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Dental Materials for Dental Assisting Exam Study Guide (page 3)

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Updated on Jun 23, 2011

Dental Cements

Dental cements are classified according to their properties and, therefore, their uses in dentistry. Type I cements are used for the placement of a restoration for long-term or short-term purposes. Type II are restorative materials. Type III are those materials utilized as bases and liners. Dental cements are either temporary or permanent.

Temporary Cements

Sometimes, there is a need for selecting a dental cement for short-term or sedative purposes. Generally, temporary cements last about six months. The operator will listen to the patient’s chief complaint and choose the cement accordingly. Temporary cements have the following qualities:

  • They are utilized for cementing provisional (temporary) restorations.
  • In some cases, they are utilized for temporarily cementing permanent restorations when the tooth is experiencing symptoms.
  • They can have sedative properties.
  • Assistants should follow the manufacturer’s instructions on whether to mix cements on paper or cooled glass, or with an automix extruder.

Brand Names of Temporary Cements

The most commonly used temporary cements are as follows:

  • Temp Bond, which is supplied in two tubes: base and catalyst
  • ZOE (zinc oxide eugenol), which comes in powder and liquid form

Permanent Cements

When seating a final cast restoration, the luting agent will act as an adhesive to hold the restoration to the tooth structure. Permanent cements are used to attach the permanent crown, which is placed in the patient’s mouth, and he or she is instructed to bite down on an orangewood stick/cotton roll. A crown and bridge cementation tray set-up would include instruments such as a low-speed hand piece, plastic instrument, temporary cement, and cement spatula, but not a gingival margin trimmer. Permanent cements have the following qualities:

  • They are utilized for permanently cementing cast restorations.
  • They are long-lasting.
  • They do not interfere with the proper fit of cast restorations.
  • They can be anticariogenic.
  • Assistants should follow the manufacturer’s instructions on whether to mix cements on paper or cooled glass, or with an automix extruder.

Brand Names of Permanent Cements

The most commonly used permanent cements are as follows:

  • Ketac Cem (glass ionomer), which comes in powder and liquid and/or applicaps
  • Panavia (resin cement), which is light-cured and used for bonding all porcelain restorations
  • Durelon (polycarboxylate), which comes in powder and liquid
  • Fleck’s (zinc phosphate cement), which comes in powder and liquid and is mixed on a glass slab since it has an exothermic reaction

Impression Materials

Impressions are taken in order to create reproductions of patients’ teeth and tissues. Assistants should follow the manufacturer’s instructions on whether to hand-mix these on a paper pad or to automix them in an extruder. When pouring an impression with dental plaster, the material is added slowly, with steady increments from one side of the impression. A positive reproduction of the impression is created in a model. Models may be used for several different purposes, including study models, prosthodontic models, and lab procedure models. There are two types of impression materials: preliminary (alginate), and final.

Preliminary Impression Materials (Alginate)

Preliminary impressions are used to create study models for “non-permanent” types of appliances. In some states, this is considered an expanded function for dental assistants. The most common material utilized for a preliminary impression is irreversible hydrocolloid, which is also known as alginate. It may be hand mixed or available for use in the Pentamix system. Preliminary impression materials have the following qualities:

  • They are used for opposing impression during crown and bridge procedure.
  • They are used for fabrication of diagnostic study models, bleach trays, occlusal guards, and some denture procedures.
  • They come in powder and liquid forms.
  • Some brands have automix cartridges.
  • They can be flavored for patient comfort.
  • They come in fast set or regular set.
  • They are inexpensive.

Final Impression Materials

Final impressions must provide an extremely accurate reproduction of the tissues and teeth. The final impression must be taken by the dentist, but the assistant is responsible for mixing and dispensing the material into the impression tray. Final impression materials have the following qualities:

  • They are utilized for master impression of the prepped tooth, and then sent to the lab for fabrication of a cast restoration.
  • They are durable and resist tearing.
  • Elastomeric impression materials are a type of final impression material.

Brands of Elastomeric Impression Materials

There are several brands/types of elastomeric impression materials: Polyether (Impregum), Polysulfide (Coe Flex), Polyvinyl Siloxane (Extrude and Express), and Bite Registration.

Polyether (Impregum): This is supplied in two tubes: base and catalyst. It is used in a Pentamix machine, which is a newer technology that “automixes” the impression material and dispenses the product much like a soft-serve ice cream machine. It eliminates the risk of improper mixing technique or exceeding the mixing time.

Polysulfide (Coe Flex): This is supplied in two tubes: base and catalyst.

Polyvinyl Siloxane (Extrude and Express): This uses a two-gun or a putty-wash technique.

Bite Registration: This technique is utilized for making a replica of the relationship of maxillary arch to the mandibular arch. It is sent to the lab with the final impression and opposing impression. Polyvinyl Siloxane bite registration material is used. It is supplied in a paste or cartridge system. This method is very accurate and is still used today.

Trays

Impression materials must be delivered into the oral cavity utilizing an impression tray. Medium- or heavybodied impression material is known as tray material. Depending on the impression material or the area to be duplicated, the assistant and operator have several choices of the tray type selected: traditional metal trays, disposable trays, triple trays, or custom acrylic trays.

Traditional Metal Trays

Traditional metal trays come in perforated or solid, full arches or quadrant. They are autoclaved and reused. They are usually reserved for use with alginate.

Disposable Trays

Disposable trays come in perforated or solid, full arches or quadrant. These trays are single-use only. Usually, a tray adhesive is used.

Triple Trays

Triple trays are used only for final impressions and bite registrations. They are used as a time-saving technique by taking the final impression and bite registration at the same time.

Custom Acrylic Trays

Custom acrylic trays are made especially for the patient’s arch. These trays are commonly used in prosthetic procedures.

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