DIRECT
RETENTION.
BY :
DR. Nora cheta
Intracoronal attachments
Extracoronal attachment
Retentive arm
CLASP ASSEMBLY
Occlusal
rest
Bracing arm
Minor connector
SURVEY LINE
NON UNDECUT AREA
Carbon Marker
HEIGHT OF CONTOUR
UNDERCUT AREA
UNDERCUT
GAUGE
DESIRABLE UNDERCUT
NON DESIRABLE UNDERCUT
DESIRABLE UNDERCUT
NON DESIRABLE UNDERCUT
Types of Survey Line
Away from the saddle
Near the saddle
A-MEDUIM SURVEY LINE
Midway between
Occlusal surface &
Gingival margin in the
Near zone
Nearer to gingival margin
In the far zone
We can use occlusally or gingivally approaching clasps
B-DIAGONAL SURVEY LINE
Near occlusal surface
In the near zone
Near gingival margin
In the far zone
Ging.app. With L bar
C clasp
Or
Back action &
Reverse back
Or
Or
Ging.app. With T bar
C-HIGH SURVEY LINE
Near to the occlusal surface
Back action or reverse back action
commonly in inclined teeth
Bracing
Arm
Wrought wire occlusally app.
TILTING THE TOOTH BUCCALLY SENDS
THE SURVEY LINE MORE OCCLUSALLY!!
BUCCAL
BUCCAL
TILTING THE TOOTH LINGUALLY SENDS
THE SURVEY LINE MORE CERVICAL!!
LINGUAL
LINGUAL
D- LOW SURVEY LINE
Near the gingival margin
Extended arm clasp
•Devan clasp engaging proximal undercut
•Crowning of the tooth
REQUIREMENTS OF CLASP DESIGN.
Retentive arm better located
In the gingival 1/3 for better
esthetics & mechanics
Bracing arm better located
In the apical portion of the
Middle 1/3
UNDERCUT IS BETTER BE FOUND WITHIN THE GINGIVAL1/3
For 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
A- depth of undercut
The greater the distance we go into the undercut the greater will be the retention
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
Clasps according to method of approach to undercut
Occlusally approaching clasp
Gingivally approaching clasp
1-Akers clasp (circlet)
2-DOUBLE AKER (embrasure)
LINGUAL
BUCCAL
CROSS ARCH STABILISATION!!
3-CIRCUMFERENTIAL `C` CLASP
B-DIAGONAL SURVEY LINE
Near occlusal surface
In the near zone
Near gingival margin
In the far zone
Ging.app. With L bar
C clasp
Or
Back action &
Reverse back
Or
Or
Ging.app. With T bar
4-R.P.A,
REST, PROXIMAL PLATE ,AKER.
5- Multiple clasp
6- Extended arm clasp
Adjacent tooth has a reasonable undercut
Abutment has no 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.)
Distal
Buccal
Lingual
Strut arm
Mesial
8-Reverse Back action clasp.
(MANDIBULAR)
M.C. originating
Mesio-buccally
Retentive arm engage
Mesio-lingual undercut
9-Back action clasp.
(MAXILLARY)
Mesial
• Single arm clasp
• Minor connector starts mesiolingually
• It engages mesio-buccal undercut.
• O.R. is located distally.
• Used in free end saddle.
Distal.
Different forms of gingivally approaching clasps
Modified T clasp
T clasp
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.I
REST, PROXIMAL PLATE, I-BAR
The base of the I bar
Should be 3mm away
From the gingival margin
Combination clasp
Gingivally app. Retentive arm
(buccally)
&
Occlusally app. Bracing arm
(lingually)
COMBINATION CASTED &
WROUGHT WIRE CLASP.
•Buccal wrought wire retentive arm soldered to the base
•Lingual casted bracing arm
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
Retention
Bracing
Gingivally
due to tripping action
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.)