alginate test

Alginate

Derived from agar (seaweed)- irreversible
Used for temporary things
Used to take diagnostic impressions
Plaster or stone (plaster not as strong)

Hydrocolloid

Not reversible
Hydro= water colloid= gelatin

Impression

Negative

Pour up

Positive

Mandibular

What Impression do we take first?

mixing time

1 min

setting time

3 min

Plaster to harden

45 min

Cold water

Longer setting time

Warm water

Shorter setting time

1 shot water

1 scoop alginate

Comes in

Cans or pouches (once opened store in can)

Why do we take alginate impressions?

For study models
Preliminary impressions for dentures
Opposing arch and gold work
Fabrication of dental appliances
Pre and post treatment records

Why do we use alginate?

Inexpensive compares to other material
Easy to mix
Acquires little equipment
Sufficiently accurate for diagnostic cast

What do alginate impressions show?

Teeth and missing teeth (restorations)
Frenum
Hard palate
Rugae
Tuberosities
Retro molar pad
Tongue space
Tori (overgrowth or bone)

Types of impressions (what they are made of)

Metal
Aluminum
Steel
Plastic
Styrofoam

Styles of trays (what kind)

Full lowers and full uppers
Combination tray (some teeth but missing others)
Edentulous tray
Pedo tray
Anterior tray
Quadrant tray

Tray should fit

Loose fitting and extend 2-3mm beyond the last tooth

Always..

Seat the heel of tray first
Hold tray in pts mouth

Mandibular impression

Fill tray from sides
Stand 9 o'clock
Lift roof of tongue
Pull pts lip out

Maxillary impression

Fill tray from back or posterior border
Stand 11-12 o'clock
Seat back first
Pt put head down and breathe in through nose out through mouth
Add wax for high palate, comfort, gagging, lengthen tray and post dam

After taking impressions

Rinse w/ water
Spray w/ cavicide spray
Wrap in moist paper towel
Add plaster on vibrator (NO BUBBLES)

Pour within (plaster)

20 min (if can't right away)

Equipment

Lab bowls - S, M, L, XL (mix alginate in L)
Alginate spatula
Vibrator
Measuring device for water and alginate

Set too quickly

Use colder water

Set too slow

Use warmer water

Mixture of powder and water too thick or too thin

Use proper proportions

Material does not set

Mixing continued after gelatin started. Mix 1 min only

Teeth elongated or enlarged in impression

Impression was moved during gelation, hold don't press

Detail lacking in impression

Too little water used

Impression fractured in pieces

Material gelled before placed in mouth

Distorted but not torn

Impression removed too slowly, remove w/ quick jerk

Alginate sticks to impression

Cast separating too soon after pouring. Allow cast to set 45 min before separating from impression

Cast too rough

Surface of impression contained water droplet

Cast powdery

Cast remained in impression too long

Teeth broke on cast

Impression not removed sufficiently soon after cast had set. Cast should be removed no later than an hour

Dental plaster and stone are manufactured from

Gypsum

Negative reproduction of the dental arch is called

An impression

All of following are types of gypsum in products except
Plaster of Paris
Zinc oxide
Investment material
Class 1 stone

Zinc oxide

An important factor in controlling the setting time of gypsum products is the

Temperature of water
Water powder ratio
Length of spatula

A working model is usually poured in

Plaster

The compressive strength of set gypsum product is determined by

The controls set by the manufacturer

Setting expansion of stone is controlled by

W/p ratio
Spatulation
The manufacturer

Casts which serve as working models are usually poured in

Model plaster

When using gypsum products, air voids are minimized by

Using a vacuum and or vibrator

One drop of water in a stored container of plaster would

Render it useless