Indirect Retainers; Denture Base Considerations Flashcards
What is an indirect retainer?
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
What is the purpose of the indirect retainer?
❑Prevents movement of the distal extension base away from the residual ridge
❑Converts Class I lever to Class II lever
What are the functions of the indirect retainer?
❑Limit RPD vertical dislodgement
❑Reduce leverage on abutments
❑Reduce tissue impingement by mandibular major connectors
❑Increase RPD stability & support
❑Stabilize the framework during relining
In an indirect retainer there is usually a _____ located on the opposite side of the fulcrum line?
rest
What are the requirements of an indirect retainer?
❑ Usually in the form of an auxiliary rest
❑ Ideal position is perpendicular to fulcrum line
❑ Place as far forward of fulcrum line as possible
What makes an indirect retainer effective?
❑ Properly prepared rest seats
❑ Distance from the fulcrum line
❑ Rigidity of the indirect retainer
What are the forms/locations of indirect retainers?
❑Occlusal rest/premolar
❑Lingual rest/Canine
❑Incisal rest/Incisor or Canine
❑Lingual plate major connector
Where is an indirect retainer placed?
❑Anterior to horizontal fulcrum line
❑Perpendicular to fulcrum line
How many indirect retainers are needed for a class I RPD?
2
How many indirect retainers are needed for a class II RPD?
1
What part of the RPD resists movement towards tissue?
rests and denture base
What part of the RPD resists movement away from tissue?
retentive clasp when there is an indirect retainer
What is the function of the denture base in a tooth-supported RPD?
- Support prosthetic teeth
- Esthetics: replace missing tissue
- Horizontal stability
What is the function of the denture base in a tooth-tissue supported RPD?
- All of the above plus the following:
- Vertical support
- Secondary retention: interfacial surface tension between base & underlying mucosa
What are the factors that affect denture base support of distal extension RPD?
- Quality of soft tissue over residual ridge
- Type of bone
❑ Cortical bone better support than cancellous - Amount of denture base tissue coverage
- Accuracy of fit of the denture base
What are the different denture base materials?
- metal
- polymethyl methacrylate (PMMA)
What are the characteristics of PMMA denture base?
❑Acrylic resin
❑Most common
❑Easily adjusted & relined
❑Good esthetics
❑Attachment to framework by lattice or mesh
What are the characteristics of metal denture base?
❑Difficult to adjust
❑Poor esthetics
❑Part of cast framework
❑Good thermal conductivity
❑Can be kept thin
What are the types of acrylic resin denture base retention?
❑ Lattice
❑ Mesh
❑ Retentive beads
What are the characteristics of lattice retention?
❑Two struts of metal
❑Strongest attachment
❑Easiest to reline
❑Preferred retention
What are the characteristics of mesh retention?
❑Thin sheet of metal with multiple holes
❑Extension over ridge similar to lattice
❑Inferior attachment strength
What is a cast stop on a mandibular RPD base?
A cast stop is essential to prevent displacement or deformation of the metal framework during resin-packing procedure
A _____ joint should be used to join acrylic resin and metal components are the INTERNAL surface of RPD
butt
The internal angles of external finish lines should be slightly _____ than 90 degrees
less
What is the purpose of the finish lines in the RPD?
create a distinict resin-metal interface and to prevent the acrylic resin from becoming too thin
What are the different types of tooth replacement for RPDs?
- acrylic
- porecelain
- tube teeth
- reinforced acrlyic pontics (RAPs)
- metal
What is the most common material for teeth in an RPD?
acrylic
