L1b-Impression materials Flashcards
(51 cards)
1
Q
What are impression materials used for?
A
- To record the details of intraoral structures in order to fabricate a reproduction of hard (teeth) and soft tissues for the construction of dental prosthesis.
2
Q
Ideal properties of impression materials:
A
- Produce an accurate replica or the intra oral structure.
- Prevent deformation.
- Be atraumatic when removing from undercuts.
- Have proper setting time and biocompatibility.
3
Q
What is an impression?
A
A negative reproduction of the tissues.
4
Q
How is a positive cast made?
A
By filling the impression with dental stone or other model material, a positive cast is made.
5
Q
impression materials Classification:
A
- elastic or
- non-elastic
6
Q
Which are the non-elastic impression materials?
A
- Impression plaster
- Impression compound
- Impression waxes
7
Q
elastic impression-subclassification:
A
- Synthetic elastomers
- Hydrocolloids
8
Q
Hydrocolloids:
A
- Reversible (Agar)
- Irreversible (Alginate)
9
Q
Synthetic elastomers:
A
- Polysulphides
- Polyether
- Silicones
10
Q
Subgroups of silicones:
A
- Additional
- Condensation
11
Q
Desirable qualities of an impression material:
A
- A pleasant odor, taste, and acceptable color.
- Absence of toxic or irritant constituents.
- Adequate shelf life for requirements of storage and distribution.
- Economically commensurate with the results obtained.
- Easy to use with the minimum of equipment.
- Setting characteristics that meet clinical requirements.
- Satisfactory consistency and texture.
- Readily wets oral tissues.
- Elastic properties that allow easy removal of the set material from the mouth and good elastic recovery.
- Adequate strength to avoid breaking or tearing upon removal from the mouth. Good dimensional stability over temperature and humidity, long enough to permit the production of a cast or die.
- Compatibility with cast and die materials.
- Accuracy in clinical use.
- Readily disinfected without loss of accuracy.
- No release of gas or other byproducts during the setting of the impression or cast and die materials.
12
Q
What is a colloid?
A
- Colloid is a mixture in which one substance of microscopically dispersed insoluble or soluble particles is suspended throughout another substance.
13
Q
Which is the form in which colloids can exist?
A
In the form of:
- viscous liquid known as a sol
- or a jelly like elastic semi-solid described as a gel
14
Q
When is a colloid called hydrocolloid?
A
If the particles are suspended in water, the suspension is called hydrocolloid.
15
Q
How can a sol change into gel?
A
16
Q
Characteristic of hydrocolloids:
A
- They are hydrophilic with very good wettability
- have very limited dimensional stability because they are composed of 85% water.
17
Q
What is agar?
A
- It is a polysaccharide (a sulfuric ester of a linear polymer of galactose) extracted from certain types of seaweed.
- Although it is an excellent impression material and yields accurate impressions, presently it has been largely replaced by alginate hydrocolloid and rubber
18
Q
What can agar be used for?
A
- For cast duplication (during fabrication of cast metal removable partial denture)
- For full mouth impressions without deep undercuts
- For crown and bridge impressions (before elastomers came to the market)
- As tissue conditioner
19
Q
What is alginate?
A
- It is a mucous extract yielding from certain brown sea weeds.
20
Q
Alginate-chemical reaction:
A
- They change from the sol phase to the gel phase because of a chemical reaction.
- Once gelation is completed, the material cannot be re-liquefied to a sol.
21
Q
Alginate-Setting reaction:
A
- Sodium/Potassium alginate powder (soluble) dissolves in water to form asol.
- The sol reacts with calcium sulfate (reactor) to form calcium alginate (insoluble gel).
- This reaction is delayed by addition of a retarder (sodium phosphate), to give more working time.
22
Q
Alginate impression powder-Ingredients
A
23
Q
Alginate-Advantages & disadvantages:
A
Advantages:
- Easy to mix and manipulate, need minimum equipment
- If properly handled, gives accuracy and good surface details even in presence of saliva.
- Low cost
- Hygienic and comfortable to the patient
Disadvantages:
- Poor tear strength and dimension stability (poured with in 15 minutes).
- Not recommended when high level of accuracy is required (crown and bridge).
- May occur distortion if the material is not properly handled.
- It cannot be corrected.
24
Q
Properties of Alginate:
A
- Syneresis
- Imbibition
25
What is Syneresis?
* Alginate impressions may lose water by expulsion of liquid molecules.
26
What is Imbibition?
* Gain water when immersed into it.
27
What can both phenomenon of Syneresis and Imbibition cause?
Both the phenomenon can cause **dimensional changes** and produce **inaccurate casts**.
* To avoid this, impression should be poured immediately (within 15 min).
28
Alginate indication:
* fabrication of **diagnostics casts**
29
What is Polysulfide?
* elastomer that is also known as mercaptan, or simply as rubber base
30
1. What is Polysulfide packaged in?
2. What does this result into?
3. What is the reaction of the two pastes?
1. in two tubes, a base and an accelerator (reactor)
2. When the two pastes are mixed equally, it results in an **increased viscosity** and finally in an **_elastic material._**
3. exothermic
31
Polysulfide:
Which is the composition of base paste and reactor paste?
32
Polysulfide-**_Properties_**:
* Stability.
* Low contraction (shrinks 0.3- 0.4% during first 24h).
* High tear strength.
* Hydrophobic.
* Excellent reproduction of details.
* Excellent shelf life.
* Highly compatible with stone and plaster.
33
Polysulfide:
**_Working_ time** - **_Setting_ time:**
**Mixing and working time:**
* 4-6 min.
**Setting time:**
* 12-16 min.
34
Polysulfide **_indication_**:
* Mostly for partial and complete dentures
35
Polysulfide:
Advantages and disadvantages:
Advantages:
* Good stability and accuracy
* It comes in different viscosities.
* Long working (4-7 min) and setting time (7-10 min)
Disadvantages:
* Lead oxide in the base paste can be toxic.
* Mixing procedure can become messy.
* Unpleasant odor and color
* Requires the use of custom tray.
36
Condensation silicones-Components:
Base:
* Polydimethyl siloxane (Hydroxy terminated).
* Colloidal silica or micro-sized metal oxide (filler).
* Color pigments.
Accelerator:
* Ortho-ethyl silicate (cross linking agent).
* Tin (Sn) Octoate (catalyst).
37
Condensation reaction-polymerization reaction:
* **_Ethyl alcohol_** eliminates from the reaction, the evaporation of which is responsible for shrinkage and dimensional instability.
38
Condensation silicones-**Properties:**
* High permanent deformation (1-3)% due to shrinkage.
* Tear strength is lower than polysulfides.
* Hydrophobic.
* Requires dry areas of mouth.
39
Condensation silicones:
Working time-Setting time:
Working time:
* 2-4 min.
Setting time:
* 6-8 min.
40
Condensation silicones-**Indications**:
Mostly for lab work (duplication of casts and wax –ups)
41
Condensation silicones:
Advantages and disadvantages:
Advantages:
* Clean and pleasant.
* Custom tray not required.
* Good working time.
* Ease of use.
* Relatively economic.
Disadvantages:
* High polymerization shrinkage.
* Low tear strength.
* Second pour is not so accurate.
* Volatile (evaporation of by-product). Hydrophobic.
42
Additional silicones-Composition:
Base paste:
* Terminal silane hydrogen groups
* Fillers
Catalyst paste:
* Terminal vinyl groups
* Platinum salt (catalyst)
* Palladium (hydrogen absorber)
* Filler
release hydrogen gas
43
additional silicones-Properties:
* Pleasant odor and color.
* Excellent reproduction of surface details.
* Good tear strength.
* Hydrophobic material.
* Wettability can be improved with surface active agents.
44
Additional silicones:
Working time-Setting time:
Working time:
* 1-4 min.
Setting time:
* 4-6 min.
45
Additional silicones- Indications:
Fixed prosthesis and implant restorations.
46
Additional silicones-Advantages & Disadvamtages
Advantages:
* Ease of use.
* Fast setting.
* Excellent dimensional stability.
* Can be re-poured
* Good shelf life (1-2 years).
Disadvantages:
* Hydrophobic (although improved). No flow if sulcus is moist.
* Sometimes is difficult to remove from mouth (undercuts).
* High cost.
47
Polyether-Composition:
Base paste:
* Poly ether polymer.
* Silica (filler).
* Glycol ether or phthalate (plasticizer)
Catalyst paste:
* Aromatic sulfonate ester (cross-linking agent).
* Silica (filler).
* Phthalate or glycol ether (plasticizer).
48
Polyether-Properties:
* Pleasant odor and color.
* Very good dimensional stability.
* Adequate tear resistance and elastic properties, approaching those to addition silicones.
* Hydrophilic material.
49
Polyether:
Working time-Setting time:
Working time:
* 3 min.
Setting time:
* 6 min.
50
Polyether- Indications:
Fixed prosthesis and implant restorations.
51
Polyether:
Advantages and Disadvantages:
Advantages:
* Ease of use.
* Excellent dimensional stability.
* Accuracy.
* Multiple pouring.
* Can be poured hours after impression is taken.
Disadvantages:
* May cause allergic reaction due to the sulphonic acid.
* Stiff set material (could be difficult to remove from mouth).
* High cost.
