L5- Impressions Flashcards
die and why
positive reproduction of prepared teeth in a suitable accurate hard substrate
need because
- accurate representation of the tooth preparation and adjacent structure
- die must be strong enough to withstand the fabrication process
requirements for die material
accurate
dimensionally stable
minimum setting contractions and expansions
fine detail reproduction
good impression requires
- tooth prep that follow biomechanical principles
- carefult soft tissue management
- knowledge of the handling properties of the impresion material
- avoiding common problems
biologic width
1mm for
1mm for
plus?
1mm for connective tissue
1mm of junctional epithelium
plus 1 to 2 mm of tooth structure for the crown margin placement and terminiation
ferrule requirements
requires 2mm BEYOND a core material finish line
ferrule requirements
requires 2mm BEYOND a core material finish line
mechanical displacement he highlighted
knitted – ultradent – type of cord used
breakdown of careful soft tissue management
- mechanical- often most common - like PLACING cord
- hemostasis in the sulcus
- tissue removal
Most popular form of retraction
mechanical dispalcemnt
small 000-00 use?
anterior with thin tissue areas – lower cord in 2 technique
medium 0-1
osterior - lower cord in 2 cord technique - premolar - molar
large 2-3
uper cord in 2 cord technique - thick gingiva
UP cords thickness from thinness to largest?
0.5 - 1.4mm
first cord is?
smaller in diameter and equal or slightly less in length than the circumference of the tooth
second cord is? - in general
larger than first
prior to light bodty impression material?
only the second cord is removed
first cord must?
secure in the sulcus and exposes the finish line
correct cord placement
tucking it in - general
leave cord in for how long?
5-10 minutes
leave enough length of cord to easily capture with cotton pliers
cord he suggests
knitted - ultradent
twisted cord
tends to be separated by the packing instrument and it has BIAS AND MEMORY
- first cord should disappear into sulcus
braided cord
is RIGID macking the packing into the sulcus challenging
has memory
knitted cord
more flexible and exerts an outward pressure once placed
will hold more hemostatic solution
NO MEMORY
easier to place
place and leave for 3-8 minutes
retarction and sulcular width - study?
Laufer et al - affect of marginal thicknesss on the distortion of different impression materials
“sulcus must be of enough width for the impression material”
0.2 mm SULCUS WIDTH IS MINIMUM REQUIRED
Class I hemostatic agents
vasoconstrictors
adrenergics
action – constricting blood vessels
can HAVE SYSTEMIC AFFECTS
class II hemostatic in the sulcus
hemostatic
ASTRINGENTS – action is precipitating proteins causing coagulation
**he suggests using this one due to no systemic affects
examples of class II
alumnimum chloride
ferric sulphate
ferric chloride
aluminum chloride gel
cord with epi?
class 1 - with systemic effects
0.2 to 1 mg/ in
max for healthy patient is 0.2mg (10 carpules)
NOT RECOMMENDED
GINGI-PAK
cord with epi – has .5 mg / in
implication of hemostatis agent OF CLASS II
changes pH – low
so need to rinse it out
because it ADVERSELY AFFECTS THE SURFACE DETAIL REPRODUCTION OF PVS IMPRESSION
% used class 1 in 1985?
79.39%
% used class 1 in 1999
14% – huge decline
electro- surgery / cautery
another way to remove tissue for impression
laser advantages
no bleeding / no referral to perio
make impression that day
makes wider area for impression materials with poor tear strength such as reversible hydrocolloid - like poly ether material
safe with implants if contacted
disadvantages of laser
can cause GINGIVAL RECESSION therefore NEVER recommended for anteriors or thin gingiva
cannot use on patients with delayed healing
does not involve osseous - no bone change = no tissue change - so not for CLP
laser vs bur
speed
- laser is slow (advantage) vs fast
bur will cause bleeding
bur – cannot use on implants – will damage implants if contacted
bur is fast – could be a disadvantage
polyether aka
impregum
polyether + sulphonic acid ester = cross linked rubber
impregum made of
polyether + sulphonic acid ester = cross linked rubber
polyvinylsiloxane
hydrogen contaiing siloxane + vinyl siloxane + chloroplatinic acid = silicone rubber
alter technique for gaggers
USE A CUSTOM TRAY
what do we want from an elastomeric impression
accurte reproduction of detail of the tooth prep and surrounding hard and soft tissue
dimensional stability to allow delayed pouring
ease of handeling
allergies?
no polyether
intitially fluid?
need this to get into the areas at first
tear resistance?
if this is adequate then wwhen remove it wont tear and remain in tact
working means
begin at START OF MIX and ENDS BEFORE ELASTIC PROPERTIES HAVE DEVELOPED
setting =
mix to removal
viscosity increase?
decreases in time
warm environemtn?
impression material is sensitive to changes in temperature - especially pvs
PVS set time in regular set
into mouth is 2:30 – do not remove for 5 mins
thixotropic means
flows smoothly under pressure in critical areas and remians fixed without pressure
snap set properties
reduces the potential for distortion during the setting process and removal from the mouth to assure a precise - fitting final restoration
polyvinl snap set?
NO - so hold in patietns mouth - if trey moves - will be distorted
thixotropic under pressure?
materials viscosity will REDUCE when it is placed under stress
greatest flow?
polyehter
impressions with deep subgingival margins and / or multiple preparations mayh be better captured wit a polyether impression material
advanatges to polyether
SNAP SET
good working time
very STIFF when set - Hi shore hardness
sets 5-6 mins
thixotropic
hydrophillic
excellent accuracy and wetting
complete wetting?
contact angle of 0 degrees
higher contact angle
greater than 90 – means lower wetting
higher contact angle
greater than 90 – means lower wetting
custom trey requires?
tray requires approximately 3mm of relief over the diagnositc cast and at least 3 vertical stops
custom trey requires?
tray requires approximately 3mm of relief over the diagnositc cast and at least 3 vertical stops
advantages of custom treys
reduced volme of the material
take advantage of the fluid dynamics of non-newtonian materials
reduced cost of the impression –(15+ estimated cost of impression in a stock trey)
improved accuracy by reducing stress due to thermal contraction and having an eve amount of material around the prepared teeth
IMPROVED ACCURACY by reducing the potential for the tray to flex
_____ the stock trey
customize the stock trey
_____ the stock trey
customize the stock trey
order of loading?
load the tray first
then load the syringe second
dual arch /triple trey
bad
FLEXIBLE – which is a very bad trait
so impression is made in an unstable situation
also bad with the triple tray dies
disadvantages of the dual arch impressions
DISTORT B-L
LACKS SUPPORT AND CONFINEMENT of impression material
VARIATION in impression MATERIAL THICKNESS
difficult to determine if patient “closed” correctly = occlusal contacts suspect
cannot be re-poured
cannot evaluate patietn’s occluson
implant impressions recommendationss
open trey
recommend custom tray often the impression coping cannot be accessed in a stock trey
transfer impression?
can use monophasic or single mix
dual phase or
heavy / light body mix
used in fabrication of INDIRECT RESTORATIONS
technique used for indirect restorations
dual-phase or heavy / light body mix
advantages of pentamix
consistent mix of material
decrease waste
ease of loading tray and syringe
decrease in air bubbles in mix
bleed material?
YES – always bleed the material first so that unmixed material does not get int the way
tip of the dispenser?
must NOT come out of the maine body of the material, keep tip in the material to prevent folds and bubbles
syringing the material? - details
DRY the field but DO NOT DESICCATE
small tips are the best
place tip in the MOST DIFFICULT area first
DO NOT LIFT THE TIP OUT OF THE BODY OF THE MATERIAL AS THIS INCOPORATES BUBBLES
allow the material to push forward around the tooth
air syringe? – need to know technique
streaks from
not mixing well
big contributoe to inadequate margins- loss of detail
poor fitting tray or tray movement upon placement
main reason we see poor bond between light and heavy body material
***too much time elapsed between mixing these materials
premature removal
latex contamination
vaseline contamination
expired material
gypsum is
forms?
calcium sulfate dehydrate
5 forms
Beta hemihydrate to alpha hemihydrate
from plaster to high strength dental stone
control we have with gypsum
ratio of POWDER TO WATER , mixing time, setting time and working time
add water to powder?
NO - add powder to water
go past the diameter on round ended bur?
created a ski slope / bad margin
connective tissue needs
1 mm of sound tooth structure
junctional epithelium needs
1 mm of tooth structure
000-00 corresponds to
small cord size
- anterior and thin tissue area
0-1 corresponds to
medium cord size – posterior lower cord in 2 cord
pre-molar / molar
thinnest to largest cord
0.5 to 1.4 mm
bias in cord means
theres a rotation to it – characteristic of twisted cord
end cord in interproximal?
NO – never
implication of cord having memory
wants to spring open once not tucked into sulcus - can be challengin
memory in terms of knitted cord
NO - knitted cord does NOT have memory to it
miscellaneous forms of tissue retraction
pastes – traxodent
impression- bite regitration material – hold cord in place too
retraction caps / compression caps – with or without gels - inject into sulcus then put it on top of prep and bite down
action of class II hemostatic agents
precipitate proteins – causing coagulation on the superficial layer of mucosa and make it mechanically stronger
aluminum chloride is example of? details
class II ASTRIGENT - AlCl2 -- shrinks or constricts tissue and extracts fluid from tissues
concentrations of 5-25% has minimum systeimc side effects
Alcl2 vs Alcl3
AlCl 3 is LESS irritating / least of the hemostatic agents used with cords but it DISRUPTS THE SETTING OF PVS IMPRESSION
hemostatic agent can disrput PVS set?
ye – like AlCl3 – so must rinse out adequatley
implications if use type I
restriction of arteries by binding alpha - adrenergic receptors - contraciton of smooth msucle
blood pressure rises due to vascular resistance
increase chances of hypertensive crisis, agina pectoris, myocardial infarcation, cardiac arrythmias
DO NOT COAGULATE - but CONSTRICT
wash and dry with cord?
YES – the alumnium chloride, ferric sulfate, and ferric sub sulfate ADVERSELY affet the surface detail reproduction of PVS impressions
hemostatic agents pH?
tend to be low and can affect surface detail of PVS - rinse and dry priot to impression
GP’s vs prosth with getting finish line?
only 14% used epi treated and 44% used PLAIN CORD if a prosth vs 79.39 GP (bad)
bur curettage induce bleeding?
yes and can DAMAGE IMPLANTS and can be too fast a method n
biological reasons for having difficulty making an impression?
- we invaded bio width
- not allowed tissue healing
- tissue trauma
- POOR marginal adaption of PROVISONAL restoration (temp crown)***
- no room in the sulcus for the impression material
undercuts, thin teeth and thin prep probably going to use?
PVS
PVS set time - quick
into the mouth 1 min do not remove for 5 minutes (6 total)
snap set?
polyether impression characteristic
- ensures that the material will not start setting before the working time ends - and then when it does set - it does so immediatley resulting in precise fitting restorations without distrotion
- reduces the potential of distortion upon removal
if use light and heavy body together process and timing?
mix heavy body - put in trey then inject light body around thetooth and put he tray in
impression material that is HYDROPHOBIC and implication
aquasil / PVS
- so if drying area is a concern may want to use poly-ether for impression
wetability
ability of liquid ro spread over a surface
complete wetting angle?
0 degrees
poly ether with wetting
more hydrophillic - spreads out more
disadvantages of polyether
LOW TEAR STRENGTH
- adhesive required
- unpleasant taste
- very STIFF when set
- 0.5% of patients allergic to catalyst
CAN NOT BE STORED WET
impression material to use for small dies?
PVS – less stiff
disadvantages of PVS
requires perforated trays
adhesive is not strong
HYDROPHOBIC
inhibited by latex / sulfur containing materials
inhibited by certain astringidents
avoid hydrogen peroxide materials
retraction cord contamination
do we need a second pour?
YES - says we should
like for adjusting contacts
custom trey vs diagnostic cast
trey needs approx 3mm of relief over the diagnostic cast and at least 3 vertical stops
advantages of custom trays
reduced volume of the material
take advantage of the fluid dynamics of non-newtownian materials
reduced cost of impression
IMPROVED ACCURACY BY REDUCING TRESS DUE TO THERMAL CONTRACTION and having an even amount of material around the prepared teeth
reduces the potential for the trey to flex?
if use a custom trey – can IMPROVE ACCURACY
high vs low viscosity materials in terms of seating
the hi viscosity material will displace the low viscosity material according to the non-Newtownian properties of viscous materials under stress
do not use triple trey for?
FPD’s – there is NOT enough information regarding the occlusion in order to deliver a resotration that has the correct function built in
not a good way to figure out the A-P orientation or the B-L
his opinion for impressions with implants
open trey – and use custom tray as often the impression coping cannot be accessed in a stock trey
monophasic or single mix impression can be used for?
transfer impression
which displaces the other in terms of materials?
heavy displaces the light body
putty wash
silicone materials
want more back pressure because of sub-gingival margin
but it is flexible – so distortions can be incoporated and then restoration does not fit
regular set PVS set vs fast
within 60 seconds – need to get on trey and into patients mouth (can remove after 5 mins)
fast - get to pt mouth by 35 seconds (Can remove in 2.5 mins)
second pours can be used for?
proximal contacts
as reference for a fixed splint case - like a 3 -unit FPD
reference for die trimming
back up in case of damage to 1st pour
inadequate retraction implication in impression
likely going to get tears in impression
polymerization problems with impression likely due to
maybe it is expired – CHECK DATE
important aspect to inadequate margins / lost details
make sure the trey fits
this is oftne due to poor fitting tray or tray movement
reasons material does not set fully
contamination (like to latex )
hemostasis material contamination
exposure to residue from custom temporary material
poor mix
expired material
material will look discolored
PVS voids or pulls likely due to
saliva in the way
voids or pulls due to
waited to long to put into patient mouth and may get separation of material
main reason for poor bond between light and heavy body material
too much TIME ELAPSED BETWEEN MIXING these materials
reaons crown does not fit
tray moved or rocked
margin was not captured
disposable tray was too flexible
did not use tray adhesive, cast is distorted upon pouring
premature setting of impression material prior to seating intra-orally
premature removal
