after class II amalgum fill , broken is happen in isthmus area why:
A- over high of filling virtically.***
B- over flair cavosurface angle or edge.
C- unproper mixed fill.
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Amalgam is a restorative material used in dentistry, it is often used to restore teeth with cavities and results from the alloy of mercury with other metals, such as copper, zinc, silver, tin or gold and other kinds of metals.
In dentistry, there is more concrete talk of "silver amalgam", to refer to the alloy used to seal the cavities that appear as a result of decay and thus restore the masticatory function and restore stability by replacing with this material the lost tissues. The amalgam will be placed in one of Black's cavities according to the type of lesion that needs to be sealed. These are always retentive since the amalgam does not adhere to the dental tissue.
The main advantages of dental amalgam over composite fillings are its long durability and low cost. Its disadvantages are the silver color, not very aesthetic for patients and the amount of dental tissue that must be removed for use. They also produce an increase in mercury exposure both in those who carry them and in dentists and their assistants.
As a result of cremation of corpses, dental amalgams are the cause of an important part of the mercury emissions into the atmosphere, and produce polluting residues in the air, garbage and drains of dentistry consultations.
The waste induces mercury poisoning due to its bioaccumulation.
Its use has been banned since 2008 in Sweden, Norway and Denmark and is restricted in other countries for some population groups. Their ban is studied throughout the European Union due to the impact they have on the environment.
preparation:
Dental amalgams are marketed in different forms. In a typical format, a dental amalgam is in a pre-dosed capsule containing 400 mg of alloy powder and 350-420 mg of metallic mercury. Both materials are separated inside the capsule.
When it is pressed they come into contact, and through a machine called amalgamator, which produces a rapid and uniform vibration, they are mixed. This process is known as amalgamation. The amalgamation process gives rise to amalgam, a ductile material that can be molded inside Black's cavities so that it takes the proper shape for retention.
It is also possible to perform this mixture manually, as it was originally done. Following this procedure, the amounts of alloy and mercury are taken approximately and mixed manually in a bucket. This form of preparation means that the manufacturer's specifications are very often not met, and that dental personnel suffer greater exposure to mercury vapors, which can be harmful over years.
A- over high of filling virtically.***
B- over flair cavosurface angle or edge.
C- unproper mixed fill.
------------------------
Amalgam is a restorative material used in dentistry, it is often used to restore teeth with cavities and results from the alloy of mercury with other metals, such as copper, zinc, silver, tin or gold and other kinds of metals.
In dentistry, there is more concrete talk of "silver amalgam", to refer to the alloy used to seal the cavities that appear as a result of decay and thus restore the masticatory function and restore stability by replacing with this material the lost tissues. The amalgam will be placed in one of Black's cavities according to the type of lesion that needs to be sealed. These are always retentive since the amalgam does not adhere to the dental tissue.
The main advantages of dental amalgam over composite fillings are its long durability and low cost. Its disadvantages are the silver color, not very aesthetic for patients and the amount of dental tissue that must be removed for use. They also produce an increase in mercury exposure both in those who carry them and in dentists and their assistants.
As a result of cremation of corpses, dental amalgams are the cause of an important part of the mercury emissions into the atmosphere, and produce polluting residues in the air, garbage and drains of dentistry consultations.
The waste induces mercury poisoning due to its bioaccumulation.
Its use has been banned since 2008 in Sweden, Norway and Denmark and is restricted in other countries for some population groups. Their ban is studied throughout the European Union due to the impact they have on the environment.
preparation:
Dental amalgams are marketed in different forms. In a typical format, a dental amalgam is in a pre-dosed capsule containing 400 mg of alloy powder and 350-420 mg of metallic mercury. Both materials are separated inside the capsule.
When it is pressed they come into contact, and through a machine called amalgamator, which produces a rapid and uniform vibration, they are mixed. This process is known as amalgamation. The amalgamation process gives rise to amalgam, a ductile material that can be molded inside Black's cavities so that it takes the proper shape for retention.
It is also possible to perform this mixture manually, as it was originally done. Following this procedure, the amounts of alloy and mercury are taken approximately and mixed manually in a bucket. This form of preparation means that the manufacturer's specifications are very often not met, and that dental personnel suffer greater exposure to mercury vapors, which can be harmful over years.
Possible risks:
Increased exposure to mercury:
In 1991, the World Health Organization determined that dental amalgams are the main source of mercury exposure for the general population.
A dental amalgam usually contains between 120 and 570 mg of this element.
This mercury is released very slowly in the oral cavity in the form of mercury vapors and ions in the saliva. Intraoral measures show that in normal circumstances a person with dental amalgams is exposed through them at a dose between 2.4 and 17 µg / day.The mercury in the urine shows similar doses, between 4 and 20 µg / day.
However, there have been cases in which the dose from amalgams was 100 µg / day.
The highest doses are produced during its setting and extraction, so for these operations it has been proposed to use a clean air supply by nasal route, rubber dam and air suction to avoid patient exposure, as well as Masks with mercury filter for the dentist and his assistant.
Some people with varied symptoms and mental type more attributable to mercury poisoning, experience improvement after the extraction of their amalgam fillings.
Toxicological aspects:
Mercury vapors are absorbed in the lungs by 80%, from where elemental mercury is incorporated into the bloodstream.
The mercury in elemental form Hg0 crosses the blood-brain barrier, however once it is oxidized to its divalent form Hg2 + it can no longer do so. The elimination half-life of mercury in the blood is usually less than 90 days, although in some cases it is longer.
The catalase enzyme rapidly oxidizes Hg0 to its divalent form Hg2 +.
Part of the Hg0 absorbed in the lungs is oxidized inside the brain, being retained in it. The lifetime of Hg2 + in the brain is several years.
Mercury causes neurodegeneration.Hg0 also crosses the placental barrier so it accesses the central nervous system of the fetus during its development and is incorporated into breast milk. One part of the inhaled mercury is exhaled and another part is excreted in the urine and feces.
Mercury ions that are incorporated into saliva are absorbed in the intestine by 10%.
Some bacteria present in the intestinal flora and saliva can methylate inorganic mercury.
Methylmercury is absorbed in the intestine by 90%, crosses the blood brain barrier and is slowly demethylated in the body to the inorganic form Hg2 +.
Inorganic mercury Hg2 + has a high chemical affinity for thiol groups, present in some sulfur amino acids, such as cysteine. Cysteine is a structural part of different membrane proteins, enzymes and tissues in which mercury accumulates. The union of mercury to these groups alters the functioning of many normal processes of the human body.
It has been verified by human autopsies the existence of a positive correlation between the number of amalgam surfaces in a person's mouth and the concentration of inorganic mercury in different tissues of his body, especially in the pituitary gland, thyroid gland and cortex. occipital of the brain.
The concentration of inorganic mercury in these tissues does not correlate with the concentration in blood, urine, hair or nails.
People carrying the e4 allele of apolipoprotein E have a greater vulnerability to the neurotoxic effects of mercury.
In the absence of treatment, the half-life of mercury in the human brain approaches 4 years.
Opinion of the health authorities:
In 2008, after Maths Berlin's report to the Swedish government and the prohibition of amalgam fillings in the Scandinavian countries, the report of the SCENIHR committee of the European Commission ratified that amalgams are a safe material for dental restoration.
This report has received harsh criticism from toxicologists.
In 2009, despite having contrary reports, the FDA also confirmed that dental amalgam is a safe material, classifying it as a class II medical device.
This decision has also received criticism among toxicologists.
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