Inelastic Impression Materials

Lecture 3. Chapter 46

Dental impression

Negative imprint of hard and soft tissue (teeth and gingiva)

Thermoplastic

A material that reversibly softens upon heating and hardens upon cooling.

Registration

A thin impression of the biting surfaces of the teeth used to set gypsum casts in the correct occlusal relationship when casts are mounted on articulators.

Dental impression makes

A positive reproduction (cast or model) can be made

Gypsum

Used to make model

Positive reproduction

What is an impression material

Fluid substances

That changes from gel form to rigid form

Impression definition

Negative replica

Model or cast

Positive reproduction

Die

Model of a single tooth or several teeth

The positive reproduction of a single tooth is described as a

Die

When several teeth or whole arch is reproduced it is called

Cast or model

Flexibility

Measure material thickness

Wetting

How well the material will “spread out”

More wetting = good

Less wetting = poor

Contact angle

angle formed when drop of liquid placed on surface

Low contact angle

less than 90 degrees, spreads easily, good wetting

High contact angle

more than 90 degrees, resists spreading &

“beads”, poor wet

Accelerators

QUICKENS the hardening process

Retarders

SLOWS the hardening process

Inelastic

Impression Compound, ZOE

Elastic

Elastomers

∗ Polysulfide, Polyether, Polyvinyl

Hydrocolloids

Irreversible Hydrocolloid

∗ Alginate

Reversible Hydrocolloid

∗ Agar-Agar

Inelastic Impression Material Characteristics

∗ Not flexible, very rigid

∗ Easily deforms

∗ Can only be used in applications where no undercuts exist

What Is an Undercut?

An area that curves under and has a tendency to lock a material within it, making the material difficult to remove.

What is ZOE?

Zinc Oxide- Eugenol

Inelastic-Impression Compound Uses:

∗ Final Impression of single crown prepped tooth with no

undercuts

∗ Spacer impressions

Inelastic-Impression Compound Properties:

∗ Thermoplastic material

∗ Material that reversibly softens upon heating & hardens

upon cooling

∗ No flexibility when in a solid state

∗ Cracks and breaks easily

Inelastic-Impression Compound Packaging

∗ Plates and Sticks

Inelastic- Zinc Oxide Eugenol Uses

• Impressions of edentulous arches

∗ Used to be very common for this but not so much now

• Bite registrations

∗ Thin impression of the biting surfaces of the teeth to capture bite

Inelastic- Zinc Oxide Eugenol Properties

∗ No flexibility once set

∗ Fractures easily

∗ Poor detail

Inelastic- Zinc Oxide Eugenol Packaging

• Two Paste System

∗ Catalyst

-Paste, eugenol, green

• Base

∗ Zinc oxide powder, and oils, white

Inelastic- Zinc Oxide Eugenol Mixing Time

30-60 seconds

Inelastic- Zinc Oxide Eugenol Working Time

30-60 seconds

Inelastic- Zinc Oxide Eugenol Setting Time

30-60 seconds in the mouth

Inelastic- Zinc Oxide Eugenol Accelerators

∗ Too much catalyst, too little base

∗ Warm room temperature

∗ High humidity

∗ Presence of water

Inelastic- Zinc Oxide Eugenol Retarders

∗ Too much base, too little catalyst

∗ Cool room temperature