Prdp - Lecture 3 Direct And Indirect Retention

Front 1

What is a direct retainer?

Back 1

component of PRDP used to resist vertical dislodgement along the path of insertion, consisting of clasp assembly or attachment

Front 2

What is a clasp assembly?

Back 2

generally consists of: a guide plate + rest + flexible retentive arm + reciprocal bracing arm.

It should accomodate minor movement of the PRDP without transmitting damaging forces to the abutement teeth

Front 3

The ____1_____ should stabilize the PRDP and the ____2_____ should remain passive until activated by dislodging forces.

Back 3

1. clasp assembly
2. retentive arm

Front 4

Which part(s) of the clasp assembly is/are flexible?

Back 4

only the retentive arm tip (terminal 1/3 of the retentive arm)

Front 5

All clasp assemblies must meet which basic requirements? (7)

Back 5

1. Support
2. Stability
3. Retention
4. Reciprocation
5. Encirclement
6. Passivity
7. Occlusion

Front 6

How do the rests support the prosthesis?

Back 6

resist movement towards residual ridge

Front 7

How do the guide planes/reciprocal arms give stability to prosthesis?

Back 7

resist horizontal and tipping movements

Front 8

What else can be done to minimize tipping besides guide planes and reciprocal arms?

Back 8

position non-flexible portion of clasp arm in the middle 1/3 of the tooth height

Front 9

Retention provided by a retentive arm is influenced by? (3)

Back 9

1. amount of undercut engaged
2. flexiblity of retentive arm
3. type of clasp arm used

Front 10

What are the types of clasp arms? (4)

Back 10

- wrought wire circlet
- cast circlet
- cast ring clasp
- cast I-bar

Front 11

Depth of undercut for retentive clasp arm?

Back 11

depth of undercut 0.25 or 0.5 for retentive clasp arm

Front 12

What kinds of things need to be considered when adding clasps to PRDP design?

Back 12

depth of undercut 0.25 or 0.5 for retentive clasp arm

- engagement of 1mm undercut distributed on both sides of the arch from all abutment teeth combined should bee sufficient to retain PRDP
- retentive arm tip at MB or DB line angles shouold be positioned in the gingival 1/3 of clinical crown optimally no closed than 1mm from gingival margin

Front 13

Flexibility of retentive clasp arm is influenced by?

Back 13

1. length (flexure proportional to length)
2. cross sectional form (round >half round)
3. diameter ( indirectly proportional)
4. taper (retainer 1/2 thickness at tip vs origin)
5. type of alloy (chromium>gold)

Front 14

What is the purpose of reciprocation?

Back 14

resists force generated against the abutement tooth by the retentive arm when the PRDP is dislodged

Front 15

When should the reciprocating elements be engaged?

Back 15

ideally the guide plane and reciprocal arm should touch before or at the same time as the retentive tip is inserted over the HOC to engage the undercut

Front 16

When is a reciprocal arm classified as a bracing arm?

Back 16

when the retentive tip touched before the reciprocal arm on insertion of the PRDP, meaning the class assembly may only be passive once fully seated

Front 17

Describe encirclement as it related to PRDP design

Back 17

clasp assembly encicles tooth by at least 1/2 (180º) of the circumference, or at least 3 contact points , to prevent tooth movements and to maintain contact (providing support, stability and retention) bw the tooth and clasp assembly

Front 18

Should direct retention be passive or active?

Back 18

Passive

Direct retention should only be active when dislodging forces are applied to the PRDP

Front 19

What is a self-reciprocating clasp assembly? Components and their general roles.

Back 19

an extracoronal direct retainer that provides support (via rest), retention (via retentive arm and guide plane) and stability (via guide plate and reciprocation)

Front 20

Role of guide plates in self-reciprocating clasp assembies?

Back 20

to reinforce the path of insertion and to stabalize the blast assembly

Front 21

Difference bw retention provided by prox plate vs retentive arm?

Back 21

retention arising from prox plate contact with the tooth is typically MORE DURABLE and so more important in the LONG TERM

direct retention provided by the retentive arm often diminishes over time

Front 22

How do rests seats provide support?

Back 22

resists movement of PRDP toward the residual ridge so that retentive tip remains in in the desired undercut position

prevents impingement of soft tissue

Front 23

How does the retentive arm provide retention?

Back 23

resists movement of the denture away from the residual ridge via retentive tip positioned PASSIVELY in a favourable undercut (below HOC)

Front 24

Location of reciprocal arm?

Back 24

above HOC on opposite side of tooth from retentive arm at or above the jxn bw the middle and gingival 1/3rds

Front 25

How does the reciprocal arm provide stability?

Back 25

1. resists tipping force generated on the tooth as the retentive tip passes over the HOC on insertion and removal or PRDP

2. stabalizes PRDP during lateral movement

Front 26

Role of minor connector?

Back 26

joins the clasp assembly to major connector

Front 27

What are the 2 types of direct retainers?

Back 27

extracoronal
intracoronal

Front 28

What are the 3 types of extracoronal retainers?

Back 28

1. suprbulge clasp assembly
2. infrabulge clasp assembly
3. precision attachment

Front 29

Which extracoronal retainer is preferable?

Back 29

suprabulge clasp assembly

Front 30

Describe a suprabulge clasp assembly

Back 30

= retentive arm approaches the undercut from ABOVE the HOC
- curved shape follows the gingival, increases length and flexibility characteristics
- half round shape (2D flexibility)
- wrought wire (omni-directional flexibility

Front 31

Describe an infrabulge clasp assembly

Back 31

= retentive arm approaches the undercut from BELOW the HOC
- vertical projection with an I, Y or L shape to the tip

Front 32

Potential problem with infrabulge clasp?

Back 32

crosses gingiva thus potentially traumatizing the gingiva and increasing plaque retention

Front 33

Describe a precision attachment

Back 33

= attachment soldered or welded to cast restoration

Front 34

Describe an intracoronal retainer

Back 34

precision or semi-precision attachment integrated into the contours of a cast restoration provide FRICTIONAL retention

Front 35

In which scernarios may intracoronal retainers be indicated

Back 35

kennedy III and IV (tooth supported PRDPs)

but most of the time extracoronal preferred over intracoronal

Front 36

List some types of suprabulge clasps

Back 36

- circumferential or circlet
- combination (WW retentive arm)
- multiple circlet clasp
- ring clasp
- reverse circlet
- C-clasp
- embrasure clasp
- onlay clasp

Front 37

T/F: at UBC a lingual retentive arm is recommended for a ring clasp

Back 37

False. facial retentive arm recommended, not lingual

Front 38

Describe the components of a suprabulge clasp

Back 38

Shoulder: originates from minor connector occlusal or incisal to survey line, tapers and is RIGID
Midsection: continues from shoulder, tapers and more flexible
Terminus: engages u/c apical to HOC, tapers and is most flexible

Front 39

T/F: at UBC infrabulge clasps are not recommended unless unavoidable

Back 39

True.

A simple I bar retentive arm is recommend if an infrabulge clasp is unavoidable.

T bar clasps are generally unnecessary option to provide encirclement.

Front 40

Describe the components of a infrabulge clasp

Back 40

approach arm: a minor connector that is first horizontal, then vertical, crosses gingiva at 90º, originates apical to survey line but does not contact tooth

terminus: continues from approach arm, only part of clasp to contact tooth apical to u/c

Front 41

What is the optimal tapering for a cast clasp?

Back 41

<1mm wide at the tip

Front 42

What alloy are cast claps

Back 42

chrome cobalt

Front 43

When are cast clasps most indicated?

Back 43

Kennedy III and IV

Front 44

Describe WW clasps: metals used, gauges

Back 44

19gauge stainless steel or gold alloy is most commonly used

19g = 0.040in = 1.02mm
20g = 0.036in = 0.91mm
higher number is more flexible and more easily distorted
thicker gauge can be tapered to <=1mm at the tip

Front 45

When are WW clasps most indicated?

Back 45

kennedy I and II as a combination clasp to control potential for excess forces on abutement teeth adjacent to distal extension denture base, and on teeth anterior to the retentive fulcrum line

Front 46

Advantages/disadvantages of using cast clasps instead of WW?

Back 46

+ simpler to fabricate
+ less likely to distort
- less flexible
- less easy to adjust
- more likely to work harden and fracture

Front 47

Undercut recommended for cast clasp and WW

Back 47

Cast clasp: less undercut (0.25mm) for increase rigidity

WW: more undercut (0.5mm) for increase flexibility

Front 48

2 things to remember when creating undercuts

Back 48

use minimum undercut for acceptable retention (need good guide plate retention)

balance bw stress to abutment (incr retention) and stress to ridge (decrease retention)

Front 49

What does RPI stand for?

Back 49

R = rest
P = proximal plate
I = I-bar retentive arm

Front 50

When could RPIs be indicated?

Back 50

proposed alternative to combination clasp for kennedy I and II (but not for simpler combination clasps)

Front 51

Describe components of RPI

Back 51

mesial rest: mesial pressure under loading towards adjacent tooth prevents distal movement

distal prox plate: disengages clasp on loading of distal free end

cast infrabulge direct retainer (I-bar) at mid-facial or toward mesial half of the facial surface

Front 52

What is the theory behind using RPI?

Back 52

forces are theoretically favorable
some esthetic advantage to I-bar

Front 53

Disadantages to using RPI

Back 53

- complexity
- plaque retention
- food impaction

Front 54

What are fulcrum lines?

Back 54

axes of rotations for PRDPs
eg around the distal rests or the retentive clasps tips under occlusal loading or lifting forces respetively involving the distal extention or an anterior denture base positioned anterior to supporting rests

Front 55

Describe fulcrum lines formed with occlusal load toward the ridge

Back 55

axis of rotation passing through the most posterior rests of kennedy I or II

resisted by broad, well adapted denture bases

Front 56

Describe fulcrum lines formed with displacing forces away from the ridge

Back 56

axis of rotation passing through the tips of the retentive clasp arms of kennedy I or II

resisted by an indirect retainer, which is any rest anterior to the retentive fulcrum line

Front 57

What is indirect retention?

Back 57

retention provided by any rest anterior to the retentive fulcum line in kennedy I and II

helps resist lifting of PRDP distal extension base AWAY from the ridge when there is no distal abutement tooth (I or II)

Front 58

Types of indirect retainers

Back 58

- rest or
- lingual plate (with rest under it)

...placed anterior to fulcrum line and on the side opposite for the distal extension base

Front 59

T/F: Indirect retainers are most effective when located at right angles and as far anteior from the retentive fulcrum line as practical (ie on opposite side of distal extention base.

Back 59

True

Front 60

T/F: In practice, it is not sufficient to have on indirect retainer.

Back 60

False. In practice it is usually sufficient to have on indirect retainer located at least one tooth anterior to fulcrum line

Front 61

T/F: It is usually necessary to compromised patient comfort in order to maximize the potential for indirect retention.

Back 61

False!

Front 62

How are indirect retainers connected to PRDP framework?

Back 62

indirect retainer rest is connected to major connector via rigid minor connector that can arise separatly from the major connector, or if possible as part of an existing reciprocating or bracing arm on the side opposite the largest distal extension

Front 63

T/F: kenney class IV do not require indirect retention

Back 63

true.... but it is recommeneded that direct retainers with rests be placed as far posterior as possible