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AMALGAM RESTORATIONS Amalgam is :a special type of alloy in that one of the constituents is mercury Dental amalgam is: a specific amalgam alloy that contains silver, tin , and copper plus mercury.

Advantages Superior adaptation to cavity walls, which uniquely improves on aging Clinical significance: it inhibits micro leakage, which may cause: Postoperative hypersensitivity, Crevicular corrosion and Recurrent caries. 2.High compressive strength. Clinical significance: it enables the restoration to sustain occlusal forces without fracture

3.Adequate form stability due to : Insolubility High wear resistance Low creep value (in modern amalgam alloys). Clinical significance: it enables the restoration to maintain surface polish, occlusal anatomy and interproximal contact. 4. Low coefficient of thermal expansion( 2 times that of the tooth structures) Clinical significance: it decreases the marginal leakage by reducing the marginal percolation.

5.Ease of manipulation. Clinical significance: it is an easy technique for general practitioner to obtain a successful and lasting restoration. 6.Relative low cost due to the relatively short time for the construction of the restorations. Clinical significance: it is the most popular restoration

Disadvantages: Low tensile and shear strength( about 25% of its compressive strength) Clinical significance: The restorations cannot resist the marginal ditching and isthmus fracture. 2. Flow and creep. Flow: deformation before setting Creep: time dependant plastic deformation( after setting) Clinical significance: it leads to marginal ditching, flattening of contact, gingival overhanges and saucering of occlusal anatomy.

3. High thermal conductivity. Clinical significance: pulp must be protected in deep cavities by intermediary base materials, otherwise pulp irritation may occur. 4. Objectionable metallic color which may be complicated by tarnish and corrosion Clinical significance: this property limits its use to inconspicuous areas of the mouth.

Indications: Small and medium sized class I & II cavities where amalgam is not subjected to tensile loads. Class V in posterior area of the mouth. Formerly, it was used for restoration of class III in distal surface of upper canine to resist the anterior components of forces and hence the mesial drifting of the upper first premolar. Core build-up under full coverage restorations. N.B.: lately due to the modification in composite resin material it replaces amalgam in this areas and in some other areas in the posterior region.

Contraindications: 1. Extensive lesions especially those including undermined cusps where cast gold serves better. 2. Conspicuous areas of the mouth in the anterior and posterior teeth where composite resin may be favored. 3. Presence of opposing gold bridge to avoid galvanic activity. 4. Rampant caries where glass ionomer can act as a control restoration.

Classification of amalgam alloys: I. According to the shape of the powdered particles: Lathe-cut Spherical Spheroidal. II. According to the size of the powdered particles: Micro-cut Fine-cut Coarse-cut

III. According to the copper content: Low copper amalgam( conventional) : with copper content is 4% or less. High copper amalgam : Admixed type: composed of a mixture of conventional alloys(45-70%) and silver –copper eutectic alloy(30-55%). N.B.: the total copper content of admixed amalgam is 9-20%. b. Unicompositional type: each particle has the same composition either β(Ag Sn), ץ(Ag3 Sn) or ε(Cu Sn)

N.B.: the total copper content of this amalgam is 13-30 wt. % In the high copper amalgam the most corrodible Y2 phase is eliminated But if excess Hg is present ץ2 phase will be produced. V. According to zinc content : Zinc containing type ( scavenger). Zinc free type.: that is used in areas where moisture elimination is impossible as: Partially erupted teeth. Decidious teeth.

Cavity preparations for amalgam restorations: Based on the inherent properties of amalgam (brittle) the cavity preparation for amalgam must be: Conservative Provides adequate bulk( increase in the cross sectional area)

Specific features: 1.90 degree CSA. e.g.,reverse curve in the bucco-proximal wall of class II. 2.The walls must be parallel or perpendicular to occlusal loads. 3.A definite gingival seat of 1.5-2 mm. in depth for compound cavities.

4.Rounded internal line angles. 5. Sufficient bulk at the isthmus area through: Saucering the pulpal floor at the isthmus. Inclining of the axial wall towards the isthmus. Rounding of the axio-pulpal line angles. 6. Each portion must have its own independent retention and resistance.

Manipulation of amalgam: 1.Selection of the alloy. 2. Propertioning 3. Trituration. 4. Condensation. 5. Carving. 6.Finishing and polishing.

I. Selection of the alloy. *Spherical alloys provides the following advantages: 1.Very soft consistency that requires only light condensation forces. 2. Requires less Hg. 3. Provides smooth surface. Therefore it is indicated in: 1. Pulp capped teeth. 2. Around pins in pin-retained restorations.

*N.B.: spherical alloys are not recommended for extensive restorations because it cannot establish better contour and contact areas. * High copper amalgam has the following advantages: 1. High strength . 2. Greater corrosion resistance. 3. Low creep value. Therefore it is indicated in extensive preparations involving centric holding areas.

The alloy may be supplied in the form of: *powder *tablets *capsules. ** capsules form is preferred than other forms as it provides a standardized pre-weighted amalgam alloy.

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