indirect retainers denture base considerations Flashcards
component of RPD that assists direct retainer in preventing displacent of distal extension denture base by functioning through level action on the opposite side of the fulcrum line when the denture base moves away from tissues in pure rotation around fulcrum line
indirect retainer
where is the indirect retainer located
anterior to fulcrum line aka most anterior rest
the indirect retainer prevents movement of the
distal extension base away from the residual ridge
indirect retainer converts class I lever to
class II lever
5 functions of indirect retainer
- limit RPD vertical dislodgement
- reduce leverage on abutments
- reduce tissue impingment by mandibular major connectors
- increase RPD stability and support
- stabilize framework during relining
indirect retainer is usually a _____located on the opposite side of fulcrum line that assist the direct retainer in resisting movement of RPD in an occlusal direction-like when eating sticky food
rest
3 requirements of indirect retainer
- usually in form of auxillary rest
- ideal position is perpendicular to fulcrum line
- placed as far forward of fulcrum line as possible
the greater the distance between the fulcrum line and the indirect retainer, the
more effective the direct retainer will be
rigidity of indirect retainer explained:
- rests are excellent
- rugae are not good indirect retainers
- **lingual plating alone is NOT acceptable
what are 4 forms/locations of indirect retainers
- occlusal rest/premolar [mesial of man 1st premolar has ‘natural’ rest seat]
- lingual rest/canine
- incisal rest/incisor or canine (less common)
- lingual palte major connector (MUST have rests at each end or else lingual plate is NOT indirect retainer)
the indirect retainer placement must be:
- anterior to horizontal fulcrum line
- perpendicular to fulcrum line
class I RPD has ___indirect retainer(s)
2
class II RPD has __ indirect retainer(s)
1
when the denture base moves towards the tissue, rotation occurs around most:
and therefore resisted by:
distal rests
resisted by rests and denture base
when the denture base moves away from the tissue, rotation occurs around:
and therefore resisted by:
distal most retentive tips
resisted by retentive clasp when there is an indirect retainer
tooth-supported RPD:
- support prothetic teeth
- esthetics: replace missing teeth
- horizontal stability
tooth-tissue supported RPD
- support prothetic teeth
- esthetics: replace missing teeth
- horizontal stability
- vertical support
- secondary retention: interfacial surface tension between base and underlying mucosa
distribute the forces of occlusion over as many teeth and as much soft tissue area as possible
broad-stress distribution
stress =
occlusal force / area
increased area=
decreased stress
what are the 4 factors affecting denture base support of distal extension RPD
- quality of soft tissue over residual ridge (more displaceable tissue, less support)
- type of bone (cortical bone better support)
- amount of denture base tissue coverage
- accuracy of fit of denture base (accurate impression important)
denture base metal:
- difficult to adjust
- poor esthetics
- part of cast framework
- good thermal conductivity
- can be kept thin (adv where inadequate inter-arch space)
polymethyl methacrylate (PMMA):
- acrylic resin
- most common
- easily adjusted and relined
- good esthetics
- attachment to framework by lattice or mesh
acrylic resin denture base retention:
- considered minor connector
mandibular:
-extend 2/3 distance to retromolar pad
maxillary:
-extend 2/3 distance to hamular notch
types of acrylic resin denture base retention
lattice
mesh
retentive beads
this is two struts of metal that extend longitudinally along residual ridge, positioned buccal and lingual to ridge crest
-avoid longitudinal strut along ridge crest
lattice retention
this type of retention is the strongest attachment, easiest to reline, and preferred rention
lattice retention
thin sheet of metal with multiple holes, inferior attachment strength
mesh rention
this is essential to prevent displacement or deformation of the metal framework during resin-packing procedures on mandibular base
cast stop on mandibular base
this projects from the tissue surface of the minor connector to contact the dental cast
cast stop (tissue stop)
a butt joint should be used to join acrylic resin and metal components at the ________of RPD. each internal finish line should display at an angle of:
internal surface
90 degrees
the internal angles of ______should be slightly LESS than 90 degrees. this results in improved mechanical retention for acrylic components
external finish lines
the purpose of this is to create a distinct resin-metal interface and to prevent the acrylic resin from becoming thin.
finish lines
want smooth transition between the two!
since acrylic resin gains its strength with increasing bulk, it should not be finished to a
thin edge
could chip or fracture
tooth replacement-> acrylic denture teeth
- most esthetic
- easily adjusted
- not wear opposing natural dentition
- chemical bond with denture base
tooth replacement-> porcelain
- fracture easily
- wear opposing dentition
- difficult to adjust
- mechanical retention only to denture base
tooth replacement-> tube teeth
- denture tooth with drilled channel
- secured to metal post
- used with metal base: inadequate space for denture tooth
tooth replacement-> reinforced acrylic pontics (RAPS)
- composite resin polymerized around projections of metal from denture base
- anterior teeth only
- inadequate interarch space
tooth replacement-> metal teeth
- used with severely inadequate interarch space
- poor esthetics
- used only in posterior
- difficult to adjust
