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Dental Materials for Dental Assisting Exam Study Guide (page 2)

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Updated on Jun 23, 2011

Restorative Dental Materials

Restorative dental materials can be either permanent or temporary. Once the dental disease is removed from the tooth, the tooth is restored to its functioning state using a restorative material. In addition to restoring function, restoring aesthetics is an important part of the material chosen. Restorative materials can be either direct or indirect. Medicaments are added in a certain order: liner, etch, primer, bond, then composite.

Direct Restorations

Direct restorations are completed in one dental visit. The material is placed in a pliable state, then hardened and polished. Examples of direct restorative materials are amalgams, composites, and glass ionomers.

Amalgam

Traditional amalgam (“silver fillings”) restorations are an example of direct restoration. Amalgams are adhered with chemical bonding or physical retention and used primarily for posterior restorations. The mixing of the mercury and alloy powder that make up the amalgam is known as trituration. The sequence for a Class II amalgam restoration is: prep tooth, place liner or base, place Tofflemire matrix, place amalgam. Instruments are used in a specific order: amalgam carrier, condenser, carver, burnisher, and articulating paper. Amalgam has the following advantages and disadvantages:

  • Amalgam is a mixture of alloy (two or more metals such as silver, tin, copper, and zinc) combined with mercury.
  • Its safety is questioned by some. For example, clinical personnel are cautioned never to touch amalgam with bare hands; to use sufficient ventilation; and to discard it in a closed, covered, impervious container. It must be treated as hazardous waste.
  • Amalgam can lead to recurrent decay, microleakage, tarnishing, fracturing teeth with expansion, and tattooing.
  • It is aesthetically inferior to other materials.
  • It is affordable.
  • It is long lasting.
  • It can be used on patients with poor oral hygiene.

Composite

Composite or resin restorations are often referred to as “tooth-colored fillings,” and are another example of direct restorations. Composites have gained in popularity due to their esthetics. They can be “bonded” to the enamel and dentin, which actually helps strengthen the remaining tooth structure. The tooth preparation for a composite may be less invasive than an amalgam due to the bonding technique utilized. Glass is added to the composite material for strength. Composite material is layered incrementally and each is light cured in large restorations. (Remember that prolonged exposure to the curing light can damage the retina, so avoid staring directly at it.) Composite restorations have various classes. For example, a Class III restoration would use a mylar strip. Composites are easily polished but not with a low-speed hand piece. Flash refers to excess composite or bond material. A discoid cleoid is never found on a composite tray. A composite has the following qualities:

  • It is currently the most popular choice of restorative material.
  • It is aesthetically pleasing.
  • It comes in many shades.
  • It bonds chemically to the teeth.
  • It can be anticariogenic (preventing tooth decay by releasing fluoride).
  • The two types of composite materials are: filled, when strength is needed; and unfilled, for sealants and similar uses.
  • Composites are cured in three ways: by using the curing light (light-cured), by mixing the base and catalyst (self-cured), or a combination of both (dual-cured).
  • Polymerization is the process of hardening.
  • It is not as strong as an amalgam.
  • It is more expensive than an amalgam.

Glass Ionomer

A third type of direct restoration is glass ionomer. Glass ionomer properties can be altered, which allows them to be formulated as restorations, liners, cements, and bonding agents. When mixing glass ionomer, always follow the manufacturer’s instructions. For example, GC Fuji suggests combining one scoop powder and one drop liquid; mix in one half of the powder for five to ten seconds, and then the second half of the powder for ten to 15 seconds.

A glass ionomer has the following advantages:

  • It is very versatile. It can be used for liners, core build-ups, restoratives, and cements.
  • It is aesthetically pleasing.
  • It is anticariogenic (preventing tooth decay by releasing fluoride).
  • It bonds chemically to the enamel and dentin of the teeth.
  • It comes in many shades.
  • It is radiopaque (visible on X-rays), which is a distinct advantage over calcium hydroxide.
  • It is compatible with all dental restorative materials.

Indirect Restorations

Indirect restorations are completed in two or more dental visits, although CEREC (Chairside Economical Restoration of Esthetical Ceramics) units create a porcelain crown in one visit. Other restorations are actually fabricated in the dental lab. These restorations are referred to as cast restorations. Cast restorations are made from impressions taken of the patient’s mouth and then sent to the lab. Sometimes, crowns have to be returned to the lab for perfecting, but not in the case of slightly high occlusion. Examples of indirect restorations are gold crowns, porcelain crowns/porcelain fused to metal crowns, and other indirect restorations (three-quarter crowns, inlays, onlays, and veneers).

Gold Crowns

Gold crowns have many advantages. These are used where aesthetics are not the primary concern and if the inter-arch space does not allow sufficient room for porcelain. Also, if the patient clenches or grinds, gold will not suffer fracture strain. Gold crowns have the following qualities:

  • The gold in these crowns is combined with other metals for strength.
  • They resist the harsh environment of the oral cavity.
  • They are available in four types.
  • They are fabricated in the dental lab.
  • They are cemented with permanent cement.
  • They are healthy for the gum tissue.

Porcelain Crowns/Porcelain Fused to Metal Crowns

Porcelain crowns and porcelain fused to metal crowns are most commonly used in fixed prosthodontics. The versatility of porcelain allows for the following advantages:

  • They are most often used in dentistry.
  • They are aesthetically pleasing.
  • They are fabricated in the dental lab.
  • They are cemented with permanent cement.
  • They match natural surrounding teeth.

Other Indirect Restorations

Other indirect restorations include three-quarter crowns, inlays, onlays, and veneers. Inlays are fabricated extraorally and cemented in place. Onlays are similar to inlays, but they must include at least one cusp. For example, a restoration that extends over the cusps of posterior teeth leaving the facial and lingual aspects of the tooth intact is an onlay. These restorations may be made with porcelain or made of full gold.

Stainless-Steel Crowns

Stainless-steel crowns come in a variety of sizes and must be contoured and trimmed to fit the tooth. Adult gingival tissues do not tolerate stainless-steel crowns, which is why they are reserved mainly for use on children. They are utilized as permanent coverage on primary teeth or as temporaries on permanent teeth. Once trimmed, stainless-steel crowns are lined with cement and seated in place.

Retraction Cord

During the crown procedure, it is necessary to retract the gingival tissue prior to the final impression. This is done utilizing a gingival retraction cord. The cord comes in a variety of sizes, the largest of which is size 3. Retraction cords have the following qualities:

  • They are utilized for temporary retraction of gingival tissues surrounding a prepped tooth so that an accurate impression of the margin can be attained.
  • They can be braided or unbraided.
  • They can be impregnated with hemostatic solution to control bleeding (epinephrine or vasoconstrictor are not to be used for patients with heart conditions).
  • Some states limit this expanded function to a dental assistant only placing a non-impregnated retraction cord.
  • Other methods, such as foaming agents and adjuncts, are utilized to retract gingival tissue.

Provisional (Temporary) Crowns

After the tooth has been prepared for a crown or bridge, the tooth needs coverage for comfort, protection, and aesthetic purposes. A provisional, or temporary, crown is prepared and placed for the interim while the final crown is fabricated in the dental laboratory. There are two types of provisional crowns: custom acrylic temporary crowns and preformed temporary crowns.

Custom Acrylic Temporary Crowns: These types of crowns can be made from powder and liquid (trim) or from a cartridge that combines a base and a catalyst in a mixing tip.

Preformed Temporary Crowns : These types of crowns have a polycarboxylate anterior and an aluminum shell posterior. Celluloid crowns are made of clear plastic material and are primarily used for anterior teeth.

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