E2: Lect 8 Investing Flashcards
What is the Method to convert wax patterns to cast metal?
Lost Wax Technique
What are the 3 requirements of an investment?
RHE 1.Reproduce detail 2.withstand Heat 3.Expansion
GOLD alloys SHRINK by approx ___% when casting!
1.5%
Nickel-chromium alloys SHRINK by as much as ___% when casting!
2.4%
Because the alloy shrinks when casting, the MOLD must be made correspondingly _______ than the original wax pattern.
LARGER
As the gypsum investment sets after mixing, it expands and slightly enlarges the mold:
Setting Expansion
In Setting Expansion, less water _________ expansion and will yield a _______ casting
increases expansion, larger casting
The investment is allowed to set in the presence of water, producing additional expansion. (1000 F or 38oC):
HygroScopic Expansion
In a lined, rigid, metal ring, the expansion attributed to hygroscopic expansion is more likely due to expansion of the _________ caused by the elevated temperature of the water
wax pattern
Wax patterns _______ while the investment is still fluid and the wax is warmed above the temperature at which it was formed….What 2 reasons??
expand…1. chemical reaction of the investment 2.immersion into a warm water bath
As the mold is heated to eliminate the wax, ______ expansion occurs.
thermal
**WHAT IS PRINCIPALLY RESPONSIBLE FOR THERMAL EXPANSION OF THE INVESTMENT MOLD?
THE SILICA REFRACTORY MATERIAL
What are the 3 types of investment materials?
1.Gypsum bonded 2.Phosphate Bonded 3.Silica Bonded
Ideal Investment: Controllable _______ to compensate precisely for shrinkage of the cast alloy during cooling.
expansion
Ideal Investment: The ability to produce ______ castings with accurate surface reproduction and without nodules.
smooth
Ideal Investment: Chemical ________ at high casting temperatures.
stability
Ideal Investment: Adequate _______ to resist casting forces.
strength
Ideal Investment: Sufficient ______ to allow for gas escape.
porosity
Ideal Investment: Easy _______ of the casting.
recovery
Gypsum = ______ = 30-35%
BINDER
Cristobalite and Quartz = __________ = 60-65%
refractory material
GYPSUM bonding investment is for ______ alloys because it is NOT stable above ____ degrees.
gold…650 degrees
What type of restoration/alloy is Gypsum Investment NOT suitable for?
PFM alloys! (heat req too high!)
What type of investment do we use for PFM?
Phosphate Bonded Investment
What is the BINDER in Phosphate Bonded Investment?
Water soluble Phosphate Ion
What is the REFRACTORY material in Phosphate Bonded Investment?
Colloidal Silica in Water
Used for high gold or palladium content alloys, because this material is stable at burnout temperatures above 650o C (1200o F).
Phosphate Bonded investment
What is more smooth and precise? Phosphate Bonded Investment or Gypsum Investment?
Gypsum
DENTAL CASTING ALLOYS: High Nobel-Content??
Noble metal of at least 60% with 40% gold
DENTAL CASTING ALLOYS: Nobel-Content??
Noble metal of at least 25% with no gold content
specified
DENTAL CASTING ALLOYS: Base Metal- Content??
Noble metal less than 25% with no gold content specified
What are the 6 Nobel Metals?
RR-PP-GO..Ruthenium, Rhodium, Palladium,Platinum,Gold,Osmium
What are the 9 Base Metals?
NC-ZG-ST-BIT….Nickel, Copper, ZInc, Gallium, SILVER, Tin, Beryllium, Indium, TITANIUM
Casting Alloy: Type I =
Soft
Casting Alloy: Type II =
Medium
Casting Alloy: Type III =
Hard
Casting Alloy: Type IV =
Extra Hard
Casting Alloy - Type I used for:
simple inlays
Casting Alloy - Type II used for:
complex inlays
Casting Alloy - Type III used for:
Crowns and Fixed Pros
Casting Alloy - Type IV used for:
partial removable dental prostheses
Casting Alloy - Porcelain used for
Porcelain: metal-ceramic alloys ? not sure I understand this one
CastingAlloy Mechanical Properties…Modulus of ______ Resists deformation
Elasticity
CastingAlloy Mechanical Properties…____ strength (proportional limit)…High value indicates difficulty in adjusting
Yield
CastingAlloy Mechanical Properties… _______-Affects ability to finish the alloy
Hardness
CastingAlloy Mechanical Properties… ______-Dimensional changes during porcelain firing
Creep
How much space do you need OVER your wax pattern when set up in the investment ring??
6mm
How much space is recommended for distance between wax pattern and the sprue?
6.0mm
Connects the wax pattern to the crucible former
sprue
Sprue-______ diameter recommended
large
Sprue- Location (attached to the bulkiest noncritical area)
Non-Fxn cusp
The sprue must enable the molten metal to flow into the mold with as little _______ as possible.
TURBULENCE!
Serves as a base for the casting ring during investing….
Usually made of rubber…. Where the sprue Attaches
Crucible Former
Container for the investment….Normally a liner is placed inside the ring to allow for more expansion (sometimes two liners are used)
Casting Ring / Liner
investing step 1. Paint pattern with _______ reducer
surface tension
investing step 2. Add investment _____ to the ______ in the mixing bowl and quickly incorporate by hand
POWDER to LIQUID
Investing step 6. Allow investment to set or for _______ technique place in a water bath for 1 hour
hydroscopic
How hot is the burn out oven? (C and F) How long?
Place in furnace at 200o C or 400o F for 30 minutes
***WHAT IS THE HOTTEST PART OF A FLAME?
Light blue CENTER/REDUCING area
Why do we NEVER want to heat our alloy with the base or end of the flame?
BASE: MOST oxidizing zone….open end: oxidixing zone
If newly cast metal is _______ while it is too hot, the gold will be softer and weaker.
quenched
Prevents removal of the restoration along the path of insertion of the tooth preparation.
Retention
Prevents dislodgments of the restoration by forces directed in an apical or oblique direction.
Resistance
Prevents any movement of the restoration under occlusal forces.
Resistance
An extracoronal restoration uses opposing ________ surfaces for retention.
opposing external
An intracoronal restoration uses opposing ______ surface for retention.
internal
A 6 degree preparation would give two opposing surfaces with __ degree inclination each.
3 degree
HAHA go figure: Studies Have shown that actual crown preps are much greater than the recommended value: on average the taper is ___ degrees! When do we lose retention?
19 degrees…lose retention @ 22 degrees
For adequate Retention and resistance form the height/base ratio should be _______ for all teeth.
GREATER than 0.4
Height Base Ratio- INCISORS and PM’s..whats the minimum height?
3mm minimum height
Height Base Ratio- Molars..whats the minimum height?
4mm minimum height
Maximum Retention has _____ path(s) of removal of the crown.
ONE PATH
Resistance of a short preparation can be improved by adding ______.
grooves
Parker et al found that ____% of anterior preparations had adequate resistance form compared to ___% on molars.
95%…46%
Margins: Round internal line angle. Preferred gingival margins for full gold crown.
Chamfer
Round bigger radius internal line angle. A 90 degree cavosurface line angle.
Heavy Chamfer
A wide ledge ( instead of a radius) design.
90 degree internal line angle….Concentrates stress and induce coronal fracture….Technically impossible to be produced by human hand.
Classic Shoulder
What is also called a BUTT MARGIN DESIGN?
RADIAL SHOULDER
Round internal line angle but does not have a circular arc like the chamfer…
RADIAL SHOULDER/ BUTT MARGIN
A ledge design margin., Round internal line angle, 120 degree cavosurface line angle.
Sloped Shoulder
The ultimate finish line that permits an acute margin of metal.
Knife Edge
Margin placement must be at least ____ mm away from the J.E.
0.5mm
What are the 4 contraindications for a full coverage crown?
1.Active Caries 2.Perio Disease 3.Large Pulp 4.if more conserve prep an option
Goal of metal design is to minimize ______ stress
tensile
What is the default labial margin?
“disappearing margin”
Minimum Metal Thicknes
0.3 to 0.5 mm
Minimum Porcelain Thickness
1.0-1.2mm
Contact Distance from M/P Junction
1.0-1.5mm
OCCLUSIAL CONTACTS in MIP ___mm from M/P Junciton ON METAL
1.0mm
OCCLUSIAL CONTACTS in MIP ___mm from M/P Junciton ON PORCELAIN
1.0mm
