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1. Stress breakers
device / myth
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

2. Contents
• Introduction
• Biomechanics of removable partial denture
• Definition
• Indications
• Advantages and disadvantages
• Types of stress breaker
• Summary and conclusion
• References

3. Introduction
• One of the most common prosthodontic problem is the
failure of distal extension partial denture
• Main reasons are poor planning, poor treatment and
poor oral hygiene.
• This may be related to the lack of awareness of the
difference between the two mechanism that support the
appliance
• Due to the difference in displacibility . . . .
• In order to reduce these forces on the abutment teeth
stress breakers are introduced in the prosthesis which
will allow the base to move slightly with less strain to the
abutments.

4. Biomechanics of removable partial
denture
• Types of removable partial denture
 Tooth supported partial denture
 Tooth and Tissue supported partial
denture

5. Tooth Borne Removable Partial DentureTooth Borne Removable Partial Denture
-Abutment teeth border all edentulous areas-Abutment teeth border all edentulous areas
-Functional forces are transmitted through-Functional forces are transmitted through
abutment teeth to boneabutment teeth to bone

6. Extension Base Removable Partial DenturesExtension Base Removable Partial Dentures
----Distal extension & anterior extension RPDsDistal extension & anterior extension RPDs
--Functional forces are transmitted through--Functional forces are transmitted through
abutment teeth & mucosa to boneabutment teeth & mucosa to bone

7. Periodontal ligamentPeriodontal ligament
(0.25mm)(0.25mm)
MucosaMucosa
(2.0mm)(2.0mm)
Different Displacement Between PDL & MucosaDifferent Displacement Between PDL & Mucosa

8. Axis of Rotation
- Passes through the rest closest to the extension basePasses through the rest closest to the extension base
edentulous area and the farthest restedentulous area and the farthest rest
- Only exist in extension-base RPDs- Only exist in extension-base RPDs

10. • Mclean has proposed functional impression
technique in which tissues are recorded in there
functional form and then related to the remainder of
the arch with the help of a secondary impression. its
objective is to equalize both tooth and tissue support
and stress distribution over a greater area.
However if a anatomic ridge form of impression is
used for a removable partial denture then serious
consideration should be given for the need of some
mechanical stress breaker to prevent the possible
cantilever action of the distal extension against the
abutment tooth.

11. Definition
• Stress breaker is defined as( GPT8)
“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”

12. Indications
• In an edentulous arch where the abutment tooth is
inherently weak.
• In case in which precision attachment must be
employed for cosmetic reasons in the mandibular
arch with the distal extension base.
Dentures with a stress breaker are also known
as a Broken stress partial dentures or
Articulated prosthesis.

13. Advantages
• Horizontal forces on the abutment tooth is minimized,
Alveolar support of abutment is preserved.
• Stress between abutment teeth and the residual ridge
is balanced.
• Intermittent pressure on denture bases massages the
mucosa, thus providing physiologic stimulation, which
prevents bone resorption and eliminates the need for
relining.
• If the relining is needed and not done, the abutment
teeth are not damaged as quickly.

14. Disadvantages
• Broken stress denture is usually more difficult to
fabricate and therefore more costly.
• Vertical and horizontal forces are concentrated on the
residual ridge, resulting in increased ridge resorption.
• If relining is not done when needed, excessive
resorption of residual ridge may result.
• The more complicated the prosthesis the less it may
be tolerated by the patient.
• The effectiveness of indirect retainer is reduced or
eliminated all together.

15. • Spaces between components are sometimes opened
up in function, thus trapping food and occasionally
the tissues of the mouth.
• Flexible connectors may be bent and distorted by
careless handling.
• Repair and maintenance of any stress breaker is
difficult , costly and frequently required

16. Stress Breakers
• Movable joint between
the denture base and
the direct retainer.
eg: hinges , sleeves and
cylinders and ball and
socket devices
• Flexible connection
between the direct
retainer and the
denture base.
eg: wrought wire
connectors , split major
connectors.

17. 12 guage chrome wire stress breaker
• This design avoids complexities of most stress breaker
designs.
• In this first the master cast is blocked out and relieved
and the refractory cast is poured. Then a 12 guage
wire is adopted to the cast. The wire is coated with die
lubricant and the wax up is completed .the wax must
not go beyond the maximum convexity of the wire. the
wire is removed and the casting is completed.

18. • After the casting the wire is either welded or
soldered to the casting and the struts between the
extension base and the minor connector have been
cut so as to activate the stress breaker.

19. • This design distributes the forces on soft tissues
more favorably than the hinge design.
Advantages
• The extension base move vertically immediately and
the resiliency of the wire quickly returns the base to
its original position.
• The rigidity of 12 guage wire avoids overloading the
mucosa
• It is easy to splint teeth with this design.
• Fabrication is simple and repairs are rarely needed.

20. Split palate stress breaker
Indication
• In Kennedy's class 1 and class 2 situation
• In cases where placement of rest on weak teeth is not
desirable
Fabrication
• The wax up is completed on refractory cast. a sharp
knife is used to cut the split in the wax. damp casting
investment is rubbed into the split and the casting is
completed.

21. • The split will nearly always have small bubbles
these can be corrected with thin diamond discs.

22. • The amount of movement can be tested by seating
the casting in the mouth and creating vertical
movement using finger pressure on the area. The
movement can be increased by lengthening the split
or can be lessened by soldering the split shorter.
Advantages
• The mucosa and the teeth are evenly loaded.
• It is easy to splint the teeth with this design.
• Fabrication is simple and repairs are rarely needed.

23. Philip V Reitz , John L Sanders and
Angelo Caputo in 1984 conducted “a photo
elastic study of a split major connector”
• The purpose of the study was to determine whether
there is reduction in torquing stresses delivered to
abutment teeth from loads applied to removable
partial denture when a split palatal design is used.
• Results have shown that high concentration of stress
patterns was observed on the mesial and distal
surface of the abutment tooth and the heaviest
concentration was on the distal side of the extension
base.

24. • With in split framework a lesser concentration of
stress was observed on the mesial and distal surface
of the abutment teeth while the stress patterns on the
extension base was throughout the ridge except a
small portion distal to the tooth. Thus a significant
amount of stress was removed from the abutment
tooth and transferred to the regions of the extension
base when a split framework is used.

25. Case report
• Female patient
• Age -49
• Teeth absent are
• 14, 15, 16, 17, 24, 25, 26,
27.
• Cuspids have lost approx.
3mm of vertical bone support
with grade 1 mobility.
• Design was made with cast
clasps, complete coverage,
and splits just distal to the
Cuspids .
• Partial denture after 4 years
with plus1 mobility and no
evidence of periodontal
disease

26. Split Bar major connector
• In this design the lingual bar major connector is
splitted from both the sides and kept intact in the mid
region. The upper portion of the bar is connected to
the rest , proximal plate and minor connectors while
the lower part is attached to the distal extension
framework.

27. • So when vertical and diagonal forces are applied to
the tissue supported base, it must pass anteriorly
along lower bar and then back along more rigid
upper bar to reach the abutment tooth. thus tipping
forces that would otherwise transmitted directly to
abutment tooth are supposedly dissipated by
flexibility of lower bar and distance traveled.

28. Philip V Reitz ,Angelo Caputo in 1985 conducted
“photo elastic study on stress distribution by a split
mandibular major connector”
They concluded that there is minimal difference in stress
generated by a the rigid and short split framework, when
the split was extended to midline. The stresses on distal
extension abutment was in a more vertical direction and
decreased in magnitude and stress on edentulous portion
was increased.

29. TICONIUM HIDDEN LOCK DESIGN
This is a two piece casting technique, the top half which
is the major connector supporting the direct retainers
and the rigid components is cast first and the bottom
half which is the connector between the denture base
is cast to the major connector.
The latter is completely independent of the first except
that it is locked in by a circle type retention prepared
in the wax pattern.

30. Stress breakers that have a movable
joint between the direct retainer and
the denture base
• Being placed between the direct retainer and the denture
base ,they may permit both vertical movement and hinge
action of the distal extension base. This serves to prevent
some direct transmission of the tipping forces to the
abutment teeth as the base moves tissue ward under
function
• Hinges allows the prosthesis to rotate around the
horizontal axis and transmit some of the occlusal forces
to the residual alveolar ridge.

31. DSE Hinge
• It is the most commonly used hinge attachment was
introduced in 1953 .
• It uses vertical stop to limit movement of the denture
base away from the tissues it also prevents lateral
movement .

32. Advantages
• Easy to construct
• Durable and economical
• It has been improved recently and the new design is
much smaller with the width of 3mm and vertical
height of 1.5 mm .

33. • Under occlusal loads the clasps or precision
attachment and lingual bar remain stationary and
passive and only the movement is confined to saddle
area.
• But if a saddle is stress broken then it is necessary to
ensure that the arc of movement of the hinge
coincides with the line of the residual ridge, otherwise
when the saddle is depressed, it will tend to swing
across the ridge producing pressure sores.

34. Thompson dowel rest
• A method of anchoring a bilateral distal extension
removable partial denture to crown restoration on
abutment teeth.
• This design is of non locking semi precision rest type and
was introduced in 1949.it provides a stress breaking
action.
• The dowel rest consist of 2
parts
-tapering recess
-Well
And has a rectangular outline

35. • Primary retention is effected from half round recess
on the lingual surface of the restoration at the level of
the shelf.
• Relationship between the rest
and the upper part of the split
major connector
• Parts of the dowel that
are relieved to allow
stress broken
displacement of the
denture base

36. • Indirect retention is effected by contact of the dowel
rest with the distal surface of the well below the shelf
and the upper part of the axial wall of the rest.
• Occlusal force transmission is provided by the base
of the dowel as it rests on the floor of the mouth.

37. Advantages
• Versatility of its design for various shapes and
positions of the terminal abutment teeth
• stress breaking effect which cannot be obtained by
the use of intracoronal retainers.

38. Modifications
• Van dam used a split major connector but did not
use lingual clasp arm mesial to retentive dimple.
• Wands used gold wrought wire lingual arm
emanating from the denture base and terminating in
the retentive recess.
• Blatterfine designed a minor connector on the far
zone .the lingual arm originates from this and extends
distally to retentive recess.

39. Dalbo attachment
• Ball and socket type of joint in which the ball is
cantilevered off the abutment tooth and the
socket is attached to the prosthesis.

40. • The wall of the metal socket has several small slits to
provide a resilient entrance to the socket and offers
some direct retention to the attachment when the
socket engages the ball over its height of contour.
• Limited vertical and
hinge movement of
the denture base is
permitted.

41. • Its action has been expanded with the addition of a spring
within the body of the socket to allow a small amount of
the virtual setting of the removable partial denture beside
the abutment tooth, without this spring the prosthesis will
retain around the horizontal axis and the distal extention
base will not be evenly supported by the edentulous ridge.

42. Disadvantages
• It is big and clumsy.
• If the ball wear out whole prosthesis has to be
made again.

43. • Bert T Cecconi, George Kaiser , Al Rahe in 1975
conducted a study on “stress breaker and removable
partial denture”. The purpose of this invitro study was
to determine the effect of two types of partial denture
stress breakers on abutment tooth movement and
ridge displacement. The movements were measured
when the stress breaker were both active and rigid.
They concluded that :
-during bilateral loading, abutment tooth movement
was significantly greater when the hidden lock stress
breaker was rigid.
-ridge displacement was significantly decreased
when the dalbo stress breaker was made rigid.
-bilateral loading was more favorable than unilateral
loading for all variables analyzed.

44. Crismani attachment
• Slightly different and more elaborate design.
• It consist of a metal block in two parts that rotates
around a fixed axis and rests on a spring that is
contained within a box on the distal surface of the
cast crown. The spring provides axial movement and
the split back allows rotation.

45. ASC-52 attachment
• It is also a ball and socket joint and generally used
for long distal extension bases.
• The mobile portion has a solid attachment to the
abutments without overloading them.
• The female portion is cast to the canine abutment.
the cylinder will be contained within the acrylic resin
base.
• The ball portion fits into the female receptacle and is
movable omni directionally

46. • The cylinders are parallel to the alveolar ridge
bearing area so that occlusal stresses will not cause
torque on the abutments.
• The prosthesis can be easily inserted and removed
without risk to abutments.
• By adjusting the springs tension, increased or
decreased retention can be obtained.
• Any part of it can be replaced at any time.
• it can be used in any case but preferred in bilateral
distal extension cases and in cases where the
abutment teeth are weak.

47. Summary and conclusion
• Whether or not a stress breaker should be used continues to be
controversial. it is not reasonable to expect a 100% success rate for
any biomechanical device. All available designs should be considered
in order to choose the right treatment for the situation.
• Regardless of the design most stress breakers effectively dissipate
vertical stresses which is the purpose for which they are used,
however this is at the expense of the horizontal stability and its
harmful effects (like excessive ridge resorption, tissue impingement
and inefficient mastication) which far outweigh the benefits of vertical
stress breaking. it is the rigid nature of the more conventional partial
denture that allows satisfaction of all requirements of support, stability
and retention without overemphasis on only one principle to the
detriment of the oral tissues.

48. References
• Applegate O.C. : Text book of Removable Partial
Prosthodontics, St. Louis, CV Mosby Co
• Graber G., Haesler V., Weill P. : “Color atlas of dental
medicine RPD”. Vol.2, Medical Publishers Inc., New
York, 1988.
• Dental Clinics of North America: stress breakers – a
practical approach.1979
• G.E.Ray : Precision attachments. Second edition.
• Henderson D., McGivney G.P., Castleberry D.J. :
McCracken’s removable partial prosthodontics, 8th Edn.
St. Louis ; CV Mosby Co

49. • Miller E.L. : “Text book of Removable Partial
Prosthodontics”. St. Louis, CV Mosby Co
• Stewart, Rudd and Kuebker : Clinical removable
Partial Prosthodontics ,2nd
edn, Euro America Inc,
publishers Tokyo, 1997
• Philip V Reitz , John L Sanders and Angelo
Caputo: a photo elastic study of a split major
connector. J. Prosthet. Dent., 1984:51; 19-23

50. • Philip V Reitz , Angelo Caputo: a photo elastic
study of stress distribution by a mandibular split major
connector. J. Prosthet. Dent., 1985:54; 220-225
• Ira D Zinner: semi precision rest system for distal
extension removable partial dentures. J. Prosthet.
Dent., 1979:42;4-11
• Bert T Cecconi, George Kaiser and Al Rahe :stress
breakers and the removable partial dentures. J.
Prosthet. Dent., 1975:34;145-151
• Neil S Mcleod: a theoretical analysis of the
mechanics of the thompson dowel semi precision
intracoronal retainer. J. Prosthet. Dent., 1977:37;19-
27

51. Thank you