Prosthodontics | Lab Processing of Crowns | INBDE, ADAT

Summary

This final video in the prosthodontics series delves into the lab processing of crowns, detailing the steps from taking a final impression to delivering the crown. It covers the creation of a master cast, die preparation, waxing, investing, burn out, casting, and quenching. The video also addresses common issues like porosity in materials and provides a mnemonic for remembering types of investments. It concludes with a summary slide and a promise of upcoming practice questions for board exam preparation.

Takeaways

• 🦷 The final video in the prosthodontics series discusses lab processing of crowns, detailing the steps from impression to final crown delivery.
• 🗿 The master cast is a replica of the dental arch or quadrant being worked on, and a die is created for the tooth receiving the crown.
• 🔍 'Ditching a die' is the process of cleaning the margin of the prepared tooth to ensure it's clearly visible for accurate crown fitting.
• 🖌 Die spacer is applied to the die to account for the cement layer, ensuring a thin film of cement between the crown and the tooth.
• 🔄 Understanding positive and negative reproductions is crucial for lab processing, starting with an impression (negative) and creating a cast or model (positive).
• 🕯 Waxing is the step where the crown is built on the die using wax, which is easily manipulated but can cause distortion due to internal stress.
• 🗝️ Speuming involves attaching wax channels (sprues) to the wax crown to create a path for the metal during the casting process.
• 🏺 Investing covers the wax and sprue with investment material to create a mold for the metal crown.
• 🔥 Burn out is the process of melting out the wax to leave a void in the investment material for the metal to be cast.
• 🗝️ Casting involves pouring molten metal into the investment material to create the metal framework of the crown.
• 💧 Quenching cools the hot cast metal, making it more malleable for finishing and delivery to the patient.
• 📊 There are dimensional changes and porosity issues to be aware of during lab processing, such as shrinkage and expansion, and different types of porosity related to sprue design.

Q & A

What is the purpose of the final impression in the process of crown preparation?

The final impression is used to create a master cast, which is a replica of the whole dental arch or the specific quadrant being worked on. This cast is essential for accurately reproducing the crown.

What is the term used for the positive reproduction of the prepared tooth?

The term used for the positive reproduction of the prepared tooth is 'die'.

What is the process of 'ditching a die' and why is it important?

Ditching a die involves scraping and cleaning away any stone below the margin of the prepared tooth so that it is clearly visible 360 degrees around the tooth. This is important to ensure that the margin is accurately reproduced in the final crown.

What is the purpose of applying a die spacer?

A die spacer is applied to allow room for the cement layer. It creates a thin film thickness of cement between the intaglio surface of the crown and the prepared tooth, which is necessary for a proper fit.

What is the significance of understanding positive and negative reproductions in lab processing?

Understanding positive and negative reproductions helps in the process of creating an accurate replica of the tooth or dental arch. A negative reproduction is the initial mold or imprint, and a positive reproduction is the final cast or model used for making the crown.

What material is typically used for waxing the crown during the lab processing of crowns?

Wax is used for building the crown on the die. It is chosen because it can be easily manipulated with hot and cold instruments and maintains its form once the waxing is completed.

What is the purpose of 'spuing' in the lab processing of crowns?

Spuing involves making a path with wax for the metal to flow into during the creation of the prosthesis. It is essential for ensuring that the metal can be properly cast into the shape of the crown.

What is the term used for the process of covering the wax and sprue with investment material?

The process of covering the wax and sprue with investment material is called 'investing'.

What are the three types of investments mentioned in the script and their respective uses?

Gypsum bonded investments are used for making gold crowns, phosphate bonded investments are used for the fabrication of PFM (porcelain-fused-to-metal) crowns, and silica bonded investments are used for base metal crowns.

What is the process called where the wax positive is melted out to leave room for the metal?

The process is called 'burn out', where the wax positive is melted out, leaving a void in the investment material for the metal to take its place.

What is the final step in the lab processing of crowns before delivering it to the patient?

The final step is 'quenching', where the hot cast metal is immediately placed in cool water to make it more malleable for finishing, after which the sprue is removed, the crown is polished, and it is delivered to the patient.

Outlines

00:00

🦷 Lab Processing of Crowns

This paragraph introduces the final video in the prosthodontics series, focusing on the lab processing of crowns. The process begins with taking a final impression of the crown preparation, creating a master cast, and making a die for the tooth receiving the crown. Two key processes are highlighted: 'ditching' the die to expose the margin of the preparation and painting on a 'die spacer' to allow room for cement. The concept of positive and negative reproductions is explained, with the lab processing involving transitions from negative to positive reproductions. The first step in lab processing is 'waxing,' where a crown is built on the die using wax, a material that can be easily manipulated. The paragraph concludes by emphasizing the importance of understanding these steps and the materials involved, especially for dental students preparing for board exams.

05:02

🔥 Steps in Crown Fabrication

This paragraph delves deeper into the steps involved in crown fabrication, starting with waxing and moving through to the final delivery of the crown. After waxing, the next steps include 'spuing' where wax sprues are attached to the wax crown, 'investing' where the wax and sprue are covered with investment material, and 'burn out' where the wax is melted out to leave a void for the metal. The 'casting' step involves melting metal into the investment, followed by 'recovery' where the cast framework is retrieved by breaking open the investment. The final steps include 'quenching,' where the hot cast metal is cooled in water to make it malleable, and then the crown is polished and delivered to the patient. The paragraph also discusses potential porosity issues related to errors in lab processing, such as inadequate content condensing of porcelain, too fast heating of acrylic, sprue being too thin, or too short. The importance of these details for board exam preparation is emphasized, and the video concludes with a summary slide that visually represents the entire process.

Keywords

💡Prosthodontics

Prosthodontics is a specialized field in dentistry that focuses on the diagnosis, treatment, and management of conditions affecting the oral and maxillofacial regions, particularly those requiring the restoration of form and function through the use of prosthetic devices. In the video, the theme revolves around the lab processing of crowns, which is a key aspect of prosthodontics.

💡Master Cast

A master cast in dental prosthetics is a precise replica of a patient's dental arch or the specific area being treated. It serves as a foundation for the creation of dental restorations like crowns. In the script, the master cast is derived from a final impression and is essential for the lab processing of crowns.

💡Die

In dental terminology, a die refers to a positive reproduction of a prepared tooth, used as a model for the fabrication of dental restorations. The script explains the process of creating a die from the master cast, which is a crucial step in ensuring that the crown fits accurately onto the prepared tooth.

💡Ditching a Die

Ditching a die is the process of exposing the margin of the prepared tooth on the die by removing any excess stone material below the margin. This ensures that the margin is clearly visible for accurate crown placement. The script describes this step as critical for the visibility of the margin 360 degrees around the prepared tooth.

💡Die Spacer

Die spacer is a thin, painted-on material applied to the die to account for the thickness of the cement layer that will be used to bond the crown to the tooth. The script mentions that the die spacer is essential for allowing room for cement, ensuring a thin film of cement between the crown and the tooth.

💡Waxing

Waxing in dental lab processing involves creating a positive model of the dental restoration, such as a crown, using wax. The script describes waxing as an essential step where the crown is built on the die out of wax, which can be easily manipulated to achieve the desired shape.

💡Sprue

A sprue in dental casting is a channel or pathway through which molten metal is poured into the investment material to create a dental restoration. The script explains that sprues are attached to the wax crown at the area of greatest bulk to facilitate the flow of metal during the casting process.

💡Investing

Investing is the process of covering the wax pattern and sprue with an investment material, which hardens to create a mold for the dental restoration. The script mentions different types of investments based on the material of the crown being fabricated, such as gypsum bonded, phosphate bonded, and silica bonded investments.

💡Burn Out

Burn out is the step in the dental casting process where the wax pattern and sprue are melted out, leaving a void in the investment material. This step prepares the mold to receive the molten metal. The script describes burn out as a critical phase that creates the space for the metal to take the shape of the dental restoration.

💡Casting

Casting in dental lab processing refers to the act of pouring molten metal into the investment material to create the dental restoration. The script explains that casting follows the burn out process, where the metal fills the void left by the wax pattern and sprue.

💡Quenching

Quenching is the final step in the dental casting process, where the hot cast metal is cooled rapidly, usually by placing it in water, to make it more malleable for finishing. The script mentions quenching as the step that follows the casting process, preparing the crown for polishing and delivery to the patient.

💡Porosity

Porosity in dental materials refers to the presence of small holes or voids within the material, which can affect its strength and quality. The script discusses different types of porosity related to dental lab processing, such as porcelain porosity due to inadequate condensing, acrylic porosity due to rapid heating, shrinkage porosity in metal due to a thin sprue, and backpressure porosity due to a short sprue.

Highlights

Introduction to the final video in the prosthodontics series focusing on lab processing of crowns.

Explanation of the process starting with a final impression of the crown prep and creating a master cast.

The importance of 'ditching a die' to expose the margin of the prep clearly for 360 degrees.

Application of die spacer to allow room for cement, ensuring a thin film thickness between the crown and tooth.

Concept of positive and negative reproductions in lab processing, starting with an object and creating a mold.

The process of waxing, creating a positive of the crown on the die using wax for easy manipulation.

Internal stress in wax and its effects on the shape and contour of the crown over time.

The step of 'spuing', attaching wax sprues to the crown for the metal to flow during the prosthesis creation.

Investing process, covering wax and sprue with investment material for the creation of a negative mold.

Memorization tips for different types of investments used for various crown materials.

Burn out step, melting out the wax positive to prepare for metal casting.

Casting step, pouring molten metal into the investment to create the crown framework.

Recovery of the cast framework, breaking open the investment and retrieving the gold crown.

Quenching process, cooling the hot cast metal to make it more malleable for finishing.

Summary of the entire lab processing steps with a color-coded diagram for better understanding.

Discussion on dimensional changes and shrinkage/ expansion throughout the lab processing steps.

Exploration of porosity issues in lab processing related to errors such as inadequate porcelain condensing, fast heating of acrylic, and improper sprue dimensions.

Conclusion of the prosthodontics series and upcoming practice questions video announcement.

Transcripts

hey everyone Ryan here and welcome back

to our prosthodontics series this will

be the last video in the series and

we'll be talking about lab processing of

crowns so let's set the scene

we took a final impression of the crown

prep poured it in dental stone and then

we have a master cast which is a replica

of the whole dental arch or maybe just

the quadrant we're working on then we

make what's called a die for the tooth

receiving the crown and the die refers

to this positive reproduction of the

prepared tooth now with the die we have

two processes that need to take place

ditching a die exposes the margin of the

prep and ditching a die basically

involves scraping and cleaning away any

stone below the margin so that it's

clearly visible and this margin is

clearly visible 360 degrees around the

prepare tooth and so we remove any

excess stone that could be obfuscating

that margin the second process is

painting on what's called die spacer to

allow room for cements and that's shown

in the bottom right picture die spacer

is this thin painted on material that

accounts for the cement layer and we

want a thin film thickness of cement

between the intaglio surface of the

crown and the prepared tooth and this

creates that miniscule amount of space

that we need so I think it's very

helpful to talk about positive and

negative reproductions with the lab

processing portion so you start with an

object that you want to reproduce like

the crown of a tooth in this case what

you'll need to do is to take a mold or

an imprint of it which we call a

negative reproduction in the dental

world we would make an impression which

is a negative imprint of the teeth and

soft tissues and then from this mold a

positive reproduction can be made in the

form of a cast or a model

and the positive is a an exact replica

or close to it of the original object

and the negative is a template for that

object so when I go through the steps of

lab processing I want you to think in

terms of positive and negative

reproductions and what each step

constitutes because will basically be

going from this to this to this alright

so step one after making the dye and

ditching it painting on the dye spacer

is going to be waxing and waxing

involves making a positive of the object

that you eventually want to make and so

essentially we're building the crown on

the dye out of wax and wax is a great

material because it can be easily

manipulated with hot and cold

instruments and it keeps this form when

you're done waxing teeth is often one of

the first things dental students will do

in the sim lab and it's often dreaded at

first and very frustrating but it can

become quite enjoyable and even relaxing

after some practice so this is an

absolutely gorgeous wax up of tooth

number 14 now wax isn't perfect though

and it builds up internal stress as it's

manipulated and these stresses will

relax over time causing distortion and

shape and contour so now we have a

positive for our crown the second step

is spewing and this involves making a

path with wax for the metal to go into

the prosthesis as it's being created and

so this is a pile of wax sprues they're

pre-made and you want to attach the

sprue to a base and then attach it to

the crown in the area of biggest bulk so

this is being attached to the thickest

point of that wax up usually at a cusp

or incisal edge the third step is

investing and this is where we make a

negative by covering that wax and the

sprue with investment material and the

same process is done for making dentures

and these investments are critical to

know for the board exam and you'll very

likely get a question on this and I have

a quick easy way to remember these so a

gypsum bonded investment will be used

for making gold crowns and you just have

to remember G&G phosphate bonded

investments are used for the fabrication

of pfm crowns and you just have to

remember P and P and lastly silica

bonded investments are used for base

metal crowns and base metal being the

only one up here that contains an S you

match that up with the S of silica so

those three things definitely remember

that for the board exam nice and easy to

memorize an easy question there alright

step four is called burn out and this is

where we melt out the wax positive to

leave room for the metal to take its

place so you're essentially left with a

void in the investment material where

the waxed up crown was and where the

sprue was step number five is called

casting and this is where we melt metal

into the investment so that sprue left a

path for the metal to flow into and we

melt metal where the void was and now

step six is recovery so we retrieve the

cast framework by breaking open that

investment and here is our positive

reproduction instead of wax now it's

made in gold and finally step seven is

called quenching this is where the very

hot cast metal is immediately placed in

cool water to make it more malleable for

finishing and this involves removing the

sprue polishing and finally delivering

the crown to the patient so this is a

great summary slide I really like this

picture because it shows all the steps

and clearly labels all the portions of

the diagram so we started with a wax

pattern

on the die we added this sprue to it we

covered it with an investment material

we melted out the wax in the sprue we

poured in cast metal material broke open

the investment and finally remove the

sprue polish the crown and delivered it

to the patient and everything's really

nice and color coded the blue color is

for the wax this purple black is for the

sprue wax the gray is for the investment

the white symbolizes the void in the

investment and the gold shows the gold

medal so this is a great picture to

study to help summarize everything that

we talked about and just important to

note there are some dimensional changes

through all these steps there's some

shrinkage and expansion but they sort of

even eachother out over this process and

it's very minimal especially for a gold

crown the amount of shrinkage and

expansion is very minimal and finally

let's talk about porosity issues related

to errors during lab processing and

there's some really good boards

questions here as well porosity of

porcelain is due to inadequate content

condensing of the porcelain porosity of

acrylic is related to to fast heating

and this is we're talking about dentures

here shrinkage porosity of the metal is

due to the sprue being too thin and this

prevents molten metal from flowing

efficiently and effectively into the

mold and backpressure porosity of the

metal is due to the sprue being too

short and this prevents venting of gas

and that means that gas was still

present in the area prohibiting fluid

from flowing in so there are two

different types of porosity which can be

a little bit confusing the shrinkage

form is due to the sprue being too thin

the backpressure form is due to it being

too short and that's definitely

important to remember for the board exam

because it could be easily confused just

with a couple words being different

all right so congratulations you made it

to the end of the prosthodontics series

I know there is a lot of material and a

lot of high-yield facts to help you do

well on the board exam so next I'll work

on a video with practice questions

testing all the concepts I went over in

this lecture series but that's it for

this video thank you so much for

watching if you're interested in

supporting my channel please check out

my patreon page a huge thank you to

Michael Raja and all of my patrons for

their support you can unlock things like

access to my video slides if you want to

take notes on them and exclusive

practice questions so go check that out

if you're interested the link is in the

description thanks again for watching

everyone I'll see you all in the next

video