Introduction
Elastic, or soft, resins cushion the hard base of a denture. They are used to reline the mucosal surface of dentures when the oral mucosa is sensitive to injury. They are also used for extraoral prostheses and for the mouthguards worn in sport.
Requirements
- Bond firmly to the denture base.
- Keep their elasticity, color and volume for a long time.
- Have a smooth surface.
Acrylic soft resins
Hard acrylic becomes elastic when 30 to 60% of a plasticizer, such as dibutyl phthalate or dibutyl glycolate, is added. They come as a powder and liquid, in cold-curing or heat-curing form. Because the plasticizer dissolves into saliva, the material stiffens, absorbs more water, and develops a rough, porous surface where bacteria and fungi grow.
Silicone soft resins
These resemble silicone impression materials and come in cartridges for automatic dosing and mixing. They keep a smooth surface and stay elastic for a long time. The problem is their attachment, so the hard resin is roughened first and a special adhesive is used. They must be cleaned carefully, because they can come away from the base.