W2: Impression Materials Techniques and Special Trays Flashcards
Give examples of non-elastic impression materials
ZOE (paste)
Plaster
Dental impression Compound
Which type of material is impression compound?
Impression compound is a non-elastic impresion material
Is plaster an elastic or non-elastic impression material?
Non-elastic
What are the two subdivisions of elastic impression materials?
Elastic impression materials are further subdivided into hydrocolloids and non-aqueous elastomers
Is impression compound an elastic or non-elastic impression material?
Non-elastic
Is ZOE an elastic or non-elastic impression material?
Non-elastic
Which materials are elastic hydrocolloids?
Agar Reversible and alginate irreversible
Which materials are non-aqueous elastomers?
Polysulfides, polyethers, condensation sillicone, addition sillicone
Are impression waxes elastic or non-elastic impression material?
Non-elastic
What are the general requirements for biomaterials used to make complete denutres?
- Bicompatible materials (minimal harmful affects on the oral tissues)
- Non-toxic
- Non-irritating
- Non-allergic
- Non-carcinogenic
- Chemically minimally degradable
- The material must fufill clinical objectives by possessing appropriate optimal physical properties
What are the optimal physical properties the material must posses to fufill clinical objectives?
The material should have:
* Adequate mechanical properties (e.g. hardness, elasticity, strength)
* Adequate thermal coefficeint of expansion
* Adeqaute conductivity properties
* Accetable aesthetic properties
* Easy to clean
* Ease of fabrication and manipulation (relatively easy to work with)
* Readily available
* Econmical
* Easy/inexpensive maintenance (material repairs and additions)
What are the optimal qualities for prosthdontic impression materials?
Optimal qualities are:
- low viscosity to adapt to oral tissues (but viscious enough to remain in the tray)
- Hydrophillic (adequate wettability of the oral tissues to accurately adapt and capture the oral structures)
- Pleasant odour and taste
- set into a rigid solid or rubber state in a resonable timeframe
- adequate elastic recovery with no permanent deformation upon removal from the mouth after impression taking
- adequate tear strength (avoids tears/breakage upon removal)
- remain dimensionally stable after setting and until cast pouring
- impression is able to remain dimensionally stable to be repoured from the cast
- compatibility with cast material
- bicompatible, non-toxic, absence of irritant constituents
- sufficent colour and opacity for proper impression evaluation by the clinician
- readily disinfected (without significant mechanical property loss or loss of accuracy)
- adequate shelf-life storage
- Cost-effective (this includes material processing time and equipment)
What were non-elastic impression materials initially used for?
For taking final impressions for edentulous patients
Why were non-elastic materials replaced by elastic materials?
Non-elastic impression materials were not able to be withdrawn without fracture from undercut areas in the mouth
What is a preliminary cast?
Result of primary impression
What is a final cast?
Result of secondary impression
If a material has adequate wettability of the oral tissues what does this mean?
This means that material is hydrophillic
Which impression material has a negligible setting shrinkage of less than 0.1% with no signifcant changes thereafter?
TEST
ZINC OXIDE EUGENOL (ZOE)
What does adequate elastic recovery refer to?
Adequate elastic recovery refers to the material to strech and return it its natural form (such as a rubber band) and not tear at suceptible areas (under cuts)
What is dimensional stability?
Dimensional stability refers to the impression to remain at its current state (not shrink or expand).
It is important for materials to remain dimensionally stable during transport to other laboratories/until pouring up of the impression.
What are benefits of using ZOE impression material?
Good surface detail and accuracy
ZOE is a non-elastic impression material, what can happen at the undercut area?
ZOE can fracture at the undercut areas
How does set ZOE react to plaster or stone?
Set ZOE is not compatible with plaster or stone but the impression is submerged in warm water to ease removal off of the cast model
Is ZOE impacted by the weather/surrounding environment?
Yes, water, heat, humidity increase the setting reaction of ZOE (some factors can be adjusted to increase or decrease setting time by the operator, turn on air-conditioning etc.)
What is ZOE mainly used for?
Final impressions of edentulous ridges with no or minimal undercuts
What are applications of ZOE?
Bite registration
Temporary liner
Surgical dressing
Washed impressions
Final Impressions (edentulous ridges)
What are the types of impression compounds?
Two types of impression compound are composition and manipulation. These are divded into to Type I (lower fusing material) and Type II (higher fusing material).
What are cakes (impression compound)?
Cakes are Type I lower fusing material. These are mucocompressive and used for primary impressions
When and how can cakes be used?
Cakes can be used for full edentulous patients by heating the material to soften, placed in the tray and against the tissues. As the material sets, cakes cool rigid.
What are green sticks (impression compound)?
Green sticks are Type II higher fusing material. Green stick is used as border molding material on special trays for taking secondary impressions.
What are elastic impression materials?
Elastic impression materials remain in an elastic or flexible state upon removal from the mouth. Elastic impression materials can be compressed or streched without risking significant damage. Even in the presence of minor undercuts, elastic impression materials **accurately ** reproduce hard and soft tissue detail.
When is agar used and for what purposes?
Agar is a reversible hydrocolloid elastic impression material used in dental laboratories for duplicating dental stone models (has high accuracy) and investement models to manufacture cobalt chrome frameworks
When can alginate be used?
Alginate can be used to take primary and secondary impressions
What are the two types of alginate?
Fast set and regular set
Is agar a reverisble or irreversible hydrocolloid?
Agar is reversible hydrocolloid
Is alginate a reversible or irreversible hydrocolloid?
Alginate is an irreversible hydrocolloid
Is alginate a reversible or irreversible hydrocolloid?
Alginate is an irreversible hydrocolloid
What is alginate used for?
Alginate impressions are used for the fabrication of primary casts (prosthodontics), study models (orthodontics), cast duplication, and for taking secondary impressions (partial dentures->pour up in a short time frame)
*cast duplication with alginate impressions is lacks accuracy
What are the advantages of using alginate impression material?
Alginate:
-is easy to use
-is inexpensive
-*has a quick setting time
-has a pleasant taste and odour (mild flavour)
-is hydrophillic (compatible with plaster/stone, pours well)
-can be used with saliva present
-is non-toxic
-does not cause staining
*alginate setting time can be controlled based on the water temperature used
If cold water is used to mix alginate, how does this affect the setting of alginate?
Cold water causes alginate to take more time to set (more working time).
If room temperature water (or warm water) is used to mix alginate, how does this affect the setting of alginate?
Room temperature (or warm water) will cause the alginate to set faster.
What are the disadvantages of using alginate?
Alginate:
-has a low tear strength
-captures less surface details (compared to other impression materials)
-is not as dimensionally stable as other impression materials
How should alginate impressions be wrapped to send/take to the dental laboratory?
Alginate impressions should be wrapped in slightly DAMP paper towel.
What happens if alginate impressions are wrapped in dry paper towel?
The alginate impression dries out and the impression distorts (paper towel will absorb to water from the impression causing shrinkage)
How is polysulfide rubber material available?
Polysulfide rubber material is two-paste system and comes in high, medium, or low consistency.
Does moisture and temperature affect polysulfide rubber?
Yes, the presence of moisture and increased temperature can cause the reaction of polysulfide rubber to accelerate.
How long after taking an impression with polysulfide rubber does the impression need to be poured up?
It is important to pour up the impression within an hour (because temperature and moisture affects the material).
What are disadvantages of polysulfide rubber material?
Polysulfide rubber:
-is hydrophbic (oral tissues have to be dried before impression taking)
-the material can stain fabric
-is messy
-has an unpleasant smell
What are advantages of polysulfide rubber material?
Polysulfide rubber:
-has a high tear strength
-is flexible (desirable)
-has a long working time
-has accurate detail reproduction
Which was the first silicone material used in dentistry?
Condensation silicone
When is condensation silicone commonly used?
Codensation silicone is often used to take impressions in preparation for inlays, onlays, crowns and bridges and can be used for complete denture impressions
What is the working time of condensation silicone?
Moderate working time of 5-7 minutes (amount of accelerator can alter the working time).
What are advantages of condensation silicone?
Condensation Silicone:
- has a plesant odor
- has a moderately high tear strength
- has excellent recovery from deformation
- can be used with compatible putty material for form fit a special tray
-can be disinfected with any disinfecting solution (accuracy is not affected/altered)
What are disadvantages of condensation silicone?
Codensation Silicone:
-is hydrophobic (problematic when pouring it into plaster or stone)
When should condensation silicone be poured up?
Within 1 hour (ideally)
What is addition silicone often called as?
Addition silicone is often called as polyvinyl siloxane/vinyl polysloxane (PVS or VPS)
How does addition silicone contrast to condensation silicone?
Addition silicone is based on addition polymerization (divnylpolysiloxane and polymethylhydrosiloxane addition polymerization with platinum salt catalyst)
What are advantages of PVS?
PVS:
-is the most accuarte elastic impression material
-has less polymerization shrinkage
-has low distortion
-has quick deformation recovery
- has a moderately high tear strength
- working time of 3-5 (can be modified)
- hydrophobic and hydrophillic forms available
- odourless
- tasteless
- putty form available to help with form fiitting impression trays chairside
- most are available in automixing devices
- can be poured up to 1 week after taking the impression
- remains stable in most sterilizng/disinfectant solutions
Which material is thixotropic?
Polyether (good surface detail because it is thixotropic)
*viscosity of the material changes with stress (e.g. hair gels)
What is polyether useful for?
Border moulding
Which material is polyether not compatible with?
Polyether is NOTcompatible with addition silicones therefore do not use polyethere impression material to border mold PVS final impressions
Is polyether hydrophillic or hydrphobic?
Hydrophilic
What is the tear strength of polyether?
Polyether has a low to moderate tear strength
What is a problem with polyether impression material?
Polyether impression material has a SHORT working and setting tmie (this is problematic)
What is polyether impression material usage limited to?
Polyether impression material may limit the use to impression procedures for removeable partial dentures (due to lowest flow and flexiblity characteristics of the elastic materials)
What are disadvantages of polyether impression material?
Polyether:
- material stiffness can lead to breakage of the cast when removing the impression of the special tray
- has higher permanent deformation that PVS
- may have an unplesant taste
- is affected by moisture, disinfectant solutions, and humidty for lengthy time periods (may disintegrate and react in the cleaning solution)
- may be poured up within 2 hours (follow manufacture guidlines)
What is mucocompressive impression material?
Mucocompressive material records the mucosa **under load. This creates more EVEN distribution of load over underlying tissues, BUT may compromise denture retention when not under load.
What determines whether an impression material is mucostatic or mucocompressive?
Viscosity
What is mucostatic impression material?
Mucostatic impression material records underlying tissues with the distribution of load which may be uneven. Close adaptation of the denture base to the mucosa may allow for EXCELLENT denture retention.
Which impression materials are mucostatic?
Plaster, ZOE, alginate (low viscosity)
Which impression materials are mucocompressive?
Impression compound, elastomers, alginate (high viscosity)
Is alginate a mucocompressive or muscostiatc impression material?
BOTH (depends on the amount of water used and the alginate mix). If less water is used the mix will be more viscous, therefore high viscosity and mucocompressive. If more water is used, the mix will be less viscous (more runny) and is mucostatic.
Should mucostatic or mucocompressive materials be used to take a primary impression?
Mucocompressive
Should mucostatic or mucocompressive materials be use to take a secondary impression?
Mucostatic
What is a key difference between deciphering dentate and edentulous impression trays?
Tray depth- The depth of dentate trays is more
When is the two stage technique for free end saddles used?
PRIMARY lower impressions with two free end saddles
What is the method for the two stage free end saddle technique?
- Get catalyst and base
- Take two equal measures of both
- Mix the catalyst and the base together until even colour
- Break the putty into two equal halves
- Place the putty in the free end saddles area of the impression tray
- Take impression
What are the steps of taking a mandibular impression?
- Stand on the side of the patient
- Enter the oral cavity at a 90 degress angle (angle hand upon entry)
- Once in the oral cavity twist hand and line up tray with the lower arch (hand and arch should be perpendicular)
- Start placing down the tray (DO NOT TRAP THE LIP)
- Patient lifts tongue to the roof of the mouth
- While placing down the tray get ull control
- Hold the tray in position with the second and third fingers in the premolar region with thumbs at the bottom of the chin
- Have patient stick tongue out side to side (captures lingual freenum)
Do plastic trays or metal trays have more accurate buccal extensions to capture posterior sulcui?
The buccal extensions of **metal trays are often more accurate than plastic trays to capture posterior sulci. **
How do you adjust plastic trays/special trays if needed?
Adjust with a straight handpiece and an acrylic bur. Remeber to ROUND of any trimmed pieces and use a dust box while adjusting the plastic trays.
Should the patient be in a supine, semi-supine, or completely upright when taking impressions?
UPRIGHT
How much does a special tray extend (i.e how short is the special tray)?
Special trays extend 2-3 mm from the deepest part of the sulcus
How can an underextended special tray be fixed?
Green stick (impression compound)
What is border moulding?
Border moulding is the shaping of impression tray border areas by manual or functional manipulation of adjcent tissue to duplicate the contour and size of the vestibule.
Which materials can be used for border molding?
Green stick (impression compound), PVS, and polyether
Where can green stick/impression compound?
Buccal and labial edges of the impression tray AND is essential for posterior palatal seal.
What temperature is water bath for green stick (impression compound)?
65 degrees celsius
True or false: green stick should be removed from the fitting surface of impression trays?
TRUE- remove
What can and should be used to prevent ZOE from sticking to beards and delicate elderly skin?
petroleum jelly
What are the steps to mixing ZOE?
Total time 4 minutes
30 seconds mixing time
1 minute loading time
2.5 minutes for impression taking and muscle trimming
How do you build up a primary impression?
Soft blue periphery wax
