RPD system of design: retention

Question 1

What is meant by retention

Answer 1

A term used to describe the resistance of a denture to lifting away from the tissues (vertical dislodging forces)

Question 2

In what way’s can you achieve retention

Answer 2

mechanical, muscular and physical means

Question 3

How can retention be achieved mechanically

Answer 3

clasps

Question 4

how can retention be achieved with muscular forces

Answer 4

shape of the denture

Question 5

how can retention be achieved with physical forces

Answer 5

coverage of the mucosa

Question 6

What are the physical forces involved in achieveing retention

Answer 6

adhesion- surface forces of saliva on denture and mucosa

cohesion - forces within saliva, viscosity

Question 7

What are the different classes of retention

Answer 7

Direct

Indirect

Question 8

What is direct retention

Answer 8

resistance to vertical displacement of denture

Question 9

what is indirect retention

Answer 9

resistance to rotational displacement of denture

Question 10

Where should direct retention be placed

Answer 10

close to the base, adjacent to the abutment teeth

Question 11

What are guide planes

Answer 11

(suppliementary retention) close to the base and parallel to the path of insertion

Question 12

What is the principle way of achieving retention

Answer 12

clasps

Question 13

what is a clasp

Answer 13

a metal arm that, when in position contacts the tooth preventing removal of the denture base

Question 14

where should a clasp be placed

Answer 14

below the bulbous part of the tooth (undercut)

Question 15

How is the undercut of the tooth identified

Answer 15

a survey of the cast is performed

Question 16

what different ways can clasps approach the undercut

Answer 16

occlusal surface (occlusally approaching) or gingival margin (gingivally approaching)

Question 17

How can you make a clasp most efficient

Answer 17

by using in conjunction with a rest (supporting component)

Question 18

what is the advantage and disadvantage of a gingivally approaching clasp

Answer 18

Advantage: most is below the midline, towards the sulcus so less noticed by patient

Disadvantage: crosses the gingival margin, creates bridge for infection

Question 19

What is reciprocation

Answer 19

as part of the clasp assembly each clasp unit will have an opposing element to the retentive clasp arm to prevent pressure from the clasp acting on the tooth

Question 20

What is the path of insertion

Answer 20

the path followed by the denture from its first contact with the teeth until it’s fully seated. This path coincides with the path of withdrawal and may or may not coincide with the path of displacement

there may be a single path or multiple paths

Question 21

How many retainers should you have on an arch?

Answer 21

3 normally

possible to have 2 or 4 as well
- every component should have purpose

Question 22

what is important to consider when deciding on clasp selection and reciprocation

Answer 22

want to prevent torque on abutment teeth

Question 23

When is the RPI stress reliving clasp system used

Answer 23

used in free-end saddle designs to prevent stress on the last abutment tooth (kennedy class 1 or 2)

Question 24

what are the components of the RPI system

Answer 24

mesial (R)est
(P)roximal plate
(I)-bar clasp

Question 25

Where should the rest on an RPI system be placed

Answer 25

occlusal

• mesial of tooth
• rounded on the impression surface

Question 26

Where should the proximal plate on an RPI system be placed

Answer 26

Adjacent to saddle

• guide surface of 2-3mm
• undercut to permit movement

Question 27

Where should the I-bar clasp on an RPI system be placed

Answer 27

Gingivally approaching

- greatest prominence of the tooth contour

Question 28

Which arch is the RPI system most often used

Answer 28

lower (upper arch has hard palate you can use)

Question 29

What is indirect retention

Answer 29

resistance to rotational displacement of denture

Question 30

How do you obtain indirect retention

Answer 30

the retainer(s) providing direct retention lie between the fulcrum and that part of the denture which is subject to the displacing force

Question 31

Is it more effective to have the resisting force in indirect retention close to the fulcrum or far away from it?

Answer 31

far away (i think)
Makes dislodging force e.g. sticky food less effective at moving the denture

Question 32

What can be used as indirect retainers

Answer 32

major connectors
minor connectors
rest
saddle
denture base

Question 33

Is retention required on every abutment tooth?

Answer 33

no

Question 34

What does indirect retention prevent

Answer 34

rotation

Question 35

If you can’t find an undercut to use for a clasp what can you do

Answer 35

do tooth prep to establish one

Question 36

What is the minimum length of a clasp

Answer 36

15mm

Question 37

what is the point of altering the path of insertion

Answer 37

to make use of undercuts

Question 38

when does it not help to adjust the path of insertion

Answer 38

when the undercuts are not present in the common path of displacement (never alter path of insertion just to find undercuts)

Question 39

What do clasps not provide

Answer 39

indirect retention

Question 40

What arch is the RPI system primarily used on?

Answer 40

mandibular free end saddles (can be used in maxillary too)