Hi….good afternoon….
DISTAL EXTENSION BASE REMOVABLE
PARTIAL DENTURE
FACTORS INFLUENCING SUPPORT OF DISTAL
EXTENSION BASE
1) Contour and quality of residual ridgeit should be high and well rounded.
2) Quality of soft tissue covering edentulous ridge
The more displaceable tissue present over the
residual ridge the less support for the denture
base can be derived from that ridge.
A firm, tightly attached mucosa, several mm thick
offers greatest support.
3) Amount of tissue coverage of
denture base
The denture base must cover the
maximum amount of surface area of
edentulous ridge. The broader the
coveragegreater will be the
distribution of the load per unit
area.
4) Amount of occlusal force
The amount of occlusal force applied to the denture base on a distal
extension ridge influences the amount of support required to
stabilize that denture base.
A denture base that is opposed by a full complement of natural teeth
requires more support than a denture base opposed by a complete
denture.
•Maximum coverage
•Narrowing of food table
•Increased efficiency of occlusal surface of artificial
teeth.
5) Denture bearing area
The majority of forces must be
directed to portions of the ridge that
are most capable of withstanding
that force.
6) Accuracy of the fit of denture base
7) Type and accuracy of imp. Registration
residual ridge has 2 forms:
1)anatomic form
2)functional form
Any method, whether it records the
functional relationship of the residual
ridge to the remainder of the arch, or the
functional form of the ridge itself, may
provide acceptable support for the
partial denture.
Whereas if anatomic ridge form is used
for the partial denture there will be a
cantilever action of the denture base
against the abutment teeth.
8) Design of partial denture
RPD be designed so that there may be minimum
movement of denture base and minimum
trauma to the remaining teeth and underlying
bone.
THE PROBLEM OF FREE END DENTURE
BASE
Free end RPD can cause harm in two
ways:
Direct effect
Indirect effect
Direction of movement can be
divided into 3 forms:
i) Movement away from the teeth and
tissues
ii) Movement towards the teeth and
tissues
iii) Movement in horizontal plane
FRAMEWORK DESIGNING
OCCLUSAL REST
Moves the point of rotation anteriorly
Transmits forces in a more vertical direction
DIRECT RETAINER
In addition to flexing during insertion and removal,
the clasp arms in a distal ext. have additional
functions of flexing when the rpd sinks towards the
tissues thus preventing ortho. forces on the
abutment.
But – clasp can not effectively dissipate this
stress because:
i) Material itself can have only limited
flexibility .
ii) 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.
Clasps currently used for DEB RPDs
1. Bar clasps:
2. Combination clasp:
Combination clasp utilizing a distal rest for DEB
RPD is claimed to have a stress breaking action.
INDIRECT RETAINER
Function: to prevent the DEB from moving away
from its seat because of cheek and tongue
forces, stick food.
Thankuuuuuu…..
Have a soooper weekend……