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9_Cement part two


9_Cement part two

Dr. Samira J. Juhi Tarfa

Zinc polycarboxylate cement
A powder and a liquid the liquid is a water solution of polyacrylic acid ( 32% -40% ).
As a powder that is mixed with water.
The cement powder is essentially zinc oxide and magnesium oxide.
The cement powder that is mixed with water contains the zinc oxide particles coated by 15% to 18% polyacrylic acid

Properties

1. It is one of the dental cement systems which have chemical adhesion to enamel and dentin, by the ability of the carboxylate groups in the cement molecule to chelate to calcium in enamel and dentin.
2. The large sizes of polyacrylic acid molecules, which can’t penetrate through dentinal tubules, make this cement low irritant to the pulp, so this cement is used as a base or for cementation with sensitive teeth.
3. Short setting time(2-6 minutes).
4. It is sensitive to disintegration and solubility more than zinc phosphate cement.


Uses
1. As a luting agent.
2. As a base material.
3. In orthodontics for cementation of bands.
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manipulation

1. Powder/ liquid ratio for the base consistency is 2-3 parts of powder to 1 part of liquid by weight. The ratio becomes ( 1.5/ 1 ) when using as a luting agent.
2. Dry and cool glass slab is used for mixing, the cooling slows the chemical reaction and thus provide longer working time.
3. The mix should be completed with in 30-40 second.


9_Cement part two

Glass ionomer cement

It may supplied as a powder and a liquid or may come as capsules.
The powder is fluoro-alumino-silicate glass.
The liquid typically is a 47.5% solution of 2:1 polyacrylic acid and itaconic acid copolymer.
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uses

1. As luting agent.
2. As base material.
3. Also can be used as filling material specially of the modified types of GIC.


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9_Cement part two

PROPERTIES

The compressive strength is greater than Z PH C.
GIC is very sensitive to contact with water during setting. The field must be isolated completely. If GIC is used as filling material, once the cement has achieved its initial set about 7 minutes, coat the cement surface with a coating agent such as a varnish, because the complete setting reaction take place in 24 hours.
GIC release fluoride, so it has anti cariogenic effect , thus this cement can be used in patient with a high caries index.


GIC bond to the tooth structure chemically by ionic interaction with calcium and / or phosphate ions from the surface of the enamel or dentin. In addition to, when the enamel surface is conditioned ( etched with 37% phosphoric acid ), the bind strength of GIC become greater, because acid etching of enamel surface will produce micro porosities on the etched surface that will improve the mechanical retention.


9_Cement part two

Resin cement

Are thin versions of restorative resins e.g. calibra and panavia resin cements.

Consist of a resin matrix with inorganic fillers that are bonded to the matrix with monomers.
The fillers level vary from 40%-80% by weights.
The bonding of the cement to enamel be attained by the acid-etch technique.
Then bonding agent is used to provide mechanical adhesion of the cement to etched surface of the tooth.


9_Cement part two

Polymerization of resin cement is achieved either by :

1. Chemical reaction ( self cure). They are typically two pastes system ( base and catalyst), while s
2. Light activation ( light cure). The light cure cement is a single component system.
3. Or both ( dual cure).
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9_Cement part two

pROPERTIES

Resin cements are insoluble in oral fluids.
Higher filler particles loading result in higher mechanical properties ( strength and stiffness) and reduce polymerization shrinkage, and a lower coefficient of thermal expansion.
In some products fluoride is added to act as anti cariogenic factor, and reduce the resin cement sensitivities.
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uses

As a luting material either for cast or for tooth colored restorations such as esthetic ceramic and laboratory processed composite restoration.
Also resin cement with high filler range can be used as a base material.
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Cavity liners

Cavity varnishes
They are solutions of natural resins or synthetic resins dissolved in a solvent such as alcohol, chloroform, or acetone.
The solvent evaporates, leaving a thin film on the cavity preparation.

functions

1. It is placed on enamel and dentin walls to reduce the penetration of oral fluids around amalgam restoration.
Varnish inhibited microleakage during the first few weeks. After that the varnish will dissolved by oral fluids and replaced by the corrosion products of the amalgam which form at the amalgam tooth interface.
2. Varnish is applied on dentin surface to minimize penetration of acid from zinc phosphate cements by occluding the orifices of the dentinal tubules.
3. Reduce post-operative sensitivity.

properties

1. Varnishes, neither possess mechanical strength, nor provides thermal insulation because of thin film thickness.
2. When GIC is used as a base material, varnish should not be used as sub-base, because GIC contains fluoride, and varnish prevents fluoride release and reaction with the tooth, also varnish prevents the chemical bonds between tooth and GIC.
3. Varnish should not be used when the restoration is composite resin. Because it inhibits polymerization reaction of composite resin . So calcium hydroxide can be used under composite resin.

manipulation

Varnish solution are usually applied by a mean of a small round piece of cotton.
A thin layer is applied on the preparation then gently dried with steam of air.
A minimum of 2 layers should be applied, as the initial layer dries it leave small voids, so the second layer fills in the voids and produce a more continuous coating.
Varnish solutions should be tightly capped immediately after use to minimize loss of solvent.


Most varnishes are supplied with a separate bottle of a pure solvent this solvent used to keep the varnish from becoming too thick, also used for removing varnish from external tooth surface.
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Bonding agent

Generally bonding agents are unfilled resins which are used for mechanical adhesion of composite restoration to the conditioned enamel and dentin.
The conditioning is achieved by using of 37%phosphoric acid for 15-60 seconds then washing and dryness of the tooth.
These bonding agents act as liner for the composite restorations especially for shallow cavities, because they occlude the orifices of dentinal tubules and reduce post- operative sensitivities.
Special bonding agents are used as amalgam bond which can act as a liner for amalgam by sealing the cavity against fluid and microleakage.

Calcium hydroxide ca(oh)2

The set material has an alkaline PH ( 9.2-11.7), which reduces the acidity of ZPHC when used as sub base material in deep cavities.
The antimicrobial action of calcium hydroxide makes this material useful in indirect pulp capping procedures.
Ca(OH)2 stimulate the odontoblast cells for the formation of secondary dentin ( stimulate the formation of dentinal bridge) when it is put directly over exposed pulp tissue, so it is used for direct pulp capping.
Water is important component for the setting reaction of calcium hydroxide based liner.



9_Cement part two

MANIPULATION

Equal lengths of the different colored pastes are dispensed on a paper pad and then mixed into a uniform color (homogenous) and then applied by using of dycal applicator.

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The setting time is short about 1-2 minute ,therefore the mix should be done quickly and then applied on a dry dentin so flow freely and easily.
Proper setting requires humidity; place a moist cotton pellet at the opening of the cavity, on the top of the newly placed cement for 30 seconds. Be sure that the cotton does not contact the cement .
After 30 seconds, check the cement gently with the explorer to ensure that it cannot be penetrated.
A resin has been added to Ca(OH)2 to improve its properties ( thermal, mechanical property and reduce solubility) and the setting is performed by light curing.


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General clinical consideration

1. The prepared cavity should be clean and dry before application of lining material, the quadrant of the prepared tooth should be isolated completely form saliva, because the entire lining and base material are sensitive to water during their application and setting.
2.All liners and base materials undergo dissolution and disintegration in saliva with time; therefore, they should not reach to the margins of the cavity (except varnish and bonding agent).
So lining is placed on : pulpal floor in CL I , pulpal floor and axial wall in CL II, axial wall in CL III, IV, and V.

3. In cavities prepared for amalgam restorations, the base material should not be extended on the walls of the cavity because this will block the undercuts convergence of the buccal and lingual walls , which are important for the retention of amalgam restoration .
Also all the retentive holes, grooves, and pins should be free from lining before amalgam placement.

Prepared cavity that extends into dentin beyond the minimal depth necessary to attain retention and strength for restorative material.
Varnish is used to coat the floor and walls, then a cement base such as ZPhC, or modified ZOE cement may be contoured to replace the missing dentine.
No need for pulpal protection (sufficient thickness of dentin).
For amalgam the cavity is coated with 2 thin coats of a varnish or amalgam bond and restore.
For composite the cavity is etched , coated with a single coat of a bonding agent and restore.

Classification of cavities

Shallow Cavity preparation
Moderate- Deep cavity



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Exposure of a small area of the pulp with no sign or symptoms of degenerating pulp.

Pulp capping is the recommended choice.
In an isolated clean field, Ca(OH)2 is placed over the pulp and the border of the dentin which surround the exposed site.
A base material is placed on the top ZPHC or reinforced ZOE ,and GIC.
The restoration of the tooth should be completed as soon as possible.
That includes some extension toward the pulp.
A liner such as Ca(OH)2 should be applied on the pulpal and axial walls.
On top a cement base is placed such as ZPHC or PCC, or modified ZOEC then a varnish is used to coat the walls.
Recently, new protocol prefers the use of dycal with GIC base, because of the present of chemical bonding between the tooth and the GIC that will reduce microleakage and the sensitivity postoperatively.
Deep Cavity

Deep Cavity with exposure of the pulp

9_Cement part two

Thank You




رفعت المحاضرة من قبل: Sajad Lateef
المشاهدات: لقد قام عضو واحد فقط و 222 زائراً بقراءة هذه المحاضرة








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