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Alginate | Agar | Impression Materials | Part 3 | Hydrocolloids | Dr. Rashmi Singh — Transcript

by Dr. Rashmi Singh · 8,304 words · 1,286 segments · language en · Watch on YouTube

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0:20Hi pitch dentists, I am Dr. Rashmi
0:22Singh and this is part three of
0:24impression materials where we are going
0:26to discuss hydrocolloid impression
0:27materials, especially agar and alginate
0:30in detail. This topic is not only
0:33important from an exam point of view
0:35but also very important clinically as
0:37it is one of the most used impression
0:39materials in dentistry. If you like my
0:42content then please subscribe, like,
0:44and share this video with your fellow
0:46dentists. So without any further ado,
0:49let's dive in. So, let's get started.
0:52Today we will discuss hydrocolloid
0:54impression materials. And primarily, we
0:57will study agar impression material and
1:00alginate in detail. So before starting
1:03these, let's first understand what a
1:05colloidal state is. We can understand
1:09it this way: whenever two substances
1:11are mixed or combined, for example, a
1:14solid and a liquid, they can change
1:16into some states. The first one is a
1:20solution. If these two substances mix
1:24completely with each other, then that
1:26gets converted into a solution. Okay?
1:29Like if we dissolve sugar in water,
1:32then in the end, when both are mixed,
1:35it forms a solution. Next is a
1:38suspension. Now, if the particle size
1:41of one of the substances we are mixing
1:44is greater than 200 millimicrons, then
1:47it creates a suspension instead of a
1:50solution. And the third is a colloidal
1:53state. It is an intermediate state.
1:56That means it has neither become a
1:57solution nor is it a suspension. It
2:00falls somewhere between the two, the
2:02colloidal state, which is not a true
2:04solution nor a suspension. Meaning, the
2:08particle size is between one to 200
2:12millimicrons. So, colloids are just
2:15microscopic suspensions of molecules in
2:18a dispersion medium. So now let's
2:21understand what a dispersion medium is.
2:23Now, a colloid has two phases. First is
2:26the dispersed phase, which means the
2:28particle we are dispersing, we call
2:30that the dispersed phase. And the
2:33medium in which we are dispersing those
2:35particles is called the dispersion
2:38medium. So, we were mixing two
2:39substances. One is the dispersed phase
2:42and the other is the dispersion medium.
2:45And when this medium is water, it is
2:48called hydro—or water—colloids. I
2:52hope you have understood this. Why do
2:54we call these hydrocolloids? Dispersed
2:57phase in a dispersion medium, and when
2:59this dispersion medium is water, then
3:02we call it hydrocolloids. These
3:06hydrocolloids usually exist in either a
3:09sol state, which means a viscous liquid
3:12state in which we take the impression,
3:14or a gel form, which we have to turn
3:17into a sol before taking the impression
3:19. Right? Now, this process of
3:24conversion from sol to gel, if it
3:26happens through a physical process,
3:29meaning through a temperature
3:31difference, then it occurs in agar and
3:34that is a kind of reversible reaction
3:36which we can reuse. And if it is
3:40converting from sol to gel through a
3:42chemical reaction, then it will be an
3:45irreversible reaction. And that happens
3:47in alginate impression material. Now,
3:51this material, as I mentioned, should
3:54be introduced into the patient's mouth
3:56in a sol state, meaning in a viscous
3:58liquid state, so that it has sufficient
4:01flow and can register the details. And
4:06after that, we leave it inside for a
4:08while to set so that it converts into a
4:10gel, meaning it sets before removing
4:12that impression, retrieving it from the
4:15patient's mouth. Now let's start with
4:19agar. We will study agar just like we
4:22break down every impression material.
4:24First is its content, so that it is
4:26easy for you to remember later and
4:29write in exams. Let's break it. First
4:32is introduction and application. How is
4:35it supplied? How is it dispensed? Then
4:38composition. What is the setting
4:40reaction? How do we manipulate it? Then
4:43what are the properties? The advantages
4:45and disadvantages. So, let's start with
4:48the introduction. In the introduction,
4:52whatever we studied in part one of
4:54impression materials in part one of the
4:57video, we will mention all those
5:00classifications. So, introduction means
5:05we introduce it. Meaning, what is it?
5:08What is it like? Let's start about agar
5:11. Agar is a reversible type of
5:13impression material. It is elastic.
5:15Thermoplastic, meaning we can modulate
5:18and manipulate it with temperature
5:20change. Second, it has a very high
5:22degree of accuracy and good surface
5:24reproduction of detail. Still, it is
5:27not used very often. We will see why.
5:30Then it is also called as agar-agar.
5:32Where does it come from? It is
5:34extracted from seaweed for dental agar.
5:37What is it? It is a blend of several
5:39species of agar-agar. Agar. Now, what
5:43is it chemically? It is a galactose
5:46sulfate that forms a colloid with water
5:48. Now, whenever we heat it, it
5:52liquefies. Liquefying means it had come
5:55in gel form. Now we will liquefy it.
5:58Meaning we will convert it into sol
5:59form so that we can take an impression.
6:01Now it converts to sol form. Actually,
6:04what happens is that the hydrogen bonds
6:07between them break. When it is heated
6:11to 70 to 100 ° Celsius, the helix
6:14structure uncoils and it gets converted
6:17into a sol, right? After that, we have
6:21converted it from gel to sol. Then we
6:25take the impression and then we let it
6:27cool. As soon as it cools, it
6:30solidifies again, the helix forms once
6:32more, and it gets converted into a gel
6:34again. So, this process is reversible
6:39in this agar impression material. All
6:43these points that I have written in the
6:46introduction are very important. And
6:49this is the only introduction you need
6:52to study, read, or even write in exams
6:55about agar. You don't need to read or
6:59write anything more than this for your
7:02exams. Let's see the applications. The
7:07primary major use of agar even today is
7:10for duplicating our models and casts,
7:13so that instead of making the
7:16prosthesis on the final impression we
7:19worked so hard to take, we duplicate it
7:22first. Like this, and then we make the
7:27prosthesis on it so that our final
7:30impression remains safe. Second is that
7:33we can take full-mouth impressions with
7:35deep undercuts. Very rarely, but a
7:37single impression can also be taken. Or
7:39to some extent, crown and bridge
7:41impressions can also be taken. But we
7:43don't take them nowadays. Mostly, we
7:48use agar to duplicate models and casts.
7:52Next, how is it dispensed; how do we
7:54get it in the market, either as a tray
7:56material? Supplied in a plastic or
7:59metallic disposable tube. As seen here
8:01in the photo. And second is the syringe
8:04material, which is supplied in small
8:06cylinders. The only difference is that
8:10the color is different and the fluidity
8:12is different. Less agar and more water
8:15in syringe material. After dispensing,
8:20let's see the composition. Now, we have
8:25already seen that we extract this agar
8:29from seaweed. Now, what is it
8:31chemically? This is an organic
8:34hydrophilic polysaccharide extracted
8:36from seaweed. Or it's a sulfuric ester
8:40of a linear polymer of galactose. If
8:44you can remember this, well and good.
8:46If you can't remember it, it is
8:47extracted from seaweed. And let's see
8:49the composition actually. It is very
8:52important for you to memorize this
8:54whole table. So, among the ingredients,
8:57the first one—since we are studying
8:59agar impression material—...is agar
9:02as an impression material. Which is 13
9:05to 17%, what is its function? It is a
9:09dispersed phase of the sol. And most
9:12importantly, do not forget these two
9:14things. If we don't remember any of its
9:16composition, we will write the
9:18dispersed phase. Which is agar, and the
9:21dispersion medium, which is water at
9:2385.5%. And agar is 13 to 17%, so
9:28together they make up most of the
9:31composition already. So, this must be
9:35remembered. So, our dispersed phase
9:37forms a continuous fibrillar micellar
9:40structure. It is a gelling agent that
9:43actually converts it from sol to gel.
9:46And water is the dispersion medium. Now
9:48, it is a hydrocolloid. As we just saw,
9:51hydro means water. Water will be the
9:54dispersion medium for both agar and
9:56alginate, which controls the flow
9:58property of the sol and physical
10:00properties of the gel. Next is now
10:04borax. Again, it improves the viscosity
10:07of the sol and its strength. Potassium
10:10sulfate acts as an accelerator, 1 to 2%
10:13—everyone is present in small amounts
10:15. Alkyl benzoate. Now, all this needs
10:17to be remembered. Okay? What are borax,
10:19potassium sulfate, and alkyl benzoate?
10:22It is a type of preservative. Now, it
10:24is in a jelly form. So, there are high
10:26chances of fungus and mold growing on
10:29it. So, to prevent that, we add some
10:31preservatives to increase its shelf
10:34life. So, that is alkyl benzoate. Then
10:36we add fillers like diatomaceous earth.
10:41Its job—whenever I have mentioned
10:43filler, I have said that wherever a
10:45filler appears, it is related to
10:47strength and viscosity. Then again, it
10:50is doing the same thing here. That is
10:52controlling the strength and viscosity
10:54of the material. Next is a thixotropic
10:57material. It helps in its thickening.
11:00Then thymol is a bactericide. Glycerin
11:03is a plasticizer, and coloring and
11:04flavoring agents are for its appearance
11:06and taste. All of this is present in
11:09very minute quantities. If nothing else
11:12, you need to remember in the
11:14composition that the dispersed phase is
11:16agar and the dispersion medium is water
11:19. Then again, some preservatives,
11:23thickeners, fillers, bactericides,
11:25plasticizers, and accelerators are also
11:28present. Next is the setting reaction.
11:33Now, how does the setting reaction of
11:36agar occur? The term is gelation.
11:39Gelation is a reversible solidification
11:42process due to temperature change. Now,
11:45we have studied sol and gel so many
11:47times. So, we already know what a sol
11:50is. The hot, viscous fluid is the sol.
11:55From which we take the impression in
11:57that stage. When it starts cooling down
11:59. Okay? It cools down and reaches 43 °
12:01Celsius. At mouth temperature, it
12:04gradually converts into a gel. And then
12:08again, if we heat that gel back to 100
12:11° Celsius, then it gets converted into
12:14a sol again. So this is the kind of
12:17setting reaction which occurs. The term
12:19used is gelation. Now, this temperature
12:22lag, the difference between gelation
12:25and liquefaction. Gelation is the
12:28solidification process, and
12:30liquefaction is when it's heated and
12:32changes back into a sol; that is called
12:35the liquefaction temperature. Right? So
12:39, the gelation temperature is the
12:40solidification temperature, and the
12:42liquefaction temperature is when it
12:44turns back into a sol, coming into a
12:46liquid form. Now, the lag between these
12:50two, the time it takes from cooling at
12:5343 ° Celsius to heating it back up, is
12:55what we call hysteresis. This is very
12:59important and is often asked in your
13:01MCQs and during viva examinations. Now,
13:03what is the significance of this
13:05hysteresis? What is it used for? This
13:07is useful to the dentist because this
13:10temperature difference gives the
13:12dentist time for the manipulation of
13:14this impression material. I hope you
13:17have understood. We have studied three
13:19things here. First is gelation, second
13:21is gelation and liquefaction
13:23temperature, and third is hysteresis.
13:26We have also seen the significance of
13:28hysteresis. Next is the mechanism of
13:34gelation. Now, we have studied gelation
13:37. I have explained in a flow chart what
13:40a sol is. It is an aggregate of
13:42molecules that is dispersed in water.
13:47After that, as the temperature drops,
13:49meaning it starts to cool, it undergoes
13:52a reaction, forms fibrils/micelles, and
13:55then agglomerates to form a network or
13:58chain, which converts into a brush-heap
14:01structure. This brush-heap structure is
14:06very important and is often asked in
14:09your MCQs regarding what final
14:11structure we get in the gelation
14:13mechanism. So that is nothing but the
14:18growing fibril branches that intermesh
14:21with each other, and that is how it
14:23converts from sol to gel. Meaning, it
14:27has set. A jelly form is created. Let's
14:30see the properties of agar now;
14:32biological properties: non-toxic,
14:35non-irritant. However, if we do not
14:38bring the impression material to an
14:41adequate temperature before placing it
14:43in the patient's mouth. Meaning, if we
14:47don't temper the impression material,
14:50there are chances of tissue burns. Next
14:53is mechanical. Its tear strength is
14:55very poor. You can imagine, have you
14:58ever seen or touched jelly? It is just
15:01like that. So the tear strength is very
15:03poor. You can use your hand and just
15:05tear that. So hence, the thickness of
15:09the impression material should be a bit
15:11more to prevent tearing. It has high
15:16elastic recovery, meaning we can use it
15:21in undercuts. Its rheological property,
15:26or flow property, is quite good because
15:29it is a hydrophilic kind of material. '
15:32Philic' means attracted towards water.
15:35So, whatever saliva is present in our
15:39oral cavity, it is attracted to it.
15:43Meaning, there will be proper flow and
15:46it will be in close contact with the
15:49oral mucosa. So when placed in the
15:52mouth, it adapts really, meaning
15:54quickly, to the oral tissues. It is
15:56highly viscoelastic. That is why when
16:00we retrieve it quickly, it must be
16:02removed with a sudden jerk or a sudden
16:04snap. It has to be retrieved from the
16:07patient's mouth. Next is thermal. What
16:10is this? It is a thermoplastic material
16:12. Meaning, its phases change according
16:17to the temperature. So, each time, we
16:22have learned that agar can be a
16:24reversible kind of material that we can
16:27reuse. So, can we reuse it an infinite
16:31number of times? No. Now, every time we
16:35reheat the material, meaning we first
16:37got it in gel form. We heated it. Made
16:40it into a sol. Took the impression.
16:42That is getting converted into a gel.
16:44Again, when we retrieve it from the
16:46mouth. Now, again we have to use it. So
16:49, we will have to reheat it again. But
16:53whenever we reheat it, its gel
16:55structure keeps breaking down and
16:57gradually this jelly form keeps getting
17:00stiffer with every use. That is why
17:04this impression material should not be
17:07heated, or used, more than four times.
17:10What happens due to overheating? The
17:12polymers, the cross-linking they have
17:15with each other, and the bonds break.
17:19And temperature changes from the
17:22water-cooled tray; when that
17:24temperature changes, coming from warm
17:27room temperature to outside, it also
17:30causes thermal expansion. So, thermal
17:34expansion occurs, and it should not be
17:36used more than four times. If we heat
17:38it again and again, the material keeps
17:41getting stiffer. Dimensional stability;
17:44it has poor dimensional stability. As
17:46we studied, its tear strength is not
17:47very high. Now, why does it have poor
17:49dimensional stability? Because of
17:51syneresis and imbibition. These two
17:54terms might be new to you. So, let's
17:56explain that first. What is syneresis?
17:59It is the process where water exudes
18:01onto the surface of the impression.
18:04Have you ever seen dew collected on a
18:06leaf during the rain? Have you seen
18:09water collected on a leaf? Like water
18:13droplets, water exudes onto the outer
18:16surface or comes out on the impression.
18:20We call that syneresis. This occurs due
18:23to internal stresses. Now, why did this
18:26water come to the outside? Because the
18:27internal stresses that were
18:29incorporated inside were relieved. As
18:32soon as the stress is relieved, the gel
18:35molecules come closer together and push
18:38the water that was between them out
18:41toward the surface. This is how the
18:44water exudes. This whole process is
18:47called syneresis. Then, the water has
18:50reached the surface. Now, this water
18:53evaporates from the surface, which
18:55causes contraction. Whatever water was
18:58between the molecules is now gone. The
19:01molecules are getting closer together.
19:03What does this mean? Contraction is
19:05happening. Right? That is called
19:07syneresis. Next is imbibition. The
19:09opposite. How does imbibition occur? If
19:12we have not stored it properly. We have
19:14taken the impression. Now, if we place
19:17it in a spot where it dries out, and as
19:20it loses water, it starts to absorb
19:23surrounding humidity or any available
19:27excess water. It starts to imbibe it
19:30within itself. The gel structure
19:32absorbs water, and that results in
19:35expansion. So, syneresis causes
19:37contraction and imbibition causes
19:40expansion. Both of these lead to
19:42distortion, and that also occurs due to
19:45the relief of internal stresses. So,
19:48what two reasons affect dimensional
19:50stability? Syneresis and imbibition. It
19:53is stable for one hour. If we must keep
19:57it, we should maintain 100%relative
19:59humidity. Only if necessary. Now, how
20:03can we achieve 100%humidity? Either we
20:06store it in a 2%K2SO4 solution or keep
20:10it in a humidifier. If nothing else is
20:13available, then at least we place that
20:16impression in a damp towel; it is never
20:18referred to as a wet towel. Damp means
20:21do not provide it with excess water,
20:23otherwise imbibition will occur. We can
20:25store it by wrapping it in a damp towel
20:29. Again, it should not be electroplated
20:32and disinfected for extended periods as
20:34it leads to dimensional change. It
20:37cannot be electroplated. So, other
20:39methods can be used to make its die. It
20:42is inexpensive and has an adequate
20:45shelf life. Next, let's see the
20:47manipulation. The most important part
20:50in agar is the manipulation. That is
20:53very extensive. We require a lot of big
20:56chambers and instruments for the
20:58manipulation. That is the major reason
21:02why agar is not used as much. Now, the
21:05manipulation of hydrocolloid can be
21:08done in a hydrocolloid conditioner,
21:10which consists of three
21:11temperature-controlled compartments as
21:14seen here. These are, first is the
21:17liquefaction chamber. Second is the
21:19storage chamber, and third is the
21:22tempering chamber. Okay? Now we will
21:25look at the function of each chamber.
21:30First is the liquefaction chamber. And
21:32now, I have divided every chamber under
21:35these three headings. This will make it
21:38easier for us to remember. First is,
21:40what is the temperature of that chamber
21:42? How long do we keep it in there? And
21:45what is happening because of that?
21:46Meaning, what is the function? Okay? So
21:49, temperature, time, and function for
21:51the liquefaction chamber is: in the
21:54liquefaction chamber, we keep the
21:56temperature at 100 ° Celsius, meaning
21:58we convert it from gel to sol, and that
22:01takes around 10 to 12 minutes for fresh
22:03material. Okay? Now, fresh material
22:06means the first time we are liquefying
22:09it. Okay? But if we are reusing it,
22:13then every time we reuse it, just add 3
22:17minutes to it. Okay? Suppose we are
22:21taking 12 minutes for fresh material,
22:23so if we use the same material a second
22:25time, how long will it take? It will
22:28take 15 minutes. Okay? So, every time 3
22:30minutes are added to it. And what is
22:33the function? It converts gel into sol.
22:37Next is the storage chamber. What is
22:39its temperature? 65 ° Celsius of water
22:42. Okay? And what is the time? As long
22:46as we want to keep it at that same
22:49temperature, meaning we converted it
22:51from gel to sol. We keep the storage
22:55chamber to maintain that sol phase. So
22:59that it remains in the sol stage. It
23:02should not cool down and convert back.
23:05What is the function? Storage of the
23:07sol phase. Next is the tempering. Then,
23:09how much in this? Temperature is 45 °
23:12Celsius and time 10 to 15 minutes. What
23:16do we do after this? Because of this,
23:18an increase in the—sorry, there is a
23:20mistake here. Not visibility, but
23:22viscosity; an increase in the viscosity
23:25occurs. And a reduction in the
23:28temperature of the sol also happens.
23:30And then we take the impression from
23:32that material. Let's see it one by one.
23:35The first step in the manipulation is
23:38liquefaction of the gel. Now we have
23:40studied all the chambers, we have
23:41studied everything. Okay? Let's see
23:42step by step. What are we doing first?
23:44We are doing liquefaction. Meaning, we
23:46received it in a container, that is, in
23:48a jelly form, in a gel form. Now we
23:50bring it, it will be available either
23:52in a syringe or in a tube. Now we have
23:54to liquefy it by putting it in the
23:55liquefaction chamber. So if we put it
23:58at 100 ° Celsius for 10 to 15 minutes,
24:00it will convert from gel to sol. And we
24:03have already studied this. Every time 3
24:05minutes are added. Second, we will do
24:07storage. Okay? Meaning, to maintain
24:11that sol stage in that same form, we
24:15put it in the storage chamber. Then
24:19third is conditioning or tempering.
24:22Before taking the impression, we put
24:24the tray material into our third
24:26chamber, the tempering chamber. And
24:29what is its purpose? That increases the
24:32viscosity of the sol. Okay? So that it
24:35stays in the tray. And second is the
24:37reduction in the temperature. We read
24:39in the biological considerations that
24:41tempering is necessary. If we try to
24:44take an impression without tempering,
24:46the tissue could burn while taking the
24:47impression inside the patient's mouth.
24:50And the same thing, if it is a syringe
24:52material, then it does not need
24:53tempering. Because if we try to temper
24:56it, the syringe material converts back
24:58into the gel form very quickly. So
25:00there is no need to do all this with
25:01syringe material. When we use tray
25:03material, then we do the tempering and
25:06then we put it in the third chamber.
25:09Next is the impression recording. Now,
25:12the syringe material is taken directly
25:14out of the storage bath. There is no
25:16need to put it in tempering. And then
25:18we put it on the prepared cavity of
25:21which we want to take the impression,
25:23and if it is a tray, we will first use
25:26water-cooled perforated rim trays. That
25:30is used. Why do we use these
25:32water-cooled perforated rim trays? So
25:35that we can provide retention to that
25:37agar. These are the water-cooled
25:40perforated rim trays. This is very
25:42important. This can be asked in your
25:45viva and your MCQs as well. And if you
25:47are writing about the manipulation of
25:49agar, then you have to mention this.
25:52All the three chambers and this tray is
25:54the major thing you have to write about
25:56the manipulation of agar. A lot happens
25:59along with this. Like this, as you can
26:02see this. Um, as you can see, you can
26:07see an outlet here. You can see an
26:10inlet here. This is where we attach a
26:13tube. Right? There are many other
26:15things as well. But you need not
26:17mention everything in your paper. You
26:20just need to know that we use
26:22water-cooled perforated rim trays to
26:25provide retention, which look like this
26:27in real life, and this is the
26:29diagrammatic representation that you
26:32can draw in your exam. We put water
26:35inside through the inlet so that it can
26:38convert back into the gel form. So, the
26:41inlet and then again the outlet. Then,
26:45gellation happens; as soon as the tray
26:48material is positioned, gellation can
26:52be induced by the circulation of water,
26:55which is the same water. Let's remove
27:00this first. As soon as the gellation
27:06occurs, once we start putting water
27:07inside, it starts gelling again.
27:10Gellation means that it will now start
27:12converting back from sol to gel form.
27:14Meaning, water will start circulating
27:16through that inlet and outlet we saw.
27:19And after reaching approximately 18 to
27:2223 degrees Celsius, we will not remove
27:25the tray before 5 minutes. Now, because
27:27of this, what will happen? It will
27:29convert from sol to gel. We should
27:31never put ice-cold water in it just to
27:34hurry things up. Because of that, again
27:37, just like we studied in waxes, if we
27:38heat wax and suddenly put it in water,
27:40then what happens? The same thing
27:42happens here. Stresses get incorporated
27:45into it, due to which the impression
27:47can get distorted. All our hard work
27:50will be wasted. Next is removal. Now it
27:53has reached the gel form, and only
27:54after it is in gel form, we take a snap
27:56impression. We just saw that we give a
28:00sudden jerk and retrieve the impression
28:02from the patient's mouth at once. Okay?
28:06Because of that sudden jerk, we are
28:08trying to minimize permanent
28:10deformation. Next is washing. Now we
28:13have taken it out. Now, whatever saliva
28:17, debris, or blood is on the impression
28:20, we will wash it thoroughly in water
28:23and then disinfect that impression. As
28:27soon as it is disinfected, we will pour
28:30the impression immediately. Because it
28:33is dimensionally unstable. This
28:36completes the manipulation of agar. And
28:39this is very important for your exams.
28:42There are some advantages to this
28:44material like it is hydrophilic. This
28:47means it will adapt completely and
28:50record very good detail. It can be used
28:53in a moist field. Again, because of its
28:56hydrophilic nature, it has good
28:57recovery from undercuts because it is
28:59an elastic type of impression material
29:01and is accurate. Then whatever is left
29:05in the tube. Right? If the same thing
29:07were elastomers or any other impression
29:09material. Once we have mixed it, it
29:12cannot be reused. But it can be reused.
29:15It is non-toxic and non-staining. In
29:17disadvantages, there is its preparation
29:20time, meaning if we have to take a
29:22patient's impression, how much in
29:24advance do we need to start preparing
29:26it. Then it is dimensionally unstable
29:29because of syneresis and imbibition. It
29:32is technique sensitive. Due to the many
29:35chambers and the special kind of
29:37impression trays, the armamentarium
29:39becomes expensive. Then water, this is
29:43also a typing mistake. Water-cooled
29:47trays are very bulky. And when we put
29:50it into the patient's mouth, it is very
29:52uncomfortable for the patient.
29:55Incomplete cooling of the impression
29:57results in tissue burns during
29:59impression making. Due to low strength,
30:03because of repeated use, the cast
30:06gradually becomes poorer. Then it
30:11cannot be electroplated. Okay? So this
30:14completes our agar impression material.
30:18The most important part in agar
30:20impression material is the setting
30:22reaction which happens through gelation
30:24and the manipulation. Let's go into the
30:28next impression material which is
30:30alginate. Again, we will look at the
30:32content first. We will read alginate
30:35under the headings of introduction,
30:38application, and how it is dispensed.
30:42Supplied in, classification, setting
30:44reaction, composition, properties,
30:46manipulation, advantages, and
30:48disadvantages. Now there are a few more
30:51headings here because alginate is the
30:54most used impression material in
30:55dentistry to date. Okay? So let's start
30:59with the introduction. We already know
31:01the introduction but let's see. E.C.
31:05Stanford in 1881 from Scotland
31:07discovered a brown seaweed algae. And
31:11he named it Algin. Now chemically, what
31:15is this Algin? It is a linear polymer
31:18with many carboxyl groups of alginic
31:21acid. What is alginic acid chemically?
31:25It is Beta-D-mannuronic acid. You will
31:28have to remember this. This is very,
31:30very important for your viva as well
31:32and for your MCQs also. And if Alginate
31:35comes up, Alginate is one of the most
31:37important impression materials, which
31:39has a high chance of appearing in exams
31:41. So, you have to write where it is
31:43obtained from? First of all, who
31:45discovered it? It is obtained from
31:47seaweed. And then, Alginic acid, whose
31:49chemical formula is Beta D-mannuronic
31:52acid. Again, it is an irreversible,
31:55non-aqueous, mucostatic, thermoset,
31:57elastic type of impression material.
32:00ADA Specification number 18, and its
32:03classification has two types of
32:06Alginate. The first is Type 1, which is
32:10fast-set. Meaning that its gelation
32:13happens very quickly, within just 60 to
32:16120 seconds. And the second is the
32:19normal set, which gels between 2 to 4.5
32:21minutes. That gives you a little time
32:24for manipulation and taking the
32:26patient's impression. Next is the
32:31application; it is most important for
32:34making impressions of edentulous and
32:36partially edentulous mouths, and to
32:38some extent, it can also be used for
32:41inlays, onlays, crowns, and bridges, or
32:43you can even use Alginate to take
32:46impressions for study or orthodontic
32:48models. Or for duplicating models,
32:52meaning what we can do with agar, we
32:54can also do with Alginate. Then for
32:57maxillofacial impressions as well; it
33:00is dispensed either in a bulk container
33:03with a plastic scoop for measuring the
33:06powder and a cylinder for water, or
33:08pre-weighed sachets are also available.
33:12Composition, again, the composition is
33:15very important. Okay? Chemically, we
33:18have seen Alginic acid. Here it is
33:21written as hydro-B, but it is not B. It
33:24is Beta D-mannuronic acid. Okay? So,
33:28Alginic acid is a high molecular weight
33:31Beta D-mannuronic acid. It is extracted
33:34from brown marine seaweed, which is
33:37algae. And what is Alginic acid? It is
33:39insoluble in water, but its salts are
33:42obtained from sodium, potassium, and
33:44ammonium, which are soluble in water.
33:47That is why we can take dental
33:49impressions with it. If you don't need
33:51to remember anything, this is just for
33:53your knowledge. So, you just have to
33:55remember that chemically, it is Alginic
33:58acid, which is a linear polymer chain
34:01of Beta D-mannuronic acid and it is
34:04extracted from brown marine seaweed,
34:07Algin. Okay? We will remember this much
34:09; we studied it in the introduction and
34:11it is also in the composition. Now, the
34:15composition is very important. Okay? It
34:19will become easier to remember the
34:21composition after we study its setting
34:24reaction. Most importantly, first you
34:27should look at the percentages; what is
34:29present in the highest percentage? Here
34:32, filler is the highest. And we are
34:34studying Alginate now. So, soluble
34:36salts of Alginic acid will also be
34:38there. Which is sodium or potassium
34:40alginate that is present. Okay? So 15%
34:43is soluble salt of alginic acid which
34:47is sodium or potassium alginate. Okay?
34:51These are the soluble alginates, which
34:54is why they react with calcium ions to
34:56give calcium alginate gel. You have to
34:59study this in the reaction ahead anyway
35:01. So, this will become a bit easier.
35:02When you read the whole thing,
35:04everything gets easier. Second is
35:06calcium sulfate dihydrate. Does it ring
35:09a bell? Where have we studied this?
35:11Calcium sulfate dihydrate in the
35:13chapter gypsum. Okay? It is basically
35:16gypsum. The chemical formula for gypsum
35:18is calcium sulfate dihydrate. So first
35:20is sodium or potassium alginate. Second
35:22is, now in the composition of alginate,
35:24the first is alginate. We saw agar in
35:27agar. So in alginate, there will be
35:28alginate. So, first is sodium and
35:31potassium alginate, then gypsum.
35:33Calcium sulfate dihydrate. Okay? What
35:36is its function? It provides calcium
35:39ions so that they can react with the
35:41alginate. The alginate is already there
35:43above. Now to react with the alginate,
35:45we need calcium ions. This is what
35:48provides them. The third major
35:50component is filler. What are the
35:52fillers? Zinc oxide, diatomaceous earth
35:55, and silicate powder. These are the
35:58fillers. Again, what is the job of the
36:00filler? One, it increases its strength
36:02and second, its viscosity. Well, within
36:05viscosity comes its stiffness and its
36:08cohesion, meaning it helps in creating
36:10a cohesive, homogeneous mixture. And
36:14then next is potassium titanium
36:16fluoride. This is an accelerator. The
36:18same thing that we just studied, there
36:20will be some accelerators in agar and
36:22some in this. But there is also a
36:25retarder. That was not there in agar;
36:27why is it there? And what is the
36:29retarder? Trisodium phosphate. As we
36:31study the reaction further, we will
36:34know why the retarder is important and
36:36what its job is. Next is potassium
36:40sulfate. Now, because of potassium
36:42sulfate, we are able to make a better
36:44die. That provides a good surface for
36:46the gypsum die. After taking the
36:48impression, we have to pour it as well.
36:51For that, to obtain a good cast, we
36:53need potassium sulfate or alkali zinc
36:56fluorides. There are some disinfectants
37:00in it. Then some organic glycols that
37:03reduce the powder dust. Then some
37:06coloring and flavoring agents for
37:08aesthetics and patient acceptance. So,
37:11try and learn this. So let's go ahead
37:16and see the setting reaction of this
37:18material. That will help you learn this
37:23component table and make it easy. Next
37:27is the properties. Biological
37:29properties. Again, we will list the
37:31properties under the same headings. As
37:32we have for every impression material.
37:34We have used the same headings. First
37:36is the biological property. That is
37:38non-toxic, non-irritant, acceptable
37:40taste; everything is perfect. Because
37:43it is the most used material in
37:46dentistry. Second, the mechanical
37:48strength is definitely poor. It is not
37:49dimensionally stable for a long time.
37:51So, we cannot keep it for very long. We
37:53have to pour it immediately. So, it has
37:56poor tear strength. That is why, again,
37:58we have to make the impression of a
38:01reasonable thickness. Okay? Then, it is
38:04sufficiently elastic and has adequate
38:06flexibility to recover from undercuts.
38:09Just like agar. Rheologically, it is
38:11sufficiently fluid to record fine
38:14details. Then thermal: the temperature
38:17of the mixing water is essential for
38:19the reaction. It's the same thing. If
38:22we use hotter water, meaning the water
38:25temperature is higher, the mixing
38:28duration decreases; it sets faster. And
38:33the changes from mouth temperature to
38:35room temperature can cause some thermal
38:38shrinkage as well. Then dimensional
38:43stability, again it is a hydrocolloid;
38:45it also undergoes syneresis and
38:47imbibition, just like we studied in
38:50agar, and it is more stable when stored
38:53at 100%humidity, i.e., in a humidifier,
38:55and casts must be constructed
38:57immediately. Again, if we cannot pour
39:01the impression immediately. Suppose our
39:04patient is sitting and we have to
39:06attend to them, and if there is a 5-
39:07minute delay, what do we do? We wrap it
39:10in a damp towel or a damp tissue. Not
39:13wet. What happens if we make it wet?
39:15Then imbibition will occur. It will
39:17imbibe excess water. And then, it will
39:20get distorted again. Let's see the
39:24setting reaction. Now, this is a very
39:26important setting reaction of alginate.
39:28When the powder is mixed with water.
39:31Okay? Now, let's understand this
39:33step-by-step. As soon as we mixed the
39:35alginate powder with water, what
39:37happened? In the composition, we saw
39:39that the very first component was salts
39:42of alginate. First, the soluble
39:45alginate starts reacting quickly with
39:47the calcium ions, which we got from
39:49where? From gypsum, from calcium
39:51sulfate dihydrate. Remember the
39:53composition. Okay? Or, you can take a
39:55photo of the composition table and keep
39:57it open separately. So, what will
39:59happen? The first thing we saw in the
40:01composition was the soluble alginate.
40:03It reacts with the second component,
40:05that is the calcium sulphate dihydrate
40:08which is releasing calcium ions, and
40:10what does it form? Calcium alginate,
40:13which is the final end result we want.
40:17Okay? Calcium alginate is formed,
40:19meaning gelation has occurred, and it
40:22quickly changes into a gel form and
40:24sets. But we do not want it to set that
40:26quickly. Because we need time. We need
40:29time for mixing. We need time to load
40:32the tray. We need time to make the
40:34patient perform all mouth movements so
40:36that we can record everything properly.
40:39So, what will we do for that? We will
40:41delay this reaction a little. I just
40:43mentioned that we also add a retarder.
40:46So, that retarder is trisodium
40:48phosphate. Now, to prevent this quick
40:50gelation, what do we do? We add
40:53trisodium phosphate. Because of that,
40:57the calcium ions that our gypsum,
40:59calcium sulphate dihydrate, was
41:00releasing, what does it start doing?
41:03Now, it starts reacting with the sodium
41:07phosphate. Okay? And what is it forming
41:10? It starts forming a precipitate. So
41:12now, the reaction is not happening
41:14between sodium alginate and calcium
41:16ions. Now, those calcium ions are
41:19reacting with sodium phosphate and
41:22forming calcium phosphate. What is this
41:26called? A delaying reaction. Now it has
41:28not left any calcium ions to directly
41:31react with alginate and form the final
41:34calcium alginate to set. Until all the
41:38calcium ions react with trisodium
41:40phosphate and precipitate, the reaction
41:42will not move forward. It will not
41:45release excess calcium ions to go and
41:48react with the soluble alginate. So,
41:51this is called a delaying reaction.
41:54This reaction occurs in two steps and
41:57is a simple double decomposition
41:59reaction. You have to remember these
42:01two steps. And whenever the setting
42:03reaction is asked in your exam, you
42:05have to mention these two steps. The
42:08first step is that sodium phosphate
42:10goes and reacts with calcium sulphate.
42:14Due to which we get adequate working
42:17time. So, what are we seeing here in
42:19this reaction? Sodium phosphate plus
42:21calcium sulphate. Okay? Now in the
42:24second step, when all the sodium
42:26phosphate has reacted. Now, the
42:29retarder we added, once it has fully
42:31reacted and precipitated. Now, the
42:34remaining calcium ions that didn't
42:38react will proceed to react with the
42:42soluble alginate, forming the final
42:45product we need: calcium alginate,
42:49completing the gelation process. Right?
42:56As this reaction proceeds, the degree
42:58of cross-linking increases, and calcium
43:01ions link the fibrils, converting them
43:04into a gel form while retaining their
43:07elastic properties. The final structure
43:13of the gel is the brush-heap structure
43:15of calcium alginate fibrils. Right?
43:19Just as we studied in the last video
43:20about Zinc Oxide Eugenol, what happened
43:22there? Zinc oxide eugenolate. Similarly
43:26, what do we have here? It is calcium
43:28alginate. So, the end product is the
43:31brush-heap structure of calcium
43:33alginate fibrils. This is your setting
43:36reaction. This reaction gets shortened
43:39when we decrease the water-powder ratio
43:41or increase the temperature. That
43:43temperature could be either by
43:45increasing the water temperature or due
43:47to the surrounding temperature, which
43:49again leads to higher water temperature
43:51. Because of this, we can shorten the
43:54reaction. Let's see the manipulation.
43:58The first step is proportioning. The
44:00manufacturer. It is the same thing. The
44:02water-powder ratio is something that we
44:05follow according to the manufacturer's
44:06instructions. There is a graduated
44:09scoop provided for it. As seen in this
44:13photo, we take the alginate in the
44:16scoop and level off the excess with a
44:19spatula back into the container. So
44:23that we can measure it properly. Or we
44:26can also use a weighing machine. After
44:29proportioning, the next step is mixing,
44:31which is very important. Now, the
44:34measured powder or pre-measured water
44:37is taken in a clean rubber bowl. The
44:41powder is incorporated into the water
44:44very carefully using either a plastic
44:47or metal spatula that is flexible
44:50enough to adapt properly to the walls
44:52of the bowl. Right? Once the powder is
44:59wetted, meaning all the powder we took
45:01is soaked by the water, then what do we
45:04do? We start mixing it using a vigorous
45:08figure-of-eight motion. Right? It is
45:11being swiped or stroked between the
45:13blades of the spatula. I will put the
45:16video for this manipulation in a
45:18separate video. This video was getting
45:20too long. That is why I haven't
45:22attached it here. But I will put a
45:24video for the manipulation of alginate
45:26separately. And then what do we do?
45:29Along with that, we keep rotating the
45:31bowl as well. Okay? Just like this. And
45:36we also keep swiping on the surface of
45:38the bowl. What happens because of this?
45:41Why do we make a figure-of-eight? You
45:43will be asked this. This is very
45:45important. In every preclinical exam,
45:47you are asked about alginate
45:49manipulation. You have to tell and show
45:52how to make a figure-of-eight. And why
45:54do we do the figure-of-eight? What does
45:56this achieve? It removes most of the
45:58air bubbles and wipes away any
46:00dissolved material from the surface of
46:03the undissolved material. Okay? This
46:07results in complete dissolution. Okay?
46:11Meaning, it incorporates any remaining
46:14undissolved material as well. Due to
46:18the figure-of-eight, we must be careful
46:21not to incorporate anything else. Water
46:25and air should not get incorporated, so
46:28there is no chance of air bubbles. Then
46:31, the mixing time for regular-set
46:33alginate. This table is very important.
46:36You have to remember this. The mixing
46:38time of alginate is 1 minute. For
46:41fast-set, it is 75 seconds. Working
46:44time for regular-set is 3 to 4.5
46:47minutes. And for fast-set, it is 1.25
46:50to 2 minutes. And the setting time is
46:53again 3 to 4.5 minutes for a complete
46:55set. And for fast-set, it is just 1 to
46:572 minutes. Okay? This is very important
47:00. Now, apart from manual mixing, we can
47:03also do this with a mechanical device.
47:05Just like this. What are the advantages
47:08of mechanical mixing? One is speed, and
47:10the second is convenience. We don't
47:12have to do anything. No figure-of-eight
47:14needs to be made. And any human
47:15variables—someone might have better
47:17motion, others might not—are removed.
47:20Whatever the manual dexterity, that is
47:23eliminated. Now, we should not over-mix
47:27or under-mix. If we over-mix, what can
47:30happen? That can result in a reduction
47:34of the final strength of the material.
47:36Because it gets destroyed, its strength
47:39is reduced. Or, due to excessive mixing
47:42, the working time is reduced. So, the
47:45working time decreases, meaning it will
47:47set very quickly. If we under-mix,
47:49meaning we don't mix it properly, what
47:51happens? Inadequate wetting. Meaning,
47:53at some places, you will see powder
47:54separately and water separately. That
47:56happens. Homogeneity is not achieved.
47:58Because of that, the strength decreases
48:00. And the mix looks very grainy. And
48:02because of that, the impression also
48:04does not get recorded properly. This is
48:06also important. External examiners may
48:08also ask you this. The third step is
48:12loading. What do we do after mixing? We
48:14load it into the tray. How do we load
48:16it? We load it into the entire tray.
48:19And then we seat the tray posteriorly
48:21first, and then after seating it
48:24posteriorly, we seat it towards the
48:26front. So that any excess material
48:30flows towards the front and does not go
48:32down into their throat. That could
48:35again cause the patient to gag. They
48:37could become uncomfortable. That is why
48:39, where do we seat it? First
48:40posteriorly and then anteriorly. So
48:43that all the excess material flows to
48:45the anterior side. Next, we record the
48:49impression. Then we remove it with a
48:51sudden jerk, just like we studied for
48:53agar. We retrieve it with a sudden jerk
48:56. By breaking the peripheral seal so
48:59that we can minimize permanent
49:01deformation. After that, we quickly
49:05wash it, disinfect it, and without
49:07wasting any time, we pour it
49:09immediately. Using gypsum, how are we
49:14disinfecting it? We thoroughly rinse
49:17the impression under tap water so that
49:19all blood and saliva are removed. Then
49:22the disinfection procedure should be
49:25relatively rapid so that dimensional
49:28changes do not occur. How can we
49:30disinfect it? Either we submerge it for
49:3410 minutes in a 0.5%solution of sodium
49:37hypochlorite or glutaraldehyde, or we
49:39can spray it with an antimicrobial
49:42agent. Wrapping the impression in a
49:45disinfectant-soaked paper towel or
49:47placing it in a sealed plastic bag for
49:4910 minutes can also be done. Unwrap it,
49:52thoroughly rinse it with water, and
49:54then remove the excess water. Again,
49:56why are we saying this? It should not
49:59be done for more than 10 minutes,
50:01otherwise, due to syneresis and
50:03imbibition, there are chances of
50:05dimensional changes and distortion. So,
50:08this is the disinfection of alginate.
50:13Recently, some synthetic phenols and
50:15iodophors are also recommended for
50:17disinfection. How can it be stored?
50:20After disinfection, pour the model with
50:23stone immediately. If there are
50:26unavoidable circumstances, you can keep
50:29it for some time, approximately 12
50:31minutes. What should the storage
50:35technique be? You can wrap it in a damp
50:38towel. Not a wet towel; again and again
50:41, I am saying it is a damp towel. Then
50:45place it in a plastic bag, which is
50:47convenient for storing alginate
50:49impressions under humid conditions. You
50:52can also keep it in a humidifier. Where
50:54100%humidity can be maintained. What is
50:57the advantage? Very nice. Reproduction
51:00of excellent surface detail. Second is
51:03the good elastic recovery of 97%, which
51:06is comfortable for the patient. Taste,
51:08color, everything. It is hygienic
51:11because we are using a fresh batch
51:13every time. It is not reversible. It is
51:17inexpensive. It is easy to manipulate.
51:20The disadvantage is the same thing. It
51:22is dimensionally unstable. Tear
51:24strength is not very high. There are
51:25chances of syneresis and imbibition as
51:27well. Low tear strength; cannot be
51:29electroplated. The shelf life is not
51:32very long and it cannot be reused.
51:37These constitute all of alginate. Okay?
51:41All the headings we studied are now
51:43finished. There are some modified
51:45alginates. Now, alginate is the most
51:48used material in dentistry that we use
51:51in the clinic. So, all the shortcomings
51:55in our alginate were addressed one by
51:58one, and alginate was modified
52:00accordingly. The first is dust-free.
52:04Second is siliconized. Alginate in sol
52:07form, chromatic alginate, soft and...
52:11Sorry, hardened and soft gel alginates,
52:13then alginates containing disinfectants
52:16, and extended-pour alginates. First is
52:18the dust-free alginate. Now, the
52:21alginate we use, as we read in the
52:23composition, the filler is diatomaceous
52:26earth, which is finely divided silica
52:29particles, a type of dust. These dust
52:33particles can cause health hazards,
52:35including respiratory health hazards,
52:38when inhaled. For this, a remedy was
52:42found: dust-free alginate. What did
52:44they do in this? We coat the powders
52:48with glycerin and glycol. Okay? So what
52:53happened? What was the result of this?
52:55This causes the powder to become more
52:58dense. Okay? Compared to the uncoated
53:00one. The one we normally use has very
53:03finely divided particles. We provided a
53:06coating to it. Because of which, what
53:08happened? It became dense. Due to this,
53:10no detectable level of dust has been
53:13measured at the operator level. After
53:15that, many studies were conducted. So,
53:18the amount of dust people were inhaling
53:21compared to normal alginate was reduced
53:24once we coated it with glycerin and
53:26glycol. So, you just need to remember
53:29this much. Glycerin and glycol are used
53:32here to coat the powder and make it
53:35more dense. Next is the siliconized
53:38alginate. What was done here? Some
53:40silicone polymers were incorporated
53:42into the alginate to improve its
53:44strength. First, we have already seen
53:47before that it contained dust, meaning
53:49filler particles. Now, the second point
53:52we observed is a shortcoming of our
53:53alginate: its tear strength is low. So,
53:56to increase its strength, we
53:58incorporated silicone polymers into it.
54:01It is provided in tray and syringe
54:04viscosities. In this siliconized
54:07alginate, the superior surface and tear
54:10resistance are quite good. And hybrids
54:13of alginates and silicone elastomers
54:16are made this way. Next is the
54:19alginates in the form of a sol. It is
54:22just like agar; alginate is also
54:25supplied in the form of a sol
54:27containing water already, but without
54:30the source of calcium ions. There are
54:34no calcium ions in it here. Now, what
54:37is done is that a reactor is provided
54:39separately, and because of that, it has
54:42been made into a two-paste system. In
54:45the normal alginate we studied, it
54:47comes as a powder in a container and is
54:49mixed with water. In which we are only
54:52adding water. That is why its
54:54composition did not contain water,
54:55unlike agar. But here, water has been
54:58added to its composition, and where was
55:00the calcium source? It was gypsum. That
55:03was removed. We put that into a second
55:06tube. Now we get the alginate with
55:08water in one tube, and the other
55:10calcium source, which is calcium
55:12sulfate dihydrate, is found in the
55:14second tube. That acts as the reactor.
55:17So, it became a two-paste system, just
55:19like we saw with zinc oxide eugenol in
55:21the last video. Next is the chromatic
55:24alginate. Now, the next shortcoming we
55:27saw in alginate was that it sets very
55:30quickly, and for those who are learning
55:33or lack skill, it becomes very
55:35difficult to make a perfectly
55:37homogeneous mixture, load it, and take
55:40the patient's impression. So for that,
55:44some chemical indicators were added to
55:46it, due to which the color of the
55:48alginate changed at every step. That is
55:52the color-indicator alginates. What
55:55happened with this? First, when we take
55:57it in powder form, it is yellow in
56:00color. As we start mixing, it turns
56:02into a pink form. This means it is in
56:05the mixing stage and loading stage.
56:07Before it turns back from pink to
56:10another light yellow color, it means
56:13the impression has set. So, this pink
56:17stage indicates that this is the stage
56:19where we must load it and record the
56:22patient's impression. This is a
56:24color-indicating alginate. Alright?
56:28Next is hard and soft set alginate,
56:31which is produced by adjusting the
56:34percentage of fillers so that the
56:37flexibility of the set impression
56:39material can be changed. Next are
56:43alginates containing disinfectants.
56:46Meaning, these are recently developed.
56:49And they contain some disinfection in
56:51the original material itself.
56:53Additional disinfectants were added to
56:56the components. Examples include
57:00quaternary ammonium salts and
57:02chlorhexidine used. Next is extended
57:06pour alginate. Now, what was another
57:08shortcoming? That it is dimensionally
57:11unstable. That is why we have to pour
57:14it quickly. So now, some things have
57:17been added to it so that we can store
57:19it for a while. Extended pour alginates
57:23were developed to prevent dimensional
57:26instability occurring with delayed
57:28pouring of the impression. Some of
57:31these products contain high calcium and
57:34less water to make them dimensionally
57:37stable. So these are all the modified
57:40alginates. I hope you have understood
57:43these two impression materials clearly
57:45because these are very, very important
57:47for your exam point of view, plus
57:49alginate is the most used material. So
57:51in clinics also, you have to use this
57:53material. So you might as well know the
57:56theory part also properly. So hope to
57:59see you in the next video where we are
58:02going to discuss elastomers, which is
58:04also very, very important for your exam
58:06point of view and for your clinical
58:08uses as well. If you like my content
58:11then please consider subscribing, like
58:13the video and please share it with your
58:15fellow dentists. Till then, happy
58:18studying.

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