Fixed Q2 Flashcards
Once the impression is in stone what is it placed on
articultor
what material should the impression be poured up in
gypsum
Gypsum. when the semi hydrate is mixed with water, a suspension is formed that is ____ and ____
fluid and workable
the hemihydrate dissolves until what point
forms saturated solution
what does the hemihydrate solution precipitate out
dihydrate
Polymers…
Stone….
Wax…
shrink
expand
temp dependent
PIMWIC, what 2 stages shrink, what 2 expand?
Impression and Cast shrink
Mount and Investment Expand
Gypsum rxn: powder + water = stone + heat
or…
hemihydrate + water = dihydrate + unreacted hemihydrate + heat
In the gypsum rxn, there is dissolution of…
precipitation of….
as long as…
hemihydrate
dihydrate
new crystals form/current crystals grow
what is the use for slurry water
to make the stone set quicker
how is gypsum classified
1-5 for compressive strength
classify the following: mounting plaster, dental stone, model plaster, dental stone-high strength low expansion, dental stone-high strength high expansion
1,3,2,4,5
what is the difference between types 4 and 5
4 low expansion
5 high expansion
What does the slurry water add that makes the gypsum precipitate more quickly?
More sites of nucleation
Gypsum classificaiton, Type I
Type II
Type III
Type IV
Type V
mounting plaster
model plaster
dental stone
dental stone - high strength, low expansion
dental stone - high strength, high expansion
Describe the particles of Plaster (gypsum) Type I/II:
This is a _____ hemihydrate:
large, irregular particles
Beta
Describe the particles of Stone type III-V:
This is a ____ hemihydrate:
small, greater strength
alpha
3 effects of adding water to the gypsum powder:
Increases Setting time
Weaker
Less expansion
why is type 3 used for making dentures
the final step of denture making involves breaking the stone. type 3 is easier to break
what class of gypsum is used for making impressions on a pt and why
*diagnostic
III
cheaper
what class is used for crowns and bridges
4 or 5
what type of gypsum should be used for high shrinking base metals
type 5 because it can compensate because it has higher expansion
what type of gypsum does Ahwatukee lab use.
Excalibur - type IV
Why should a cast be soaked in water before trimming?
Easier to trim, clean up, rid of particles
what are the advantages/disadvantages of the removable die system
advantages: it can get to all areas when doing a wax up. easier to fabricate.
Disadvantages: we have moving parts and movement can make contacts stronger or weaker
why does the lab send back a solid metal
Verify seating/interproximal contacts
allows for better testing of inter proximal contacts
3 ways we mount the 2 arches against each other
maxillo-mandibular jaw relation record
jaw relation record (JRR)
Bite registration
In mounting the arches against each other, it is possible to hand articulate when?
What verifies the mounting?
If max intercuspation is stable
bite registration
if MIP is not stable what is required to mount the cast accurately
bite registration
2 types of Bite Registration matl:
Take 1
Regisil
Take 1 (bite reg. matl) Working Time:
Setting time:
Rigidity:
color:
15 secs
1 min.
extremely rigid
green
Regisil (bite reg. matl) Working Time:
Setting time:
Rigidity:
color:
45 secs
1 min. 30 secs
less rigid than Take1
purple
Working time PVS:
Setting time PVS:
1 min 10 secs
5 min
Wax up: why do we mark the margin
to make sure we place it properly
What is the purpose of a die spacer?
To make room for cemet
Recommended space of die spacer:
comes in various thickness - but factors that influence amount of relief are the type of cement and _____
25-40 micrometers
TOC
type 1 wax is ____ hardness and used for _____ technique for making patterns
medium
direct
type 2 wax is ______ wax and used for _____ fabrication of castings
softer
indirect
Wax expands when heated, contracts when cooled and needs to be burned out cleanly leaving less than ___ % residue.
0.1%
T/F
The wax up should look like a tooth
True
What is the function of the sprue?
Allows molten wax to escape from mold
The design of the sprue must enable the molten metal to do what?
Flow in with little turbulence
where should the sprue be attached and what is a common placement
the bulkiest noncritical part and the non functional cusp is usually used
How far is the wax pattern usually placed from the top of the investment?
6 mm
What is the sprue attached to?
crucible and casting ring
The metal within the sprue remains molten slightly longer than the alloy that has filled the mold, providing a ____ to compensate for the shrinkage that occurs during solidification
reservoir
What factors influence the expansion of the investment?
Liner
Ring/Ringless
Setting, hygroscopic, thermal expansion
Adding liners allows for more expansion of the ______
investment
Ringless design allows for what?
unrestricted expansion
Hygroscopic expands the most, and is accomplished by doing what?
submerging ring in 100 degree F water bath for 1 hr immediately after investing
T/F
In order of increasing Investment expansion: Normal, 1 liner, 2 liner, Hygroscopic
True
3 requirements of Investment matl:
Precisely reproduce wax up
Strong enough for heat and casting
Expand to compensate for alloy shrinkage
What 3 binding matls regulate Rigidity of the Investment?
Gypsum
Phosphate
Ethyl Silicate
What regulates thermal expansion of the Investment matl?
refractory
Silica
What Investment matl is generally used only for Gold b/c it can’t be heated above 650 C?
*not used much any more
Gypsum
What Investment matl can be heated above 650 C but has rough casts and is difficult to remove?
Phosphate
What Investment matl is used for high fusing base metal partial denture alloys
Ethyl silicate
What type of investment material do we use at ASDOH
GC fujivest II which is a phosphate bonded investment that can withstand high temps.
GC fujifest II (Investment matl) working time:
Setting time:
6 mim
20 min
How are metal alloys classified?
Noble metal content
Why do we use noble metals?
Stable, don’t corrode
High noble alloy:
40% Au
60% nobles
*by weight
Noble alloy:
25% noble
*by weight
Predominately Base Metal:
less than 25% noble
7 Noble metals:
Au, Pt, Pd, Rh, Ru, Ir, Os
Elastic Modulus =
Stress/Strain
rise/run
The stress at which a matl shows a specific amount of plastic strain:
Yield strength
Classify metal ceramic crowns: Argebond 80
Argedent Euro
Noble
High noble
Classify Full Gold Crown: Argenco 56
Argenco Y+
High noble
Noble
What kind of bur would you use to cut through porcelain, metal?
Porcelain - diamond
Metal - carbide
High noble, Melting temp:
Shrinkage:
Castability:
Hardness
Corrosion:
lower
less
better
softer
less
PVS shrinks and is hydrophobic
True
When doing investments what does gypsum, phosphate, and ethyl silicate determine?
Temperature
When doing investment what does quartz cause?
Expansion
What are the 3 properties of Excalibur Type IV mounting material that we use at ASDOH?
quick setting
low strength
low expansion
PVS differentiated by viscosity
stone (I-IV) by strength
Investment by matl (gypsum, phosphate, ethyl silicate, quarz/cristobiolite)
Cast by Nobility
True
Lowest point of the Orbitale to highest point of the external auditory meatus
Frankfort Horizontal Plane
How should the Frankfort horizontal plane be aligned with the floor?
Parallel
What acts as the 3rd point of reference (1. upper margin ext. aud meatus. 2. lower orbitale)
Nasion
The average distance between the Nasion and the Frankfort horizontal plane?
23 mm
What is the purpose of the Facebow?
Position Max cast onto articulator relating to pts hinge axis in 3 dimensions
The path of the condyle follows what?
Articular Eminence
As the condylar inclination increases what also increases?
Space between posterior teeth in disclusion
What allows the mandibular movements of the articulator to simulate the movement of the mouth?
Facebow record
3 things captured in triple tray:
opposing arch
jaw relation
prep (and adjacent teeth)
In group function what teeth contact in laterotrusive movement?
posterior
Why are we less concerned if pt has canine guidance?
posterior teeth don’t contact each other in laterotrusive movement
What is the anatomical average Condylar Guidance Angle?
25-30 degrees
What info is lost using a triple tray?
guidance in non-working movement
relationship between teeth and hinge axis
canine guidance
What are the advantages to using a triple tray?
Minimize use of impression matl
no need for separate impression of opposing arch
jaw relationship w/ PDL in compression
T/F
A fully adjustable articulator can move condyles, ours can’t
True
In what type of articulator dose the condylar inclination stay the same?
Arcon
*we have arcon
An Arcon articulator has the condyle on the ______, while a non-Arcon has the condyle on the ______
Mandible
Maxilla
In an Arcon articulator, when you open the pin in a vertical dimension, what happens to Vertical Dimension?
Condylar inclination?
Increases
Stays the same
Changing the vertical dimension in an Arcon articulator will not change the angle
True
What are 5 contraindications to using a triple tray?
Multiple fixed units
Fixed partial denture
survey crown
Class 2 and 3 occlusion
Implants
Which articulator do we currently use?
Arcon
What establishes the chemical bond between the Metal and Porcelain?
Controlled Oxide layer
How do we create an Oxide layer so porcelain can bond to metal?
Put in oven
What type of metal has a controlled oxide layer?
What is uncontrolled?
What is a side effect of uncontrolled oxide layer?
Nobles
Bases
Bad adhesion
5 Steps to adding Porcelain onto metal:
*in decreasing temperature
Oxidize
Opaque (blocks out metal color)
Margin
Dentin
Glaze
Why do all the steps of adding porcelain decrease in temperature?
Sintering
What has a higher CTE (coefficient of thermal expansion) - porcelain or metal?
Metal
What are the 2 phases of Feldspar?
Glassy
Crystalline
If something is 100% gold, could you stack porcelain?
Would be difficult b/c doesn’t readily form oxide layer
What 2 factors influence the amount of die spacer we use?
Type of cement
TOC
How does TOC affect the space in a die spacer?
Less TOC, more die spacer
*If a lot of TOC (lots of taper), cement will flow and less die spacer needed
What 4 elements are often added to Noble metals to ensure an Oxide Layer forms?
Iron
Tin
Indium
Gallium
Base metals are principally ______ and _______
_______ oxidation provides chemical bonding for porcelain adherence
Nickel, Cobalt
Chromium oxidation
T/F
Base metals used for metal-ceramic restorations go through continuous oxidation
True
What can the continuous oxide formation by base metals cause?
Potential failure via a Thick Oxide Layer that can’t be controlled
The oxide layer close to the surface is mostly made up of what element?
Silica (Si)
What is the main raw component of dental porcelains?
Feldspar
What does Feldspar look like in its mineral state?
Crystalline and opaque
2 Types of Feldspar:
Potassium aluminosiclicate “potash feldspar”
Sodium aluminosilicate “soda feldspar”
Most veneering ceramics are derived from what type of feldspar?
Potash
Potassium aluminosilicate
Feldspathic Porcelain exists in what 2 phases?
Glassy (silica)
Crystalline (leucite)
What phase of Feldspathic porcelain provides strength?
Crystalline
Describe both phases of Feldspar:
Glassy: high translucency
Crystalline: strength
How much of Feldspar is made up of the Crystalline phase?
15-25%
T/F
Porcelain is stronger when in compression
True
The process of forming a solid mass by heat/pressure without melting to lequefaction
Sintering
4 Steps to the Firing Chart:
High to low temp
Opaque
Margin
Dentin/Mod/Enamels
Glaze
Why would a thick oxide layer cause fracture?
Not as strong, if too thick of a hybrid layer can cause structural problems
What is a problem of sintering porcelain?
What is a solution?
Fused mass too viscous to allow air to escape = Trapped air/voids
Vacuum firing
What is the purpose of the Opaque Layer?
Block the metal from view
What has a higher thermal expansion - porcelain or metal?
Metal
Because the metal contracts more during cooling than porcelain, this creates what?
Porcelain in slight residual compression
T/F
Porcelain does well under tensile stress and not well under compression
False
*Porcelain does well under compression - flat marginal ridge
What makes porcelain less sensitive to the tensile stresses induced by mechanical loading?
Residual compression due to metal shrinking more on cooling
Bond failures between 2 materials:
Bond failures within a dental material:
Adhesive failure
Cohesive failure
Fractures at the metal to metal/oxide layer is a _______ failure and commonly observed with poor ________
adhesive
bonding
Why would a fracture occur through the oxide layer?
If oxide layer too thick
*cohesive failure in METAL
If everything is properly bonded, where would a fracture occur in a metal/porcelain crown?
Porcelain
*cohesive
Dipping a die into molten wax produces an Even Thickness - doing what to the porcelain layer?
Consequence:
Makes uneven
porcelain fractures due to lack of support
For predictable success in creating an even porcelain layer onto the metal, use a _____ technique
Cut-back
from full contour wax up
2 Aqueous Hydrocolloids:
3 Non-aqueous Elastomers
(these are the Elastic categories)
Agar, Alginate
Polysulfide, Polyether, PolyVinyl Siloxane (Condensation/addition)
What non-aqueous elastomer is Hydrophilic and rigid, with a defined working time (“snap set”)?
Polyether
Bottom cord should be what size?
Top cord?
small - 000 or 00
larger - 0
Cords are typically soaked in what?
Hemostatic agent
2 techniques for Gingival Retraction other than cord:
Expasyl - paste
Laser
Advantages to a Supragingival margin:
Disadvantages:
No cord, verify margins
Not esthetic, tooth structure exposed
Advantages to an Equigingival margin:
Disadvantages:
minimal retraction
recession will expose margin
Advantages to a Subgingival margin:
Disadvantages:
Esthetics
Retraction difficult
7 Requirements for Provisional Restorations:
Pulpal protection
Positional stability
Occlusal function
Ease of cleaning
Nonimpinging margins (overhangs, etc)
Strength/Retention
Esthetic
If you haven’t reduced the occlusal surface enough, the lab sends you…
Reduction Coping
A lab prescription should have what 3 surfaces specified for a restoration?
*and another thing:
Facial
Occlusal
Lingual
*shade of porcelain
Facial and Occlusal surfaces can be in what materials?
Lingual?
Porcelain or metal
metal
When will the lab send you a 360 metal collar?
When facial/lingual surfaces both in metal
T/F
360 metal collar has the best marginal integrity
True
4 cases in which the used of metal over porcelain on the occlusal surface:
Bruxism
Large mm.
Hx porcelain fracture
Most posterior tooth
Why would the most posterior tooth not get a porcelain occlusal restoration?
Teeth shorter - not enough pulpal room for big reduction
The vasoconstrictor for cord is usually:
Viscostat:
Viscostat clear:
Aluminum chloride
Ferric sulfate
Aluminum chloride
Pack 2 cords and take the top out after __ minutes. You need a clean, dry, field.
5
If making an FMC do the final impression using _______, then look for bubbles/clean margin
Custom tray
Why can’t you do a bite registration off of a stone cast?
Has expanded
What shrinks more - noble or base metals?
What must you use to offset the higher shrinkage?
Base
Type V dental stone
Casts (yellow) are in Type ____
Plaster (white) that connects to the Articulator is Type _____
3
1
In posterior teeth, porcelain tends to fracture where?
Marginal Ridges
Ringless means a _____ ring and allows for expansion of ______
Plastic
Investment
Invest, Cast - then break, cut off Sprue. If metal - you’re good. If stacked to porcelain, then _______
Coping
What do you have to do to the prep before you wax?
Lube
