Prosthodontics | Impression Materials | INBDE, ADAT
Summary
TLDRIn this video, Ryan delves into dental impression materials, crucial for prosthodontics and board exams. He covers tissue management, including fluid control and tissue displacement, and details the various impression materials: aqueous hydrocolloids (reversible agar and irreversible alginate) and non-aqueous elastomers (polysulfide rubber, condensation silicone, polyether, and addition silicone/PVS). Key points include the materials' properties, setting times, and how to handle them to avoid distortions like imbibition and syneresis. The video also emphasizes critical information for board questions and practical tips for clinicians.
Takeaways
- 🦷 Tissue management is crucial for dental impressions and involves fluid control and tissue displacement to provide clear access to the crown prep.
- 🧪 Fluid control can use local measures like cotton rolls and suction, while tissue displacement often employs retraction cords and medicaments like aluminum chloride or epinephrine.
- 🚫 Electrosurgery can be used for tissue management but is contraindicated for patients with implanted devices like pacemakers.
- 📊 Dental impression materials are categorized into aqueous hydrocolloids and non-aqueous elastomers, each with unique properties and applications.
- 🔄 Reversible hydrocolloid, like agar, changes phases with temperature and is highly accurate but requires a complex procedure.
- 🌡 Irreversible hydrocolloid, alginate, is quick-setting and commonly used but has the lowest accuracy among the discussed materials.
- ⏱ Factors affecting setting and working times of hydrocolloids include water temperature and the ratio of water to powder.
- 💧 Imbibition and syneresis are phenomena that can distort hydrocolloid impressions and should be avoided for accurate dental models.
- 🌡 Polysulfide rubber is an elastomeric material that leaves a water byproduct and is prone to syneresis, requiring prompt pouring after impression.
- 🍺 Condensation silicone leaves an alcohol byproduct and can cause shrinkage, highlighting the importance of pouring timing to prevent distortion.
- 💧 Polyether is hydrophilic, stable but easily influenced by water and humidity, making it prone to imbibition and challenging to remove from the patient's mouth.
- 🌟 Addition silicone (PVS) is the premium choice with no byproducts, excellent fine detail, and dimensional stability, but is inhibited by sulfur in latex gloves and rubber dam.
Q & A
What are the two main components of tissue management in taking dental impressions?
-The two main components of tissue management in taking dental impressions are fluid control and tissue displacement. Fluid control involves managing saliva and gingival crevicular fluid, while tissue displacement involves moving the tissues to provide clear access to the crown prep for a clean and accurate impression.
What are some local measures used for fluid control in dental impressions?
-Local measures for fluid control include the use of cotton rolls, suction, and anti-style gags. These methods help isolate the area and manage fluids like saliva and gingival crevicular fluid.
What is the purpose of using retraction cords in dental impressions?
-Retraction cords are used to displace the tissue, specifically to stretch the circumferential fibers of the periodontal apparatus out of the way. This helps in obtaining a clean and accurate impression by placing the cords right under the margin of the prepared crown.
What medicaments can be used to impregnate retraction cords to prevent bleeding?
-Medicaments such as aluminum chloride, iron sulfate, or epinephrine can be used to impregnate retraction cords. These substances help in promoting hemostasis, preventing bleeding which can interfere with the impression process.
Why is electrosurgery not always recommended for tissue displacement in dental impressions?
-Electrosurgery is contraindicated in certain patients, such as those with implanted pacemakers or insulin pumps, because the electrode must not contact the teeth. This makes it a less universally applicable method for tissue displacement.
What are the two main categories of impression materials discussed in the video?
-The two main categories of impression materials discussed are aqueous hydrocolloids and non-aqueous elastomers. Aqueous hydrocolloids are water-based materials mixed with water, while non-aqueous elastomers are elastomeric impression materials that do not involve mixing with water.
What is the difference between reversible and irreversible hydrocolloids?
-Reversible hydrocolloids, like agar, can change between a sol phase (solution) and a gel phase by changing temperature, allowing them to be reused. Irreversible hydrocolloids, like alginate, cannot change back into a different phase once set and are used for single-use impressions.
Why is alginate not recommended for taking final impressions for a crown or bridge?
-Alginate is not recommended for taking final impressions for a crown or bridge because it has the worst accuracy among the materials discussed. It is acceptable for diagnostic impressions but not for those requiring high accuracy.
What factors can influence the setting time and working time of hydrocolloids like alginate?
-The setting time and working time of hydrocolloids can be influenced by the temperature of the water used and the water to powder ratio. Hotter water or using less water can decrease the setting time, while colder water or increasing the water to powder ratio can increase it.
What is the significance of imbibition and syneresis in relation to hydrocolloid impression materials?
-Imbibition is the absorption of water, which can cause the impression to swell and distort. Syneresis is the loss of water, causing the impression to shrink and distort. Both phenomena can negatively affect the accuracy of the impression and the model poured from it.
What are the characteristics of polyether impression material that make it prone to distortion?
-Polyether impression material is hydrophilic, meaning it loves water and can swell up and be affected by the relative humidity in the room. This makes it prone to imbibition and distortion. Additionally, it is very stiff once set, making it difficult to remove from the patient's mouth and prone to breaking teeth from the cast.
Why is addition silicone (PVS) considered the best impression material despite its high cost?
-Addition silicone (PVS) is considered the best impression material because it offers the best fine detail, elastic recovery, and dimensional stability. It has no byproducts and is very stable, allowing for a longer time before pouring is necessary. However, it is inhibited by sulfur in latex gloves and rubber dams, which is a clinically significant factor.
Outlines
🦷 Introduction to Dental Impression Materials
In this video, Ryan introduces the topic of dental impression materials, highlighting its importance for board exams and its frequent requests. The initial focus is on tissue management, encompassing fluid control (saliva and gingival crevicular fluid) and tissue displacement to ensure clear access to the crown prep. Various methods for fluid control (cotton rolls, suction, anti-sialogogues) and tissue displacement (retraction cords, impregnated cords, electrosurgery) are discussed, emphasizing their roles in achieving accurate impressions.
🌊 Aqueous Hydrocolloids: Agar and Alginate
Ryan elaborates on the first category of impression materials: aqueous hydrocolloids. Agar, a reversible hydrocolloid, changes phases with temperature and offers high accuracy but is complex to use. Alginate, an irreversible hydrocolloid, is commonly used in practice due to its quick setting time (3-4 minutes) and primary ingredient diatomaceous earth. The segment also covers tips for mixing alginate and factors influencing its setting and working times, stressing the importance of water temperature and ratios.
⚖️ Imbibition and Syneresis in Hydrocolloids
This paragraph discusses the critical concepts of imbibition (water absorption) and syneresis (water loss) that affect hydrocolloids like alginate and agar. Ryan explains how these phenomena can distort impressions and provides guidelines for avoiding them, such as wrapping impressions in a moist paper towel and pouring them within ten minutes. The importance of these concepts for board exams is emphasized, with examples of how they can affect impression materials.
🔄 Non-Aqueous Elastomers: Polysulfide Rubber and Condensation Silicone
Ryan transitions to non-aqueous elastomeric impression materials, starting with polysulfide rubber, which leaves a water byproduct and is prone to syneresis. He explains its moisture tolerance and the necessity to pour it within 30-45 minutes. Condensation silicone, the first type of silicone impression material, leaves an alcohol byproduct that can cause shrinkage. The timeframe for pouring this material is also discussed, emphasizing its implications for clinical practice and board exams.
🧲 Polyether and PVS: Advanced Elastomers
This section covers polyether and addition silicone (PVS) impression materials. Polyether is stable but highly influenced by water and humidity, making it prone to imbibition and challenging to remove from the patient's mouth due to its stiffness. PVS, known for its superior qualities (fine detail, elastic recovery, dimensional stability), is expensive but offers significant advantages, including a long pouring time. Ryan highlights the clinical significance of PVS's sensitivity to latex gloves and rubber dams, a common board exam question.
Mindmap
Keywords
💡Prosthodontics
💡Dental Impression Materials
💡Tissue Management
💡Fluid Control
💡Tissue Displacement
💡Hydrocolloid
💡Alginate
💡Elastomeric Impression Materials
💡Imbibition
💡Evaporation
💡Polyether
💡Addition Silicone (PVS)
Highlights
Introduction to dental impression materials and their importance for board exams.
Tissue management for taking proper impressions involves fluid control and tissue displacement.
Fluid control methods include local measures of isolation like cotton rolls and suction.
Tissue displacement methods include retraction cords, which can be impregnated with medicaments like aluminum chloride, iron sulfate, or epinephrine.
Electrosurgery is another method for tissue displacement but is contraindicated for patients with implanted pacemakers or insulin pumps.
Aqueous hydrocolloid impression materials include reversible hydrocolloid (agar) and irreversible hydrocolloid (alginate).
Agar can change between sol and gel phases with temperature changes, allowing for reuse, but requires a complex procedure.
Alginate is commonly used in dental practice for its quick setting time but is not recommended for final impressions due to its lower accuracy.
Setting and working times for alginate can be adjusted by using hotter or colder water and by changing the water-to-powder ratio.
Imbibition and syneresis are phenomena affecting hydrocolloids, causing them to swell or shrink, which distorts impressions.
Non-aqueous elastomeric impression materials include polysulfide rubber, condensation silicone, polyether, and addition silicone (PVS).
Polysulfide rubber is moisture-tolerant but prone to syneresis, requiring quick pouring of impressions.
Condensation silicone leaves an alcohol by-product, which can cause shrinkage and distortion.
Polyether is hydrophilic, stable, but can swell with water, making it difficult to remove from the patient's mouth and prone to breaking teeth from casts.
Addition silicone (PVS) offers the best fine detail, elastic recovery, and dimensional stability with no byproducts, but is expensive and inhibited by latex gloves.
A summary of all discussed impression materials: agar, alginate, polysulfide rubber, condensation silicone, polyether, and PVS.
Announcement of the launch of the creator's Patreon page for supporting and accessing extra materials.
Transcripts
hey everyone Ryan here and welcome back
to our prosthodontics series in this
video we're going to talk about dental
impression materials and I'm really
excited about this video because there
are so many boards questions that come
from this topic and I know it's been a
topic that's been requested for quite
some time so I'm really excited to cover
this information so first we have to
talk about tissue management for taking
proper impressions and tissue management
has two components fluid control which
includes both the saliva and the
gingival crevicular fluid and tissue
displacement so the idea of both of
these components is to provide clear
access to the crown prep for taking a
clean accurate impression so for fluid
control we typically employ local
measures of isolation like cotton rolls
and suction anti style gags which are a
type of medication aren't typically
employed for this purpose tissue
displacement we can use a number of
options
retraction cords are probably the most
prevalent we place them right under
where the margin of the prep was
prepared and into the periodontal
apparatus as used to stretch the
circumferential of periodontal fibers
out of the way in order for us to get a
clean accurate impression so we can also
impregnate those cords with certain
medicament aluminum chloride iron
sulfate or even epinephrine these are
all commonly employed in practice and so
this is if we have a cord placed with
something that's going to be preventing
bleeding of which all of these things do
they're promoting hemostasis in other
words blood is another fluid that can
get in our way and can mess up an
otherwise perfect impression so these
things are often used and cords are
often soaked in these medicaments in
order to prevent bleeding
electrosurgery can also be used but it's
contraindicated with certain patients
they have implanted pacemakers or
insulin pumps and the electrode must not
contact the teeth all right so let's
dive into impression materials this is a
helpful flow chart I think for laying
out the different categories of
impressions the main two are the aqueous
hydrocolloid and these are all the water
based impression materials where you mix
a powder with water and the non aqueous
elastomers and these elastomeric
impression materials are not water based
and you do not mix a powder with water
so let's talk about this first category
first so the reversible hydrocolloid
otherwise known as agar so agar was the
first successful elastic impression
material used in dentistry and it's
unique and that it can change between
two phases a Sala phase think of soul as
being short for solution and a gel phase
just by changing the temperature so it's
softened by heating and hardened by
cooling back and forth so it can be
reused several times in this manner
simply by changing the temperature which
explains why it's called reversible it
is a highly accurate material but it
requires a complex procedure with
multiple water baths of different
temperatures so that we can take
advantage of this phase change so it's
not used routinely in practice although
it is very accurate so this word
hydrocolloid is pretty interesting
colloid refers to particles of one
substance that are evenly dispersed
throughout another substance and if it's
a hydrocolloid that means one of those
substances is water
so a very basic definition would be a
mixture within water and that's exactly
what the two hydrocolloids
our first one we just talked about the
second one is the irreversible
hydrocolloid which is alginate and so
this is talking about how once we set
the material it can't be changed back
into a different phase so alginate is
commonly commonly used in dental
practice it's setting time is pretty
quick in three to four minutes in the
patient's mouth and it should be poured
with gypsum within ten minutes so you
don't have a whole lot of time to take
advantage of the impression and to pour
it in with dental plaster or dental
stone and we're gonna talk all about
gypsum materials in the next video the
primary ingredient of alginate is
diatomaceous earth the active ingredient
is potassium alginate where it gets its
name so for this material
you essentially mix a powder into water
and a lot of clinicians and assistants
mix the water into the powder myself
included but mixing the powder into the
water is supposed to reduce the amount
of bubbles formed and result in an
overall cleaner mix so how I remember
this is P comes before W in the alphabet
and so the supposed recommended method
is to pour the powder into a bowl of
already prepared water so just remember
that P comes before W in the alphabet
and you can remember this now the
problem with alginate is it has the
worst accuracy of the materials that
we're talking about in this video so
while it's perfectly acceptable for
diagnostic impressions this is one
material I absolutely would not
recommend for taking final impressions
for a crown or bridge where you need
really really good
accuracy now here's some really critical
information you will certainly get board
questions on this so we need to know
what increases and decreases the setting
time and the working time of impression
materials specifically the hydrocolloids
like alginate so setting time is how
long it takes for the material to
completely set whereas working time is
how long you have to use it before it
starts to set so they're pretty similar
and for the purposes of this this
information here we can interchange
setting and working so for decreasing
the setting time we could use hotter
water or just use less of it so we can
also call using less water a decreased
water to powder ratio so these are
things that we can do to influence the
setting time if we use hot water or just
less of it or both the material is going
to set a whole lot faster than normal
and remember usually three to four
minutes is our typical setting time if
we wanted to increase the amount of
setting time say we're taking a longer
than usual time to mix the material or
we just usually you want to decrease the
setting time for patient comfort but if
we want it to increase we would just do
the opposite so instead of using hotter
water we'd use colder water and we could
increase the water to powder ratio so
these things are incredibly important to
memorize I would just recommend
memorizing one of these columns and then
just remembering that the other one is
exactly opposite to that okay now we can
talk about both the hydrocolloids this
slide was more pertinent for just the
alginate component but this one we can
talk about both agar and alginate and
this is really
information to know for the board
questions as well imbibition is the
absorption of water so I use these
images of Spongebob to very eloquently
illustrate these phenomena so imp
abyssion is the absorption of water so
if you were to leave the alginate
impression in a bowl of water for
instance after it has set it would
absorb some of the water in the bowl and
swell up and distort maybe not to this
extent but it would still be noticeable
when you poured it likewise if you were
to leave the alginate impression out on
the table water would evaporate from it
and it would shrink up and distort in
that way and that's sinha resis the
exact opposite the loss of water so we
have to be careful when we're talking
about hydrocolloids to avoid imbibition
and cinah resis both of which distort
the impression and then distort the
model that we pour from that impression
which causes problems so the perfect
balance is to spray a small amount of
disinfectant onto the impression wrap it
in a moist paper towel and then pour it
in plaster or stone within that ten
minutes not waiting too much longer than
that and again this applies to both
hydrocolloids both agar and alginate so
a boards question could ask which of the
following impression materials are
affected by imbibition or cinta rhesus
and you've looked for either alginate or
agar reversible or irreversible
hydrocolloid now there are two
exceptions where later I will share with
you that one of the elastomeric
materials is affected by senna rhesus
and one of them is affected by
imbibition so keep an eye out for that
alright now we're into the elastomeric
the non aqueous impression materials the
first of which is poly sulphide rubber
so this impression material leaves
a water byproduct for some reason this
is really important to know for the
board exam so definitely memorize that
polysulfides rubber is moisture tolerant
so we can also sort of call this
hydrophobic and hydrophobic from our
chemistry days it means that something's
water fearing or it's scared of water
and won't mix with it and for this exact
reason this is why we have a water by
product because this impression material
won't mix with the water that's present
in the oral cavity and we'll leave a
water by-product it's also because of
this reason very prone to sinner rhesus
or drying out the evaporation or loss of
water to the environment so that's one
of the first exceptions I was talking
about this one we have to pour within 30
to 45 minutes
remember alginate we had ten minutes
this one we have a little bit longer
because it's not quite as finicky as
something like alginate with the
imbibition and cinah rhesus alright next
we have condensation silicone so
condensation silicone was actually the
first type of silicone impression
material used in dentistry this one
leaves an alcohol by-product again these
byproducts are really important to know
for the board exam so definitely
memorize that and this by-product can
cause the shrinkage of the impression
when it's evaporated so again another
form of distortion not the quite the
same as Sinha rhesus which is talking
about the loss of water first
condensation silicone we're talking
about alcohol this one AB similar
timeframe about 30 minutes to pour this
one up all right the next impression
material is poly ether polyter has some
really important facts that I can almost
guarantee will occur
and pop up on the board exam as many of
these things certainly well this is
probably one of the more important
videos I've made on this channel so
definitely let's keep an eye out for
these facts polyether impression
material is very stable but easily
influenced by water and the humidity of
the room that you're in so this is
complete opposite to the poly sulphide
rubber in this one we're talking about a
material that's hydrophilic so
hydrophilic means it's water loving so
it likes to mix with water and so it can
swell up and be affected even by the
relative humidity in the room and
because of this it's prone to imbibition
or swelling up with water now since it
loves water can actually function quite
well with a very wet oral cavity but it
is prone to imbibition and distortion in
that way now another thing is that it's
also really hard to remove from the
patient's mouth because it's so stiff
it's a very very stiff material once it
sets and not only is it hard to get out
of patients mouth it sticks to their
teeth it's very easy to break teeth from
the cast
after the gypsum has set so you're
pulling you've poured this material you
pour this impression with gypsum it it
sets into you a nice dental cast you
have to then remove this impression from
that cast and it's very easy to break
teeth off just because of how rigid and
how stiff polyether is now good news is
you have an hour before you have to pour
this one so you have a little bit more
time to work with if you're busy now the
last impression material I'm going to be
talking about in this video is addition
silicone also known as PVS PVS is
awesome it's a great material it
very expensive but it's the best
material basically has the best of
everything it has no byproducts no water
no alcohol no byproducts at all the PV S
stands for polyvinyl siloxane if you're
curious it provides the best fine detail
the best elastic recovery and the best
dimensional stability again basically
offers the best of everything you have a
whole lot of time to pour it up 60 plus
minutes you can even honestly you can
even probably wait weeks to pour this up
because of how stable it is but it's
recommended to do so in at least a
couple days the only negative besides it
being expensive is that it's inhibited
by the sulfur in latex gloves and the
rubber dam so the fact that it gets
affected by latex gloves is clinically
significant and it's also a very very
common boards question so definitely
remember that one so those are all of
the impression materials we have talked
about we talked about the aqueous
hydrocolloids agar and alginate and we
talked about the four non aqueous
elastomers polysulfides rubber
condensation silicone poly ether and
addition silicone otherwise known as PVS
so thanks so much for watching everyone
i'm really excited to announce that i
recently launched my patreon page so if
you're interested in supporting me there
and unlocking extras like access to my
video slides to take notes on go check
that out will link will be in the
description thanks so much for watching
everyone and I'll see you all in the
next video
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