Direct Retainer Flashcards
(42 cards)
Def, direct retainer
Resistance to tissue away movement ( vertical displacement of RPD) by vertical dislodging force.
RPD retained in place by:
1-direct retainer *resist vertical tissue away movement of denture.
2-indirect retainer *resist rotational tissue away movement in free end saddle.
intracoronal retainer ex; ….
extracoronal retainer ex …..
internal attachment
clasps, external attachment
Parts of clasp assembly
Circumferential clasp
Reciprocating arm
Distal occlusal rest and seat
Proximal plate
Def , Attachments
any attachment has (projection and depression ) projection → called patrix, depression → called matrix.
Clasps def
Is a Component of RPD used to resist vertical tissue away movement by dislodging force of RPD
type of survey line
1-medium survey line → at middle of teeth
2-diagonal survey line → near to occlusal surface at near zone and near to gingival surface at far zone
3-high survey line→ near to occlusal surface (more undercut area)
4-low survey line → near to gingival surface (less undercut area )
*Undercut areas near to saddle → called near zone, away from saddle → called far zone
Best survey line ….
medium and diagonal for clasp retention
components of clasp
1-rest.
2-reciprocal arm. * Rigid place on or above height of contour
* Functions:
1-reciprocation → counteract /resistance to tipping force generated by retentive arm of the clasp. 2-bracing.
Note: * give reciprocation during insertion and removal of denture, but after that give bracing. 3-retentive arm. * Tapered from its origin toward its tip.
*Consist of
a-body : * rigid above height of contour
b-shoulder:
* rigid (limited flexibility ), above height of contour
c-retentive terminal: * flexible, below height of contour * engage undercut give retention
* passive at rest and be active during dislodging force 4- proximal plate ( minor connector )
Requirement /quality of clasp affected by some factors
1-retention 2-support
3-stability 4-reciprocation
5-encirclement 6-passivity
retention
* Should be
minimal to resist dislodging force
Factors affecting of retention:
1- depth of retentive undercut
2- extent of clasp below survey line
3- flexibility
* Increase flexibility, decrease retention
Factors affecting flexibility
1-length → increase length, increase flexibility
2-diameter → increase diameter, decrease flexibility
3-taper → increase tapering ,increase flexibility
4-cross section → round cross section more flexible than half
5-matrial → (chrome-cobalt alloy has higher modulus of elasticity than gold). So more rigid and less flexible.
support
Done by rests (occlusal, cinglum, incisal),to
resist tissue ward movement
stability
* All component of clasp are rigid except
retentive terminal is flexible
encirclement
* Clasp should encircle tooth by more than
180°to avoid tipping force or orthodontic movement to tooth.
passivity
* Clasp is completely passive except
during dislodgement
Classification of Clasps
1-occlusally approach (circumferential clasp)(suprabulge clap) *Originate from oclussal to engage undercut below height of contour
2-gingivally approach clasp (bar clasps) (infrabulge clasp)
*Originate from gingival origin to engage undercut below height of contour
Occlusally approach clasp types
1-aker, simple circlet clasp
2-reverse aker (reverse circlet clasp
3-double aker (embrasure clasp)(butterfly clasp)
4-ring clasp
5-extended arm clasp
6-combination clasp
7-RPA clasp
clasp of choice as full fill all requirement (support, stability, reciprocation,
encirclement) than other types of clasps.
aker, simple circlet clasp
aker, simple circlet clasp , Use …undercut, away from saddle
0.01
aker, simple circlet clasp is rigid clasp. So mostly used in…
-tooth supported RPD ‘‘bounded saddle’
aker, simple circlet clasp , not used in free end saddle except usage of
stress breaker
reverse aker , used in
distal extension as it is stress breaking
