This document discusses the preparation of abutment teeth for removable partial dentures. It covers preparing guiding planes, modifying height of contour, creating retentive undercuts, and preparing rest seats. Guiding planes are prepared to direct the path of insertion for the denture. Height of contour is modified to allow ideal placement of clasps and connectors. Undercuts can be created through enamelplasty. Rest seats are prepared using round burs to provide support and force distribution for rests on the denture. Proper preparation of abutment teeth helps ensure retention, stability, and support of the removable partial denture.

1. Mouth Preparation For Removable
Partial Dentures
Presented by:
Dr. Mujtaba Ashraf
MDS II
Preparation of Abutment Teeth

2. INTRODUCTION

3. After surgery, periodontal treatment, endodontic
treatment, and tissue conditioning of the arch
involved, the abutment teeth may be prepared to
provide support, stabilization, reciprocation, and
retention for the removable partial denture.
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4. Non-prosthetic mouth preparation is done to prepare
unwanted oral structures that interfere with the
placement of a prosthesis.
Whereas prosthetic mouth preparation is done to
modify the existing structures to further enhance the
placement of a prosthesis.
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5. Objectives
• Direct stress along the axis of the tooth.
• Eliminate interferences by recontouring of teeth.
• Create retention by simple alteration procedures.
• Allow placement and removal of prosthesis without
transmitting wedging types of stress against teeth with
which it comes in contact.
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6. CLASSIFICATION OF ABUTMENT TEETH
The subject of abutment preparations may be grouped
as follows:
• those abutment teeth that require only minor
modifications to their coronal portions,
• those that are to have restorations other than
complete coverage crowns,
• those that are to have crowns (complete coverage)
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7. Sequence of Abutment Teeth preparation That Require
Only Minor Modifications To Their Coronal Portions
The following sequence of mouth preparation is
followed:
1. Preparation of Guiding Planes
2. Modification of Height of Contour
3. Preparation of Retentive Undercuts
4. Rest seat preparation
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8. Burs Used In Preparation
The two pear-shaped, multifluted burs-used for cingulum rests
and rounding marginal ridges;
the longer straight, multifluted enamelplasty bur is ideal for
height of contour adjustments and guide plane preparation;
round multifluted or carbide burs- used for occlusal rest
preparation
the inverted cone-used for cingulum rests as well.
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9. Abrasive rubber polishing points are necessary to
ensure a smooth surface finish following any
enamelplasty procedure.
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Every preparation is treated with fluoride gel
Dr Mujtaba

10. Preparation Of Guiding Planes
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11. Guiding planes are those surfaces on the
teeth, parallel relationship to each other,
so that they may serve to determine
positively the direction of appliance
movement (Applegate 1954)
Two or more vertically parallel surfaces on
abutment teeth and/or fixed dental prostheses
oriented so as to contribute to the direction of the
path of placement and removal of a removable
partial denture, maxillofacial prosthesis, and
overdenture. (GPT-9)
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12. Advantages Of Guide Surface And Guide Plate
• Food impaction is prevented.
• Hypertrophy of the soft tissue between the tooth and
the prosthesis is prevented.
• The friction force in these areas supports the retention
and stability of the prosthesis in great proportion.
• Controlling of the movement of the teeth by supporting
in antero-posterior direction.
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13. A natural appearance is obtained by full contact of
tooth and RPD without any space in between.
Otherwise, the area between the teeth and the
prosthesis will appear as a dark space, which will
cause esthetic problems
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14. Guide surfaces means making proximal surfaces of
two or more supporting teeth parallel to each other
and determining only one path of insertion for the
RPD
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15. Allows a reciprocating component
to maintain continuous contact with
a tooth as the denture is displaced
occlusally.
The retentive arm of the clasp is
thus forced to flex as it moves up
the tooth. It is this elastic
deformation of the clasp that
creates the retentive force
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16. A reciprocating element must brace the abutment as the
retentive element passes to and from its fully seated position,
(a)If reciprocation is ineffective, potentially destructive lateral
forces (arrow) will be transferred to the abutment
(b) A properly prepared guiding plane permits sustained contact
between the reciprocal element and the abutment and prevents
the application of unopposed lateral forces.
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17. The Preparation
Guide surfaces are usually prepared, somewhat imprecisely,
by eye.
The position in which the handpiece must be held to prepare
the required guide surfaces, so that they are all parallel to
each other and to the path of insertion, should be established
on the study cast.
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18. Guiding planes should be at least 1/2 to 1/3 of the axial
height of the tooth (generally 2 mm-4mm in height).
Use a light sweeping stroke continuing past the bucco- and
the linguo proximal line angles.
Abutment Teeth Adjacent To Tooth-supported Segments
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19. A cylindrical diamond or carbide
bur is generally used for the
preparation of guiding planes
Prepared surfaces are polished with
a carborundum-impregnated rubber
point or wheel in a low-speed
handpiece.
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20. Abutment teeth adjacent to distal extension edentulous
spaces
A guiding plane adjacent to a distal extension space is 1.5 to
2.0 mm in height
Reduced height results in decreased contact with the minor
connector and permits greater freedom of movement for the
removable partial denture. Hence, potentially damaging
forces are minimized.
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21. Lingual Surfaces Of Abutment Teeth
This is done to provide maximum resistance to lateral stresses
A lingual guiding plane should be 2
to 4 mm in occluso-gingival height
and should be located in the middle
third of the clinical crown as
viewed from the mesial or distal
surfaces
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22. Modification Of Height Of Contour

23. Enameloplasty to change height of contour is
performed to provide ideal placement of clasp
arms and remove interferences for placement of
major connectors.

24. Maxillary posterior teeth tend to tip buccally making
placement of retentive terminal unaesthetic.
Mandibular posteriors tip lingually making it difficult to
place reciprocal arm and lingual major connectors.
In both these situations, height of contour will be near
occlusal surface.
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• Minor recontouring of facial
surfaces will frequently permit
more ideal placement of the
bracing portion of the retentive
clasp arms.
• Frequently improve the position
of the survey line to allow
placement of the reciprocal clasp
arm in its proper position.
Dr Mujtaba

26. • Amount of correction depends upon thickness of
enamel.
• If dentine is exposed, placement of restoration is
considered.
Preparation is best done with tapered diamond burs, then
smoothed using a carborundum-impregnated rubber point
or wheel..
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27. Preparation Of Retentive Undercut ( Dimpling)

28. Enameloplasty to modify retentive undercuts is termed
“dimpling”.
Performed to increase a less than adequate retentive
undercut.
Should be avoided if other undercuts exist and can be
utilized to provide adequate design.
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29. This technique is successful only when the facial and
lingual surfaces of the tooth must be nearly vertical.
A depression should exhibit
smooth, flowing contours.
Sharply defined dimples and
pits should be avoided
Preparation is done using a round or football-shaped
diamond bur in a high-speed handpiece.
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30. • Depression should be parallel
and close to the gingival
margin.
• The depression should be
approximately 4 mm in mesio-
distal length and 1-2 mm in
occluso-gingival height.
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0.01
RW Rudd. Preparing teeth to receive a removable partial denture. J Prosthet
Dent 1999;82:536-49
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Should establish an undercut of 0.010
inches relative to the proposed path of
insertion.
It should be highly polished.
Dr Mujtaba

32. Preparation Of Rest Seats

33. The components of a removable partial denture that transfer
forces down the long axes of the abutment teeth are called
rests. -Stewart
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. GPT-9
Rest Seat: the prepared recess in a tooth or restoration
developed to receive the occlusal, incisal, cingulum, or
lingual rest. –GPT-9
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34. 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
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35. • 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
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36. 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 1958
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37. PREPARATION
• 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 anesthesia
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38. OCCLUSAL REST IN ENAMEL
The outline form of an occlusal rest
seat should be a rounded triangular
shape with the apex toward the
center of the occlusal surface.
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39.  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.
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The marginal ridge of the abutment
tooth at the site of the rest seat should
be approximately 1.5 mm
To permit a sufficient bulk of metal
for strength and rigidity of the rest
and the minor connector.
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40. 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.
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41. When using a round bur, care must be taken to ensure that
mechanical undercuts are not created,
(a)Round bur positioned above enamel surface,
(b)Bur moved vertically into enamel,
(c)Bur moved laterally,
(d)Upon removal of the bur, a distinct overhang is present.
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42. A tapered cylinder may help eliminate mechanical undercuts.
Upon removal of bur, no overhang is present.
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A. Occlusal view to show direction
of successive cuts.
B. Proximal view of tooth showing
depth and location of first 2
cuts that start in fossa and
continue over marginal ridge.
Island of marginal ridge enamel
remains as depth gauge.
After depth is established, island of
enamel is removed to make spoon
shape of floor of preparation and
preparation is flared to facial and
lingual at marginal ridge.
C. Lingual view of tooth to show
relative depth of preparation.
RW Rudd. Preparing teeth to receive a removable partial denture. J Prosthet
Dent 1999;82:536-49
Dr Mujtaba

44. The form and depth of an occlusal
rest seat is evaluated using red
boxing wax.
Boxing wax should be formed into
a disk approximately 4 mm in
thickness and 15 mm in diameter
The disk is pressed against the
prepared surface or surfaces, and
the patient is asked to close firmly.
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45. After the patient is directed to open
and the wax disk is carefully
removed, the form of each rest seat
is carefully inspected.
Available space is evaluated by
measuring rest seat areas with a
wax thickness gauge. The boxing
wax should be at least 1 mm thick
in rest seat areas
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46. Occlusal Rest Seats As Part Of A New Cast-metal
Restoration
• Should always be placed while making wax-pattern
• Sufficient occlusal clearance be created for rest and
restoration.
• A depression is added to the preparation to
accommodate rest seat.
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47. Embrasure Rest Seats
This preparation crosses the occlusal embrasure of two
approximating posterior teeth, from the mesial fossa of one
tooth to the distal fossa of the adjacent tooth.
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48. Must have through-
and-through clearance
wide enough to
accommodate two 18-
gauge round wires
side-by-side
Sharp corners and undercuts should be avoided
During preparation, should not break the
interproximal contact.
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49. 1. Reduce the marginal ridges of the approximating teeth
adjacent to the mesial and distal fossae with a no. 4 round
bur or equivalent sized diamond bur.
2. When the marginal ridges are uneven on the teeth to be
prepared, they should remain uneven when the
preparations are complete.
3. A minimum clearance of 1 mm must be provided with the
opposing occlusion.
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50. Buccal clearance can also be obtained by using a
cylindrical diamond stone. It is held horizontally from
buccal surfaces of teeth pointing towards lingual
surface
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51. Should remove sufficient tooth structure at the
facial and lingual surfaces of the abutments.
If not these areas of the removable partial
denture framework are extremely thin and
susceptible to fracture.
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52. Rest Seat Preparations For
Anterior Teeth

53. Lingual Or Cingulum Rest
A cingulum rest seat should be crescent shaped when viewed
from the lingual aspect
When viewed in profile, the rest seat should be V-shaped.
The rest seat should form a smooth curve from one marginal
ridge to the other.
Sharp angles should be avoided.
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54. An inverted cone bur is used to
establish the outline form of a
cingulum rest seat.
The preparation begins on one
marginal ridge, passes over the
cingulum, and terminates on the
opposite marginal ridge.
The preparation is finished using a
green stone in a low-speed
handpiece.
Round the sharp angles with Knife-
edged rubber wheel.
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55. Polished the preparation using carborundum-containing
rubber point in a low-speed handpiece.
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56. If a fixed restoration is to be placed
on an anterior abutment, a
cingulum rest seat should be
incorporated into the wax pattern.
This rest seat should exhibit ideal
contours and should direct forces
along the long axis of the abutment.
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57. Incisal rest seats Preparation
It is prepared only on enamel surfaces.
If a cast restoration is planned, cingulum rest is
preferred.
Preparation is made using small safe sided diamond
disc or tapered cylindrical diamond, parallel to path of
insertion
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58. First cut is matle 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
The groove must be carried slightly
over to labial surface to prevent
facial tipping.
A=2mm
B= 1.5mm
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59. Finishing and polishing on a
completed incisal rest seat, are
accomplished using a green stone
and carborundum-impregnated
rubber point
A completed incisal rest seat
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60. SUMMARY

61. • The more significant aspect of treatment with removable
partial dentures is the careful planning and execution of
mouth preparations and their accurate reproduction through
the fabrication process.
• The benefits of careful planning, designing, and executing
mouth preparations are substantial.
• Properly prepared rest seats and accurately fitting rests will
direct the forces of mastication so that the teeth and the
partial denture will mutually support each other.
• Properly balanced and distributed forces can contribute to
enhanced longevity of both the remaining oral structures
and the restoration.
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62. References

63. • 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.
• RW Rudd. Preparing teeth to receive a removable partial
denture. J Prosthet Dent 1999;82:536-49
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64. 64
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