69. Retention and stability of complete denture. Biophysical methods and biomechanical methods.
Explains how a complete denture stays in place, separating retention (resistance to lifting away from the tissues) from stability (resistance to horizontal and rotating forces). Covers the biophysical factors such as adhesion, cohesion, surface tension, capillarity and atmospheric pressure, with a table, then the peripheral and posterior palatal seals. Next it describes the biomechanical methods in a second table, including base extension, polished surfaces, neutral zone, occlusion and muscular control, followed by mechanical aids and primary and secondary retention.
Topic 69 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 218 words (3 min of reading), with 14 flashcards.
In this note
Introduction
Biophysical (physical) methods
Biomechanical methods
Mechanical aids
Primary and secondary retention
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.
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