Dental amalgamby Kazhan Omer Abdulrahman

Amalgam—An alloy containing mercury.

Dental amalgam—An alloy that is formed by reacting mercury with silver, copper, and tin, and which may also contain palladium, zinc, and other elements to improve handling characteristics and clinical performance.

Dental amalgam alloy (alloy for dental amalgam)—An alloy of silver, copper, tin, and other elements that is processed in the form of powder particles or as a compressed pellet.

amalgam alloys

irregularly shaped

as spherical particles

as a mixture of both lathe-

cut and spherical particles

composition of amalgam alloy:

Low-Copper Alloys

Silver-tin alloys are quite brittle and difficult to blend uniformly unless a small amount of copper is substituted for silver. Within the limited range of copper solubility, an increased copper content hardens and strengthens the silver tin alloy.

High-Copper Alloys

The first high-copper alloy

This modification raises the copper content to 11.8% by weight. This is often called “dispersed-phase alloy” or “admixed high-copper alloy.”

A second type of high-copper alloy

This process yields a single composition system. The

copper content of this group of alloys can be as

high as 30% by weight.

Gallium-Based Alloys

In an attempt to eliminate mercury from direct

metallic restorative materials.

gallium , has been considered as a substitute

which is also a liquid when alloyed with indium

and tin at room temperature. Like mercury, this

metal element can be triturated with alloys for

high-copper amalgam.

POWDER CONFIGURATION

the physical configuration and condition of the particles will have a significant influence on the setting process.

Lathe-Cut Powder versus Spherical Powder Amalgams made from lathe-cut powders or admixed

powders tend to resist condensation better than amalgams made entirely from spherical powders.(why?)

Spherical alloys require less mercury than typical lathe-cut alloys(why?)

Particle Size Smaller particles greatly increase the surface area per

unit volume of the powder. A powder containing tiny particles requires a greater amount of mercury to form an acceptable amalgam.

During carving, the larger particles may be pulled out of the matrix, producing a rough surface. Such a surface is probably more susceptible to corrosion than a smooth surface. A smaller average particle size tends to produce a more rapid hardening of the amalgam with greater early strength.

The physical properties of the hardened amalgam depend on the relative percentages of each of the micro structural phases.

The greater the number of unconsumed Ag-Sn particles retained in the final structure, the stronger the amalgam will be.

The γ2 phase is the weakest and least stable in a corrosive environment and may suffer corrosion attack especially in crevices of the restorations.

the addition of more than 6% of copper by weight can reduce or eliminate the γ2 phase by formation of the Cu-Snphase.

Clinical manipulation of amalgam for restorations

The amount of alloy and mercury to be used can be described as the mercury/alloy ratio.

The mercury content of the lathe-cut alloy is about 50% by weight and that for spherical alloys is 42% by weight.

Triturators

A triturator should be used at the speed recommended by the alloy manufacturer.

For a given alloy and mercury/ alloy ratio, increased trituration time and/or speed shorten the working and setting times.

appears rounded with a smooth shiny surface , the strength will be optimal and the smooth carved surface will retain its luster long after polishing.

has low strength and poor resistance to corrosion. the rough surface left after carving of the granular amalgam will increase its susceptibility to tarnish ,The mixture may appear in solid mass, but the surface remains without luster as shown.

is shinier than that of the properly triturated one, and because of more fluid consistency the mass appears flattened by the force of trituration.

Condensation The goal of condensation is to compact the alloy into the

prepared cavity so that the greatest possible density is attained, This results from a reduction of excess mercury and porosity within the set amalgam.

The field of operation must be kept absolutely dry during condensation.

Sufficient pressure should be used to remove voids and to adapt the material to the walls.

The longer the time that elapses between mixing and condensation, the weaker the amalgam will be(why?)

Carving and finishing

The objective of carving is to simulate the anatomy rather than to reproduce extremely fine details.(why?)

Carving should not be started until the amalgam is hard enough to offer resistance to the carving instrument. (why? )

PROPERTIES OF AMALGAM1-dimensional stability

Amalgam can expand or contract, depending on its manipulation.

Severe contraction can lead to microleakage , plaque accumulation, and secondary caries.

Excessive expansion can produce pressure on the pulp and postoperative sensitivity. Protrusion of a filling can also result from excessive expansion.

expansion will occur if sufficient mercury is present in the mix.

manipulation with less mercury in the mix, as occurs for lower mercury/alloy ratios and higher condensation pressures, will favor contraction. In addition, manipulative procedures that accelerate setting and consumption of mercury also favor contraction, including longer triturationtimes and use of smaller alloy particles.

What is delayed expansion or secondary expansion?

When a zinc-containing, low-copper or high-copper amalgam is contaminated by moisture during trituration or condensation, a large expansion can take place. This expansion usually starts 3 to 5 days after placement and may continue for months, reaching values greater than 400 μm/cm (4%) .

2-strength

The strength of amalgam is more than adequate under compressive loads. However, amalgam is much weaker in tension than in compression.

More common are defects at the margins of amalgams.

factors affectingamalgamstrength :

Trituration

MercuryContent

CondensationPorosity

Amalgam Hardening

Rate

3-creep

occurs when a solid material slowly deforms plastically under the influence of stresses.

Creep rate has been found to correlate with marginal breakdown of conventional low-copper amalgams; that is, the higher the amount of creep, the greater is the degree of marginal deterioration.

4-tarnish and corrosion resistance tendency toward tarnish, does not affect or hange the

mechanical properties of the amalgam.

Corrosion, on the other hand, has a negative effect on the properties.

Every effort should be made to produce a smooth, homogeneous surface on a restoration in order to minimize tarnish and corrosion.

Whenever a gold restoration is placed in contact with an amalgam, corrosion of the amalgam can be expected as a result of the large differences in electromotive force (EMF) of the two materials. The corrosion process can liberate free mercury, which can contaminate and weaken the gold restoration. Biological effects such as galvanism can also result.

Clinical performance of amalgam restorations

Amalgam does not adhere to the tooth structure. At best it affords only a reasonably close adaptation to the walls of the prepared cavity. For this reason cavity varnishes are used to reduce the gross leakage that occurs around a new filling.

The use of dentin bonding agents with amalgam is another relatively new method to reduce microleakage.

If the amalgam is properly inserted, leakage decreases as the restoration ages in the mouth.(how?)

marginal breakdown Although the ditching of a margin may not have progressed

to the point where secondary caries may have developed, the restoration is unsightly and further deterioration may be anticipated.

Survival of amalgam restorations

The median survival times for posterior amalgam restorations were 7 to 15 years in general practices. Larger, more complex restorations fall within the lower range.

Repaired amalgam restorations

The important factor related to the quality of the amalgam repair is the interfacial bond between the new and the existing amalgam.

The surface of an old amalgam to be bonded should be roughened to remove corrosion and saliva contaminants and freed of loose debris.

When a freshly triturated amalgam is condensed directly onto the roughened surface of an existing amalgam, the flexural strength of the repaired structure can reach 50% of that of unrepaired amalgam.

Making a slot on the existing amalgam to establish mechanical interlocking between the two materials also improves the quality of the repair joint.

Another repair option for areas that exhibit minor marginal breakdown—gaps that are 250 μm or less in width—is to etch the enamel adjacent to the restoration and, after rinsing and drying the marginal gap area, sealing the gap with a dentin bonding adhesive.

When secondary caries is diagnosed, it inevitably requires the replacement of the restoration, but an alternative treatment is to remove part of the restoration to the full depth at the site of the defect.

The repair should be attempted only if the area involved is one that will not be subjected to high stresses or one in which the two restoration parts are adequately supported and retained.

Safety of amalgam fillings

Toxicity

total amount of mercury vapor released during occluding on amalgam restorations is far below the “no effect” level

Allergy

are experienced by less than 1% of the treated population

Mercury hygiene in dental offices The operatory should be well ventilated.

All excess should be collected and stored in well-sealed containers.

Proper disposal through reputable dental vendors is mandatory to prevent environment pollution.

The use of an ultrasonic amalgam condenser is not recommended.

Instruments can be used that yield a time-weighted average for mercury exposure to sample the air in the operatory.

Film badges are also available that can be worn by office personnel in a manner similar to radiation exposure badges.

Biological determinations can be performed on office staff to measure mercury levels in blood or urine.

Thanks for your attention