Dental Impression Materials: ZOE Paste & Elastomers

ZOE Impression Paste

Advantages: Good adhesion, adequate working time, requires no insulation to the plaster model, is fluid allowing copying of fine details, and is economical.

Disadvantages: The Eugenol is acidified, and some patients are allergic to eugenol.

Elastomers

Organic materials formed by weak interaction with polymer molecules, forming a three-dimensional network with elastic properties.

Mercaptan Elastomers

Elastic impression materials with mercaptan groups in the polymer chain, which when hardened, forms a semisolid paste.

Synonyms: Polysulphide rubber, synthetic rubber, tiocoles.

Commercial presentation: Pasta-pasta

Consistencies: Light, regular, heavy.

Chemical Composition:

Paste: Polysulfide polymer (base), titanium dioxide (filler) can be replaced by titanium oxide, zinc oxide, zinc sulfate, copper carbonate, or silica.

Paste Catalyst: Lead peroxide (base catalyst oxidizing agent) can be replaced by copper hydroxide, butyl peroxide, or zinc carbonate. Sulfur (facilitates polymerization-viscosity), phthalate (plasticizer).

Mercaptan Chemical Reaction

Polysulfide (base) + lead peroxide (catalyst) = polysulphide + H20 (polymerized material)

Byproduct: Water

Handling Technology: Instrumental (or glass block tile waterproof elastomers mixing spatula or wooden paddle)

Proportions: Equal length

Mixture: To obtain a homogeneous color

Stroke: Mixed for 45 seconds

Working Time: Light: 4-7 minutes, Regular: 3-6 minutes, Paste: 2.5-5 minutes

Polymerization: Light: 7-10 minutes, Regular: 6-8 minutes, Paste: 5-7 minutes

Impressions for Prosthesis

Extra hard plaster cast type IV in a time of no more than 1 hour. To increase working time, use slab cooling, slightly decrease the amount of catalyst in relation to the base, and add a small drop of oleic acid.

Properties: 97.9% tear strength, tear resistance, flexibility (Light: 10%, Regular: 7%, Paste: 5%), runoff (Light: 0.9%, Paste: 0.3%), adequate dimensional stability for half an hour, hydrophobic.

Indications: Taking impressions for edentulous and teeth, making fixed prosthesis, removable partial, total, in cavities prepared for inlays, and in special cases like cleft palate.

Advantages: Easy to remove because of its flexibility, high tear resistance, accurate copy with fine detail, is the cheapest of elastomers, and has good longer tool life and work.