Amalgam Restoration – Dental amalgam has long been the material of choice for posterior restorations. It is also used as a core material to prepare a base for a crown or bridge.
However, in cases where the darkness of the amalgam might be visible in the patient’s smile, dentists are now more frequently choosing the latest composite resin bonding systems, which closely match the tooth shade of the patient rather than Amalgam Restoration.
Cavity Preparation for Amalgam Restoration
After viewing the appropriate X-rays to determine the size and probable shape of the decayed or missing tooth structure for amalgam restoration, the dentist will select the rotary instruments (carbides or diamonds) for use in the high-speed hand piece. The cutting of tooth structure is always done with sufficient water spray as a coolant.
The assistant should hold the high-volume evacuator on the opposite side of the tooth to draw the water across the tooth, providing maximum cooling effect. The prepared cavity is then rinsed with a water spray and dried with an air syringe for final assessment. The dentist examine the preparation before starting the amalgam restoration step to make sure that:
• All unsound tooth structure has been removed.
• The proper retention form has been created.
• The preparation is clean and dry.
If the cavity preparation is deep enough to be in proximity of the pulpal tissues, the calcium hydroxide liner is placed before the use of cement base (ZOE, polycarboxylate, glass ionomer, or resin ionomer). This base must be sufficiently thick as to provide an insulative layer between the pulp and the amalgam. After the cement base is hardened, any excess will be removed with an excavator or explorer. The inside surfaces of the cavity preparation are then evenly coated with varnish.
Amalgam Placement for Amalgam Restoration
While the varnish is drying, the Dental Surgery Assistant triturates the alloy capsule in the amalgamator. Once mixed the amalgam is placed onto a squeeze cloth or into an amalgam well. The assistant loads the amalgam into an amalgam carrier by pressing the tip of the empty carrier into the amalgam mass until full. The Dentist places the carrier tip into the cavity and fills it layer by layer, while using the amalgam condenser to condense or pack the material in box type cavity. The layers of amalgam are placed until the cavity is overfilled.
Carving for Amalgam Restoration
The various shaped carvers are used to recreate the dental anatomy of the tooth. Shapes such as the discoid (flat and circular) and cleoid (claw- shaped) are often used for the occlusal anatomy. An occlusion check is made, after the initial carving, to ensure that the recreated anatomy meshes with the opposing teeth. Premature contacts, or high spots, can cause the new amalgam to fracture and also interfere with proper chewing. An occlusion check is made with articulating paper. The high spots, if any, are then carved away.
Finishing and Polishing for Amalgam Restoration
After final check of the occlusion, the amalgam is burnished with a ball-shaped instrument, burnisher, to ensure tight marginal contacts. This burnishing also enhances the surface smoothness and fmish of the amalgam restoration. Before the patient is dismissed, the patient is instructed not to eat for about 2—3 hours (as most modern amalgams will reach sufficient strength in that time).
Usually, final polishing of amalgams is often done on a normal recall appointment (after a minimum of 24 hours) by the dentist or hygienist. This polishing is most commonly accomplished with rubberized abrasive points and cups. Care must be taken to use these polishing compounds or abrasives at slow speeds. Heat buildup in the amalgam can cause distortion or warping of the Amalgam Restoration, thermal shock to the tooth, and the release of mercury vapours.
Moisture Contamination in Amalgam Restoration
Water or saliva that accidentally enters the amalgam restoration procedure or cavity preparation can contaminate the restorations. Water is an oxidant in the presence of air. It interferes with the proper hardening of the amalgam by creating tin and copper oxides that in turn weakens the restoration.
Water contamination also interferes with the cements, bases, liners, and cavity varnishes by preventing their penetration into the dentinal tubules or adhesion to the tooth structure. Care must be taken to keep the amalgam restoration isolated. Whenever the cavity preparation is rinsed, it must be thoroughly dried with a gentle stream of dry air from the air syringe.