What is Dental amalgam?
It is a direct restorative material.
Amalgam: defined as metal alloy of mercury.
Alloy: is a combination of two or more metals.
Dental amalgam: is a mixture of mercury, silver, tin, copper, and other elements.
Composition of traditional dental amalgam:
% of total
Other elements as gold, palladium and indium
Function of components:
Silver: causes setting expansion , increases strength and corrosion resistance.
Tin : causes setting contraction.
Copper: as silver.
Zinc: reduces oxidation of other metals in the alloy.
Setting reaction of amalgam:
It starts when mix Ag-Sn alloy and mercury together as follows:
Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn2Hg.
γ + mercury γ + γ1 + γ2
Powder + liquid unreacted alloy + amalgam matrix
γ phase and γ1phase have similar hardness while γ2 phase is softer and weaker.
Classification of dental amalgam:
A. Low copper amalgam(conventional or traditional amalgam) 5%.
13-30%): ) B. High copper amalgam
It requires less mercury in the mix (lower Hg/alloy ratio).
The first reaction is the same as the traditional alloy(low copper amalgam):
γ + mercury γ + γ1 + γ2
Followed by second reaction:
γ2 + Ag-Cu Cu6Sn5 + γ1 .
The final high copper amalgam contains little or no γ2 phase and is superior in its clinical performance .
C. Non-zinc amalgam:
Zinc usually added to amalgam alloy because of its ability to unite with oxygen and other impurities present in the alloy.
Amalgam containing zinc may expand and corrode if moisture is incorporated during manipulation.
Non-zinc alloy may be used to overcome this problem that occur when moisture is present during placement.
D. Non-mercury amalgam(mercury free amalgam) :
It used gallium as a substitute for mercury but it is sensitive to moisture which can cause corrosion and expansion.
2- The shape of alloy particles :
It requires more force during condensation than spherical amalgam.
B- Spherical amalgam:
it requires less mercury to wet the particles and it set faster than lathe-cut amalgam.
C- Admixed amalgam:
A mixture of lathe-cut and spherical alloys .
Common amalgam supplies and instruments:
1)Amalgam restorative material:
A-2 bottles (one contains powder and one contains liquid(mercury).
B- Tablets form contained in the tube and mercury in bottle.
C-Preproportioned amalgam capsules contain preweighed alloy powder separated from a preweighed amount of mercury by separating membrane. It also contain a small mixing device called a pestle.
Advantages of premeasured amalgam capsules:
4-Minimal handling before mixing process.
*Premeasured capsules are usually color coded to indicate single, double and triple spills.
*Non-disposable mixing capsules should be tested for leakage by placing transparent tape over the seal, mixing a normal spill and then observing the tape for any leakage.
It is a machine that mixes mercury with silver alloy to produce plastic mass of amalgam.
A disposable capsule is prepared for mixing by breaking the separating membrane using an amalgam activator.
Amalgamator is equipped with a timer to control the mixing time.
The mixing process is called trituration.
All mixing of mercury should be done with closed cover of amalgamator to prevent spilling of mercury.
Variations in the conditions of trituration of alloy and mercury:
Undertriturated alloy has a dry, crumbly appearance , set too quickly and result in weak restoration, not cohesive,and break easily into pieces.
Overtriturated alloy is too wet, sticks to the walls of the mixing capsule and set quickly because of the heat produced by prolonged mixing.
Properly triturated alloy has a satin appearance, homogenous and smooth mix and produces the desired physical properties.
After amalgam is mixing, it must be transferred to the cavity preparation in small increments by using amalgam carrier.
Carrier is filled with amalgam by pressing the opening of carrier into the mix, it is refilled repeatedly until the preparation is completely filled with amalgam.
Carefully transfer the amalgam carrier to the dentist because the amalgam could fall out of the carrier.
The dentist usually uses the smaller end of the carrier first to fill the interproximal spaces.
4-Dappen dish (amalgam well):
It is a special amalgam holding dish used to consolidate the mixed amalgam and facilitate filling the amalgam carrier.
It is an instrument with a flat surface on the working end that is used to press amalgam against the cavity walls and floor.
Usually double ended, with one end smaller than the other.
Is a thin strip of stainless steel metal used to create a form around a prepared cavity that is not completely surrounded by tooth structure as class II.
After the restorative material acquires its desired shape, the matrix can be removed.
Matrix band is held in place around a prepared tooth by a matrix retainer (Tofflemire retainer is the most popular retainer today).
It is a triangular wooden or plastic stick that is inserted between the teeth after the matrix band is placed.
-hold the matrix band tightly against the tooth to ensure that amalgam cannot escape into interproximal area during condensation.
-it separates the teeth slightly to compensate for the thickness of the matrix band.
Two of the most popular designs are the cleoid-discoid and Hollenbeck carvers that are facilitate the carving of the occlusal surfaces of the restoration.
During the carving process the assistant should be using the oral evacuator to pick up excess amalgam.
Is a smooth-tipped hand instrument used to smooth and enhance the occlusal anatomy of an amalgam restoration.
after complete carving, the dentist checks proper occlusion by having the patient close the jaws while holding a piece of articulating paper on the biting surface.
Polishing of amalgam:
Final finishing should be delayed for 24hours to avoid damaging the margins.
It is done by using a series of abrasive rubber polishing points and rubber cups.
They are available in different grades and abrasiveness.
They are used in this color order:
-Brownie abrasive rubber point/cup.
-Greenie abrasive rubber point/cup.
-Super greenie abrasive rubber point/cup.
It is the amount of mercury mixed with the amalgam alloy.
The set dental amalgam depend on :
1- mercury/alloy ratio:
mercury mercury-containing reaction products (γ2 phase).
mercury mercury-containing reaction products (γ2 phase).
*Inadequate Hg/alloy ratio results in voids and poor restoration.
2- proper trituration ( mixing) and condensation techniques :
Also reduce the mercury content of the set amalgam.
Factors affecting handling and performance:
Factors are controlled by both the manufacturer and the dentist.
2-particles shape and size.
3-mercury content(if preproportioned capsules are used)
4-The anatomical form and finishing techniques.
Uses of dental amalgam:
1- used to restore various carious lesions(class I ,II ,V , VI,class III in invisible areas and cingulum pits).
2- used in amalgam build-up or amalgam core.
Advantages of amalgam:
2- Ease of handling.
3- Good physical characteristics(toughness and wear resistance).
4- Cost effective restorative material.
Disadvantages of dental amalgam:
1 -Poor aesthetic.
2- Mercury toxicity.
3 -High thermal conductivity.
4 -Galvanic effects.
5- Lack of adhesion.
Mercury is toxic in high levels to the kidneys and central nervous system.
Proper handling of mercury will prevent harm to dental staff.
It is not a problem for patients (except patients who are allergic to mercury).
The most significant danger is from mercury vapor.
The main sources of mercury exposure:
-leaking amalgam capsules.
-improper disposal of amalgam capsules and waste.
-improper storage of amalgam scrap.
-mercury droplets collecting on amalgamator.
-Placement of new and removal of old restorations.
-amalgam particles trapped in high volume evacuation system.
The threshold for air-mercury exposure hazard for general population is 50 µ g/m3 of air.
Mercury safety is considered from 3 aspects:
1-Safety of the patient:
The amount of mercury released from a set amalgam is very small and not dangerous to patients.
2-Safety of the dentist and staff:
Precautions should be taken in dental office to limit the exposure to the dental team.
3-Safety of the environment.
Methods for mercury vapor reduction:
1-work in a well-ventilated space.
2-use amalgam capsules not bulk alloy and mercury that could spill.
3-use amalgamator with enclosed mixing arm.
4-store amalgam scrap under water in sealed container.
5-recap used amalgam capsules and dispose of them in a sealed container.
6-use rubber dam, copious water and high volume suction when removing old amalgam.
7-use facemask and shield to avoid splatter and vapors.
8-use filters in evacuation systems, check and clean them regularly.
9-avoid carpeted clinics, use floor coverings that are nonabsorbent and easy to clean.
10-avoid direct skin contact with mercury.
11-using monitoring devices periodically to assess the contamination level of the work area.
12-Analyze urine samples of dental personnel periodically.
If the threshold is exceeded ,signs of mercury poisoning will appear:
Leg cramps, itching, excessive perspiration, rapid heartbeat, low grade fever, marked personality change, insomnia, headache, hypertension and nerve dysfunction.
Mercury spill kits:
They should be available in all dental offices.
The spill kit for small amounts of mercury should contain mercury-absorbing powder, mercury-absorbing sponges and a disposal bag.
A mask and utility gloves should be worn when cleaning up a mercury spill.