C18    Identify at least two adverse effects which could be induced during carving and burnishing.

During Burnishing:

During burnishing, excess mercury is collected in the surface layer. It is important to have a sufficient thick layer of amalgam excess to make sure that all the mercury moved to the surface during burnishing can be carved away. If the burnisher touches the enamel surface during the burnishing procedure, it will be impossible to remove the mercury rich surface.

Remove unnecessary amalgam excess before the matrix band is removed. By removing the band with too much amalgam access (see above), one increases the risk for fracturing the amalgam during matrix band removal.

During Carving:

a. Micro-gap formation. This can occur if the plastic amalgam is carved from the enamel margin toward the plastic amalgam. This defect cannot be seen with a naked eye, but can leave an open path for microorganisms.

b. Submargination. This occurs if the plastic amalgam is carved from the amalgam toward the hard enamel margin. This defect is easy to detect by sliding an explorer over the surface. At the same time, this defect is not as serious as the micro-gap formation, because the amalgam adaptation to the enamel is still intact.

To avoid any of the above problems, excess amalgam should be removed by carving along the margins (see A below). The carver should be angled so it cuts downwards (alternative a shown in B) and removes excess by forcing it out over the enamel surfaces like a snow-plow (like in A).

During carving, it is VERY important to remove amalgam flash (see a below). If the flash is not removed during carving or polishing, it will sooner or later fracture (b and c) and cause marginal defects that increase retention and cause inconvenience to the patient (the tongue will detect these regions).

After completed carving, the surface can be smoothened with a burnisher or a beaver-tail instrument. This is done by surfacing the amalgam towards the margins (see below) to optimize marginal adaptation. Just remember! This is not a burnishing process (involving significant plastic deformation and excessive mercury accumulation at the surface), just a light surface smoothering procedure.

Amalgam Polishing:

Amalgam polishing is conducted after the amalgam has set for at least 24 hours. The most efficient way to polish an amalgam is to start with large 20 blade pear shaped finishing burs. Large size reduces the risk for local "pitting" (lower local pressure due to the larger surface area contact).  Finer and finer pear shaped burs are used to characterize the fissures. The pear shaped burs are preferred instead of the round, since the pear shaped minimizes the risk for removing more amalgam close to the margin (see figure below). The use of a round finishing bur could result in a thin and fracture prone amalgam margin. Proximal surfaces are finished with flame shaped finishing burs. All these trimmings are done with the turbine and water-cooling.

Soflex disks are then used to smoothen the margins, and sharp rubber point are used to finish the fissure systems. It is important to use water cooling when these procedures are conducted.

The final polish is done with rubber cups and and a prophy paste containing fluoride. If a super-shiny surface is the goal, mix zinc oxide and alcohol and coat the surface with this paste. After the alcohol has evaporated, use a very soft brush and polish away the dry zinc oxide paste.