How to properly wet a cast. For rinsing while trimming/wax seperation/duplication/processing.

[Denturepropgh]

I know that it has been discussed before. Some people use diluted soap. But one thing you should really try to keep from doing is rinsing/soaking with water. Water erodes the cast and will compromise fit; leading to sore spots in the mouth. I would like to share a little section of what I have learned from the Air Force Manual in regards to wetting/soaking models.

2.19.2. Saturated Calcium Sulfate Dihydrate Solution (SDS) Preparation:

2.19.2.1. SDS is a clear, true solution of water and a maximum amount of dissolved dihydrate (set) gypsum product. Cast surfaces exposed to SDS do not erode nearly as much as cast surfaces bathed in tap water. If a cast must be soaked for more than 1 or 2 minutes, SDS should be used.

2.19.2.2. SDS is made by immersing fragments of gypsum casts in water for about 5 days. A saturated solution consists of about 0.2 grams of dehydrate in 100 cc of water.

2.19.2.3. If a slurry water suspension is left to settle out for 3 to 4 days, the clear fluid above the sediment is SDS. For use, siphon off the SDS into another container without agitating the sediment layer.

2.19.2.4. SDS can be made from plaster, dental stone, or gypsum bound investment, whichever is best suited for the kind of cast you expect to wet.

2.19.3. Wetting Casts:

2.19.3.1. Occasionally, casts require quick superficial wetting (for example, cleansing cast surfaces). SDS must be used instead of tap water for this purpose.

2.19.3.2. When a cast is shaped on a cast trimmer, gypsum slurry splashes onto its surface. If this slush layer is allowed to dry, it is hard to remove and cast damage could occur. As the slurry buildup accumulates, rinse the cast in a suitable container of SDS to remove the slurry. The SDS must be changed often or it will also turn into concentrated gypsum slurry.

2.19.3.3. When outright cast soaking must be done in conjunction with a laboratory procedure, the cast must not be completely submerged in SDS. Total immersion slows down the soaking process because air trapped in the cast cannot readily escape. Instead, the fluid level should be maintained below the tissue surface of the cast. A cast can be moistened in this manner in 20 to 30 minutes.

2.19.3.4. The wetting process can be seen gradually working up from the base of the cast to the tips of the teeth, much the same as oil dampens the wick in a lamp. If relief wax has been placed on the cast, there is danger of the escaping air from the cast lifting the wax from the stone. Instead of setting the cast on its base, set it on its end in the SDS.

I haven't done it yet, but I'm even thinking about using SDS in the pressure pot instead of water. It would probably need changed daily to keep from scaling up though.
What I do to make my solution is save any bits of extra stone from pouring models, put them all in a bucket that I saved from hydrocolloid, and fill with water. I put a sticky note on the lid for when the sds is ready to use, about 5 days from the current date. I have noticed that my cast really doesn't get soft or erode like I have experienced in the past.

Hope this helps with the quality of your work. Have a nice day!

 

[ztech]

I know that it has been discussed before. Some people use diluted soap. But one thing you should really try to keep from doing is rinsing/soaking with water. Water erodes the cast and will compromise fit; leading to sore spots in the mouth. I would like to share a little section of what I have learned from the Air Force Manual in regards to wetting/soaking models.

2.19.2. Saturated Calcium Sulfate Dihydrate Solution (SDS) Preparation:

2.19.2.1. SDS is a clear, true solution of water and a maximum amount of dissolved dihydrate (set) gypsum product. Cast surfaces exposed to SDS do not erode nearly as much as cast surfaces bathed in tap water. If a cast must be soaked for more than 1 or 2 minutes, SDS should be used.

2.19.2.2. SDS is made by immersing fragments of gypsum casts in water for about 5 days. A saturated solution consists of about 0.2 grams of dehydrate in 100 cc of water.

2.19.2.3. If a slurry water suspension is left to settle out for 3 to 4 days, the clear fluid above the sediment is SDS. For use, siphon off the SDS into another container without agitating the sediment layer.

2.19.2.4. SDS can be made from plaster, dental stone, or gypsum bound investment, whichever is best suited for the kind of cast you expect to wet.

2.19.3. Wetting Casts:

2.19.3.1. Occasionally, casts require quick superficial wetting (for example, cleansing cast surfaces). SDS must be used instead of tap water for this purpose.

2.19.3.2. When a cast is shaped on a cast trimmer, gypsum slurry splashes onto its surface. If this slush layer is allowed to dry, it is hard to remove and cast damage could occur. As the slurry buildup accumulates, rinse the cast in a suitable container of SDS to remove the slurry. The SDS must be changed often or it will also turn into concentrated gypsum slurry.

2.19.3.3. When outright cast soaking must be done in conjunction with a laboratory procedure, the cast must not be completely submerged in SDS. Total immersion slows down the soaking process because air trapped in the cast cannot readily escape. Instead, the fluid level should be maintained below the tissue surface of the cast. A cast can be moistened in this manner in 20 to 30 minutes.

2.19.3.4. The wetting process can be seen gradually working up from the base of the cast to the tips of the teeth, much the same as oil dampens the wick in a lamp. If relief wax has been placed on the cast, there is danger of the escaping air from the cast lifting the wax from the stone. Instead of setting the cast on its base, set it on its end in the SDS.

I haven't done it yet, but I'm even thinking about using SDS in the pressure pot instead of water. It would probably need changed daily to keep from scaling up though.
What I do to make my solution is save any bits of extra stone from pouring models, put them all in a bucket that I saved from hydrocolloid, and fill with water. I put a sticky note on the lid for when the sds is ready to use, about 5 days from the current date. I have noticed that my cast really doesn't get soft or erode like I have experienced in the past.

Hope this helps with the quality of your work. Have a nice day!

As an AF trained tech this was beat into our heads. Quickest way to make SDS is grind scrap stone on a model grinder and catch the affluent in a container. Leave it undisturbed for a few hours and the clear is SDS. As far as your pressure pot, we didn't use SDS in there because most didn't submerse the model. We used stands to keep the model above the water. The benefit of the water in the pressure pot is a humid environment, the acrylic doesn't need to be immersed to benefit from it. In fact, ortho appliances come out clearer when you don't submerge them.

 

[JKraver]

I understand the science, never had an issue with tap water myself. I use good stone and vacuum mix it. Never experienced etching that would effect the fit of a denture.

 

[Denture Dude]

I understand the science, never had an issue with tap water myself. I use good stone and vacuum mix it. Never experienced etching that would effect the fit of a denture.

Ditto this.

 

[ztech]

I understand the science, never had an issue with tap water myself. I use good stone and vacuum mix it. Never experienced etching that would effect the fit of a denture.

I agree. As a manager in a larger AF lab, standards had to be established to ensure a consistent product and although a quick rinse under tap water doesn't harm the surface properties of a gypsum model, a model left overnight will result in damage to the surface. I personally haven't made SDS since I retired from the military, but I am super careful about the way I handle the materials that I use.

 

[JKraver]

I agree. As a manager in a larger AF lab, standards had to be established to ensure a consistent product and although a quick rinse under tap water doesn't harm the surface properties of a gypsum model, a model left overnight will result in damage to the surface. I personally haven't made SDS since I retired from the military, but I am super careful about the way I handle the materials that I use.

I get the this is the correct best way to do it, but even leaving a model in SDS overnight will 'damage the model'. Because of how chemistry works, polar solutions will etch and deposit at random areas. How about a tech should know not to leave a model in water overnight? I rarely soak a model for more than 5 min.

 

[ModelTech]

Does this apply to the pre-soak before duplicating a model in hydrocolloid? I have always used hot tap water for 5-10 minutes and completely drying the model before I place it in my flask.

 

[JKraver]

Does this apply to the pre-soak before duplicating a model in hydrocolloid? I have always used hot tap water for 5-10 minutes and completely drying the model before I place it in my flask.

Well I have never heard of using hot tap water, I wouldn't do that. The model needs to be saturated so it doesn't pull the hydrocolloid into the model. Do you mean completely drying it as in setting it on the bench for a few hours or just blowing off the excess? SDS which is basically your model stone that has been allowed to separate is just gentler on the model than tap water.

 

[ModelTech]

Well I have never heard of using hot tap water, I wouldn't do that. The model needs to be saturated so it doesn't pull the hydrocolloid into the model. Do you mean completely drying it as in setting it on the bench for a few hours or just blowing off the excess? SDS which is basically your model stone that has been allowed to separate is just gentler on the model than tap water.

Bego also recommends 100 degree water and I usually blow off the excess then damp a dry towel on the models. I suppose the logic is to get the model closer to the temperature of the hydrocolloid which is about 135 degrees when it comes out of the machine? I have used room temp water, cold water, hot water all having the same results which are usually good, just aiming for more consistency. We have never soaked models in an SDS solution however I'm interested what results that could yield.

 

[sidesh0wb0b]

you've gotta lick it before you stick it







that's what the old ceramists say anyway. weirdos.

 

[JKraver]

Bego also recommends 100 degree water and I usually blow off the excess then damp a dry towel on the models. I suppose the logic is to get the model closer to the temperature of the hydrocolloid which is about 135 degrees when it comes out of the machine? I have used room temp water, cold water, hot water all having the same results which are usually good, just aiming for more consistency. We have never soaked models in an SDS solution however I'm interested what results that could yield.

How do you heat your colloid? How many times do you reuse it?

After pouring at 70c or so, I bench set for a minute or two, then I put bottom 1/3 under ice cold water for 10 min, then I fill to the top with ice cold water for 30.

 

[ModelTech]

How do you heat your colloid? How many times do you reuse it?

After pouring at 70c or so, I bench set for a minute or two, then I put bottom 1/3 under ice cold water for 10 min, then I fill to the top with ice cold water for 30.

Using a Mestra hydrocolloid machine changing out the colloid once a month, pouring at 56c. Air cooled today with no issues just not sure if its really having an impact on the result. Common sense tells me we shouldn't shock that very warm colloid with ice cold water however like I previously stated we have done that for years and years.

 

[kimba]

you've gotta lick it before you stick it







that's what the old ceramists say anyway. weirdos.

I’ve lived my life using that motto since I was 18 yo