Term
| Differentiate between a direct and indirect restoration. |
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Definition
Direct - done directly in the mouth Indirect- prepared in the laboratory |
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Term
| What are the stages in preparing an indirect restoration? |
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Definition
- Impression
- Pour a cast/die from impression
- Make a wax pattern
- Make a mold from the pattern
- construct restoration using the mold
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Term
| What are requirements of an impression material? |
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Definition
- Long shelf time
- Resistance to tearing
- Acceptable odor and taste
- Quick setting time
- Non irritant/non toxic
- DIMENSIONAL ACCURACY AND STABILITY (A RESTORATION IS ONLY AS GOOD AS THE IMPRESSION FROM WHICH IT WAS MADE)
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Term
| Impression materials can be either: |
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Definition
- Non-elastic
- Impression plaster
- Impression paste
- Impression compound
- Elastic
- Elastomers
- Polysulfides
- Condensation silicones
- Polyethers
- Addition silicones
- Hydrocolloids
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Term
| What are properties of a non-elastic material? |
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Definition
| Rigid when set, will deform or fracture when displaced from undercuts |
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Term
| Differentiate between hydrocolloid and non-aqueous elastomers. |
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Definition
Hydrocolloid - aqueous with poor strength and stability Elastomer - non-aqueous synthetic rubber - STRONER AND MORE STABLE THAN HYDROCOLLOID |
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Term
| Distinguish between colloid and hydrocolloid. |
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Definition
Hydrocolloid - dispersion medium is water Colloid - a suspension of finely divided particles in a continuous medium (dispersion medium) from which particles do not settle out rapidly and cannot be readily filtered |
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Term
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Definition
| Sol is a viscous liquid that can be converted into a gel - a gelatin like substance which is formed by the agglomeration of dispersed molecules; forms fibrils surrounding the dispersion medium |
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Term
| What are the two ways of converting a sol to a gel? |
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Definition
Reversibly through cooling - agar Irreveribly through chemicals - alginate |
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Term
| Describe the physical properties of a gel |
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Definition
- Set materials are elastic
- Poor strenght - tears easily
- Water may be lost or taken up by the material
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Term
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Definition
| Loss of fluids by a material |
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Term
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Definition
| Taking up of fluids by a material |
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Term
| What are the consequences of syneresis and imbibition? |
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Definition
Syneresis - shrinkage Imbibition - expansion |
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Term
| What are the main constituents of alginate? |
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Definition
- Water
- Powder
- Sodium salt of alginic acid
- Calcium salt
- Trisodium phosphate
- 70% filler for gel strength
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Term
| List the application of alginate. |
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Definition
Orthodontic and prosthetic impressions Insufficiently accurate and stable for inlay crown and bridge impressions |
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Term
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Definition
Fine detail Tears easily Dimensionally unstable Comparatively inexpensive Elastic Well-defined working time |
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Term
| Correct steps for alginate maniplation. |
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Definition
Shake powder container. Mix powder and water Retention to tray Vigorous mixing Don't move during impression taking Displace sharply Wash and disinfect Keep moist and prepare cast ASAP |
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Term
| Describe alginate setting reactions. |
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Definition
- Calcium sulfate + trisodium phosphate --> calcium phosphate (PRECIPITATE)
- Calcium sulfate + sodium alginate --> calcium alginate (GEL)
- Reaction 2 cannot take place until Reaction 1 is substantially complete
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Term
| What does the alginate retarder do? |
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Definition
| Slows down reaction 2 so that it doesn't become elastic so quickly |
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Term
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Definition
| A cast is a replica of teeth and/or associated bony structure of a jaw made from an impression |
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Term
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Definition
| Model of a single tooth prepared from an impression |
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Term
| What are the desired properties of a cast/die material? |
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Definition
- Economical
- Color contrast
- Compatible w/ impression material
- Dimensional accurcy and stability
- Detail reproduction
- Mechanical
- Bulk properties -strength
- Surface properties - hardness, resistance to abrasion
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Term
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Definition
| the dihydrate of calcium sulfate CaSO4,2H2O |
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Term
| Do cast and die materials contain gypsum? |
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Definition
| No, but they are made from gypsum |
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Term
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Definition
| A transparent form of gypsum |
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Term
| What happens when gypsum is heated? |
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Definition
| It loses some or all of its water of crystallization |
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Term
| What is the gypsum byproduct we use in lab? |
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Definition
| Calcium sulfate hemihydrate (CaS04, 1/2 H20) |
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Term
| What happens when calcium sulfate hemihydrate is mixed with water? |
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Definition
| Hydration of the hemihydrate to reform the dihydrate, gypsum and sets as gypsum crystals |
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Term
| What are the two methods of going from a dihydrate to a hemihydrate and what type of gypsum do they form? |
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Definition
Wet (autoclave) forms alpha-hemihydrate (dental stone, colored) Dry (calcination) forms beta-hemihydrate (dental plaster, white) |
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Term
| Classify gypsum materials |
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Definition
Type I - impression plaster -beta Type II - model plaster - beta Type III - dental stone - alpha Type IV - high strength dental stone - alpha Type V - high strenght, high expansion dental stone - alpha |
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