced,

the compressive strength and the micro hardness

will be enhanced.

The superplasticizer is simply a water soluble polymer,

it will adhere to the cement particles

and with less water, you can get an adequate mix

and no segregation will occur.

Another innovation to the water, or to the mixing liquid,

has been the addition of an anti-washout gel.

One particular brand of tricalcium silicate-based material

has the use of a gel rather than water as the mixing liquid.

The whole idea with using this gel is to avoid washout.

To define washout, washout is basically the material

that will tend to come off the surgical site

when there is irrigation

or when the blood clot is being formed.

If a gel is used, and again the gel used

is a water-soluble polymer, this washout has been shown

to be prevented in freshly set material.

More modifications has been also

that removing the water completely

and the use of light-curable resins,

or salicylate-based resins for various applications.

The light curable resins are used

for pulp capping materials, the water is not used,

but a resin-base is used.

The idea is, obviously using a resin

which is, allows water permeation.

Again, the cement types depend on the surrounding water,

the environmental water for reaction.

If this environmental water does not penetrate inside the resin matrix,

the hydration reaction of the cement will not occur,

the calcium hydroxide is not produced,

and the pulp capping material will obviously be used less.

Salicylate resins are preferred for sealer types.

The salicylate resins are rigid and again,

they should be permeable too.

The environment influence because that is the only way

that the material can form the calcium hydroxide.

Another modification, which is also not present

in the first generation materials in the MTA

is the use of additives.

The second generation materials incorporate additives with them,

which again, enhance the material properties.

One such additive is calcium carbonate,

calcium phosphate, and also silicon dioxide.

Some brands have the addition of calcium carbonate.

This calcium carbonate is added as a nucleating agent.

The nucleating agent,

the scope of using this nucleating agent,

is to enhance the material hydration.

Usually, hydration is disorganised and clumps of hydration material

will form around the cement particle.

When there is this nucleating agent,

the material hydration is more ordered

and this will result in a better microstructure,

and better compressive strength,

and better physical and mechanical properties.

More modifications include the addition

of the calcium phosphate.

The calcium phosphate will provide phosphate ions

for the material.

When there is the formation of calcium hydroxide,

the phosphate ions, which are readily available,

will react with the calcium hydroxide formed,

forming calcium phosphate.

The calcium phosphate has been shown

to be the formation of the hydroxyapatite,

which is responsible for the material bioactivity.

The problem with the formation

of this calcium phosphate is that the pH

of the material will be reduced

because the calcium hydroxide is reacting.

If in the long term,

this calcium hydroxide is not available,

the main function of the material,

which is obviously the formation

of the calcium hydroxide, will be reduced,

if the calcium hydroxide reacts completely

with the phosphate ions in the short term.

The antimicrobial properties are usually a function

of the high pH.

If the pH is reduced because of the formation

of the calcium phosphate, the hydroxyapatite,

or carbonate apatite which is formed

over the material's surface,

the reduction in pH will lead to a reduction

in antimicrobial properties.

This has been shown in a recent study conducted

by my research group where bacteria were shown to grow

inside dentinal tubules when the root canal was irrigated

with a phosphide-based solution.

The reaction of the calcium hydroxide formed

by the root canal sealers,

which were tricalcium silicate-based,

resulted in a reduction in antimicrobial properties.

Reduction in antimicrobial properties is problematic

for root canal sealers because there will be infection

and re-infection of the root canal

with root treatment failure.

Another modification is the addition of the silicon oxide(SiO2).

The silicon oxide(SiO2) is added in some brands

to enhance the material physical properties.

Enhancement of the material physical properties is caused

by reaction of the silicon oxide(SiO2), again,

with the calcium hydroxide formed from the reaction

of the material during hydration, there is again,

another reaction carried out between the calcium hydroxide

and the silicon oxide(SiO2) to form more calcium silicate hydrate

which is the material matrix,

but due to this reaction,

the calcium hydroxide is depleted.

This is another problem because

if the calcium hydroxide is depleted,

the material function may not be well in the clinical sense,

because if there is no calcium hydroxide,

if the material's being used for pulp capping purposes,

obviously, there may be problems with the pulp.

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