Prosthodontics | Impression Materials | INBDE, ADAT

Summary

In 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

00:00

🦷 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.

05:03

🌊 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.

10:05

⚖️ 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.

15:05

🔄 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.

Keywords

💡Prosthodontics

Prosthodontics is a dental specialty that focuses on the restoration and replacement of missing or damaged teeth. In the context of the video, it is the overarching theme as the speaker discusses various dental impression materials used in this field. The script mentions a 'prosthodontics series,' indicating a sequence of videos dedicated to this specialty.

💡Dental Impression Materials

Dental impression materials are substances used to capture the shape and structure of a patient's teeth and surrounding tissues. They are essential for creating accurate dental prosthetics. The video script delves into different types of these materials, explaining their properties and applications in prosthodontics.

💡Tissue Management

Tissue management is a critical aspect of taking dental impressions, involving techniques to control fluids and displace tissues to ensure a clear path to the crown preparation area. The script discusses the importance of fluid control and tissue displacement for obtaining clean and accurate impressions.

💡Fluid Control

Fluid control in dental impressions refers to the management of saliva and gingival crevicular fluid to prevent interference with the impression process. The script mentions local measures such as cotton rolls and suction as methods to control these fluids.

💡Tissue Displacement

Tissue displacement involves techniques to move soft tissues out of the way to access the area of interest for impression taking. The script describes the use of retraction cords soaked in medicaments to achieve this, which also helps in preventing bleeding and promoting hemostasis.

💡Hydrocolloid

Hydrocolloid refers to a category of impression materials that include water as a component. The script differentiates between reversible hydrocolloids like agar, which can change phases with temperature, and irreversible hydrocolloids like alginate, which cannot revert to its original state once set.

💡Alginate

Alginate is an irreversible hydrocolloid used for taking dental impressions. It is known for its quick setting time and is commonly used in dental practice, although it is not recommended for highly accurate final impressions due to its lower accuracy compared to other materials.

💡Elastomeric Impression Materials

Elastomeric impression materials are non-aqueous, rubber-like materials that do not require mixing with water. The script discusses various types, including poly sulphide rubber, condensation silicone, poly ether, and addition silicone, highlighting their unique properties and clinical applications.

💡Imbibition

Imbibition is the absorption of water by an impression material, which can cause it to swell and distort. The script warns against leaving alginate impressions in water, as this can lead to imbibition, affecting the accuracy of the final model.

💡Evaporation

Evaporation refers to the loss of water from an impression material, leading to shrinkage and distortion. The script contrasts imbibition with evaporation, noting that both processes can negatively impact the accuracy of dental impressions.

💡Polyether

Polyether is a type of elastomeric impression material that is hydrophilic, meaning it readily absorbs water and can be influenced by humidity. The script points out that polyether is prone to imbibition and is challenging to remove from the patient's mouth due to its stiffness.

💡Addition Silicone (PVS)

Addition silicone, also known as PVS (polyvinyl siloxane), is an elastomeric impression material that offers excellent fine detail, elastic recovery, and dimensional stability. The script emphasizes its lack of byproducts and its resistance to distortion, although it mentions that it is inhibited by sulfur in latex gloves.

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

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description thanks so much for watching

everyone and I'll see you all in the

next video