Prosthodontics | Lab Processing of Crowns | INBDE, ADAT

Mental Dental
18 Jul 201909:42

Summary

TLDRThis 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

  • ๐Ÿฆท The final video in the prosthodontics series discusses lab processing of crowns, detailing the steps from impression to final crown delivery.
  • ๐Ÿ—ฟ 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.
  • ๐Ÿ” 'Ditching a die' is the process of cleaning the margin of the prepared tooth to ensure it's clearly visible for accurate crown fitting.
  • ๐Ÿ–Œ 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.
  • ๐Ÿ”„ Understanding positive and negative reproductions is crucial for lab processing, starting with an impression (negative) and creating a cast or model (positive).
  • ๐Ÿ•ฏ 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.
  • ๐Ÿ—๏ธ Speuming involves attaching wax channels (sprues) to the wax crown to create a path for the metal during the casting process.
  • ๐Ÿบ Investing covers the wax and sprue with investment material to create a mold for the metal crown.
  • ๐Ÿ”ฅ Burn out is the process of melting out the wax to leave a void in the investment material for the metal to be cast.
  • ๐Ÿ—๏ธ Casting involves pouring molten metal into the investment material to create the metal framework of the crown.
  • ๐Ÿ’ง Quenching cools the hot cast metal, making it more malleable for finishing and delivery to the patient.
  • ๐Ÿ“Š 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

๐Ÿฆท 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

๐Ÿ”ฅ 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.

Mindmap

Keywords

๐Ÿ’กProsthodontics

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.

๐Ÿ’กMaster 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.

๐Ÿ’กDie

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.

๐Ÿ’กDitching 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.

๐Ÿ’กDie 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.

๐Ÿ’กWaxing

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.

๐Ÿ’กSprue

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.

๐Ÿ’กInvesting

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.

๐Ÿ’กBurn 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.

๐Ÿ’กCasting

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.

๐Ÿ’กQuenching

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.

๐Ÿ’กPorosity

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

play00:00

hey everyone Ryan here and welcome back

play00:03

to our prosthodontics series this will

play00:06

be the last video in the series and

play00:08

we'll be talking about lab processing of

play00:10

crowns so let's set the scene

play00:14

we took a final impression of the crown

play00:16

prep poured it in dental stone and then

play00:19

we have a master cast which is a replica

play00:22

of the whole dental arch or maybe just

play00:24

the quadrant we're working on then we

play00:27

make what's called a die for the tooth

play00:30

receiving the crown and the die refers

play00:33

to this positive reproduction of the

play00:36

prepared tooth now with the die we have

play00:40

two processes that need to take place

play00:43

ditching a die exposes the margin of the

play00:46

prep and ditching a die basically

play00:49

involves scraping and cleaning away any

play00:52

stone below the margin so that it's

play00:55

clearly visible and this margin is

play00:57

clearly visible 360 degrees around the

play01:00

prepare tooth and so we remove any

play01:03

excess stone that could be obfuscating

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that margin the second process is

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painting on what's called die spacer to

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allow room for cements and that's shown

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in the bottom right picture die spacer

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is this thin painted on material that

play01:21

accounts for the cement layer and we

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want a thin film thickness of cement

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between the intaglio surface of the

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crown and the prepared tooth and this

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creates that miniscule amount of space

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that we need so I think it's very

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helpful to talk about positive and

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negative reproductions with the lab

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processing portion so you start with an

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object that you want to reproduce like

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the crown of a tooth in this case what

play01:50

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

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an imprint of it which we call a

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negative reproduction in the dental

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world we would make an impression which

play02:02

is a negative imprint of the teeth and

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soft tissues and then from this mold a

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positive reproduction can be made in the

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form of a cast or a model

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and the positive is a an exact replica

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or close to it of the original object

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and the negative is a template for that

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object so when I go through the steps of

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lab processing I want you to think in

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terms of positive and negative

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reproductions and what each step

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constitutes because will basically be

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going from this to this to this alright

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so step one after making the dye and

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ditching it painting on the dye spacer

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is going to be waxing and waxing

play02:47

involves making a positive of the object

play02:50

that you eventually want to make and so

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essentially we're building the crown on

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the dye out of wax and wax is a great

play02:59

material because it can be easily

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manipulated with hot and cold

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instruments and it keeps this form when

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you're done waxing teeth is often one of

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the first things dental students will do

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in the sim lab and it's often dreaded at

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first and very frustrating but it can

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become quite enjoyable and even relaxing

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after some practice so this is an

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absolutely gorgeous wax up of tooth

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number 14 now wax isn't perfect though

play03:25

and it builds up internal stress as it's

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manipulated and these stresses will

play03:30

relax over time causing distortion and

play03:32

shape and contour so now we have a

play03:36

positive for our crown the second step

play03:40

is spewing and this involves making a

play03:43

path with wax for the metal to go into

play03:46

the prosthesis as it's being created and

play03:49

so this is a pile of wax sprues they're

play03:54

pre-made and you want to attach the

play03:56

sprue to a base and then attach it to

play03:59

the crown in the area of biggest bulk so

play04:03

this is being attached to the thickest

play04:05

point of that wax up usually at a cusp

play04:08

or incisal edge the third step is

play04:13

investing and this is where we make a

play04:16

negative by covering that wax and the

play04:20

sprue with investment material and the

play04:25

same process is done for making dentures

play04:27

and these investments are critical to

play04:31

know for the board exam and you'll very

play04:33

likely get a question on this and I have

play04:36

a quick easy way to remember these so a

play04:39

gypsum bonded investment will be used

play04:42

for making gold crowns and you just have

play04:45

to remember G&G phosphate bonded

play04:49

investments are used for the fabrication

play04:51

of pfm crowns and you just have to

play04:53

remember P and P and lastly silica

play04:56

bonded investments are used for base

play04:59

metal crowns and base metal being the

play05:01

only one up here that contains an S you

play05:04

match that up with the S of silica so

play05:07

those three things definitely remember

play05:09

that for the board exam nice and easy to

play05:11

memorize an easy question there alright

play05:17

step four is called burn out and this is

play05:20

where we melt out the wax positive to

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leave room for the metal to take its

play05:25

place so you're essentially left with a

play05:27

void in the investment material where

play05:30

the waxed up crown was and where the

play05:32

sprue was step number five is called

play05:37

casting and this is where we melt metal

play05:40

into the investment so that sprue left a

play05:44

path for the metal to flow into and we

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melt metal where the void was and now

play05:53

step six is recovery so we retrieve the

play05:56

cast framework by breaking open that

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investment and here is our positive

play06:01

reproduction instead of wax now it's

play06:04

made in gold and finally step seven is

play06:09

called quenching this is where the very

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hot cast metal is immediately placed in

play06:14

cool water to make it more malleable for

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finishing and this involves removing the

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sprue polishing and finally delivering

play06:23

the crown to the patient so this is a

play06:29

great summary slide I really like this

play06:31

picture because it shows all the steps

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and clearly labels all the portions of

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the diagram so we started with a wax

play06:40

pattern

play06:40

on the die we added this sprue to it we

play06:44

covered it with an investment material

play06:46

we melted out the wax in the sprue we

play06:49

poured in cast metal material broke open

play06:52

the investment and finally remove the

play06:54

sprue polish the crown and delivered it

play06:57

to the patient and everything's really

play06:59

nice and color coded the blue color is

play07:02

for the wax this purple black is for the

play07:05

sprue wax the gray is for the investment

play07:08

the white symbolizes the void in the

play07:11

investment and the gold shows the gold

play07:14

medal so this is a great picture to

play07:18

study to help summarize everything that

play07:20

we talked about and just important to

play07:23

note there are some dimensional changes

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through all these steps there's some

play07:27

shrinkage and expansion but they sort of

play07:29

even eachother out over this process and

play07:32

it's very minimal especially for a gold

play07:36

crown the amount of shrinkage and

play07:38

expansion is very minimal and finally

play07:43

let's talk about porosity issues related

play07:46

to errors during lab processing and

play07:48

there's some really good boards

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questions here as well porosity of

play07:52

porcelain is due to inadequate content

play07:55

condensing of the porcelain porosity of

play07:58

acrylic is related to to fast heating

play08:01

and this is we're talking about dentures

play08:04

here shrinkage porosity of the metal is

play08:08

due to the sprue being too thin and this

play08:12

prevents molten metal from flowing

play08:14

efficiently and effectively into the

play08:17

mold and backpressure porosity of the

play08:20

metal is due to the sprue being too

play08:23

short and this prevents venting of gas

play08:25

and that means that gas was still

play08:27

present in the area prohibiting fluid

play08:30

from flowing in so there are two

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different types of porosity which can be

play08:35

a little bit confusing the shrinkage

play08:37

form is due to the sprue being too thin

play08:39

the backpressure form is due to it being

play08:42

too short and that's definitely

play08:45

important to remember for the board exam

play08:46

because it could be easily confused just

play08:49

with a couple words being different

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all right so congratulations you made it

play08:56

to the end of the prosthodontics series

play08:58

I know there is a lot of material and a

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lot of high-yield facts to help you do

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well on the board exam so next I'll work

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on a video with practice questions

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testing all the concepts I went over in

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this lecture series but that's it for

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this video thank you so much for

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watching if you're interested in

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supporting my channel please check out

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my patreon page a huge thank you to

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Michael Raja and all of my patrons for

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their support you can unlock things like

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access to my video slides if you want to

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take notes on them and exclusive

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practice questions so go check that out

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if you're interested the link is in the

play09:35

description thanks again for watching

play09:37

everyone I'll see you all in the next

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video

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Related Tags
ProsthodonticsCrown CraftingDental LabMaster CastDie SpacerWaxing ProcessInvestment MaterialCasting TechniquePorosity IssuesBoard Exam Prep