Prosthodontics | Lab Processing of Crowns | INBDE, ADAT
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
- ๐ฆท The final video in the prosthodontics series discusses lab processing of crowns, detailing the steps from impression to final crown delivery.
- ๐ฟ 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.
- ๐ 'Ditching a die' is the process of cleaning the margin of the prepared tooth to ensure it's clearly visible for accurate crown fitting.
- ๐ 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.
- ๐ Understanding positive and negative reproductions is crucial for lab processing, starting with an impression (negative) and creating a cast or model (positive).
- ๐ฏ 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.
- ๐๏ธ Speuming involves attaching wax channels (sprues) to the wax crown to create a path for the metal during the casting process.
- ๐บ Investing covers the wax and sprue with investment material to create a mold for the metal crown.
- ๐ฅ Burn out is the process of melting out the wax to leave a void in the investment material for the metal to be cast.
- ๐๏ธ Casting involves pouring molten metal into the investment material to create the metal framework of the crown.
- ๐ง Quenching cools the hot cast metal, making it more malleable for finishing and delivery to the patient.
- ๐ 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
๐ฆท 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.
๐ฅ 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
๐กProsthodontics
๐กMaster Cast
๐กDie
๐กDitching a Die
๐กDie Spacer
๐กWaxing
๐กSprue
๐กInvesting
๐กBurn Out
๐กCasting
๐กQuenching
๐กPorosity
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
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