impression materials ch 46 Flashcards
used to obtain an impression of teeth and or the surrounding oral tissues
impressions
are negative reproductions of dental structures. Gypsum products are used to make positive reproductions of the oral cavity
impression
preliminary impressions & used to make
taken either by the dentist or an dental assistant. Used to make trays, orthodontic appliances, diagnostic models
taken by dentist , used to make most accurate reproduction of the teeth and surrounding tissues. Used to make indirect restorations, partial/full dentures, implants
Final impressions & used to make
impression trays
used to hold impression materials.
must sufficiently rigid to carry material into oral cavity, hold material close to the teeth, avoid breaking during removal, prevent warping the complete impression
impression trays
stock trays
not custom fitted to the patients mouth so you must try them prior to taking the impression
you have to make sure that the stock tray is
2-3 mm beyond the third molar, allows 2-3 mm of material between the tray and the incised/occlusal edges of teeth
quadrant tray
covers one half of the arch
section tray
covers the anterior portion of the arch
full arch tray
covers the entire arch
perforated tray
holes in the tray create a mechanical lock to hold the material in place
smooth tray
interior of the tray is painted with an adhesive to hold the impression material
custom trays
are constructed to fit in the mouth of a specific patient
hydro means
water
colloid means
gelatin substances
the phase in which a colloid is a semi solid is the
gel phase
types of hydrocolloids
reversible hydrocolloids - agar
irreversible hydrocolloids- alginate
what are utility wax strips for
can be used to extend tray
waxing the tray is called
beading
t/f; setting time is reduced by warmer water, the warmer the water the faster the set
True
normal set
working time- 2 mins
setting time-4.5 mins
fast set
working time- 1 1/4 min
setting time 1-2 mins
mandibular impressions level/scoop/temp
scoops- 2
levels- 2 levels of water
temp- 20-21 degree
maxillary impression level/scoop/temp
scoops-3
levels- 3 levels of water
temp-20-21 degree
mixing technique
add powder to water in small amounts
use rubber bowl and wide spatula
After done, Clean dirty spatula
smoothing the surface of the alginate by wiping a moistened finger along the surface
glazing
place additional alginate in undercuts on the occlusal surface on the palate. Done to create less discrepancy in the anatomy of the impression
smearing
imbibition
the alginate impression absorbs additional water and expands
syneresis
the alginate impression loses moisture causing it to shrink and distort
impression materials that dislike moisture are considered
hydrophobic
occlusal impressions
taken by the dentist or dental assistant.
reproduction of the occlusal relationship between max and mand teeth
accurate registration of the normal centric relationship of the max and man arches, commonly referred as
bite registration
useful when diagnostic casts are trimmed
Most common technique is to use a softened baseplate
Pateint closes normally onto softened wax
wax bite
t/f; ZOE paste has little to no resistance to bite closure and is a fast setting material
true
create positive reproduction of the teeth and soft tissue called study casts, study models/diagnostic models
gypsum products
3 types of gypsum products
dental plaster
dental stone
high strength stone
dental plaster
white
requires more water for mixing than stone and produces a weaker cast
dental stone
yellow
used when a more durable diagnostic cast is needed or for a working model to make dentures
high strength stone
has strength, hardness and dimensional accuracy which is ideal for dental lab tech in creating die.
Requites least amount of water out of the 3 products
gypsum mixing
powder added to water
too much water weakens them and takes longer to set
too little water gives shorter working time and dry mix
model consists of two parts
anatomic portion - created from the alginate impression
art portion- forms the base of the cast
trimming study models
always wear masks, do not wear gloves, must be soaked in water for 5 mins before trimming
art portion
one third
anatomic portion
two thirds
anterior art portion of maxillary model is trimmed from
canine to the midline at an angle
