Claire's Quiz 1 (Alginate & Gypsum)

from claire_kini on quizlet

what is gypsum

Calcium sulfate dihydrate
CaSo4 2H2o

uses of diagnostic/study casts

evaluating patient's dentition/occlusion
treatment planning
patient education
evaluating progress of ortho/prosth treatment

uses of definitive casts

used in fabrication of dental restorations (indirect)

what is a die

reproduction of a single tooth made out of gypsum, epoxy resin, metal, or refractory material

can be continuously removed and replaced in a working cast

when are casts with removable dies used

fabrication of crowns or fixed partial dentures (bridges) when access to prepared margins is needed

impressions

negative replica of the oral cavity

casts

reproduction of the shape/surface that was made in an impression

what is the lay term for a cast

a model

calcination

the process of driving a specific amount of water out of gypsum to create specific plasters, stones, or investment die stones

t/f varying heat of calcination varies the type of product

true

110-130°C product

plasters and stones (calcium sulfate hemihydrate)

130-200°C

hexagonal anhydrite

200-1000°C

orthorhombic anhydrite

mode of use of gypsum

mixed with water in specific proportion
exothermic reaction-> hemihydrate to dihydrate as material sets
slurry water can speed up the setting reaction

Two types of gypsum powder particles

B-hemihydrate (plaster)
a-hemihydrate (stone)

characteristics of B-hemihydrate

irregular
spongey
requires more water for rxn

characteristics of a-hemihydrate

regular in shape
dense
less water required for reaction

die stone

modified a-hemihydrate
shorter and thicker crystals
requires even less water than a-hemihydrate
higher strength stone

type I gypsum

impression plaster--- impressions and occlusal records

type II gypsum

model plaster (study casts and ortho models)

type III gypsum

dental stone (definitive casts)

type IV gypsum

high strength dental stone (die stone for wax patterns)

type V gypsum

High strength, high expansion dental stone

what types are b-hemihydrates

type I and II

what types are a-hemihydrates

type III, IV, and V

desired properties of gypsum

adequate working time
short setting time
high strength, harness, and resistance to abrasion
low setting expansion (except type V)

when does setting time begin for gypsum

upon contact with water

inadequate wetting does what to gypsum product

reduces strength, hardness, and resistance to abrasion

longer mixing time does what to the working time

reduces

T/F the water to powder ratio is critical

true

what does the water:powder ratio tell us

the amount (in mL) of water needed to add to 100g of powder

dry compressive strengths (compressive strength at one hour (mPa))

type I: 4
type II: 9
type III: 20.7
type IV: 34.5
type V: 48.3

what happens to dry compressive strengths over time

after initial set, dry compressive strength increases for about 24 hours and then remains constant

dissolution-precipitation theory

supersaturated solution precipitation

upon mixing with water a solution is formed
hemihydrate dissolves forming a concentrated solution of calcium and sulfate
dihydrate precipitates out of solution and recrystallization occurs to form the stone

initial setting time

when the mix cannot be penetrated by light Gillmore needle pressure

final setting time

barely perceptible mark left by heavy Gillmore needle pressure

two types of mixing times

1. mechanical mixing time (use a vacuum mixer)
-20-30seconds

2. handmixing- (bowl and stone spatula)
-approx. 60 seconds

3 ways to control setting time

1. solubility of hemihydrate
-increase solubility= rate of crystallization

2. number of crystalline nuclei
-increased number=increased rate of crystallization

3. retardants/accelerants

result of increased water to powder ratio

increased working and setting times
decreased hardness, strength, and resistance to abrasion
decreased setting expansion

how does mixing time affect setting time

longer and more vigorous mixing shortens setting time

what does water temp due to setting time

warmer water: decreases setting time (erratically)
colder water: increases setting time

effect of slurry water on setting time

increases rate of crystallization by providing additional seeds of nucleation

shortens setting time

chemical accelerants

potassium sulfate
sodium chloride
sodium sulfate
borox

difference of uses of borax dependent on concentrations

low conc: accelerant
high conc: retardant

setting expansion

the slight swelling of the gypsum while it is getting hard; crystals push against each other creating porosities

initial contraction, expansion, smaller contraction

hygroscopic setting expansion

expansion that occurs when gypsum or a gypsum-bonded investment sets while immersed in water

2x more than normal setting expansion

crystals can grow more freely

most effective method at controlling setting expansion

chemical modulation

does increasing or decreasing the water:powder ratio decrease setting expansion? why?

increasing water: powder ratio

solution is more dilute and there is less crowding when gypsum is setting so less impinging and therefore can grow without crowding

two ways to increase setting expansion

lower W:P ratio
longer mixing time

wet strength vs dry strength

wet strength=green strength
-strength when excess water is still present

dry strength
-strength after all excess water is used
2-3x that of wet strength

what is the result of increased W:P ratio on strength

decreases strength
fewer crystals per unit volume

mixing time on strength

increasing mixing time increases strength

too much mixing can decrease strength by preventing crystal interlocking

additives on strength

additives can increase strength of final product

is hand mixing or mechanical mixing preferred method

mechanical

two things needed for handmixing

parabolic bowl and rigid/stiff spatula

how long should you handmix

thoroughly for 1 minute

what does increasing mixing time do to working time

decreases

what is the advantage of mixing on a vibration table

decreases incorporated air

what type of vibration should be used

high frequency/low amplitude

what can too much vibration cause

air bubbles

how to pour an impression with gypsum

surface of impression should be free from excess water/surfactant

add small amount of stone to one end of the impression, adjust vibration speed to allow to flow freely
tilt impression to control movement
add more stone to same spot under light vibration

mound stone on flat plate (two pour technique)

disinfection of gypsum cast

should be disinfected

solution shouldnt disrupt accuracy or details

can be incorporated into material but hasnt been FDA approved yet

what is the effect of water on gypsum casts

dissolves it

what temperature can you not store/heat gypsum casts past

130°

what gypsum is used at marquette

buffstone (whipmix)

water:powder ratio of buffstone

0.3

30mL/100g

working time of buffstone

6-8 minutes

setting time of buffstone

15 minutes

setting expansion of buffstone

0.15%

compressive strength, wet of buffstone (1 hour)

28 mPa

compressive strength, dry of buffstone (48 hours)

56 mPa

3 ways to classify impression material

1. usage/clinical application
-preliminary(low accuracy)
-definitive (very high accuracy

2. elastic vs non-elastic
-nonelastic (edentulous)
-elastic (edentulous and dentulous)

3. setting rxn
-reversible (not used anymore)
-irreversible

two types of impression trays

stock and custom

two types of tissue management

perioral (lips/cheeks)
intraoral (hard and soft tissues, gingiva)

types of stock metal trays

quadrant
full arch
maxillary
mandibular

use of adhesive with stock metal trays

no adhesive used

stock plastic trays

quadrant
full arch
mandibular
maxillary

use of adhesive with stock plastic trays

generally use an adhesive

how are custom trays made

fabricated on a cast

use of adhesive with custom trays

generally use an adhesive

purpose of perforations and ridges in impression trays

retention of impression material

T/F adhesives are material specific

true

what is working time

time from beginning of mixing to initial setting

what is setting time

Time elapsed from the onset of mixing until the end of setting

importance of elasticity in impression material

after removal from mouth, material should return to its original dimensions without permanent deformations

viscoelastic behavior

allow for accurate impressions of undercuts of teeth

types of hydrocolloids

reversible (agar)
irreversible (alginate)

what type of impressions does alginate produce

preliminary

what can be produced from alginate impressions

study (diagnostic) casts, treatment planning, patient education, preparing custom trays

accuracy needed for preliminary vs definitive impressions

minimum for preliminary: 75 micrometers

minimum for definitive: 25 micrometers

imbibition

Absorption of water from environment, swelling

syneresis

Loss of water, shrinkage

what is the result of a volatile byproduct of an impression

shrinkage

alginate used by marquette

jeltrate (dentsplysirona)

mixing time

60s

working time

2 min 15 seconds

initial setting time of jeltrate

2 min 30 s

setting time of jeltrate

3 min 30s

ratios for partial/quadrant impression

1 scoop, 1/3 measure of water

ratios for medium maxillary / any mandibular impression

2 scoops, 2/3 measure water

ratio for large maxillary impression

3 scoops and 1 measure of water