STRESS CONSIDERATION IN
DISTAL EXTENSION PARTIAL
DENTURE
Direct retainers
 But – clasp can not effectively
dissipate this stress because:
1. Material itself can have only limited
flexibility .
2. Clasp are made half round in
shape it can flex only in one
direction therefore can not
effectively dissipate, by flexing all
stresses placed on it. Therefore
most of the tilting stress is
transmitted to abutment as
leverage.
 I bar ( RPI design)
 Combination clasp
I bar
Combination clasp
INDIRECT RETAINER
 Function :-
to prevent the DEB from moving away
from its seat because of cheek and
tongue forces, stick food.
Effectiveness of indirect retainer
depends upon:
 Its distance from the
fulcrum line
 Effectiveness of the direct retainer
Direct retainer must be effective if the
indirect retainer is to function when the
denture rotates - otherwise the partial
denture will be dislodged.
 The quality of support of
the indirect retainer
An indirect retainers
effectiveness is
reported to decrease
when it is placed on an
inclined plane because
the tooth moves and the
retainer slips*.
*JPD 1975;34;24-30
 use of a mesial rest instead of a distal
rest on the terminal abutment tooth
does not decrease indirect retention.*
Frank and Nicholls ,JPD ,1977:38;494
 Thus the choice of indirect retainer
location should be made mostly on the
basis of
1. abutment tooth support,
2. a crown form favoring adequate rest
seat preparation, and
3. the patients esthetic desires.
 Removal of the indirect retainers from a
RPD results in the application of more
pressure to the direct abutment teeth.
 The indirect retainer probably is
effective in distributing forces to teeth
other than direct abutments, and in
preventing denture base lifting.
Frechette et al ,JPD, 1956;6:195-212
 Placing rests of DEB RPDs more anteriorly
provides an axis of rotation that directs
applied forces in a more vertical direction.
STRESS BREAKERS/ STRESS
DIRECTORS
 GPT 8- A device or system that relieves
specific dental structures of part or all of
the occlusal forces and redirects those
forces to other bearing structures or
regions
Rationale*
Merrill ,JPD,1968,20,204
 Concept of stress breaking—insists on
separating the action of the retaining
elements from the movement of the
denture base by allowing independent
movement of the denture base( or its
supporting frame work) and the direct
retainers
2 types
 HINGE DESIGN
 ROTATIONAL TYPE:
Hinge design
 Base is permitted to move in a vertical
plane only. The hinge type device
spares the tooth virtually all of the stress
which results from vertical movement of
the base, but it is still subjected to all
the lateral loads and torsional stress.
D-E hinge type
Baca design
Rotational type:
 Works on the ball and socket principle,
movements of the base is allowed in all
planes, and the tooth is relieved of
virtually all stresses.
 DALBO
 CRISMANI
 ASC -52
DALBO
SPLIT BAR MAJOR CONNECTOR
 Henderson and
Steffel suggested a
split lingual bar to
redirect the force on
the abutment tooth
INDICATION
 Because the stress breaker does, in far
relieve the abutment tooth of the forces
generated by the masticatory load, the
stress is then borne by the residual
ridge. Therefore a prime indication for
the application of this principle would be
the mouth where in an abutment tooth is
inherently weak.
ADVANTAGES
 Horizontal forces acting on the
abutment teeth are minimized.
 If rebasing is not undertaken when
required, the abutment tooth is not
necessarily damaged.
DISADVANTAGE
 Appliance is difficult to construct.
 There is concentration of forces on
edentulous alveolus, resulting in its
speedier resorption.
 More complicated appliance is some times
not tolerated by patient. Spaces between
components are sometimes opened up in
function, thus trapping food and tongue.
 Can be bent and distorted easily in cleaning
or as a result of a accident can induce a
continuous stress on abutments.
 Repair is difficult.