Rest and rest seat - Components in CPD

1. Rest and Rest Seat
31 December 2017 1
Presented By:
Dr Divya Toshniwal
III year PG
Dept. of Prosthodontics
RDC, Loni

2. Contents:
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• Introduction
• Definitions/Terminologies
• Types/ Classification
• Functions
• Requirements
• Occlusal Rest and rest seats
- Internal
- Long or continuous
- Ring
- Interproximal
- Extended

3. • Lingual rest and rest seat
• Incisal rest and rest seat
• Review of Literature
• Summary
• Conclusion
• References
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4. • Less than one-half of the fibers in molars and premolars are
available to resist lateral displacement.
• With increase in age, the periodontal membrane is less able to
withstand lateral forces applied to it.
• The use of rest with removable partial denture prostheses has
been developed since rests were first described by Bonwilll in
1899.
31 December 2017
Gerald W. Gaston. Rest Area Preparations For Removable Partial Dentures. J Pros.
Dent.1960 Jan-Feb;10(1):124-34. 4
Introduction

5. The component of removable partial denture that transfer
forces down the long axis of the abutment teeth are called
Rests.
The prepared surface of the teeth in to which rests fit are
called Rest seats.
31 December 2017
Stewart’s. Clinical removable partial prosthodontics in Major Connectors, Minor Connectors,
Rests and Rest Seat. Quintessence Publishing Co, Inc. 4th ed. pp. 43. 5
Definition

6. • Any component of a partial denture on a tooth
surface that provides vertical support is called
rest.
• The prepared surface of an abutment to receive
the rest is called the rest seat.
31 December 2017 Mc Cracken’s Removable partial denture prosthodontics, ed. 12. 6

7. Rest:
A projection or attachment, usually on the side of an object.
A rigid extension of a removable partial denture that contacts the
occlusal, incisal, cingulum, or lingual surface of a tooth or restoration,
the surface of which is commonly prepared to receive it.
Rest seat:
The prepared recess in a tooth or restoration developed to receive the
occlusal, incisal, cingulum, or lingual rest.
31 December 2017 Glossary of Prosthodontic Terms, Edition Nine, J Prosthet Dent 2016 May. 117(5S). 7

8. • According to Stewart:
- Primary rest
- Secondary rest / Auxiliary
• According to Kratochvil on the basis of their location:
- Anterior
- posterior
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Classification

9. • According to surface:
 Occlusal – Mesial
Distal
Interproximal
Extended
Onlay
Rest on restoration
 Incisal
 Cingulum
31 December 2017 Mc Cracken’s Removable partial denture prosthodontics, ed. 12. 9
Classification

10. Functions
(1) To provide resistance against occlusal load
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11. Functions…
(2) To direct forces of mastication parallel to the long
axis of the abutment tooth
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12. Functions…
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(3) To maintain the retentive terminal of the clasp arm
in its intended position

13. Functions…
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(4) To prevent the denture base from seating past its intended
position

14. Functions…
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(5) To give lateral stability against undue horizontal
stresses to the soft tissue of the ridges

15. Functions…
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(6) To deflect food away from the area of contact between
denture and tooth

16. Functions…
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(7) To maintain occlusal contact with opposing teeth

17. Functions…
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(8) To close a small space between teeth bridging that
space with occlusal rests

18. Functions…
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(9) To prevent extrusion of abutment teeth.
(10) To provide indirect retention with auxiliary rests.
(11) To act as a rigid reciprocal arm of a retaining clasp.

19. • Forces that are applied to a removable partial denture must be
transferred to the supporting teeth and tissues in an atraumatic
fashion.
• Rest should be sturdily placed in properly prepared rest seat.
• Rest seat should be within the confines of the greatest tooth
mass-more PDL fibres.
• It should always be in enamel.
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Basic Consideration

20. • Should not be placed on inclined tooth surface.
• No sharp angles, should be round in aspects.
• Minimum 1mm thick.
• No undercuts in the path of insertion.
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Basic Consideration

21. • Outline form : roughly triangular with the base of triangle located
at the marginal ridge and the rounded apex directed towards the
center of the tooth.
• If there is one descriptive phase that can be applied to occlusal
rest it is “ smooth gentle curves”.
31 December 2017 Stewart’s. Clinical removable partial prosthodontics in Major Connectors, Minor Connectors,
Rests and Rest Seat. Quintessence Publishing Co, Inc. 4th ed. pp. 43.
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Occlusal Rest

22. • The shape of the rest seat should follow the outline of
the mesial or distal fossa for the chosen abutment.
• Floor of the occlusal rest seat should be inclined slightly
toward the center of the tooth.
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23. The rest should occupy one-third to one-half the mesiodistal
diameter of the tooth and approximately one-half the buccolingual
width of the tooth measured from cusp tip to cusp tip.
31 December 2017
Stewart’s. Clinical removable partial prosthodontics in Major Connectors, Minor Connectors,
Rests and Rest Seat. Quintessence Publishing Co, Inc. 4th ed. pp. 43.
23

24. • The enclosed angle formed by the line dropped down the
proximal surface and the floor of the rest seat must be < 90
degrees.
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25. 31 December 2017 25

26. • Amalgam rest: not preferred
• Cast restorations: wax pattern
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27. • Rest seats must always be prepared after preparation of
guiding planes.
• Rests seats should be prepared using light pressure
with a high-speed handpiece with or without water spray.
• Preparations are usually entirely in enamel it is best to
avoid local anaesthesia.
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Preparation

28. • When using a round bur, care must be taken to ensure
that mechanical undercuts are not created
/2017
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29. 31 December 2017 29

30. 31 December 2017 32

31. • Primarily on maxillary canines.
• Lingual rest on incisors are rare.
• Aesthetically superior than incisal rest.
• Less subjected to breakage and distortion.
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Lingual or Cingulum rest and rest seat

32. • In cross section- V shaped.
• The preparation should display a relatively upright lingual wall
that originates at the level of the cingulum and extends incisally.
• The remaining wall should originate at the crest of the cingulum
and inclined labiolingually towards the center of the tooth.
• From lingual aspect , the outline form of lingual rest seat should
be crescent shaped.
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33. • Placement of lingual rest seats in enamel surface is a
sound practice provided the following circumstances
exist:
1. The cingulum is prominent enough to permit
appropriate tooth recontouring.
2. The patient practices good oral hygiene
3. The caries index ids low
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34. 31 December 2017 36
Incorporated into the wax pattern Lingual rest seat on cast restoration

35. 31 December 2017 37
The preparation is finished using a
green stone in a low-speed
handpiece.
Round the sharp angles with Knife-
edged rubber wheel.
An inverted cone bur is used to
establish the outline form of a
cingulum rest seat.

36. 31 December 2017 38
Polished the preparation using carborundum - containing rubber
point in a low-speed handpiece.

37. Incisal rests and rest seats
• Less desirable than lingual.
• Nevertheless they may be used successfully if abutments are sound
and cast restorations are not indicated.
• Most frequently used on mandibular canine.
• Should be positioned near the incisal angles of abutment teeth.
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38. • An incisal rest seat should appear as a small v shaped notch located
approximately 1.5- 2 mm from the proximal incisal angle of the tooth.
• The deepest part of the preparation should be towards the center of the tooth
mesiodistally.
• The notch should be rounded and should extend slightly in to the facial
surface to provide a positive seat for the rest.
• The enamel on the lingual surface should be prepared as a shallow
depression to accommodate the minor connector and avoid annoying the
tongue.
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39. • Preparation is made using small safe sided diamond
disc or tapered cylindrical diamond, parallel to path
of insertion
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40. • First cut is made vertically 1.5-2 mm deep in the form of a
notch, and 2-3mm inside the proximal angle of the tooth
Enamel walls and base of notch is rounded with small flame
shaped diamonds
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Preparation

41. The groove must be carried slightly over to labial surface
to prevent facial tipping.
• A=2mm
• B= 1.5mm
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42. • Finishing and polishing
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Completed preparation

43. • This article described an alternative cingulum rest seat design to
that of the conventional “inverted V” described for use with teeth
having a prominent cingulum.
• A U-shaped cingulum rest seat is prepared.
31 December 2017 J prost dent.1985;54(3); 395-96 45
Alternative cingulum rest seat
John R. Ivanhoe
Alternative crescent-shaped rest seat.
Review 1

44. 31 December 2017 J prost dent.1985;54(3); 395-96 46

45. • Advantages
• The possibility of undercutting the preparation and creation of
sharp angles or lines are less.
• The rest seat created is deepest near the center of the tooth and
therefore helps direct the forces in long axis of the tooth.
• Because of its U shape, rest seat conforms to the cementoenamel
junction of the tooth and may therefore be placed as far gingivally
as possible. This provides for maximum interocclusal clearance
for rest
31 December 2017 J prost dent.1985;54(3); 395-96 47

46. Purpose:
To evaluate the level of tissue removal that takes place on enamel and
dentin during cingulum rest seat preparation.
31 December 2017 J Prosthet Dent 1998;80:319-22. 48
Review 2
Thickness of the remaining enamel after the preparation
of cingulum rest seats on maxillary canines
Artemio Luiz Zanetti, Marcos Antonio Mengar, Moacyr Domingos
Novelli and Dalva Cruz Laganá.

47. Material and methods:
A quantitative evaluation of the thickness of the remaining enamel
of cingulum seat preparations to receive removable partial denture
rests was carried out in 20 maxillary canines with a light optical
microscope.
Results:
Thirty percent of the preparations were overextended into dentinal
tissue, and 85% had depths that were insufficient to receive rests.
31 December 2017 J Prosthet Dent 1998;80:319-22. 49

48. Within the limits, the following conclusions were drawn.
1. A total of 85% of the preparations exhibited insufficient, below average depths;
15% of the preparations were overextended.
2. Only 10% of the preparations were close to average.
3. Twenty-five percent of the rest seats had depths below 0.5 mm to render an
excessively thin and shallow prosthesis rest, which thus increased the
chances of fracture or dislocation during function.
31 December 2017 J Prosthet Dent 1998;80:319-22. 50

49. • Rest and rest seat deserves special consideration.
• Proper understanding of the biomechanical design, function and
placement of the rest is necessary.
• It plays crucial role in maintaining the health of the tissues.
• Topography of the rest should be such that it restores the
topography of the tooth before rest seat preparation.
31 December 2017 51
Summary and conclusion

50. • Stewart’s. Clinical removable partial prosthodontics in Major Connectors,
Minor Connectors, Rests and Rest Seat. Quintessence Publishing Co, Inc.
4th ed. pp. 43.
• Russell J. Strattonand Frank J. Winebelt An atlas od removable partial
denture design in Rests. Quintessences Pub. Co.Inc 1998. pp 19.
• Gerald W. Gaston. Rest Area Preparations For Removable Partial Dentures.
J Pros. Dent.1960 Jan-Feb;10(1):124-34.
• John R. Ivanhoe. Alternative cingulum rest seat. J prost dent.1985;54(3);
395-96
31 December 2017 52
References:

51. • Davenport, Basker: A colour atlas of removable partial dentures, ed.1,1980.
• Mc Cracken’s Removable partial denture prosthodontics, ed. 12.
• Glossary of Prosthodontic Terms, Edition Nine, J Prosthet Dent 2016 May.
117(5S).
• Artemio Luiz Zanetti, Marcos Antonio Mengar, Moacyr Domingos Novelli
and Dalva Cruz Laganá.Thickness of the remaining enamel after the
preparation of cingulum rest seats on maxillary canines. J Prosthet Dent
1998;80:319-22.
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References:

52. 31 December 2017 54