1. Mouth preparation for removable partial dentures involves several steps including surgical procedures, periodontal therapy, conditioning abused oral tissues, conservative restorative treatment, and prosthetic therapy. 2. Prosthetic therapy includes preparing guide surfaces, lowering survey lines, widening embrasures, creating retentive undercuts, and preparing rest seats. Rest seats are prepared on posterior and anterior teeth to act as stops and indirect retainers. 3. Preparing rest seats involves reducing marginal ridges, deepening adjacent fossas, and blending them together into a triangular shape for posterior teeth and U-shaped notches for anterior teeth.

1. STEPS OF MOUTH PREPERATION
1- Completion of required surgical procedures:
-
Conditions requiring surgery include:
-
Extraction of unrestorable teeth , teeth with insufficient periodontal support
- Elimination of tori or prominent exostosis.
- Removal of hyperplastic tissue
- Ridge augmentation, vestibular extension and implant placement should be performed early.
- Surgical reduction of maxillary tuberosities to provide adequate restorative space
2- Periodontal Therapy
- Should be done early in treatment plan
- Periodontal scaling and root planning to eliminate local factor.
- Elimination of pockets and periodontal flap when necessary .
-
Gingivoplasty and gingivectomy
-
Remaining natural teeth with dead periodontal support and stabilization for RPD and
resistance of abutment to applied force
This includes:
Fixed Splinting
- include completion of partial coverage restoration.
-
Fixed splinting of posterior teeth
a- teeth distal to canine  anteroposterior resistance
b- teeth mesial to canine  mediolatral resistance
Disadvantages of fixed splinting:
-Inability to adequately clean splinted unit (inability to floss) 
leading to inadequate oral hygiene
-High cost
Splinting with removable partial denture

2. Designed so that its components join the teeth as functional units .
- This include:
1- multiple buccally positioned clasp arm
2- lingual plating
3) Conditioning of abused oral tissues:
May develop due to ill-fitting or poorly occluding old RPD so tissue must get rest and treatment in the
following sequence:
1.Patient education and oral hygiene instruction
2.Removal of the dentures from the oral cavity
3.Oral hygiene measures
4.Use of tissue conditioners
5.Modifications to existing prosthesis
6.Provisional prosthesis or Interim prosthesis
4) Conservative treatment :
Include  -Restorative fillings
- Crowning
Endodontic treatment
5) Prosthetic Therapy
a) Occlusal equilibration analysis.
1- Correction of irregular occlusal plane.
2- Correction of malaligned occlusal plane.
3- Verifying the occlusion
4- Treatment of traumatic vertical overlap
b) Teeth reshaping
1- Development of guiding planes
2- Change the height of contour

3. 3- Enhance retentive undercuts
c) Rest Seat preparation
1- For posterior teeth
2- For anterior teeth
d) Precision attachment
OCCLUSSAL EQUILIBRATION ANALYSIS:
1-correction of irregular occlusal plane (occlusal plane discrepancies) , this includes:
*supra eruption (over eruption)
*infra eruption
*tipping
Phases of mouth preparation for removable partial dentures
I- Phase
. Periodontal
. Operative
. Endodontic
. Orthodontic
. Surgical
II-Phase
. Involves the alteration of tooth
contours to allow the proper fit
and functioning of the proposed
removable partial denture.
Suggested clinical sequence for tooth preparations

4. 1- Prepare guide surfaces
2- Lower survey lines to improve clasp location
3- Carry out embrasure widening
4- Create retentive undercut.
5- Prepare rest seats
1- Guide surfaces
. Are prepared on proximal surfaces of abutments adjacent to edentulous spaces.
. Proximal guide surfaces should be about as wide the distance between tips of buccal & lingual
cusps.
Guide Surfaces
A guide surface should
be prepared by even
reduction of the tooth
surface
maintaining
its contour and not as
flat surface.
Guide Surfaces
A proximal guide
surface should be
2-3mm high and
about as wide the
distance between
the buccal and
lingual cusps.

5. Guide Surfaces
Checking orientation
of the bur to the path
of insertion on the
surveyed cast.
Guide Surfaces
Cylindrical diamond bur is moved back and
forth around involved tooth surface
Lowering Survey Lines
Lowering survey lines by reduction of tooth bulbosity will improve clasp placement by allowing :1. The origin of clasp arm to be placed well below the
occlusal surface.
Restoring abutments with cast restorations (surveyed crowns)
Indications
. Large carious tooth
. Weak tooth because of large restorations
. Recurrent caries
. Abutment with inadequate contours or
required contouring will expose the
dentine.
Lowering Survey Lines
Using Cylindrical bur.
The bur is placed
against the involved

6. surface, the head of
hand piece is tipped
slightly towards the
centre of the tooth
and moving the bur
back and forth.
Embrasure widening
Achieved by enlarging
the lingual embrasure
with a narrow tapered
diamond bur.
Rest seat preparation
Functions of Rests
. Acts as a stop to prevent injury to
and overdisplacement of soft tissues
under partial denture bases.
. Maintains the attached clasp assembly
its proper surveyed position.
. Acts as an indirect retainer.
Rest seats in Posterior teeth
. The outline form is basically triangular
with the base of the triangle at the
marginal ridge and apex extending
toward the center of the tooth.
. The apex of the triangle should be

7. rounded.
Rests in posterior teeth
. This shape follows the outline of the
mesial or distal fossa of the occlusal
surface of the tooth.
. The length varies from one third to
one half the mesiodistal length of
the tooth (3-4mm).
Rests in Posterior teeth
. The bucco-lingual width should be at
least one half the distance between
the cusp tips( one third the bucco-lingual
width of the tooth).
. The floor of the occlusal rest should be
inclined slightly toward the center of the
tooth ( concave or spoon shape).
Rests in Posterior teeth
. 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.
Rests in Posterior teeth

8. . 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
1- The preparation is started by first
reducing and rounding the middle
third of the marginal ridge using a
round bur of an appropriate size
( no.6 for molars, no.4 for premolars).
Clinical Treatment Options
2- This is followed by deepening the
of the adjacent fossa which is then
blended into the reduced marginal
ridge.
Clinical Treatment Options
3- Verify the depth of the preparation
by having the patient close on a
small piece of red utility wax placed
over the preparation.
Clinical Treatment Options
4- Once complete, the preparation
should be examined to ensure that
no interferences to the path of
insertion have been created and
any small enamel “lips” should be

9. smoothed.
Rests
Cingulum Rest seat
in
. Is usually prepared on the cingulum of a maxillary canine.
. 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.
Cingulum Rest Seat
. The outline form should be in the
shape of crescent and for 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,
round high speed diamond bur (no.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
towards the apex of the tooth.
Anterior
teeth

10. Cingulum rest in anterior teeth, clinical treatment options
. 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.
Incisal Rests
. 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 mesio-distally.
Incisal Rests
. The notch should be rounded and
carried slightly over the labial surface
to provide positive seating.
. The enamel, lingual to the notch, may
be prepared to accommodate some of
the bulk of the minor connector.
Incisal Rests in anterior teeth, clinical treatment options
. Use a small knife-edged diamond

11. wheel or green stone to prepare a
a U-shaped notch 1.5 to 2 mm inside
the proximal corner.
Incisal rests in anterior teeth, clinical treatment options
. Move the cutting instrument in an
inverted U-shaped motion and
extend the cut to the labial and
lingual surfaces of the tooth.
. Use it to partially prepare the lingual
surface to accommodate the minor
connector.