Alberto Gambino & Andrea Quirico
The silver amalgam is a repair material, constituted by a silver (40-70%), tin (20-30%), copper (2-30%), zinc (0-2%) alloy combined with the mercury at the solid state and ambient temperature.
On the market there are various types of alloy which are different in the form and types of particles: in shavings or flakes, floccular, spherical, mixed with shavings prevalence, speroidal, mixed with spheres prevalence. The dimension and the form of the particles affect the amount of mercury: little particles better fill the cavity but they need more mercury; opposite speech about big particles. Quantity of mercury is higher, physical characters of the alloy are lower, so a right compromise must be found.
Today the use of the amalgam is on the decrease for:
- aesthetic reasons,
- delicate mercury to handle,
- excessive healthy tissue removal to create retention
- fixed time of work
There are some situations in which his job is irreplaceable in subgengival fills still where modern composites isolate species of pathogenous bacteria, in extensive rebuildings of the rear elements for patients who for several reasons cannot support the cost of an inlay and the patients who are not collaborative (Down syndrome) which need a longeval material for the treatments in narcosis.
There are several types of amalgam classified on the basis of the contents of copper:
- Conventional alloy with low contents of copper: it produces unsettled g2 (Sn7-8Hg) phase and today not any longer used
- no g2 with high Cu ALE: with big size traditional particles plus spherical particles of eutectic alloy
- no g2 with high Cu SCS: spherical particles in single composition.
REACTION OF AMALGAM
The amalgams are obtained for alligation of the MERCURY with the already preformed alloy. Conventional amalgams:
Hg + phase g(Ag3Sn) = phase g1 ( Ag2Hg3) + phase g2 (Sn7-8Hg)
Amalgams with high Cu (not g2)
Hg + phase g= phase g1 + phase e (Cu3Sn)
In conseguence of such reaction one quote of mercury freed by the electrochemical activity of the g2 phase which acts as anode in opposition to g1 and g, it appears for capillarity towards the surface of the obturation in shape of metal drops. Such phenomenon is principally due to the instability of the g2 phase while the corrosion of the metal holds a marginal role.
TOXICITY OF AMALGAM
According to few studies the prolonged exposure can cause the following symptomatology:
- iperemotionality, irritability, insomnia, psychomotorial agitation, sadness, apathy,
- memory enfeeblement,
- lesions to the organ of the sight: optic nerve atrophy and mercurialentis (outside absorption of the mercury by the crystal)
- troubles of the sensitivity: parestesy (for degeneration of the peripheral nerves), ataxy, deafness.
- compromission of the liver: total serum proteins reduction, decrease of the cholesterol/ total cholesterol relationship, increase alkaline fosfatasi.
- kidney: nefrotoxicity
- amalgam allergy: it regards less than 0,1% of the population, it causes: dermatitises, nettle rash, eczema, eritematose reactions with interest of face, neck, arms and thorax, oral lichenoidi reactions,
- "amalgam syndrome": psychiatric pathology in which the urinary mercury is normal even though psychosomatic symptoms appear.
Predisposing factors to the exposure for dentists:
- Professional practice: number of obturations executed and removed by the week, number of of training years , methods of storage, number of years in the location of the dentist‘s surgery.
Various professionals and their studies have faced the problem:
factors contributing to mercury exposure in dentists
mercury excretion and occupational exposure of dental personnel
- personal characteristics: age, diet, number of obturations in amalgam.
- working place: casual reversals of mercury, material of the flooring, ventilation and not excessive temperature (which supports the vaporizzation of the mercury )
- prevention rules: use of protective clothing, personal hygiene (careful hands washing), use of conventional aspirator during removal and polishing obturations.
Predisposing factors to the exposure for patients:
- personal characteristics: age, diet, number of obturations in amalgam, presence of gold prothesic handmade articles near to amalgam obturations which set off oral galvanism.
THE WHO INDICATIONS
In 1991 WHO has stated it’s not possible claim whether the amalgam obturations are toxic or not :
- the daily Hg dose released by fillings, which has been seen in patients with many rebuildings, is only at par with 10% of the normal assumption through the diet, the air and water, of a person who is not in contact with the mercury for professional reasons.
- at the moment there isn’t obturation material that has the extent of therapeutic indications, manipulation easiness and goodness of physical properties as the amalgam.
- the restorations in amalgam are considered safe, but the components can cause rare local collateral effects or allergic reactions; it has not been shown that the little amounts of mercury which free themselves from the restorations cause damaging effects for the health; scientific test does not exist that shows the symptoms of systemic character regress after removing the fillings
- if the conditions of work of the sanitary staff are not organized correctly there is a potential risk for the operators' health but the adoption of the appropriate hygienic requisites and the control of the mercury steams in the environment reduces in determinant way the risk factors.
- mercury used by the dentists can contaminate the environment, so the use of correct methods of draining of rubbish is required.
Thought not existing scientific evidences, in 1999 in Italy the superior health council has decided to limit partly the use of amalgam in pregnant women , under 5 years old and in nefropatic patients.