Trays, Materials and Techniques Flashcards
What are impression trays?
A device used to
carry, confine, and control
impression material
while making an impression
What are the various types of impression trays
stock (denate and endentulous)
water cooled
custom
tripple
Describe custom trays?
Maintains optimal thickness of impression materials, 2.0 to 4.0 mm for elastomers
Require less impression material
Provide proper flange extensions
How should trays extend distally?
Trays should extend distally to cover the maxillary tuberosity and cover the mandibular retromolar pad for maximum anatomical reproduction
What height should trays be?
Tray height should fully cover the length of anterior and posterior teeth
How should trays extend regarding the facial aspect?
Tray should extend beyond the facial aspect of the teeth with ¼ inch of space between the tray and soft tissue
Utility wax beading
Wax may be added to the borders of the tray to extend its length or height
Wax can be placed in the palatal area of patients with high palates to eliminate voids in the palatal area
Wax may be placed around the tray periphery to protect and cushion the soft tissues in the oral cavity
The placement of utility wax on the posterior region of the maxillary tray prevents excessive alginate from flowing down the throat
What are the different types of impression materials?
Alginate Hydrocolloids
Agar Hydrocolloids
Elastomeric Impression Materials
Imbibition
to take in water
Syneresis
to give up water (dry out)
Tensile strength
ability to withstand tearing
Working time(WT)
time before the material begins to set; starts from the time you began mixing & includes the time you have to load material into a tray or syringe
Setting time(ST)
time it takes for the material to be completely set (from start to finish)
Mixing time
time you have to mix the material
Alginate is classified as an?
irreversible hydrocolloid
Why is alginate classified as a hydrocolloid?
Hydrocolloid because it is particles of a gelatinous (colloid) state in water (hydro).
What is alginate particles composed of?
Salts of alginic acid, a product of marine kelp (a type of seaweed)
An activator, usually calcium sulfate
A retarder like sodium phosphate
An inert filler to reduce stickiness, produce a smooth texture, and add strength
Flavoring
What are disadvantages of alginate?
Poor tear strength when thin
Poor dimensional stability
Distorts if shifted during setting
What are advantages of alginate?
Easy to mix and manipulate
No expensive equipment needed
Elastic and removes from undercuts easily
Cost effective
Pleasant taste and odor
What is type 1 Fast set alginate?
WT 1 minute
ST 1-2 minutes
What is type 2 normal set alginate?
WT 1-2 minutes
ST 2-4 minutes
What temperature should water be for aliginate?
73
How should impressions be removed?
with a snap-out motion
Describe agar in agar hydrocolloids
13-17% for tray material and 6-8% for syringe materi
Describe borates in agar hydrocolloids
Gel Strength, retards set of stone (disadvantage)
Describe potassium sulphate in agar hydrocolloids
retards effect of borates
Describe wax in agar hydrocolloids
filler
Describe Thixotropic Materials in agar hydrocolloids
Plasticizer, Glycerine or Thymol (bactericide)
Describe Alkylbenzoates in agar hydrocolloids
preservative
Describe water in agar hydrocolloids
Dispersion Medium
What are the types of elastomeric impression materials?
Polysulfide
Condensation Silicones
Addition Silicones (VPS- Vinylpoly Siloxanes and PVS- Polyvinyl Siloxanes)
Polyethers
PolySulfides are commonly called what?
rubber base
what are the two types of pastes?
base and reactor
what is base paste?
Liquid polysulfide polymer
Inert fillers (titanium oxide, zinc sulfate, silica)
What is reactor paste?
Lead dioxide
Dibutyl phthalate
Sulfur
Deodorants
Disadvantages of polyethers
Flexibility is low, and stiffness high
Easy to break stone cast upon removal
Absorbs water so must be stored dry or will experience significant dimensional change
Allergic Reactions have been reported
What is contact angle?
Contact angle measurement on unset material is a method used to determine hydrophilicity (having a tendency to mix with, dissolve in, or be wetted by water).
What is the contact angle on hydrophilic surfaces?
less than 90 degrees
What is the contact angle on hydrophobic surfaces?
greater than 90 degrees
what is the cost comparison of impression materials?
Lowest to highest
Alginate
Agar = polysulfide
Condensation silicone
Addition silicone (PVS)
Polyether
What is the rank of impression material by dimension stability?
Best to Worst
Addition silicone
Polyether
Polysulfide
Condensation silicone
Hydrocolloid
What is gypsum?
Naturally Occurring Mineral
Calcium Sulfate Dihydrate + Water
Heated to 230-250o F to remove the water (Calcination)
Results in Calcium Sulfate Hemihydrate
Set by an Exothermic Reaction
types of gypsum powder?
Plaster
Stone
Improved Stone
Investment Materials
what is the difference in the different types of gypsum powders?
Principal difference between plaster, stone, and improved stone is in the shape and form of the hemihydrate crystals. Crystals of dental stone and improved dental stone are more dense and regular in shape.
what choice of gypsum is recommended for study models?
Plaster or stone is the recommended choice of gypsum products for use in dentistry for study model construction for presentation purposes
what are accelerators?
Increase in water temperature above 68 degrees F when mixing the plaster
Increase room temperature or humidity
Faster rate of spatulation time
will hasten the setting time
Pinch of table salt (sodium chloride)
Decrease the amount of water specified by the manufacturer
What are retards?
Cooler than room temperature water
Decrease in room temperature and humidity
Slower rate of spatulation will slow down the setting time
Borax (calcium salts) in small concentrations
Increase in the amount of water specified by the manufacturer, although this weakens the cast
