mouth prepration in rpd.ppt

Mouth preparation in removable
partial denture

Introduction
The treatment plan for the patient who is to
receive removable partial denture can be
finalized only after diagnostic casts have been
mounted on an articulator and surveyed and
the proposed partial denture has been
designed.
The design procedures will have disclosed
procedures that are necessary to prepare the
mouth to receive a removable partial denture.

Relief of pain and
infections
 The first step in mouth preparation is
the relief of pain and infections.
 teeth -pain –treated
 discomfort because of caries or defective
restorations should be treated.
 calculus accumulations should be debrided.
 plaque should be controlled, preventive dental
hygiene program should be started and vigorously
monitored.

Oral surgical procedures
 As a general rule conditions requiring oral surgical
intervention are treated first.
 non restorable,
 impacted or unerupted teeth
 Interferences such as palatal or mandibular tori or bony
exostoses that would complicate partial denture construction
should be surgically excised.
 Preprosthetic procedures such as ridge augmentation and
vestibular extensions must also been performed if needed.

Severely extruded molars -interfere with
placement of acrylic resin retention minor
connector and artificial teeth must be
considered for extraction.

This is a case of malposed lateral
incisors frequently complicate design
of prosthesis.

Periodontal therapy
 The periodontal procedures necessary to restore the
mouth to state of health required the definitive
treatment also must be carried out early in the
clinical sequence.
 Some teeth may not be able to share the stress of the
removable partial denture, for this reason the
periodontal health must be ascertained before the
patient is committed to other steps in treatment
plan.
 The periodontal health of the teeth also hugely
influence the removable partial denture design.

Surgery
 Surgical repositioning of one or both jaws one
or segments of one both jaws to correct mal-
relationship is a procedure.
 This type of correction done by a specialist,
but the prosthodontist should be aware what
can be accomplished for the patient.

Endontics with crown or coping
 If some important tooth are over erupted or lost some
periodontal support needed to serve as an abutment.
 In such cases, endodontic therapy and if inter-occlusal
space is available, construction of a crown will allow
the teeth to serve as normal abutments
 If over eruption is so gross as to nearly obliterate the
remaining inter arch space, the crown of the tooth can
be removed at the level of gingival crest and a coping
constructed.
 This will prevent excessive vertical and horizontal
movement of prosthesis.

Orthodontic realignment
 The technique of orthodontically moving the
malposed teeth should be considered first ,if it is
not possible other treatment options should be
considered.

Extraction
 It should be the goal of a designer of removable
partial denture to retain as many of the
remaining teeth as possible.
 If orthodontic realignment, crowning is not
possible, then we need to proceed with the
extraction.

The success or failure of a removable partial denture (RPD) is
dependent on many factors, which include
1. the condition of the patient’s mouth,
2. the management of periodontally compromised
teeth, and
3. the long-term prognoses of such teeth.
4. In addition, the practitioner must consider the
effects of the framework design, clasp
configuration, and denture base extension and
during the clinical phases of treatment, the
practitioner must establish excellent a) guiding
planes,(b)properly contoured rest seats, and(c) well-
designed crowns (if applicable).

The practitioner also must
 make accurate impressions and casts
 and must provide clear instructions to dental
laboratory personnel.
The completed framework must be meticulously fitted to the
teeth and soft tissues
prosthetic teeth must harmonize with the remaining natural teeth
and denture bases must display proper contour and tissue
coverage.
appropriate verbal and written instructions regarding the use,
maintenance, and wearing of the RPD.

A Six steps of mouth and tooth preparation are given in
chronological order:
(1) establish occlusal plane
(2) recontour proximal surfaces of posterior teeth
(3) recontour proximal surfaces of anterior teeth
(4) recontour facial and lingual surfaces of teeth
(5) fabricate rest preparations and
(6) smooth and polish all altered surfaces.

Occlusal plane
which is defined in the Glossary of
Prosthodontic Terms as “the average
plane established by the incisal and
occlusal surfaces of the teeth…it is not a
plane, but represents the planar mean of
the curvature of these surfaces

Occlusal plane correction
It can be achieved by
 Enameloplasty
 Onlays
 Crowns
 Endodontics with crown or coping

►When a tooth is lost in an arch, the remaining teeth have a
tendency to drift.
►This is particularly troublesome when a posterior tooth is
lost and is not replaced.
The remaining posterior teeth, in attempting to close the space,
tip mesially rather than move in an upright position.
► This tipping can result in the mesial portion of the occlusal
surface being out of contact with the opposing occlusion and
the distal portion being in supra occlusion.

Teeth also tend to extrude when occlusal contact with the
teeth of the opposing arch is lost.
When the occlusal plane is not in harmony with the
dental arches, placement of artificial teeth and creation of a
harmonious, functional occlusion becomes difficult or
impossible to accomplish.
The dentition in the arch opposing the RPD, and the teeth
in the arch being treated, must be returned to as normal an
occlusal plane as possible,.”

Clinical treatment options
1. The occlusal plane can be corrected by judicious reshaping of enamel
by removing up to 2 mm of enamel, Care must be taken to maintain
normal occlusal anatomy and not expose the dentin.
2. When more than 2 mm of enamel must be removed to bring the
protruding teeth in line with the occlusal plane, the tooth should be
restored. Remove enough tooth structure for a cast restoration to have
adequate thickness and be in line with the occlusal plane after the
restoration is placed.
3. An extruded tooth may be shortened considerably without danger of
pulp exposure. Endodontic therapy will be necessary if pulp exposure
occurs.

4. Crown lengthening may be required to create
sufficient occlusogingival height of the clinical
crown to make a preparation with adequate retention.
5. A restoration may be required to restore teeth in
infraocclusion to the desired plane of occlusion.
6. Malaligned teeth may be corrected by
orthodontics, recontouring, or placement of a
restoration.

7. Endodontic therapy and reduction of the tooth to
approximately 2 to 3 mm above the gingival level will
allow otherwise hopelessly extruded or mobile teeth to
be used as overdenture abutments. Teeth used in this
manner can contribute outstanding vertical support to a
RPD. A third molar that is malformed or too weak for
clasping may be prepared in a dome shape and
covered with a denture base and used as vertical
support. This will prevent the RPD from having a distal
extension base supported only by soft tissue.
8. When the preceding considerations are not feasible
or practical, the offending teeth should be extracted.
Removal of teeth is always a last resort.

.
RECONTOURING PROXIMAL SURFACES OF POSTERIOR
TEETH
Proximal recontouring must always precede the
preparation of rests. When the rest seat is prepared
first, a sharp marginal ridge and even loss of part of the
rest preparation may result.
 Any sharpness is difficult to reproduce in the
definitive cast, the refractory cast and the RPD casting.
Fitting the framework to the mouth is more difficult.
A sharp marginal ridge is the first place to look for
interference, which prevents the framework from
seating. This defect can be found by using disclosing
wax .

Enameloplasty of a facially
tipped first premolar
recontoured to lower height
of contour to a more
favorable position

Recontouring the proximal surfaces of posterior
teeth reduces proximal undercuts, which permits
the minor connectors to be placed closer to the
proximal surface of the teeth.
Recontouring reduces the gingival embrasure
space and lessens the possibility of food
entrapment between the tooth and minor
connector or proximal plate.
Removing a small amount of proximal enamel
can often greatly reduce the undesirable undercut

Survey lines near occlusal surface
of tooth may be lowered by
recontouring., Survey line high on
interproximal of molar and premolar

Guiding planes are vertically parallel surfaces on
abutments and other teeth oriented so as to
contribute to the direction of the path of placement
and removal of a RPD. Guiding planes may be
prepared on any axial surface of a tooth but most
often are on mesial, distal, and lingual surfaces.
Guiding planes

Preparation of the
guiding plane

 Posterior proximal recontouring is also
used to create proximal guiding planes
that provide a more definitive path of
insertion and removal, making the
clasps more retentive.
 Proximal guiding planes aid in
stabilizing the abutments against
lateral forces and in stabilizing the
RPD against horizontal forces and they
reduce wedging stresses and provide
some retention.

1. Place the surveyed and designed diagnostic cast on the surveying
table at the correct tilt. Use it as a reference for correct
orientation of the handpiece in the mouth
2. With a smooth cut carbide fissure bur or a cylindrical diamond
rotary instrument (diamond bur) in the handpiece, use gentle,
light, sweeping strokes to extend the preparation from line angle
to line angle, following the normal proximal facial-lingual contour
of a tooth . At the same time, create a parallel surface that is 2 to
4 mm in occlusogingival height

Reduction of proximal surfaces of
posterior teeth.
Reduction must follow facial-lingual contour of
individual tooth. Reduction occlusal-gingivally must be
parallel to path of insertion.

RECONTOURING THE PROXIMAL SURFACES OF
ANTERIOR TEETH
Anterior edentulous spaces tend to close
rapidly after removal of teeth by a combination
of drifting and tipping, especially in younger
patients.
Judicious recontouring of teeth adjacent to
the edentulous space, which is smaller than
normal, can provide for a more
esthetic replacement of the missing teeth

Proximal surfaces of anterior teeth may be
reduced to permit using a slightly larger
replacement tooth on RPD and to reduce
unsightly large gingival embrasures.

 Use a cylindrical smooth cut carbide fissure bur such as a
no. 57 or 52, or a fine diamond instrument (bur) of a
comparable shape, to recontour the proximal surfaces.
Original facial-lingual contour of the proximal surfaces
should be maintained
 Tipped teeth require the greatest reduction to reduce
unsightly large gingival embrasure spaces.
 Combination of tooth reduction and tilting the cast in the
surveyor to change the path of insertion may often
establish a more esthetic result.

RECONTOURING FACIAL AND LINGUAL SURFACES
This procedure is performed almost exclusively on
posterior teeth, although it is occasionally necessary on
canines and other anterior teeth..
The retentive tip of a clasp is ideally located no higher
than the juncture of the gingival and middle third of the
clinical crown.
Although the retentive undercut is usually on the facial
surface of the tooth, and the same rule applies when the
retentive undercut is on the lingual surface .

Facial and lingual surfaces of teeth may be recontoured to
place retentive portion of clasp arm in gingival one third of
tooth.Crown of premolar divided into thirds showing undercut
(shaded portion) .

Proper position of circlet clasp with bracing portion of
clasp in middle third and retentive tip in gingival third.

Mandibular molars and second premolars are tipped
lingually and present problems such as high survey
lines with concomitant unusually large spaces adjacent
to the gingiva to trap food. Lingual plate could be used
to stabilize tooth but creates large space to trap food.

Survey line being lowered by reducing tooth with cylindrical-
shaped diamond rotary instrument. Reduction of tooth to
lower survey line creates guide plane, reduces amount of
space between lingual plate and tooth, and permits lingual
plate or reciprocal clasp arm to remain in contact with tooth
while retentive clasp arm is seated.

(REST SEATS)
FABRICATION OF REST PREPARATIONS:
A preparation must be made for each rest before making
impressions for the definitive casts.
A metal rest should never be placed on a tooth that has
not been adequately prepared to receive that rest.
When a rest is placed on an unprepared or improperly
prepared tooth, the action will be as if 2 inclined planes
were placed opposing each other.

Rests should not be placed on inclined planes
when related to long axis of tooth.

When it is in inclined planes,
the consequences-
 Inclined surfaces in contact with each other react to
applied force by moving away from each other.
 Rest on inclined planes of unprepared canine force
tooth and RPD in opposite directions under
masticating stress.
 Improperly prepared rest on premolar reduced only
marginal ridge for clearance with opposing
occlusion but inclined plane of rest seat still
remains. Tooth and RPD are forced away from each
other.

. Properly prepared rest seats change direction of
applied force, by 180 degrees, to pull tooth and RPD
toward each other to make them mutually supportive.
 Rest seat made with fossa deeper than marginal ridge
will pull abutment and RPD toward each other, during
mastication, to make them mutually supportive of each
other and system will direct force more directly along long
axis of abutment.
 Cingulum hook rest on maxillary canine will have
same effect.
Properly prepared rest seats

occlusal shows facial-lingual width of rest seats that should
be as wide as possible but approximately one half distance
between cusp tips of teeth and in length about one fourth
mesial-distal crown length of tooth.

Proximal view of preparations show spoon shape
of rest seat, maximum depth of 1 to 2 mm, and
that they flare at marginal ridge. Cross-section of
teeth showing that deepest part of preparation

Cross-section of teeth showing that deepest part of
preparation is in the fossae (and that marginal ridge is
higher than fossae. Angle formed between inclination of floor
of rest and vertical projection of greatest contour of proximal
surface must be less than 90 degrees.

The rest acts as a stop to prevent injury to and
overdisplacement of soft tissues under partial denture bases.
The rest maintains the attached clasp assembly in its
properly surveyed position.
The rest functions as an indirect retainer for distal extension
denture base additional rests may be positioned anteriorly or
posteriorly to the axis of rotation to act as indirect retainers.
The rest prevents food from becoming impacted between
the clasp and the proximal surface of the abutment.This is
one reason the rest is placed in an adjacent position to the
denture base.
Rests can close a small space between teeth by bridging
that space with back-to-back occlusal rests to restore
continuity.

Rests in posterior teeth
The outline for an occlusal rest is basically
triangular with the base of the triangle at the
marginal ridge and the apex extending toward the
center of the tooth.The apex of the triangle should
be rounded This shape follows the outline of the
mesial or distal fossa of the occlusal surface of
the tooth in which the rest seat is prepared

Step-by-step conventional single rest
preparation as made in posterior teeth.
Occlusal view to show
direction of successive
cuts.

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.

Lingual view of tooth to show
relative depth of preparation.

The length of a conventional rest varies from
onethird to one-half the
mesiodistal length of the tooth, approximately 3 to 4 mm.
 The facial-lingual width should be at least one half the
distance between the cusp tips or approximately one third the
facial-lingual width of the tooth .
The floor of the occlusal rest seat should be inclined slightly
toward the center of the tooth and should be concave or spoon-
shaped throughout.
The angle formed by the inclination of the floor of the rest
preparation and the vertical projection of the greatest contour of
the proximal surface of the tooth should be less than 90
degrees.

 Only when the angle is less than 90
degrees will occlusal forces be directed
more nearly parallel to the vertical axis of
the abutment and the framework and the
tooth forced together for mutual support
 The deepest part of the occlusal rest
preparation should be in the center of the
fossa of the tooth

Rests in posterior teeth clinical treatment options
 Occlusal rests should be prepared with a no. 4 round bur or
diamond bur of approximately the same size.
For larger teeth, a slightly larger round bur may be used.
 Start the bur in the floor of the fossa and make a cut about
one half the depth of the bur. Extend the cut the same depth
along the facial wall of the rest seat and over the marginal
ridge.

 Repeat the procedure for the lingual wall of the
fossa to make an inverted V-shape of the remaining
marginal ridge.
 Observe the cuts from the proximal surface to
determine the depth of the cut .
 When the cut is at the desired depth, remove the
enamel left between the 2 cuts to form the base of
the rest preparation. Blend the outside edges of the
bur cuts with the contours of the occlusal surface to
eliminate undercuts .

5. Flare the cuts slightly as they cross the facial and lingual
aspects of the marginal ridge .
6. Verify the depth of the rest preparation by having the
patient close on a small piece of red utility wax placed over
the preparation. Remove the wax and measure the depth of
the preparation with a thickness gauge made to measure
wax. (The most critical dimension is the amount of reduction
over the marginal ridge. The wax may also disclose
undercuts in the preparation if any are present.)
7. Round the marginal ridge to eliminate any sharp angles.

The outline form of an embrasure rest seat must
have through-and-through clearance wide enough
to accommodate two 18-gauge round wires side-by-
side if a double embrasure or crib clasp is to be
used.
Embrasure rests

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. A minimum clearance of 1
mm must be provided with the opposing occlusion.
3.The outline form developed for the rest must be
consistent with that of the usual occlusal rest
preparation for posterior teeth .
4. Extend the rest preparations over the facial and
lingual occlusal embrasures using the same bur or
diamond.

5. With the teeth in occlusion, guide the
patient through excursive movements and
carefully examine the space for the clearance
of the rest.
6. Blend the sides of the rest preparations into
the cuspal contour of the teeth.
7. An alternate method is to make a cut with a
cylindrical diamond instrument held flat facial-
lingually across the occlusal surface, along the
distal incline of one tooth and the mesial
incline of the other. This will provide ample
space for the metal of the cast clasp .

Long box rests
This type of rest is used almost exclusively for the
rotational path of insertion RPDs because the
conventional clasp arms are replaced by specially
designed rigid retainers that must fulfill the
requirements for bracing and encirclement and must
prevent rotation of the abutment.
In their syllabus on RPD design wrote “the most
critical elements in utilizing the rotational path are
the rest seat preparations and the development and
maintenance of intimate contact between the rigid
retainers and their corresponding tooth surfaces.

Dovetail rest preparation
Straight rest preparation
Proximal view of box preparations. Facial and lingual sides are nearly parallel to
each other and must be parallel to path of insertion and removal in lateral tilts of
cast.
Long box rests:

Long box rest clinical treatment options
1.After the path of insertion has been determined on
the diagnostic cast, it is meaningful to prepare the
rests in the stone cast to get a feel for the
angulations that will be required when preparing the
tooth in the mouth.
2. Use a carbide bur or diamond rotary instrument
(bur) to cut the rests. It must extend more than half
the mesial to distal length of the crown of the tooth
measuring from 1 marginal ridge.
3. Make the rest preparations 1.5 to 2 mm deep and
the lateral walls nearly parallel to each other or
slightly divergent toward the occlusal surface .

4.Make the floor flat and at right angles to
the long axis of the tooth.
5. The occlusal outline may be made
asymmetrical (dovetailed) or it may be
made straight for severely tipped teeth.
6. Slightly bevel the occlusal edge of the
cavosurface.

Cingulum rest in anterior teeth clinical treatment
options
1.An inverted cone carbide bur no. 37, inverted cone
green stone, or a small knife-edged diamond wheel
may be used to prepare the cingulum rest. Cut slowly
and with extreme caution.
2. Start the preparation incisal to the cingulum. The flat
side of the cutting instrument should follow the incline
of the lingual surface of the tooth cutting toward the
apex of the tooth. Continue cutting gingivally by
moving the tool mesially and distally in an arc to form
the notch. Care should be used not to create an
undercut

 3. Use a small knife-edged carborundum
impregnated rubber abrasive wheel to
remove sharp edges and polish the
preparationThe desired shape and
sharpness of the knife-edged rubber wheel
can be maintained by rotating it against a
diamond disk.
 4. Never attempt to round sharp edges of
this preparation with a bur or stone.

Rests in anterior teeth—cingulum rest
The cingulum rest seat is usually prepared on the cingulum of a maxillary
canine.
Profile of canine seen from distal view
Reduction made in enamel for rest preparation in cingulum of maxillary
canine..
Crescent-shaped contour of preparation

Rarely does the mandibular canine have the anatomic
contours or the thickness of enamel necessary for a cingulum
rest preparation. The rest seat is an inverted U shape.
 The lingual surface of the tooth makes up the inner wall,
while the outer wall of the U-shaped notch starts at the apex of
the cingulum and inclines gingivally toward the center of the
tooth to meet the inner wall of the preparation.
 Sharp angles should be avoided because they create
problems in casting and fitting of the framework
The outline form should be in the shape of a crescent and
form a smooth curve from one marginal ridge to the other. The
deepest portion should be in the center of the tooth over the
cingulum.

Cingulum rest in anterior teeth clinical
treatment options
 An inverted cone carbide bur no. 37, inverted
cone green stone, or a small knife-edged
diamond wheel may be used to prepare the
cingulum rest. Cut slowly and with extreme
caution.
 Start the preparation incisal to the cingulum. The
flat side of the cutting instrument should follow
the incline of the lingual surface of the tooth
cutting toward the apex of the tooth. Continue
cutting gingivally by moving the tool mesially and
distally in an arc to form the notch. Care should
be used not to create an undercut .

Use a small knife-edged carborundum
impregnated rubber abrasive wheel to remove
sharp edges and polish the preparation.
The desired shape and sharpness of the knife-
edged rubber wheel can be maintained by
rotating it against a diamond disk.
Never attempt to round sharp edges of this
preparation with a bur or stone.

Incisal rests in anterior teeth
Usually used on mandibular canines, the rest seat consists of a
small inverted U-shaped notch on the incisal surface just inside
the proximal corner of the tooth with the deepest part of the
preparation toward the center of the tooth mesial-distally .
Lingual view of preparation. It may extend down lingual surface to make room for
metal.

Preparation from proximal surface.
Facial view of preparation
The notch should be
rounded

The notch should be rounded and carried slightly over the
facial surface to provide positive seating. The enamel, lingual
to the notch, may be prepared to accommodate some of the
bulk of the minor connector .
Sharp points and angles must be avoided. Although the
incisal rest seat may be used on a maxillary or mandibular
canine, it is most often used on the mandibular canine. When
a cast restoration is made for a canine tooth, a cingulum rest is
the rest of choice.

Incisal rests in anterior teeth clinical treatment options
 Use a small knife-edged diamond wheel or green stone to
prepare a U-shaped notch 1.5 to 2 mm inside the proximal
corner . Move the cutting instrument in an inverted U-shaped
motion and extend the cut to the facial and lingual surfaces of
the tooth. Use it to partially prepare the lingual surface to
accommodate the minor connector .
 Round the notch and remove any sharp points or angles with
a small knife-edged carborundum impregnated rubber wheel.
Caution should be taken to use light pressure and intermittent
contact of the rubber wheel with the tooth; prolonged contact
may create considerable heat and cause severe pain for the
patient. The groove should continue to be polished and shaped
with the same U-shaped motion, used to cut the notch or
groove in incisal rest option above, until the cut surfaces are

SMOOTH AND POLISH ALL GROUND SURFACES
All surfaces that have been prepared must be
smoothed and polished. Scratches and
roughness contribute to
plaque accumulation.
When proper instrumentation and procedures are
used, the prepared surfaces can be returned to
the same degree of smoothness and polish as
existed before tooth preparation.

When extensive recontouring of the teeth is required,
it is advantageous to verify the accuracy of the
preparations by making an irreversible hydrocolloid
impression and then pouring a cast. The cast can be
poured with an accelerated mix of stone (use
concentrated slurry water from the cast trimmer to
accelerate the set). While the stone is setting, proceed
with finishing and polishing the prepared surfaces of
the teeth. When the cast is hard, place it on a
surveyor and analyze the preparations. There may be
some areas of the preparation that can be markedly
improved by a small additional amount of
recontouring.

 When deep scratches are present in the enamel, they
should be removed by lightly preparing the scratched
surface with a fine diamond or white stone before
attempting to polish them.
 The most effective method of polishing enamel
involves the use of rubber abrasive wheels or points
impregnated with carborundum. Use them with light
intermittent pressure and moderate speed as they
can generate considerable heat, which may cause
pulpal damage and can be painful for the patient.

 For posterior rest preparations, use a dulled
carbon steel bur of the same size as the bur
used to make preparations. Run the bur in
reverse to polish the otherwise inaccessible floor
of the rest seat preparations. This will eliminate
fine scratches and produce a good degree of
smoothness.
 Apply fluoride gel to the surfaces after
polishing.

Flouride gel is placed in mouth
guard which is worn by a
caries prone patient for
prescribed period.

A vacuum adapting machine
is used to form plastic
mouth guards

Restoring abutments with cast restorations (surveyed
crowns)
A cast restoration may be required on an abutment,
when the tooth has a large carious lesion or is
weakened because of large restorations whether or
not it has recurrent caries.
An abutment may require a cast restoration because
it has inadequate contours for clasping or required
recontouring will expose the dentine. Teeth may be
restored when they are in infra- or supra-occlusion to
correct the occlusal plane. Regardless of the reason
for placing cast restorations on abutments, the cast
restoration should provide ideal contours for clasping
the abutment.

To ensure proper tooth preparation, it is important that all
abutments involved in the RPD design that do not require cast
restorations have been prepared to accommodate the RPD
design.
1. After carefully studying and planning the reduction of the tooth
on the diagnostic cast, prepare the tooth. The lateral walls of the
preparation must be in line with the path of insertion of the RPD
as much as possible. Frequently, more tooth removal is required
than for a routine preparation so the ideal position of the survey
lines and crown contours may be obtained. The preparation
should include the removal of enough tooth structure to
accommodate the rest seat. If possible, tipped molars should be
prepared to align the axial surfaces with the path of insertion.

 2. Make an elastomeric or agar impression
of the entire arch containing the
preparations and a complete arch
impression of the opposing dentition.
 3. Make a definitive cast with removable
dies and an opposing cast with type 4 or 5
dental stone.
 4. Make interocclusal records and use a
face-bow to aid in mounting the casts in an
articulator.

Wax the crown(s) with ideal contours, guiding
planes,and rest seats keeping in mind the need for
retention, bracing, and support for the clasps of the
RPD.
 A surveyor must be used to verify the contours in
relation to the path of insertion.(Wax cutters are
available for use in handpieces and milling devices in
varying sizes with tapers from 0 to 4 degrees.)

 Sprue, invest, cast, recover, finish, and
polish the casting(s).
 Both the wax crown and the casting can be
machined with a handpiece and a bur or a
stone by using a handpiece holder attached
to the dental surveyor or self-contained
milling devices, such as the Bachmann
parallelometer instrument or similar
instruments.

Precise guide planes can be perfected by this
procedure. Milled surfaces must be carefully
repolished before cementing them.
 Milling carbides and polishing stones for metal can
be purchased in various sizes with
tapers from 0 to 4 degrees.

 Never cement a cast restoration until the contours,
guiding planes, and the retentive undercuts have
been verified with the castings on the definitive cast
mounted in a dental surveyor. This verification must
be made with the polished casting(s) on the
surveying table at the tilt used for the design of the
partial denture framework to make certain that the
desired contours and undercuts have not been lost
in the finishing and polishing process of the cast
restoration.
 After the surveyed crowns and RPD have been
fitted to the cast, they must be fitted to the mouth
with disclosing wax or other disclosing medium

Preparing teeth to receive a removable partial
denture(J Prosthet Dent 1999;82:536-49.) Robert
w.ruddDDS,MSa,etal
The success or failure of a removable partial denture is dependent on
many factors. To achieve success, the practitioner must develop and
sequence a sound treatment plan based on clinical and radiographic
evidence. These findings must be carefully considered in prosthesis
design and mouth preparation. Particular attention must be given
to the proper placement of guiding planes and well-made rest
seats and the use of surveyed crowns on abutment teeth. This
article describes the rationale, importance, and clinical procedures
for abutment preparation for removable partial dentures.
Related articles:

Dentinal Exposure Resulting
From Ball Rest Seat Preoarations on
Mandibular Canines
Lay D.Haisch, DDS, and CarlA. Hansen, DDSf, J Prosthod
2:70-72,year1993 by the American College of Prosthodontists
Twenty extracted mandibular canine teeth were prepared with
lingual ball rest seats.
The preparations were placed in the area with the greatest
horizontal component.
The depth of tooth penetration was determined by the
establishment of a positive seat.
In all specimens, the enamel was penetrated and the dentin
exposed.

 The authors note that, when ball rests are placed in
mandibular canines, one should assume dentin
exposure. The authors also recommend that suitable
restorations be placed on a routine basis.
.

Surveying removable partial dentures: the
importance of guiding planes and path of insertion
for stability , O.L. Bezzon DDS, PhDa, M.G.C.
Mattos DDSa and R.F. Ribero DDSb
(J Prosthet Dent 1997;78:412-18
This article uses an academic approach to describe
the criteria used to determine the path and removal
a removable partial denture. A fundamental
requirement for understanding the correct use of
dental surveyor is to prevent indiscriminate use of a
path of insertion perpendicular to the occlusal
and extreme inclinations of the cast in the attempt
create undercuts on some teeth.

Thickness of the remaining enamel after the
preparation of cingulum rest seats on
maxillary canines
(J Prosthet Dent 1998;80:319-22.)
Artemio Luiz Zanetti DDS,etal
Purpose. This study evaluated the level of tissue
removal that takes place on enamel and dentin during
cingulum rest seat preparation.
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.

conclusion
 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.

mouth prepration in rpd.ppt

More Related Content

What's hot (20)

Similar to mouth prepration in rpd.ppt (20)

Recently uploaded (20)

mouth prepration in rpd.ppt