DIRECT RETENTION.
description
Transcript of 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.)