5.Dental Amalgam.pdf

Dental Amalgam Salma Abuelgasim Mohamed 2022 By the end of this lecture you are suspected to know: Definition. Composition and classification of dental amalgam Role of components of amalgam. Setting reaction. Advantage & Disadvantage Uses Manipula...

Dental Amalgam Salma Abuelgasim Mohamed 2022 By the end of this lecture you are suspected to know: Definition. Composition and classification of dental amalgam Role of components of amalgam. Setting reaction. Advantage & Disadvantage Uses Manipulation Failure Definition An amalgam is an alloy of mercury and one or more other metals. Dental amalgam is produced by mixing liquid mercury with solid particles of an alloy containing predominantly silver, tin, and copper. Zinc and palladium may also be present in small amounts. Classification its classified according to: Particle size Copper Zinc Content & Geometry Content Lathe cut High Zn Spherical Copper Containing Irregular Content Zn Free Mixed Low Copper Content Classification 1.Particle size and Geometry Lathe cut (irregular):regular cut, fine cut, and micro fine cut. Spherical particles : different sizes Admixed: mixture between spherical & lathe cut  1.Particle size and Geometry Lathe cut The lathe-cut particles are produced by machining ingot of the alloy on a lathe. The ingot is cut on a lathe to produce shaving which is subsequently reduced in size to regular cut, fine cut or micro fine cut. Clinical significance: Irregular powder particles packed together poorly and require a large amount of mercury to fill in the spaces (50% to 60% by weight in the mixture). Also, the irregular shape of many of the particles makes a mass that requires more condensation pressure. Spherical particles A spherical amalgam contains small, round alloy particles. Classification spherical types. The various ingredients of the alloy are melted together. Then molten alloy is atomized(sprayed) in a stream of inert gas, where the droplets solidify as small spherical pellets of various sizes. Clinical Significance They pack more efficiently and required much less mercury to make a practical mixture (less than 50% by weight). Also the material is condensed into the tooth preparation with little condensation pressure. High early strength so is good for large amalgam restorations. Easy to carve and the carved surface is generally smoother. Irregular particles These are produced by atomization of the molten alloy through a nozzle under high pressure. Admixed particles The admixed alloy comprises the lathe- cut and the spherical alloy in a proportion which varies with manufactures. 2. Copper Content Low-copper (2%- 5% copper) “Conventional Amalgams”. High-copper alloys (12% - 30% copper). Low-copper amalgam alloy (conventional amalgam) May contain 69.4% Ag, 26.2% Sn, 3.6% Cu, and 0.8% Zn. The low-copper alloys are either irregular or spherical High copper amalgam alloys contain High copper amalgam alloys contain 60% Ag, 27% Sn, 13% Cu, and 0% Zn. High copper alloys contain either all spherical particles of the same composition(unicompositional). Mixture of irregular and spherical particles of different or the same composition (admixed).  Cont.. It is estimated that more than 90% of the dental amalgams currently placed are high-copper alloys. The high-copper alloys, admixed alloys are used more often than spherical types, and fewer irregularly shaped or lathe-cut types are selected. A high-copper alloy is selected to obtain a restoration with high early strength, low creep, good corrosion resistance, and good resistance to marginal fracture. Zinc Content Alloys with more than 0.01% zinc are zinc containing. Those with less than 0.01% non-zinc alloys. It is estimated that more than 90% of the dental amalgams currently placed are high-copper alloys. The high-copper alloys, admixed are used more often than spherical types, and fewer irregularly shaped or lathe- cut types are selected.  Amalgam's Components Roles Silver 1. Increases strength due to increased γ phase in the matrix. 2. Decreases flow. 3. Increases setting expansion 4. Resist tarnish & corrosion 5. Reducing setting time because the reaction of silver & mercury is very fast. 6. It whitens the alloy Tin 1. Reduces strength because the Ag Hg is decreased and the Sn Hg is increased which is a weaker phase. 2. Helps in amalgamation (tin has great affinity to mercury). 3. Increased setting time 4. Decreased setting expansion 5. Reduces the resistance to tarnish & corrosion Copper 1. Increased strength 2. Reduces flow 3. Increased setting expansion Zinc 1-Prevents oxidation during manufacture of the alloy. (Zinc tends to oxidize forming a zinc oxide film that covers the surface of liquid alloy during manufacture and suppresses oxidation of other key elements). 2- The presence of zinc has been shown to produce a delayed expansion if water-based fluids such as blood or saliva are present within the amalgam during condensation Setting Reaction  Setting Reaction for Low copper Alloys:- Setting Reaction for Low copper Alloys:- Ag3Sn + Hg Ag3Hg + Sn2Hg + Ag3Sn γ γ1 γ2 γ Gamma+ mercury gamma1+gamma2+gamma γ :Un-reacted particles γ1 +γ2 Matrix γ 1 :Is the first phase formed because silver dissolves faster than tin when mixed with mercury.  Sn- Hg (γ 2 ) phase, which is the weakest phase and most susceptible to corrosion in a low-copper amalgam. Disadvantage of low copper alloy. Y2 phase lead to amalgam that has 1. low compressive strength. 2. More prone to creep. 3. Increased susceptibility to corrosion. Creep The associated expansion makes the amalgam protrude from the tooth preparation. On non occlusal surfaces, the entire amalgam restoration may appear extruded. and this can produce unwanted esthetic problems or over-hangs in some areas. On occlusal surfaces, abrasion and attrition tend to limit the overall extrusion. However, occlusal margins become fracture- susceptible ledges elevated above the natural contours of the adjacent enamel. Extrusion at margins is promoted by electrochemical corrosion, during which mercury from Sn-Hg rereacts with Ag-Sn particles and produces further expansion during the new reaction. Corrosion Sn-hg +oral fluids(o2) tin salts (oxides and chlorides ) +free hg. The y2 phase is more electro negative than others so that in presence of electrolytic solution the y2 act as anode of the oxidation reaction which gradually dissolve. proper carving, burnishing and polishing to prevent gap, with proper condensation to remove hg. Setting Reaction for High Copper Alloys:- Setting Reaction for High Copper Alloys:- The initial reaction is the same as the low copper alloys Ag3Sn + Hg Ag3Hg + SnxHg + Ag2Sn3 γ γ1 γ2 γ The secondary slow slide state reaction Sn7-8Hg + AgCu Cu6Sn5 +Ag2Hg3 +AgCu γ2 γ1  Setting Reaction for high copper alloy. High copper amalgam eliminates Sn7-8Hg (gamma 2 phase) by replacement with Cu3- Sn phase which are much less corrosion- prone than the gamma 2 phase. Advantage of high copper alloy 1. Higher compressive strength. 2. More rapid set to full strength. 3. Reduction in creep. 4. A reduced susceptibility to corrosion. 5. Well-placed high-copper amalgam restorations may last from 24 to 25 years. Therefore, restorations using amalgam made with sufficient copper tend to have superior physical and mechanical properties and a longer period of clinical serviceability than restorations made from the low- copper amalgams. Advantages of Amalgam 1.Ease of use. 2. Wide range of application 3. Biologically stable with minimal allergic reactions. 4. Economic 5.High-copper amalgams exhibit no clinically relevant creep or flow 6.Ecxelant wear resistance Advantages of Amalgam 7.Favorable long term clinical success. 8. Physical characteristics are comparable to enamel and dentine. Disadvantages of Amalgam 1.Poor aesthetics 2. Marginal degradation (ditching) in low copper amalgam less in high copper amalgam (bulk fracture) 3. Excessive cutting is required due to its poor edge strength (weakens tooth structure) the retention is mechanical. 4. Initial marginal leakage Disadvantages of Amalgam 5.Silver is a good thermal conductor , so liner &/or base is required under these restorations. 6. Low tensile strength 7. Brittle 8. Galvanic corrosion may occur with gold restorations. 9. Oral linchen Planus has been reported 10. Mercury toxicity 11. Mercury hyper sensitivity. Disadvantages of Amalgam Brittle tensile strength 8 Metal 1 Metal 2 cathode anode  Mercury toxicity Like all other materials in the world, mercury has the potential to be hazardous if not managed properly. Mercury toxicity sources of mercury : (1) Amalgam raw materials being stored. (2) Mixed but unhardened amalgam during trituration, insertion, and intraoral hardening. (3)Amalgam scrap that has insufficient alloy to completely consume the mercury present. (4) Amalgam undergoing finishing and polishing operation. (5) Amalgam restorations being removed Mercury hygiene 1. Avoid spilling mercury. 2. Waste amalgam should be stored in a screw top bottle under old radiograph (X- ray) fixing solution. 3. When removing old amalgams, safety glasses, masks, and high-volume aspiration are a wise precaution. 4. Use mechanical mixing.  Uses 1.Moderate to large Class I and Class11 restorations especially i) Those with heavy occlusion. ii) That cannot be well isolated. iii) That extend onto the root surface. 2. Class V restorations including i)Those that are not aesthetically critical. ii)That cannot be well isolated. iii) Are located entirely on the root surface. 3. Foundations  Amalgam Manipulation Steps of amalgam manipulation Mixing Carrying Condensation Carving Burnishing Finishing and polishing  Amalgam Manipulation Amalgam may be supplied as powder or pellet alloy with automatic dropper mercury bottle or Pre capsulated alloy and mercury The ideal alloy/mercury ratio is 1:1 Amalgam Manipulation Amalgam trituration should be carried out mechanically in an amalgamator or manually with mortar & pestle  Amalgam Capsule A round-ended hollow plastic cylinder containing amalgam alloy, mercury, and a mixing pestle. It is mechanically activated to bring the mercury into contact with the alloy and then vibrated in an amalgamator. The capsules are visually coded to designate different quantities (spills) of alloy and mercury  Amalgam Manipulation Amalgam trituration should be carried out mechanically in an amalgamator or manually with mortar & pestle Adequate mixing is essential to ensure plastic mass and thorough amalgamation. Mixing time depend on type of alloy used and dispensing and mixing system. Mixing time range from 5-20 sec.  Amalgam Manipulation Amalgam should be condensed into the cavity in small increments. The condensation time should not exceed 3 min. Amalgam Manipulation Maximum condensation pressure helps to provide high compressive strength prevents void formation accelerates the setting reaction and hardening. Amalgam Manipulation Amalgam should be carved with a sharp instrument (hollenback or cleoid- discoid carver), the blade of which should lie across the amalgam enamel junction.  Amalgam Manipulation Post carved burnishing reduces surface porosity improves the marginal seal increases the surface hardness of the restoration Amalgam Manipulation Finishing of amalgam can be done with a flame shaped finishing bur an abrasive disc or abrasive strips for the proximal surface Amalgam Manipulation Amalgam should not be polished until at least 24 hrs after the restoration insertion. However high copper amalgam can be polished as early as 30 min. after condensation. Amalgam Manipulation Amalgam polishing is performed with a stiff mix of pumice , glycerin and water using a rubber cup or mounted brush. Finishing and polishing of amalgam result in A restoration more resistant to corrosion Less injurious to the soft tissue Accumulates less plaque. Failure of the Amalgam Restoration 1. Inadequate cavity preparation 2. Improper amalgam manipulation 3. Intrinsic properties of amalgam 4. Recurrent caries 5. Fractured amalgam 6. Tooth fracture 7. Postoperative sensitivity or pain Failure of the Amalgam Restoration 4.Recurrent caries Pt has high caries risk rate Marginal ditching of amalgam restoration as a result of: Amalgam brittleness Low tensile strength Electrochemical corrosion Undermined enamel or reactivated residual caries Failure of the Amalgam Restoration 4.Recurrent caries  Failure of the Amalgam Restoration 5. Fractured amalgam Low amalgam tensile strength Occlusal interference Inadequate bulk of amalgam faulty cavity preparation over carving of the restoration Failure of the Amalgam Restoration 6. Tooth fracture faulty cavity prep. Inadequate resistance form. 7. Postoperative sensitivity or pain Dimensional changes of amalgam during setting in improperly manipulated or condensed amalgam Electrochemical galvanism Acute apical periodontitis as a result of premature occlusal contact Failure of the Amalgam Restoration 8. Thermal diffusivity If dentine is not adequately sealed with solution liner or bonding agent then fluid flow in the tubules may be induced and sensitivity could result, after a few hours corrosion products eliminate the problem  Bonded Amalgam New amalgam is bonded amalgam Although amalgam has been a highly successful restorative material when used as an intercoronal restoration, it does not bond to tooth structure. and therefore does not restore the original strength of the clinical crown.  Bonded amalgam For large restorations, features such as pins, slots, holes, and grooves must be supplied to provide retention for large restorations, but they do not reinforce the amalgam or increase its strength. Bonded amalgam There is no true adhesion between amalgam and tooth structure.  Bonded amalgam The technique for placing a bonded amalgam consists of: initially placing the bonding agent into the cavity and before the bonding agent has completely polymerized the amalgam is condensed into the cavity. This represents the technical challenge of filling the retentive features of the preparation with amalgam mixed together with the bonding agent. Thank you