Impressions ELCS Exam 2

Impression

negative imprint of the oral cavity

Cast

model of teeth and surrounding structures

Alginate is an...

irreversible hydrocolloid

Irreversible

once it is mixed and is set, it cannot be changed

Hydrocolloid

hydro= water

colloid= two phase mixtures with one small sized phase

Ingredients in alginate

sodium alginate, calcium sulfate, trisodium phosphate, diatomaceous earth, zinc oxide, and potassium titanium fluoride

Sodium alginate reacts with what? What does this form?

calcium sulfate, sodium sulfate and calcium alginate

Is alginate hydrophilic or hydrophobic?

hydrophilic

Advantages of alginate

cheap

hydrophilic

easy to use

Disadvantages of alginate

does not capture much detail

can only be used for a single pour

can distort easily

Alginate must be poured up in ______________ min

10

Syneresis

the contraction of a gel accompanied by the separating out of liquid

Alginate is hygroscopic, meaning ?

it has the property of absorbing water from the environment

Impressions must be:

accurate (not distorted)

complete

detailed

Does alginate have good elasticity?

yes

Does alginate have a high tear strength?

no

Tear strength

the thickness needed for material to avoid tearing

Dimensional stability

distortion over time

alginate distorts quickly

Should the tray extend beyond what you are trying to capture?

yes, 3-6 mm

Do trays get wider?

no, only longer

Where do you place the back of the tray?

beyond the most posterior teeth

How do you ensure clearance in the anterior?

rotate the tray forward

What can you do to modify the tray for comfort?

place wax around the edges

What can be done to widen the tray?

melting it

Is rope wax strong enough for tray extension?

NO it will not support the weight of the alginate

What is the adhesive called?

TAC

tray adhesive compound

What needs to be done to the tray after trying it in?

placing adhesive before doing the impression

What can adhesive be cleaned with if it is spilled?

isopropyl alcohol

What component will slow down reaction time?

sodium phosphate

What are the types of setting rates of alginate?

fast set and regular set

What water temp speeds up setting?

warmer water = faster setting

Using less water will make the mixture __________, but may alter other physical properties

less runny

Do you add powder or water first when mixing?

water

How do you get out the air bubbles when mixing?

mix while pushing against the bowl to get out the air bubbles

What hand do you hold the bowl and spatula in?

bowl in non dominant hand

spatula in dominant hand

What is the time for mixing?

45 seconds

What is the working time (mixing + loading into tray)?

1 min 30 seconds

Initial setting time

1 min 45 seconds

Total setting time

2 min 30 seconds

Maxillary impression points

stand behind the patient and lean them back

insert tray at the posterior and rock it forwards

try to center the handle in line with the nose

lean patient up once tray is in

Mandibular impression points

lean patient up so the mandible is parallel

stand in front of patient

make patient lift up tongue, then relax once the tray is seated

What do you do after you remove the impression from the mouth?

rinse in sink

spray with cavicide

wrap in damp paper towel

place in sealed biohazard bag