List of factors resulting in looseness of dentures

Denture borders
Over-extension in depth
Slow rise of lower denture when mouth half open, line of inflammation at reflection of sulcal tissues; ulceration in sulcal region.
Deep post dam on upper base may cause pain, ulceration

If buccal to tuberosities, denture displaces on mouth opening, or cheek soreness occurs. Thickened lingual flange enables tongue to lift denture; thick upper and lower labial flanges may produce displacement during muscle activity

Slightly under-extend denture flange and accurately mould softened tracing compound. Check borders of record rims and trial dentures at the appropriate stages. Deep post dam to be cautiously reduced and denture worn sparingly until inflammation clears

Overextension in width
Cheeks appear plumped out. In lower, the buccal flange may be palpated lateral to external oblique ridge

Design error

Reduce over-extension. Use disclosing material to determine what is excessive

Poor fit to supporting tissue
Recoil of displaced tissue lifts denture

Poor/inappropriate impression technique especially in posterior lingual pouch area

Reline if all other design parameters satisfactory, otherwise remake. Ensure denture is removed from mouth 90 mins prior to impression

Denture not in optimal space

Molars on lower denture lingual to ridge, optimum triangular shape of dentures absent Posterior occlusal table too broad, causing tongue trapping
Thick lingual flanges encroaching on tongue space, causing lifting.
Excess lip pressure to lower anterior aspect - teeth anterior to ridge, thick periphery Excess pressure from upper lip to upper denture arising from teeth too labially sited to acute naso-labial angle; or failure to adequately seat denture during relining impression procedure

Remove lingual cusps and lingual surface from relevant area, repolish.
If triangular form not restored, reset teeth or remake dentures
Narrow posterior teeth and/or remove most distal teeth from dentures. Reshape lingual polished surface
Thin lower labial flange, ensure optimal extension to retromolar pads to resist displacement, reset anterior teeth if necessary
Usually requires remaking denture