Polyether Impression Material in Dentistry: Composition, Properties, and Manipulation

Polyether

Write a short note on polyether rubber base impression material.
Answer:

It is a polyether-based polymer which is introduced in Germany in the late 1960s. It was developed in an attempt to combine the good mechanical properties of polysulfides with the dimensional stability of silicones.

Composition of polyether rubber base:

• Base paste
  • Polyether polymer—80 to 85%
  • Colloidal silica—acts as the filer
  • Glycolether or phthalate—plasticizer
• Reactor or accelerator paste
  • Aromatic sulfonate ester—crosslinking agent
  • Colloidal silica—filer
  • Phthalate or glycol ether—plasticizer.

Setting Reaction of  Polyether Rubber Base

Polyether Rubber Base is cured by the reaction between aziridine rings which are at the end of branched polyether molecules. The main chain is a copolymer of ethylene oxide and tetrahydrofuran. Crosslinking is brought about by the aromatic sulphonate ester via the imine end groups. The reaction is exothermic. No by-product is formed.

Polyether + Sulfonic ester → Crosslinked rubber

Properties of polyether rubber base:

• Polyether Rubber Base taste and odor are pleasant.
• Polyether Rubber Base can lead to skin reactions due to the presence of sulfonic ester. Thorough mixing is done before making an impression.
• Polyether Rubber Base setting time is 6 to 8 minutes, mixing is done quickly, i.e. in 30 seconds. Heat decreases the setting time.
• Dimensional stability is good. Curing shrinkage is low, i.e. 0.24%.
• Permanent deformation is low, i.e. 0.8 to 1.6%.
• Polyether absorbs water and can change dimension, so prolonged contact with water and humid climate is not recommended.
• The material is stiff and it is difficult to remove it from undercuts so additional spacing is required.
• Tear strength is good, i.e. 3,000 g/cm.
• Since the material is hydrophilic, moisture in the impression field is not critical.
• Polyether Rubber Base has best compatibility with stone among all elastomers.
• Polyether Rubber Base shelf-life is excellent, i.e. more than 2 years.
• Polyether Rubber Base can be electroplated with silver or copper.

Manipulation of polyether rubber base

Following are the methods of manipulating polyether rubber base impression material, i.e.

1. Hand mixing
2. Static auto-mixing system
3. Dynamic mechanical system

1. Hand Mixing:

• High-viscosity material, i.e. putt is usually supplied in small tubs with different colored scoops for identification and dispensing. Equal quantities of both pastes are taken.
• Mixing is done by hand by kneading the material together to obtain a uniform mix without any streaks.
• Manufacturers also supply base and catalyst in separate tubes with a much smaller diameter opening for catalyst to enable dispensing equal lengths of base and catalyst,
  though the volume being different.
• In polyether rubber base impression material the quantity of reactor paste needed is very little. So the base and reactor pastes are extruded on the mixing pad with unequal length without touching each other.
• The required amount of thinner when supplied is added to the base and accelerator depending on the viscosity needed. Reactor paste is incorporated into the base paste. Mixing is done by using a tapered stiff bladed metal or plastic spatula. A streak free mix is obtained in 45 seconds.

2. Static Automixing System:

• These days many of the materials are now dispensed by an extruder gun with a mixing tip.
• The base and catalyst are stored or supplied in separate cylinders of the plastic cartridge.
• The extruder gun contains two plungers on which these cylinders are placed.
• Now the base and catalyst are forced through the mixing tip.
• It consists of a stationary plastic internal spiral that brings together the correct volume of both base and catalyst and dispenses it premixed.
• Apply the mixed material directly over the prepared teeth and/or the impression tray.
• The advantages of the mixing tip include dispensing of the correct ratio of base
  and catalyst, and uniform mixing without the incorporation of air bubbles.
• Polyethers are available in these systems.

3. Dynamic Mechanical System:

• It is also known as an automated mixing system.
• It consists of a separate mixing machine with cartridges for the base and catalyst and a plastic mixing tip.
• The base and catalyst are supplied in collapsible plastic bags.
• After housing of the base and catalyst in the cartridge, the mixing tip is placed in the front of the machine.
• On pressing the button on the top, the machine automatically mixes the base and catalyst by the movement of the plungers pushing against the collapsible plastic bags.
• Here in this system, the internal spiral is the motor drive that rotates.
• A uniform, thorough mixing can be accomplished even for higher-viscosity materials.
• In this system, the benefit is of uniform mixing and the speed of mixing and the disadvantage is the equipment is expensive.
• Polyethers are available in these systems.