Direct Retainers Flashcards
what does retention do
resists dislodging forces
what is primary retnetion
mechanical from retaining elements on abutment teeth
what is secondary retention
- intimate contact of minor connector with guide planes
- intimate contact of denture base and maxillary major connector with underlying tissues
what is a direct retainer used for
retain and prevent dislodgment
what are the type of direct retainers
- intracoronal
- extracoronal
describe intracoronal direct retainers and disadvatnages
- internal precision attachment: key/keyway
- most esthetic
- disadvantge: require crown, complex fabrication and high maintenance
describe extracoronal direct retainers
- clasp assembly
- more commonly used
what are the clasp types
- suprabuldge and infrabuldge
describe suprabuldge clasps and their names
-retentive arm approaches undercut from above the survey line
- circumferential, akers or circlet
describe infrabuldge clasps
retentive arm approaches undercut from below survey line
- bar clasps
where is the retentive clasp usually located
buccal/facial side
what are the components of a suprabuldge or infrabuldge clasp assembly
- rest
- retentive clasp
- reciprocal element
- one or more minor connector
what are the specific design features of the various components in a clasp
- vertical and horizontal approach arms
- clasp termini
- clasp bodies
- clasp shoulders
where is the rest located
on occlusal, lingual and incisal surfaces
what does the rest do
prevent tissueward movement of clasp
what are the reciprocal components
- rigid component
- above height of contour
- reciprocal clasp, lingual plate, proximal plate, guide plate
describe the retentive clasp arm
-proximal 2/3
- rigid portion above the height of contour
describe the retentive terminal
- distal 1/3
- flexible
- below height of contour
- provides direct retention
describe the minor connector
joins body of clasp to framework
- rigid
describe the approach arm
- component of bar clasp
- connects clasp to frameowrk
- flexible minor connector
what does support do and what part of the clasp provides support
- resists vertical movement towards tissue
- rests
what does stability do and what part of the clasp provides stability
- resists horizontal displacement
- areas above the survey line
- all rigid components of direct retainer
encirclement of more than ____ degrees
180
describe encirlemnet
- may be continuous or broken
- minimum of 3 points used
- prevents tooth from moving away from the clasp
describe reciprocation
- reciprocal component contact tooth at the same time or sooner than the retentive clasp
- remain in contact while retentive tip passes over height of contour
- resist retentive tip lateral forces
- requires parallel surface to path of insertion
what is passivity
components of direct retainer exert no force when fully seated
what does retention do
resists displacement of RPD away from supporting tissues
where is retention located
area below survey line ideally in gingival 1/3
where is the clasp arm tip located
terminal 1/3 below survey line
retention portion of tooth must be _____ in relation to path of prosthesis insertion
undercut
what are retention factors
- angle of convergence of the undercut
- depth of undercut (0.01”, 0.02”. 0.03”)
- flexibility of the retentive clasp
when should retentive clasps become active
only when disclosing forces are apllied to them
a retentive clasps ability to provide retention is based on what?
the resistance of the metal to deformation
what are the retentive clasp flexibility factors
- length: the longer the more flexible
- diameter: the thicker the clasp the less flexible
- taper: clasp terminal 1/2 as thick as origin (1mm-0.5mm) and clasp terminal 1/2 as wide as origin (2mm to 1mm)
4. cross sectional form: round clasp more flexible than half round
what planes do round clasp flex in
spatial
what planes do half round clasps flex in
one plane
desscribe half round clasps
- almost always as in circumferential clasp
describe round clasps
in wrought wire clasps
- provides maximum flexibility
what materials are the most to least flexible
wrought > cast gold > cast chromium
what undercuts should you use with each material
- cast chrome alloy: 0.01”
- cast gold alloy: 0.015”
- wrought wire: 0.02”
what alloy is used in casting the framework
usually ticonium (NiCr) or vitallium (CoCr)
how is wrought wire produced
by drawing metal through dies of smaller diameter
what are the retentive qualities of circumferential clasps
- approaches undercut from above the survey line
- pulls toward occlusal to resist displacement
what are the retentive features of bar clasp
- approaches undercut from below survey line
- pushes toward occlusal to resist displacement
- easier to seat more difficult to remove than circumferential clasp
describe the reciprocal clasp
- must be rigid
- shaped different than flexible retentive clasp
- not tapered
what is reciprocation
the means by which one part of the framework opposes the action of the retainer in function
how is reciprocation achieved
- rigid plating (lingual plate)
- minor connectors
- guide planes extend around the vertical line of abutments
- reciprocal clasp arms
- contact areas of proximal teeth
what type of RPD are circumferential clasps used in
tooth supported RPD - kennedy class III
what are the advantages of circumferential clasps
- excellent stabilization, support, bracing
- easiest to design and construct
- easier to repair
what are the disadvantages to circumferential clasps
- covers more tooth surface: more conducive to caries by more plaque retention
- increases tooth circumference: may cause greater occlusal force on tooth
- more difficult to adjust
why is the circumferential clasp kept as low on crown as survey line permits
- less torquing on tooth
- less interference with occlusion
what do you do if survey line is too hgih
recontour enamel surface to lower it
what do you do if survey line is too low
surveyed crown required
describe the retentive clasp in circumferential clasp configuration
- cast 1/2 round
- proximal 2/3: in middle 1/3 of tooth above the survey line
- terminal retentive 1/3: in gingival 1/3 below survey line, tip curves to occlusal
- tapers from origin (2mm) to tip (1mm)
describe the reciprocal clasp in circumferential clasp configuration
- cast 1/2 round
- entire clasp in middle 1/3
- above survey line
- no taper: unifrom width 1.5- 2 mm
what are the types of circumferential clasps
- circlet
- embrasure clasp
- ring clasp
- combination clasp
describe the circlet clasp
- circumferential clasp of choice Class III RPD
- engage undercut remote from edentulous area
describe embrasure clasps
- 2 circlet clasps joined at body
- used when retainer is necessary in a dentate area : Class III with no mods, Class II with no mods, Class IV
- requires heavy reduction of abutment adequate clasp bulk
when are ring clasps indicated
mesiolingually tipped mandibular molars Class III RPD
describe the ring clasp
- engage mesiolingual undercut
- auxillary bracing arm for reciprocity
- additional occlusal rest: support, prevent further mesial movement
- avoid if possible
when are reverse circlet clasps indicated
retentive undercut adjacent to edentulous space
- class III RPD
- tooth-tissue supported RPD (Class I or II distal extension
- 1/2 T bar clasp preferred, if no tissue undercut at approach arm
describe reverse circlet clasps
- difficult to obtain adequate occlusal clearance
- avoid if possible
describe combination clasp
- wrought round wire retentive clas
- cast 1/2 round reciprocal clasp
what is the indication for combination clasp-
- distal extension RPD class I and II
- mesial rest not possible, distal rest must be used
- mesiofacial undercut
