Midterm Flashcards
In ceramics, what are they two key phases that occur after firing
crystalline: most common today
glassy phase: surrounds the crystalline phase
in ceramics, the crystalline phase affects what
Depending on the nature and amount of crystalline phase present, the mechanical and optical properties vary greatly
o Increase in glassy phase = lowers resistance to crack propagation BUT increase translucency
All-ceramic restorations have inc/dec amounts of crystalline phase
INCREASE.
allows for better mechanical properties
after an impression is made,itispouredinagypsumproductsuchasdental stone. The section reproduced which represents a form of the prepared tooth is referred to as a:
DIE
what type if reproduction is a die/cast -/+
+
What is a die
reproduction of the form of a prepared tooth in a hard substance
o Impression of prepared tooth, trimmed down: die
what is a cast
reproduction of the surface form of oral/facial tissues obtained from
impressions
o Impression = (-) form of teeth
full arch poured up= cast
Whatistheprimarydifferencebetweendigitalimpressionsandtraditional impressions (i.e. alginate)?
Digital impressions are a positive reproduction of the oral structures and
traditional impressions are a negative reproduction.
are digital impressions pos or neg
POS
are aliginate impressoins pos or neg
NEG
Howdoesthechemicalformulaofcalciumsulfateα–hemihydratedifferfromthe chemical formula of calcium sulfate β-hemihydrate?
There is no difference in chemical formulas. Just physical shape, size,
crystal form
what is the chemical formula for naturally occuring gyspum
(CaSO4)2 * H2O
Calcium sulfate hemihydrate
what is plaster
plaster: BETA-hemi, open air kettle P,B,O
what is stone
stone: ALPHA- hemi, autoclave
Impressionmaterialshavemanycharacteristicsthateitherenhancetheir qualities as such or reduce their values for certain techniques. The characteristic that makes hydrocolloids useful impression materials is their tendency to be:
hydrophilic
Are Reversible Hydrocolloid impressions a chemical set impression?
NO- thermal
what is a reverisble hydrocolloid
agar agar which is THERMAL SET
what is an ireeversible hydrocolloid impression
alginate
what impression materials are chemcial set
alignate, polyether and elastomeric
what impression materails are thermal set
agar agar - reversible hydrocolloid
Digital scan is useful for
Crown, night guard, splints, edentulous impressions (do not do much of yet)
○ Indirect restorations (i.e., crowns, bridges, inlays/onlays, veneers) fabricated chairside in lab
○ Orthodontic tray fabrication (invisalign)
○ Virtual study models (implant treatment plan)
○ Any case sent to a lab
Autoclavingcalciumsulfatedihydrateinthepresenceofcalciumchlorideand magnesium chloride will produce what?
) High strength dental stone. chemicals
Intheconversionofcalciumsulfatedihydratetocalciumsulfatehemihydrate, which process would yield the beta version of hemihydrate?
Heatinginopenairkettles.Dentalplaster
stone characterics
stone is alpha- autoclave
■ Low Porosity/regular, less linear expansion
model plaster characterics
Model plaster is beta- open kettle
■ Porous/irregular, more linear expansion
what is used to form high strength stone
chemicals
The attribute of impression materials which allows them to be removed by stretching over a bulge and returning to its original shape without distortion is called:
memoruy
11.The tendency for wax to return to its original shape is referred to as:
elastic memory
Elastomeric impressions / alginate impressions are able to rebound to original shape / rebound in memory
○ What is in it that allows it to rebound to the original shape?
elastic memory
advantages of digital impressions
No impression materials needed
■ No models to pour
■ Download impressions directly to milling unit
■ Can store/send impression scans much easier
■ No distortion or warping
■ More accurate
■ Stable
■ Faster turnaround; more convenient to you and to your patients.
disadvantages of digital impressions
■ High initial cost
■ Data loss
■ Technique sensitive
■ Time consuming
■ Need to work in a digitally equipped lab
What causes the linear expansion of calcium sulfate dihydrate during the setting reaction?
a) The growth and pushing of the dihydrate crystals.
2 things happen when dental stone & plaster is setting:
Volumetric contraction: volume of calcium sulfate dihydrate formed is ~7%
less than the sum of volumes of calcium sulfate hemihydrate & water
○ Linear expansion: caused by growth and pushing action of the calcium
sulfate dihydrate crystals, results in porous material
Volumetric contraction:
volume of calcium sulfate dihydrate formed is ~7%
less than the sum of volumes of calcium sulfate hemihydrate & water
Linear expansion:
caused by growth and pushing action of the calcium
sulfate dihydrate crystals, results in porous material
Key concept in setting rxn of calcium sulfate 3
○ EXOTHERMIC
○ Water temp & solubilities
○ There is a definition
Temperature generated is equal to that used to heat during calcination
● Rxn takes place regardless of how the gypsum is being used
.Both irreversible and reversible hydrocolloids exude a liquid on their surface after setting which is partially water but has a different pH. This phenomenon is called:
Syneresis
where do you see hygroscopic expansion and syneresis
hydrocolloid impressions
Syneresis
excludes water on surface
Not pure water b/c pH is different
○ Gel shrinks
where can you find syneresis
agar and hydrocolloid impressions
If dental plaster/stone is left to set under water, what will happen?
Hygroscopic expansion. More water = more crystal growth, less surface tension
Hygroscopic expansion
the expansion that occurs if rxn is allowed to occur under water
○ Used w/ investment material for greater expansion
greater than the amount of expansion in air bc of constant supply of H2O
allowing additional crystal growth
What do you isolate to get a digital impression?
An ISOLITE, you would NOT use a rubber dam!
Which phase directly affects the mechanical and optical properties of all
ceramics??
The amount of crystalline phase
In the setting reaction of irreversible alginates, trisodium phosphate, sodium pyrophosphate, and tetrasodium pyrophosphate are able to expand the “working time” to allow for thorough mixing, loading the tray, and seating of the tray. As a group they are referred to as:
retarders
what is a retarder
Retarder: keeps “reactor” busy so it does NOT immediately combine w/ the
alginate sol’n
once retarder is used -> CaSO4 combines with soln to form gel
Isolation is necessary when taking a frame scan (YES/NO)
YES. need surfaces of teeth dry and free of shit
All of the following will decrease the set time of dental plaster/stone EXCEPT: a) Decrease the water powder ratio.
Hygroscopic expansion. More water = more crystal growth, less surface
tension
b) Increase the mixing time and mixing speed.
c) Use slurry water.
d) Use very hot water (near boiling). Boiling solubilities of hemi and di are
equal
d) Use very hot water (near boiling). Boiling solubilities of hemi and di are
equal
Best way to decrease setting time of plaster stone
decrease setting time -> increase speed of set BEST WAY!!!
increase the speed and temp of mix
When dispensing elastomeric impressions materials, it is essential to dispense equal volumes of the materials.
FALSE
Base and accelerator: mix out equal LENGTHS, not volume
take an impression & their blood from the gingiva gets on it & you do NOT rinse
it out… What will this do to the setting time of the stone?
● Leave debris (from body or whatever) increases set time, so clean it (takes longer)
o Sets slower/increase setting time
How do you influence the set time of alginate?
Hot water = decreases set time so it sets faster
○ Cold water = increases set time so it sets slower
Good hemorrhage control, but cannot be used near metal (i.e. implants).
Electrosurgery improved hemorrhage control, unable to use near metals
Maximum hemorrhage control and visibility, safe to use near metal, but has safety issues in the military.
Soft tissue laser Max hemorrhage control and visibility, no tissue charring,
used near metals (implants) not in military
Cheap, but has poor hemorrhage control and visibility.
Scalpel cost efficient, poor hemorrhage control and visibility, 2nd appointment
Standard method for soft tissue management and hemorrhage control. Prefered method used at Creighton.
Retraction Cord
Acceptable forms of tissue management when taking an impression (implant) w/ excess tissue– Use:
Laser
○ Scalpel
○ Cold steel (scalpel)- cheap but great hemorrhage
○ Electrosurgery- can NOT use with metal, little hemorrhage
○ Packing cord
○ Laser- can use with metal, no hemorrhage
You prepared a tooth for a gold inlay. You would like to make a wax pattern using the indirect waxing technique. Which classification of dental inlay casting wax would you use?
Type1.Soft,greatflow,formwaxpatternsondentaldie,outsidetooth
type 1 wax is used for
Soft,greatflow,formwaxpatternsondentaldie,outsidetooth
type 2 wax is used for
direct,harder,lowerflow,directintooth
Where will Type 1 and Type 2 inlay wax be used?
Type I- indirect restoration (softer)
○ Type II- direct (in mouth) restoration (harder)
The major reason for removing the impression from the cast shortly after it is completely set is:
To prevent the imbibing of moisture from the cast by the drying, shrinking
alginate.
The preferred way to control the dimensional stability of both Reversible and
Irreversible Hydrocolloids, prior to pouring up the impression, is to:
put in wet paper towel
If an impression cannot be poured up immediately: best thing to do is wrap impression in wet paper towel soaked in cold water
Which of the following was not listed as a common error when taking digital impressions?
Image file taking up too much memory.
Common errors when taking digital impressions:
○ Moving camera too fast
○ Poor isolation
○ Capturing things you don’t want (ex.finger)
Common errors when taking digital impressions:
○ Moving camera too fast
○ Poor isolation
○ Capturing things you don’t want (ex.finger)
slurry water does what
Use of Slurry water decreases set time/increases the rate of set.
What can generate polymerization of acrylic
o Heat (warm water) o Microwaves
o Light cured
● Chemical activation at room temp
2.True or False. Waxes are chosen based on their specific melting point.
FALSE. waxes have a melting RANGE
waxeshave large/small coefficients of thermal expansion
LARGE!!
waxes have low/high thermal conductivity
LOW
What happens to wax when you heat it?
hermal expansion
○ Thermal contraction
Many waxes are not good thermal conductors t/f
TRUE
Hard wax is not a good thermal conductor
○ Dental Waxes have the highest coefficient of thermal expansion
Slip cast ceramic materials – know what that is
○ Low or High strength?
HIGH
advantages: it’s high in strength
○ Disadvantages: long time to process, high opacity
○ Two Types: Zirconia/Spinel Based, and Alumina Based
■ Zirconia is the STRONGEST ceramic material
zirconia is what type of ceramic material
slip cast
in light activated resin, the photoinitiator is:
CAMPHORQUINONE-AMINE
Chemicals present in monomer in polymethyl methacrylate: will keep it from
setting automatically or auto polymerizing - what is it
Hydroquinone
base material for triad light cured material =
Urethane Dimethacrylate
Repairing denture, we used a self-repairing acrylic– it is GOOD if it is HARD
○ TRUE/FALSE
TRUE! its good if its hard
unit of polymer
mers
Both are good
○ Condensation Silicone has more shrinkage / shorter die
○ Use PVS (best mechanical stability)
● Condensation silicone impression material has more significant shorter dye so
we like to use polyvinyl siloxane instead
Take impression materials, we talk about the wetting characteristics - low or high angle
A LOWER angle b/c the material will spread out on the tooth we are impressing. means it is hydrophilic
Denture teeth – 2 little buttons on the back of porcelain teeth – for mechanical
retention
○ Buttons are called
diatorics
what is stronger denture tooth- arycrlic or porecelain
porcelain is stronger but that will wear nature teeth down
on denture, what type of teeth are used
acrylic bc is easier to adjust b/c it is softer
○ Less likely to wear opposing surfaces
■ Better bond with acrylic & denture than with porcelain ○ **Porcelain = a strong wearing tooth
Elastomeric impressions
○ Which one forms hydrogen gas? – you do not want to pour this impression too soon b/c hydrogen gas will be coming off of it
Poly Vinyl Siloxane (PVS) impression material
what can you add to PVS so it wont form hydrogen gas
palladium
Is the least flexible of the impression materials
Polyether Impression Material
impression:
Forms ethyl alcohol as a byproduct
Condensation Silicone Impression Material
impression:
Uses lead dioxide as a catalyst
C: Polysulfide Impression Material
impression:
Polymerization reaction is exothermic
ALL
impression:
Uses a platinum salt as a catalyst
PolyVinyl-Siloxane Impression Material
impression:
contracts during curing
ALL impression materials
impressoins:
Has greatest dimensional stability (least linear contraction)
PolyVinyl-Siloxane Impression Material
impressoins:
May form hydrogen gas
PolyVinyl-Siloxane Impression Material
- All of the following were listed as dental uses of gypsum EXCEPT: a. Dentalcasts.
b.Impressionsonpatientswithfulldentitions
c. Dental dies.
d. Dentureflaskingprocedures.
e. Attachingcaststoanarticulator.
Impressionsonpatientswithfulldentitions.–can’tputinpatientmouth
What is the key concept to understand in the setting reaction of calcium sulfate dihydrate?
Calciumsulfatehemihydrateismoresolublethandihydrate.
The linear polymer of galactose extracted from seaweed and used as an impression material is:
Agar-Agar. Galactan
The impression materials discussed in class that were referred to as Non- Elastics were waxes, impression compound, impression plasters, and :
Zinc oxide and eugenol.
the characteristic of Reversible Hydrocolloids that make it compatible for use on humans is the big difference between their “Liquifaction Temperature” and their “Gelation Temperature.” That characteristic is called:
. Hysteresis.
The large variation in temperatures between liquefaction and gelation in a Reversible Hydrocolloid permits us to use it in a range that is reasonably comfortable to use on a human being. That property is called:
c. Hysteresis.
Which of the following is NOT true about reversible hydrocolloids:
a. Agarisapproximately10-15%water.
b. Containsboraxtoincreaseviscosityandstrength.True
c. Agglomerates to form micelles upon cooling.
d.Utilizessulfatesasahardenerwhichoffsetsthetendencyofboraxto retard the setting of gypsums.
A. 10-15% hydrocolloid
Sodium, potassium, and triethanolamine alginates require another chemical to drive the reaction toward its gel stage. That chemical is:
CalciumSulfate.Onceallretarderisused,drivestobecomegel
If one desired to increase the “setting time” or slow the “rate of set” of an irreversible hydrocolloid (alginate), one could do the following:
use water that is 10 degrees cooler
Which wax was described in lecture as being the base or primary wax in many of the waxes we use in dentistry?
paraffin
Used to enclose impressions; forms a wax box.
Boxingwax
waxes:
Joins or stabilizes components temporarily.
Stickywax
waxes:
Can be used as a temporary crown form.
baseplate wax
waxes:
forms borders on impression trays.
utility wax
waxes:
Used in the fabrication of indirect restorations (i.e. cast crowns).
inlay wax
Volumetric contraction- occurs due
due to the precipitation of dihydrate out of solution
Linear expansion-occurs due
to pushing action of the calcium sulfate dihydrate crystals
What is the key reaction with calcium dihydrate?
Workable Hemihydrate suspension forms upon mixing, and hemihydrate
dissolves until solution is saturated. The saturated hemihydrate solution
becomes supersaturated with dihydrate.
● Hemihydrate is 4.5x as soluble as dihydrate, dihydrate will precipitate out.
● Hemihydrate continues to dissolve as dihydrate precipitates out
Where do you see syneresis?
Will see in hydrocolloids but NOT in elastomeric impression materials.
Accelerator- type of one
speeds up set (Potassium Sulfate)
PSA
type of retarder
slows down set (Borax)
What chemical is present in the monomer in acrylic keeps it from setting automatically?
Hydroquinone
mixing time
time from addition of powder to water until mixing is complete
working time
time available to use a workable mix
loss of gloss
loses gloss when dihydrate takes up excess water. not strong
setting time
beginning of mix until haed and compeletey set
ready for use
time elasped when product can safetly be handled
