Introduction
Retention is a denture's resistance to being lifted away from the tissues, in the direction opposite to its path of insertion: by sticky food, gravity (upper denture) or the muscles. Stability is its resistance to horizontal and rotating forces. A complete denture needs both, and they come from two groups of methods.
Biophysical (physical) methods
All these depend on a close fit and a large area: the better the base copies the mucosa and the more of it it covers, the stronger the retention. Thin, watery saliva gives a better film than thick, ropy saliva; a dry mouth weakens retention.
The seal
- Peripheral seal: rounded borders shaped by border moulding to fill the functional depth of the vestibule.
- Posterior palatal seal (post dam): a slight raised ridge on the upper denture along the vibrating line that presses gently into the soft tissue.
Mechanical aids
- Undercuts on the ridge used by a slightly flexible flange.
- Implants, overdenture attachments (balls, bars, magnets) on retained roots or implants.
- Denture adhesives (pastes, powders) as a help, not a cure for a poor fit.
- Historically: rubber suction discs and springs, now abandoned because they damage the tissues.