9- Impression Materials Flashcards
What is the main purpose of Impression Materials
Impression materials are used to construct models or casts which are used in numerous dental procedures
Various types of casts and models can be made from gypsum products using an impression mold or negative likeness of a dental structure.
What is one of the main requirements of impression materials.
They MUST be accurate.
because different prosthesis and restorations are made from models
What are the main criteria of an impression material?
- Fluid enough to adapt to structures in the mouth
- viscous enough to stay in tray during placement
- reasonable setting time (~7 min)
- not distort/tear when removing
- dimensionally stable (at least till poured)
- dimentisonally stable after cast removed so multiple casts can be made with one mold
- Biocompatible
- Cost Effective
Acronymn FVS DDBC
Environmental and Characteristics of tissue dictate 3 things:
choice of materials
quality of the impression
quality of the cast
What materials were first used for impressions- general order
- inelastic materials (i.e.. plaster)•
- Hydrocolloid for hard tissue impressions
- synthetic rubbery materials called elastomers developed and used for making hard and soft tissues
what are the 3 main ways impression materials are classified?
- How materials react to become solid
- mechanical properties
- uses
what are the 2 main ways impression materials set?
irreversible reactions
reversible reactions
What makes a material irreversible
name 2 materials that fall under this classification
- they do not revert to their preset state, they usually undergo chemical reactions
- Alginate and ZOE are examples
What makes a material reversible?
name 2 materials that fall under this classification:
Reversible: soften under heat and solidify when cooled, with no chemical change taking place
-reversible hydrocolloid, wax
What is one problem with using Rigid Impression Materials?
They are difficult to remove from undercuts without breaking, tearing or distorting.
give one example of a “Mucostatic impression material”:
what does this term mean?
-ZOE
this means they do not compress the tissue during seating of the impression tray.
Great for impressions of edentulous jaw structures
What is unique about “elastic impression materials”?
what is one example of an elastic impression?
this means they can be stretched or compressed slightly, but will rebound without permanent deformation when removed from mouth
example: hydrocolloids
What types of impressions are elastic impression materials good for?
Elastic impression materials are good for hard and soft tissue impressions,
hard and soft structures of the mouth including undercuts and interproximal spaces
reparation of casts for fixed and removable partial dentures and single restorative units
what are elastomers?’
what are some of their key features?
- rubbery polymers that are chemically or physically cross-linked
- easily stretched and rapidly recover original dimensions when applied stress is released
What are the 4 types of elastomers?
polysulfide
condensation-polymerizing silicone
addition-polymerizing silicone
polyether
how many components are in a elastomer impression?
usually 2 that are different colors and come in separate tubes which need to be mixed together to initiate the crosslinking polymerization and setting process.
what is a rheologic property?
why is this an important characteristic of elastomeric impressions?
rheologic is a fancy word that means the “flow of the material”.
the flow of the material plays a major role in their application as high-accuracy impression materials
elastomeric impression material is inserted into the mouth as a ___ ____ and then sets into a _____ _____.
elastomeric impression material is inserted into the mouth as a viscous paste and then sets into a viscoelastic solid.
Define Working Time
Working Time of an impression material begins at the start of mixing and ends just before the elastic properties have developed.
What is the main requirement for working time?
Working time must be longer than the time required for mixing, filling the syringe and/or tray, injecting the material on the tooth preparations, and seating the tray.
Define Setting Time:
the time from the beginning of mixing until the impression has cured enough that the impression can be removed from the mouth with minimal distortion
True or false?
Polymerization of an impression material finishes before it sets.
FALSE
Polymerization can continue for a long time after setting.
What is the main component of poly sulfides?
Multifunctional Mercaptan (-SH) or Polysulfide Polymer
What is the role of Lead Sulfide in Polysulfides impression materials?
Lead oxide acts as a oxidizing agent that initiates polymerization through crosslinking. It also gives polysulfides their brown color.
Polymerization reaction using lead oxide begins _________ and reaches maximum rate ________.
Polymerization/ Cross-linking reaction starts at the beginning of mixing and reaches its maximum rate soon after the spatulation is complete.
Describe the characteristics of Polysulfide impressions once they have fully set:
After Polysulfide impressions have fully set they are elastic and strong enough to be removed from undercuts.
What two things have a significant effect on the course of the polysulfide reaction?
Moisture and Temperature.
Hot humid conditions ACCELERATE the setting of the Polysulfide.
In Polysulfide impression materials, What 4 things does the BASE PASTE contain?
- polysulfide polymer
- suitable filler
- plasticizer to confer viscosity
- small quantity of sulfur to accelerate the reaction
In Polysulfide impression materials what 4 things does the catalyst paste contain?
Lead oxide
filler
plasticizer
STEARIC ACID, acts as a retarder to control rate of setting.
What is the main component of condensation silicone?
α-ω-hydroxyl-terminated polydimethyl siloxane
how long are the average polymer chain in condensation silicones?
average polymer chain are about 1000 units.
formation of the elastomer occurs through _______ between terminal groups of the ______and the ________ to form a three-dimensional network.
formation of the elastomer occurs through cross-linking between terminal groups of the silicone polymers and the alkyl silicate to form a three-dimensional network.
in Condensation Silicone
what is the important by-product produced by the condensation setting reaction?
why is it important?
Condensation Silicone
Ethyl alcohol is the important by-product of the condensation setting reaction
Its evaporation accounts for much of the contraction that takes place in a set silicone rubber impression
What are the 2 components of a condensation silicone?
Base Paste and low-viscosity liquid catalyst.
what is the function of the high viscosity putty?
Why is this possible?
High viscosity “putty” overcomes the polymerization shrinkage of the condensation silicone impression materials.
this is possible due to its high concentration of filler making polymerization shrinkage smaller.
What is another name for Addition Silicone?
Vinyl Polysiloxane
Hint: an “Addition” for the real presodent is the Vice president (VP)
how are condensation and addition silicones different?
Addition silicones- addition reaction polymer is terminated with vinyl groups and is cross-linked with hydride groups activated by a platinum salt catalyst
Condenstion Silicones- cross-linking between terminal groups of the silicone polymers and the alkyl silicate form a three-dimensional network
Why is it important to maintain proper proportions of Vinyl silicone and hydride silicone?
It is important to maintaint these proportions so that no by-products are produced.
in Addition silicones what results from the secondary reaction between moisture and residual hydrides?
the secondary reaction will create pinpoint voids due to the production of Hydrogen gas.
What two metals do manufacturers add to addition silicones in order to scavenge hydrogen gas produced by secondary reactions?
They add either Palladium or Platinum
Instead of adding paladium or platinum to addition silicones to prevent the production of hydrogen gas (causing micro voids) what can one do clinically to prevent this from happening?
Instead of adding these metals to scavenge the hydrogen gas, you could just wait an hour and then the secondary reaction wont occur.
What does the base in an addition silicone contain?
The base paste contains polymethyl hydrogen siloxane along with other siloxane prepolymers
what does the catalyst in addition silicones contain?
The catalyst paste contains the platinum salt activator, sometimes along with a retarder.
What is one DISADVANTAGE to addition silicones?
how is this minimized?
they are HYDROPHOBIC, thus moisture can cause distortion to the margins.
This is minimized with surfactants to make them hydrophillic.
True or False?
Addition silicones always require a dry field
True
What is a polyether impression material?
a polyether-based polymer cured by a reaction between aziridine rings, which are at the end of branched polyether molecules.
Poly Ethers come as two pastes what are they?
-
base paste- polyether polymer, colloidal silica as filler, and a plasticizer such as a glycoether
accelerator paste- alkyl-aromatic sulfonate in addition to the filler and plasticizer
Who makes the best flashcards around?
Dallin does.
