Alginate Impression Material and Gypsum Products

Mounted diagnostic casts (on articulator)

-Serve as a complement tool in addition to clinical examination

-Provide a legal proof of pt's current occlusion

-Allow clinician to modify occlusal pre-treatment plan prior to establish a definitive Tx Plan

-Allow clinician to evaluate pt's occlusion in centric and eccentric positions

-Allow clinician to determine inter-arch distance, relationship between the teeth and alveolar ridge and allow clinician to make as many alteration to as clinician's desire w/ absence of the patient.

metal trays

Which type of impression tray?

-autoclavable

-ring-lock technology

-perforation

Plastic trays

Which type of impression tray?

-disposable

-perforated

-requires alginate adhesive

irreversible hydrocolloid

Alginate is classified as what?

impression

What type of material?

-Used to register and reproduce the form and relationship of teeth and oral tissues

-Hydrocolloids and synthetic elastomeric polymers are the materials most commonly used to make impressions

-The impression will create a negative reproduction of the tissues, and by filling the impression with dental stone or other model material, a positive cast can be made

casts

What are used to evaluate the relative alignment between maxillary and mandibular arches, occlusal relationship, and fabrication of restoration and prostheses?

tray

How is impression material carried to mouth?

impression materials

These are desirable qualities of what?

Pleasant odor, taste, and color

Absence of toxic or irritant constituents

Adequate shelf life

Economic

Easy to use

Good setting characteristics

Satisfactory consistency and texture

readily wets oral tissues

impression materials

These are more desirable qualities of what?

Resistance to permanent distortion

Adequate strength

Dimensional stability over temperature and humidity normally found in clinical and laboratory setting

Compatibility with cast and die materials

Accuracy in clinical use

Readily disinfected without loss of accuracy

No release of gas during the setting of the impression or cast and die materials

irreversible hydrocolloid

Alginate hydrocolloid is also called what?

Reversible hydrocolloid

Agar hydrocolloid is also called what?

true

T/F These are other types of impression materials

Elastomeric materials

Zinc oxide-eugenol materials Gypsum

Compound impression materials

alginate

What is the most widely used impression material in dentistry?

alginate hydrocolloids

These are advantages for which impression material ?

Inexpensive

Easy manipulation

Pleasant taste

Able to displace blood and body fluids

Hydrophilic

Easily poured

Can be used with stock trays

Accurate if handled properly (for diagnostic casts)

alginate hydrocolloids

These are disadvantages for which impression material?

Low tear resistance

Must be poured immediately Limited detail reproduction

Dimensionally unstable (syneresis vs imbibition)

Can only be used for single casts Incompatible with epoxy resin die materials

sodium/potassium alginate, calcium sulfate dehydrate, sodium potassium (others are reinforcing filler, potassium sulfate/alkali zinc fluorides, coloring/flavoring agents)

What are the three components of alginate hydrocolloids that are most important?

jeltrate

What brand of alginate do we use at TUSDM?

Ca alginate + Na2So4 (gel)

The first main reaction that occurs when the alginate powder (Na alginate + CaSO4) is mixed with water produces what?

speeds up (add SO4 to slow down setting time)

If you have too much calcium, or too little sodium, what is the effect on alginate setting time?

1:1

What is the ratio of powder to water for alginate?

water

Should powder or water be added first to the mixing bowl for alginate?

1 minute

How long should you mix alginate for regular setting alginate?

45 seconds

How long should you mix alginate for fast-setting alginate?

3.5 min (after mixing)

What is the set time for regular set alginate?

lower

(alginate) Lower or Higher W/P ratio?

increase in strength

lower

(alginate) Lower or Higher W/P ratio?

increase in tear strength

lower

(alginate) Lower or Higher W/P ratio?

"better" consistency

lower

(alginate) Lower or Higher W/P ratio?

decrease in working time

lower

(alginate) Lower or Higher W/P ratio?

decrease in setting time

lower

(alginate) Lower or Higher W/P ratio?

decreased flexibility

higher

(alginate) Lower or Higher W/P ratio?

decrease in strength

higher

(alginate) Lower or Higher W/P ratio?

runny consistency

higher

(alginate) Lower or Higher W/P ratio?

decrease in tear strength

higher

(alginate) Lower or Higher W/P ratio?

runny consistency

higher

(alginate) Lower or Higher W/P ratio?

increase in working time

higher

(alginate) Lower or Higher W/P ratio?

increase in setting time

higher

(alginate) Lower or Higher W/P ratio?

increased flexibility

colder

(alginate) Colder/warmer water will increase the working and setting times

grainy, poor

(alginate) Insufficient mixing results in ____ mix and ____ recording of details

true

(alginate) T/F Storage in either air (syneresis) or water (imbibition) results in significant dimensional change

store impression at 100% humidity (damp paper towel and zip lock bag) for 30 min

How do you avoid syneresis or imbibition if you can't pour up right away?

sodium hypochlorite/iodophors

How do you disinfect impressions?

syneresis

What is loss of water due to dehydration that causes shrinkage?

imbibition

What is the tendency to absorb water that results in swelling?

inadequate working/setting time, distortion, tearing

What are common problems with impressions?

calcium sulfate (hydrous and anhydrous)

Gypsum products are generally composed of what?

impression plaster (no longer used)

What is ISO type 1 of gypsum?

plaster

What is ISO type 2 of gypsum?

Stone (diagnostic casts)

What is ISO type 3 of gypsum?

stone, high-strength, low-expansion (prosthesis)

What is ISO type 4 of gypsum?

stone, high-strength, high-expansion

What is ISO type 5 of gypsum?

thick slurry

When the hemihydrate is mixed with water in correct proportions, what is formed?

exothermic

The setting reaction of the hemihydrate (gypsum) is the reverse of the first stage of dehydration and is exothermic/endothermic

slurry water

The use of what can have these effects?

- decrease setting time or shorten setting time

- decrease compressive strength (not good)

- increase dimensional change (not good)

density of power

Why do plaster, stone, and high-strength stone have differences in water requirement?

fluid

What is the first stage of setting?

plastic

What is the second stage of setting?

friable

What is the third stage of setting?

carvable

What is the fourth stage of setting?

decrease

The setting reaction causes a increase/decrease in the true volume of the reactants

isotropic expansion

What is observed when the mix begins to solidify?

w/p ratio

What will affect the chemical reaction during the setting of gypsum products?

Water temperature

Aside from w/p ratio, what can change the rate of reaction?

Low

High/Low water/powder ratio harden more quickly, and will produce less microporosities related to residual unreacted water.

increases

Low water/powder increases/decreases microporosity related to crystal growth

spatulation (speed and time)

Aside from w/p ratio and water temp, what is another variable that will affect setting time?

true

T/F properties of gypsum products mixed by hand and under vacuum will differ

inversely

Setting expansion is inversely/directly proportional to the water-powder ratio

true

T/F Air moisture contamination can affect the setting time and expansion

K2SO4, sodium citrate

What compounds can be added/taken away to control setting expansion of gypsum?

inversely

Strength is inversely/directly proportional to the water/powder ratio

increases

Using a low water/powder ratio for maximum strength increases/decreases setting expansion

doubles

Removal of uncombined water from cast gypsum by low-temperature drying has what effect on strength?

shrinkage, reduction of strength

If drying of gypsum is not controlled, what can occur?

true

T/F Long-term immersion in water is contraindicated

calcium sulfate

If stone needs to be hydrated, what is an appropriate solution to use?

increase

(gypsum) Increase W/P Ratio has what effect on setting time?

increase

(gypsum) Increase W/P Ratio has what effect on consistency?

decrease

(gypsum) Increase W/P Ratio has what effect on setting expansion?

decrease

(gypsum) Increase W/P Ratio has what effect on compressive strength?

decrease

(gypsum) Increase rate of spatulation has what effect on setting time?

decrease

(gypsum) Increase rate of spatulation has what effect on consistency?

increase

(gypsum) Increase rate of spatulation has what effect on setting expansion?

no effect

(gypsum) Increase rate of spatulation has what effect on compressive strength?

decrease

(gypsum) Increasing water temp has what effect on setting time?

decrease

(gypsum) Increasing water temp has what effect on consistency?

increase

(gypsum) Increasing water temp has what effect on setting expansion?

no effect

(gypsum) Increasing water temp has what effect on compressive strength?