How Separating Medium Works: Preventing Acrylic Adhesion in Prosthodontics

Separating Medium

 

Separating media is defied as a coating applied to the surface and serves to prevent as second surface from adhering to the fist.

Types of Separating Media:

Various separating media used are:

Tin foil: It is widely used in the past but due to its time-consuming manipulation and laborious technique, it is replaced by tin foil substitutes.

Tin foil substitutes: A variety of alternating separating media was introduced instead of tin foil. So they are known as tin foil substitutes. Tin foil substitutes are:

1. Cellulose lacquers
2. Aqueous solution of sodium silicate
3. Calcium oleate
4. Soaps and starches
5. Water soluble alginate solutions: Sodium and aluminum alginate solutions are commonly used.

1. Cold Mold Seal:

• Sodium alginate solution also known as cold mold seal is the most commonly used separating media.
• Usually, two coats of sodium alginate solution are painted on gypsum cast as well as investment material which is left for drying, so it is called as paint-on separating media.

2. Mode of Reaction:

• When it is applied on gypsum surfaces sodium alginate reacts with calcium sulfate to form a thin insoluble film of calcium alginate.
• This coat of separating medium forms a barrier against acrylic flowing in micropores in gypsum which when polymerized is difficult to separate from the gypsum cast.

3. Method of Application:

• A small amount of separating medium is dispensed on a disposable container.
• A fine brush is used to spread the separating medium on the exposed surfaces of the warm, clean stone mold.
• Two coats of separating medium should be applied.

4. Precautions:

• The separator should not contact the exposed portions of acrylic resin teeth. This prevents the bonding of teeth with the denture base.
• Mold should be warm and not hot. Continuity of fim will break if mold is hot.
• Wax or oils remaining on the mold surface will interfere with the action of separating the medium.
• The coating must be thin and continuous without trapping air bubbles.

5. Purpose of Applying Separating Medium:

• To prevent water from the mold surface for entering in acrylic resin. This can affect the rate of polymerization and color. This can also lead to crazing.
• To prevent monomer from entering in mold material which causes plaster to adhere to acrylic resin and produce a rough surface.
• It helps in the easy retrieval of dentures from the mold.