13- Indirect Retainers Flashcards
what lever do indirect retainers convert
class I lever to class II lever
what is an indirect retainer
component of the 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 are the functions of indirect retainer
-limit RPD vertical dislodgement
- reduce leverage on abutments
- reduce tissue impingement by mandibular major connectors
- increase RPD stability and support
- stabilize the framework during relining
where is the indirect retainer
usually a rest located on the opposite side of the fulcrum line that assists the direct retainer in resisting movement of the RPD in an occlusal direction like when eating sticky food
what are the requirements of an indirect retainer
- usually int he form of an auxillary rest
- ideal position is perpendicular to fulcrum line
- place as far forward of fulcrum line as possible
what determines the effectiveness of an indirect retainer
- properly prepared rest seats
- distance from the fulcrum line
- rigidity of the indirect retainer
how does the distance from the fulcrum line affect the effectiveness of an indirect retainer
the greater the distance between the fulcrum line and the indirect retainer the more effective the direct retainer will be
what helps increase the rigidity of the indirect retainer
- rests are excellent
- rugae are not good indirect retainers
- lingual plating alone is not acceptable
what are the forms/location of indirect retainers
- occlusal rest/premolar
- lingual rest/ canine
- incisal rest/ incisor or canine
- lingual plate major connector: must have rests at each end, otherwise lingual plate is not an indirect retainer
describe indirect retainer placement
- anterior to horizontal fulcrum line
- perpendicular to fulcrum line
- class I RPD: 2 indirect retainers
- class II RPD: 1 indirect retainer
describe denture base movement towards the tissue
- rotation occurs around most distal rests
- resisted by rests and denture base
describe denture base movement away from the tissue
- rotation occurs around distal most retentive tips
- resisted by retentive clasp when there is an indirect retainer
what are the denture base functions of tooth supported RPD
- support prosthetic teeth
- esthetics: replace missing tissue
- horizontal stability
what are the denture base functions of tooth tissue supported RPD
- support prosthetic teeth
- esthetics: replace missing tissue
- horizontal stability
- vertical support
- secondary retention: interfacial surface tension between base and underlying mucosa
describe broad stress distribution function of the denture base
- distribute the forces of occlusion over as many teeth and as much soft tissue area as possible
- increased area: decreased stress
what is the formula for stress in broad stress distribution
stress = occlusal force/area
what are the factors affecting denture base support of distal extension RPD
- quality of soft tissue over residual ridge: more displacable but less support
- type of bone: cortical bone is better support than cancellous
- amount of denture base tissue coverage
- accuracy of fit of the denture base: importance of accurate impression
what are the requirements of an ideal denture base material
- accurate and dimensionally stable
- tissue compatibility
- thermal conductivity
- low specific gravity: light weight
- sufficient strength: resist fracture
- esthetic
- potential for future reline
describe metal as a denture base material
- difficult to adjust
- poor esthetics
- part of cast framework
- good thermal conductivity
- can be kept thin- good for inadequate inter arch space
describe polymethyl methacrylate (PMMA) as a denture base material
- acrylic resin
- most common
- easily adjusted and relined
- good esthetics
- attachment to framework by lattice or mesh
what is acrylic resin denture base retention considered
a minor connector
where does the acrylic resin denture base extend in mandibular? maxillary?
- mand: 2/3 distance to retromolar pad
- max: 2/3 distance to hamular notch
what are the types of acrylic resin denture base retention
- lattice
- mesh
- retentive beads
describe lattice retention
- two struts of metal
- strongest attachment
- easiest to reline
- preferred retention
describe the two struts of metal in lattice retention
- extend longitudinally along residual ridge
- positioned buccal and lingual to ridge crest
- avoid longitudinal strut along ridge crest: interferes with tooth placement, cleavage action occurs within denture base
describe mesh retention
- thin sheet of metal with multiple holes
- extension over ridge similar to lattice
- inferior attachment strength
- incorrect mesh construction : longitudinal strut across ridge crest, interferes with tooth placement, high stress site: cleavage of denture base
what does a cast stop do
prevents displacement or deformation of the metal framework during resin packing proceudres
where is the cast stop located
projects from the tissue surface of the minor connector to contact the dental cast
where is a butt joint used and why
used to join acrylic resin and metal components at the internal surface of a RPD. each internal finish line should be 90 degrees
what should the internal angles of the external finish lines be and why
slightly less than 90 degrees
- improved mechanical retention for acrylic resin components
what is the purpose of finish liens
to create a distinct resin metal interface and to prevent the acrylic resin from becoming too thin
acrylic resin ____ strength with increasing bulk
gains
what might happen if acrylic resin is finished to a thin edge
the material may chip or fracture creating unhygienic or irritating conditions
what material is used with external finish lines
acrylic and metal
describe acrylic denture teeth
- most common
- easily adjusted
- not wear opposing natural dentition
- chemical bond with denture base
describe porcelain denture teeth
- fracture easily
- wear opposing dentitino
- difficult to adjust
- mechanical retention only to denture base
describe tube teeth
- denture tooth with drilled channel
- secured to metal post
- used with metal base: inadequate arch space
describe reinforced acrylic pontics (RAPs)
- composite resin polymerized around projections of metal from denture base
- anterior teeth only
- inadequate interarch space
describe metal teeth as replacement teet
- used with severely inadequate interarch space
- poor esthetics
- used only in posteiror
- difficult to adjust
