(C). None of the above
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. It can be used as a fertilizer, chalk, or stone for the fabrication of models in dentistry. Borax and potassium sulfate can be added to the gypsum to modify the setting speed.
- Borax is a retarder
- Potassium sulfate is an accelerator
Borax is also used as a retarder in other materials such as concrete.
Tips: BORed (being slow) rhymes with BORax. Do you see the image?
Answer: (A). Retarder
While we are at it, why don’t we learn a little more about gypsum? It is the most commonly used material for replication in dentistry. Here are different types of gypsum, from low to high strength:
- Plaster (type II): irregular porous particles. High setting expansion and low compressive strength. Requires more water.
- Stone (type III): less irregular particles. Low setting expansion and higher compressive strength. Used for study models.
- Diestone (type IV and V): non-porous, smoothest, and dense particles. Highest compressive strength. Used for crowns and bridges.
One more thing to know about gypsum is that it produces heat (exothermic reaction) from the chemical reaction of hemihydrate and water.
Hope your day became a little more fulfilling knowing that you learned something for the dental hygiene board exams (NBDHE, NDHCE) with StudentRDH. Next time you are in the lab fabricating a replica, try to recall this knowledge. It takes at least 3 times to remember a new information according to science, so make sure you keep looking at the same info again and again. This way, you will be more ready for the dental hygiene board exams (NBDHE, NDHCE)!
Mini Boards Reviews for the National + Local Anesthesia Dental Hygiene Boards. Weekly Sample Questions at www.StudentRDH.com. Find COMPLETE review courses too. “I wish I did not spend money on other review courses!” – Bethany, Bergen CC, March 2016