Impression materials

Question 1

Impression

Cast or Die

Answer 1

• dimension, + dimension - balances

Question 2

Investment

Restoration

Answer 2

+ dimension, - dimension - balances

Question 3

 Rigid or Brittle (Edentulous)

Answer 3

Zinc Oxide & Eugenol Impression Paste

• Dental Impression Plaster

Question 4

Plastic

Answer 4

• Impression Compound • Wax

Question 5

 “Elastic” – but really

Answer 5

viscoelastic

Question 6

 Hydrocolloids

Answer 6

Reversible (Agar) Hydrocolloid
• Irreversible (Alginate) Hydrocolloid
[Jeltrate® - Dentsply]

Question 7

Synthetic Elastomers:

Answer 7

Oligomers polymerize into elastomers

Question 8

Silicone

Answer 8

 Condensation Silicone
 Addition Silicone – Poly (vinyl siloxane)
[Aquasil Ultra - Dentsply]

Question 9

Hydrocolloids: Water is bound within a

Answer 9

Colloid matrix

Question 10

Both systems lack dimensional stability with time and require immediate pouring of models.

Answer 10

Alginate (irreversible): Convenient & relatively inexpensive
• Agar (reversible): Good initial dimensional accuracy, but requires special equipment.

Question 11

 Thermoplastic: No

Answer 11

Cross-linking; Physical state is reversibly controlled by temperature (e.g., wax).

Question 12

Thermoset: Transformation from

Answer 12

monomer to polymer involves irreversible cross-linking.

Question 13

Addition polymerization releases no

Answer 13

by- products.

• Free-radical • Ring-opening • Ionic

Question 14

Condensation polymerization results in a

Answer 14

by-product.

Question 15

Hydrocolloids

Answer 15

• Reversible (Agar) Hydrocolloid

* Irreversible (Alginate) Hydrocolloid

Question 16

Synthetic Elastomers: Oligomers polymerize into

Answer 16

elastomers

Question 17

During the change from liquid or paste into a solid,

Answer 17

Good: advantageous final properties are increased.
Bad3: the inherent density increase causes a
volumetric contraction.
Meh: heat of reaction causes material to heat up (usually minor).
Bad: there is a contraction on cooling.

Question 18

Polysulfide: Low molecular weight oligomers containing

Answer 18

reactive mercaptan groups

Question 19

Polysulfide: conform well to a

Answer 19

prepared tooth, resulting in good surface detail, and are

Question 20

Polysulfide: oxidized by

Answer 20

lead dioxide or copper hydroxide to form a polysulfide rubber with a water condensate.

Question 21

Polysulfide:  To be accurate, this material requires a

Answer 21

rigid custom tray for minimal thickness of impression material.

Question 22

Polysulfide: They do not recover from

Answer 22

permanent deformation as well as some other impression materials.

Question 23

Polysulfide: Models should be poured

Answer 23

as quickly as possible.

Question 24

Silicones (Polysiloxanes) are inherently hydrophobic but the Addition type can be made more

Answer 24

hydrophilic.

Condensation type was first introduced.
 Addition type can be made more hydrophilic
by:
• simple addition of surfactant, or
• chemical incorporation of hydrophilic moieties into the silicone backbone.

Question 25

Contact Angle important for:

Answer 25

Unset impression material over wet oral structures. • Unset gypsum-water mix into set impression.

Question 26

Condensation Silicone

Answer 26

Low molecular weight oligomers containing reactive terminal hydroxyl groups which
 react with ortho-ethyl silicate and stannous octoate to form a three dimensional network rubber with the liberation of ethyl alcohol.
 Models should be poured as quickly as possible.

Question 27

Addition Silicone: Poly (vinyl siloxane) or Vinyl Polysiloxane

Answer 27

Low molecular weight polymers with terminal silane groups and low molecular weight polymers with vinyl terminal groups, are now supplied with a surfactant to make this material hydrophilic.
 In the presence of chloroplatinic acid, ionic polymerization produces chain-lengthening and cross linking.

Question 28

If there is residual hydroxyl groups present from the

Answer 28

mucosa, a secondary reaction occurs which produces hydrogen gas. Although finely divided palladium or platinum will absorb some of this the hydrogen, pouring of the model should be delayed until all of this hydrogen is liberated.

Question 29

For extensive impressions, working time of addition silicones may be lengthened by the

Answer 29

addition of a retarder without adversely

affecting the other properties.

Question 30

Contamination of addition silicone impression material with sulfur or dithiocarbamate compounds before setting will either

Answer 30

lengthen the setting time or cause the material to not set.

Addition Silicone: Poly (vinyl siloxane) or Vinyl Polysiloxane

Question 31

Since sulfur and dithiocarbamate compounds are used in the

Answer 31

vulcanization of latex rubber gloves, latex gloves often contaminate this impression material either directly or indirectly, causing unacceptable impressions.

Thorough washing of these gloves with detergent, water and agitation before handling or manipulating either the impression material or the tissues of which the impression is being made will usually eliminate this problem.

Addition Silicone: Poly (vinyl siloxane) or Vinyl Polysiloxane

Question 32

Polyether: Low molecular weight polyether oligomer with terminal ethylene imine reactive ring groups will react
 with

Answer 32

aromatic sulfonic ester by dual ring opening, with the resultant polymer being cross-linked.

Question 33

Polyether: Contact of the skin or mucous membranes with the unmixed ester may cause

Answer 33

contact dermatitis, but irritation has not been observed with a thoroughly mixed material.

Question 34

Polyether: This material requires a

Answer 34

rigid custom tray.

Question 35

Polyether: This impression material may be available in one

Answer 35

viscosity with a thinner (diluent); in this case there is control of viscosity with adjustment in the thinner/impression material ratio.

Question 36

PolyetherRequirements of Ideal Impression Materials

with Respective Range of Properties of Currently Available Impression Materials.

Answer 36

1. Low cost.
2. Long shelf life.
3. Biocompatibility.
4. Pleasant to patient.

Question 37

(e) Compatibility with die and cast materials.

Answer 37

I. Contact angle of gypsum-water mix.
II. Chemical interference (retardation) effects of impression material to surface of the cast. Alginate materials interfere with the setting of gypsum, but manufactures add ingredients to off-set this interference.

Question 38

methods using light and heavy body impression systems

Answer 38

reinserted into mouth or add light body first

Question 39

Oligomers polymerize into elastomers:

Answer 39

already formed into “longer chemistry” has some body to it

Question 40

Contact angle double count

Answer 40

once in mouth, again when stone is made (not as detailed)

Question 41

P sulfide for patients with

Answer 41

poor tooth health - very flexible, so not as likely to remove tooth when removing impression material.

Question 42

Hydrocolloids

Answer 42

tear easily

Question 43

you want tear with least amount of

Answer 43

deformation. High strain rate*

Question 44

Alginate has low

Answer 44

compatibility, retards gypsum formation.

Question 45

Dimesional change happens in

Answer 45

different direcitons. Will always occur with impression trays depending on where the walls are.