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Applied Biomaterials
Exam 1 App. Biomat
31
Other
Not Applicable
03/26/2008

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Cards

Term
Differentiate between a direct and indirect restoration.
Definition

Direct - done directly in the mouth

Indirect- prepared in the laboratory 

Term
What are the stages in preparing an indirect restoration?
Definition
  • Impression
  • Pour a cast/die from impression
  • Make a wax pattern
  • Make a mold from the pattern
  • construct restoration using the mold
Term
What are requirements of an impression material?
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)
Term
Impression materials can be either:
Definition
  • Non-elastic
    • Impression plaster
    • Impression paste
    • Impression compound
  • Elastic
    • Elastomers
      • Polysulfides
      • Condensation silicones
      • Polyethers
      • Addition silicones
    • Hydrocolloids
Term
What are properties of a non-elastic material?
Definition
Rigid when set, will deform or fracture when displaced from undercuts
Term
Differentiate between hydrocolloid and non-aqueous elastomers.
Definition

Hydrocolloid - aqueous with poor strength and stability

Elastomer - non-aqueous synthetic rubber - STRONER AND MORE STABLE THAN HYDROCOLLOID 

Term
Distinguish between colloid and hydrocolloid.
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 

Term
What is a sol and a gel?
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
Term
What are the two ways of converting a sol to a gel?
Definition

Reversibly through cooling - agar

Irreveribly through chemicals - alginate 

Term
Describe the physical properties of a gel
Definition
  • Set materials are elastic
  • Poor strenght - tears easily
  • Water may be lost or taken up by the material
Term
Define syneresis
Definition
Loss of fluids by a material
Term
Define imbibition
Definition
Taking up of fluids by a material
Term
What are the consequences of syneresis and imbibition?
Definition

Syneresis - shrinkage

Imbibition - expansion 

Term
What are the main constituents of alginate?
Definition
  • Water
  • Powder
    • Sodium salt of alginic acid
    • Calcium salt
    • Trisodium phosphate
    • 70% filler for gel strength
Term
List the application of alginate.
Definition

Orthodontic and prosthetic impressions

Insufficiently accurate and stable for inlay crown and bridge impressions 

Term
Critique alginates.
Definition

Fine detail

Tears easily

 Dimensionally unstable

Comparatively inexpensive

Elastic

Well-defined working time 

Term
Correct steps for alginate maniplation.
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 

Term
Describe alginate setting reactions.
Definition
  1. Calcium sulfate + trisodium phosphate --> calcium phosphate (PRECIPITATE)
  2. Calcium sulfate + sodium alginate --> calcium alginate (GEL)
  • Reaction 2 cannot take place until Reaction 1 is substantially complete
Term
What does the alginate retarder do?
Definition
Slows down reaction 2 so that it doesn't become elastic so quickly
Term
Define cast.
Definition
A cast is a replica of teeth and/or associated bony structure of a jaw made from an impression
Term
What is a die?
Definition
Model of a single tooth prepared from an impression
Term
What are the desired properties of a cast/die material?
Definition
  • Economical
  • Color contrast
  • Compatible w/ impression material
  • Dimensional accurcy and stability
  • Detail reproduction
  • Mechanical
    • Bulk properties -strength
    • Surface properties - hardness, resistance to abrasion
Term
What is gypsum?
Definition
the dihydrate of calcium sulfate CaSO4,2H2O
Term
Do cast and die materials contain gypsum?
Definition
No, but they are made from gypsum
Term
What is selenite?
Definition
A transparent form of gypsum
Term
What happens when gypsum is heated?
Definition
It loses some or all of its water of crystallization
Term
What is the gypsum byproduct we use in lab?
Definition
Calcium sulfate hemihydrate (CaS04, 1/2 H20)
Term
What happens when calcium sulfate hemihydrate is mixed with water?
Definition
Hydration of the hemihydrate to reform the dihydrate, gypsum and sets as gypsum crystals
Term
What are the two methods of going from a dihydrate to a hemihydrate and what type of gypsum do they form?
Definition

Wet (autoclave) forms alpha-hemihydrate (dental stone, colored)

Dry (calcination) forms beta-hemihydrate (dental plaster, white) 

Term
Classify gypsum materials
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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