DIRECT RETENTION.

DIRECT DIRECT RETENTION.RETENTION.

BY :DR. Nora cheta

Intracoronal attachments

Extracoronal attachment

CLASP ASSEMBLYRetentive arm

Bracing arm

Occlusal rest

Minor connector

SURVEY LINE

UNDERCUT AREA

NON UNDECUT AREA

HEIGHT OF CONTOUR

Carbon Marker

DESIRABLE UNDERCUTNON DESIRABLE UNDERCUT

UNDERCUT GAUGE

DESIRABLE UNDERCUTNON DESIRABLE UNDERCUT

Types of Survey Line

Near the saddle

Away from the saddle

A-MEDUIM SURVEY LINEMidway between

Occlusal surface& Gingival margin in the Near zone

Nearer to gingival marginIn the far zone

We can use occlusally or gingivally approaching clasps

B-DIAGONAL SURVEY LINE

Near occlusal surfaceIn the near zone

Near gingival marginIn the far zone

Or Or Or

Back action& Reverse back

C clasp

Ging.app. With T bar

Ging.app. With L bar

C-HIGH SURVEY LINE

Near to the occlusal surface

Wrought wire occlusally app.

Back action or reverse back action commonly in inclined teeth

Bracing Arm

TILTING THE TOOTH BUCCALLY SENDS THE SURVEY LINE MORE OCCLUSALLY!!

BUCCALBUCCAL

TILTING THE TOOTH LINGUALLY SENDS THE SURVEY LINE MORE CERVICAL!!

LINGUALLINGUAL

D- LOW SURVEY LINE

Near the gingival margin

Extended arm clasp

•Devan clasp engaging proximal undercut•Crowning of the tooth

REQUIREMENTS OF CLASP DESIGN.

Bracing arm better locatedIn the apical portion of the Middle 1/3

Retentive arm better locatedIn the gingival 1/3 for better esthetics & mechanics

UNDERCUT IS BETTER BE FOUND WITHIN THE GINGIVAL1/3For mechanical reasons

Post Is More Readily Removed by Application of Force Near Its Top

Than by Applying Same Force Nearer Ground Level

RECOPRICATION

Each retentive terminal should be reciprocated as retentive arm exerts some orthodontic movement

during placement and removal as it flexes about the height of contour.

BRACING

THE DIFFERENCE IS!!!!!

• RECOPRICATION IS TO PREVENT THE NATURAL TOOTH MOVEMENT.

• BRACING IS TO PREVENT THE WHOLE DENTURE MOVEMENT.

• BOTH ARE APPLIED USING THE SAME COMPONENT

---------BRACING ARM-----

OCCLUSAL 1/3, FOR SUPPORT

MIDDLE 1/3, FOR BRACING &RECOP.

GINGIVAL 1/3, FOR RETENTION.

180 degrees ENCIRCLEMENT OF THE TOOTH.

Tooth can't move horizontally away from the clasp

Amount of retention depends on

The greater the distance we go into the undercut the greater will be the retention

A- depth of undercut

2 .FLEXIBILITY OF CLASP ARM

LENGTH Increasing arm length increases the flexibility ,thus decreasing the retention

SHAPE OF THE CLASP CROSS SECTION

Round clasps have universal flexibility thus lowers the retention than ½ round and flat clasps

Degree of taper Retentive arm should be tapered in two dimensions.

The diameter of retentive arm The material of the alloy (gold alloy are more

flexible than cobalt chrome alloy )The type of alloy (wrought wire

C- Angle of cervical convergence

Occlusally approaching clasp Gingivally approaching clasp

Clasps according to method of approach to undercut

1-Akers clasp (circlet)

2-DOUBLE AKER (embrasure)

LINGUAL

BUCCAL

CROSS ARCH STABILISATION!!

3-CIRCUMFERENTIAL `C` CLASP

B-DIAGONAL SURVEY LINE

Near occlusal surfaceIn the near zone

Near gingival marginIn the far zone

Or Or Or

Back action& Reverse back

C clasp

Ging.app. With T bar

Ging.app. With L bar

4-R.P.A ,REST, PROXIMAL PLATE ,AKER.

5- Multiple clasp

6 -Extended arm clasp

Abutment has no undercut

Adjacent tooth has a reasonable undercut

D- LOW SURVEY LINE

Near the gingival margin

Extended arm clasp

•Devan clasp engaging proximal undercut•Crowning of the tooth

7- Half & Half clasp

• 2 M.C., 2 O.R. & 2 arms.• Mainly indicated for

dual retention commonly in unilateral cases.

SINGLE ARM CLASPS!!!

THESE ARE FLEXIBLE CLASPS, DUE TO THEIR ELONGATED SINGLE ARM,

AND THEY PROVIDE POOR BRACING.

7-RING CLASP)ISOLATED, BADLY LINGUALLY TILTED, LOWER MOLAR(.

Buccal

Lingual

Distal

Mesial

Strut arm

8-Reverse Back action clasp.)MANDIBULAR(

M.C. originatingMesio-buccally Retentive arm engage

Mesio-lingual undercut

9-Back action clasp.(MAXILLARY)

• Single arm clasp• Minor connector starts mesio-

lingually• It engages mesio-buccal

undercut.• O.R. is located distally.• Used in free end saddle.

Distal.

Mesial

T clasp

Modified T clasp

Different forms of gingivally approaching clasps

I clasp

Contraindications for the use of gingivally approaching clasps

TISSUE UNDERCUT.

TRIPPING ACTION!!!!

OCCLUSALLY APP. ARE PULLED OUT.

GING. APP. ARE PUSHED .

(TRIP. ACTION.)

R.P.IREST, PROXIMAL PLATE, I-BAR

The base of the I barShould be 3mm away

From the gingival margin

Combination clasp

Gingivally app. Retentive arm) buccally(

& Occlusally app. Bracing arm (lingually)

•Buccal wrought wire retentive arm soldered to the base•Lingual casted bracing arm

COMBINATION CASTED & WROUGHT WIRE CLASP.

SO WHAT DID WE LEARN??????

Clasps with splinting action

• Double Aker clasp• Extended arm clasp• Multiple Aker clasp

Clasps used in free end saddle cases.(class I&II)

• All gingivally approaching clasps. • Occlusally approaching clasps

– Reverse Aker clasp– Back action clasp– Reverse back action clasp– R.P.A.

• Combination clasps ( 2 types).

Occlusally Gingivally

Retention due to tripping action

Bracing aAbove survey line provide bracing.

Esthetics less visible due to gingival position

Tolerance Gingivally app.clasp arm relieved from gingiva creating space accumulating food and causing discomfort.

Caries More tooth coverage increasing the risk for caries

Gingival health Trauma may occur due to distortion or inadequate relief

Consideration for Clasps in Free End Saddle Cases!!!!

THE PROBLEM OF THE FREE END SADDLE IS

DISPARITY OF SUPPORT!!!!!!

MOVEMENT OF CLASP CAUSES TORQUEING.

WHAT DO WE DO????

NO. 1: USE FLEXIBLE CLASPING.

Clasps with stress breaking action (class I&II)

• All gingivally approaching clasps. • Occlusally approaching clasps

– Reverse Aker clasp– Back action clasp– Reverse back action clasp

• Combination clasps ( 2 types).

WROUGHT WIRE CLASP DURING FUNCTION

NO 2: PLACE OCCLUSAL REST MESIALLY.

CLASS 1 LEVER.

CLASS 2 LEVER.

DISENGAGEMENT FROM THE UNDERCUT.

NO 3: DISTRIBUTE THE LOAD.

NO 4: VARY THE CONNECTION BETWEEN D.BASE AND THE

RETAINER.

NO 5: RECORD THE RIDGE IN FUNCTIONAL FORM.

To reduce the denture base movement, record the ridge in

compressed form (functional form.)