Since we had a 2-hr session of practical-revision on dental cements today, thought it'd be good for me, and for other dental students that I'd write a concise (read:brief but comprehensive) post about it.
I'll be writing on;
1. Definition
2. Classification & Main Types
3. Composition, mixing & uses
4. Mixing time (MT), working time (WT) and setting time (ST)
1. Definition
Dental cements are hard, brittle materials formed by mixing powder and liquid together. They are either resin cements or acid-base cements. The former sets via polymerisation reaction while the latter via acid-base reaction.
2. Classification & Main Types
Type I: Luting agents that include permanent and temporary cements
Type II: Restorative applications
Type III: Liner or base applications
Main types of cements you would probably use in dental school;
1. Glass ionomer cement (GIC) -exist as liners/restoration
2. Resin-modified Glass Ionomer Cement (RMGIC)
3. Calcium Hydroxide cement (Dycal)
4. Zinc Oxide Eugenol cement (ZOE)
5. Zinc Phosphate cement
6. Zinc Polycarboxylate
3. Composition, Mixing & Uses
Glass Ionomer Cement
Composition
Liquid: Itaconic acid, tartaric acid, maleic acid, and water
Powder: Zinc oxide, aluminum oxide, and calcium
Dispensing
*important: Use plastic instead of metal spatula to avoid glass particles to abrade metal surface and incorporate them into the cement. This will weaken the cement structure.
*always read manufacturer's instructions beforehand
*for accurate dispensing of powder, tap the bottle gently. do not shake or invert.
*for accurate dispensing of liquid, hold the liquid bottle vertically and squeeze gently.
*LINER ratio: One level scoop of loosely packed powder and one drop of liquid provide the
recommended powder to liquid ratio of 1.4 to 1 by weight. The powder to liquid
ratio may be altered to change the viscosity of the mix. Ratios ranging from 1 scoop powder/2 drops liquid to 2 scoops powder/1 drop liquid are acceptable.
Mix ratios beyond this range are not recommended.
*RESTORATIVE ratio : 1 level scoop of powder to 2 drops of liquid.
Mixing
-divide powder into equal halves
-spread liquid out into a thin layer
-pull half of the powder onto the liquid and mix with lapping strokes (like impression materials) for 10-15 seconds (can be up to 20 for restorative GIC)
-pull remaining half of powder and mix thoroughly to reach glassy consistency.
Manufacturer's instructions for 3M ESPE Vitrebond HERE!
Calcium Hydroxide (Dycal)
Read all about it here: http://www.dentsply.es/DFU/eng/Dycal_eng.pdf
Zinc Oxide Eugenol (ZOE)
Read all about it here : http://www.spofadental.com/media/Products/ProductFamily/117/en-US/Documents/31002/Caryosan_IFU_EN.pdf
Zinc Phosphate
Zinc Polycarboxylate
4) Mixing time (MT), working time (WT) and setting time (ST)
Mixing time: Time from addition of powder/base to the liquid/catalyst until the right/desired consistency is achieved.
Working time: Time from start of mixing to the point at which consistency of mix is no longer acceptable for the usage of intended purpose.
Setting time: Time duration between start of mixing & point where material hardens/completes its reaction.
Based on our experiment today, here is the tabulated data regarding the above matter;
We didn't note the setting time because that is already determined by the manufacturers and besides, materials like GIC has ongoing setting reaction even after 24hrs.
That's all for today ! Hope you'll benefit from this ! All the best :)
http://www.dentistrytoday.com/dental-materials/6151-dental-cements-an-overview
http://free-ed.net/free-ed/Courses/06%20MedHealth/060401/DentalMaterials/default.asp?iNum=0103
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