Ella's Quiz 1: Alginate & Gypsum

from halec_serlin on quizlet | has alginate AND gypsum

impressions are ____ and casts are _____

impressions are NEGATIVE

casts are POSITIVE

we classify impression materials based on 3 things:

1. USAGE/clinical app (ie low/high accuracy)

2. physical state after setting (ie elastic/ nonelastic)

3. setting RXN (chemical irreversible, reversible)

preliminary impressions vs definitive impressions (usage or clinical application)

preliminary are low accuracy

definitive are high accuracy

non-elastic vs elastic (physical state after setting): when do you use these impression materials?

non elastic are for edentulous (NO teeth) mouths

elastic is for both edentulous and dentulous mouths

reversible vs irreversible (setting reaction)

reversible (thermally softened and hardened)

irreversible (chemical reaction)

2 types of impression trays

stock (metal)

custom (plastic)

perioral vs intraoral tissue management

perioral: lips and cheeks

intraoral: hard/soft tissues AND gingiva

which tray uses adhesive and which doesn't

NO adhesive: metal

GENERALLY YES adhesive: plastic, custom trays (fabricated on a cast)

what is the purpose of perforations and ridges in the tray

provide retention of impression material so that it doesn’t separate & distort

adhesives are…

material specific

3 types of manipulation of impression materials

1. hand mixing

2. static mixing

3. dynamic mechanical mixing (what dr. michelle uses)

setting reaction starts when

mixing starts

wtf is “working time” according to manufacturers? vs general public

manu: end of mixing to when manipulation is IMPOSSIBLE

general public: ALL of mixing time + ALL manipulation time

wtf is the “manipulation” period?

when you STOP mixing … until the material HARDENS and you can’t move it anymore

setting time should be

ASAP (as short as possible)

all the time values (mixing, working, setting) start when…

mixing starts

“setting” time value =

mixing + manipulation + setting

(aka, from when you FIRST mix the materials together UNTIL the impression sets HARD)

general requirements of impression materials

1. adequate shelf life

2. easy to manipulate and handle

3. non toxic and non allergenic

4. adequate working time and short setting time

5. elastic and strong to resist tearing

6. dimensionally stable for long periods of time

7. compatible with model and die materials

8. disinfection without distortion or loss of details

viscoelastic behavior means

material should returns to its original dimensions ASAP after removing from mouth

the should be no permanent deformation

(ie, you pull out the impression and accidentally bang it against the crown of the tooth… now there’s a PERMANENT dent despite the material already having “set” Be FR)

examples of REVERSIBLE and IRREVERSIBLE hydrocolloids

reversible: agar

(literally think jello. it’ll turn to liquid at high temps)

irreversible: alginate

wtf is a “hydrocolloid”

water soluble polymers (make a gel when mixed with water)

ie alginate and agar

alginate is less ____ and not as ______

so, we only use it…

accurate

dimensionally stable over a period of time

only used for prelim impressions! ie diagnostic casts for TREATment planning, patient education, making custom impression trays!!

what accuracy is needed for alginate

75 um (micrometers) for primary impressions and 25 um for definitive

good alginate impressions….

do NOT change in shape/dimension btw mouth removal and stone model pouring

imbibition is…

SWELLING: absorption of water from the environment

syneresis is…

SHRINKAGE: loss of water

(opposite of inbibition)

broadly speaking, besides with WATER specifically (syneresis), what IS shrinkage?

ANY volatile byproduct that evaporates

pros and cons of alginate?

pros: hydrophillic, cheap

cons: obvi not as accurate

poor tear strength

need to pour IMMEDIATELY bc it shrinks after 10-15 mins!

musod alginate: mix time, work time, initial set time, set time

60 sec, 2 min 15, 2 min 30, 3 min 30 sec

after taking alginate how quickly do you need to pour it

10-15 min (cannot repour the same alginate)

warm water vs cold water on alginate setting

warm: faster
cold: slower

can the mix be lumpy for alginate and how much adhesive would you use on a stock plastic tray

no lumps, and minimal amount

before making an impression, the adhesive should be…

THIN and fully dry.

where does alginate waste go

trash

what does it mean if an impression is “not retained”?

and is this okay for pouring it up?

not retained = impression literally peeling off the tray

HELL NO you can’t pour it up

when can you practice with alginate?

in class on the BENCHTOPS

NOT on any humans- needs to be supervised by faculty.

gypsum is

calcium sulfate dihydrate (CasSO4)

use of gypsum in dentistry: what’s the DIAGNOSTIC casts used for VS DEFINITIVE?

diagnostic:

1. evaluate pt’s articulation & dentition

2. plan & track treatment

3. pt education

definitive:

INDIRECTLY making dental restorations.

wtf does gypsum have to do with articulators

MOUNT stone casts ON an articulator

wtf does gypsum have to do with “die”?

to make a tooth from a cast removable!! can slide in and out

(helpful for bridges and crowns where u want to access the margin)

cast (verb):

reproducing a shape/surface by pouring up a NEGATIVE impression

what’s a MODEL in dentistry? example of a model?

a POSITIVE likeness of an object

a cast is a MODEL!

wtf is calcination?

heating a solid material to evaporate off volatile, chemically combined components (water & CO2)

how tf is gypsum made from CaSO4 as opposed to OTHER products?

heat at a CERTAIN temp to evaporate off a CERTAIN am of water

plaster and stones: temp of heating

aka?

110-130 C

“calcium sulfate hemihydrate”

hexagonal anhydrite: temp of heating

130-200 C

orthothrombic anhydrite: temp of heating

200-1000 C

as gypsum material sets…

exothermic rxn converts HEMIhydrtate to DIhydrate

using few crystals from past gypsum reaction makes what?

why tf would you ever do this?

slurry water

can use to ACCELERATE the setting rxn

manufacturing VERSUS actually setting gypsum… describe the rxns

manufacture: dihydrate + heat → hemihydrate + H2 gas

set: H2O+ hemihydrate → dihydrate + heat

beta hemihydrate compared to alpha ?

(water, strength, shape)

what types of gypsum powder is it, and what’s it used for ?

gypsum powder that’s IRREGULAR shaped, spongey, requires HELLA water to react

type 1 & 2 used for impression & model plaster)

alpha hemihydrate compared to beta?

what’s it used for?

REGULAR shape, dense, needs less water (no duh- it’s a STONE)

type 3,4,5 - dental stone, high strength dental stone, high strength and high expansion dental stone

what is modified alpha hemihydrate with shorter and thicker crystals, uses even less water, and has a higher strength stone

Die stones

lowest to highest strength of type 1-5 gypsum products? what hemihydrates are they made from?

beta (1-2): impression plaster, model plaster

alpha (3,4,5): plain dental stone, high strength dental stone, high strength and high expansion dental stone

4, 9, 20.7, 34.5, 48.3 strength at 1 HOUR (MPa)

over time, the compressive strength of gypsum products…

INCREASES.

longer it’s allowed to dry, the STRONGER it becomes!

dental gypsum PROS

(time, expansion, strength)

ADEQUATE working time + HELLA short setting time (+ doesn’t expand a ton AFTER setting!)

hella strong, resistant to abrasion

the longer you mix gypsum…

the SHORTER the working time!

(literally eating up working time)

if you don’t use enough water for gypsum?

DECREASE in strength, hardness, abrasion resistance

wtf is the W:P ratio?

water (mL) : 100 g powder

a W:P ratio of 0.4 means…

40 mL water / 100 g powder

most widely accepted mechanism describing setting process of gypsum?

what does it mean?

supersaturated solution precipitation SSP

hemihydrate dissolves → dihydrate PRECIPITATE

gypsum: what defines the INITIAL setting time vs FINAL setting time?

initial: when the mix cannot be penetrated by light gillmore needle pressure

final is barely perceptible mark left by heavy gillmore needle pressure

time to mix mechanical vs hand?

what supplies do you use for these?

mechanical is 20-30 sec; vacuum mixer

hand is 60 sec; mixing bowl & stone spatula

rate of gypsum dihydrate crystal formation INCREASES with:

hemihydrate solubility

number of nuclei

accelerators (aka catalysts)

increased water to powder ratio (more water) does what to

working and setting times

strength and hardness

expansion

increased working and setting times

decreased strength and hardness

decreased setting expansion

chemical accelerants are

potassium sulfate (K2SO4)
sodium chloride (NaCl)
sodium sulfate (Na2SO4)

borax at LOW concentrations (at HIGH concentrations it is retards)

what happens during HYGROSCOPIC setting expansion of gypsum?

happens when gypsum SETS while completely dumped in water

2x normal setting expansion amount

increased setting expansion results from ________ water to powder ratio and ________ mixing times

lower w:p
longer mixing

what happens during gypsum setting expansion?

initial contraction

expansion

smaller contraction

wet strength (green strength) vs dry strength

what are they? how do they compare?

wet strength: strength when water in excess

dry strength: strength when all excess water used and 2-3 times that of wet strength

increase W:P ratio _____ strength? because…

decreases

FEWER am of crystals per UNIT volume of gypsum-water

aka more DILUTE slurry

effect of mixing on strength…

longer mixing time INCREASES strength

… until OVERMIXING which decreases strength :(

there are additives to gypsum which can…

STRENGTHEN the final product

for clinical care cases, the preferred method of mixing is ?

mechanical/ vacuum mixing

(demonstration videos are on D2L and should be watched before class)

HOW do you hand mix gypsum?

thorough mix for 1 min

bowl on VIBRATION table to minimize incorporated air

(reduces air by HIGH frequency, LOW amplitude vibration)

HOW do you pour a gypsum impression?

add stone to one end, while impression ON LIGHT vibration

tilt impression to fill with material

continue adding to SAME spot and tilting :)

what typically causes BAD gypsum casts?

saliva/ blood contamination

how do we prevent BAD gypsum casts?

hardening chemicals in the alginate impression material

treat impression

RINSE impression of ALL saliva and blood

has FDA approved disinfecting agent in the gypsum itself? where do we use disinfectant?

NO

use on the FINISHED teeth models- SHOULD NOT affect detailing.

not safe to store or heat casts above

130 C

what dissolves gypsum?

water

what gypsum are we going to be using?

properties? (w:p, expansion, compressive strength)

Buffstone (whip mix)

30ml/100g
.15% expansion
compressive strength wet (1 hour) 28 MPa and dry (48 hours) 56 MPa

what’s the working and setting time of OUR gypsum?

6-8 mins

15 mins

how much does OUR gypsum expand?

0.15%

what’s the compressive strengths of our gypsum?

wet (1 hr) = 28 MPa

dry (48 hrs) = 56 MPa

wtf is a “gypsum based investment”?

“refractory” material: gypsum mixed with silica

used to make a MOLD for metal casting process

normal setting expansion is defined as…

expansion when gypsum or gypsum bonded investment SETS in ambient air

wtf is “plaster of paris”

dental PLASTER

aka BETA calcium sulfate hemihydrate (CaSO4 × ½ H2O)