Indirect Retainers; Denture Base Considerations

Question 1

What is an indirect retainer?

Answer 1

The component of a RPD that assists the direct retainer in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of the fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line

Question 2

What is the purpose of the indirect retainer?

Answer 2

❑Prevents movement of the distal extension base away from the residual ridge
❑Converts Class I lever to Class II lever

Question 3

What are the functions of the indirect retainer?

Answer 3

❑Limit RPD vertical dislodgement
❑Reduce leverage on abutments
❑Reduce tissue impingement by mandibular major connectors
❑Increase RPD stability & support
❑Stabilize the framework during relining

Question 4

In an indirect retainer there is usually a _____ located on the opposite side of the fulcrum line?

Answer 4

rest

Question 5

What are the requirements of an indirect retainer?

Answer 5

❑ Usually in the form of an auxiliary rest
❑ Ideal position is perpendicular to fulcrum line
❑ Place as far forward of fulcrum line as possible

Question 6

What makes an indirect retainer effective?

Answer 6

❑ Properly prepared rest seats
❑ Distance from the fulcrum line
❑ Rigidity of the indirect retainer

Question 7

What are the forms/locations of indirect retainers?

Answer 7

❑Occlusal rest/premolar
❑Lingual rest/Canine
❑Incisal rest/Incisor or Canine
❑Lingual plate major connector

Question 8

Where is an indirect retainer placed?

Answer 8

❑Anterior to horizontal fulcrum line
❑Perpendicular to fulcrum line

Question 9

How many indirect retainers are needed for a class I RPD?

Answer 9

2

Question 10

How many indirect retainers are needed for a class II RPD?

Answer 10

1

Question 11

What part of the RPD resists movement towards tissue?

Answer 11

rests and denture base

Question 12

What part of the RPD resists movement away from tissue?

Answer 12

retentive clasp when there is an indirect retainer

Question 13

What is the function of the denture base in a tooth-supported RPD?

Answer 13

1. Support prosthetic teeth
2. Esthetics: replace missing tissue
3. Horizontal stability

Question 14

What is the function of the denture base in a tooth-tissue supported RPD?

Answer 14

1. All of the above plus the following:
2. Vertical support
3. Secondary retention: interfacial surface tension between base & underlying mucosa

Question 15

What are the factors that affect denture base support of distal extension RPD?

Answer 15

1. Quality of soft tissue over residual ridge
2. Type of bone
   ❑ Cortical bone better support than cancellous
3. Amount of denture base tissue coverage
4. Accuracy of fit of the denture base

Question 16

What are the different denture base materials?

Answer 16

• metal
• polymethyl methacrylate (PMMA)

Question 17

What are the characteristics of PMMA denture base?

Answer 17

❑Acrylic resin
❑Most common
❑Easily adjusted & relined
❑Good esthetics
❑Attachment to framework by lattice or mesh

Question 18

What are the characteristics of metal denture base?

Answer 18

❑Difficult to adjust
❑Poor esthetics
❑Part of cast framework
❑Good thermal conductivity
❑Can be kept thin

Question 19

What are the types of acrylic resin denture base retention?

Answer 19

❑ Lattice
❑ Mesh
❑ Retentive beads

Question 20

What are the characteristics of lattice retention?

Answer 20

❑Two struts of metal
❑Strongest attachment
❑Easiest to reline
❑Preferred retention

Question 21

What are the characteristics of mesh retention?

Answer 21

❑Thin sheet of metal with multiple holes
❑Extension over ridge similar to lattice
❑Inferior attachment strength

Question 22

What is a cast stop on a mandibular RPD base?

Answer 22

A cast stop is essential to prevent displacement or deformation of the metal framework during resin-packing procedure

Question 23

A _____ joint should be used to join acrylic resin and metal components are the INTERNAL surface of RPD

Answer 23

butt

Question 24

The internal angles of external finish lines should be slightly _____ than 90 degrees

Answer 24

less

Question 25

What is the purpose of the finish lines in the RPD?

Answer 25

create a distinict resin-metal interface and to prevent the acrylic resin from becoming too thin

Question 26

What are the different types of tooth replacement for RPDs?

Answer 26

• acrylic
• porecelain
• tube teeth
• reinforced acrlyic pontics (RAPs)
• metal

Question 27

What is the most common material for teeth in an RPD?

Answer 27

acrylic