DENTAL AMALGAM : DENTAL AMALGAM INTRODUCTION : INTRODUCTION Dental amalgam is a metallic restoration composed of a mixture of silver and other metals with mercury.
Silver amalgam was developed in europe in the 1820s.
It was introduced in united states in the 1830s. DEFINITION : DEFINITION AMALGAM:-This is an alloy of mercury with any other metal
DENTAL AMALGAM:-This is an alloy of mercury with silver, tin and varying amounts of copper ,zinc and other minor ingredients.
DENTAL AMALGAM ALLOYS:- There are silver tin alloys with varying amounts of copper ,zinc and other metals. CLASSIFICATION OF DENTAL AMALGAM ALLOY : CLASSIFICATION OF DENTAL AMALGAM ALLOY ACCORDING TO THE NUMBER OF ALLOYED METALS
Binary alloys- contain silver and tin.
Ternary alloys- contain silver, tin and copper.
Quaternary alloys-contain silver, tin, copper and zinc or indium.
2. ACCORDING TO THE SHAPE OF THE PARTICLES
Irregular- alloy particles are irregular in shape in the form of spindles or shaving.
Spherical-alloy particles have a smooth spherical shape Slide 5: c) Spheroidal:-alloy particles are spherical with irregular surfaces.
3)ACCORDINDING TO THE COPPER CONTENT OF THE ALLOY
Low copper alloys- contain copper in the range of 2% to 6%
High copper alloys- contain copper in the range of 12% to 30%
4)ACCORDING TO ZINC CONTENT
Zinc-containing alloys- contain zinc in the range of 0.01% to 1%
Zinc-free alloys- contain less then 0.01% zinc Slide 6: 5)ACCORDING TO WHETHER THE ALLOY IS UNMIXED OR ADMIXED
Single composition or unicompositional alloys- each particle of the alloy has the same chemical composition.
Admixed alloys- these alloys are a physical blend of lather-cut and spherical particles.
6)ACCORDING TO THE PRESENCE OF NOBLE METALS-
Noble metal alloy- contian small amounts of palladium or gold.
Non-noble metal alloy- do not contain any noble metals. PROPERTIES OF AMALGAM : PROPERTIES OF AMALGAM MICROLEAKAGE
Penetration of fluids & debris around the margins may cause secondary caries.
Dental amalgam has an exceptionally fine record of clinical performance because of its tendency to minimize micro leakage.
Amalgam may expand or contract,depending upon the manipulation. Ideally,dimensional change should be small. Excessive contraction can lead to Microleakage & secondary caries. THEORY OF DIMENSIONAL CHANGE-CONTRACTION : THEORY OF DIMENSIONAL CHANGE-CONTRACTION WHEN THE ALLOY & MERCURY ARE MIXED CONTRACTION RESULTS AS THE PARTICLES DISSOLVE & THE gamma1 GROWS.THE FINAL VOLUME OF gamma1 IS LESS THAN THE INITIAL VOLUMES OF SILVER AND MERCURY THAT UNDERGOES INTO MAKING OF gamma1. THEREFORE,CONTRACTION WILL CONTINUE AS LONG AS GROWTH OF gamma1 CONTINUES.
FACTORS FAVOURING CONTRACTION ARE-
Low Mercury-alloy ratio
Higher condensation pressure
Smaller particle size
Longer Trituration times. EXPANSION THEORY : EXPANSION THEORY GAMMA1 CRYSTALS AS THEY GROW,IMPINGE AGAINST ONE ANOTHER & PRODUCE AN OUTWARD PRESSURE TENDING TO OPPOSE CONTRACTION.IF THERE IS SUFFICIENT MERCURY PRESENT TO PROVIDE A PLASTIC MATRIX,AN EXPANSION WILL OCCUR WHEN gamma1 CRYSTALS IMPINGE. DELAYED EXPANSION : DELAYED EXPANSION If a zinc containing low copper or high copper amalgam is contaminated by moisture during trituration or condensation a large expansion can take place it usually starts after 3 5 days and may continue for months
H2O + Zn -> ZnO + H2 (gas)
This hydrogen gas does not combine with the amalgam but collects wihtnin the restoration, creating extreme internal pressure and expanison of the mass this causes protrution of the restoration out of the cavity Strength : Strength Hardened amalgam have good compressive strength
Compressive strength 1 Hour 7 days
Low copper 145MPa 343MPa
Admixed 137MPa 431MPa
Single composition 262MPa 510MPa Tensile strength : Tensile strength Amalgam cannot withstand high tensile or bending stresses
Low copper - 60MPa
Admixed - 48MPa
Single composition - 64MPa Factors Affecting Strength : Factors Affecting Strength Trituration
Porosity Creep : Creep It is defined as the time dependent plastic deformation
Creep of dental amalgam is a slow progressive permanent deformation of set amalgam which occurs under constant stress or intermittent stress.
Low copper amalgam 0.8 to 8.0%
High copper amalgam less than 0.17% Factors Affecting Creep : Factors Affecting Creep Microstructure
Effect of manipulative variables
Mercury alloy ratio
Timing of trituration and condensation Tarnish and corrosion : Tarnish and corrosion Amalgam restorations often tarnish and corrode in the months
Factors related to excess tarnish and corrosion
High residual mercury
Surface texture small scratches and exposed voids.
The most common corrosion products found with traditional amalgam alloys are oxides and chlorides of tin these are found along the tooth amalgam interface and within the bulk of older amalgam restorations.
Corrosion products containing copper can also be found in higher copper amalgams. Restorative technique for amalgam : Restorative technique for amalgam Choice of the amalgam alloy :-
lathe-cut copper alloys no longer used due to their poor properties.
Admixed or unicompositonal high copper alloys are preferred
Zinc-containing alloys are popular ADMIXED VS. UNICOMPOSITIONAL ALLOYS : ADMIXED VS. UNICOMPOSITIONAL ALLOYS ADMIXED ALLOY
1)Require more mercury.
2) Require more condensation pressure.
3)Adapt well to cavity walls.
4) Create good contacts.
5)Set slower Unicompositional alloy
Require less mercury
Require less condensation pressure.
Do not adapt well to cavity walls.
Do not create good contacts
Set faster 2)MERCURY : 2)MERCURY The mercury should have a bright, mirror like surface without any impurities.
For dental amalgam the mercury shd be triple distilled and shiny leaving no residue on pouring as specified by ADA specification no 6.
3) proportioning the alloy and mercury:- eames technique recommends the use of alloy and mercury in a 1:1 ratio by wt.
Presently capsules with proportioned amounts of alloy and mercury are more widely used. These have preweighted alloy powder with the appropriate quantity of mercury separated by a membrane which is ruptured just before trituration either by manual compression of the capsule or by self activation 4)TRITURATION : 4)TRITURATION This is the process of combining or mixing of liquid mercury with dry amalgam alloy powder. Trituration can be perfomed with hand or mechanical amalgamators.
trituration can produce different types of mixes:-
1)NORMAL MIX:- This is plastic in consistency, convenient to handle, shiny and homogenous.
2) UNDER TRITURATION MIX:-This mix is dry and crumbly, dull in appearance and cannot be manipulated.
3)OVER TRITURATION MIX :-This mix is warm, too hard due to premature setting of the amalgam and is not easy to condense. 5)MULLING : 5)MULLING It is a step done after trituration so as to make the mix homogenous and cohesive. In hand mixing using a motor and pestle, mulling is achieved by collecting the amalgam in a dry piece of rubber dam or chamois skin and rubbing it vigorously between the thumb and forefinger for 2 to 5 seconds.
While mixing in an amalgamator mulling is done by continuing the trituration for an additional 2 to3 seconds.
6) MATRIX PLACEMENT
This step is done in case one or more walls of the tooth are missing. It is necessary while performing class I extension restoration, class II, class v restorations and complex amalgam restorations.
Condensation of amalgam should be done soon after trituration or else the setting reaction of the amalgam may have progressed considerably to prevent its proper adaptation.
Condensation pressure applied for amalgam is between 5 to 10ibs for spherical amalgam.
8) PRE CARVE BURNISHING
This step is done soon after condensation when the cavity is overfilled with amalgam. This is done using a large round, cone or egg-shaped burnisher by applying firm and gentle strokes on the amalgam moving the burnisher from the amalgam to the tooth margins. It is done for 15 seconds. 9)CARVING : 9)CARVING Carving is the anatomical sulpturing of the amalgam restoration. Carving of amalgam is done in order to create a funtional occlusion and proper physiologic contours for the restortion . This is achieved using sharp carvers. The recommended carver are the hollenback carvers, cleoid-discoid carver and frahms carver ( diamond-shaped carver).
10)ADJUSTING THE OCCLUSION
A very important step to be done soon after carving the amalgam restoration is to check the occlusion so as to remove any areas left high in the restoration. Place an articulating paper between the opposing teeth and guide the patient to perform centric and eccentric movement. Areas that are marked on the restoration shd be carved using a discoid carver or spoon excavator. 11) Post-carve burnising : 11) Post-carve burnising This is the final burnising that is done after the carving is complete and occlusion is adjusted. this is done using a large burnisher and gently burnishing the amalgam outwards towards the margins. This produces a shiny, smooth surface by removing scratches and irregularities on the amalgam surface. 12) Finishing and polishing
In the past, amalgam restoration were polished to attain a high luster so as to prevent plaque accumulation and corrosion. Polishing is done 24 hr after the restoration. Sings of failures of amalgam restoration : Sings of failures of amalgam restoration Marginal ditching
Poor anatomic contours
Marginal ridge incompatibillity
Improper proximal contacts
Bulk fracture of the tooth or amalgam
Poor occlusal contacts Mercury : Mercury Disposal of scrap amalgam:- the scrap amalgam which remains after insertion and the excess amalgam removed after condensation sholud be collected and stored under water, glycerine or spent x-ray fixer solution is a source of both silver and sulfide ions which can react with mercury and keep the mercury levels low.
Mercury toxicity is primarily due to chronic exposure to high levels of methyl mercury concentrated in food. This form is less readily excreted than other forms of mercury. Excess mercury tends to concetrate in the liver, kidney and brain where its toxic effects are evident. Toxic effects of mercury vary depending upon the mercury levels present in urine.
Even when there are expensive amalgam restorations in a patient”s mouth, the maximum urinary mercury levels are only upto 4ug/gm of creatinine in the urine. This is well below the level at which any toxic changes occur. Slide 31: Mercury level upto 25ug/gm of creatnine in urine, mercury causes a decrease in verbal skills and reduction in nerve conduction tests.
Between 25 to 100ug/gm of creatining in urine, mercury causes a decrase in verbal skills and reduction in nerve conduction tests.
Mercury level between 100 to 500ug/gm of creatinine in urine leads to irritability, depression, memory loss, mild tremors, other nervous disturbances and early kidney dysfunction.
When mercury levels are over 1000ug/gm of creatinine in urine, toxic signs include kidney inflammation, swollen gums, pronounced tremors and nervous system disturbances. THANK YOU : THANK YOU