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MOUTH PREPARATION FOR REMOVABLE PARTIAL DENTURES.pptx
1. MOUTH PREPARATION FOR
REMOVABLE PARTIAL DENTURES
PRESENTED BY- DR VAISHALI SHRIVASTAVA
1ST YEAR POST GRADUATE STUDENT
DEPARTMENT OF PROSTHODONTICS,
CROWN & BRIDGE AND IMPLANTOLOGY
1
2. CONTENTS
• Introduction
• Objectives
• Preparation of Mouth
A) NON PROSTHODONTIC PREPARATION
B) PROSTHODONTIC PREPARATION
• Preparation of Abutment tooth
• Conclusion
• References
2
3. INTRODUCTION
Mouth preparation are identified as those procedures that are accomplished to
prepare the mouth for reception of prosthesis
prescribed prosthesis not only must replace what is missing but also must
preserve the remaining tissues and structures that will enhance the removable
partial denture
Mouth preparation follows the preliminary diagnosis and the development of a
tentative treatment plan, following this the master cast is made.
3
4. OBJECTIVES
4
the objectives of the procedures involved are to create optimum health
and eliminate or alter any condition that would be detrimental to the
functional success of the removable partial denture
5. NON PROSTHODONTIC PREPARATION
Relief of pain and infection
Pre-Prosthetic Considerations in
Partially Edentulous Mouths
Periodontal Preparation
Optimization of the Foundation for
Fitting and Function of the Prosthesis
Endodontic and restorative treatment
Orthodontic treatment
5
Preparation of
Mouth
6. Relief of pain and infection
• Dental conditions that are causing discomfort should
be addressed as soon as possible.
• Necessary endodontic and surgical procedures
should be completed.
6
7. Pre-Prosthetic
Considerations in Partially
Edentulous Mouths
• Extractions
• Impacted teeth
• Malposed teeth
• Cysts and odontogenic tumours
• Exostoses and tori
• Hyperplastic tissue
• Muscle attachments and freni
• Bony spines and knife edge ridges
• Polyps, papillomas and traumatic haemangiomas
• Hyperkeratoses, Erythroplasia and ulcerations
• Dentofacial deformity
• Augmentation of Alveolar bone
• Dental implants
7
8. Extractions-
Extraction of nonstrategic teeth that would present complications or those that
may be detrimental to the design of the removable partial denture is a
necessary part of the overall treatment plan.
.
8
10. Removal of residual roots-
• Generally, all retained roots or root fragments should be removed.
• Residual roots adjacent to the abutment teeth may contribute to the progression of periodontal pockets and
compromise the results of subsequent periodontal therapy.
10
11. 11
Impacted teeth-
• All impacted teeth, including those in edentulous areas,
as well as those adjacent to abutment teeth, should be
considered for removal.
12. Malposed teeth
• The loss of individual tooth or groups of teeth may lead to extrusion, drifting, or combinations of
malpositioning of remaining teeth.
• Surgical repositioning of these teeth is contemplated only after orthodontic treatment is ruled out.
12
13. Cyst and Odontogenic tumours
• OPG should be taken for ruling out unsuspected pathology . If there is any
pathology surgical removal should be done.
Exostoses and Tori
• the existence of abnormal bony enlargements should not be allowed to
compromise the design of the removable partial denture.
• Removable partial denture components in proximity to this type of
tissue may lead to irritation and chronic ulceration.
13
14. Hyperplastic tissue
• Hyperplastic tissues are seen in the form of fibrous
tuberosities, soft flabby ridges, folds of redundant
tissue in the vestibule or floor of the mouth, and
palatal papillomatosis.
• Removal of this excess tissue provides a firm base for
the denture and reduces stress on supporting teeth and
tissues.
14
15. • As a result of the loss of bone height, muscle
attachments may insert on or near the
residual ridge crest. The mylohyoid,
buccinator, mentalis, and genioglossus
muscles are most likely to introduce
problems of this nature.
• Maxillary labial and mandibular lingual
frenum most commonly interfere with denture
design.
Muscle attachments and freni
15
16. Bony spines and knife edge ridges
• Sharp bony spicules should be removed and knife like crests gently
rounded.
16
17. Polyps, Papillomas, and Traumatic Hemangiomas
all abnormal soft tissue lesions should be excised and submitted for pathologic examination before a
removable partial denture is fabricated
17
polyps papilloma hemangioma
18. Hyperkeratoses, Erythroplasia, and Ulcerations
hyperkeratoses erythroplasia ulcerations
• All abnormal white, red, or ulcerative lesions should be investigated, regardless of their relationship to
the proposed denture base or framework.
• The lesions should be removed and healing accomplished before the removable partial denture is
fabricated.
18
19. Dentofacial Deformities
Cleft palate
• Patients with these deformities have multiple
missing teeth and malocclusion as a part of the
problem.
• Correction of the deformity should form part of
the treatment plan to replace teeth and develop a
harmonious occlusion
19
20. • Ridge augmentation is done for atrophic ridges, flat palatal
vault and mild to moderate anteroposterior ridge relation
discrepancy.
• It is done with graft materials
• It enhances the support and stability of denture
Augmentation of Alveolar Bone
20
21. Dental Implants
• Implants are carefully placed using
controlled surgical procedures and, in
general, bone healing to the device is
allowed to occur before a dental
prosthesis is fabricated.
Hobo S, Ichida E, Garcia LT: Osseointegration and occlusal rehabilitation, Tokyo, 1989
• These devices offer a significant
stabilizing effect on dental
prostheses through a rigid
connection to living bone.
21
23. fig
A, An anterior implant-supported bar demonstrating excellent access for hygiene and a
parallel relationship to opposing occlusion
. B, Prosthesis with implant bar space (housing three retentive male components for
retention and a flat surface for bar contact and support) and bilateral posterior
embrasure clasps.
C, Prosthesis seated and in occlusion. (Courtesy of Dr. N. Van Roekel, Monterey, CA.)
23
24. A Class II, modification 1, maxillary arch with a posterior implant at the distal location of the
extension base
. B, Maxillary gold framework with broad palatal coverage, maximum stabilization through
palatal contacts of multiple maxillary teeth, and implant position at the distal extension base. A
single implant should be protected from excessive occlusal forces; consequently the broad palatal
coverage and maximum bracing are important features of the overall design. The ball attachment
abutment was used for retentive purposes.
C, Occlusal view of the prosthesis with implant (see A), which provides improved retention to the
distal extension base. (Courtesy of Dr. James Taylor, Ottawa, Ontario.
24
25. Periodontal Preparation
*Vanchit John, DDS, Associate Professor and Chair, Department of Periodontics and Allied Dental Programs, Indiana University School of Dentistry, Indianapolis, Indiana
• The periodontal health of the remaining teeth, especially those to be used as abutments, must be
evaluated carefully by the dentist and corrective measures instituted before a removable partial
denture is fabricated.
25
26. Periodontal Preparation
• OBJECTIVES OF PERIODONTAL THERAPY
• PERIODONTAL DIAGNOSIS AND TREATMENT
PLANNING
• INITIAL DISEASE CONTROL THERAPY (PHASE 1)
• DEFINITIVE PERIODONTAL SURGERY (PHASE 2)
• RECALL MAINTENANCE (PHASE 3)
• ADVANTAGES OF PERIODONTAL THERAPY
26
27. Objectives of Periodontal
Therapy
1. Removal and control of all etiologic factors
contributing to periodontal disease along with
reduction or elimination of bleeding on probing
2. Elimination of, or reduction in, the pocket depth of
all pockets with the establishment of healthy gingival
sulci whenever possible
3. Establishment of functional atraumatic occlusal
relationships and tooth stability
4. Development of a personalized plaque control
program and a definitive maintenance schedule
27
28. Periodontal Diagnosis and Treatment Planning
The diagnosis of periodontal diseases is based on a systematic and carefully
accomplished examination of the periodontium.
Depending on the extent and severity of the periodontal changes present, a variety of
therapeutic procedures ranging from simple to relatively complex may be indicated.
28
29. Initial Disease Control Therapy (Phase 1)
• Oral Hygiene Instruction
• Scaling and Root Planing
• Elimination of Local Irritating Factors Other Than Calculus
• Elimination of Gross Occlusal Interferences
• Temporary Splinting
• Use of a Nightguard
• Minor Tooth Movement
29
30. Definitive Periodontal Surgery (Phase 2)
Periodontal Surgery
• After initial therapy is completed, the patient is reevaluated for the surgical phase.
• If oral hygiene is at an optimum level, yet pockets with inflammation and osseous defects are still
present, a variety of periodontal surgical techniques should be considered to improve periodontal health.
30
31. Periodontal flaps
Periodontal flap surgery involves the elevation of either mucosa alone or both the mucosa and the
periosteum
Other goals of the flap approach include access for pocket elimination, caries control, crown
lengthening to allow for optimum restorative dental treatment, root amputation or hemisection, as
required and access to the furcation of the tooth
Guided Tissue Regeneration.
GTR has been defined as those procedures that attempt regeneration of lost periodontal structures
through differing tissue responses.
This technique has the potential to lead to substantial improvement of the periodontal condition
when used around carefully selected two and three-walled osseous defects and mandibular furcation
involvements
31
33. Periodontal Plastic Surgery
33
Mucogingival surgery consists of plastic surgical procedures that are
used for correction of gingiva–mucous membrane relationships that
complicate periodontal disease and may interfere with the success of
periodontal treatment.
Gingival recession addressed with subepithelial connective tissue graft procedure
34. Recall Maintenance (Phase 3)
• This is very important in maintaining periodontal health
• It includes reinforcement oral hygiene measures and thorough scaling and root
planning
• patients with a history of moderate to severe periodontitis should be placed on a 3- to
4-month recall system to maintain results achieved by nonsurgical and surgical therapy
34
35. OPTIMIZATION OF THE
FOUNDATION FOR FITTING
AND FUNCTION OF THE
PROSTHESIS
• Conditioning of Abused and Irritated Tissues
• Use of Tissue Conditioning Materials
• Abutment Restorations
• Contouring Wax Patterns
• Rest Seats
35
36. Conditioning of Abused and Irritated Tissues
Conditioning of tissue is required if:
• Inflammation and irritation of the mucosa
covering denture-bearing areas
• A burning sensation in residual ridge areas,
the tongue, and the cheeks and lips
These conditions are usually associated with
ill-fitting or poorly occluding removable
partial dentures. Tissue conditioners are used
to provide a soothing effect on irritated
mucosa
36
37. Use of Tissue Conditioning Materials
Maximum benefit from using tissue conditioning materials may be obtained by
(1) extending denture bases to proper form to enhance support, retention, and stability
(2) relieving the tissue side of denture bases sufficiently (2 mm) to provide space for even thickness and
distribution of conditioning material
(3) applying the material in amounts sufficient to provide support and a cushioning effect
(4) following the manufacturer’s directions for manipulation and placement of the conditioning material.
37
38. A, Mandibular removable partial denture with underextended bases, which contributed to tissue irritation. B, Denture bases
properly extended to enhance support, stability, and retention
38
39. Abutment Restorations
Esthetic veneer types of crowns should be used when a canine or premolar abutment is to be restored or
protected.
when preparing abutments that will receive surveyed crowns, it is important to plan for the tooth reduction
necessary to allow placement of sufficient restorative material for durability, contour, and esthetics, as well
as the contours prescribed for the desired clasp assembly (fig).
39
40. 40
Diagnostic cast at an orientation best for all abutments
considered. The buccal survey line is too close to the marginal
gingival. A surveyed crown is indicated.
Cast of seated crown demonstrate desired contours for clasp
design chosen
41. Contouring Wax Patterns
41
• All abutment teeth to be restored with castings can be prepared at one time and an impression made that will
provide an accurate stone replica of the prepared arch.
• Wax patterns may then be refined on separated individual dies or removable dies.
• All abutment surfaces facing edentulous areas should be made parallel to the path of placement by the use of
the surveyor blade
42. 42
Completed prosthesis splinted between retainer
crowns and across the midline. Splint bar with added
vertical support provides indirect retention.
43. Rest Seats
43
Buccal and lingual contours have been established to satisfy the
requirements of stability and retention with the best possible esthetic
placement of clasp arms, the occlusal rest seats should be prepared in the
wax pattern rather than in the finished restoration
spoon shape or saucer shape can permit locking of the occlusal rest and the
transmission of tipping forces to the abutment tooth.
44. Endodontic and
restorative treatment
44
Teeth with pulpal involvement and root end pathology are
candidates for endodontic therapy.
Restorative therapy like – crowns, inlays, onlays,
restoration of carious lesions and replacement of
defective restorations should be integrated with
endodontic treatment.
45. Orthodontic treatment
45
Orthodontic preparation is carried out to achieve the following:
• Reduce the need for prosthetic teeth as much as possible.
• Position the teeth to allow the most natural prosthetic
replacement of teeth.
• Create sufficient vertical height to allow room for placement of
artificial teeth.
• Allow sufficient occlusal guidance on natural teeth
46. Prosthodontic
preparation
46
• Correction of occlusal plane
1) Enameloplasty
2) onlay
3) crowns
4) Endodontics with crown or coping
5) Extraction
6) surgery
• Correction of malalignment
1) orthodontic realignment
2) Crown
3) Enameloplasty
• Provision of support for weakened teeth
1) Removable splinting
2) fixed splinting
3) overdenture abutment
47. Correction of occlusal plane
47
Uneven occlusal plane is common in partially edentulous situations due to:
• Supraeruption and infraeruption
• Mesial migration
• Tipping of teeth
• Malrelationship of jaws
48. 48
Enameloplasty-
• occlusal reshaping, Esthetic Reshaping (GPT9)
• The intentional alteration of the surfaces of teeth to change their form
• The enamel is contoured using high-speed tapered diamonds and polished with carborundum wheels or
points. Fluoride treatment of the tooth surface increases its resistance to caries.
Irregular occlusal plane
Enameloplasty done to correct the
occlusal plane.
49. 49
onlay
• It is a conservative method of correcting occlusal plane as minimal tooth preparation
is required compared to a full veneer crown.
• It maintains the natural contours of facial and lingual enamel surfaces as only
occlusal surface is prepared.
• The occlusal surface of the tooth being prepared should be free of pits and fissures.
It can be made of chrome or gold alloy.
• If chrome alloy is used, the occluding surface should be processed with tooth
colored acrylic resin to prevent attrition of opposing tooth.
• Disadvantages: • Less retention • More metal display
50. 50
crowns
When the height of contour, retentive
undercut or guiding plane needs to be
altered, crown is preferred to change
the occlusal plane
51. 51
• Retaining teeth in strategic positions will
greatly improve the prognosis of the partial
denture.
• Retaining mandibular second or third molars
to serve as posterior abutments will support
the prosthesis and will prevent it from being
a more complicated distal extension situation
• Endodontics followed by crown or
overdenture coping will restore occlusal
plane and allow the teeth to be retained.
Endodontics with crown or coping
Retaining a distal abutment will prevent a distal extension situation .
52. 52
Extraction
Malposed teeth and teeth interfering with placement of major connector require
extractions to correct occlusal plane as they compromise the success of treatment
Surgery
Surgical repositioning of one or both jaws, fully or partly, can be contemplated to
correct occlusal plane. These include osteotomies and repositioning procedures.
53. Correction of malalignment
53
Malaligned teeth create the following difficulties:
• Maintenance of oral hygiene.
• Determining a simple path of insertion.
• Establishing guiding planes.
• Placement of clasp arms of direct retainers.
54. 54
Teeth which are malposed facially or lingually are more difficult to correct than supraerupted teeth
I . Orthodontic realignment -
it is the treatment choice , multiple missing teeth can not be corrected
• Partial or full veneer crowns may be used.
• Indicated to correct buccal or lingual tipping.
• If tipping is extensive, endodontic treatment followed by a post will correct the
same.
However, long axis of crown and root should not be too dissimilar, as undesirable
horizontal forces will occur on tooth. Hence, severe malposition cannot be corrected
by crowning
II. Crown
55. 55
this is always considered first, but amount of correction that is possible is limited.
• Enameloplasty can be used to recontour buccal or lingual surfaces to eliminate
the interferences to the path of placement of major connector.
III. Enameloplasty
56. Provision of support for weakened teeth
56
• Over denture abutment Teeth strategically positioned in the arch with more than 50% bone loss can be retained
as overdenture abutments.
They resist the tissueward forces and provide support.
Retaining such a tooth distal to edentulous space will convert a potential distal
extension base into a tooth supported situation, improving the function of denture.
59. Objectives
59
• Direct stress along the tooth axis
• Eliminate interferences by recontouring of teeth
• Create retention by simple alteration procedure
• Allow placement and removal of prosthesis
classification
Abutment teeth that require only minor
modification to their coronal portions
Abutment teeth that have
cast restoration
60. 60
Sequence of preparation
1. Preparation of guiding planes
2. Modification of height of contour
3. Preparation of retentive undercuts
4. Rest seat preparation
Enameloplasty: conservative
procedure involve only minor
modification and reshaping of
enamel
61. Preparation of guiding planes
61
Preparation of
guiding planes
Abutments adjacent
to tooth supported
segments
Abutments adjacent
to distal extension
bases
Lingual surface of
abutment
Anterior abutment teeth
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 removable partial denture(GPT9)
62. 62
Abutments adjacent to tooth supported segments
• cylindrical diamond or carbide bur is used for the preparation (fig a)
• The chosen bur is placed in a high-speed handpiece.
• Diagnostic cast mounted on surveying table at the desired tilt, handpiece with bur is positioned
over abutment tooth on cast to visualize the correct angulation, same is reproduced in the
mouth.
Stewart’s clinical removable partial prosthodontics 4th edition
63. 63
• A light, sweeping stroke from the facial line angle to the lingual line angle is then used to create a gently
curving plane. (fig b)
• Surface should be 2 to 4 mm in occlusogingival height, not resemble a straight slice when viewed from the
occlusal or incisal surface. Instead, it should follow the natural curvature of the tooth surface(fig2).
• All prepared surfaces are polished with carborundum impregnated rubber point or wheel in low speed
handpiece
65. 65
Abutments adjacent to distal extension
bases
• Occlusogingival height of preparation is (1.5- 2mm) fig i
• The reduced height results in decreased contact with the associated minor connector (i.e.
proximal plate) and permits greater freedom of movement for the associated removable partial
denture (fig ii)
• As a result, potentially destructive torquing forces are minimized
Fig ii
Fig i
Stewart’s clinical removable partial prosthodontics 4th edition
66. 66
Lingual surface of abutment
1)To enhance reciprocation
Reciprocation -Mechanism by which lateral forces generated by retentive clasp passing over a height of
contour are counterbalanced by reciprocal clasp passing along a reciprocal guiding plane (GPT9)
2) preparing lingual guiding planes is to minimize the number of pathways by which the prosthesis may enter
and exit its fully seated position
Stewart’s clinical removable partial prosthodontics 4th edition
67. 67
3) preparing guiding planes on the lingual surfaces of the remaining teeth is to provide maximum resistance to
lateral forces. The more teeth that are used to stabilize the removable partial denture, the less stress will be
transmitted to any individual tooth.
• Occlusogingival height of preparation is 2-4 mm located in the middle third of crown fig2
68. 68
Lingual surface of abutment
(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
A properly prepared lingual guiding
plane should be 2 to 4 mm in
occlusogingival height and should
be located in the middle third of the
clinical crown.
69. 69
Anterior abutment teeth
Guiding planes may be prepared on anterior teeth to enhance stabilization of the
prosthesis, to decrease undesirable space between the prosthesis and an abutment
tooth, and to increase retention through frictional resistance
Stewart’s clinical removable partial prosthodontics 4th edition
70. Modification of height of contour 70
Enameloplasty is necessary when teeth have drifted or tipped.
Maxillary posterior teeth often tip in a facial (buccally) direction, while
mandibular teeth generally tip in a lingual direction
Preparation is best done with tapered diamond stone
72. Preparation of retentive undercuts
72
The facial and lingual surfaces of the tooth must be nearly vertical.
Under these circumstances, a gentle depression may be created on one of these surfaces(fig1)
fig1
A depression should exhibit smooth,
flowing contours. Sharply defined dimples
and pits should be avoided since retentive
clasps cannot flex into and out of these
indentations
Stewart’s clinical removable partial prosthodontics 4th edition
73. 73
A gentle depression is prepared using a round diamond
bur in a high-speed handpiece. The bur is moved in an
anteroposterior direction
The depression should be approximately 4 mm in mesiodistal length
and 3 mm in occlusogingival height.
More importantly, it should establish an undercut of 0.010 inches
relative to the proposed path of insertion
Preparation should be polished with a carborundum-impregnated
rubber point.
Stewart’s clinical removable partial prosthodontics 4th edition
74. Rest seat preparation
74
• Rest seats must always be prepared after preparation of guiding planes
• The function of a rest is to direct the forces of mastication parallel to the long axis of the associated
abutment
• If rest seats are not adequately prepared, the forces transmitted from the prosthesis to the abutments may
not be directed within the long axis of these teeth. This may result in irreparable damage to the
abutments.
75. 75
Rest Seat Preparations for
Posterior Teeth
• Occlusal rest seats in enamel
• Occlusal rest seats as part of a new cast-metal
restoration
• Occlusal rest seats on the surface of an
existing cast-metal restoration
• Occlusal rest seats on an amalgam restoration
• Embrasure rest seats
76. 76
Occlusal rest seats in enamel
• The outline form of an occlusal rest seat is basically triangular,
the base of the triangle at the marginal ridge
the apex pointing toward the center of the tooth
• The apex of the triangle should be rounded, as should all
external margins of the preparation (fig)
• the floor of the occlusal rest seat must be inclined toward
the center of the tooth and should display gently rounded
contours.
• The enclosed angle formed by the floor of the rest seat
and the proximal surface of the tooth must be less than 90
degrees (Fig).
77. 77
A variety of burs may be used in the preparation of rest seats .
These include round burs and tapered cylinders.
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) Round bur moved vertically into
enamel. (c) Bur moved laterally. (d) Upon removal of the bur, a distinct overhang is present
78. 78
A tapered cylinder may help eliminate mechanical undercuts.
(a) Tapered bur positioned above enamel surface. (b) Tapered
bur moved vertically into the enamel. (c) Bur moved laterally.
(d) Upon removal of bur, no overhang is present
79. 79
An occlusal rest should be at least 1 mm thick at its thinnest point..
Failure to achieve sufficient reduction may make a rest more susceptible to fracture
The outline form for an occlusal rest seat is established using a
rounded-end, tapering bur in a high-speed handpiece .
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
80. 80
. 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.
Finishing procedures are performed using a green stone in a low-speed handpiece. The green stone is intended to
round sharp angles (represented by the solid line at periphery of preparation) and to eliminate scratches produced by
the diamond bur
82. 82
Occlusal rest seats as part of a new cast-metal restoration
• No. 4 or No. 6 round bur is used to begin preparation of the rest seat
• occlusal rest seats for cast gold restorations should always
be placed during the wax pattern stage.
• Required rest seats are carved into the wax pattern
following placement of guiding planes
• The rest seat is then refined with a rounded carver. At
this stage, the wax pattern may be sprued, invested,
and cast in an appropriate alloy
83. 83
Occlusal rest seats on the surface of an existing
cast-metal restoration
• Crown restoration has adequate marginal integrity and occlusal harmony.
• During preparation if perforation of crown occurs, new restoration must be made.
• Adequate tooth preparation is essential, otherwise it will results insufficient framework thickness and
failure of the removable partial denture.
• Procedure is same to rest seat preparation on enamel .
84. 84
Occlusal rest seats on an amalgam restoration
• Amalgam alloys tend to deform when a sustained load is applied.
• conservative amalgam restorations are quite capable of providing support for removable
partial dentures. Therefore, rest seats may be prepared on conservative single- and multiple-
surface amalgams.
• The instrumentation and procedures for preparing rest seats on amalgam restorations are
the same as those for preparing rest seats on enamel surfaces.
85. 85
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
diamond bur with a rounded end and tapering sides is
ideal for preparing embrasure rest seats
86. 86
• same bur is used to prepare the facial and lingual extensions of the embrasure rest seat
• Clearance may be evaluated by placing two pieces of 18-gauge wire across the preparation
• The patient should be able to close without contacting these wires
87. 87
• the form and depth of the rest seat is evaluated using red boxing wax and a wax-thickness
gauge.
• At the facial and lingual embrasures, the embrasure rest seat should be 3.0 to 3.5 mm wide
and 1.5 to 2.0 mm deep.
• All contours should be gently rounded and no undercuts should be present
88. 88
Rest Seat Preparations for
Anterior Teeth
• Cingulum rest seats in enamel
• Cingulum rest seats in a new cast-metal or metal-
ceramic restoration
• Placement of cingulum rest seats using dental bonding
techniques
• An alternative cingulum rest seat
• incisal rest seats in enamel
89. 89
Cingulum rest seats in enamel
• if tooth contours are favorable, sufficient enamel is present, and the patient exhibits good oral hygiene, the
cingulum rest prepared.
• The outline form of a cingulum rest seat should be crescent shaped when viewed from the lingual aspect
(a)cingulum rest seat as viewed from the
lingual surface
(b)the proximal surface.
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
90. 90
The preparation is finished using a
green stone in a low-speed handpiece.
Care must be taken to round sharp
angles (denoted by solid line). The
preparation is then polished using a
carborundum containing rubber point
in a low-speed handpiece.
cingulum rest seat .
91. 91
Lingual rest placed nearer the centre of rotation of supporting tooth and so it does not tip the tooth.
92. 92
Cingulum rest seats in a new cast-metal or metal-ceramic
restoration
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
A mandibular metal-ceramic restoration with a cingulum rest seat
A cingulum rest seat may be placed in a wax
pattern. This is easily accomplished using a
cleoiddiscoid carve
93. 93
• mandibular canines do not display prominent cingula, nor do they
have appreciable thicknesses of enamel on their lingual surfaces.
• Attempts to prepare cingulum rest seats on mandibular canines
often result in exposure of the underlying dentin and greatly
increase the risk of caries.
Placement of cingulum rest seats using dental bonding techniques
94. 94
• initial stages of tooth preparation are accomplished using a small, tapering diamond bur in a
high-speed handpiece.
• A limited area on the lingual surface of the proposed abutment is prepared to a depth of 0.5 to
0.7 mm.
• indentations are prepared using a No. 2 carbide bur and should be no deeper than one third to
one half the bur’s diameter
95. 95
The preparation for a bonded cingulum rest seat includes
a shallow indentation (arrow) and two or three circular
indentations . The depression helps disguise the thickness
of the metal, while the circular indentations guide
placement of the completed restoration.
The wax pattern must exhibit a properly
contoured cingulum rest seat and excellent
adaptation at its margins
97. 97
An alternative cingulum rest seat
alternative cingulum rest seat may be described as a crescent-shaped depression located in the
middle and apical thirds of the clinical crown
in many ways, this rest seat resembles an inverted
cingulum rest seat.
The alternative cingulum rest seat is prepared using a No.
38 carbide bur or a small diamond disk in a high-speed
handpiece
98. 98
An inverted cone bur is used to prepare an
alternative cingulum rest seat
The preparation begins within the enamel of one marginal
ridge, progresses apically to the level of the cingulum, and then
sweeps incisally within the enamel of the remaining marginal
ridge
99. 99
Incisal rest seats in enamel
• incisal rest seats are the least desirable rest seats for anterior teeth .
• The accompanying rests are unesthetic and may interfere with occlusion. More importantly, incisal rests are
located far from the rotational centers of the abutments. Hence, these teeth may be damaged by tipping or
torquing forces
• An incisal rest seat is usually placed near a proximal surface (Fig)
(A)An incisal rest seat as viewed from the facial surface
(B)lingual surface
100. 100
• Incisal rest seat preparation is begun with a flame shaped diamond bur in a high-speed
handpiece.
• The bur is oriented parallel to the proposed path of insertion, and a notch is created
• This notch should be located 2 to 3 mm from the proximal angle of the tooth and
should be 1.5 to 2.0 mm in depth
101. 101
• The notch is extended slightly onto the facial surface of the tooth.
• This provides a method to prevent facial movement of the abutment. On the lingual
surface of the tooth, a small channel is created. This channel helps disguise the thickness
of the associated minor connector
102. Abutment teeth that have cast restoration
102
Cast restorations like inlays, onlays and crowns are planned on abutments in the following situations:
• If Enameloplasty does not achieve usable natural contours, as in tipping, rotation, malalignment,
supra- and infraeruption of abutment.
• Presence of caries, defective restorations, tooth fracture and endodontic treatment in abutment tooth.
• The guiding planes, height of contour, retentive undercuts and occlusal rests are prepared on the wax
patterns of these restorations with mounted casts on the surveyor.
103. 103
When inlay is the restoration of choice, proximal and occlusal surface that support minor
connectors and occlusal rests require modification in preparation.
• Buccal and lingual proximal margins must be extended well beyond line angles of tooth.
• Axial wall is carved to confirm with external proximal curvature of tooth.
• There should be 1–1.5 mm of restorative material between occlusal rest and inlay margin.
• The rest is made on the wax pattern of inlay
Inlays
104. 104
(A) View of distal surface of MOD preparation for
lower left second premolar showing broad
extension of box, where occlusal rest with minor
connector will be placed.
(B) View of mesial surface, not as broad where there
is only contact with adjacent tooth with no rest
Occlusal view showing axial wall
curvature in conformity with external
proximal tooth curvature
There should be 1–1.5 mm of
restorative material between
occlusal rest and inlay margin.
105. 105
Crowns
• Three quarter crowns, complete coverage cast crowns and porcelain veneer crowns can be
used. Ideal for partial denture is complete coverage crown.
• Preparation should be made to accommodate the depth of occlusal rest, which is seen as a
depression in the prepared tooth, in the rest area.
• If crowns are to be veneered with acrylic resin or porcelain, they are surveyed again after
veneering to confirm the established contours.
106. conclusion
The success or failure of a RPD depends on
how well the mouth preparations are
accomplished.
It is only through intelligent planning and
competent execution of mouth preparations
that the partial denture can satisfactorily
restore lost dental functions and contribute to
the health of the remaining oral tissues
106
