Prosthodontics2 Flashcards
Which luting agent (cement) has the lowest solubility? • zinc phosphate • zinc polycarboxylate • glass ionomer • resin-modified glass ionomer
resin-modified glass ionomer
tooth should be wiped dry before cementation of a crown as opposed to drying the tooth with ? to decrease the possibility of pulp damage
alcohol and warm air
Which of the following marginal designs is theoretically the best finishing margin for cast gold restorations, allowing burnishing and adaptation of the gold to the tooth? • shoulder • shoulder with a bevel • chamfer • bevel or feathered edge
bevel or feathered edge (It also offers the least marginal strength to the casting and hard to read so the chamfer preparation is the preferred finishing line for cast gold restorations)
? preparation is the finishing line of choice for porcelain jacket and all-ceramic crown preparations.
The shoulder
What is the general rule for sprue pin diameter when using a centrifugal type of casting machine?
• the diameter of the sprue pin should be equal to or greater than the thickest portion of the pattern
• the diameter of the sprue pin should be equal to or smaller than the thickest portion of the pattern
• the diameter of the sprue pin should be equal to or greater than the thinnest portion of the pattern
• the diameter of the sprue pin should be equal to or smaller than the thinnest portion of the pattern
the diameter of the sprue pin should be equal to or greater than the thickest portion of the pattern
A non-rigid connector is comprised of:
• a key
• a keyway
• a key and a keyway
a key and a keyway (Its use is restricted to a short span bridge, replacing one tooth. It is indicated when retainers cannot be prepared to draw together without excessive tooth reduction. Prostheses with nonrigid connectors should not be used if prospective abutment teeth exhibit significant mobility)
All-ceramic restorations are popular because of their superior esthetics and generally favorable gingival tissue response. The finish line of choice when fabricating an all-ceramic crown is a:
• 90 degree, 1.0 mm shoulder
• bevel
• chamfer
• 45 degree, .25 mm shoulder with a bevel
90 degree, 1.0 mm shoulder — to prevent unfavorable stress distribution and minimize the risk of fracture
Which of the following are indications for electrosurgery. Select all that apply.
• to remove hyperplastic gingival tissue where it has proliferated into preparations or over crown margins
• in place of a gingival retraction cord where substantial attached gingiva is present
• where attached gingival tissues are thin, or where an underlying dehiscence is suspected
• for crown-lengthening procedures prior to fabricating a provisional crown
- to remove hyperplastic gingival tissue where it has proliferated into preparations or over crown margins
- in place of a gingival retraction cord where substantial attached gingiva is present
- for crown-lengthening procedures prior to fabricating a provisional crown
Half-closed eyes can increase the sensitivity of retinal rods to better choose the “value” of the color.
“Blue” fatigue accentuates “yellow” sensitivity. This means that if you look at blue color objects (drapes, charts, wall-color or any other object around) while selecting the shade, it will help to accentuate the ability to discriminate yellow shades.
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
both statements are true
If a mold that is created for investing and casting does not ? to compensate for the action of the metal alloy, the casting will not fit. • equate • contract • expand • none of the above
expand
A seven-eighths crown is a three-quarter crown whose vertical:
• mesiobuccal margin is positioned slightly distal to the middle of the buccal surface
• distobuccal margin is positioned slightly mesial to the middle of the buccal surface
• mesiolingual margin is positioned slightly distal to the middle of the lingual surface
• distolingual margin is positioned slightly mesial to the middle of the lingual surface
distobuccal margin is positioned slightly mesial to the middle of the buccal surface
Which type of dental ceramic is the best in mimicking the optical properties of enamel and dentin?
• predominantly glass
• particle-filled glass
• polycrystalline
predominantly glass (have a high content of glass)
All of the following metals are considered to be base metals EXCEPT one. Which one is the EXCEPTIONl • nickel • cobalt • chromium • silver
silver (is a precious metal but not considered noble; it is reactive and improves castability but can cause porcelain “greening.”)
Noble metals are precious, but not all precious metals are noble (i.e., silver).
All of the following are resins used for fabricating provisional restorations EXCEPT one. Which one is the EXCEPTION?
• polymethyl methacrylate
• polyethyl methacrylate
• polyvinyl methacrylate
• polyacryl methacrylate
• bis-acryl composite resin
• visible light-cured (VLC) urethane dimethacrylate
polyacryl methacrylate
There are four types of gypsum products approved for use in dentistry. Which of the following types is used rarely today? • type I • type II • type III • type IV
type I
In mixing dental stone, why should the powder be sprinkled onto the water in the bowl?
• the addition of powder prevents the mix from becoming exothermic
• this is not recommended; the water should be added to the powder
• this process results in better powder mixing and reduced chance for air bubbles
• the powder is added to the water to avoid using more than one bowl
this process results in better powder mixing and reduced chance for air bubbles
When a high proportion of water is used, the powder particles are farther apart. This results in ?
less expansion with a retarded setting time and a weaker product.
rapid spatulation for a time equal to normal hand mixing for 1 minute results?
accelerates setting time and produces the greatest strength
Dental stone and dental plaster both have a slightly different type of principal component (calcium sulfate hemihydrate). Dental plaster has:
• beta-hemihydrate and dental stone has gamma-hemihydrate
• alpha-hemihydrate and dental stone has beta-hemihydrate
• gamma-hemihydrate and dental stone has beta-hemihydrate
• beta-hemihydrate and dental stone has alpha-hemihydrate
beta-hemihydrate and dental stone has alpha-hemihydrate (When the alpha-hemihydrate is mixed with water, the product obtained (dental stone or die stone) is much stronger and harder than that resulting from beta-hemihydrate (plaster). The chief reason for this difference is that the alpha-hemihydrate powder (stone) requires much less gauging water when it is mixed than does the beta-hemihydrate)
Dental plaster and stone are vibrated after mixing to: • minimize distortion • reduce setting time • eliminate air bubbles • increase the setting time
eliminate air bubbles
All types of gypsum products are ? in tensile strength than compressive strength.
weaker
- heating gypsum in an open vessel at 150-160°C
- heating gypsum under steam pressure in an autoclave at 120 -150°C
- by boiling gypsum in a 30% aqueous solution of calcium chloride and magnesium chloride
- Dental plaster is produced, the weakest gypsum product which is porous and irregularly
- produces dental stone. This process produces particles that are uniformly shaped and less porous
- produces high strength (improved) die stone. This process produces the least porous and strongest particles
Dr. Lozier requested that you mix alginate and take an impression. While measuring the water, you got involved in a conversation with your patient and did not notice how cold it was. This oversight will: • shorten the gelation time • make the mix unusable • lengthen the gelation time • not affect the gelation time
lengthen the gelation time
Which impression material is very stiff, which makes it very difficult to remove without rocking? • irreversible hydrocolloids • polysulfides • polyethers • condensation silicones
polyethers (excellent dimensional stability. They are also truly hydrophilic, resulting in superior wettability.)
With which of the following impression materials is it advisable to wait 20 to 30 minutes before pouring of models for stress relaxation to occur? • polysulfides • condensation silicones • polyvinyl siloxanes • polyethers
condensation silicones (also called conventional silicones)
All of the following are characteristics of ZOE impression paste EXCEPT one. Which one is the EXCEPTION?
• dimensionally unstable
• sets quickly
• excellent detailed reproduction
• sets hard
• no shrinkage even if store for many days
dimensionally unstable
The popularity of agar impression material (reversible hydrocolloid) is limited by the: • difficulty in pouring the impression • poor reproduction of detail • need for special equipment • high cost
need for special equipment
- The setting time of a zinc oxide-eugenol impression paste may be accelerated by ?
- The setting time of a zinc oxide-eugenol impression paste may be retarded by adding ?
- adding a drop of water to the mix.
* inert oils (olive or mineral oils) during mixing.
The filler in alginate gives the mixed material "body" that allows acceptable handling. Without filler, the mixed material would be too runny for use. Which of the following is a main component of the alginate powder and functions as the filler? • zinc oxide • calcium sulfate • potassium titanium fluoride • diatomaceous earth (silica) • potassium alginate • tri-sodium phosphate
diatomaceous earth (silica)
You are taking an impression with alginate and unbeknownst to you there is debris on the tissue. How will this affect the final impression? • it will be grainy • it will tear easily • there will be irregularly shaped voids • it will be distorted
there will be irregularly shaped voids
When using which impression material can you delay pouring up of the model for up to one week? • polyether • polysulfide • reversible hydrocolloid • vinyl polysiloxane
vinyl polysiloxane (also known as addition silicones) (the most accurate, a moderately high tear strength, The sulfur in latex gloves will retard the setting)
Which impression material has the best wettability?
• polyether
• polysulfide
• hydrocolloids (reversible and irreversible)
• polyvinyl siloxane
hydrocolloids (reversible and irreversible)
Which of the following impression material has the longest working time? • polyether • polysulfide • reversible hydocolloid • polyvinyl siloxane
reversible hydocolloid (Reversible and irreversible hydrocolloids have the advantage of wetting oral surfaces well, but they have very limited dimensional stability because they include as much as 85% water in their composition)
Some impression materials are most accurate when at least 3 mm of space is present between the impression tray and the oral tissue. Which impression material below shows this characteristic? • polyethers • polysulfides • silicones • irreversible hydrocolloids
irreversible hydrocolloids (alginate)
Fast removal of impression from the mouth will cause?
increases both the compressive and tear strength of the impression.
Today was a very busy day for Ashley, the dental hygienist in our office. Ashley took alginate impressions on her first patient in the morning, who needed a nightguard. Since she was so busy, Ashley left the alginate impressions in the lab most of the morning. You place the alginate impressions in a bowl of water so that they would not dry up before you have a chance to pour them up in dental stone. Which of the following is the result of leaving these impressions immersed in water for a few hours? • gelation • hysteresis • syneresis • imbibition
imbibition (expands the dimensions of the impression so shrinkage occurs)
syneresis (loss of water to the air or surrounding environment)
If your patient indicates a tendency to gag while taking alginate impressions, which of the following maneuvers can help make the procedure easier for the patient. Select all that apply.
• lessening the time to take an impression
• using cold water to mix the alginate
• having the patient breathe through his/her nose
• seating the patient in an upright position
• seating the anterior portion of the tray first
• mixing the alginate rapidly
- lessening the time to take an impression
- having the patient breathe through his/her nose
- seating the patient in an upright position
- mixing the alginate rapidly
? is the term given to the setting process (changingfrom a sol to a gel) of hydrocolloid material.
Gelation
Elastomers are rubbery polymers that are capable of elastic deformation from undercut areas to produce a complete impression for dentate situations.
Impression materials must have some strength, but generally their design is focused more on accuracy, dimensional stability, and flexibility (or tear resistance).
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
both statements are true
Custom trays are an important part of rubber base impression techniques, since elastomers are:
• more accurate in uniform, thin layers 0.5 to 1.0 mm thick
• more accurate in uniform, thin layers 1.0 to 1.5 mm thick
• more accurate in uniform, thin layers 2.0 to 4.0 mm thick
• more accurate in uniform, thin layers 5.0 to 6.0 mm thick
more accurate in uniform, thin layers 2.0 to 4.0 mm thick (Let adhesive that is applied to the tray dry completely. If it is wet, impression material may pull away)
