Stress Breakers in Removable Partial Dentures
Class I, Class II And Class IV Are Greater Subjected to
Stresses Than Class
III
because support for a
prosthesis must be derived from both
teeth
and
soft
tissue. Soft tissue being compressible, vertical and
horizontal movements permits rotational
Definition
• A stress breaker is a device that allows
some movement
between the denture base or its supporting framework and the
direct retainers [whether they are intracoronal or
extracoronal]
• Or may be defined are those elements of a partial denture
which are interposed in a connector system in order to
introduce a
controlled
and intentional degree of
flexibility
into
the structure.
•
Stress equalizer
is an
integral
part of a partial
denture that will enable the operator to
limit
the
movements between the clasps on the abutment
teeth and the free end saddle to such a degree that
the movement will be within the
physiologic
tolerance
of the underlying tissues and equalize the stress
between the abutment teeth and edentulous area.
Types of
stresses
created on the abutment teeth In
general there are three types of stresses on the
abutment teeth
•
Vertical
•
Lateral
• Oblique/anteroposterior
Thus
vertical stress
results from a lack of distal tooth
support.
lateral stress
results from a horizontal movement of
the denture.
anteroposterior stress
is a result of a combination of
the first two. In all types of stress, the
abutment
becomes the
fulcrum
. To control these stresses and to
distribute them between mucosa and the adjacent
teeth requires a careful consideration of:
1] The
condition
of the
teeth
and
mucosa
2] The
impression
techniques
3] The denture design
4] The distribution of stress between the mucosa and
as many supporting teeth as possible
Aims of stress breaking
• To direct occlusal forces in the
long
axis
of the abutment teeth.
• To prevent
harmful
loads being applied
to the remaining natural teeth.
• To
share
load as evenly as possible
between the natural teeth and saddle
areas according to the ability of these
different tissues to accept the loads.
• To ensure that part of the
load
applied to
the saddle area is distributed as evenly as
possible over the
whole
mucosal
surface.
• To provide greater
comfort
to the
patient.
Guidelines for stress breaker To decide whether to use
a stress breaker or a rigid design
Rule 1:
If the teeth are
strong
and the ridge is
poor
flat, knife edged, or narrow- use a rigid design.
Rule 2
: If the teeth are weak e. g. , loss of supporting
tissues so the mobility is plus or more and the
ridge
is
strong
, use a stress breaker.
Classification Stress breakers can be classified
according to their mode of action:
•
Type 1
Those utilizing a hinge or moveable joint.
( moveable joint between direct retainer and the
denture base )
•
Type 2
Those utilizing flexible connection.
Type 1 Stress breakers
• These can be used in association with either precision
attachments or clasp units as tooth bearing direct retainers. In
this group fall the hinges,
sleeves
and
cylinders
, and
ball
and
socket
devices.
• The hinge is usually of a
rigid
design, the soft tissue absorbs
a minimum of load adjacent to the hinge and a
maximum
of
load toward the
distal
of the ridge. The base is permitted
movement in a vertical plane only.
• An example of this group are the various hinges, the
Swiss made
Dalbo
attachment and the
Crismani
attachment.
• If the device works on a
ball
and
socket
principle,
movement of the base is allowed in all planes and the
tooth is relieved of all stress.
Type 2 Second group include those design having a
flexible
connection between the direct retainer and
the denture base including
wrought
wire connectors,
divided major connectors and other
flexible
devices
for permitting movement of the distal extension base
also included in this group are those using a
movable
joint
between
two
major
connectors.
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e
Various forms which are commonly applied are:
1.
Torsion bars/split bar
major connectors Used in
the design of a lower partial denture carrying
bilateral
free end saddles. Bars extend anteriorly from the
clasp units on each side to
join
a lingual bar near the
midline
. Flexibility can be controlled by varying the
cross section of the torsion bars, the method of
construction (cast or wrought) and the material of
construction (normally
gold
alloys or
cobalt
chromium
alloys).
Disadvantages are
• In a torsion bar structure in
that the double bar system is
liable
to
trap
food and cause
irritation to the tongue.
• Some split connectors used as
stress breakers have been known
to
pinch
the underlying soft
tissues or the tongue as they
open
and
close
under function.
2.
Partial division of connectors
This principle can be
applied in both upper and lower dentures. For
example, in a lower denture, a lingual plate may be
partly divided by an
antero posterior slot
. The upper
portion of the plate is attached to the retainer unit on
the abutment tooth and the lower portion is attached
to the saddle ,a degree of
flexibility
between the
retainer unit and the saddle is so developed.
3. Mesial placement of occlusal rests
This offers the simplest available approach to
stress breaking. The degree of stress
breaking achieved is
though
, much less than
that available where more complex devices
are employed. It may be used in the design of
either upper or lower dentures.
By positioning the rest of the clasp unit on
the
mesial
instead of on the
distal
fossa of
the abutment tooth and by using a minor
connector to link the rest to a major
connector some
flexibility
may be introduced
into the
clasp
unit/saddle
link.
Other types of stress breakers
(12 gauge) chrome wire stress breaker
The advantages
: The extension base moves vertically
immediately and the
resiliency
of the wire quickly returns the
base to its original position The
rigidity
of the 12 gauge wire
avoids overloading the mucosa. The mucosa is also more
evenly loaded. It is easy to splint teeth with this design. The
fabrication is relatively simple.
Repairs
are rarely needed.
Split palate stress breaker
A stress breaker for a maxillary partial
denture is often
not necessary
, has there is
more
alveolar
ridge for support. In case of
Kennedy
class V
, partial denture may be
difficult to design, as the placement of a
rest on the
remaining
weak anterior incisor
is not considered desirable. The molar
would be required to absorb most of the
load of mastication on the left side. In such
cases a split palate stress breaker was
designed.
Advantages
1. Since the horizontal forces acting
on the abutment teeth are
minimized, the
alveolar
support
of
these teeth is
preserved
.
2. By careful choice of the type of
flexible connector, it is possible to
obtain a
balance
of stress between
the abutment teeth and the residual
ridge.
3 Intermittent pressure of the denture
bases
massages
the mucosa, thus
providing
physiologic
stimulation, which
prevents bone resorption and eliminates
the need for relining.
4 If relining is needed but not done, the
abutment
teeth are not
damaged
as
quickly.
5
Splinting
of
weak
teeth by the denture
is made possible despite the
movement
of a distal extension base.
Disadvantages
1.
The
broken
stress denture is usually
more difficult to
fabricate
and therefore
more
costly
.
2.
Vertical
and
horizontal
forces are
concentrated on the residual ridge,
resulting in increased
ridge
resorption.
Many stress breakers designs are not
well stabilized against horizontal forces.
3. If relining is not done when needed,
excessive
resorption
of the
residual
ridge may result if exceed flexibility
limits.
4. The
effectiveness
of
indirect
retainers is
reduced or eliminated altogether.
5. The more
complicated
the prosthesis , the
less it may be tolerated by the patient.
Spaces between components are sometimes
opened up in function,
thus trapping food
.
6. Flexible connectors may be
bent
and
distorted by careless handling. Even a
slightly distorted connector may bring more
stress to bear on the abutment
7.
Repair
and
maintenance
of any stress
breaker is difficult, costly, and frequently
required.
Quadrilateral Configuration
The
quadrilateral configuration is
indicated most often for Class
III
arches particularly when there is a
modification
space on the opposite
side of the arch.
A
retentive
clasp should be
positioned on each abutment tooth
adjacent to the edentulous spaces.
This results in the denture being
confined within the outline of the
four clasps, and
leverage
on the
denture is effectively
neutralized
.
For a Class III arch where
no modification
space
exists, the goal should be to place one clasp as far
posterior
on the dentulous side as possible and one as
far
anterior
as space and esthetics permit. This retains
the quadrilateral concept and is the most effective
way to control
stress
.
Tripod Configuration
Tripod
clasping is used primarily for
Class
II
arches. If there is a
modification
space on the dentulous side, the
teeth
anterior
and
posterior
to the
space are clasped to bring about
the tripod configuration. If a
modification space is not present,
one clasp on the dentulous side of
the arch should be positioned as far
posterior
as possible, and the other,
as far anterior.
Bilateral Configuration In case of
bilateral
distal extension group
class 1
.the single retentive clasp
arm on each side of the arch should
be located near the
centre
of the
dental arch or the denture bearing
area. In the bilateral configuration
the clasps exert
little
neutralizing
effect on the leverage induced
stresses generated by the denture
base.
Removable partial dentures in dentistry encounter various stresses, with Class I, II, and IV being more susceptible than Class III due to the need for support from both teeth and soft tissue. Stress breakers and equalizers play crucial roles in managing and distributing stresses effectively on abutment teeth, ensuring proper function and comfort of the denture.
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Presentation Transcript
Stress Breakers in removable partial denture Class I, Class II And Class IV Are Greater Subjected to Stresses Than Class III because support for a prosthesis must be derived from both teeth and soft tissue. Soft tissue being compressible, vertical and horizontal movements permits rotational
Definition A stress breaker is a device that allows some movement between the denture base or its supporting framework and the direct retainers [whether they are intracoronal or extracoronal] Or may be defined are those elements of a partial denture which are interposed in a connector system in order to introduce a controlled and intentional degree of flexibility into the structure.
Stress equalizer is an integral part of a partial denture that will enable the operator to limit the movements between the clasps on the abutment teeth and the free end saddle to such a degree that the movement will be within the physiologic tolerance of the underlying tissues and equalize the stress between the abutment teeth and edentulous area.
Types of stresses created on the abutment teeth In general there are three types of stresses on the abutment teeth Vertical Lateral Oblique/anteroposterior Thus vertical stress results from a lack of distal tooth support. lateral stress results from a horizontal movement of the denture.
anteroposterior stress is a result of a combination of the first two. In all types of stress, the abutment becomes the fulcrum. To control these stresses and to distribute them between mucosa and the adjacent teeth requires a careful consideration of: 1] The condition of the teeth and mucosa 2] The impression techniques 3] The denture design 4] The distribution of stress between the mucosa and as many supporting teeth as possible
Aims of stress breaking To direct occlusal forces in the long axis of the abutment teeth. To prevent harmful loads being applied to the remaining natural teeth. To share load as evenly as possible between the natural teeth and saddle areas according to the ability of these different tissues to accept the loads. To ensure that part of the load applied to the saddle area is distributed as evenly as possible over the whole mucosal surface. To provide greater comfort to the patient.
Guidelines for stress breaker To decide whether to use a stress breaker or a rigid design Rule 1: If the teeth are strong and the ridge is poor flat, knife edged, or narrow- use a rigid design. Rule 2: If the teeth are weak e. g. , loss of supporting tissues so the mobility is plus or more and the ridge is strong, use a stress breaker.
Classification Stress breakers can be classified according to their mode of action: Type 1 Those utilizing a hinge or moveable joint. ( moveable joint between direct retainer and the denture base ) Type 2 Those utilizing flexible connection.
Type 1 Stress breakers These can be used in association with either precision attachments or clasp units as tooth bearing direct retainers. In this group fall the hinges, sleeves and cylinders, and ball and socket devices. The hinge is usually of a rigid design, the soft tissue absorbs a minimum of load adjacent to the hinge and a maximum of load toward the distal of the ridge. The base is permitted movement in a vertical plane only.
An example of this group are the various hinges, the Swiss made Dalbo attachment and the Crismani attachment. If the device works on a ball and socket principle, movement of the base is allowed in all planes and the tooth is relieved of all stress.
Type 2 Second group include those design having a flexible connection between the direct retainer and the denture base including wrought wire connectors, divided major connectors and other flexible devices for permitting movement of the distal extension base also included in this group are those using a movable joint between two major connectors. sleeve
Various forms which are commonly applied are: 1. Torsion bars/split bar major connectors Used in the design of a lower partial denture carrying bilateral free end saddles. Bars extend anteriorly from the clasp units on each side to join a lingual bar near the midline. Flexibility can be controlled by varying the cross section of the torsion bars, the method of construction (cast or wrought) and the material of construction (normally gold alloys or cobalt chromium alloys).
Disadvantages are In a torsion bar structure in that the double bar system is liable to trap food and cause irritation to the tongue. Some split connectors used as stress breakers have been known to pinch the underlying soft tissues or the tongue as they open and close under function.
2. Partial division of connectors This principle can be applied in both upper and lower dentures. For example, in a lower denture, a lingual plate may be partly divided by an antero posterior slot. The upper portion of the plate is attached to the retainer unit on the abutment tooth and the lower portion is attached to the saddle ,a degree of flexibility between the retainer unit and the saddle is so developed.
3. Mesial placement of occlusal rests This offers the simplest available approach to stress breaking. The degree of stress breaking achieved is though, much less than that available where more complex devices are employed. It may be used in the design of either upper or lower dentures. By positioning the rest of the clasp unit on the mesial instead of on the distal fossa of the abutment tooth and by using a minor connector to link the rest to a major connector some flexibility may be introduced into the clasp unit/saddle link.
Other types of stress breakers (12 gauge) chrome wire stress breaker The advantages : The extension base moves vertically immediately and the resiliency of the wire quickly returns the base to its original position The rigidity of the 12 gauge wire avoids overloading the mucosa. The mucosa is also more evenly loaded. It is easy to splint teeth with this design. The fabrication is relatively simple. Repairs are rarely needed.
Split palate stress breaker A stress breaker for a maxillary partial denture is often not necessary, has there is more alveolar ridge for support. In case of Kennedy class V, partial denture may be difficult to design, as the placement of a rest on the remaining weak anterior incisor is not considered desirable. The molar would be required to absorb most of the load of mastication on the left side. In such cases a split palate stress breaker was designed.
Advantages 1. Since the horizontal forces acting on the abutment teeth are minimized, the alveolar support of these teeth is preserved. 2. By careful choice of the type of flexible connector, it is possible to obtain a balance of stress between the abutment teeth and the residual ridge.
3 Intermittent pressure of the denture bases massages the mucosa, thus providing physiologic stimulation, which prevents bone resorption and eliminates the need for relining. 4 If relining is needed but not done, the abutment teeth are not damaged as quickly. 5 Splinting of weak teeth by the denture is made possible despite the movement of a distal extension base.
Disadvantages 1. The broken stress denture is usually more difficult to fabricate and therefore more costly. 2. Vertical and horizontal forces are concentrated on the residual ridge, resulting in increased ridge resorption. Many stress breakers designs are not well stabilized against horizontal forces. 3. If relining is not done when needed, excessive resorption of the residual ridge may result if exceed flexibility limits.
4. The effectiveness of indirect retainers is reduced or eliminated altogether. 5. The more complicated the prosthesis , the less it may be tolerated by the patient. Spaces between components are sometimes opened up in function, thus trapping food. 6. Flexible connectors may be bent and distorted by careless handling. Even a slightly distorted connector may bring more stress to bear on the abutment 7. Repair and maintenance of any stress breaker is difficult, costly, and frequently required.
Quadrilateral Configuration The quadrilateral configuration is indicated most often for Class III arches particularly when there is a modification space on the opposite side of the arch. A retentive clasp should be positioned on each abutment tooth adjacent to the edentulous spaces. This results in the denture being confined within the outline of the four clasps, and leverage on the denture is effectively neutralized.
For a Class III arch where no modification space exists, the goal should be to place one clasp as far posterior on the dentulous side as possible and one as far anterior as space and esthetics permit. This retains the quadrilateral concept and is the most effective way to control stress.
Tripod Configuration Tripod clasping is used primarily for Class II arches. If there is a modification space on the dentulous side, the teeth anterior and posterior to the space are clasped to bring about the tripod configuration. If a modification space is not present, one clasp on the dentulous side of the arch should be positioned as far posterior as possible, and the other, as far anterior.
Bilateral Configuration In case of bilateral distal extension group class 1 .the single retentive clasp arm on each side of the arch should be located near the centre of the dental arch or the denture bearing area. In the bilateral configuration the clasps exert little neutralizing effect on the leverage induced stresses generated by the denture base.
