The document discusses denture bases and stress breakers. It defines a denture base as the part of a removable partial denture that contacts the oral mucosa and supports the artificial teeth. There are three main types of denture bases: acrylic, metallic, and denture base resin on a metal framework. Stress breakers, also called equilizers, are devices that allow movement between the saddle unit and retainer unit of a partial denture to reduce forces on abutment teeth. The two main types are flexible clasp designs and movable joints between the direct retainer and denture base. Stress breakers help preserve abutment teeth but can be difficult to construct and repair.

1. DENTURE BASE
Dr. Waseem Bahjat Mushtaha
PhD in prosthodontics

2. Definition:
The denture base is that part of the RPD, which contacts the
oral mucosa and in which the artificial teeth are attached.
Requirements for an ideal denture base
1-Accuracy of adaptation to the tissues, with minimal
dimensional changes.
2-Thermal conductivity.
3-Non irritant and can maintain good finish and polish and
easily kept clean.
4-Low specific gravity (light in weight(
5-Sufficiently strong to resist fracture or distortion.
6-Esthetically acceptable.
7-Can be relined.
8-Low coast.

3. Functions:
1-Support artificial teeth and transfer stresses
to the supporting structures.
2-Add to esthetics by reproducing natural
tissue contour.
3-Stimulation of underlying tissues by the
denture movement.
4-Prevent vertical and horizontal migration of
the remaining natural teeth.

4. 5-In addition, the distal extension base has
the following functions:
a-Support; the broad coverage provides the
best support with minimal load per unit
area.
b-Retention; is provided by intimate contact
of the base and palatal plates with the
underlying tissues and by proper molding of
the polished surface.

5. Types of denture bases
I-Acrylic denture base:
Advantages:
1-Low specific gravity.
2-Ease of relining.
3-Good esthetics.
4-Low coast.
5-Ease of fabrication.
Disadvantages:
1-Less accurate fitness and high dimensional changes.
2-No thermal conductivity.
3-Low strength, so it is made more thick and bulky.
4-Law abrasion resistance, so it becomes rough and tend to accumulate
food particles and calcareous deposits.

6. Acrylic denture base

7. 1I- Metallic denture bases:
Indications:
1-For short span tooth borne denture.
2-When there is insufficient vertical space
for use of resin.
3-When there is a deep vertical overlap of
anterior teeth.

8. Metallic denture bases

9. Advantages:
1-Accuracy and dimensional stability.
2-High abrasion resistance.
3-Contributes to the health of the underlying tissues by its
cleanliness.
4-Thermal conductivity may help in patient's acceptance to
the denture.
5-High strength; can be made in thin sections especially
cobalt­chromium and titanium alloys.
Disadvantages:
1-It cannot be relined.
2-Difficult in fabrication.
3-Poor esthetic.
4-Expensive.

10. III- Denture base resin on metal framework
Indication:
l­For extension bases.
2-When denture base resin is needed to
restore anatomic contour and esthetics.
3-When there is a need for relining.
4-For long span tooth supported saddle.

11. Design considerations:
1-The open lattice design with large openings provides the
greatest retention to the resin. The retentive mesh makes
the resin packing more difficult and the bond between the
resin and the metal is weak.
2-A relief should be provided to the metal framework. at the
ridge area to provide a space to allow resin to completely
surround it.
3-The internal and external finish lines should have less than
90" angle to provide mechanical retention for the resin.
4-A metal stop should be used on the extension base
framework for stabilization of the framework during
packing of resin

16. STRESS BREAKERS (EQUILIZERS)
Definition:
It is any device that allows movement
between the saddle unit and the retainer
unit. It is used to reduce the lateral and
tipping forces on the abutment teeth in the
tooth- tissue borne partial dentures

17. Types of stress breakers:
1-Any flexible clasp design
that permits tissueward movement of the extension base with minimal
leverage on the abutment tooth. These clasps include the wrought wire
clasp, the RPI systems, the roach clasp and the C clasp. These types of
clasps are commonly used to equitably distribute the load between the
abutment and the ridge.
2-A more complicated designs include:
a- movable joints:
between the direct retainer and the denture base: This type permits both
vertical movement and hinge movement of the distal extension base.
These movements prevent direct transmission of tipping forces to the
abutment teeth during function. These devices include hinges, sleeves
and cylinders, and ball and socket.
b- A flexible connection:
between the direct retainer and the denture base for example split major
connector

19. movable joints

20. flexible connection

21. Advantages of stress breakers:
1-Preservation of the abutment tooth alveolar
support by minimizing the horizontal force falling
on it.
2-Distribution of the masticatory forces between the
abutment teeth and the residual ridge.
3-Physiologic stimulation of the mucosa by the
intermittent movement of the denture base.
4-If relining was needed but not done; the abutment
teeth are not damaged.

22. Disadvantages:
1-Difficult to construct and expensive.
2-More stresses are falling on the residual ridge
resulting in increase bone resorption.
3-The effect of indirect retainer is reduced.
4-lt may allow food and tissue trap.
5-lt is liable for distortion and fracture.
6-It is difficult to repair.
7-If relining was not done when needed, excessive
resorption of the residual ridge will occur.