Impression Materials and Techniques for Fixed Prosthodontics Flashcards
1
Q
What are the other categories that alginate fits into?
A
- elastic
- hydrocolloid
- irreversible (alginate)
2
Q
What is a reversible hydrocolloid?
A
Softens under heat and solidifies when cooled
3
Q
Why is a reversible hydrocolloid reversible?
A
There is no chemical change making the changes permanent. Therefore, this is reversible
4
Q
What is an irreversible hydrocolloid?
A
Chemical reaction that cannot revert to preset state
5
Q
Is alginate a reversible or irreversible hydrocolloid?
A
Irreversible
6
Q
Alginate was developed as a substitute for _____ impression material when its supply became scarce during the WW II
A
Agar
7
Q
What is alginate based on?
A
a natural substance extracted from brown seaweed
8
Q
When the soluble alginates are mixed with water, they form a…
A
gel
9
Q
Alginate is hydrophilic or hydrophobic?
A
hydrophilic
10
Q
_________ is hydrophilic, so moist tissue surfaces are not a hindrance to the impression unlike PVS materials.
A
Alginate
11
Q
What is a colloidal material?
A
any substance consisting of particles substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye
12
Q
What is an example of a colloidal material?
A
Agar or Alginate dissolved in water
13
Q
What is sol to gel?
A
a process that converts a colloidal solution (sol) into a gel-like network (gel)
14
Q
Agar: reversible due to __________ change
A
temperature
15
Q
Alginate: irreversible due to _________ reaction
A
chemical
16
Q
What are properties related to gel network?
A
- Evaporation (shrinkage)
- Syneresis: gel relaxation; water extruded from gel (shrinkage)
- Imbibition: absorption of water causing expansion
17
Q
What is syneresis?
A
gel relaxation; water extruded from gel
18
Q
What is imbibition?
A
absorption of water causing expansion
19
Q
Alginate is provided as a powder, which contains the following reacting ingredients:
A
- Potassium or Sodium Alginate(15-20%): reacts with calcium ions
- Calcium Sulphate Dihydrate (14-20%): reacts with Potassium Alginate to form a dihydrate insoluble alginate gel
20
Q
What does the potassium/sodium alginate do?
A
reacts with calcium ions
21
Q
What does calcium sulphate dihydrate do?
A
reacts with Potassium Alginate to form a dihydrate insoluble alginate gel
22
Q
What is the powder part of alginate?
A
potassium or sodium alginate
23
Q
What is the gel part of alginate?
A
calcium alginate
*formed by interactiuon b/w potassium alginate and calcium sulphate dihydrate
24
Q
When mixing alginate you add ______ first and then ________
A
Add water first, then powder
25
What is the mixing time for alginate?
45 – 60 sec
26
Thickness of Alginate should be ___ mm in tray
3
27
CDC recommend ______ dilution of household bleach for disinfection of impressions
1:10
28
How do you keep the impressions moist?
Impression placed in small Ziploc baggie or head rest cover with a few drops of water in the bottom of the baggie and is sealed.
29
After pouring the impression, the stone castshould not be separated for ___ min with yellow stone
60 minutes
30
What are the two major factors that affect the shelf life of the impression?
Storage temperature and moisture
31
If you remove your impression from the mouth, rinse it off, and then wrap the impression with a wet paper towel, what will happen?
- The alginate absorbs more water as it continues to harden and the material swells.
- Now anything made from that impression will NOT fit because the model has distorted as it absorbed water.
32
The diagnostic cast should be removed from the impression approximately_____ hour(s) after its final set.
one
33
Small nodules and projections on the impression surface should be ___________
removed
34
If you delay in pouring up impressions what problem arises?
dimensional changes
35
What can cause inadequate working or setting time?
- high water temp
- incomplete spatulation
- low water/powder ratio
- improper storage of alginate powder
36
What can cause distortion of impression?
- movement of tray during gelation
- premature removal of tray
- no snap quick removal of tray
- delay in pouring cast
37
What can cause tearing of impression?
- impression removed before set
- slow rate or removal of impression
- thin mix used
- presence of deep undercuts
- inadequate material in tray
38
What can cause of loss of detail of impression?
- premature tray removal from the mouth
39
What can cause issues with consistency of impressions?
- incorrect water/powder ratio
- inadequate mixing
- hot water used for mixing
40
What can cause dimensional changes to an impression?
- delay in pouring the impression
41
What can cause porosity issues in an impression?
air entrapped in the mix during spatulation
42
What can cause poor stone surface?
delay in separating the cast from the impression
43
What is an analogue impression?
* A negative likeness or copy in reverse of the surface of an object
* An imprint of the teeth and adjacent structures for use in dentistry
* Made from soft semi-fluid material allowed to set
44
What is an impression technique?
a method and manner used in making a negative likeness
45
What is an impression tray?
a device that is used to carry, confine, and control impression material while making an impression
46
What do we look for in a dental impression?
-Exact duplication of the prepared teeth
-Includes uncut tooth structure beyond finish line
-Accurate reproduction of the other teeth and tissues
-Free of air bubbles specifically in the finish line and occlusal surfaces
-Extended enough to capture the vestibule, tuberosities, and retromolar pad is ideal
47
How do you select what impression tray to use?
* Tray should feel comfortable to the patient
* Extended slightly beyond the facial/buccal surfaces of the teeth
* Extended approximately 2 -3 mm beyond the 3rd molar, retromolar, or tuberosity
* Sufficiently deep to allow 2 -3 mm of material between the tray and the occlusal/incisal edges
* Sufficiently rigid
48
How much material should be b/w the tray and occlusal surfaces?
2-3mm
49
An impression tray must be sufficiently rigid to:
* Carry the impression material into the oral cavity
* Hold the material in close proximity to the teeth
* Avoid breaking during removal
* Prevent wrapping of the completed impression
50
What are stock trays?
* Plastic or metal; perforated or rimmed
* Complete arch, quadrant, or dual arch
* Dentate or edentulous arch
51
What are custom trays?
* Made in advance
* Light cured, auto cured, or thermoformed
* Better fit than stock trays
* Less material waste
* Controlled thickness of material
* Increased accuracy
52
___________ is used to prevent impression distortion due to material pulling away from tray
Adhesive
53
Adhesive provides a _______ adhesion
chemical
54
What are the needs for adhesive?
* Specific for each material; including Alginate
* Should always be used
* Apply and dry
55
What are the ideal impression material characteristics?
* Easy to mix and handle
* Suitable working time
* Suitable setting time
* Compatible with die and stone materials
* Not toxic or allergenic to the patient
* Dimensionally stable
* Accurate to record the fine details
* Acceptable odor and taste
* Adequate stretch
* Adequate shelf life
* Ready to be disinfected without loss of accuracy
* Fluid or plastic when inserted into the mouth
* It must be an exact record of all the aspects
* Economic
56
What is the goal of a single crown impression technique?
a fully or slightly overextended impression of the arch, with all anatomical landmarks
57
What is the purpose of impression techniques of a single crown?
* Evaluate arch form
* Anatomical landmarks
* Musculature
* Hard and soft tissue anomalies
* Restorative space
58
The impression material selected is dependent on....
the type of impression required for the procedure
59
What is the tissue retraction part of a single crown impression?
single or double cord technique; cord/s removed right before impression making
60
The _____ bodied consistency dispensed into the sulcus, over and around the prepared teeth and onto the surrounding tissues
light
61
The custom tray for a single crown impression with dried adhesive is loaded with medium or heavy body material is seated with some downward pressure for approximately ______ min
4 – 6
62
What is a nonelastic impression material?
* Rigid, cannot be removed from undercuts
* Best used for edentulous impressions
63
What is an elastic impression material?
* Can be removed from undercuts without distortion
* Best for dentate impressions
64
What are the first impression materials that were popular?
* Plaster of Paris
* Impression plaster
* Gutta percha
* Modeling compound
* Zinc Oxide Eugenol
* Various waxes
-less commonly used now
65
What are the options for elastic materials?
* Reversible Hydrocolloid (AGAR)
* Irreversible Hydrocolloid (Alginate)
* Polysulfide Rubber
* Vinyl Poly Siloxanes
* Polyether
66
What is an aqueous elastomeric (hydrocolloids)?
* Water is the major component
* Hydrocolloid
* Reversable and irreversible
* Reversable is not commonly used today
67
What is a non-aqueous elastomeric (polymers)?
* Polysulfide
* Vinyl Polysiloxane (silicone)
* Polyether
68
If the contact angle of wetting is less than 90 degrees what happens?
- hydrophilic
- surface wetted
69
What is wettability?
ABILITY OF LIQUID TO FLOW OVER A SOLID SURFACE
- RELATED TO SURFACE ENERGY OF THE SOLID AND SURFACE TENSION OF THE LIQUID
70
Non-Aqueous Elastomers provide:
➢ Accuracy
➢ Dimensional stability
➢ Tear resistance
➢ Viscoelasticity
71
If the contact angle of wetting is greater than 90 degrees what happens?
- hydrophobic
- surface not wetted
72
What is accuracy?
Ability to replicate the intra-oral surface details
73
What is dimensional stability?
Ability to retain its absolute dimensional size over time
74
What is tear resistance?
Ability to resist tearing in thin sections, such as through the feather edge material within the gingival sulcus
75
What is viscoelasticity?
Characteristic of a solid that behaves as an elastic, solid, and a viscous liquid
76
_______nature improves tear strength and elastic limit
Viscus
77
What is a condensation polymerization reaction?
loses water as it combines
* By product: H2O or OH
78
What is an addition polymerization reaction?
* No by product
79
Elastic polymers can come in different consistencies. What are the examples?
* Polysulfide or rubber base PS
* Vinyl Polysiloxane VPS
* Polyether PE
80
What are nonaqueous elastomerics made of?
synthetic rubber
81
Non aqueous elastomeric materials offer potential solutions to the two main problems associated with Hydrocolloids (alginate):
* Poor tear resistance
* Poor dimensional stability
82
What are the characteristics of polysulfide?
* It is known also as Mercaptan or simply rubber base
* It is provided as two tubes of base and accelerator
* It requires a custom tray
* Longer setting time, malodor, stain cloths
83
What is the composition of polysulfide?
* Base: polysulfide polymer mixed with inert fillers
* Catalyst: lead dioxide mixed with small amounts of sulfur and act as oxidation initiator
84
What are the characterisitics of vinyl polysiloxane?
* Limited shelf life
* Requires special tray adhesive
* It is provided as an auto-mix unit, syringe, and mixing tips
* No syneresis or imbibition, however, responds with shrinkage over time
* More flexible; so, there is more chance for distortion during removal
* Best dimensional stability among impression materials (addition silicon)
85
Wait _____ min before pouring up a vinyl polysiloxane impression for stress relaxation. It can be delayed up to 7- 10 days
20 – 30
86
What is the composition of addition silicon?
- Base
- Catalyst
- Cross-linking agent
- Filler
87
What type of reaction occurs with VPS?
addition reaction, no by-product
88
Is vinyl polysiloxane hydrophilic or hydrophobic?
Hydrophobic
. dry field needed
. surfactant added; improve wettability & less cast bubbles
89
What can change the setting of vinyl polysiloxane?
* Sulfur inhibits the polymerization
* Latex gloves retards the setting
90
What is release during setting of vinyl polysiloxane?
H2
*secondary reaction NOT a by product
91
How long should you delay before pouring up vinyl polysiloxane?
15 – 30 min delay before pouring
92
What are the characteristics of polyether?
* Hydrophilic
* High elastic recovery
* It is provided as hand, auto-mix unit, or electronic mixing
* Light, medium, and heavy body
* Difficult removal from mouth or cast: need to block out undercuts
* More stiff than VPS
93
How do you remove a polyether impression?
When removing the impression, break the seal and rock slightly to prevent tearing
94
What affects polyether in terms of marginal discrepancy?
Water, saliva, and blood affects the material; increase the marginal discrepancy
95
What causes increased water absorption with polyetehers?
thinning agent used
96
What is the composition of polyethers?
- Base
- Catalyst
- Cross-linking agent
- Filler
97
What type of reaction occurs with polyethers?
addition reaction; no by product
98
Polyethers are known for their...
hydrophilic properties and good flowability
99
Polyvinyl siloxanes are known for their...
excellent elasticity, high tear strength and stability
100
The preferred elastomeric impression materials on the market are...
polyvinyl siloxanes (PVS) and polyethers (PE)
101
Polyethers are considered to have the ________ tear strengths
highest
102
hydrocolloids have relatively ______ tear strengths
low
103
Polysulfide impression materials have a _______ resistance to tearing but stretch and do not recover completely elastically
high
104
What are unacceptable impressions?
- voids
- tacky unset VPS material in the preparation area
105
How do you disinfect impressions?
➢ Rinse and spray the impression
➢ Acceptable disinfectants include: glutaraldehyde, iodophors, sodium hypochlorite, synthetic phenols, dual or synergized quaternaries, and sodium bromide and chlorine
➢ All impression materials are not compatible with all disinfectants
106
How does disinfectant soaked paper towel effect the different impression materials?
- no adverse effect on VPS
- potential expansion for PS and PE
- imbibition and expansion for alginate
107
Are all impression materials compatible with all disinfectants?
NO
108
What is the purpose of tissue retraction?
to atraumatically displace gingival tissues to allow access for impression material to record the finish line and provide sufficient thickness of the impression
109
What are the techniques for tissue retraction?
* Mechanical
* Chemo- mechanical (Impregnated cords)
* Surgical:
--Electrosurgery
--Rotary curettage (handpiece)
--Laser
110
What are the classifications of retraction cords?
▪ Depending on the configuration:
-Twisted
-Knitted
-plain
▪ Depending on the surface finish:
-waxed
-unwaxed
111
What is the chemo-mechanical technique for tissue retraction?
* Pack the retraction cord, soaked in hemostatic agent, then lightly dried; use cord packing instrument to place
* Double or single cord technique (two knitted cords with different diameters are used;smaller diameter will be deep into the sulcus)
* Remove cords after 4 minutes
* Impression material is injected into the sulcus once the cords are removed
112
What is GPT-9?
A digital impression: is NOT a negative likeness or copy in reverse of the surface of an object
113
What is a digital scan?
capturing the optical image directly of the patient’s anatomy or indirectly of a definitive cast of the anatomy
114
What are some digital impression systems?
* CEREC Primescan, Omnicam or Bluecam (Sirona)
* Tiors, 3 Shape (3D Biocad)
