Retention in RPD's Flashcards
What is meant by retention?
erm used to describe the resistance of a denture to LIFTING AWAY from the tissues (vertical dislodging forces)
In what 3 ways can mechanical retention be achieved?
- mechanical means
- muscular means
- physical means
What ways can a denture be mechanically retained?
by clasps
How can a denture be retained by muscular force?
-shape of the denture
How can a denture be retained by physical forces?
Coverage of the mucosa
How does coverage of the mucosa lead to physical retention?
Forces of adhesion between the saliva and mucosa
Forces of cohesion between the saliva particles and denture base
Creation of a peripheral seal to try and achive suction to keep the denture in place
In what kind of dentures is it harder to gain suction in mucosal coverage?
Metal
What are the 2 classifications of retention?
Direct
Indirect
What is direct retention?
Resistance to vertical displacement of the denture
What is indirect retention?
Resistance to rotational displacement of the denture
Where should direct retention ideally be?
As close to the saddle area as possible
Close to the base, adjacent to abutment teeth
In an ideal situation it would be interproximally but not realistic
What are guide planes?
Two or more parallel axial surfaces of abutment teeth
Found close to the base and parallel to the path of insertion Provide supplementary retention
What is a clasp?
A metal arm that, when in position, contacts the tooth preventing removal of the denture base
Where are claps placed in order to be effective as a retainer?
Below the bulbous part of the tooth i.e. in an undercut
How are the bulbous portions of teeth identified?
By surveying
What are the 2 ways that clasps can approach an undercut?
Occlusally approaching
Gingivally approaching
Describe occlusally approaching claps.
Get to the undercut via over the bulbosity of the tooth
Describe a gingivally approaching clasp.
Tends to come from the sulcus onto the tooth
Which kind of clasp is more aesthetically pleasing?
Gingivally approaching because most of it is below the lip line
Clasps work most effectively when in conjunction with what?
A rest (supporting component)
Describe the reciprocation feature of clasps.
Each clasp will have an opposing element to the retentive clasp arm to prevent pressure from the clasp acting on the tooth
What can altering the path of insertion do?
Utilise undercuts and therefore create a point of retention
What is the ideal number of retainers you would have on an arch and what format should they take?
3 in the biggest triangle as possible
What is the stress relieving clasp system (RPI) used to describe and where/when is it used?
Used to describe the components around the abutment tooth in a free-end saddle to prevent stress on this tooth
What components make up the RPI system?
-mesial rest -proximal guide plate -gingivally approaching I-bar clasp
I-bar clasps
