retention and stability Flashcards
What is retention?
resistance to tissue-away forces
What re the physical factors that affect retention of denture?
- adhesion
- cohesion
- interfacial surface tension (similar to cohesion)
- atmospheric pressure (peripheral seal)
What is adhesion?
physical attraction of unlike molecules to each other
What are examples of adhesion?
- saliva to mucosa
- saliva to denture
What is cohesion?
physical attraction of like molecules for each other
What is an example of cohesion?
saliva
Is cohesion and adhesion related?
yes
What forces does peripheral seal resist?
vertical and lateral forces
What forces does adhesion resist?
lateral forces
What forces does cohesion resist?
lateral forces
What forces does interfacial surface tension resist?
lateral forces
What are the intra-oral factors and biomechanical considerations of denture retention?
- arch size
- disharmony of jaw sizes
- arch form
- ridge form
- vault form
- soft palate
- undercuts on basal seat
- interarch distance
- polished surface of denture
- gravity
What is the recommended arch size for retention of denture?
large arch size
What is the recommended harmony of arch size for retention of denture?
angle class 1
What is the recommended arch form for retention of denture?
square
What is the least favorable prognosis for arch form for retention?
tapered
What does a flat vault resist?
vertical displacement but it
provides little resistance to lateral displacement (retention is good)
What does a V-shaped vault resist?
- unfavorable for the retention of dentures
- provides no adaptation –> decrease adhesion and cohesion –> decrease retention –> increase resistance to lateral forces (good stability)
What is the most recommended vault form for retention and stability?
u-shaped as it resists both vertical and lateral dislodging forces and goo adaptation
What is the most favorable retention form of soft palate?
class I soft palate has a gentle curvature and demonstrates little muscular movement, hence it is the most favorable
Are undercuts good for retention?
- no, it needs to be open flanges
- if only one undercut present, it increases retention (undercut is in path of removal and insertion)
What are the uses of flexible resins?
- undercuts
- v-shaped palate (increased adaptation)
- sharp mylohyoid ridge
What is the normal interarch distance?
2-3mm
What is the interarch distance?
distance between maxilla and mandible (teeth and freeeway space) where denture is placed
What is the interarch distance recommended for better retention and stability?
2-3mm (small interarch distance)
What happens if the interarch distance is more than 2-3mm?
- longer teeth are used
- lateral forces increase (alters stability and retention)
What should the shape of polished surface be to be retentive?
concave (more muscle adaptation and stability)
What should the shape of lingual surface be?
covex then concave to avoid formation of undercuts
Does gravity aid upper denture?
no
Does gravity aid lower denture?
yes
What is stability?
resistance to rocking or lateral forces
What is the most retentive shape for ridge form?
ideal form is a high ridge with flat crest and parallel or nearly parallel sides (square ridge)
What ridge form provides most stability?
square
What is the best arch form for better stability?
square
What happens if mucosa is very low (hard bony areas)?
rocking and instability and pain
What is the faorable prognosis for better stability for mucosa supporting prosthesis?
2-3mm
What happens if the mucosa supporting denture is mpre than 10mm (flabby ridge)?
- rocking and instability
- selective pressure impression technique
What is the arrangement of teeth buccolingually?
on crest of the ridge to avoid cramped tongue
What happens if teeth are arranged lingual to the crest of the ridge?
cramped tongue
What happens if teth are arrangedbuccal to the crest of the ridge?
- cheek biting
- rocking
- instability
What is the arrangement of teeth occlusogingivally?
below lateral borders of the tongue to allow lower denture stability
What is the arrangement of teeth antro-posteriorly?
- away from retromolar pad (posterior) to avoid inclination of teeth (which might increase lateral forces leading to instabiliy)
Does arrangement of teeth alter stability?
yes
What should be done to flabby and bony ridges?
relieved
What should the occlusion be for better stability?
even occlusion
