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Amalgam restoration

Amalgam functions as a direct restorative material (metal-likr restoration) by easily being inserted into tooth preparation to restore tooth for proper form and function. it composed of a mixture of silver-tin-copper alloy and mercury. Amalgam restoration require a specific tooth preparation form into which the amalgam material is inserted.

The required tooth preparation form must allow the amalgam to:

Possess a uniform thickness for strength.
Produce a 90 amalgam angle(butt joint form) at margin.
Mechanically retained in the tooth.

Without this preparation form, the amalgam could possibly be dislodge or fracture.

Amalgam: Alloy of mercury with one or more metals.
Dental amalgam: Alloy that is combind with mercury to form amalgam used for dental purposes.
Amalgamation: the setting reaction of amalgam
Condensation: the process of placing amalgam mass into the tooth cavity and applying forces on to it to adapt amalgam to prepared cavity walls.
Burnishing : the action of smoothing the surface and margins of amalgam.

Composition:

Silver(Ag).
Tin(Sn).
Copper(Cu).
Zinc(Zn).
With trace amount of indium (In) and palladium.


Classification
According to copper content.
Low copper Amalgam.(conventional amalgam) : it continent of copper about (3.6%).
High copper Amalgam: its predominately used today. it continent of copper about (12% or greater).
According to amalgam alloy particle geometry and size.
Spherical amalgam (unicomopsitional): it contains small, round alloy particles that are mixed with mercury to form the mass that into prepared tooth cavity. because of the shape of the particles, the material condensed into tooth with little condensation pressure.
Lathe cut (unicomopsitional): irregular shapes ranged from spindle to shavings.
Sheroidal (unicompositional) spherical but irregular surfaces.
Admixed amalgam: it contains irregular shaped and sized alloy particles, sometimes a mixture of spherical and lathe cut. The irregular shape of many of the particles makes a mass required more condensation pressure(preferred by many dentist).
According to zinc content.
Zinc containing alloy: alloys contains more than (0.01% zinc) zinc added to suppress oxidation . during manufacturing it forms zinc-oxide film or layer covering the alloy and suppress oxidation of other elements. And delay the setting expansion .
Zinc free alloy: alloys with less (0.001%) zinc . it used for retrograde filling due to difficult moisture control and danger of setting expansion.

New amalgam alloys

Because of the concern about the mercury toxicity, many new compositions of amalgam are being promoted as mercury-free or low-mercury amalgam restorative materials. Alloys with pallodium or indium or those using cold-welding techniques are presented as alternatives to mercuy-containing amalgam.

Advantages

Ease of use and less sensitive technique.
Excellent wear resistance.
Lower cost as compared with composite.
Bonded amalgam hass "bonding" benefits.
Less microleakage.
Less interfacial staining.
Slightly increased strength of remaining tooth structure.
Minimal post operative sensitivity.


Disadvantages.
Noninsulator.
Nonesthetic.
Less conservative( more removal of tooth structure during cavity preparation.
Initial microleakage.
More difficult tooth preparation.

 Tarnish: oxidation that attacks amalgam surface and extends slightly below the surface. The restoration has dark and dull appearance. Tarnish is more likely to occur with rough surfaces.

Corrosion: what causes it,

Chemical reaction between amalgam and saliva/food leading to oxidation of amalgam.
Contact between to dissimilar metals (galvanism) oxidation of amalgam.
Interaction of amalgam components

Corrosion maybe minimized by:

High copper alloys
Polishing of amalgam

Creep (plastic deformation): usually seen with low-copper amalgam (due to gamma 2 phase). It involves a change in the shape of the restoration due to compression from chewing and opposing teeth. Creep causes protrusion of amalgam which is susceptible to fracture and corrosion. This leads to formation of a ditch around amalgam. This decreased by:
High copper alloys
Palladium or indium in the alloy


Dimensional change: expansion and contraction during setting occurs in amalgam. It is important that the net effect does not change the dimensions of the restoration.
During the 1st half hour, contraction occurs
Followed by expansion due to crystallization
End result is either final expansion or contraction.



High thermal conductivity: so, expansion and contraction occur and may lead to microleakage. 3 times the coefficient of thermal expansion of dentine. In large cavities an insulator is needed underneath amalgam to protect the pulp.

Body maybe exposed to higher amounts during placement, polishing, corrosion and removal of amalgam fillings. One possible effect is allergic reaction to mercury:
Contact dermatitis
Lichenoid reactions




رفعت المحاضرة من قبل: Sultan Alsaffar
المشاهدات: لقد قام 13 عضواً و 231 زائراً بقراءة هذه المحاضرة








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