Definition

definition
Types of
Retention
Types of Direct
Retainers

Definition:
Is that quality inherent in the
prosthesis acting to resist the
forces of dislodgment along
the path of placement

Direct Retainers
Indirect Retainers
Frictional fit between
Natural & Artificial teeth
The use of undercut areas
on the teeth & soft tissue
Physical factors of
Retention

Internal
Attachment
Clasps
Precision &
Semipercision
Intracoronal
&
Extracoronal

Attachments:
Ready made pairs of male and female parts, part
fixed to natural teeth, and part attached to
denture
Advantages:
1. No buccal & labial clasp arm
2. It is less stressful to the abutment than
clasps
3. The efficiency of retention is not affected by
contour of the abutment
4. More tolerated by the patient than clasps
5. Hygienic

Disadvantages:
1. It require prepared abutments and
casting
2. It require complicated clinical &
laboratory procedures
3. It eventually wear , resulting loss of fit
4. Difficult to repair & replace
5. Expensive

A Clasp is a metal component of
a partial denture engages the
external surface of an
abutment aiding in the retention
& bracing of RPD

Retentive Arm
Occlusal Rest
Reciprocal Arm
Minor connector

Retentive Arm
Reciprocal Arm

List the teeth in order of suitability
for clasping from the point of view
of Shape, Strength, Size:
Molars
Premolars
Canines
Upper central incisors
Upper laterals and all lower incisors are
useless

Two clasps
Bisect the denture
Three clasps
Triangle shape
Four clasps
Quadrilateral shape

Physical form of
clasps
Wrought
Wire Clasps
Cast Clasps
Round
Half-Round

Point of comparison Cast Clasps Wrought wire clasps
Fit to tooth surface More Less
Flexibility Less More
Friction with tooth
surface
More
Less
Contact with tooth
surface
Area
Line
Esthetic More visible Less visible
Distortion by
miss-handling
Less
More

Near & Far Zone
Medium survey line
Diagonal survey line High survey line Low survey line

1. Retention
2. Stabilization
3. Support
4. Encirclement
5. Reciprocity
6. Passivity

1. Depth of the undercut engaged
2. Angle of approach
3. Flexibility of the clasp arm….
depends on:
a) The length of the clasp arm
b) The diameter of the cross-section
c) Cross- section form
d) Taper
e) Modulus of elasticity
f) Curvature of clasp

1.Occlusally Approaching Clasps.
The retentive arms of these clasps originate
occlusal to the survey line.
2. Gingivally Approaching Clasps.
The retentive arms of these clasps originate
gingival to the survey line.

These clasps are also called encircling,
circumferential, or suprabulge clasps.
The two arms of these clasps originate
occlusal to the survey line.
The reciprocal arm is rigid and placed
totally occlusal to survey line of the tooth.
Occlusally

1. Aker
2. Aker’s family:
a. Recurved Arm form
b. One arm form
c. Half& half

d. Compound( Double Aker)
d. Multiple
e. Extended-Arm
f. Reversed Aker
g. R P A

3. Back- Action
4. Reverse-Back Action
5. Ring clasp

1. T shape
2. U shape
3. I shape
4. C shape
5. R P I
6. Ball and socket

Indications:
A. In distal extension cases, as it
provides a stress releasing action.
B. When tissue undercuts are not
severe
Contraindications
A. Shallow vestibule.
B. • High floor of the mouth
C. • Severe tissue or tooth undercut to
avoid food or tissue trap.

Double Aker clasp
Extended arm clasp
Multiple Aker clasp