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66 Cards in this Set
- Front
- Back
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Meaning of amalgam |
Mixture or blend |
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Properties of mercury that make dental amalgam possible |
Liquid metal at room temperature Can be mixed with other metal particles some of which it dissolves and precipitates Hardens on mixing but gives some time for manipulation |
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Y copper was added to traditional dental amalgam |
Copper strengthens the brittle silver tin alloy. But above 5%, it forms copper tin particle. Hence, it was traditionally limited to 5% |
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What are the names of the different crystals forming in amalgam matrix while setting? |
Gamma 1 = silver mercury Ag2Hg3 Gamma 2 = tin mercury Sn 7 8 Hg Eeta = copper tin Cu3 Sn |
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Traditional silver tin alloy made from? |
Lathe cutting or milling a cast ingot of silver tin alloy |
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Admixed alloy is made by |
Mixing lathe cut silver tin particles with spherical silver copper eutectic alloy particles |
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Types of High copper alloys |
Admixed or single composition |
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What is annealing? |
A controlled heating and cooling process designed to produce desirable properties in a metal |
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Y is silver alloy in amalgam annealed? |
The controlled heat and cooling treatment reduces residual stresses in the alloy that was caused by lathe cutting or milling. The stresses can over time cause changes in alloy properties like rate of amalgamation or dimensional change during hardening. Annealing causes the alloy to have more stable properties if stored for longer time properties like rate of amalgamation or dimensional change during hardening. Annealing causes the alloy to have more stable properties if stored for longer time like rate of amalgamation or dimensional change during hardening. |
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How is spherical alloy powder produced? |
The desired elements are melted together. Then the liquid metal is atomised into fine droplets of the metal that retain their spherical shape if solidified before touching a surface. |
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Y modern manufacturers prefer smaller particle size in alloys? |
It hastens hardening after mixing with mercury and gives a smoother surface while carving, thereby reducing corrosion |
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What is single composition alloy? |
A recent high copper alloy where each particle has the same chemical composition. |
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What are the advantages of spherical powder alloy? |
Uses less mercury because the spherical shape has less surface area. Less mercury improves properties. |
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Disadvantages of spherical powder alloy |
Less resistance to condensation pressure. Therefore condensation can't be used to form proximal contour. Need to use contoured and wedged matrix band to prevent improper contacts. |
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Y do we have high copper alloys? |
Increasing copper % from 6% to near 30% causes tin to combine with copper instead of mercury because it has more affinity to copper.Also, copper is almost insoluble in mercury. This prevents gamma 2 tin mercury crystal formation which is the weakest phase in amalgam and less corrosion resistant. The resulting copper tin crystals are called eeta phase and form in-between the gamma 1 crystals. This gives an amalgam with better properties in strength and corrosion resistance and marginal integrity |
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Structure formation in low copper amalgam |
When mercury is mixed with silver tin alloy by trituration, the mercury starts dissolving the outermost parts of the silver tin particles. As silver has less solubility than tin in mercury, it precipitates first as gamma 1. Tin mercury precipitates later as gamma 2. As the alloy mercury ratio is 1:1 , there is insufficient mercury to dissolve all the alloy particles. Therefore silver tin alloy particles are embedded in a matrix formed mainly by gamma1 crystals and a few gamma2 crystals. As the mercury gets used up, the amalgam hardens. |
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Strongest phase in amalgam? |
Unconsumed silver tin alloy particles |
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Weakest phase of amalgam |
Tin mercury phase gamma 2 |
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G.V. Black's formula for dental amalgam |
Silver 65%. Tin 25 to 29%. Copper 6% Zinc 0-2% palladium 0-1% indium 0-4% |
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Y is silver used in dental amalgam? |
Silver increases strength, has less corrosion and tarnish, it increases setting time. Promotes setting when mixed with mercury. Reduces flow |
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Disadvantage of silver in amalgam |
High degree of setting expansion |
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Y tin added to amalgam? |
It aids in formation of gamma 1 as it has greater solubility than silver in mercury. Decreases setting expansion and increases flow |
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Disadvantages of tin in amalgam |
Forms the weakest phase in amalgam, the gamma 2 phase thereby decreasing strength. Gamma 2 phase is more prone to tarnish and corrosion. |
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Y zinc added to amalgam? |
Oxygen scavenger during manufacturing. It forms oxides during melting, thereby preventing other oxides from being formed. Alloys with zinc are less brittle, less plastic during condensation and carving. |
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Disadvantage of zinc in amalgam |
Zinc reacts with moisture in the mouth during condensation if there is improper isolation. This happens only before the amalgam sets. Zinc releases hydrogen from water, which collects in the voids of amalgam. After a few days or weeks, the pressure builds up and causes the amalgam to expand. This is known as delayed expansion. It is a form of creep. This can cause pressure on the pulp. The dimensional change can cause corrosion, fracture. |
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How does zinc in amalgam get contaminated by moisture ? |
Zinc can be contaminated by the air water syringe, a wet operative area, direct contact with hands or by saliva during condensation. It can happen only during trituration or condensation. Setting amalgam doesn't have a problem. |
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Amalgam termed zinc containing if |
It contains more than 0.01% zinc |
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Palladium added to amalgam to |
Increase corrosion resistance and improve mechanical properties. Near 1% |
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Indium added to amalgam to |
Reduces evaporation of mercury and amount of mercury required to wet the alloy particles |
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What is the phase that replaces the gamma 2 phase in high copper amalgam? |
Eeta phase or Cu6 Sn5 |
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Factors affecting dimensional change in amalgam |
More mercury favours expansion. Therefore principles like less mercury to alloy ratio and more condensation pressure reduces mercury and promotes contraction. Higher condensation pressure squeezes out mercury, reducing mercury:alloy ratio . Procedures that accelerate setting and mercury consumption also cause contraction. Longer trituration time caused by modern mechanical amalgamators accelerate setting . Low particle size uses up mercury faster because it has higher surface area which encourages faster silver dissolution and gamma 1 crystal formation thereby mercury consumption is faster. |
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Factors affecting strength in amalgam |
Defective cavity design reduces strength Over or under trituration reduces strength Lack of mercury in the mix can cause a granular mass to form that has poor corrosion resistance. Excess mercury left in the mix after setting reduces strength Higher condensation pressure for lathe cut amalgam reduces residual mercury and voids, increasing strength. Under trituration and delayed condensation pressure increases porosity and voids reducing strength. Increased condensation pressure reduces voids. High copper single composition alloy gains strength faster than admixed alloy. |
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Factors affecting creep in amalgam |
High copper amalgam has less creep rates than low copper. Increased creep rates cause more marginal deterioration Higher gamma 1 volume fractions increase creep Increased gamma 1 grain sizes reduce creep Increase in gamma 2 phase increases creep Absence of gamma 2 and presence of eeta rods reduce creep in single composition alloys |
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How is marginal leakage reduced in amalgam? |
Use of cavity varnish and dentin bonding agents |
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How does marginal leakage reduce in time in amalgam? |
Corrosion products formed at the margins seal the amalgam against further marginal leakage. |
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What is tarnish? |
A process by which a metal tends to lose lustre or discolor due to interactions with its environment like air or water. |
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What forms on dental amalgam due to tarnish? |
Black silver sulfide |
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What is corrosion? |
A gradual process by which a metal degrades on reaction with its environment to form oxides that cause surface changes on the metal |
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How is corrosion in amalgam a self sealing process? |
In a newly restored tooth , active corrosion occurs on the metal surface at the interface between the restoration and tooth surface. Electrolyte leakage in the space between results in a concentration cell corossion and buildup of corrosion products. These seal the gap gradually and the amalgam thus self seals. |
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Factors in corrosion |
Gamma 2 has been implicated as the primary phase prone to corrosion. Corrosion products have been identified as tin oxides and chlorides in low copper amalgam. Products with copper have been found in high copper amalgam but the rate of corrosion seen is lesser. If gold is filled on an opposing tooth, the large difference in EMF (electromotive force) can cause amalgam corrosion. It can release mercury that may damage the gold filling and cause galvanism. A smooth homogeneous surface of the restoration can prevent tarnish and corrosion. |
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The amalgam with the longest lifespan |
High copper amalgam with zinc |
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Factors affecting amalgam longevity |
Cavity design, choice of alloy, proper manipulation |
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What is Eames technique? |
Also called Minimal mercury technique, it advocates use of minimal mercury to alloy ratio in modern day alloys . |
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How excess mercury was removed from low copper amalgam |
Squeeze cloth removes excess mercury after trituration. Hard condensation pushes the mercury rich layer to the top where it can be easily removed. |
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Ratio of mercury to alloy in lathe cut and spherical |
50% in lathe cut and 42% in spherical alloy |
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What is the need for trituration? |
Alloy particles are coated with an oxide. This has to be rubbed off to allow mercury to react with the alloy. This is done by mechanically rubbing the alloy particles together by hand trituration or by a amalgamator. |
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Increased trituration time can |
Reduce manipulation and setting time |
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What is the goal of condensation? |
To get the max possible densely packed mass of amalgam in the cavity. This increases strength and decreases creep. The mercury rich layer must be pushed up to the top so that there is enough mercury to bond to the next increment. Excess mercury can also be removed. |
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Partially set amalgam if used for condensation can cause |
Internal fractures and voids. Can also break the matrix already formed in the cavity. Thus condensation should start immediately after trituration |
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Indication for proper condensation |
Shiny layer of mercury. The condensation should be from the middle outwards. |
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Points to remember while condensing spherical alloy amalgam |
Use large condenser as it has less force per area. Overhangs and weak proximal contacts can result due to less resistance to condensation |
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Goal of carving |
To reproduce anatomy of tooth structure |
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Points in carving |
It should be started only after amalgam is hard enough to offer resistance to the Carver. After carving, the surface should be smoothed by burnishing . a ball burnisher or a burnishing cup with prophylaxis paste is used. Temperature above 60 degree avoided. Ball burnisher used for occlusal anatomy while a flat sided one used for smooth surfaces. Finishing needed to remove surface defects. Final finishing done after the amalgam has set. Preferably 24 hours. Use wet abrasive discs |
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What is the recommended condensation pressure? |
66.7 N or 15 lb |
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Main causes of amalgam failure |
1. Secondary caries 2. Marginal fracture 3. Bulk fracture 4. Tooth fracture |
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Pain 1 day after amalgam fillings |
Maybe due to high points. But not due to delayed expansion. Can be fractures too |
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Signs of delayed expansion |
Pain after 10 to 12 days after placing amalgam. Protruding restoration |
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Side effects of mercury |
Allergy and toxicity |
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% of people allergic to mercury |
1% |
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Safe occupational dose for mercury recommended |
50 mugrams of mer ury per cubic metre of air per day |
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Precautionary measures for mercury |
1.Well ventilated operator 2.All excess mercury sealed in disposable containers. This includes waste, disposable capsules, amalgam removed during condensation. 3.Proper disposal through regulated dental vendors to prevent environmental pollution 4.Amalgam scrap and materials contaminated by mercury shouldn't be heat sterilized. 5.Spill on carpet shouldn't be removed by vacuum cleaner. Mercury suppressant powders should be used. 6.Any spill should be removed quickly 7.Mercury contact with skin,area washed thoroughly with soap and water immediately 8.If reusable capsule in amalgamator, it should have tight fitting cap. 9.When grinding amalgam, use water spray and suction 10.Use eye protection, face mask and disposable gloves. 11.Ultrasonic amalgam condenser not recommended 12.Instruments to monitor mercury in air. A chkup recommended every year 13.Film badges to detect mercury 14.Blood tests annually on staff in clinic |
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Mercury influence on restoration quality |
Mercury content above 55%. More marginal breakdown and surface deterioration. More gamma 2 phase formed. Which is more susceptible to corrosion and tarnish. Also causes more creep and strength reduction |
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Causes for marginal deterioration |
1.Improper cavity prep or finishing Unsupported enamel can cause fracture. Failure to remove mercury rich layer after condensation. 2.High residual mercury 3. Alloys with more creep or low copper alloys with more gamma 2 phase . zinc containing amalgam contaminated by moisture |
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Advantages of amalgam restoration |
1. Less technique sensitive 2. More durable 3. Cheaper coz time to fill is lesser 4.Excellent wear resistance 5. abrasiveness to enamel negligible 6. Corrosion self sealing 7. Bacteria has less chance to adhere to polished amalgam |
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Indications for amalgam |
Large contact bearing areas and areas with less aesthetic importance |
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How marginal deterioration repaired? |
Remove nearly half of amalgam and refill. The new part should have adequate support and retention. Or use bonding agent for small gaps. |
