Test review Flashcards
T/F Polysulfide is accurate but not stable compared to other elastomers because of its biproduct
True
Which elastomers can be poured multiple times with reasonable accuracy?
PVS
Polyether
What is the stiffest of the elastomers
Polyether
What has the best tear strength of the elastomer
Polysulfide
What is the second best tear strength of the elastomer
PVS
Why don’t we use alginate for all of our impressions?
-Alginate doesn’t reproduce fine detail well even though it is an accurate impression
T/F Polysulfide doesn’t smell very good
True
Which elastomer doesn’t taste very good?
-Polyether
What are the two variables that relate to create distortion in impression material?
- Time
- Compression
What principles deal with elastic recovery?
- Time
- Compression
How long does it take alginate to rebound (elastic recovery)?
8 - 10 minutes
How much is an alginate compressed during removal?
10%
How do we decrease the amount of time alginate is compressed during removal?
-Snap it out (get air into vestibule)
which temporary material has a higher exotherm?
-Polymethylmetacrylate
Which temporary material shrinks more?
-Polymethylmethacrylate
What properties make polymethylmethacrylate desirable?
- Great fracture toughness
- Not brittle
- Easily added to (modify its shape easily)
What can unifast do that others can’t?
Light curable so you can control the set.
T/F Polyethylmethacrylate (SNAP) is soft
True
Would you want to use polyethylmethacrylate for anything other than a single unit?
No
What is one method to take a gypsum stone die reinforced and stronger to be more resistant to abrasion?
-Low viscosity cyanoacrylate (basically super glue)
T/F Calciumsulfatedihydrate is mined out of the ground
-True
What type of stone is densate used to make?
-Type IV and Type V
What type of stone is hydrocal used to make?
-Type III
What is the most refined form of gypsum?
-Calciumsulfatehydrite
What is the most refined form of gypsum?
-Calciumsulfatehydrite
What are the two most common ways to manufacture ceramic crowns?
- Milled
- Heat pressed ceramic (EMAX/llithium disilicate)
Zirconia is so hard it is milled in its green state?
Yes
Zirconia is in a pre-sintered (green state/larger form) and then is heated, what happens when it is heated (sintered)?
-It shrinks
If the light body is in the setting phase and then you insert the heavy body what happens to your bite record?
-It is inaccurate (open)
If the heavy body material is starting to set but the light body is still fine what happens when you insert the heavy body?
-The die will shrink or be smaller
What are the two biggest draw backs of hydrocolloids?
- Imbibition
- syneresis (sweating)
Dental stone casts reach their maximum strength after how many hours?
24 hours
What does the modulus of elastisitity define?
-The stiffness of a material
What material has the highest elastic modulus?
-Polyether
Clinically the resistance and retention form are satisfied, where is the most ideal place to put your margins with respect to the gingiva (esthetics is not a factor because it is the back of the mouth?
-1 mm above the gingiva (.5 mm pre clinically)
Clinically the resistance and retention form are satisfied, where is the most ideal place to put your margins with respect to the gingiva (esthetics is not a factor because it is the back of the mouth?
-1 mm above the gingiva (.5 mm pre clinically)
What is alginate made from?
-Potassium alginic salts from seaweed
If you under-reduce occlusaly what are consequences?
- Material to thin
- Over contouring by the lab
If you don’t have enough axial reduction what are the consequences?
- Margins to thin
- Over contoured axial crown
- Create plaque trap with final crown
If you increase taper do you increase or decrease resistance and retention?
-Decrease in both
If you increase the surface area do you increase or decrease resistance and retention?
- Increase retention
- Doesn’t always increase resistance
What will the final marginal gap be if everything is perfect (done with the lost wax technique)?
-10 microns
What three things always should be taken into consideration when doing a preparation?
- Biological
- Esthetics
- Mechanical
Why don’t we want you to use a posterior plastic bite tray in the clinic?
-They can bend
Which impression materials can have their setting interfered with latex gloves?
-Addition PVS (sulfur in the latex)
Which impression materials can have their setting interfered with latex gloves?
-Addition PVS (sulfur in the latex)
Why is important to capture the area apical to the margin?
- Makes it easier to trim and find the margin
- Helps make contours
When impressions are set and done what do you want to avoid?
- Extremes of temperature
- Extremes that cause distortion
What are the main things you are trying to capture in your crown impression?
- Die
- Prepared tooth
- Opposing anatomy
- Occlusion
- Good adjacent tooth surfaces
What are some of the ways the impression material is kept adherent to trays?
- Perforation
- Rim lock
- Adhesive sprays
T/F Double sided mouth mirrors are a good retractor and a good visualizer
True
Name some hemostatic chemicals?
- Ferric sulfate
- Epinephrine
- Aluminum chloride
Why do we use retractions cord?
- Displace soft tissue temporarily
- Carrier of hemostatic agent
T/F Retraction cord can be braided or woven
True
What is the situation where you have to be careful using epinephrine as a hemostatic agent?
- Heart problems
- Lacerated tissues can cause tachycardia
How many ADA recognized gypsum types are there?
-5 types
What is calcination?
-Process of driving water off of gypsum products during refinement process
What type of stones are the hardest stones?
- Type IV
- Type V
Which stone is really hard and expands a lot?
-Type V
What is the advantage of vacuum mixing stone?
- Remove air bubbles
- Harder set stone
- More dense set stone
- More abrasive resistant stone
Which type dental stone exhibits the least amount of expansion?
-Type I MOUNTING Stone
What is the Centrum?
-Cuspal tip against a flat surface at MI
What is tripodisation?
-The mountain engages the valley near the tip but not directly at the tip. Need to have equal contact between the three points or else teeth will move
What is the order that you place your models in the 3 M scanner
1) preparation arch
2) opposing arch
3) together
4) Die
Where is the buccal placed in the scanner?
-The back
