8/22 - Retraction cord, Pindex Refresher, Impression Materials (Heavy Emphasis), S5-S8 Flashcards
S5-S8 in above decks
are we doing single or double retraction cord
single
about how much a retraction cord do we initially cut off
2 inches
placement of retraction cord is begun by pushing it where
sulcus on the mesial surface of the tooth. can also be tacked lightly into distal crevice
what are common problems students have when packing cord
- angulation
- packing too much cord at a time
what angle should cord be packed
30-45 degrees
what happens if the force of the instrument is directed away from area previously packed
cord already packed will be pulled outo
what to do if cord is not going in when packing
recheck angle
can you hold the cord with one instrument and packing it with a second instrment
YES
when packing, the instrment should be angled where
towards the root
what happens to the retraction cord if the instrument is held parallel to the long axis of the tooth
retraction cord will be pushed against the wall of the gingival crevice and will rebound
what is the thinnest retraction cord
000
T/F: it’s okay if the retraction cord just goes on side of margin. it does not need to physically go in.
FALSE! needs to physically go in
what to do with extra cord
cut it out or keep looping around
how long to keep retraction cord in
5-10 minutes
do you numb patient when placing retraction cord
YES
hardrock cast has ___ mm bevel
3 mm
how thick is hardrock cast B-L and O-G
15-18mm
short pins [lingual, buccal]
long pins [lingual, buccal]
short = lingual
long = facial
what side of pins enter stone, short or long
SHORT
gray sleeves on [short, long] pins
black sleeves on [short, long] pins
gray = short
black = long
how much flowstone to add
barely cover apical part of bevel
how many mm extension of flow stone
3-4 mm
how to trim die: start at occlusal or gingival
gingival
common mistakes when taking impressions
- voids and bubbles
- separation from tray
- embedded retraction cord
- prep debris
what does “the greater the contact angle, the greater the probability of air entrapment during pouring” in regard to
wettability
what do we look at when comparing the different types of ipressions
wettability and cost
large angle [bad, good] wetting
bad wetting/hydrophobic
acute angle [bad, good] wetting
good/hydrophilic
does hydrophilic or hydrophobic have a higher incidence of voids and is more readily repelled by hemorrhage or moisture in the gingival sulucs
phobic
is polysulfide, PVS, and condensation silicone hydrophilic or hydrophobic
phobic
what is effective in reducing both the contact angle and the number of voids trapped in resuling cast
surfactant
is hydrophilic or hydrophobic have a lower incidence of voids and more able to withstand hemorrhage or other moisture in gingival sulcus
hydrophilic
is hydrophilic or phobic less resistant to wetting by gypsum
hydrophilic
are revesible hydrocolloid, irreversible hydrocolloid and polyether hydrophilic or hydrophobic
hydrophilic
what is the decrease viscosity of the material under shear load
shear thinning
what is thick enough to stay in tray yet fluid enough to express thru syringe
thixotropic
is light-body polysulfide and condensation silicone least or most viscous
least
is heavy body sulfide least or most viscous
most
what are examples of chemical disinfectants
- chlorine compounds
- combination synthetic phenolic compounds
- glltaraldehydes
- iodophors
- phenol-alcohol combinations
process of disinfecting impressions
- rinse
- trim
- spray
- seal
what is agar made frmo seaweed
reversible hydrocolloid
what is made of 85% water
reversible hydrocolloid
what is water seeping rom surface
syneresis
what is imbitition
absorbing water
what are the risks of using reversible hydrocolloid
syneresis, evaporation, and imbitition
when should you pour reversible hydrocolloid
ASAP
why do you place reversible hydrocolloid in tempering batch
lowers temp to decrease viscosity and because it’s boiling from previous baths
sodium tetraborate is also called what
borax
modifiers placed in reversible hydrocolloid
- sodium tetraborate/borax
- potassium sulfate
- thymol
- plasticizers, fillers, flavoring agents and pigmetns
since the set of gypsum is retarded by contact w/ any gel resulting in soft surface of cast, what is added
potassium sulfate (to accelerate set-up)
irreversible hydrocolloid is also called what
alginate
what is inexpensive and has low tear strenegth
irreversible hydrocolloid/alginate
what material has less surface detail than other materials
irreversible hydroc
what material is not as dimensionally stable as other materials
irreversible hydro
how quick to pour irrversible hydro
15 minutes
what is an elastomer known as mercaptan, thiokol, or rubber base
polysulfide
is polysulfide hydrophilic or phobic
hydrophobic
does hydrocolloid or polysulfide have greater dimensional stability
polysulfide
what must you do when completing polysulfide impression
block out large undercut areas in inerproximal region with soft wax prior to impression making
when must polysulfide impression be poures
within 1 hour
what are the two tubes for polysulfide impression
- base
- accelerator
what is a liquid polysulfide polymer mixxed with an inert filler
base
what is usually a lead dioxide mixed wih small amounts of sulfur and oil
accelerator
the accelerator in polysulfide is an oxidation iniator on what on the polymer
on terminal thiol groups
do polysulfide acelerators have toxicity and tendency to irritate soft tissues
YES
does the accelerator show up radioopaque
yes
what impression material has a limited shelf life
organo-tin silicones
is the two paste system of condensation silicone cross linked by reaction
ys
what is a liquid silicone polymer w/ terminal hydroxyl groups, mixed w/ inert fillers
base paste of condensation silicone
what is a viscous liquid, cross-linking agents, ethyl silicate with an organo-tin activator in tin
reactor of condensation silicone
is condensation silicone dimensionally stable or insable
instable
when to pour up condensation silicone impressions
ASAP
process of putty/wash or putty/reline
- heavy body (putty) w/ stock tray and thin plastic spacer
- thin wash of light body material to reline the putty
what is a copolymer of 1,2-epoxyethane and tetrahydrofuran
reacted with alpha, beta-unsaturated acid, such as
protonic acid to produce esterification of the
terminal hydroxyl groups
polyether impression
is polyether impression resistant to tearing upon removal
yeS
is polyether impression somewhat brittle
yeah
is it okay if you dont block out for polyether impression
NO! stiff material so needs to be blocked out
people with allergic rxns to polyether are allergic to what
aromatic sulfonate catalyst
is polyether hydrophobic or hydrophilic
philic so imbibition likely
is polyether accurate when poured weeks after removal from mouth
yes
what impression material used in complete denture
polyether
what is PVS also called
polyvinyl siloxane, addition silicone, vinyl polysiloxane, and vinl silicone
what uses two pastes with mixing dispensers
PVS
what are the two pastes in PVS
- silicone w terminal silane hydrogen groups and inert filler
- silicone w/ terminal vinyl groups, chloroplatinic acid catalyst, and filler
is PVS hydrophilic or phobic
phobic
are surfactants added to PVS
yes
does PVS have less stability than condensation silicone
NO! it’s dimensional stabilit is GREATER than condensation silicone
can you use latex gloves when doing PVS impression? why??
no - sulfur impedes material
when to pour PVS impression
15-20 minutes after. still accurate after 1 week
