DDMT MIDTERM 1

Elastomeric (Rubber) Impression Materials

A type of elastic impression material which is soft and rubber-like in nature, technically known as an elastomer.

condensation or ionic reaction in the presence of chemical reactors

The RIMs are two component systems, in that polymerization/ cross-linking occurs by

Thermoset / Elastic IM / Final impression materials

Classification of RIM

1. as a single impression

2. can be used for quadrant impression

3. for bite registration (addition silicone)

Uses of RIM

1. 2-paste type (polysulfide & polyether)

2. Paste-liquid type (silicone)

Methods of Dispersing RIM

Polysulfide RIM

The first rubber impression material

2-paste system - base & catalyst/reactor

Composition of RIM

Type I soft or light-bodied

Type II regular-bodied

Type III heavy-bodied

3 types of consistencies of base

vulcanization or curing

The process of changing the rubber base product, or liquid polymer, to a rubber-like material is generally known as

80% polysulfide polymer

Base material of polysulfide rim consists of?

20% reinforcing agents

– for strength, prevent tearing = titanium dioxide, zinc sulfate, copper carbonate, or silica

sulfur

= promoter

plasticizer - dibutyl phtalate

= controlling viscosity of the rubber

Lead dioxide

the most common catalyst; using it results in the paste being dark brown to dark gray

Copper hydroxide

and when mixed with the white base paste, a blue- green color results

Retarder

controls the rate of setting time; oleic acid, stearic acid (controls polymerization of rubber) castor oil (controls reaction of the 2 pastes)

Loaded on syringe then ready for injecting into the cavity preparation

If the material is light bodied

It is placed on a custom-tray made of acrylic. The inside is painted with a rubber cement adhesive.

If regular- or heavy –bodied,

5-7 minutes

Working time of RIM

25c = 8-12 minutes, 37c = 4-6 minutes

Setting time of RIM

Condensation Silicone, Addition Silicone

Composition of silicone rim

Dimethyl Siloxane, Reinforcing Agents

Condensation type: The base material is a paste containing:

reinforcing agents

= silica, added to give the proper consistency to the paste and stiffness to the set rubber

dimethyl siloxane

a low-molecular weight silicone liquid

two-paste

Silicone RIM Addition type

1. Polymethyl Hydrogen Siloxane

2. Reinforcing Fillers

3. Chloroplatinic Acid Catalyst

Base of Silicone RIM

Latex Gloves

Cannote be used in silicone rim. It will retard the setting time. Vinyl gloves or bare hands are acceptable

25oC = 6-7 minutes, 37oc = 4-5 minutes

Setting time of Silicone RIM

Polyether RIM

offer the possible combination of better mechanical properties than those of the polysulfides along with less dimensional change than those of condensation silicone materials.

Short working time and high stiffness

Disadvantage of Polyether RIM

Single impression technique

base and catalyst mixed and a single impression is taken.

Double impression technique

paste-putty system; preliminary impression using putty followed by a wash impression (thinner consistency) placed on top of putty as second or corrective impression.

Syringe technique

= light-bodied + catalyst material injected into prepared tooth then followed by a secondary (regular body + catalyst) paste impression for a more accurate detailed impression with no bubbles. Ideal for laminates.

Polyether

= short working & setting time, low tear strength, and are very stiff

Excellent elasticity

The polysulfide are allowed 4% & silicones 2% permanent deformation after a 12 % strain is held for 30 seconds. - The elastic properties of the rubber impression materials improve with time of curing. The longer the impression can remain in the mouth before removal, the more accurate it will be after removal.

Dimensional stability

very low shrinkage in RIM which makes them much more stable dimensionally than hydrocolloids. Degree of contraction or shrinkage: - Polysulfide RIM = 0.3-0.4% during first 24 hours - Condensation silicone = 0.6% - Addition silicone = 0.1% - Polyether RIM = 0.2-0.4%

Polysulfide

long working & setting time, moderately high permanent deformation and flow, high flexibility

Condensation / addition silicone

short working & setting time, moderate flexibility and tear strength; however addition silicones have very low shrinkage on setting flow, making them the most accurate impression material.