Chapter 15 impression

Question 1

An impression is a __ of the oral tissues
A model or cast is a __ reproduction of the oral tissues. A die is a __ reproduction of a single or multiple tooth preparation

Answer 1

An impression is a negative reproduction of the oral tissues
A model or cast is a positive reproduction of the oral tissues. A die is a positive reproduction nof a single or multiple tooth preparation

Question 2

stock trays

Answer 2

a. Stock trays can be metal or plastic
b. Can be solid or perforated
c. May need adhesive

Question 3

custom trays

Answer 3

a. Usually constructed in the lab with chemically cured, light-cured, or thermoplastic resins

Question 4

triple tray

Answer 4

6) Triple Tray: (Double arch or Double bite)
a. Used to make an impression of the teeth being treated
b. Makes an impression of the opposing arch

Question 5

types of inelastic

Answer 5

1) Dental compound (impression compound)
2) Impression plaster – not used today
3) Zinc oxide eugenol
4) Impresion wax

Question 6

• A colloid

* Hydrocolloids

Answer 6

• A colloid is a glue-like material composed of two or more substances in which one substance does not go into solution but is suspended within another substance.
• Hydrocolloids are water based colloids that contain large amounts of water, even after they have set

Question 7

irreversible vs reversible

Answer 7

agar(R)
 and alginate(IR)

Question 8

alginate

Answer 8

Most widely used impression material. Used for impression for diagnostic casts, etc. Not accurate enough for final impressions for inlays, onlays, crown and bridge preparations.

Question 9

agar

Answer 9

introduced in 1925. Glue-like suspension that entraps the water making a colloidal suspension called (sol). When the agar gel is heated, it will reverse its state back into a liquid suspension (sol).

Question 10

alginate working and setting time

Answer 10

i. Regular Set – 2 to 3 minutes
ii. Fast Set – 1.25 to 2 minutes
b. Setting Time:
i. Regular Set – 2 to 5 minutes
ii. Fast Set – 1 to 2 minutes

Question 11

elastomer

Answer 11

• Sets by an irreversible chemical reaction and does not have water as a main component, therefore they are more dimensionally stable over long periods of time

Question 12

zinc oxide eugenol

Answer 12

periodontal dressing
cavity base
temporary cement
temporary restorative material

Question 13

alginate components :5

Answer 13

calcium sulfate-causes reaction
sodium retards the chemical reaction
potassium sulfate ensures surfaces of stone is good quality
b. Silica fillers – provide “body” & rigidity
e. Quaternary ammonium aids in the disinfection process

Question 14

Thixotropic Materials

Answer 14

Thixotropic Materials – Liquids that flow more easily under mechanical forces

Question 15

zinc eugenol is manufactures in 2 forms ?

Answer 15

a) Two Paste System
b) Paste – Liquid formulation

1. Catalyst Paste – Brown in color
2. Base Paste – White in color

Question 16

elastomer types

Answer 16

a. Polysulfides
b. Condensation silicones
c. Polyethers
d. Addition Silicones (Polyvinyl Siloxanes)

Question 17

polyethers

Answer 17

Yields water as a by-product also known as a rubber base. The oldest and most economical of elastomers contain many sulfhydryl (-SH) groups.

Question 18

sulfhydryl (-SH) groups are known as

Answer 18

mercaptan.
in polyethers
makes sulfur smell and will stain clothes

Question 19

base of condensation silicone

Answer 19

• The base is a paste that contains a moderately low molecular weight silicone liquid called a dimethylsiloxane which has a reactive -OH group

Question 20

condensation silicone gives off what as a by product

Answer 20

• Gives off ethyl alcohol as a by-product

Question 21

addition silicone

Answer 21

3. Heavy putty (base & catalyst are supplied in tubs) they are scooped out and mixed by hand or vinyl gloves. No latex. No by-product. Under normal reaction.

Question 22

which has better mrchanincal properties polyether or polysulfide

Answer 22

polyether Better mechanical properties than those of polysulfides.

Question 23

in condensation silicone __ is added as a scavenger for the release hydrogen gas

Answer 23

b. Palladium is added as a scavenger for the release hydrogen gas

Question 24

__ is the component that gives polysulfide its characteristic brown color

Answer 24

a. Lead dioxide is the component that gives polysulfide its characteristic brown color

Question 25

hand Mixing:

Answer 25

hand Mixing Equal amounts of material are placed on a mixing pad

Question 26

Static Mixing:

Answer 26

Static Mixing: this technique transforms two fluid or paste like materials into a homogenous mixture without mechanical mixing. Materials make a 180°C turn

Question 27

Dynamic Mechanical Mixing:

Answer 27

Dynamic Mechanical Mixing: a motor drives parallel plungers forcing the materials into a mixing tip and out into an impression tray or syringe

Question 28

Requirements of Impression Materials

Answer 28

1) Case of manipulation and reasonable cost
2) Adequate flow properties
3) Appropriate setting time and characteristics
4) Sufficient mechanical strength not to tear or permanently deform during removal
5) Good dimensional accuracy
6) Acceptability to the patient
7) Safety (not toxic or irritating)
8) No significant degradation of properties as a result of disinfection
9) Compatibility with all die and cast materials
10) Good keeping qualities (no deterioration of unused material in the dental office)