I’ve seen it stated both ways (that setting expansion increases and that it decreases with an increased W/P ratio). To be honest, I think it depends on the type of gypsum and also how much water exactly is being used.
Can you please tell more about guaging water? Is this term only used with gypsun products? why not with alginate or other products as we add water to them too?
Hello! Dental decks and some articles describe the addition of water resulting in more expansion of the gypsum particles. "Water/powder ratio: the water/powder ratio is an important factor in determining physical properties. When a high proportion of water is used, the powder particles are farther apart. This results in more expansion with a retarded setting time and a weaker product. Dental plasters generally require about twice as much water compared to stones. Plaster has a higher setting expansion than does stone." Any way to clear up this concept?
Hey Doc! ...I have small query about IMPRESSION PLASTER I read it somewhere that it's the plaster we use obtaining occlusal records ...but acc to ur vdo it's a plaster helping holding cast ...... Hoping for the answer 🙂
I believe that increasing temperature results in a slower setting reaction for gypsum ..but your video says otherwise .can u give a little clarification please .appreciate your good work .
Can you point to any resource that says this? All of the notes and sources I have say that hotter water accelerates the reaction. Maybe this has to do with a maximum water temperature, where after a certain point of heating the water, the reaction no longer accelerates but actually slows down and will stop all together if the water were boiling for instance.
That is an interesting concept! I imagine the increased salinity would indeed decrease setting time, but might have some side effects regarding the quality of the final mix and detail capture.
Love your videos! thank you for taking the time, just one question... Mosby: "The increase in water:powder ratio decreases the number of nuclei of crystallization per unit volume and increases the amount of space between crystalizing nuclei, thus increasing porosity when drying. This causes a decrease in the interaction of dihydrate crystals and diminishes any outward thrust of the mass. Consequently, setting expansion is decreased" (which is the same as your video). Dental Decks: "When a high proportion of water is used, the powder particles are farther apart. This results in more expansion with a retarded setting time and a weaker product" (which is totally opossite). So... more water is more or less expansion? I was taught more water, the cristals are farther apart and there is expansion, now I am really confused. Hope you can help me. Thanks
Hi there! Thank you for your question, and for including all of those details. I was surprised to hear this at first, but perhaps both of these explanations are correct! A thick mix with a decreased water:powder ratio means that more gypsum crystals will be interacting with each other which will increase expansion and increase the amount of heat released. This is how I always understood it. But, this decreased amount of water is still within the bounds of the manufacturer-recommended mixing ratio range. Once we go outside that range, that is when the rules change. Beyond this, excess water causes increased expansion beyond what is normal and is called hygroscopic expansion. Does that make sense?
@@mentaldental Got it! Thanks I just found: when a thick mix is used, setting expansion is increased due to the saturation of nuclei of crystallization. When a think mix is used, setting expansion is decreased since the nuclei of crystallization are less dense. But if there is excess of water in the hygroscopic investment technique will produce an over expansion of the gypsum used for the investment!
Your videos are great as always. But I’m confused for what you said in the begging between type 3 and 4. Type 3 have low expansion Type 4 have a high expansion When you are explaining in detail in type 4. You said least amount of expansion which it’s the opposite if what you wrote in the begging. Please explain PLEASE. THX A LOT FOR ALL YOUR HELP.
Mental Dental I see my mistake. You are right. Thx a lot. Your videos are excellent. I love them. I donated $ to your patron website for a few months. Your hard work deserves a compensation. Thanks again for your fast response. 👍
:( i was using chatgpt to help study for this and one of the questions: Which type of dental gypsum is commonly used for creating dies for crown and bridge restorations? a) Type I gypsum b) Type II gypsum c) Type III gypsum d) Type IV gypsum i remembered watching YOUR vid and i knew it wasn't the first two and i put D. THEN it tells me this : d I apologize, but that answer is incorrect. The correct answer is: Which type of dental gypsum is commonly used for creating dies for crown and bridge restorations? a) Type I gypsum b) Type II gypsum c) Type III gypsum d) Type IV gypsum The correct answer is a) Type I gypsum. Type I dental gypsum, also known as impression or mounting plaster, is commonly used for creating dies or replicas of teeth and oral tissues in crown and bridge restorations. It provides high detail reproduction and accuracy, making it suitable for creating precise dental prostheses. :( I'm so done with that website. It messed me up on the water-to-powder ratios too and now i feel like i have to relearn everything. All because i told it to quiz me. Unless there's something else I'm not understanding with that question???
