Amalgam Dental Presentation PDF

Amalgam Shimaa Abdallah El-saady Assistant professor of Dental Biomaterials Faculty of Dentistry Aqaba Medical Sciences University Definition Amalgam : Any alloy containing mercury.  Definition Dental Amalgam Alloy: It is a distinct alloy that is formed of silver, tin, copper...

Amalgam Shimaa Abdallah El-saady Assistant professor of Dental Biomaterials Faculty of Dentistry Aqaba Medical Sciences University Definition Amalgam : Any alloy containing mercury.  Definition Dental Amalgam Alloy: It is a distinct alloy that is formed of silver, tin, copper and occasionally zinc. Composition of dental amalgam alloy  Definition Dental Amalgam: It is the restoration results from mixing dental amalgam alloy with mercury at room temperature to give a plastic mix that is placed into the prepared cavity. Composition of Dental amalgam:  Composition of Dental amalgam: Role of zinc Act as a scavenger (deoxidizer). Improve plasticity during condensation. Classification of Dental amalgam: Classification of Dental amalgam: Admixed amalgam: Amalgam with spherical & irregular silver alloy particles. Classification of Dental amalgam: Classification of Dental amalgam: Percentage Composition of Dental Amalgam Alloy:  Manufacturing of Dental Amalgam: 1.Ingot production: The constituent elements are melt & cast into a cylindrical ingot (=3.8 X 25 cm). It is slowly cooled under 480 C to produce an intermetallic compound Ag3Sn ( -phase). It is non-homogenous in nature (cored structure).  Manufacturing of Dental Amalgam: 2. Homogenous heat treatment: The cored ingot should be subjected to homogenization heat treatment to improve mechanical properties & corrosion resistance. It is done by heating the ingot at 400 C for 24 hours.  Manufacturing of Dental Amalgam: 3. Powder production: Lath cut: The constituent elements are melted & cast into an ingot. The ingot is lathe cut or ball milled into irregular particles.  Manufacturing of Dental Amalgam: 3. Powder production: Spherical: The constituent elements are melted & atomized (sprayed) into inert gas.  Manufacturing of Dental Amalgam: 3. Powder production: Spheroidal: The constituent elements are melted & atomized (sprayed) into water.  Manufacturing of Dental Amalgam: 4. Aging or annealing heat treatment: Lathe cutting develops internal stresses in the powder. The internal stresses lead to very fast setting & sever setting expansion. Aging or annealing eliminates the internal stresses.  Manufacturing of Dental Amalgam: 4. Aging or annealing heat treatment: Aging: Store the powder at room temperature for several months. Annealing: Heat the powder at 100 C for 1-6 hours.  Manufacturing of Dental Amalgam: 4. Aging or annealing heat treatment: Spherical & spheroidal require homogenization heat treatment only. They do not require aging or annealing heat treatment.  Manufacturing of Dental Amalgam: Advantages of spherical particles over lath cut: 1. Have lower surface area...require less mercury to obtain homogenous mix ………… produce amalgam with superior properties( increase mechanical properties & increase corrosion resistance). 2. Produce smooth surface during carving & finishing. 3. Requires less condensation pressure. Amalgamation reaction:  Amalgamation reaction: 1.Low copper amalgam: The powder is formed mainly of (Ag3Sn) phase. After amalgam mixing with the alloy powder, the following stages occur: a) Wetting. b) Diffusion. c) Surface reaction.  Amalgamation reaction: 1.Low copper amalgam: a) Wetting: The liquid mercury is added to the powder alloy & triturated (vigorous mix). The mercury wets the surface of the (Ag3Sn) particles.  Amalgamation reaction: 1.Low copper amalgam: b) Diffusion: The mercury diffuses into the outer layer of the phase leads to its dissolution into silver & tin.  Amalgamation reaction: 1.Low copper amalgam: c) Surface reaction: The mercury reacts with the silver & tin leading to formation of new phase (phase Ag2Hg3 ‘silver-mercury phase’ & phase Sn8Hg ‘tin- mercury phase).  Amalgamation reaction: 1.Low copper amalgam: c) Surface reaction: The new phases production increase with time leading to hardening of the plastic mix. The new phases ( &) surrounds & bound the unreacted parts of phase.  Setting reaction: Ag3Sn (ɤ)+ Hg Ag2Hg3(ɤ1) + Sn8Hg(ɤ2) + unreacted Ag3Sn(ɤ) + Voids Setting reaction:  Microstructure: Cored structure Formed of unreacted Ag3Sn (ɤ) + Sn8Hg (ɤ2). They are surrounded & bonded by a matrix of Ag2Hg3 (ɤ1) with some voids.  Properties of the different phase: Ag3Sn (ɤ) phase: The strongest & most resistant to corrosion. Ag2Hg3 (ɤ1) phase: less strong & less resistant to corrosion. Sn8Hg (ɤ2) phase: The weakest & least resistant to corrosion.  Properties of the different phase: Excess mercury will produce more ɤ1 & ɤ2 on the expense of ɤ phase will lead to: Decrease strength. Decrease corrosion resistance. Increase creep.  Properties of the different phase: Elimination of Sn8Hg (ɤ2) phase will lead to improve dental amalgam properties.  High copper amalgam (ɤ2 free amalgam): Increase the copper content of the dental amalgam alloy will lead to elimination of Sn8Hg (ɤ2) phase & improving the dental amalgam properties. The copper content varies from 13-30%.  Admixed high copper amalgam (ɤ2 free amalgam): The copper content of the dental amalgam alloy increased by mixing two alloys particles: Silver copper (Ag-Cu) eutectic alloy. Silver-tin Ag3Sn (ɤ) alloy.  Setting reaction: The setting reaction occurs in two steps: 1.Amalgamation reaction. 2.Solid-state reaction.  Setting reaction: 1.Amalgamation reaction: Like the low copper amalgam reaction. The silver-copper eutectic alloy does not participate in the reaction. Ag3Sn (ɤ) + Ag-Cu (eutectic) + Hg Ag2Hg3 (ɤ1) + Sn8Hg (ɤ2) + unreacted Ag3Sn (ɤ) + unreacted Ag-Cu (eutectic) + voids.  Setting reaction: 2. Solid-state reaction: It is Sn8Hg (ɤ2 ) phase elimination step. The reaction between Ag-Cu (eutectic) & Sn8Hg (ɤ2 ) take place slowly resulting in formation of Ag2Hg3 (ɤ1) & a new phase Cu6Sn5 (ɳ) ‘eta phase’ as a reaction zone around Ag-Cu eutectic particles. Setting reaction:  Microstructure: Cored structure: It is formed of a matrix of Ag2Hg3 (ɤ1) surrounds the unreacted Ag3Sn (ɤ) & unreacted Ag-Cu (eutectic). The Ag-Cu (eutectic) particles is surrounded by halos of Cu6Sn5(ɳ) Microstructure: Drawbacks of admixed high copper amalgam: 1.Uneven distribution of the two particles in the powder due to sedimentation of one particles in the container. 2.Surface oxidation of the silver-copper eutectic alloy. Unicompositional high copper amalgam: 1.The amalgam alloy powder is formed of one particle type with a copper content 13-30%. 2.Each particle contains Ag3Sn (ɤ) & Cu3Sn (ɛ) ‘eppsilon’ phases. Unicompositional high copper amalgam: This unicompositional form overcome the drawbacks of admixed type. The Sn8Hg (ɤ2 ) phase is eliminated at the beginning of the reaction. Unicompositional high copper amalgam:  Microstructure: Cored structure: It is formed of a matrix Ag2Hg3 (ɤ1) surrounds unreacted particles of [(Ag3Sn (ɤ) + Cu3Sn (ɛ)]. The Cu6Sn5 (ɳ) phase formed in a rod shape structure. The Cu6Sn5 (ɳ) phase surrounds the unreacted particles of [Ag3Sn (ɤ) + Cu3Sn (ɛ)] and embedded as crystals in Ag2Hg3(ɤ1) phase. Microstructure: Manipulation of Dental Amalgam Mode of presentation: 1.Tablets & mercury. 2.Preproportional capsules. 3.Powder & mercury. Manipulation of Dental Amalgam Selection of Dental Amalgam Alloy According to several factors such as; particle shape, particle size, zinc content & copper content. Manipulation of Dental Amalgam Proportioning: Two techniques are recommended: 1.Wet technique: the mercury/alloy ratio is slightly more than 1:1. 2.Dry technique (Eam’s technique): the mercury/alloy ratio is 1:1. Manipulation of Dental Amalgam Proportioning: Prepropotioned capsules are widly used nowadays. Manipulation of Dental Amalgam Proportioning: Excess mercury leads to more formation of & on the expense of stronger phase. This results in decrease strength and corrosion resistance & increase setting expansion and creep. Manipulation of Dental Amalgam Proportioning: Less mercury leads to wetting of all powder particles with mercury. This results in friable mix, decrease strength and corrosion resistance & increase voids. Manipulation of Dental Amalgam Trituration: It is the vigorous mixing of dental amalgam alloy with the mercury. Trituration could be performed manually (using mortar & pestle) or mechanically (using amalgamator). Manipulation of Dental Amalgam Advantages of mechanical trituration: 1. Less risk of mercury exposure. 2. Lower mercury/ alloy ratio can be used. 3. More uniform & reproducible mix. 4. Save time & effort. Manipulation of Dental Amalgam The properly triturated mix: It has a shiny surface & soft consistency. It results in the best mechanical properties & corrosion resistance. Manipulation of Dental Amalgam The over triturated mix (increasing time or speed): It tends to crumble & stick to the capsule. It is difficult to condense. It has lower working time. It has higher contraction & creep. Manipulation of Dental Amalgam The under triturated mix (decreasing time or speed): It is grainy & friable with dull appearance. It has lower working time & more excess mercury( poor properties). Manipulation of Dental Amalgam Manipulation of Dental Amalgam Mulling It is the rubbing of the triturated mix into a rubber finger-stall. Manipulation of Dental Amalgam Condensation It is the packing of the triturated amalgam mix inside the prepared cavity incrementlly with condensation of each increment separtely. Manipulation of Dental Amalgam Condensation It is the packing of the triturated amalgam mix inside the prepared cavity incrementlly with condensation of each increment separtely. Manipulation of Dental Amalgam Condensation Manipulation of Dental Amalgam Objectives of condensation: Increase adaptation of the restoration to the cavity wall. Decrease the mercury content by express excess mercury to the surface. Reduce the porosity providing a strong compact mass. Manipulation of Dental Amalgam Condensation: Condensation should not be done after 3 minutes from trituration. Manipulation of Dental Amalgam Effect of delayed condensation (after 3 minutes from trituration): Reduce strength due to breaking up of partially formed matrix. Partially se matrix contains excess mercury & excess porosities. Decrease the adaption to the cavity wall due to decrease plasticity. Decrease the bonding between increments. Manipulation of Dental Amalgam Carving: The cavity is overfilled, then the top mercury-rich layer is carved. Manipulation of Dental Amalgam Carving: The cavity is overfilled, then the top mercury-rich layer is carved. Objectives of carving: Reproduce the anatomy of the tooth. Removal of the top mercury-rich layer. Manipulation of Dental Amalgam Finishing & polishing: Finishing is done using finishing bur. Polishing is done using rubber cups & soft brushes with pumice. Manipulation of Dental Amalgam Timing of Finishing & polishing: Conventional low copper amalgam....after 24 hours. High copper amalgam...shortly after insertion. Manipulation of Dental Amalgam Timing of Finishing & polishing: Avoid overheating of restoration to prevent raising the mercury to the surface. Manipulation of Dental Amalgam Objectives of Finishing & polishing: 1. Increase patient acceptance to restoration. 2. Increase corrosion resistance by obtaining smooth surface. Properties of Dental Amalgam 1. Dimensional changes ( immediate + delayed). 2. Flow & creep. 3. Strength. 4. Bond to tooth structure. 5. Biological properties. Dimensional changes ( immediate + delayed). Ideally, any restoration should be dimensionally stable during setting. Dimensional changes Contraction of restoration: It leads to leakage at the tooth- restoration interface. This leakage leads to recurrent caries & hypersensitivity.  Dimensional changes Expansion of restoration: It leads to tooth fracture or protrusion of the restoration from the cavity. Protrusion occlusally....overhanging margins that may ditch or accumulate food. Protrusion gingivally....gingival irritation. Dimensional changes during setting It is the dimensional changes between 5 minute & 24 hours after amalgam insertion. It should be less than 20 mm/cm according to ADA specification which is achieved by all types of dental amalgam. Dimensional changes during setting After trituration the following changes occurs: Initial contraction in the first 30 minutes due to solubility of amalgam powder by mercury. Expansion due to outward pressure of growing crystals. Dimensional changes become constant after 6-8 hours. Dimensional changes during setting Any manipulation variable that decrease mercury ratio leads to contraction: 1. Lower Hg/alloy ratio. 2. High condensation pressure. 3. Small particle size (high surface area that react with mercury). Dimensional changes during setting The modern dental amalgam showed net contraction due to using smaller particles & using of mechanical amalgamators (low Hg/Powder). Dimensional changes during setting Marginal adaptation of dental amalgam restoration achieved by: 1.Good condensation. 2.Self-seal property of dental amalgam (the corrosion products of dental amalgam are precipitated at the tooth-restoration interface & seal this gap in 2-3 months). Dimensional changes during setting Dimensional changes during setting Delayed expansion: It occurs in zinc containing amalgam when exposed to moisture during trituration or condensation. It starts after 3-5 days after restoration insertion & may continue for months.  Dimensional changes during setting Delayed expansion: It is value may reach 400 mm/cm. The zinc reacted with the water leads to evolution of hydrogen gas. Zn+ H2O........ZnO +H2 Dimensional changes during setting Delayed expansion: The H2 gas leads to post-operative sensitivity & blistering. Dimensional changes during setting Delayed expansion: Using zinc free amalgam is recommended in case of achieving isolation is difficult as in children, handicapped patients & inaccessible area. Dimensional changes during setting Flow: It is a time dependent plastic deformation due to stresses application below the yield strength before complete setting of amalgam restoration. Dimensional changes during setting Creep: It is a time dependent plastic deformation due to stresses application below the yield strength after complete setting of amalgam restoration. Dimensional changes during setting Causes of creep: 1.Dental amalgam is a viscoelastic material. 2.Subjected to stresses below the proportional limit inside the mouth. 3.The oral temperature near the softenning temperature of amalgam.  Dimensional changes during setting Clinical significance of creep: 1.Marginal breakdown (ditching). 2.Gingival overhanging margins....gingival irritation. 3.faltting of the contact area. Dimensional changes during setting Clinical significance of creep: 1.Marginal breakdown (ditching). 2.Gingival overhanging margins....gingival irritation. 3.faltting of the contact area. Dimensional changes during setting Creep & flow Methods of decreasing creep: 1.Using high copper alloy. 2.Decrease mercury content. 3.Proper condensation. Strength Dental amalgam develops its strength slowly & reaches its final strength after 7 days. Dental amalgam should reach 80% of its final strength after 1 hour. Strength The one-hour compressive strength is more important than the final strength to avoid fracture of the restoration by biting of the patient. Strength Dental amalgam is brittle i.e strong in compression & weak in tension. Dental amalgam is viscoelastic material i.e sensitive to rate of loading. Strength To maximize strength of dental amalgam restoration: 1.Cavity preparation: Adequate cavity depth & width to provide bulky restoration. 90 C cavo-surface angle to avoid thin restoration. Rounding of all sharp line angles to avoid stress concentration. Strength To maximize strength of dental amalgam restoration: 2. Insulating base: Using rigid insulating base under amalgam restoration. Strength To maximize strength of dental amalgam restoration: 3. Amalgam manipulation: Selecting high copper amalgam. Decrease Hg/ alloy ratio. Strength To maximize strength of dental amalgam restoration: 3. Amalgam manipulation: Correct trituration time. Adequate condensation. Finish & polish restoration to decrease surface cracks & flaws. Strength Bond to tooth structure: Dental amalgam bonds to the tooth structure by macro-mechanical retention. Amalgam bonding systems have been introduced. Biological properties 1.Corrosion. 2.Thermal properties. 3.Mercury toxicity. Causes of corrosion: Dental amalgam undergoes corrosion because its heterogenous structure. Corrosion leads to: 1.Decreasing strength. 2.Release of metallic products inside oral cavity. Corrosion could be decreased by: 1.Selecting high copper amalgam alloy. 2.Decrease Hg/alloy ratio. 3.Proper condensation. 4.Finishing & polishing. Thermal irritaion Dental amalgam is good thermal conductor. In deep cavities, it should be proceeded by an isolating base. Mercury toxicity Pure mercury has high vapor pressure at room temperature. It is highly toxic (4000mm/kg of body weight). Mercury toxicity The main resources of mercury exposure in dental clinic arises from: 1.Accidental spills. 2.Direct contact with mercury. 3.Amalgamator. 4.Remove old restoration. Mercury hygiene 1. Using no touch technique. 2. Clean up spilled mercury immediately. 3. Store amalgam scrap under sodium thiosulfate (fixer of dental X-ray film processing solution). 4. Use water coolant & suction during removing old amalgam restoration.