Direct Retainers Part 1

Question 1

Intracoronal Direct Retainers

Answer 1

Advtantages:
+Internal attachment
+Most esthetic

Disadvantages:

• Costly
• Requires Crown
• Complex fabrication (not all dental labs can process)
• High Maintenance

Question 2

Extracoronal Direct Retainers

Answer 2

Clasp Assembly

More commonly used

Question 3

Extracoronal Clasp Types

Answer 3

Suprabulge
&
Infrabulge

Question 4

Suprebulge

Answer 4

Top portion above the contour of the abutment type
Retentive arm approaches undercut from above the height of the contour (above the survey line)

Circumferential, Akers, Circlet

Question 5

Infrabulge

Answer 5

The retentive arm approaches the undercut from BELOW the survey line

Has Bar Clasps

Question 6

******Where are these located:
Rest
Reciprocal Clasp
Retentive Clasp
Proximal Plate

go over this question again

Answer 6

Rest ~ on the occlusal

Reciprocal Clasp - on the lingual

Retentive Clasp ~ on the buccal

Proximal Plate (guide plate) ~ type of minor connector

Question 7

Clasp Assembly

Answer 7

Lies on the:
occlusal, lingual, or incisal surface

~Prevent tissue ward movement of clasp

Question 8

Reciprocal Components

Answer 8

~Rigid Component

~Above height of contour

~Reciprocal Clasp, Lingual Plate, Proximal Plate, Guide Plate (minor connectors)

Question 9

Retentive Clasp Arm

Answer 9

~Proximal 2/3 of tooth (which is rigid)

~Rigid portion, above the height of the contour

Question 10

Retentive Terminal

Answer 10

~Distal 1/3

~Is Flexible

~Below the height of contour

~Provides a direct retention

Question 11

Minor Connector

Answer 11

~Joins the body of the clasp to the framework

~Is Rigid

Question 12

Approach Arm

Answer 12

~Is a component of the bar clasp

~Connects the clasp to the framework

~Flexible minor connector
~Exception to the rule

Question 13

What are the requirements of Clasp Assembly?

Answer 13

1. Support
2. Stability
3. Encirclement of more than 180 degrees
4. Reciprocation
5. Passivity
6. Retention

Question 14

What is Support for Clasp Assmebly?

Answer 14

~Resists vertical movement toward tissues

~Rests

Question 15

What is Stability for Clasp Assembly?

Answer 15

~Resists horizontal displacement

~Areas above the survey line

~All rigid components of direct retainer

Question 16

What is Encirclement?

Answer 16

– May be continuous or broken
– Minimum of 3 points used
– Prevents tooth from moving away from the
clasp

Question 17

What is Reciprocation?

Answer 17

– Reciprocal component contact tooth at same 
time or sooner than 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

Question 18

What is Passivity?

Answer 18

– Components of direct retainer exert no force

when fully seated

Question 19

What is Retention?

Answer 19

– Resists displacement of RPD away from
supporting tissues
– Area below survey line: ideally in gingival 1/3
• Clasp arm tip: Terminal 1/3 below survey line

Question 20

Retention portion of tooth must be _____ in relation

to path of prosthesis insertion

Answer 20

undercut

Question 21

Retention amount minimum necessary to resist

reasonable ____

Answer 21

dislodging forces

Question 22

Undercut must always

Answer 22

come from below the height of the contour

1mm from the gingival margin on the apical 1/3

Question 23

What are the 3 Retention Factors?

Answer 23

• Angle of convergence of the undercut

• Depth of undercut
– 0.010”, 0.020”, 0.030”
(undercuts we are looking for)

• Flexibility of the retentive clasp

~Retention should not be too much or too little~

Question 24

Retentive Clasp

Answer 24

• Retentive clasps should become active ONLY
when disclosing forces are applied to them.

• Their ability to provide retention is based on
the resistance of the metal to deformation

Question 25

Longer Cusp arm =

Answer 25

more flexible

Question 26

Retentive Clasp Flexibility Factors

Answer 26

1. Length 2. Diameter 3. Taper 4. Cross-sectional form 5. Material

Question 27

Retentive Clasp Flexibility Factors Length

Answer 27

– Flexibility = length3 • Double length, 8x more flexible – Increase length, curve clasp

Question 28

Retentive Clasp Flexibility Factors Diameter

Answer 28

– Flexibility = 1/diameter3 • Double diameter, 8x less flexible

Question 29

Retentive Clasp Flexibility Factors Taper

Answer 29

– Clasp terminal ½ as thick as origin • 1mm to 0.5 mm – Clasp terminal ½ as wide as origin • ~2mm to 1mm

Question 30

Retentive Clasp Flexibility Factors Cross-sectional form

Answer 30

– Round clasp more flexible than halfround • Round flexes in all spatial planes • Half-round flexes in one plane

Question 31

Retentive Clasp Flexibility Factors Material

Answer 31

– Cast chromium alloys less flexible than cast gold alloys – Wrought alloys more flexible than cast alloy – Cast Chromium

Question 32

What alloy is used in casting the Clasp Framework?

Answer 32

Usually Ticonium (NiCr) or Vitallium (CoCr) Is easy to fabricate

Question 33

How is Wrought wire produced?

Answer 33

‣ Produce by drawing metal through dies of smaller | diameter

Question 34

Wrought wire is ....

Answer 34

the most flexible of all clasps

Question 35

What are other Clasp Materials?

Answer 35

Stainless steel, type IV gold

Question 36

The design of a retentive clasp arm should be ____

Answer 36

‣ Produce by drawing metal through dies of smaller | diameter

Question 37

Circumferential Clasp should ____

Answer 37

– Approach undercut from above the survey line – “Pull” toward occlusal to resist displacement

Question 38

The Bar Clasp ____

Answer 38

– Approaches undercut from below survey line – “Pushes” toward occlusal to resist displacement – Easier to seat, more difficult to remove than circumferential clasp

Question 39

The Reciprocal Clasp must be ____

Answer 39

Rigid

Question 40

The Reciprocal Clasp is

Answer 40

is shaped different than the flexible retentive clasp and Not tapered

Question 41

What is Reciprocation?

Answer 41

Reciprocation is the means by which one part of the framework opposes the action of the retainer in function.

Question 42

How can Reciprocation be achieved?

Answer 42

Reciprocation may be achieved by: ``` • Rigid plating (LINGUAL PLATE) • Minor connectors • Guide planes extended around the vertical line of abutments • Reciprocal clasp arms • Contact areas of proximal teeth ```

Question 43

Circumferential Clasps are the most logical clasp for

Answer 43

tooth-supported RPD (CLASS III)

Question 44

What are the advantages of Circumferential CLasps?

Answer 44

~Excellent Stabilization, support and bracing ~Is the easiest to design and construct ~Is the easiest to repair

Question 45

What are the disadvantages of Circumferential Clasps?

Answer 45

~Covers more tooth surface; is more conducive to caries by more plaque retention ~Increases tooth circumference >May cause greater occlusal force exerted on tooth ~More difficult to adjust

Question 46

Circumferential Clasp is kept ____

Answer 46

as low on the crown as the survey line permits because of: ~Less torquing action on tooth ~Less interference with occlusion ~If the survey line is too high, the enamel surface must be recontoured to lower the survey line ~the survey line being too low, so surveyed crown will be required

Question 47

Describe a Retentive Circumferential Clasp

Answer 47

``` – Cast ½ 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 (2.0mm) to tip (1.0 mm) ```

Question 48

Describe a Reciprocal Circumferential Clasp

Answer 48

• Reciprocal clasp – Cast ½ round – Entire clasp in middle 1/3 – Above the survey line • If survey line too high, must recontour • Prepare surface parallel to path of insertion – No taper: Uniform width 1.5 – 2.0 mm

Question 49

What are the types of Circumferential Clasps?

Answer 49

1. Circlet 2. Embrasure clasp 3. Reverse Circlet (hairpin) clasp 4. Ring clasp 5. Reverse Circlet clasp 6. Combination Clasp 7. RPC clasp

Question 50

What is Circlet Circumferential Clasp?

Answer 50

• Circumferential clasp of choice Class III RPD • Engage undercut remote from edentulous area

Question 51

What is Embrasure Circumferential Clasp?

Answer 51

• 2 circlet clasps joined at body • Used when retainer is necessary in a dentate area – Class III with no modification space – Class II with no modification space – Class IV • Requires heavy reduction of abutment teeth for adequate clasp bulk – Inadequate preparation, clasp fracture common

Question 52

What is Reverse Circlet (Hairpin) Circumferential Clasp?

Answer 52

• Engage undercut adjacent to edentulous area Class III RPD • Covers extensive tooth surface, increased caries risk • Difficult to fabricate • Indication: Mesially-tipped mandibular molar with mesiofacial undercut – ½ T preferred for this situation, if no tissue undercut at approach arm • “Last choice” for mesially-tipped molars

Question 53

What is Ring Circumferential Clasp?

Answer 53

``` • Indication: Mesiolingually-tipped mandibular molars Class III RPD • Engage mesiolingual undercut • Auxillary bracing arm for reciprocity • Additional occlusal rest: – support, prevent further mesial movement • Avoid if possible • Incorrect Ring clasp: No reciprocation No support ```

Question 54

What is a Reverse Circlet Circumferential Clasp?

Answer 54

• Indication: Retentive undercut adjacent to edentulous space – Class III RPD – Tooth-tissue supported RPD (Class I or II distal extension) – ½ T bar clasp preferred, if no tissue undercut at approach arm • Difficult to obtain adequate occlusal clearance • Avoid, if possible

Question 55

What is Combination Circumferential Clasp?

Answer 55

• Wrought round wire retentive clasp • Cast ½ round reciprocal clasp • Indication: Distal extension RPD (Class I & II) – Mesial rest not possible, distal rest must be used – Mesiofacial undercut • Wrought wire soldered to framework

Question 56

What is RPC Clasp (RPA)?

Answer 56

``` • Rest (mesial), Proximal Plate, Circumferential (Akers) clasp • Indication: – Class I, II RPDs – Mesiofacial retentive undercut • Circumferential retentive clasp – Cast ½ round (ALWAYS) except in periodontally compromised teeth, cast round. • Reciprocation: – Distal proximal plate – ML minor connector ```