Stress breakers /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Role of St r ess
Br eaker s in
r emovable
par t ial dent ur e

Contents
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Introduction
Definition
Types of stresses created on the abutment teeth
Concept
Aims of stress breaking
Guidelines of stress breaking
Classification
Advantages and disadvantages
Factors that influence the magnitude of stress that is transmitted to
the abutment tooth
Design considerations in the control of stress
Precision attachments
Swing lock denture
Review of literature
Summary & conclusion
References

Introduction
Stress may be defined as force per unit area within a
structure subjected to an external force or pressure.
Stress exerted against the teeth and their attachment
apparatuses by occlusal forces may be within the
adaptive capacities of the tissues or else the tissues may
not be capable of compensation and adaptation and the
result is tissue destruction.


Of all partial dentures an all tooth supported or class III
partial denture can best resist forces because it, like the
fixed partial denture, is supported by abutment teeth on
either side of the edentulous space, however there may
be only limited movements and the prosthesis may lift in
function .These movements create stress that need to be
controlled by additional teeth, soft tissues or components
of the denture .

Classes I ,II,IV removable partial dentures are subjected
to

greater

stresses

because

their

support

is

a

combination of tooth and soft tissue. Forces must be
controlled by maximum coverage of soft tissue by proper
use of direct retainers , by placement of the components
in the most advantageous position no matter how the
impression is made there will be more movement when
the prosthesis is supported by soft tissue that is an
extension base.

Various approaches are been made to distribute the
stress or forces acting on a partial denture between the
soft tissue and teeth one among them is stress breaker.
The stress breaker is suggested as a means to allow
the base to move slightly with less strain to the
abutments .


Class I, Class II And Class
IV

Are

Greater

Subjected
Stresses

To
Than

Class III because support
for a prosthesis must be
derived from both teeth and
soft

tissue.

being
permits

Soft

tissue

compressible,
vertical

and

rotational movements.

CLASS III


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] by McCracken
• Stress breakers 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. [Alan A grant and Wesley Johnson]
• Stress breaker is a flexible or a movable joint between
the teeth and the metal framework, so that the denture
base can move independently of the clasp. [Joseph.E.
Grasso]

• 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 .[Herman levitch]


Types of stresses created on the abutment teeth
In general there are three types of stresses on the
abutment teeth
•

Vertical

•

Lateral

•

Oblique/anteroposterior


A fundamental fact is that the periodontal ligament is not
designed by nature to provide a cushioning effect for the
tooth but is a suspensory ligament by means of which
the tooth is suspended in its alveolus thus, the horizontal
stress applied against the tooth will be resisted by fewer
than half of the periodontal membrane fibres, whereas a
vertical stress will be resisted by all of the fibres with the
exception of those at the apex.

The forces that act on the tooth in a direction along its
long axis are transferred by the periodontal ligament to
the bone as tension, which is tolerated quite well. In
contrast to this, the transverse or torsional stresses that
are transmitted to the tooth are transferred to the
periodontal ligament and to the bone as pressure, which
is not well tolerated. Depending on the magnitude and
the duration of the stress, the result may be crushing of
the periodontal ligament, or even necrosis and bone
resorption.

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

Concept
A partial denture base that is unsupported at one end
may move on its displaceable foundation when
masticatory loads are applied, the prospect of this
movement will transmit torsional stress to the
abutment through the direct retainer which may affect
the health and longevity of the abutment tooth.
According to Steiger and boitel the resiliency of the
average tooth under load is 0.1 mm,whereas the
alveolar ridge which is 4 to 20 times as displaceable
as a natural tooth, may be displaced between 0.4 to
2mm.


These have led to the concept that the abutment tooth
should be relieved of this load and that part of this
burden should be placed on the residual ridge. The
transfer of stress is accomplished either by the
employment of specially designed device interposed
between the denture base and the clasps or the frame
work design that permits movement of the base
independently of the clasp .The direction and extend of
the movement that the base

is permitted to make

depends on the design and the construction of the
particular stress breaker device being used.

According to Kennedy a well designed round wire clasp
is itself a stress breaker and allows enough saddle
movement to prevent excessive strain on the abutment
teeth.
The basic requisite for an ideal stress breaker is to
equalize the stress placed on the abutment teeth and
edentulous areas so that the work load for each will
approach their physiologic tolerance.


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.

The

movement may be unrestricted, or it may be controlled within definite limits
by a stop arrangement built into the device. This serves to prevent some
direct transmission of tipping forces to the abutment teeth as the base
moves tissue ward under function. The hinge type of device spares the
tooth from all stresses that results from vertical movement of the base, but
it is still subjected to all the lateral and torsional stresses .

• 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 moveable
joint between two major connectors. These are generally
fabricated by the laboratory with a dual casting technique. The
earliest of such connectors were double lingual bars of wrought
metal, one supporting the clasp and the other components and
the other supporting and connecting the distal extension bases.
These are normally used in association with clasp units as
direct retainers .

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 freeend 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 crosssection 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.

Torsion bar stressbreaker used in a
lower partial
denture.


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 anteroposterior 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.

A lower partial denture
framework

with

partial

division of a lingual plate
to

achieve

breaking.

stress

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 www.indiandentalacademy.com
.

Mesial placement of occlusal rests


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.

Fabrication

A master cast with wax
block outs and reliefs

A 12- gauge wire is
adapted to the
refractory cast

Finished stress breaker

The wire is coated
with die lubricant
and the wax up is
completed

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 weak
lateral incisor is not considered desirable. The left
second 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.

Split palate stress breaker


The amount of movement is tested by seating the casting
in the mouth and creating vertical movement using finger
pressure on the area of the extension base. The isolated
molar is now splinted to the right side by the rigid major
connectors and the use of multiple clasps. During
loading, the denture base will move vertically with equal
force on the soft tissues.

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.

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.

Factors influencing the magnitude of stresses
transmitted to the abutment teeth
The amount of stress that is transmitted to the abutment
tooth, by means of the clasp in a distal extension base
type of partial denture, depends on a number of factors
Length of the span
Longer the edentulous span, the longer will be the
denture base and the greater will be the force
transmitted to the abutment teeth .

Quality of ridge
Large well formed ridges are capable of absorbing
greater amounts of stress than are small, thin, or knife
edged ridges. Broad ridges with parallel sides permit the
use of longer flanges on the denture bases which help
stabilize the denture against lateral forces.
Type of mucosal covering
A healthy mucoperiosteum is capable of bearing a
greater functional load than a thin atrophic mucosa .Soft,
flabby, displaceable tissue contributes little to the vertical
support of the denture and nothing to the lateral stability
of the denture base. This type of tissue allows excessive
movement of the denture, with resultant transmission of
stress to the adjacent abutment tooth .

Clasp as a factor in stress
The type, design and construction

of the partial

denture clasp can greatly affect the severity of the
stress that is transmitted to the abutment tooth.
Type of clasp
The more flexible the retentive arm of the clasp, the
less stress is transmitted to the abutment tooth. A
flexible clasp arm contributes less resistance to the
more destructive horizontal stresses.

As the flexibility of the clasp increases both the lateral
and vertical stress transmitted to the residual ridge
increase. If the periodontal support of the abutment is
good, a less flexible clasp such as a vertical projection
clasp would be indicated because the tooth would
more likely be able to withstand a greater amount of
stress. If the periodontal support has been has been
weakened, a more flexible clasp with a wrought wire
retentive arm should be used so that the residual ridge
would share more of the resistance to horizontal forces
acting on the partial denture.

Clasp design
•

A clasp that is designed so that it is passive when it is
completely seated on the abutment tooth will exert less
stress on the tooth than one that is not passive.

• Only when the framework is completely seated will the
retentive clasp arms be passive.
• During insertion or removal of the prosthesis the
reciprocal arm contacts the tooth before the retentive tip
passes over the greatest bulge of the abutment tooth.
This will stabilize or neutralize the stress to which the
abutment tooth is subjected as the retentive terminal
passes over the greatest bulge of the tooth.

Length of clasp
Flexibility can be increased by lengthening the clasp.
Doubling the length of the clasp will increase its flexibility
five times. Clasp length may be increased by using a
curved rather than a straight course on an abutment
tooth.
Material used in clasp construction
A clasp made of chromium-cobalt alloy exerts more
stress on the abutment tooth than with a gold clasp .A
retentive clasp arm made of wrought alloy is more
resilient than one made of cast alloy and thus will
transmit less stress to the abutment.

Amount of clasp surface in contact with the tooth
The greater tooth to metal contact between the clasp
and the tooth, the more will be the stress exerted on the
tooth.
Type of abutment tooth surface
A gold surface offers more frictional resistance to
movement of the clasp than will enamel, thus more
stress will be exerted against the tooth that has been
restored with a gold casting

Occlusal harmony
A disharmonious occlusion ,one in which deflective
occlusion contacts between opposing teeth are present
generates horizontal forces that ,when magnified by the
factor of

leverage can transmit destructive forces to

both the abutment teeth and the residual ridges .The
type of opposing occlusion can play a

role in

determining the amt of stress generated by occlusion .

A partial denture constructed to oppose a complete
denture will be subjected to much less occlusal stress
than one opposed by natural dentition .That is because
some individuals with natural teeth can exert a closing
force of 300 pounds per square inch, whereas the
closing force of a person wearing complete denture may
not exceed 30 pounds per square inch.

The area of the denture base against which the occlusal
load is applied influences the amount of stress
transmitted to the abutment teeth and ridge .If the
occlusal load is applied to the base adjacent to the
abutment tooth, there will be less movement of the
denture base and less stress transmission than if the
load is applied at the distal end of the denture base.
Ideally the occlusal load should be applied in the center
of the denture bearing area both anteroposteriorly and
buccolingually.

Design considerations in the control
of stress
No removable partial denture can be designed
or constructed that will not be destructive in the
mouth. However Long term clinical observation
enables the partial denture planner to use a
combination of design and construction
principles that will distribute the functional
stresses equally between the hard and soft
tissues. So that the effect of leverage is
minimized and neither structure is stressed
beyond its physiologic tolerance.

Retention as a method of stress control
The retentive clasp is the element of the partial denture that is
responsible for transmitting most of the destructive forces to the
abutment teeth . A removable partial denture should always be
designed to keep clasp retention to a minimum yet provide
adequate retention to prevent dislodgement of the denture by
unseating forces.
Any retention supplied by units of the prosthesis other than the
clasps has the effect of reducing the amount of retention that
the clasps are required to provide, which in turn diminishes the
stress that must be borne by the abutment teeth.

• Clasp position
Leverages can be controlled entirely by means of clasps,
if there are sufficient abutment teeth and they are
distributed strategically in the dental arch .Usually the
position or the

relation of the retentive clasp to the

height of the contour is more important in retention and
in controlling stress than is the number of clasps .


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.

Quadrilateral Configuration


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.

TRIPOD CONFIGURATION


Bilateral Configuration
In case of bilateral distal extension group 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.


Clasp design as a method of stress control
The conventional circum-ferential
cast clasp originating from a distal
occlusal rest on the terminal
abutment tooth and engaging a
mesiobuccal
retentive
undercut
should not be used on a distal
extension removable partial denture.
The terminal of this clasp reacts to
movement of the denture base
toward the tissue by placing a distal
tipping or torquing forces on the
abutment tooth. This particular force
is the most destructive force a
retentive clasp can exert.

A reverse circlet clasp,
approaching a distobuccal
undercut from mesial
occlusal surface, may be
acceptable for a distal
extension partial denture.
As the denture base
moves towards the tissue,
a retentive clasp tip will
tend to move into an area
of greater undercut .This
action releases torquing
forces that can damage
an abutment tooth.

A bar clasp is used on the
terminal abutment tooth on a
distal extension partial denture
when the retentive undercut is
located on the distobuccal
surface .As the denture base is
loaded toward the tissue, the
retentive tip of the T clasp rotates
gingivally to release the stress
being transmitted to the abutment
tooth the bar clasp does not
produce the wedging force. The
clasp that subjects the abutment
tooth to the least unfavorable
torque is the T clasp with a distal
occlusal rest and a rigid
circumferential
reciprocating
clasp

A combination clasp
When a mesiobuccal undercut exists on an abutment
tooth adjacent to the distal extension edentulous ridge,
the combination clasp can be employed to reduce the
stress transmitted to the abutment tooth. Wrought alloy
wire, by virtue of its internal structure, is more flexible
than a cast clasp. It can flex in any spatial plane,
whereas a cast clasp flexes in the horizontal plane only.
The wrought wire retentive arm has a stress-breaking
action that can absorb torsional stress in both the vertical
and horizontal planes.

Splinting of Abutment Teeth
Adjacent teeth may be splinted by means of crowns to
control stress transmitted to a weak abutment tooth.
Splinting two or more teeth will increase the periodontal
ligament attachment area and distributes the stress over
a larger area of support.
Splinting by means of crowns also has the effect of
stabilizing the abutment teeth in a mesiodistal or
anteroposterior direction. Splinting is also indicated when
the proposed abutment tooth has either a tapered root or
short roots such that there is not an acceptable amount
of periodontal ligament attachment present. The tying
together of two such teeth by crowns will in effect
produce an acceptable multirooted abutment tooth .

Occlusion
A smoothly functioning occlusion that is in harmony with the
movements of both the temporomandibular joints and the
neuromusculature will minimize the stress transferred to the
abutment teeth and residual ridge. The occlusal surfaces of
the artificial teeth can transmit various amounts of stress to
the supporting structures.

A large or broad occlusal surface delivers more
stress than does one that has been reduced in
buccolingual width. The number of teeth being
replaced may also be reduced to decrease the
stress. Steep cuspal inclines on the artificial
teeth should be avoided because they tend to
introduce horizontal forces that can produce
torsional stresses on the abutment teeth.
Artificial posterior teeth should possess sharp
cutting surfaces and sluiceways for the escape
of food between the teeth to be as efficient as
possible and to relieve some of the unnecessary
force in mastication.

Denture Base
The denture base should be designed to cover
as extensive an area of supporting tissue as
possible. The stress created by the partial
denture in function will thus be distributed over
a large area, so no single area will be
subjected to stress beyond its physiologic limit.
The denture base flanges should be made as
long as possible to help stabilize the denture
against horizontal movements.

The distal extension denture bases must always
extend onto the retromolar pad area of the
mandible and cover the entire tuberosity in the
maxilla.
Equal care must be taken not to overextend the
borders of the denture base. Interference with
the functional movements of the surrounding
tissues by an overextension will produce and
transmit significant stresses to the remaining
teeth.


The more accurate the adaptation of the
denture base to the residual ridge, the
better will be the retention, in part because
of the forces of adhesion and cohesion.
There will be fewer tendencies for the
denture base to move in function, and as
a result less stress will be transmitted to
the abutment teeth.

The type of impression used to record the
mucoperiosteum of the residual ridge will influence the
amount of stress on the residual ridge and the abutment
tooth. If the ridge is recorded in its functional state rather
than its resting form when the denture base is actually
subjected to occlusal loading, the tissue wouldn't be
displaced to any great extent. The magnitude of the
stress transmitted to the abutment teeth would be
minimal.

The contours of the polished surface of the
denture base need to be developed in order to
assist in retention of the denture. If done
properly, this will reduce movement of the partial
denture

and

thereby

decrease

the

stress

transferred to the abutment teeth and supporting
tissues.

Major Connector
In the mandibular arch the lingual plate major connector that is
properly supported by rests can aid in the distribution of functional
stresses to the remaining teeth. It is particularly effective in
supporting periodontally weakened anterior teeth.
The lingual plate also adds rigidity to the major connector. The
added rigidity contributes to the effectiveness of cross-arch
stabilization. Stresses created on one side of the arch are
transmitted through the major connector to the teeth on the opposite
side, thus reducing the stress applied to any single portion of the
arch.

In the maxillary arch the use of a broad palatal major
connector that contacts several of the remaining natural
teeth through lingual plating can distribute stress over a
large area.
• The hard palate often provides a valuable area for
support. A maxillary major connector that uses maximum
coverage of this area can contribute greatly to the
support, stability, and retention of the prosthesis. This in
turn substantially reduces the stress that ordinarily would
be transferred to the abutment teeth.

Rests
• Properly prepared rest seats help control stress
by directing forces transmitted to abutment teeth
down the long axis of those teeth. The
periodontal ligament is capable of withstanding
vertical forces of far greater magnitude than
horizontal or torsional forces
• In all Class I and II partial dentures the rest seat
preparation must be saucer-shaped, completely
devoid of any sharp angles or ledges.

• As forces are applied to the partial denture, the
rest must be free to move within the rest seat to
release stresses that would otherwise be
transferred to the tooth. This movement of the
rest within the rest seat is similar to the action of
a ball-and-socket joint. If ledges or walls are
developed in the rest seat, the releasing action
cannot take place and undesirable forces are
concentrated on the abutment tooth.
• The number of abutment teeth influences the
amount of force each tooth must absorb. The
more teeth that bear rest seats, the less will be
the stress placed on each individual tooth.

Precision attachment
Introduction
The precision attachment is a special type of
direct retainer used in partial denture
construction. It consists of a closely fitting
key/keyway mechanism, one part of which is
attached to the abutment tooth and the other to
the metal framework.
When the two units are fitted together they
provide direct retention by means of a
combination of friction and spring action.

Frequently used synonyms are
• Internal attachment
• Frictional attachment
• Slotted attachment
• Key/keyway attachment
• Parallel attachment

History
• The principle of modern day precision
attachment was first formulated by
Dr.Herman E.S.Chayes in 1906, the
modifications of which are still in use and
are called the Chayes attachments. There
is a male and a female part having a 'T'
shape in cross section. In the early stages,
the female part was placed within the
abutment tooth and the male one in the
prosthesis.

• Brown suggested a modification to the
Chayes design and this was called the
"Brown Attachment". It had a dumbell
shaped cross section.
• Bayler suggested another modification
where the male component was having a
dove tail like preparation which was
tapering.

In 1960, Schatzmann introduced an
attachment where retention was enhanced
by a spring loaded plunger, in the male
unit engaging a slot in the female unit.
Some of the attachments that has come to
the market recently include:
• Ney – Chayes attachments
• Stern-Goldsmith attachments
• Baker’s attachments

Precision and Semi precision Attachments
Precision attachments may be prefabricated by
a manufacturer or they may be fabricated in the
dental laboratory. The former is called precision
and the latter semi-precision attachment. The
manufactured type of attachment is made of
precious metal and thus is more precise in
construction than is the typical laboratory
fabricated attachment. The male portion most
often takes the shape of a "T" or "H," which fits
an appropriately shaped slot.

The female attachment is fitted into the restoration in the
tooth either by casting the gold to it or by placing it in a
prepared receptacle in the restoration and by attaching
the two together with solder .
The semi precision attachment is also referred to as the
"precision rest," the "milled rest," or the "internal rest."
This type of retainer takes the form of a dovetail-shaped
keyway built into the proximal surface of a wax pattern
of a gold crown. The stud or male portion is then made
as an integral partwww.indiandentalacademy.com
of the metal framework.

Advantages
• They can provide excellent transfer of vertical and
horizontal loads from the denture saddles to the
abutment teeth on which they are placed.
• The precision
attachment is less stressful to the
abutment tooth than is the conventional clasp. The
reason is that it is located deep within the confines of
the tooth, all stress is directed along the long axis of the
tooth, thus being resisted by virtually all of the fibers of
the periodontal ligament. Stress directed in this manner
is concentrated nearer to the center of rotation of the
tooth than is the case with a conventional clasp.

• When four strategically located teeth (in all four
quadrants of the mouth) are available, it must be
conceded that masticatory stresses are almost
ideally controlled with precision attachments.
• Good aesthetics are obtainable, with no clasp
arms being visible, for instance.
• They may be more hygienic, with minimal
external components present to trap food and
accumulate plaque.
• They are generally well tolerated by patients &
as their form normally avoids irritation of the
tongue, lips or cheeks.

Disadvantages
• Their application is usually much more time
consuming in both the clinical and laboratory
areas. In addition, the intrinsic cost of many of
the attachments is high. Thus their use may
need to be limited by economic considerations.
• Placement of an attachment on an abutment
tooth may necessitate the removal of a
considerable amount of sound tooth substance.


• Special problems can arise where a precision
attachment is to be used to provide retention of a freeend saddle. If an attachment is used which provides a
rigid link between the saddle and the abutment tooth,
then destructive overload of the periodontal attachment
of the abutment tooth can occur. Instead, it is usually
recommended that an attachment of a more complex
(and hence expensive) type should be used which
provides some form of flexible link between the saddle
and the abutment tooth, as well as providing direct
retention. Attachments of this type are referred to as
stress-broken attachments.

Limitations of the Precision Type
of Attachment
• precision

type

of

attachment

will

not

be

successful when used with the tooth that has
either a short or a very small crown.
• Another factor limiting the use of the precision
device is the size of the pulp, because of the
danger of encroachment on this sensitive organ.

Classification
(Alan A grant , Wesley)
A primary classification of precision attachments
based on the site of attachment to the
abutment tooth:
• Class 1 - Coronal attachments
• Class 2 - Root-face attachments

• For Class 1, sub-classification may be
made on the basis of the site at which
retention is achieved:
Class IA - Extra-coronal attachments
Class IB - Intra-coronal attachments
• Class 2, sub-classification may be made
on form of the attachment:
Class 2A - Stud type
Class 2B - Bar type

Classification [G.E.Ray]
•
•
•
•
•
•

Intracoronal
Extracoronal
Conjunctors
Anchors
Bars
Accessory components

Classification according to rigid or
movable articulations [G.E.Ray]
• Rigid articulations
Group I: Attachments used principally with
vital teeth
Group II: Anchorage used principally with pulp
less teeth
• Movable articulations
Group I: Conjunctors used principally with vital
teeth
Group II: Conjunctors used principally with
pulpless teeth

• Extracoronal attachments
The retentive element lies external to the crown of the
abutment tooth. The extra coronal type of retainer often
has built into a movable joint of one type or another (a
stress breaker) that permits the base to move
independently of the retainer.
Three Groups Of Extra Coronal Precision Attachments:
1.Those attachments that project from the crown of a
tooth to which prosthesis is attached. E.g.Dalbo-669.
The advantage is that, there is minimal preparation of the
abutment tooth. Also where there is insufficient bucco
lingual width.
disadvantage - It may cause gingival irritation.

2.Connecting Rotating Attachment:
These do not anchor a prosthesis to the tooth as such,
they merely provide a joint which may allow some
movement between abutment tooth and denture.
e.g.: Steiger and Boitel rotation joint
3.Combined Units:
These consist of a hinge type of connecting element
outside the tooth which is joined directly to an
attachment.
e.g : Crismani combined unit [spring controlled]
stern stress breaking unit [simple hinge]

Intracoronal attachments
These are generally much more complicated in form than
the extra-coronal attachments. The female unit of the
attachment is set within an abutment inlay or crown and
presents a dovetailed slot. The male unit is attached to
the denture saddle. When the two units slide into each
other they provide frictional grip retention, which may be
augmented in some types by a spring action.
These are of two types:
•

Retention by friction

•

Retention enhanced by mechanical lock

Types Of Intracoronal Attachments
• Earlier designs introduced by Chayes had
'T' shaped flanges. Later 'H' shaped
flanges came to the market. These
flanges help increase the frictional surface
area and hence the bracing action and
retention.

Retention

is

adjusted

by

opening the base of the male unit with a
special instrument.

Factors To Be Considered Before Choosing
Intracoronal attachment designs:
• Bulk - A retentive device requiring a large female
element is not a good indicator for intracoronal
attachment.
• Adjustment- Adjustment for compensating the
large frictional wear should be simple and
straight forward and there should be easy
access.

• Breakage - A sturdy attachment should be
selected. The springs if present, should be
protected from food impaction.
• Provision For Trimming The Attachment - It may
be necessary to shorten an attachment to
accommodate it within the tooth. If it engages
near the occlusal surface, it will be damaged as
soon as attachment is shortened .

Application Of Intra-coronal Attachment
1. R.P.D Retainers:to retain bilateral bound
saddle and free end saddle partial denture.
Unilateral bound saddle denture
2.

Connectors:Sections of a fixed prothesis may
be

joined

in

groups

by

intracoronal

attachments. In case of long space edentulous
cases, it also provides stress breakage.

3 Free end Saddle Removable Partial Denture:
Precision attachment may be the choice of
attachment

in

such

attachment

should

situations.
be

selected

A

strong
as

the

attachments used here are subjected to
considerable forces.

Ball and socket /stud type attachment
• As a preliminary to the use of such attachments,
root treatment of the abutment tooth is carried
out and the crown is cut off near to the level of
the gingival margin. They are particularly
indicated for use where the periodontal status of
the root is adequate but the condition of the
crown is judged to be unsuitable to allow
placement of a coronal attachment. A cast metal
post and diaphragm are prepared for the root,
the diaphragm offering retention for the base
unit of the stud .

BALL AND SOCKET /STUD TYPE ATTACHMENT


The male unit is attached to the root face
diaphragm and carries a ball-shaped head. The
female unit is placed within the denture saddle
and has a hemi-spherical cavity to provide
frictional fit on the ball head of the male unit.
Vertical slits in the female unit allow a degree of
flexibility and provide grip action as the two
units are fitted together. These are used in a
nearly edentulous conditions where only 2 or 3
teeth are remaining. e.g. 1) Gerber
attachment2) Dalbo system3) Rothermann
attachment
Adjustments for wear is done either by
unscrewing or compressing the sleeves.

Bar type attachments.
As in the use of attachments of the Class 2A
type, abutment teeth are root filled and the
crowns removed near to gingival level. Posts
and diaphragms are again prepared. The
attachment takes the form of a bar which
extends between and is attached to each of two
diaphragms.
eg., dolbar bar

Swing lock denture
The term swing lock describes a special design of
partial denture which can be used in any situation in
the mouth but is particularly useful where there has
been loss of a considerable number of teeth. The
appliance is designed with a rigid lingual or palatal
plate connector to which is attached, by means of a
hinge, a labial or buccal bar. This bar is placed in the
sulcus and has struts or fingers, extending to contact
the labial or buccal surfaces of the natural teeth below
the survey line, so providing retention.

Swing lock denture


The labial bar or acrylic veneer is designed to
move on its hinge in the manner of a gate. The
denture is inserted with the 'gate' open and
when it is closed, it is fastened to the main
framework by means of a latch or lock
positioned on the opposite side of the arch from
the hinge.

The principle behind this type of denture is that it
allows wide distribution of stress during function
to all the remaining teeth and residual ridges
rather than to just a few abutments. When the
appliance is inserted and locked into position,
the enclosed natural teeth are held rigidly in
fixed position. This acts as a splinting or
stabilizing action on these teeth which may have
a poor periodontal condition. The splinting,
therefore, spreads the applied stress allowing it
to be shaped and also resists tipping and
rotation of the appliance.

This denture is, therefore, suitable for use in
compromised clinical situations and particularly
useful where only a few teeth remain and load
distribution may be a problem due to mobility or
inadequate periodontal support .

Review of literature
Meyer 1936 stated that in the act of mastication,
the denture is forced against tissues without any
apparent stress on the supporting teeth. When
the pressure on the teeth has been relieved the
stress breakers automatically allow the denture
to re-assume its rest position in relation to the
tissues. This connective pressure followed by
relaxation, massages the gum tissues and
should tend to keep them in a healthier
condition.

Van Hinden(1943)suggested in his article
that we must see that the abutments shall
bear only the vertical and lateral stresses
that properly should fall on them during
mastication. As a result of the equitable
distribution of the masticatory stress over
the entire alveolar ridge the need of
rebasing is reduced.

NEUROHR (1944) FAVOURS STRESS BREAKING BY
STATING

THAT

IT

IS

A

MISTAKE

TO

TAKE

IMPRESSIONS OF THE SADDLE AREAS UNDER
PRESSURE . When such sustained pressure is
incorporated in a applaince, we invite periodontal lesions
and abnormal recession of the alveolar process
.impressions should be taken without pressure with the
tissue in a passive state. The restoration should be
designed such that the masticatory forces are distributed
evenly over the largest area possible

Capt. Arthur R.Frechette (1951) divided stress
distribution in partial denture under three
headings of bracing, support and retention. He
advocated the use of rigid connectors whereby,
force imparted to any point on the denture is
transmitted through out the appliance and
delivered to all the teeth and the edentulous
ridges. For poor ridges with weak teeth, it is
imperative to obtain optimum ridge coverage
and to utilize additional teeth for bracing. When
extensive saddles are used with rigid connection
and properly selected clasps, effective bracing is
obtained, torque is reduced and horizontal
forces are controlled.

• Luzerne G.Jordan, (1952) in his article on designing
RPD, wrote about stress breakers designed with the
primary purpose to decrease the occlusal load on the
abutment and thus divert it to the mucosa. He wrote that
their application should be to those who have only a few
teeth remaining in the arch for such cases where it is
considered absolutely essential where the edentulous
ridge would offer no retention for the complete denture or
for cleft palate patients.

Lamie and Osbourne (1954) in his article on
“Bilateral free end saddle lower dentures”
classified stress breakers as
1. Those that have a movable joint between the
saddle and the direct retainer.
2. Those that have a flexible connection between
the direct retainer and the saddle.
He outlined the advantages and disadvantages of
each type.


George W. Hindels (1957) states that the load as
received by the artificial teeth during mastication
is transmitted through the denture base and the
various parts of the clasps to the contacted
anatomic structures. This resulted in 2 types of
stress.
1.Unaltered stresses – These were stresses which
were transmitted by the partial denture to the
supporting anatomic structures in the same
direction as received.
2. Altered stresses – These were altered in
magnitude and direction by the contacts
established between different parts of the
appliance and the anatomic structures.

E.Hirschtritt (1957) gave a design for partial
dentures with the stress broken basis. He kept
strict differentiation between the tooth and the
tissue bearing areas of the mouth. The tooth
borne unit with its splitting and supporting ability,
protects the teeth against overstress, in spite of
the fact that it receives a fair amount of the
masticatory forces transmitted from extension
bases. The firm but flexible stress breaking bar
keeps the base in a well balanced position.
Therefore, an independent movement of the
base becomes possible and a better protection
of the ridges is achieved.

• Charles V. Caldarone (1957) stated that it is
advantageous to use a precision attachment as retainers
where there is great amount of force and stress, or
where the periodontal condition of the abutment tooth is
questionable.
• R.I.Nairn (1966) in his article on problems of denture
bases states that partial dentures incorporating a stress
breaking feature do attempt to provide a more even
pattern of load distribution on the teeth and the
displaceable soft tissues. There are circumstances
where the preservation of some remaining natural teeth
is of paramount importance and it is here that such
design should be seriously considered.

• Cecconi, Kaiser (1975) did a study to determine
the effect of 2 types of partial dentures stress
beakers on 1.Abutment tooth movement and
2.Ridge displacement. These movements were
measured when stress breakers were both
active and non-active (rigid). They used the pin
dalbo precision attachment stress breaker and
the ticonium hidden lock stress breaker. Results
showed that ridge displacement was significantly
decreased when the dalbo was made rigid and
tooth movement was significantly decreased
when the hidden lock was made rigid.

• P.V.Reitz(1985) studied to determine
whether there was a reduction in stresses
to abutments from loads applied to the
removable partial denture with a
mandibular split lingual bar as major
connector. They concluded that there
were minimal differences in stress
generated by the rigid and the short split
framework. When the split extended to the
midline, the stress on distalextension
abutment was in a more vertical direction
and decreased in magnitude .

• H. Itoh (1998) studied the effects of periodontal
sopport and fixed splinting on load transfer by
removable partial dentures. They came to the
conclusion that under the same load conditions
the highest stresses developed in the model with
the largest osseous defect .increasing the
number of splinted teeth did not provide a
proportional decrease in maximum stress
levels . The more severe the osseous defect, the
greater assistance was provided by splinting to
periodontally sound teeth . This study suggests
that routine cross arch splinting may not be
appropriate.

• Ray S Krug (2003) in his article said that
in case of distal extension R.P.D. a clasp
assembly that creates minimal stress is
desirable . The combination clasp ,which
uses

an

18-gauge

Paladium

based

wrought wire has been used extensively
as a gentle yet retentive clasp assembly
that reduces stress to the abutment tooth .

Summary & Conclusion
All RPD, regardless of the method employed for their support
and retention should restore esthetics and the function of
mastication while contributing to the preservation of the
remaining dentition and its supporting structures.
The decision can be influenced by factors like length of the
saddle, condition of the abutment and their periodontal health,
compressibility of the mucous membrane covering the ridge,
economical consideration. The methods to restore a free end
saddle should attempt to control the load delivered to the teeth
and residual ridges. Many attachments allow a certain degree
of movement between the components, they are known as
“stress breakers”.

Though the stress breaker is a device which would not be
used indiscriminately, it should be used according to the
case with constant recall and monitoring. The patient
should be educated and advised on its maintenance and
importance of periodic check-up visits for the long term
use of the restoration.


Thank you
For more details please visit


Stress breakers /certified fixed orthodontic courses by Indian dental academy

More Related Content

What's hot

Viewers also liked

Similar to Stress breakers /certified fixed orthodontic courses by Indian dental academy

More from Indian dental academy

Recently uploaded

Stress breakers /certified fixed orthodontic courses by Indian dental academy