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Dental Materials
Impressions
| Question | Answer |
|---|---|
| Is the completed replica or model a positive or negative reproduction of the teeth and tissues? | positive |
| Is the completed impression a positive or negative reproduction of the teeth and tissues? | negative |
| What are advantages of plastic impression trays? | inexpensive and disposable |
| What is an advantage of metal impression trays? | they can be sterilized and re-used |
| How are custom impression trays made? | they are constructed in the laboratory with chemically cured, light-cured, or thermoplastic resins on casts of the teeth |
| What are stock trays made of ? | metal or plastic |
| What is a triple tray? | It is a stock sectional tray that is used to make an impression of the teeth being treated and the opposing teeth at the same time |
| What type of impression material is agar? | reversible hydrocolloid |
| After agar is mixed, what is the colloidal suspension called? | sol |
| What type of tray is used with agar? | stock metal trays with tubing running through them that connects to a water line by rubber hoses |
| What is an example of an irreversible hydrocolloid? | alginate |
| What is a reversible hydrocolloid? | an impression that when heated can go back to its original state |
| What is an elastomer? | highly accurate elastic impression material that have qualities similar to rubber |
| What are some examples of elastomers? | polysulfides, condensation silicones, addition silicones, polyvinyl siloxane, and polyether |
| Which types of impressions are used when a crown is done on a tooth? | both preliminary and final impressions as well as a bite registration |
| What is alginate used for? | preliminary impressions |
| What is the best way to shorten the setting time of alginate? | use warmer water |
| When removing an alginate impression from the mouth, what can be done to prevent deformation? | remove it quickly with a rapid "snap" |
| What criteria need to be considered for choosing the correct impression tray? | deep enough to provide 2 mm of space for alginate beyond the incisal edge and occlusal surface and it should extend into the facial and lingual vestibules without impinging the tissues |
| What should containers of alginate be "fluffed" before using? | to decompress the powder and mix the ingredients |
| Why should a mask always be worn when mixing alginate? | it is potentially hazardous to inhale because it contains silicon dioxide in the diatomaceous earth fillers. |
| Why should alginate be loaded into the trays in large increments as quickly as possible? | reduces the chance for entrapped air |
| When taking a maxillary alginate impression, where should the operator stand? | behind the patient in the 11:00 position |
| What steps are needed to take an alginate impression? | select tray size, fluff material, add water to bowl, add powder to bowl |
| What type of elastomer is the most hydrophilic, or wettable? | polyether |
| What is it called when the material contracts, squeezing some of the liquid out of the gel? | syneresis |
| What is the act of absorbing moisture? | imbibition |
| Which elastomeric impression material has the smallest rate of dimensional change? | Addition silicone |
| What are the characteristics of polyvinyl siloxane? | hydrophobic, contains a wetting agent, cannot displace moisture on the tooth, must be used in a dry field because moisture causes loss of detail |
| What type of die could be made with a specially formulated addition silicone material in an automatic mixing cartridge system? | a die for an indirect composite inlay |
| When using elastomers, what should be blocked out with wax to prevent the impression from locking under them and preventing removal of the impression tray? | Open embrasures, undercuts around bridge pontics, and implants |
| What are the characteristics of vinyl polyether silicone? | hydrophilic so it can tolerate some moisture, it is available in regular and fast sets and has five viscosities, flows well and has high tear strength. |
| What helps reduce or stop bleeding to the gingiva caused during preparation of the tooth? | local anesthetic with epinephrine, packing the sulcus prior to finalizing the margins, use a laser, use an astringent agent |
| What types of disinfectants are compatible with addition silicone impression materials? | sodium hypochlorite, iodophors, glutaraldehydes, and complex phenolics |
| What is the suggested maximum timeframe for pouring polyvinyl siloxane impressions? | 1 week |
| How long are impressions taken with polyether impression materials dimensionally stable? | 2 weeks |
| What are you evaluating when you look at your completed impression after a crown prep? | All of the teeth and tissue needed for the restoration are visible, the margin visible all the way around, and you can see the preparation clearly |
| What happens to the working time when the water temperature decreases when mixing alginate? | it increases |
| What are considered to be critical errors of a final impression? | large voids, a portion of the margin is missing or torn, margins look shiny and rounded rather than clearly demarcated, a fold, crease or pull is present in the margin of the preparation |
| What are the characteristics to consider when choosing an impression tray? | large enough to fit all oral structures, strong enough to support the impression material, and accurately reproduce vestibules |
| What are advantages of digital impressions? | They can create pre- and post-operative models and they can be more accurate than conventional impressions |
| What are the differences between addition silicone and condensation silicone? | Addition silicone impression materials are an improvement over condensation silicone materials because of greater dimensional stability and accuracy. |
| When should impressions be disinfected? | chairside as soon as the impression is removed from the mouth |
| Name the different types of impression trays. | custom tray, stock tray, triple tray, quad tray, bite registration tray |
| How can the length or the depth of the impression tray be changed? | utility wax |
| How should the patient be positioned when taking an alginate impression? | sitting up |
| What type of material is used for a preliminary impression? | alginate |
| What is the purpose of a bite registration? | To record the relation between the maxilla and the mandible |
| What are the characteristics of an acceptable impression material? | Biocompatible, chemically compatible, accurate, dimensionally stable |
| What are some types of aqueous elastomeric material? | alginate, agar, irreversible hydrocolloid |
| What are some types of non-aqueous elastomeric material? | Polysulfide, Polyether, Addition silicone, Condensation silicone |
Created by:
BrendaAlberts