3)DENTAL AMALGAM.pdf

Dental Amalgam Dr. Öğretim Üyesi Merve KÜTÜK ÖMEROĞLU TERMINOLOGY ´ Amalgam technically means an alloy of mercury (Hg) with any other metal. ´ Dental Amalgam alloy is a silver-tin alloy to which varying amounts of copper (Cu) and small amounts of zinc (Zn) have been added. Classification ´ According...

Dental Amalgam Dr. Öğretim Üyesi Merve KÜTÜK ÖMEROĞLU TERMINOLOGY ´ Amalgam technically means an alloy of mercury (Hg) with any other metal. ´ Dental Amalgam alloy is a silver-tin alloy to which varying amounts of copper (Cu) and small amounts of zinc (Zn) have been added. Classification ´ According to number of alloy metals 1. Binary (Silver-Tin) 2. Ternary (Silver-Tin-Copper) 3. Quarternary (Silver-Tin-Copper-Indium) Classification ´ According to the shape of the powdered particles 1. Spherical shape (Smooth surface spheres) 2. Lathe Cut shape (Irregular ranging from spindles to shaving) 3. Admixed (Combination of spherical and lathe cut) ´ According to powder particle size 1. Regular (coarse) cut 2. Fine cut 3. Microfine cut Classification ´ According to copper content of powder 1. Low copper content alloy – less than 4% 2. High copper content alloy – More than10% ´ According to addition of Noble metals 1. Platinum 2. Gold 3. Pallidum Classification ´ According to compositional changes of succeeding generations of amalgam 1. First generation amalgam 3 parts silver 1 part tin (peritectic alloy) 2. Second generation amalgam alloys 3 parts silver, 1 part tin, %4 copper, %1 zinc 3. Third generation: first generation+ spherical amalgam(copper eutectic alloy) 4. Fourth generation: first generation+ %24 copper= ternary alloy 5. Fifth generation: quaternary alloy ( Silver, tin , copper, indium) 6. Sixth generation: Eutectic alloy Classification ´ According to presence of zinc 1. Zinc containing (more than 0.01%) 2. Non zinc containing (less than 0.01%) INDICATIONS ´ Class I and Class II cavities- moderate to larger restorations ´ As a core build up material ´ Can be used for cuspal restorations (with pin usually) ´ As a die material ´ Restorations that have heavy occlusal contacts ´ Restorations that cannot be well isolated ´ In teeth that act as an abutment removable appliances ´ Class V lesions in nonesthetic areas (especially when acces limited and moisture control is difficult and for areas that are deep gingivally) CONTRAINDICATIONS ´ Anterior teeth where esthetics is a prime concern ´ Esthetically prominent areas of posterior teeth ´ Small to moderate classes I and II restorations ´ Small Class VI restorations Advantages ´ Ease of use, easy to manipulate ´ Relatively inexpensive ´ Excellent wear resistance ´ Well condensed triturated amalgam has good compressive strength ´ Relatively not technical sensitive Disadvantages ´ Non esthetic ´ Tarnish and corosion ´ Metallic taste and galvanic shock ´ Discoloration of tooth structure ´ Mercury toxicity ´ Delayed expansion ´ Weakens tooth structure Composition of Amalgam ´ Conventional Amalgam Alloys (Silver-Tin Alloy or Low Copper alloy) Low Copper Composition: Silver : 63-70% Tin : 26-28% Copper : 2-5% Zinc : 0-2% Role of Individual Components Silver ´ Constitutes approximately 2/3rd of conventional amalgam alloy ´ Contributes to strength of finished amalgam restoration ´ Decreases flow and creep of amalgam ´ Increases expansion on setting and offers resistance to tarnish ´ To some extent it regulates the setting time Role of Individual Components Tin ´ Second largest component and contributes 1/4th of amalgam alloy ´ Readily combines with mercury to form gama-2 phase ´ Reduces the expansion but at the same time decreases the strength of amalgam ´ Increases the flow ´ Controls the reaction between silver and mercury Role of Individual Components Copper ´ Contributes mainly to hardness and strength ´ Decreases the flow ´ Increases the setting expansion Role of Individual Components Zinc ´ Acts as Scavenger of foreign substances such as oxides ´ Helps in decreasing marginal failure ´ The most serious problem with zinc is delayed expansion, because of which zinc free alloys are preffered nowadays. Role of Individual Components Indium/Pallidum ´ Increase the plasticity ´ Increase resistance to deformation AMALGAMATION (SETTING REACTION) Conventional Amalgam Alloy Ag-Sn Alloy ´ Dissolution and precipitation Hg ´ Hg dissolves Ag and Sn from alloy ´ Intermetallic compounds are formed Hg Ag Sn n -S Ag lloy A Sn Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg g g g1 g2 Ag Ag Sn Hg Sn g A lloy A AMALGAMATION (SETTING REACTION) Gamma Phase(g) = Ag3Sn ´ Unreacted alloy Ag-Sn Alloy ´ Strongest phase ´ Corrodes the least Hg Hg ´ Forms 30% of volume of set amalgam Sn Ag Ag g g1 g2 Sn y Hg Ag -Sn g o All -Sn Ag Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg Sn A ll oy Ag AMALGAMATION (SETTING REACTION) Gamma 1 Phase (g1) = Ag2Hg3 Ag-Sn Alloy ´ Matrix for unreacted alloy ´ 2nd strongest phase ´ 10 micron grains binding gamma (g) ´ 60% of volume of set amalgam g g g1 g2 -Sn Ag y o All Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg AgAllo Sn y g1 AMALGAMATION (SETTING REACTION) Ag-Sn alloy Gamma 2 (g2) = Sn8Hg ´ Weakest and softest phase ´ Corrodes fast, voids form Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg g g g1 g2 Sn Ag - y Allo ´ Volume decreases in time due to corrosion g2 Ag allo -Sn y ´ 10% of volume of set amalgam HIGH COPPER AMALGAM ALLOY Final reaction Initial Reaction h Ag-Cu Alloy Ag A Al g-S lo n y Sn Sn Hg Hg A Al g-S lo n y Ag Ag Ag Ag3Sn + Ag-Cu + Hg ÞAg3Sn + Ag2Hg3 + Sn8Hg + Ag-Cu A Al g-S lo n y g1 A Al g-S lo n y Hg Ag-Cu Alloy Sn8Hg + Ag-Cu Þ Cu6Sn5 + Ag2Hg3 + Ag-Cu h g1 g2 MANIPULATION of DENTAL AMALGAM Proportion of Alloy to Mercury ´ Correct proportioning of alloy and mercury is essential for forming a suitable mass of amalgam ´ Some alloys require mercury- alloy ratios of 1:1 (Eames Technique) ´ Whereas others use ratios of less than 1:1 with the percentage of mercury varying from 43% to 54% ´ Today, Mercury-alloy ratios are used in capsules prepared during production. Proportion of Alloy to Mercury ´ Manufacturers commonly supply capsules containing 400, 600, or 800 mg of alloy and the appropriate amount of mercury. ´ Appropriate doses of capsules should be used according to cavity size. TRITURATION ´ Process of mixing the amalgam alloy particles with mercury. ´ Mechanical amalgamation; Saves time Standardizes the procedure TRITURATION ´ Mechanical amalgamators are available in the following speeds: Low speed: 32-3400 cpm (spherical low Cu) Medium speed: 37-3800 cpm High speed: 40-4400 cpm (high Cu) ´ Time of trituration on amalgamation ranges from 3-30 seconds. ´ Variations in 2-3 seconds can also produce an under or over mixed mass. TRITURATION ´ Over Trituration: Alloy will be hot, hard to remove from the capsule, shiny wet and soft. Working time is shortened. Creep is increased. Concentration is increased. Over trituration ´ Under Trituration: Alloy will be dry, dull and crumbly. Corrodes easily. Resistance is decreased, hardens quickly. Under Trituration ´ Normal Mix:Shiny appearance separates in a single mass from the capsule. Normal Mix Objectives of Trituration are: ´ To achieve a workable mass of amalgam within a minimum time ´ To remove the oxide layer ´ To pulverize pellets into particles, that can be easily attacked by the mercury ´ To reduce particle size ´ To keep the amount of g1 or g2 matrix crystal as minimal as possible Mixing Variables 1. Working Time& Dimensional change All types of amalgam, over trituration; ´ decrease the working time ´ Increase the contractions 2. Creep ´ Overtrituration increases ´ Undertrituration decrease 3. Compressive&tensile strength Irregular shaped alloys-increase by overtrituration Spherical alloys greatest at normal trituration time CONDENSATION CLASS I CAVITY CONDENSATION CLASS I CAVITY CONDENSATION CLASS I CAVITY Pre-Carve Burnishing Pre-carve burnishing application with the help of light force moving from the center of the restoration outwards to the margins. CONDENSATION Carving Creation of central grooves Adaptation of cavity lines Using remaining enamel as a guide, carve gently from enamel towards the center and recreate the lost anatomy of the tooth Amalgam should be hard enough to offer resistance to carving instrument CONDENSATION Removal of excess And the final shape CONDENSATION Post Carve Burnishing Use a large burnisher at a low load and burnish outwards towards the margins Improves smoothness CONDENSATION Class II Cavity Condensation to the proximal area Pressure to the pulpal wall Placing amalgam to the cavity CONDENSATION Class II Cavity Condensation to proximal ridge Condensation to cavity line Forming occlusal embraces MODELLING Class II Cavity Removal of the wedge Removal of the matrix band Removal of excess material MODELLING Checking the interproximal area Finishing&Polishing ´ Finishing; can be defined as the process, which continues the carving objectives, removes flash and overhangs and corrects minimal enamel underhangs ´ Polishing is the process which creates a corrosion resistant layer by removing stratches and irregularities from the surface. Finishing&Polishing The reason not to remove the roughness on amalgam filling surface; ´ Plaque retantion , ´ Perıodental disease ´ Causes Secondary caries. Finishing&Polishing ´ Can be done using descending grade abrasive, eg.rubber mounted stone or rubber cups. PROPERTIES ADA specification No.1 for amalgam lists following physical properties as a measure of quality of the amalgam ´ Creep ´ Compressive strength ´ Dimensional changes ´ Modulus of elasticity PROPERTIES Compressive Strength Amalgam is the strongest in compression and weaker in tension and shear The prepared cavity design and manipulation should allow for the restoration to receive compression forces and minimum tension and shear forces The compressive strength of a satisfactory amalgam restoration should be at least 310 Mpa PROPERTIES Tensile Strength Amalgam is much weaker in tension Tensile strengths of amalgam are only a fraction of their compressive strength Cavity design should be constructed to reduce tensile stresses resulting from biting forces High early tensile strengths are important— Resist fracture by prematurely applied biting forces PROPERTIES The Factors Affecting Strength of Amalgam PROPERTIES The Factors Affecting Strength of Amalgam ´ Amalgam looses 15% of its strength when its temperature is elevated from room temperature to mouth temperature ´ Loses 50% of room temperature strength when temperature elevated to 600C. PROPERTIES The Factors Affecting Strength of Amalgam ´ Effects of trituration on strength depends on the type of the amalgam alloy, the trituration time and the speed of amalgamator. ´ Under trituration or over trituration decreases the strength. ´ Excess trituration after formation of matrix crystals will create cracks in the crystals, lead to decrease in strength of set amalgam PROPERTIES The Factors Affecting Strength of Amalgam ´ Low mercury alloy content causes stronger alloy particles and less of the weaker matrix phase, therefore more strength. ´ Mercury is too less; dry, granular mix, results in a rough, pitted surface that invites corrosion. ´ Mercury content of amalgam mix more than 53-55% causes decrease of compressive strength by %50. PROPERTIES The Factors Affecting Strength of Amalgam For lathe cut alloys ´ Greater the condensation pressure, the higher the compressive strength. ´ Higher condensation pressure is required to minimize porosity and to express mercury from lathe cut amalgam For spherical alloys ´ Amalgams condensed with lighter pressure produce adequate strength. PROPERTIES The Factors Affecting Strength of Amalgam Causes of Porosity ´ Under trituration ´ Particle shape ´ Insertion of too large increments into the cavity ´ Delayed insertion after trituration ´ Non-plastic mass of amalgam PROPERTIES The Factors Affecting Strength of Amalgam Porosity causes ´ Stress concentration, ´ Propagation of cracks, ´ Corrosion, ´ Fatique failure of amalgam restoration PROPERTIES The Factors Affecting Strength of Amalgam ´ Patient may be dismissed from the dental chair within 20 min, rate of hardening of the amalgam is of considerable interset ´ At the end of 20 min, compressive strength- 6%of the 1 week strength. ´ ADA specification stipulates minimum compressive strength of 80 Mpa at 1 hr Clinical significance: patient should be cautioned not to subject the restoration to high biting force for 8 hrs after placement PROPERTIES Modulus of Elasticty ´ High copper alloys tend to be stiffer than low copper alloys ´ When rate of loading increased, values of approx 62 Gpa have been obtained PROPERTIES Dimensional Changes ´ Stage 1: Initial contraction, occurs for about 20 minutes after beginning of trituration. Contraction results as the alloy particles dissolve in mercury. (@ 4.5 µm) ´ Stage 2: Expansion- this occurs due to formation and growth of the crystal matrix around the unconsumed alloy particles ´ Stage 3: Limited delayed expansion PROPERTIES Dimensional Changes Delayed Ø Protrusion of the entire restoration out of the cavity. expansion; Ø Increased microleakage space around the restoration. occur 3-5 days Ø Restoration perforations after insertion Ø Increased ‘’flow and creep’’ and continues Ø Pulpal pressure pain. 10-12 days later , the patient for months. comes with pain. Zn + H 2O ® ZnO + H Delayed expansion PROPERTIES ’’Flow and Creep’’ Time dependent plastic deformation ´ The copper alloys, as compared with conventional silver tin alloys, usually tend to have lower creep values. Factors influencing creep: ´ Phases of Amalgam Restorations creep rates increase with larger g1 volume fraction and decrease with larger g1 grain size. ´ g2 is associated with high creep rates. ´ In absence of g2 , low creep rates in single composition alloy may be due to h phase which act as barrier to deformation of g1 phase PROPERTIES ’’Flow and Creep’’ Time dependent plastic deformation Factors influencing creep: Manipulation ´ Greater compressive strength will minimize creep rates ´ Low mercury: alloy ratio, greater condensation pressure and time of trituration will decrease the creep rate PROPERTIES Corrosion ´ Increased porosity ´ Reduced marginal integrity ´ Loss of strength ´ Release of metallic products into the oral environment. Ag2Hg3 Ag3Sn, Ag-Cu Cu3Sn Cu6Sn5 Sn8Hg. PROPERTIES Corrosion ´ Corrosion occurs in amalgams in two ways: o Chemical Corrosion Occurs more on occlusal surface Produces a black Ag sulphide tarnish film It occurs when the sulphides in silver amalgams corrode and form a black film layer on the surface. It occurs when metals including high amount of copper oxide and form a green layer on their surface. PROPERTIES Corrosion ´ Corrosion occurs in amalgams in two ways: o Electrochemical Corrosion It is the decomposition of the amalgam from different areas with the contact of a conductor such as saliva as a result of the formation of anodes and cathodes. It has potential to occur anywhere within the set amalgam PROPERTIES Corrosion ´ Stress Corrosion Regions within an amalgam that are under stress also display a greater propensity for corrosion. ´ Galvanic Corrosion It amalgam is in direct contact with an adjacent metallic restoration such as gold crown, tha amalgam is the anode in circuit results in galvanism. ´ Local Galvanic Corrosion Electrochemical changes that occur as a result of different phases within a single material. MERCURY HYGIENE ´ Mercury is an element that is always present in our enviroment and can enter the body everyday by air, water or food. ´ Mercury exist in three chemical form o Elemental mercury (liquid&vapour) o İnorganic mercury o Organic mercury ´ The elemental mercury in the form of vapor can be inhaled and it can be absorbed by alveoli and lungs at a rate of 80%. ´ Inorganic mercury is the safest mercury type. ´ Organic mercury is a toxicological product. o Methyl mercury is a very dangerous product The amount of toxic mercury effective in blood is 30 mg/ml. Sources of Hg Exposure ´ Dental amalgam raw materials being stored for use. ´ Mixed but unhardened dental amalgam during triturations, insertion and intraoral setting. ´ Dental amalgam scrap that has insufficient alloy to completely consume the mercury present. ´ Dental amalgam undergoing finishing and polishing procedure. ´ Dental amalgam restoration being removed. Clinical Findings of Mercury Poisoning ´ Ataxic gait ´ Convulsions ´ Numbness in mouth&limbs ´ Difficulty in speaking ´ Restriction in the visual fields Dental Mercury Hygiene ´ The work place should be well ventilated ´ Mercury and unset amalgam should not to be touched by the bared hands. ´ Skin accidentally contaminated by mercury should be washed thoroughly with soap and water. ´ It should be stored in containers filled with water. ´ Floors should be cleaned frequently. ´ Do not use a house hold vaccum cleaner to clean spilled mercury. Amalgam repair Benefit of Repair ´ More conservative of tissue ´ Reduce risk of iatrogenic damage ´ Reduce need for the use of local anesthesia ´ Opportunity to enhanced patient experience ´ Saving in time and resources ´ Composite can be used as repair material. o Interfacial bond between amalgam and resin composite o Strengthening of the tooth-material interface o The adhesive used for the connection between amalgam and composite resin should contain 4-META. Amalgam Failures o Bulk restoration fracture o Corrosion& excessive marginal fracture o Sensitivity or pain o Secondary caries o Fracture of tooth structure forming restorative- tooth preparation walls o Marginal gap formation Which of the following components that make up amalgam is responsible for delayed expansion caused by moisture contamination? (DUS 2019) A) Tin B) Mercury C) Copper D) Zinc E) Silver What is the plastic deformation of amalgam under stress called? (DUS 2017September) A) Creep B) Flow C) Corrosion D) Expansion E) Elasticity Which of the following is not one of the factors limiting the long-term use of amalgam restorations? (DUS April 2012) A) Breakage of restoration B) Corrosion C) Abrasion D) Secondary caries E) Sensitivity Formation of a lack film on the surface as a result of the corrosion of sulphides in amalgam restorations is an example of which of the following? (DUS September 2016) A) Galvanic Corrosion B) Electrochemical corrosion C) Chemical corrosion D) Consensed cell corrosion E) Stress corrosion ´ Which of the following is the element that prevents oxidation of other elements and causes delayed expansion in amalgam alloys? (DUS September 2012) A) Silver B) Tin C) Copper D) Iron E) Zinc ´ Which of the components of amalgam does not provide antibacterial effect? (DUS September 2014) A) Copper (Cu) B) Silver (Ag) C) Lead (Pb) D) Mercury (Hg) E) Zinc (Zn) Which of the following is the restorative material that increases its marginal seal feature in addition to its antibacterial properties over time? (DUS September 2016) A) Glass ionomer cements B) Glass carbomer restorative material C) Nanocomposites D) Dental amalgams E) Compomers