Transcript for:
Understanding Gypsum and Wax in Dentistry

hi everyone this is Miss O'Brien in this presentation we are going to go over chapter 16 of your dental materials textbook and this is the chapter on gypson and wax products okay and our objectives for this presentation are to be able to differentiate between negative and positive reproductions differentiate among diagnostic cast working cast and dyes describe the chemical and physical nature of gypsum products we're going to explain the manufacturing process for gypsum products and how this affects their physical characteristics we're going to compare the following properties behaviors of gypson products including strength dimensional accuracy solubility and reproduction of detail additionally we're going to list the a recognized gypsum products and their most appropriate uses we're going to explain initial and final set of gypsum and the factors that affect things like setting time setting expansion and strength we're also going to explain the procedure for mixing and handling gyps and products to create diagnostic casts we're going to identify common components of dental waxes uh compare the properties of waxes and describe the clinical and laboratory significance of each we're going to discuss the three classifications of waxes we're going to differentiate between direct and indirect waxings and identify which property of dental waxes is most important in their differences and finally we're going to describe the usual color form and use of inlay casting base plate boxing utility and sticky waxes okay so let's get started we're going to talk about gypsum products first so gypsum and wax products um gypsum is a mineral that's found in nature uh so it's actually basically Rock that's um mined from a quarry and then made into a a powder that we can use to make um Dental reproductions so it's actually been used to make dental cast since about 1756 so it's an old material it's been in use for very long time um so as we learned in our our last uh lecture for the last chapter um an impression that we take whether it's with a hydroc coloid product or PBS or you know some kind of elastomere um this creates a negative reproduction so you can see here on the uh right there's a bite registration um within this this study model so this bite registration that would be considered a negative reproduction so the negative reproduction is taken with soft elastic material um and then the impression is filled with gypson material uh which when it starts out it's a fine powder and we mix it with water and then this creates the cast which is a positive reproduction so this part the um the cast or the study model whatever uh this whatever purpose this uh model serves um is the the gypsum product right so the the impression um is a negative reproduction that's usually um polyvinyl sline for instance um and then the the study model or diagnostic cast this is usually poured up with some sort of gyps and product like Dental stone or uh plaster perhaps and this is your positive reproduction um so again that's a review from the last chapter positive reproductions may be used to plan and track progress of treatment so we can see how the the tooth teeth move like if the patient's an orthodon IC treatment for instance um and we can track that with positive reproductions um Dental waxes also have many uses in the dental office they can be used for bite registrations we learned about that last chapter um we can use them to make alterations to stock trays we also saw that last chapter where you use utility wax to actually lengthen a stock tray if somebody has their third MERS or a larger mouth or whatever okay so the use of gypson so again we talked about about this last chapter um we can make uh casts dyes or models and we can use gypsum products to make all of these things so gypson products are most frequently used to make diagnostic cast working cast and dyes and remember the D is the single tooth reproduction and cast and models are usually a full Arch or full mouth so diagnostic casts sometimes they are called study models um these are used to plan treatment and observe the structures of the mouth um so sometimes they're used by orthodontist um they're used quite a bit to see the way the teeth are moving during orthodontic treatment um working cast or working models they might be called uh these are used to fabricate appliances um like retainers bleaching trays or dentures so these have to stand up to a little more wear and tear than a diagnostic cast where you're just you know you're just studying the teeth more or less and then dyes are replicas of individual teeth or groups of teeth um you can see here's individual tooth or group of teeth and these are used to fabricate crowns and bridges so these have to be really really strong and resistant to um to like things like carving you know sometimes you carve wax on top of the dye to create a restoration um so they have to be somewhat resistant to abrasion so the desirable quality of uh gyps and products there's lots of qualities that you want the gyps and product you're using to have so um you know all these casts and dyes they have to be accurate uh some gyps and products are more accurate than others um they have to be able to reproduce fine detail um you know a lot of times you're going to be making Restorations on these um on these models and casts and they they really need a high level of detail for that restoration to fit properly and you know work successfully in the patient's mouth long term um they have to be dimensionally stable you don't want them to expand or contract uh too much um because that that changes the representation of the tooth and then the restoration may or may not fit the tooth um they have to be hard strong resistant to abrasion resistant to solubility uh fairly easy to use um they have to be uh you know of a reasonable cost you can't you don't want something that's way too expensive um sometimes the color uh will provide a contrast between the dye material and the wax inlay pattern um you know you might need to have contrasting colors for that um and you want it to be safe because you know we're going to be working with these materials as dental assistance and we don't want to be using something that's that's potentially hazardous to our health okay so chemical properties of gypsum so um so gypsum is a mineral um and it's it's a dihydrate of calcium sulfate and it's mined as a solid Mass so um so if you look up here these big rocks that's how gypson comes out of the earth you know they they go into a quarry and they dig up Rock and they they get something like this right so so this rock that comes out of the Earth this is a gypson mineral and it's a a dihydrate of calcium sulfate so don't be intimidated by this you know kind of chemistry talk because it's not it's not that difficult to understand really um you know when you look at the words dihydrate die is two hydrate means water right so the calcium sulfate that's the cao4 and uh the molecule also has two um two water molecules two uh waterers so so dihydrate to h2os right so when you dig this rock out of the earth it's it's a dihydrate so two waters connected to calcium sulfate okay so when they dig the rock out you know you it wouldn't be much use to us if they brought a big rock to the dental office and just dropped it off what would we do with it you know so so basically they have to process it to turn it into this powder you know we use this powder quite a bit when we pour up this study model or this diagnostic cast whatever it is so um so this rock has to be broken down to this powder so it can be something that we can use in the dental office right um so so the what happens is the the Rocks they're transformed to this powder uh via heating of the Rocks so so when you heat the Rocks um they they lose water and they become ground down um so so after they're heated and they lose the water and they're ground down into this powder then this powder is actually called a hemihydrate so um so the hemihydrate uh you know just look at the word again hydrate is water Hemi is half like hemisphere is half a sphere you know like the northern hemisphere of the earth and the southern hemisphere of the earth that's half of the earth basically so Hemi is half and hydrate is water so now you know the rock that came out of the earth that was the calcium sulfate with two waters attached to it right once you heat it and grind it and process it it loses water Right Heating causes evaporation of water so once you heat this product and turn it into you know this kind of Flowery substance it's a hemihydrate of calcium sulfate so you still have your same calcium sulfate caso4 but now instead of two h2os or two waters you have a half a water right so this process is called calcination so any gyps and minerals that we use in the dental office have been through cination um you know otherwise we you know what would we do with this big rock you know carve it up I don't know I wouldn't be able to do it so um so calcination is just the process of turning that rock into a powder and that's what we need it to be in order to use it in the dental office in the process it loses water it goes from a a dihydrate to a hemihydrate so when the hemihydrate is mixed with water then the the product is viscous right it's kind of a thick kind of um uh thick kind of product you know it it's a thick mixture I should say um it's still able to flow but it's not like water it's much thicker than that so so the hemihydrate the the powder what we do is we mix that with water right and we pour it into the impression and then we get this this cast when we're done or this model when we're done so um so we pull it from the earth as a dihydrate and then we process it and becomes a hemihydrate then what do we do we add the water back in when we're making a pouring up a model you know so it's like the the circle completes itself more or less so we we add water to it and it becomes a dihydrate again so you know full circle there um so uh so after the chemical reaction completes the hemihydrate goes back to being a dihydrate in solid Mass form so here's the the form It ultimately takes when we pour up a model right so um so now this model is actually back to being a dihydrate it's just a cyclical thing so what happens is um adding water to uh to the gypsum powder or the hemihydrate it causes a a chemical reaction and it's an exothermic reaction meaning that heat is produced so when you guys will see this in lab when you mix this powder with water and you pour up your model as it starts to harden and as it continues to harden it's going to be real warm you know it's going to release heat and it's kind of neat to hold it like especially when it's cold in the lab it's a winter day or whatever it kind of warms up your hands but um you know it's an exothermic reaction So eventually the heat dissipates once the um material is set um so excess water evaporates and from the um final product and it leaves spaces or air voids so um so as this heats up water is actually being released from there so um and as the water is released the spaces where the water was those are going to be empty right so so that leads to these little voids and that can make the material uh less resistant to to abrasion so it makes it not as hard not is strong and you know and the resistance to abrasion is is not as good you know if there was as if there was left water in there so um so the differences in calcination and the amount of evaporated water leads to physical differences like hardness and we'll we'll talk more about that so if you don't quite understand that yet um you will in a few more slides okay so just a review calcination with calcination we start off with a dihydrate right and that's the gypsum from the earth we add heat to it and what happens is once we add the heat water evaporates out and then we have the hemihydrate which is the gypsum powder that we use in the dental office plus H2O the H2O separates from the um from the powder okay so that's calcination that's how we turn gypson rocks into gypsum powder that we can use in the dental office okay then the reverse side of the coin is the setting reaction okay so the setting reaction is just the opposite the setting reaction takes place you know we get out our process DPS and powder in the dental office that's our hemihydrate and we add water to it right we mix it up with water and then once we mix it up with water the hemihydrate goes back to being a dihydrate just like it was when we first dug it out of the Earth right so the dihydrate is the processed gypsum powder mixed with water that's your dihydrate and then heat is also released as a um consequence of the setting reaction so this is an exothermic reaction so just remember that these are opposite sides of the coin calcination is the exact opposite of your setting reaction right so calcination just go back calcination you take the dihydrate the gypson rocks from the earth and then you heat them up and it turns into a hemihydrate which is the process gypsum powder with water as a byproduct and then you have your setting reaction and that's when you start with your processed gyps and powder like you're getting ready to to make a study model in the lab you take the powder you add water and then those two combined become a dihydrate again okay so this is the powder mixed with the water becomes a dihydrate and then you have heat released as well so this is an exothermic reaction opposite of the reaction of calcination okay so the production of gypson products so first thing they do to get the gypson is they go to a quarry and they dig out the gypson Rocks right like you guys probably know what a quarry is maybe you watch Fred Flintstone or whatever you know he and Barney Rubble worked at a quari they would dig rocks out of the Earth all day so then these rocks are are processed in these big Vats um in manufacturing facilities like this so what happens is the the ground gypson um the gypson rocks are ground down then they're heat it okay and heating them causes them to lose water due to evaporation so that turns that that gypson from the earth um that dihydrate into a hemihydrate like we said so if um if the heating occurs in open Vats at 115 degrees celsus the resulting hemihydrate is porous and irregular in shape right and that's not real desirable that's kind of a cheap product and that's what plaster is Plaster is not real strong it chips pretty easily um it's not super resistant to abrasion um but it's cheap you know and sometimes it works for what you need it for if you're just using it for Diagnostic cast or study models you know just to look at the teeth you don't really have to carve anything on it or attach anything to it or make a bleaching tray then then plaster might be a good choice for you you know a Frugal choice I should say um so so plaster is you know it's pretty easy to make you know it just needs to be heated in the these open Vats at a certain temperature and then you get um but microscopically it's a very porous material and the um the particles are not uniform so leads to to a lot of uh water in the mixture um that evaporates and causes the model to be weak um now if the heating occurs under pressure in Steam at 125 degrees celsus then you still get a hemihydrate but it's less porous and more regular in shape and this produces Dental Stone so dentl Stone because it's less porous and it's more regular in shape uh you need less water to mix it you know so that means there's fewer voids in the the final model so it means it's stronger right so so Dental stone is stronger than plaster and you use this to make working cast or Master cast things that you know you can make something on those you don't have to worry about them breaking uh like plaster would so dentl stone is more expensive than plaster because it takes a little more processing to make it um and it's much stronger okay now there's a a third thing Third Way to do it if the gypsum is first boiled in 30% calcium chloride solution the resulting product is densite so denite is even stronger than Dental Stone and more abrasion resistant and better um so the densite which is then washed and heated with pressure then ground more ultimately this densite produces a high strength or die Stone right and this is the best stone it's also the most expensive and the hardest to make right because here you are boiling it in calcium chloride uh you know you have to bring it to a certain temperature um there's there's a lot that goes into making densite or the high strength or die Stone um so so densite or the high strength or die stone that results from densite it's stronger and denser than plaster or dental Stone okay and sometimes they mix it with silica to make something called Dental investment and that's really valuable for um if you're making Restorations with molten metal there's a way to do that and I have a video that shows um it's called The Lost wax technique um so you really need something that can withstand a lot of heat in order to make certain Restorations uh you know using this lost wa lost wax technique so um so just remember plaster is the weakest right dentl stone is better than plaster but not quite as strong as Dental investment or high strength or die Stone okay so physical properties of gypson products gypson products are manufactured as plaster Stone high strength stone or gypson bonded Dental investment right so this is going from the weakest plaster up to the you know strongest which is the the investment the main differences depend on the variation in size shape and paracity of the powders okay so if the powder has larger more regular and it's more porous this results in a weaker less resistant to abrasion final product okay and that's going to be your plaster okay plaster has very irregular um particles and it's porous right so it's going to retain more water when you mix up that model then when that water evaporates from the model during that exothermic reaction you're going to be left with a lot of spaces in that in that model microscopic but still a lot of spaces so that makes it weaker so if your um if your product is smaller and and more regular in shape um this results in a stronger final product so so like gypson Bond at investment is you know the part the particles are much smaller they're more regular shape and they're less porous right so so less water is retained in there and evaporates off the model so it winds up being a much stronger type of material so um so diagnostic cast are placed under very little stress you know we don't need them to be super strong so a weaker less expensive material to make those you know like plaster for instance or you know the the not high strength DL Stone would be acceptable you know you want to use the material that that works well enough basically otherwise you're spending a lot of money on something that you don't really need um because diagnostic casts we just look at them you know we're not making anything on them they don't have to be super strong we're just you know looking at the bite of the teeth and the occlusion and all that um working casts and dyes these require greater strength and accuracy because we're going to be making something on those you know we'll be making crowns or Bridges or things like that so we really need a a strong cast um that can withstand heat because it's going to be exposed to heat and has to be very very accurate uh because if you're Bridge or crown or whatever or even like a regular filling if there's even a little bit of a high spot on there or if it's even a little bit off it can really affect a person's occlusion which can lead to a lot of problems down the road um or immediately um I had a filling about two weeks ago and after a few days my jaw was so so sore and I kind of realized that was a high spot on my filling I mean it was probably even a fraction of a millimeter high but just that little bit made my whole entire jaw hurt you know like it was I wouldn't say Agony but it was painful so so these Restorations have to be really really precise you know so um so that's why we need this High degree of accuracy um and strength as well so these working casts and dyes these require greater strength and accuracy and we need to use stronger products that have less setting expansion so if something expands as it's setting it's going to make the restoration bigger than what the tooth should have basically you know it's going to be a representation of the tooth that's larger than it actually is and then you could wind up having restoration that that's too large for the tooth and maybe the margins aren't sealed for instance so um so we really want to minimize the setting expansion in most cases okay so this just shows you um over here on the the left we have particles of calcium sulfate this is a beta hemihydrate so basically this is Dental plaster right so look at the big chunks I mean this is in blown up 235 times so this is really microscopic you you can't see this obviously but but look at the the large large particles and they're very irregular in size um so there's lots of paracity you know there's lots of spaces when you have these large particles like this if you look at dentl Stone um the particles are smaller um there there's less paracity you know this would retain less water in a model made from dentl Stone than from plaster and that's basically why dentl stone is so much stronger than plaster because of the the morphology of these particles or the size and shape of these particles so when you have bigger particles you're going to have more pores you know the particles aren't going to fit together as well there's going to be more more spaces so it's going to be a weaker product um when the particles are smaller and more uniform in size it's going to be less porous so so the the outcome is that you have a stronger product so that's that's the difference between um plaster Dental plaster and dental stone and you see that reflected in the price right Dental plaster is cheap very cheap dentl stone is fairly expensive so um it's because it takes more processing to get the the particles you know the gypsum particles to be this size and this uniformity versus this size takes a lot more grinding and processing okay so the physical properties of gypson um and we went over some physical properties back in an earlier chapter I think it was chapter two um we want to look at the the strength of the uh the stone the abrasion resistance um the solubility the setting expansion and the setting time so just like when we were looking at the um the impression materials you know you want to choose the correct material for the situation right you you don't want to use um algen it if you really need to use polyvinyl soloxine for whatever reason um so just like in that situation in this situation we want to make sure that we choose you know a product that's the right strength you know are we looking at a a diagnostic model where we're just looking at the occlusion and you know how the teeth come together and everything or do we need a model where we're actually going to carve wax on top of it and put it into a a heated vat you know so so these are are the properties that we want to consider when we're choosing uh the material okay so strength hardness resistance to abrasion so uh the morphology that means the shape of gypsum products determine the properties and the behavior of the some products so we saw that when we were looking at the picture of the plaster under the microscope versus the dental Stone right the the shape of the particles were very different the plaster had larger more irregularly shaped particles so it's going to be a weaker product than the stone um so two factors contribute to the strength and abrasion resistance of the final product it's the shape of the particles and their paracity and how much water is needed to mix the product so that's actually three factors but your book says two so I'm just calling it two so um so so really the you know like we said the shape of the particles and their paracity that contributes to the strength of the product and the abrasion resistance um because when you have particles that are large and they're more porous you're going to need more water to mix those right and the more water you have in the mix the more water that's going to EV evaporate out of that final product out of that model and when that water evaporates you have these little spaces right and the more air spaces you have where water evaporated that means that final product's going to be not as strong you know if you have very few airspaces where the water evaporated you know you have a very uh low paracity product that you start with you're going to have a much much stronger you know outcome stronger model or a stronger cast or Dot whatever you're making um so strength and hardness of the gyps and products is related to the amount of water used in producing the cast so just remember the more water that's used to mix the gypsum product the weaker it will be okay you need a lot of water to mix plaster you don't need a lot of water to mix investment plaster is going to be the weaker product because you're using a lot of water a product with less water has higher density of crystals and is strong longer um increased paracity makes it necessary to use more water to convert the hemihydrate particles back into dihydrate particles okay so just remember the bottom line is the more water you use the weaker the product will be okay um larger more irregularly shaped particles are prevented from fitting closely together and results in more airs space and a weaker product again we saw large regularly shaped um particles in the plaster uh when we looked at that under magnification the plaster had large large particles compared to dentl Stone um the strength of a gypson product indicates its ability to resist fracture you know and sometimes we want something that's really strong because we might be exposing it to molten metal for instance if we're making a a metal Crown um plaster is weaker than stone or densite okay plaster is the weakest ST Dental stone is in the middle densite is the strongest uh minimal compression strength of any gyps and product must be reached within one hour after setting per the American Dental Association specs so the Ada has certain guidelines and regulations and they say that this has to you know they have one hour after setting to reach maximum strength or minimal compression strength so that's just something the Ada sets okay um so dimensional accuracy we talked about this a little bit with the impression materials um because it's always a concern um so setting expansion occurs with all gyps and products and this is a result of the growth of crystals as the particles join so you know so there's always going to be some expansion it's going to get larger as it sets um plaster expands the most um expands 3% which doesn't sound s like that much but remember we're dealing with you know we're dealing with structures that are fractions of a millimeter so it can be a lot um high strength Stone Products expand the least so that's 0.1% so remember plaster is cheap you kind of get what you pay for right you get more expansion with plaster and it's weaker high strength Stone you pay a lot more you get less expansion and uh a stronger product um so controlling setting expansion is critical for the production of accurate models and dyes um so you can never use plaster to make a die because it's just not precise enough it's not accurate enough it expands too much um and then if you work in a lab um sometimes they have these power-driven vacuum mixed high strength Stone which expands less than if it's hand mixed so you may have this in a in a dental office probably not you know this is this kind of Machinery you usually find in a dental lab um but just remember that if you if you mix stone with a power-driven vacuum mixer it's going to expand less than if you hand mix it it's a more efficient way of mixing um so setting expansion happens only during the hardening of the gyps and product so once the final set occurs there's no expansion but until that final set occurs that's you know that's when you can have that um expansion which can affect the accuracy of the reproduction okay um so reproduction of detail so like we said the greater the paracity of the final gypsum product the less surface detail is produced right so this paracity not only does it make the product weaker but it also doesn't produce detail as well so again I hate to keep picking on plaster but but plaster has a great deal of paracity right we saw it when we looked under the microscope had really large particles IR regularly shaped so that leads to a lot of paracity and when you have that the surface detail is not great right when you have dental Stone that's better than plaster the the particles are smaller there's less paracity so you get a little more detail when you get into you know the high strength Stone you get even more detail Dental investment the best of all more detail it's also the most expensive um we also have to be aware of contamination of an impression with blood or food or saliva because this is going to affect the surface detail so you know imagine that you took an impression of someone and they had a sesame seed sitting on their tooth right it doesn't seem like a big deal but you know if that sesame seed is in the impression and you pour the stone into there around the sesame seed you're not going to get an accurate reproduction of the tooth right so you need to rinse that that um impression off before you pour up any study model you know you need to make sure it's free of like any any debris or blood or even saliva like you would be surprised even a little bit of saliva can cause the reproduction not to be accurate it can cause like a convexity um somewhere you know where there isn't on the tooth and then that can be a a restoration that's not successful that doesn't work for the patient um so just make sure you rinse off the impression with water and inspect it before pouring you know make sure you're looking for any tears any voids any air bubbles you know everything we talked about in the last chapter um and all water should be poured should be removed before pouring up your model um and you can use the air water syringe at the unit you know the compressed air can blow off all the water so you know is to make sure that it's rinsed and dry before you um and you know and and used infection control obviously as well you want to um disinfect it before you pour up your model as well um so the compatibility of the impression material and the gypson material can influence the quality of the surface reproduction so we want to look at the and we talked a little bit about this last chapter too um you know you want to use materials that that go together um it's you can't really you know algen it and dentl stone uh they work pretty well together right they um they're both uh hydrophilic materials you know but if you have an algen impression or um or I'm sorry if you have a PVS impression that's hydrophobic if you try to pour Dental stone in there you're not going to get a great reproduction unless you use a surfactant so um so you really need to be aware of this compatibility between the impression material and the gypson material that you're using you may need to make modifications um so gypson material uh flows best when there's compatible wetting with the surface of the impression um Impressions that are water-based or hydrophilic like hydrocolloids these work better with water-based gypson materials um like all of these you know the dental um Stone and all that um elast mirrors uh this is like your polyvinyl soloxine your PVS for instance these May benefit from the addition of surfactant before or pouring to Aid wedding um the gypson will flow better into the impression in this case so remember these elasaur are are mostly hydrophobic you know some of them are less hydrophobic than others but they're not going to like this gypson very much you know it can lead to a poor reproduction so if you put a product called a surfactin on first then that will help you get a better reproduction okay so solubility um set gips and product products are not highly soluble in water but they're they're a little bit soluble so you never want to soak them you know um solubility is directly related to paracity right so so what's going to be more soluble plaster or uh Dental investment or denite um well the plaster is going to be more soluble because plaster is more porous right and we saw that when we looked at it under a microscope um so plaster is more soluble than Dental Stone okay and then classification of gyps and products so once again the Ada has these specifications and they officially recognize five different gypsum products uh used in dentistry um so remember diagnostic cast they can be fabricated with plaster or stone um it just depends you know diagnostic cast or a study model you're not doing a lot with it so you don't need a lot of strength um you don't usually you're looking at the occlusions so you don't need a great deal of detail uh so plaster can be okay to use um they used it here right when it's white it's plaster um if it's a different color it's some sort of dental Stone um so if strength is needed stone or high strength Stone may be used um but if you really don't need strength you know why not use plaster right it's cheaper you'll save some money um you know less processing um so the selection of a gypsum product it's based on the desired physical property so what do you do you need a model that's very very strong or do you need something or strength and an abrasion resistance doesn't matter quite as much that's what that's how you make your decision do I use plaster do I use Dental stone do I use high strength Dental Stone you know okay so um so this is an articulator I think we saw one of these in our last presentation um and you can see look here's plaster right so so sometimes they'll use plaster to build up the base to Ed on an articulator um and then the dentl stone is usually a yellowish color so that's your dental Stone there um so we talked about this in last chapter um the impression plaster this is your type one plaster it's really not used today because as an impression material it just isn't good you know you have to basically fracture it to get get it out of the mouth so you know anything even remotely rubbery is better so um so the impression plaster has been replaced by by less rigid elastic impression materials you know like um alginate mostly but also um the elastom mirors like PVS or poly sulfides so um so impression plaster it may be used as a final impression for edentula larches but it's I you would be hardpressed to find a practice that actually still uses impression plaster um it may be used to mount cast on an articulator and that's how it's used here right so so you can save a little money by you know building this up with plaster versus the more expensive dentl Stone okay and then model plaster type two so this is the this is this um usually when you see a white uh study model that's plaster um so model plaster the type two this is frequently used for Diagnostic cast and articulation of stone cast um so with model plaster the water to powder ratio is .45 milliliters of water to 100 grams of powder which doesn't sound like a lot of water but relatively speaking you know when you're comparing it to these other Dental Stones it is a lot of water right so this makes um you know this makes us much weaker when you have more water um it's durable but a relatively weak cast compared to Stone um the irregular shapes of particles keep them from fitting together tightly right so there's a lot of space between the particles a lot of paracity um model plaster it's available in Fast and regular set it's easy to manipulate um usually it's white so if you see a white model almost guaranteed that's plaster the the model plaster and it's the least costly of all gypsum products so if you're on a budget or you're just careful with your money you know use the plaster when you're making something simple like a study model or a diagnostic cast Okay and then Dental Stone type three um this is what we're going to be using in lab um so this is usually your dentl stone is usually a color yellowish color you know sometimes it's a little bit darker it just depends on the brand um but the dentl stone this is ideal for making full or partial denture models orthodontic models you know where they put the the bands and the brackets on there to see how they fit um and cast that require higher strength and abrasion resistance so um the dentl stone is uniformly shaped and it's relatively nonporous and again we looked at the picture of it under a microscope and you can see compared to plaster it's much more uniformly shaped and there's there's less space between the crystals because they're smaller and you know they're they are shaped more like each other so the water um to powder ratio for dentl stone is30 right so that means um let me just go back to the plaster uh the plaster is 045 milliliters of water to 100 G of powder so the dental Stone is30 Mill of water to 100 G of powder so it's much less water is used to um mix the dentl stone than the plaster so the particles um in dentl stone they pack together much more tightly you know two and a half times stronger than plaster so dentl stone is is a superior product to to plaster in many ways except for price um dentl stone is is also easily easy to use moderately expensive and traditionally colored yellow or white it usually has some sort of yellow color to it to distinguish it from plaster um so again this is what we'll be using in lab um it's definitely more expensive than plaster but it's you know stronger as well okay um so so dentl Stone high strength low expansion this is your type four and this is referred to as die stones or densite so with this type of um Stone you can actually fabricate wax patterns for cast restoration so you can actually put wax over this and actually carve the wax in the shape of the the tooth with all the morphology and then make a crown out of that or a bridge or whatever you're making um so it's hard abrasive resistant um surface it um when needed to resist the abrasion of sharp instruments needed to carve um on the stone D so so a lot of times you'll make this model and then you'll cut out a d from this a single tooth and then you'll fabricate some sort of a restoration on it um the crystals are slightly larger and denser than Stone um this requires strict handling so usually unless you work in a dental lab you're probably not going to use this type of stone um but you know you never know um so the water powder uh to powder ratio is 0.23 so remember with the the dental Stone it was 30 and with the um uh with the model plaster is 045 so as we get stronger material we're getting you know we're needing less water 023 um so the type four stone it's usually Pinker green so you can just add a glance know that it's not plaster or regular Dental Stone um and it's almost twice as strong as the type three Dental Stone which is really significant so um okay so next up we have type five now this is Dental Stone that's high strength but High expansion and you might be thinking wait a minute Miss O'Brien I thought you said that high expansion was not good right and I did say that so but but in some instances you do want High expansion right so and that's why they produce this so um so this is actually a recent addition to the Ada gypson products they didn't used to have the um High expansion Stone um but this was developed to meet the need for high higher strength High expansion stones that can withstand higher temperatures used in the casting process so when we make uh you know Restorations these these things are exposed to a lot of heat right so what they do with this type of stone is they add silica which is a product made from Sand um they or you know silicone is a product made from silica um silica is added to improve resistance to heat and causes increased thermal expansion and the reason we need this is to compensate for casting shrinkage which can occur with some types of processing you know restoration so in some cases you do want something that that expands more um so you might hear this also called gypson based investment um and this has a water powder ratio of 0.2 um whereas the uh the the low expansion is .23 so less water A Little Bit Stronger um this is usually like a blue or green color and again they they make these uh different colors so you can just at a glance distinguish you know what it is you know you don't want to be uh thinking you're pouring that plaster and grab like some very very expensive High expansion high strength type of H Stone okay so um so metal plated and epoxy dyes and resin reinforced Stone so your type four and five these are the high strength Stones um the type four and five chips and products are commonly used dye materials so remember the dye is when we take a single tooth out of this uh out of this cast and make use it for restoration so um so these stones are they're they are very very hard but when you're carving wax patterns on top of here uh it can you know you can cause little Nicks in the in the Dy or in the stone um and again that can lead to an unsuccessful restoration so what they can do is um electroplate uh these these dyes like basically they pour metal onto them and this protects the Stone from abrasion when you're carving that that wax um you know U restoration model so um so they can use metal or they can use um epoxy um epoxy dyes they use a resin like a plastic and a hardener to produce a harder dye that's more resist than high you know high strength Stone so you're just adding a a layer of protection on here if you use some sort of a resin or a metal plate to um uh to create a stronger dye um so if you do use a resin the epoxy usually sets in about 16 to 24 hours um so it is a an investment of time okay and then investment materials so again these are very very strong kind of uh heat resistant material investment materials combine gypson and silica right so um these are used to form metal casings through the Lost wax technique which we'll talk about in a minute and they're used to produce strong models that can withstand molten metal so when you use this lost wax technique um you know your your dye is going to be exposed to um to to very very hot metal so investment has increased setting expansion um and it compensates for for the shrinking of metal casting so that's your your type Five Stone okay um and then manipulation of gyps and products material selection so again selection should be based on desired properties right plaster is a good strength is a good choice for Diagnostic cast or you know things with low strength requirements Dental stone is good for a working cast a working cast will require more strength more accuracy more hardness and then high strength Stone you need that to make those dyes um it requires High dimensional accuracy strength and abrasion resistance so so again you're probably in the regular dental office you're probably going to be using dental Stone most of the time maybe plaster you know if if your practice is you know veryy into their budget um and then high strength Stone usually that's going to be used more in a dental lab I would be surprised if you were using that on a regular basis and then any sort of regular you know um dental office okay so proportioning water to powder ratio um so properties of gyps and products are directly related to their um water to powder ratio right we said more water equals a weaker product right so um so we want the the product to be wet enough you know the mix material should have sufficient flow that it can reproduce surface detail you know you want that that material that gypsum whatever it is to flow into all the various fissures and pits and you know every every aspect of the tooth we want that represented you know in in our reproduction so we want it to be able to flow into all those areas but we kind of have to balance it with not putting too much water in because then it becomes weak and can be a you know break or a braid or whatever um so an increase and the recommended water is going to result in a thinner mix and will take longer to set and the final product will be weaker and less accurate right so don't be tempted to add too much water and you know it's it's going to take a little you know strength and work to mix this stuff up you you really have to um mix the water in well and get a smooth consistency um you're going to be tempted you know at least I I am a lot um to put more water into the mix to make it easier to mix it up but what's going to happen is if you do that you're going to get a weaker less accurate you know model at the end of things so so don't be tempted to put more water in there um that's you know it don't be tempted to put more water in there or less water because a decrease in the recommended water that's going to result in a thicker mixture and that's not going to flow into all those uh Fishers and pits and grooves and you know all those things on the occlusal surfaces of the tooth you're not going to get a good representation if it's too thick so always always always stick with the manufacturer's suggested water to powder ratio okay that's the bottom line so too much water is going to be weak not accurate too little water is going to be too thick again not accurate um you want to you know the the manufacturer's directions are there for a reason so so measure it out and and you know stick with their their directions um water should be measured with a graduated cylinder and powder weighed on a scale um you know ideally you'll weigh the powder on the scale but the reality is that most people just use a scoop you so um so it would be nice to weigh it on a scale but that doesn't always happen um so it's not recommended to measure powder with Scoops due to the condensing of powder but you know I hate to say it but realistically that's that's what most people do in an office okay so again ideally you want to uh use a scale to to weigh how much powder you're using and a graduated cylinder uh to to measure the water um inappropriate measuring devices and techniques will lead to one of two results um you can have a cast a stone cast with too low water to powder ratio which means not enough water the stone will be too thick and detail will be lost it won't flow into to all those nooks and crannies on the tooth uh Stone cast with too high of a water powdered to ratio meaning you use too much water you're going to have stone that will be too thin and strength will be diminished it'll be more likely to break or braid you know you might not be even be able to separate it from the algen impr pression it'll be so weak okay um so mixing or spatulation so this is what you guys are going to be doing in lab you're going to be mixing this up by hand because we don't have a mixer and you know most offices don't have a mixer either so it's good good practice um so plaster and stone are usually mixed in a flexible rubber Bowl um so the rubber bowls are kind of like this the ones that we have in lab are a dark green color and you see that quite a lot for some reason um and then you mix it with a broad uh metal spatula so it's got a wooden handle and then a metal part here and we'll see another picture that shows you that better um so the mixing process they call it spatulation so that's the official name um mechanical vacuum mix devices may be used um but again that's not the usual route in a in a regular office um place the measured water in The Mixing Bowl first and then slowly sift powder into the water that should take you about 30 seconds so again when you go into real practices everybody seems to put the powder in first and then the water which is not the right way to do it you know you're going to get more air bubbles if that's the case so so try to do it the other way you know we teach you the correct way but then you kind of go out and see everybody else doing it a different way so um but you know the the best way is put the water in first and then sift the powder in um even wedding powder even wetting of powder will occur with sifting um clumps are avoided and it minimizes trapped air so just add it don't add a whole big Clump at once just you know kind of sift it in like a little bit at a time um and then you want to vigorously wipe the mix against the side of the bowl when mixing so you're really gonna it's just like when you mix the algen it you know you're going to press that spatula against the bowl and you're you're getting that air you know out of the mix um so you want to spatulate for one minute um at two Revelations per second until a smooth homogeneous mix with a glossy service is produced so um it needs to look glossy you know that that means it's mixed and you can't see any clumps of powder you know everything has to mix be mix pretty well um and don't take more than a minute um for mixing otherwise it'll start to set before you start pouring up your model um an increase in the time and rate of spatulation will shorten setting time and increase the rate of setting expansion so again you don't want to mix it for longer than a minute and you don't want to exceed about two revolutions per minute you know if you go too fast then you're going to get you know the the setting time will be shortened and you'll get more expansion in the model which affects the um the accuracy okay initial setting time and working time so after you're mixing for one minute uh this is when your working time begins so during this time the the mixture you're going to pour it into the impression on a mechanical vibrating plate so this is the the vibrating plate and you turn this on and it vibrates you know then you start adding the um the mixture in usually start at the um you know on the upper right or the upper left whatever you're pouring up um you start on one side and you kind of let it kind of go into the the entire impression and I have a video in just a few slides that will show this um so during this time the mixture is poured into the impression on a mechanical vibrating plate and then once the the glossy um look of the material is gone that indicates that the the gypson has set it's has reached its initial set okay and then the final set is reached when the material can be handled safely but has minimal hardness and resistance to abrasion so the final set is basically when when it cools off so remember we said this was a exothermic reaction uh when you're you know the setting reaction it's exothermic so it's going to release heat and it's going to feel kind of warm for a while um and then once that warmth that warm feeling is no longer there uh and it's cooled the touch that means that the the final setting has been accomplished but you don't want to separate it just yet even though that that reaction has completed um it hasn't reached its ultimate hardness yet you know so you want to wait about 45 to 45 minutes to one hour before you actually separate the impression from the the model okay so so that one hour of extra time will allow it to continue to harden um but you don't want to um you know you don't want to leave it in there longer than an hour make sure you separate it by the time an hour comes um the material will continue to harden um and become two to three times harder over 24 hours so so over 24 hours it's still hardening uh but you want to get the uh you know the tray and the alginet off of there um within an hour of the final setting time okay so this is done Stone you can see by the yellow um okay so um altering the uh um controlling the setting times altering the water to powder ratio again please don't do that it's just not a good idea um increase in the proportion of water will slow the setting times you know it's going to take longer for that water to evaporate out um and an increase in water can reduce the strength by 50% or more that's huge that's a big problem so it's not recommended so no matter what you do please don't add more water you know beyond what the manufacturer recommends um a decrease in the proportion of water will accelerate setting times you know there will be less water to evaporate out of there so it's going to set faster um the problem is you know with this decrease in water it's going to make the mixture thicker you know it's going to be more difficult to manipulate there's going to be more air bubbles caught in there it's not going to get the detail of the tooth especially the accusal surfaces so we want to avoid using too little water right we got to get it just right um decreasing the proportion of water is recommended only when pouring the base if needed so the base of the model it's this part right and up here so with the base you know you have a little more freedom with the base because it doesn't have detail like like the actual teeth so when you pour up the base um you can use a little less water and make it thicker um that way it'll set faster and when you when you set the um this portion the anatomic portion um on the base it won't syn so again this is all stuff that we'll see in lab okay um so control of setting time spatulation so a longer and more rapid spatulation of gypson results in accelerated setting time so if you start it longer and faster uh the setting time's going to accelerate but it also results in an increased setting expansion so it's not a good idea um you can also control setting times with the temperature of the water this is probably the most acceptable way to do it um So within limits an increase in temperature of the water that you mix in with the gypson will accelerate the setting time right so it'll set faster with warmer water um you know really gypson should be mixed with room temperature water but if you're a pro and you know what you're doing you can mix and War more water and it'll set faster and you know maybe you want to do that if you're really really busy okay um so this is a trimmer you guys will see a bunch of these in the lab um this spins around and you you trim the model on here again I have a a video of this in a few more slides um so be careful because with the spinning it's it's metal you know and you want to keep your fingers away from there because it can be dangerous um so control of setting times um acceler ators and retarders so manufacturers can add in these chemicals that accelerate or the the change um you know that that changes the solubility of the hemihydrate and water so what happens is accelerators they will reduce the the time between the initial um and final set and an accelerator will make gypson quote unquote fast set um if no accelerators are added then the product is regular set there's also called something called uh slurry water so when you're using this trimmer water is actually spraying through this to keep it cool right so so you're trimming in the water sprays through this and you're getting little bits of your model or little bits of the gypson in there and this thing actually um spits out the water that's coming through here into the sink and it's got this mashed up gypson in it so um that's your slurry water and what happens if you use slurry water for something um I'm not sure why you would but this will accelerate the chemical reaction because there's already crystals formed so it'll be easier for more crystals to form because they already have a framework so um so this slurry water it accelerates the chemical reaction and leads to a shorter setting time so you know theoretically you could use the the water that's discarded from here the slurry water and mix it with gypson for your base and then your base would set faster that might not be a bad use of slurry water um um but you know be careful okay so here's here's the bowl this is a you know a soft mixing bowl and then here's the spatula it's got a wooden handle and then it's a metal spatula um so so make sure when you're when you use these things they have to be clean right you have to get all the old uh alanate off of them you have to get all the Old dentl Stone or gypson whatever you're using off of them they have to be really really clean um because if you have any old gypson that's set that's going to cause your material to set faster and maybe unevenly as well because again the set gypsum is making creating this framework right so so your material is going to set faster on you know if there's a framework there than if it has to build the framework you know itself through crystallization um so just remember if set materials are left on mixing bowls or the spatula they can become part of the fresh mix right and this results in um acceleration of the setting process and uneven setting you know if it's in like some of the mix but not all of the mix um all equipment should be cleaned after use um blood saliva and algen it can the set of gypson so so again you have to rinse off your um impression as well as dry it um so so rinse The Impressions before you pour them and disinfect them as well of course okay so fabricating and trimming Diagnostic and working cast um uh the diagnostic and working casts have two parts they have an anatomic portion and this replicates the heart and soft structures um so this is poured by vibrating small increments of flowable gypson into the impression again we'll see this in a video in a minute um so your anatomic portion is the teeth you know it's like the muscle attachments into the vestibule here you know where the gingiv is represented the frenum that's all your anatomic portion then your art portion or base this AIDS in the handling and articulating of the cast so um so you can make this a lower strength product than the anatomic portion this is really the important part as far as the detail goes this is just kind of like holds it there you know so you could use plaster here and stone here potentially uh usually you just use all Stone um but this can be a lower strength product than the anatomic portion and it can be poured by one of three methods according to your book um so we've got the uh the Double por method and um this is your base um method as well uh so this involves two separate mixes and two separate setting times so what you do is you pour up a mix and you pour up that anatomic portion first right and then you leave it in an upright position so you pour you make one mix for this the anatomic portion and then you set that aside um and then approximately 10 minutes after the gloss is gone from this you do a separate mix for your base you make the base and sometimes you can make the base thicker you know that might be helpful when you're um it just depends it can hold it in place better um so the base should be about one inch thick and you place it on a tile like this so it doesn't stick so then this filled impression is inverted on the base with the tray um handle parallel to the base so what you do is you turn this upside down and you put it on here and then you have something that looks like this right you got the anatomic portion up here in the tray in the algen impression and then you have the base portion here so that that's so you pour up two you know so you do two mixings you know this is your double por method so remember the base material must be thick enough to support the weight of the impression um with no sinking that's why you might want to make this a little bit thicker so this doesn't sink down into it and then you have too short of a base right so do not let the base material contact the impression tray and lock you have to be real careful that this impression material doesn't get around this tray because then it'll lock in place and you won't have you won't be able to separate it without breaking it usually um so if a cast is a working cast um the anatomic portion is dentl Stone and the base portion is Plaster again you don't want to spend a lot of money making the base you know you can use a cheaper material because that doesn't have to be as strong or as abrasion as um you know resistant so okay and then the single pore method this um is also called the inverted pore method so with this you just do one mix of gypsum right you don't have to do two mixes you just do one and then you pour both the anatomic any art portions of the cast at once so after the impression is poured the rest of the gypsum is used for the base so you pour the impression you still have gypson you know liquid gypson in the bowl and then once you're um the you know the impression is poured the anatomic portion then you use the rest for the base so you use the rest for the base you place it on a tile and uh and invert this on top of it so so you wind up with the same product as your double por method but a single pour you really have to know what you're doing like you have to work fast and efficiently so it requires better skill and timing so you know we always do the double pour method um in our Labs because most of you don't have a lot of experience doing this so it's just a little bit easier for a beginner okay and then something called the boxing method so the boxing method this is kind of interesting um use a strip of boxing wax so this is boxing wax it's kind of like um very firm you know so it holds everything in place um so what you do is you surround the impression with this boxing wax um and you form a wall and then you pour the gypsum inside there um so the wax should extend at least a half an inch higher than the highest point of the impression and uh the base should be parallel to the accusal plane so we always want we don't want to lops it basically so what you do is you you take this boxing wax and put it around here and then you pour in the gypsum and it's basically a one poor method more or less and um I was visiting an office this last semester and one of my students was showing me um the assistant at the office kind of showed her a little technique and instead of using boxing wax she used a wet paper towel to make this border and then poured it up and it was kind of like interesting to see it was the boxing method but using a paper towel instead of um wax and it actually looked really nice it worked quite well so okay storage so um I'm G to stop here and uh I'm G to record part two just so it's not too long uh so we'll pick up with storage in in part two of this chapter's presentation so I will see you over in the next recording thank you for listening