removable dental prosthesis

1. Minor
connectors
Rests & Rest
seats
Presented by:
Dr. Mujtaba Ashraf
MDS II
Dept of Prosthodontics

2. Contents:
 Minor Connectors
Functions
Form and location
Tissue stops
 Rests and Rest Seats
Role of Rests in Control of Prosthesis Movement
Form of the Occlusal Rest and Rest Seat
Lingual Rests on Canines and Incisor Teeth
Incisal Rests and Rest Seats
2Dr Mujtaba

3. Minor Connectors
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4. Definition
 The connecting link between the major connector or
base of a partial removable dental prosthesis and the
other units of the prosthesis, such as the clasp
assembly, indirect retainers, occlusal rests, or
cingulum rests. –GPT8
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5. Connects components to the major
connector
Direct retainer
Indirect retainer
Denture base
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6. Functions of Minor Connectors
 Unification and rigidity
 Transfers functional stress to the abutment teeth. This is
a prosthesis-to-abutment function of the minor
connector.
 Transfers the effects of the retainers, rests, and
stabilizing components throughout the prosthesis. This
is an abutment- to-prosthesis function of the minor
connector.
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7. Form and location
 Sufficiently bulky to be rigid
 Should be located in the
embrasure
 The deepest part of embrasure
should be blocked
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8.  Should be thickest towards lingual surface and tapering
towards the contact area.
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9. Types of minor connectors
 Minor connectors that
join clasp assemblies
to major connectors
 Minor connectors that
join indirect retainers
or auxiliary rests to
major connectors
-Stewart 9Dr Mujtaba

10.  Minor connectors that join
denture bases to major
connectors
 Minor connectors that
serve as approach arms
for vertical projection or
bar-type clasps
-Stewart
Types of minor connectors
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11. Minor connectors that join clasp
assemblies to major connectors
 Join clasp assemblies to major connectors must be
rigid, because they support the active components of
the removable partial denture, the retentive clasps.
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12. Support the rests, which prevent vertical movement
of a prosthesis toward the underlying tissues.
These minor connectors should be broad
buccolingually, but thin mesiodistally.
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13. A minor connector should be positioned in the
associated lingual embrasure. This results in a
sufficient bulk of metal without encroaching on the
tongue space.
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14. Minor connectors that join indirect retainers
or auxiliary rests to major connectors
These minor connectors
should form right
angles with the
corresponding major
connectors, but
junctions should be
gently curved to
prevent stress
concentration
14Dr Mujtaba

15. Minor connectors that join denture bases to
major connectors
 These minor connectors must be strong enough to
anchor a denture base to the removable partial
denture framework.
 They must be rigid enough to resist fracture and
displacement.
 These components must provide minimal
interference with the arrangement of artificial
teeth.
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16. In maxillary distal extension bases, it must
extent to cover the tuberosity, and
In mandibular distal extension bases it should
extend two-third the length of residual ridges,
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17. Minor connectors that join the denture base to the
major connector may be described as follows
 Open/ Lattice construction
 Mesh construction
 Bead, wire, or nail-head components on a metal
base
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18. Open/ Lattice construction
 Open construction consists of longitudinal and
transverse struts that form a ladder-like network.
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19.  Placement of the longitudinal and transverse struts is
a critical factor in prosthetic tooth arrangement.
 In the mandibular arch, one longitudinal strut should
be positioned buccal to the crest of the ridge and the
other lingual to the ridge crest.
 In the maxillary arch, one longitudinal strut should
be positioned buccal to the ridge crest.
 The border of the major connector generally will act
as the second longitudinal strut.
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20.  Positioning of a longitudinal strut along the crest
of the ridge must be avoided. This not only
interferes with the placement of artificial teeth, but
also leads to the denture base to fracture.
 Transverse struts also must be positioned to
facilitate the placement of artificial teeth.
 Ideally, transverse struts should be designed to
pass between the necks of the artificial teeth. This
aids in tooth arrangement and often results in
improved esthetics.
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21. Advantages of open construction
 Used for multiple teeth replacement
 Provides strongest attachment of acrylic resin
 Facilitates rebasing and relining
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22. Mesh construction
 A mesh minor connector may
be compared to a rigid
metallic screen.
 Channels that pass through
the connector are intended to
permit acrylic resin
penetration.
 This allows resin
encirclement of the minor
connector and mechanical
retention of the denture base.
22Dr Mujtaba

23. Drawback
• During the packing of acrylic resin, increased
pressure is needed to force resin through the small
holes in the minor connector.
• Insufficient packing pressure may result in
inadequate resin penetration and a weak attachment
to the framework.
• Also interfere with the arrangement of prosthetic
teeth.
The smaller the openings in this minor connector, the
weaker the attachment. 23Dr Mujtaba

24. Bead, wire or nail-head construction
Bead, nail-head, or wire components are often used in
conjunction with metal denture bases.
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25. Its is indicated on short-span, tooth supported with well
healed ridges.
The primary advantage of a metal base is related to
improved hygiene and thermal stimulation.
Disadvantages
Include difficulty in adjusting and relining cast metal
bases.
Furthermore, the attachment of resin is relatively weak.
25Dr Mujtaba

26. Tissue stop
 Used in all distal extension partial dentures using
lattice work or mesh retention.
 Provide stability and prevent distortion to framework
during packing of acrylic resin.
 Engage buccal and lingual slopes for stability.
26Dr Mujtaba

27. Made by removing approximately 2 square mm of the
relief wax used to create space beneath the lattice
work or mesh from the point where the posterior end
of minor connector crosses the centre of the ridge.
During waxing this little depression is waxed as a
projection of latticework or mesh.
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28. Relief
Mechanical retention of denture base resin
Allows the acrylic resin to flow under the construction
Relief wax is placed in the edentulous areas of 1 mm
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29. Finish Lines
The planned junction of different materials. (GPT-8)
In RPDs it denotes the junction of acrylic resin denture
bas and metal major connector.
Internal
External
If they are located on the outer surfaces of major
connectors, they are called external finish lines.
If they are positioned on the inner or tissue
surfaces, they are termed internal finish lines.
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30. Internal finish lines are formed as a result of relief
wax placed on the edentulous ridges of a master cast
prior to duplication.
The relief wax (24 to 26 gauge) creates an elevated
area on the resultant refractory cast.
The margins of the relief wax establish internal finish
lines in the completed metal framework. The margins
of the relief wax should be sharp and well defined.
30Dr Mujtaba

31. External finish lines also must be sharp and should be
slightly undercut to help lock the acrylic resin to the
major connector.
The internal angle formed at the junction of the major
or and minor connectors should be less than 90
degrees.
31Dr Mujtaba

32. When viewed from an occlusal
perspective, the external finish
line should follow an arc
established by the lingual surfaces
of the remaining teeth.
This permits the development of
contours that are not irritating to
the patient.
The contour of the external finish line should be
consistent with the contours of the major connector.
Transition from the external finish line to a denture base
should be smooth and flowing.
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33. Approach Arm Minor connector
 This serves as an approach arm for a bar clasp,
supports a direct retainer and engages an undercut from
the gingival margin.
 Only minor connector that is not required to be rigid.
 Should be smooth, even and taper from its origin to its
terminus.
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34. Rests and Rest Seats
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35. Definition
 Rest: A rigid extension of a fixed or removable dental
prosthesis that prevents movement toward the mucosa
and transmits functional forces to the teeth or dental
implant. GPT-8
 The components of a removable partial denture that
transfer forces down the long axes of the abutment teeth
are called rests. -Stewart
 Rest seat: The prepared recess in a tooth or restoration
created to receive the occlusal, incisal, cingulum or
lingual rest. GPT-8
35Dr Mujtaba

36. Functions
 Support: Prevent movement of prosthesis toward the
tissues.
 Force transfer: To direct the forces of mastication
parallel to the long axis of the abutment tooth.
Occlusal rests and rest seats, Albert Seiden, JPD 1958
36Dr Mujtaba

37.  To act as a stop, preventing injury and over
displacement of the soft tissues under partial denture
bases.
 To maintain the clasp, which is usually attached to the
occlusal rest, in its properly surveyed position.
 To function as an indirect retainer in a free-end denture
base partial denture.
Occlusal rests and rest seats, Albert Seiden, JPD 1958
37Dr Mujtaba

38. Functions
 To help maintain the partial denture in position. This is
done when the rests contact or occlude with opposing
teeth during mastication and deglutition.
 To transmit to the abutment teeth some of the lateral
forces applied to the partial denture during mastication.
 To prevent impaction of food between the clasp and the
proximal surface of the abutment tooth.
Occlusal rests and rest seats, Albert Seiden, JPD 195838Dr Mujtaba

39. Functions
 To close a small space between teeth by bridging that
space with occlusal rests.
 To build up an abutment tooth with a large occlusal
onlay rest. This is necessary if there has been a loss of
occlusal contact due to the drifting of teeth
 To act as a rigid reciprocal arm of a retaining clasp.
This function is most pronounced when the rest is set
into a tapered box-lock seat in a gold crown or inlay.
 To prevent extrusion, of abutment teeth.
Occlusal rests and rest seats, Albert Seiden, JPD 1958
39Dr Mujtaba

40. Classification
Based on Relation to Direct Retainer
 Primary rests
 Secondary rests
Based on Area of Placement
 Occlusal rests
 Lingual or cingulum rests
 Incisal rests
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41. Primary rest
 A rest that is part of a retentive clasp assembly is referred to as a
primary rest.
 Prevent vertical movement of a prosthesis toward the tissues and also
help transmit applied forces to the supporting teeth.
 Should be shallow and saucer shaped, and should function as ball-
and-socket joint. This geometry permits dissipation of potentially
harmful lateral forces.
41Dr Mujtaba

42. Auxiliary or secondary rests
 A rest that is responsible for additional support or indirect
retention is called an auxiliary rest or secondary rest.
 Are used as indirect retainers in extension base removable partial
dentures (Class I, Class II, and long-span Class IV applications).
 These rests are placed anterior or posterior to the axis of rotation
to prevent the extension bases from lifting away from the
underlying ridges.
42Dr Mujtaba

43. Occlusal rest
A rigid extension of a removable dental prosthesis that
contacts the occlusal surface of a tooth or restoration,
the occlusal surface of which may have been prepared
to receive it. –GPT8
43Dr Mujtaba

44. Form of the Occlusal Rest
and Rest Seat
 The outline form of an occlusal rest seat should
be a rounded triangular shape with the apex
toward the center of the occlusal surface.
44Dr Mujtaba

45.  It should be as long as it is wide, and the base of the
triangular shape (at the marginal ridge) should be at
least 2.5 mm for both molars and premolars.
 Rest seats of smaller dimensions do not provide an
adequate bulk of metal for rests, especially if the rest
is contoured to restore the occlusal morphology of
the abutment tooth.
45Dr Mujtaba

46. The marginal ridge of the abutment tooth at the site
of the rest seat must be lowered to permit a
sufficient bulk of metal for strength and rigidity of
the rest and the minor connector. This means that a
reduction of the marginal ridge of approximately
1.5 mm is usually necessary.
46Dr Mujtaba

47. The floor of the occlusal rest seat should be apical
to the marginal ridge and the occlusal surface and
should be concave, or spoon shaped.
Caution should be exercised in preparing a rest seat
to avoid creating sharp edges or line angles in the
preparation.
47Dr Mujtaba

48. The angle formed by the occlusal rest and the vertical
minor connector from which it originates should be
less than 90 degrees. Only in this way can the
occlusal forces be directed along the long axis of the
abutment tooth.
48Dr Mujtaba

49. An angle greater than 90 degrees fails to transmit occlusal
forces along the supporting vertical axis of the abutment tooth.
This also permits slippage of the prosthesis away from the
abutment, which can result in orthodontic-like forces being
applied to an inclined plane on the abutment, with possible
tooth movement.
49Dr Mujtaba

50. An occlusal rest seat should occupy one third to one
half the mesiodistal diameter of the abutment and
approximately one half the buccolingual width of the
tooth measured from cusp tip to cusp tip.
50Dr Mujtaba

51. Lingual or cingulum rests
 A metallic extension of a partial removable dental
prosthesis framework that fits into a prepared
depression within an abutment tooth’s lingual
surface. –GPT8
51Dr Mujtaba

52. Lingual or cingulum rests are used primarily on
maxillary canines. The normal morphology of a
maxillary canine permits preparation of a satisfactory
rest seat with minimal tooth reduction.
52Dr Mujtaba

53. The thickness of enamel on the lingual surface of a
mandibular canine rarely allows a lingual rest to be
used.
Lingual rests on incisors are also rare.
The main indication for their use is missing canines.
In this instance, multiple incisors should receive
lingual rests to distribute the stresses over a number
of teeth because a single incisor seldom offers
adequate support.
53Dr Mujtaba

54. A lingual rest is located closer to the rotational
center of the supporting tooth and does not tend to
tip the tooth.
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55. Form
Outline form of lingual rest is half-moon shaped, making
a smooth curve from one marginal ridge to the other,
crossing the centre of the tooth above the cingulum with
deepest point over the cingulum.
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56. The rest is is V-shaped and has two inclines
Labial incline and lingual incline
Labial incline is parallel to the labial surface of tooth
Lingual incline begins at the top of cingulum and
converges labiogingivally towards centre of the tooth, to
meet the labial incline at the apex of rest seat.
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57. The mesiodistal length of the preparation
should be a minimum of 2.5 to 3 mm,
labiolingual width about 2 mm,
incisal-apical depth a minimum of 1.5 mm.
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58. Round Lingual Rest Seat Form
 Mesial of the canine teeth when typical
cingulum rest contraindicated
 Large restoration
 Lack of clearance with the opposing teeth
 Poor cingulum
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59. Spoon shaped, similar to occlusal rest seat
More difficult due to the incline of the lingual
surface
Easily incorporated into crowns
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60. Lingual rest seats on cast restorations
 When a crown is to be placed on an anterior tooth and
a rest seat is required, the rest seat should be placed in
the wax pattern
The floor of the rest seat is
readily carved to be the most
apical portion of the
preparation. A saddle-like
shape, which provides a
positive rest seat located
favorably in relation to the long
axis of the tooth, is formed.
60Dr Mujtaba

61. The framework of the denture is made to fill out the
continuity of the lingual surface so that the tongue contacts
a smooth surface without the patient being conscious of
bulk or irregularities.
The lingual rest may be placed on the lingual surface of a
cast veneer crown a three-quarter crown, an inlay, a
laminate veneer, a composite restoration.
61Dr Mujtaba

62. Incisal rests
 Incisal rests are placed at the incisal angles of anterior
teeth and on prepared rest seats.
 Less desirable than lingual rests and rest seats for
anterior teeth. Nevertheless, they may be used
successfully if abutments are sound and cast
restorations are not indicated.
62Dr Mujtaba

63. The incisal rest may be used on a canine abutment in
either arch, it is more applicable to the mandibular
canine. This type of rest provides definite support
with relatively little loss of tooth structure and little
display of metal.
Esthetically it is preferable to the three-quarter crown.
63Dr Mujtaba

64. Three views of an incisal rest seat preparation on the
mandibular canine adjacent to a modification space.
The labial view demonstrates inclination of the floor of
the rest seat, which allows forces to be directed along
the long axis of the tooth as nearly as possible.
64Dr Mujtaba

65. The proximal edge of the rest seat is rounded rather than
straight. The lingual view shows that all borders of the rest
seat are rounded to avoid sharp line angles.
It is especially important to avoid a line angle at the
junction of the axial wall of the preparation and the floor
of the rest seat
65Dr Mujtaba

66. Should appear as a small , V-
shaped notch located approximately
1.5 to 2.0 mm from the proximal-
incisal angle of the tooth.
The deepest part of the preparation
should be toward the center of the
tooth mesiodistally.
The notch should be rounded and
should extend slightly onto the
facial surface to provide a positive
seat for the rest. A=2mm
B= 1.5mm
66Dr Mujtaba

67. References
 Stewart’s clinical removable partial prosthodontics, 3rd ed
 McCrackens removable partial prosthodontics, 12th ed
 Removable partial dentures-A Practitioners’ Manual, Olcay
Şakar
 Seidin A. Occlusal rests and rest seats. J Prosthet Dent
1958;8: 431-440.
 Dunny JA, King CIE. Minor connector design for anterior
acrylic resin bases: A preliminary study. J Prosthet Dent
1975;34:496-502.
67Dr Mujtaba

68. 68Dr Mujtaba