• Microanalyser is a type of surveyor which electronically measures
• Cast should not be tilted more than 10° at the time of surveying.
• One of the most important functions of the clasp is to distribute the
• The main purpose of tilting the cast in surveying is to determine the
most desirable path of placement.
• The scriber on the surveyor marks the greatest convexity of the
Objectives of Mouth Preparation and Preprosthetic Phase of Mouth
Preparation in Partially Edentulous Patients, 289
Relief of Pain and Any Infection, 290
Conditioning of Abused or Irritated Tissues, 290
Prosthetic Phase of Mouth Preparation in Partially Edentulous
Preparation of the Rest Seat, 293
Rest Seat Preparation on Tooth Enamel, 293
Rest Seat Preparation on New Gold
Rest Seat Preparation in Amalgam
Rest Seat Preparation for Embrasure
Rest Seat Preparation on Anterior Teeth, 294
Incisal Rest Seat Preparation, 294
Creation of Retentive Undercuts, 294
Modification of Height of Contour, 294
Preparation of the Guiding Planes, 295
Preparation of the Guiding Planes, 295
Mouth preparation is one of the most critical steps in successful
removable partial dentures (RPDs). It helps not only in replacing what
is missing but also in preserving the remaining tissues. It aims to
bring oral tissues to optimum health and removes any cause which
may interfere in success of RPD.
Objectives of mouth preparation and
preparation in partially edentulous
Mouth preparation is a procedure which changes or modifies the
existing oral conditions in order to facilitate the placement and
removal of the prosthesis and to ensure its long-term functioning.
• To eliminate any condition which may interfere in the placement or
• To establish abutment teeth and supporting structures in optimum
• To establish an acceptable occlusion plane
• To alter or shape the contour of the abutment tooth so that it can
best accommodate the removable prosthesis
Mouth preparation is often accomplished by two phases:
• Preprosthetic phase: This involves the elimination of any condition
which can hinder the placement or removal of the prosthesis and
long-term success of the prosthesis.
• Prosthetic phase: This involves shaping or altering the contour and
form of the teeth or supporting structures to receive the removable
Preprosthetic phase of mouth preparation includes the following
(i) Relief of pain and any infection
(iii) Conditioning of abused tissues
(vi) Orthodontic correction for misalignment
(vii) Splinting of weakened teeth for better support
Relief of pain and any infection
• Any aetiology which causes pain to the teeth should be treated first
• The most common cause of pain is caries or defective restoration.
• Acute pain or abscess should be treated first in this phase of
• Deep carious lesions need to be treated with intermediate
restoration until definite treatment plan is formulated.
After the relief of pain, oral surgical procedures should be done so
that enough time is given between the surgery and the impression
• These procedures include extraction of teeth with hopeless
• Extraction of residual root, impacted teeth or unerupted teeth
• Surgical removal of cysts, palatal or mandibular tori, exostosis
• Preprosthetic surgical procedures such as ridge augmentation or
• Removal of abnormal soft tissue lesions such as polyps and
• Removal of sharp bony spicules and rounding of sharp knife-edge
• Surgical correction of jaw deformity
Note: In any surgical procedure, the main objective should be
preservation of as much bone as possible.
Conditioning of abused or irritated tissues
All the abused or irritated tissues should be treated before
impressions are made of the edentulous ridges.
• Inflammation of the mucosa covering the denture-bearing area.
• Burning sensation in residual ridge, the tongue, the lips and the
• Distortion of normal anatomical structures such as retromolar pads,
incisive papilla or the rugae region.
• Causes: Ill-fitting dentures, unstable removable prosthesis with
deflective occlusion, nutritional deficiencies and endocrine
imbalance are the probable causes.
• Treatment: It depends on the condition of the tissues. If the tissues
are slightly inflamed, then symptomatic treatment such as massage,
saline rinses and rest to the tissues are advised. If tissues are
abused, wearing of the prosthesis is discontinued for some time.
Tissue conditioners are advised, which give a cushioning effect on
This therapy is done to restore the mouth to a healthy state. The
objective is to establish and maintain the periodontium in a healthy
The criteria to satisfy the objective are as follows:
• To eliminate aetiological factors causing periodontal disease
• To eliminate periodontal pockets
• To establish harmonious occlusal relationship
• To develop a proper plaque control programme
Caution: It is important to ensure that the periodontium is in a
healthy state before other phases of the treatment are initiated.
It is often observed that in partially edentulous patients the occlusal
plane is uneven. This may be due to supraeruption of the opposing
teeth or due to mesial migration of the adjacent teeth or tipping of the
teeth adjacent to the edentulous area.
There are many methods to correct the uneven occlusal plane;
however, selection of a particular method depends on the severity of
Methods to correct uneven occlusal planes
1. Enameloplasty: It is a procedure involving intentional removal of a
portion of tooth structure in order to correct the occlusal plane.
However, the amount of correction possible by this method is very
limited. Often the reduction is confined to tooth enamel, except in
older patients where the reduction can be in dentine. The cut surface
should always be polished (Fig. 18-1).
2. Onlay: Occlusal surface of teeth to be restored with onlay should be
free of pits and fissures. Cast gold onlays are most effective in
establishing the occlusal plane through this method.
• Natural contours of tooth can be maintained.
• It requires lesser tooth reduction.
• Chrome alloy onlays can rapidly wear the enamel of
3. Crown: A full veneer crown is normally indicated, if crown height
of the tooth is desired to be changed or if the facial, lingual or
proximal surfaces are to be altered. The mounted diagnostic casts are
an important diagnostic aid to decide the desired amount of tooth
4. Endodontically treated tooth with a coping: Teeth which are
supraerupted or with compromised bone support can be
endodontically treated and covered with a coping or a crown and can
be used as an abutment tooth (Fig. 18-2).
5. Extraction: It is indicated when tooth is severely malposed and
those that cannot be orthodontically corrected should be removed. It
is also advised in the following situations:
• When certain teeth can complicate and compromise
• Teeth interfering with the placement of the major
connector wherein it cannot be corrected by crown
6. Surgical repositioning: This involves repositioning of the jaws (by
surgical methods) to correct severe malocclusion.
FIGURE 18-1 Enameloplasty done to correct the occlusal
FIGURE 18-2 Endodontically treated tooth with coping can
be effectively used as abutment tooth.
Following are the methods used to correct misalignment:
Provision of support to weakened teeth
Teeth with compromised periodontal support require additional
support which can be provided by the following methods:
Prosthetic phase of mouth preparation
in partially edentulous patients
The prosthetic phase of mouth preparation includes the alteration of
the tooth contour usually in the enamel or on the surface of existing
restoration or on new restoration in the form of crown, onlay, etc. It is
always better to do the desired reduction on the mounted diagnostic
cast before doing the reduction into the mouth. Clinicians should
employ conservative approach during mouth preparation.
Prosthetic phase of mouth preparation includes the following stages:
(i) Preparation of the guiding planes
(ii) Preparation of the rest seat
(iii) Creation of retentive undercuts
(iv) Modification of height of contour
Rest seat is always prepared after guiding planes are prepared on the
abutment tooth. Rest seat preparation is done differently for tooth
enamel, existing restorations or new restorations.
Rest seat preparation on tooth enamel
A small round diamond stone bur is used for the preparation of the
rest seat on the tooth enamel.
• The outline form of reduction is triangular with the base of triangle
at the marginal ridge and the apex towards the centre of the tooth.
• It is 1 mm thick at the thinnest portion, if chrome alloy is used and
1.5 mm thick, if gold is used.
• Properly prepared rest seat is round, smooth and spoon-shaped.
• The rest in the rest seat should act as a ball and socket joint
(especially in the distal extension cases).
• Beading wax is used to check the amount of available space for the
occlusal rest by asking the patient to bite on the wax in the centric
• Thickness of the wax is then measured by using Boley gauge.
• After preparation, the altered tooth surface should be highly
Rest seat preparation on new gold restorations
The proposed rest seat preparation is carved in the wax pattern after
the guiding planes are carved.
• A small depression is made on the wax pattern to accommodate the
thickness of the rest and the crown casting.
• Once the restoration is cast with gold, the rest seat is highly
• In cases of existing gold restorations, the rest seat is directly
• If the existing restoration is not adequately thick, a new restoration
should be advised to the patient.
Rest seat preparation in amalgam restorations
This procedure is less desirable than tooth enamel or gold
• The rest seat is prepared with a small round bur.
Note: Amalgam alloys tend to warp when placed under constant
• If care is not taken during the preparation of proximal portion, it
may result in fracture of the amalgam restoration.
• Polishing of the prepared rest seat on the amalgam restoration is a
Rest seat preparation for embrasure clasp
Embrasure clasps are two simple circlet clasps joined together at the
• The rest seats are prepared on two adjacent posterior teeth
extending from the mesial fossa of one tooth to the distal fossa of
• The preparation is continued on the buccal and lingual surfaces.
• A small round diamond stone is used to accomplish the reduction.
• Marginal ridges on both the teeth are simultaneously reduced.
• Contact point between the teeth should be left intact to prevent
wedging action between the teeth.
• Alternatively, preparation can also be done by cylindrical diamond
• The preparation for this clasp should be 1.5–2 mm wide and 1–1.5
• The occlusal clearance is checked by utility wax.
Rest seat preparation on anterior teeth
Cingulum or lingual rest seat preparation is more preferred than the
• In cast restorations, the lingual rest seat is carved in the wax pattern.
• Safe-sided disk or inverted cone diamond stone is used to prepare
• The preparation should be polished with carborundumimpregnated rubber wheel.
These rest seats are usually placed on the incisal angles of the canines.
• The seat should be avoided on the incisors because of poor
aesthetics and poor mechanical advantage.
• It is prepared by small safe-sided diamond disk.
Creation of retentive undercuts
• If the proposed abutment does not have sufficient retentive
undercut, it should be created.
• It is created in the form of gentle depression by a small round-ended
• The procedure for creating a retentive undercut is called dimpling.
• It is prepared parallel and as close as possible to the gingival
• The preparation is created approximately 0.010-inch deep with
slight concavity when measured from the perpendicular line which
parallels the path of insertion.
• The dimension of the depression is approximately 2 mm of
occlusogingival height and 4 mm of the mesiodistal length.
• The prepared depression should be highly polished with the
carborundum-impregnated rubber (Fig. 18-4).
FIGURE 18-4 Dimpling done with round-ended tapered
diamond bur to create retentive undercut.
Modification of height of contour
This procedure is performed to ideally locate the clasp arm and
• It is done by reshaping the abutment tooth in tooth enamel.
• Minor reshaping of the tooth surface can drastically improve the
mechanical and aesthetic properties.
When the cast restoration is indicated on the abutment tooth, the
retentive undercut, height of contour and the guiding planes can be
incorporated in the wax pattern itself.
• First the diagnostic cast is surveyed and carefully analysed.
• If the tooth planned for cast restoration is lingually tilted, more
reduction should be accomplished lingually.
• Wax patterns of the crowns to be placed on the abutment are carved
• In a casted restoration, the contour created in the wax patterns is
verified on the surveyor table.
Preparation of the guiding planes
Guiding planes are parallel surfaces on the proximal or the lingual
surface which are made parallel to the planned path of insertion of the
removable prosthesis. The intentional conservative tooth reduction to
prepare guiding planes is called enameloplasty. It is defined as ‘the
intentional alteration of the occlusal surface of the teeth to change their form’.
Guiding plane is defined as ‘vertically parallel surfaces on the abutment
teeth or/and dental implant abutments oriented so as to contribute to the
direction of the path of placement and removal of the removable dental
Guiding planes are necessary for smooth placement and removal of
the dentures. These are prepared during the prosthetic phase of
mouth preparation of the abutment teeth (Fig. 18-5).
FIGURE 18-5 Guide plane with 2–4 mm occlusogingival
• Guiding plane helps in smooth placement and removal of the
• It helps in stabilization of the prosthesis against horizontal forces.
• It ensures predictable clasp assembly function.
• It helps in reducing wedging forces between the teeth.
• It improves retention by frictional resistance.
• It decreases undesirable space between the tooth and the prosthesis,
thus aiding in oral hygiene maintenance.
• It can provide indirect retention to the prosthesis.
• It helps in restoring original width of the edentulous space.
Types of guiding planes on the basis of their
(i) Guiding planes on the abutment in tooth-supported cases
(ii) Guiding planes on the abutment next to the distal extension
(iii) Guiding planes on the lingual surfaces of the abutment teeth
(iv) Guiding planes on the anterior abutment teeth
Preparation of the guiding planes
• After the diagnostic cast is surveyed and the tilt of the particular
design of partial dentures is planned.
• Similar relationship is duplicated in the patient’s mouth during
• A cylindrical diamond point is used to make the preparation. A
light sweeping stroke from the buccal to the lingual line angle is
• Approximately, 2–4 mm of flat surface is created on the
occlusogingival surface parallel to the planned path of insertion.
• Usually, five to six light sweeping strokes are sufficient to produce
• Reduction should always follow the contour of the tooth.
• All the prepared tooth surfaces should be polished with
carborundum-impregnated rubber wheel after preparation.
• Fluoride gel application can be advantageous on the prepared
• In distal extension cases, the occlusogingival height of the plane is
reduced to 1.5–2 mm in order to facilitate the rotation of the partial
denture around the distal occlusal rest.
• Guiding planes on the lingual surface ensure maximum resistance
to the lateral stresses, thereby, providing additional stabilization.
• Shape of the rest seat in natural posterior teeth should be saucershaped.
• A rest helps to transmit the occlusal stresses parallel to the long axis
Impression making in removable
Impression Making in Tooth-Supported Partial Denture Cases, 297
Factors Influencing the Support of the Distal
Factors Influencing the Support of the Distal
Extension Partial Dentures, 298
Impression making is done after the mouth preparation is completed.
This is one of the most fundamental areas for the success of removable
partial denture (RPD). The impression of the teeth is made using
impression material in anatomic form, whereas impression of residual
ridge is recorded in functional form. Therefore, dual impression is
required to obtain the master cast. It is essential to study various
impression techniques and impression materials used in fabrication of
Impression making in tooth-supported
The impression making in tooth-supported partial denture cases is
simpler when compared with tooth tissue-supported denture cases. In
tooth-supported partial denture cases (Kennedy class III and most of
Kennedy class IV), the functional forces are transmitted directly along
the long axis of the teeth through the rests. In this case, the edentulous
ridge will not contribute to the support of partial denture, as the
abutment teeth bear the forces before they reach the edentulous ridge.
Therefore, in tooth-supported partial denture cases, functional
impression is not required and the impression can be made in
anatomic form. The denture can be fabricated on the cast made by
impression of the tissues in anatomic form. Irreversible hydrocolloids are
the most widely used material for making impression in anatomic
form. The alginate impression should be poured within 12 min after
being removed from the mouth. The alginate impression material is
easy to handle, relatively inexpensive, dimensionally accurate and
does not require expensive armamentarium.
Factors influencing the support of the distal
In distal extension cases, the support is derived from both the
edentulous ridge and the abutment tooth. Therefore, a dual
impression technique is advocated to equalize the support derived
from both the edentulous ridge and the abutment teeth. The
impression of the teeth is recorded in the anatomic form and the
impression of the soft tissues is recorded in the functional form.
Factors influencing the support of the distal
Type of soft tissue covering the edentulous ridge: A firmly bound
adequately thick attached mucosa provides the maximum support
Type of alveolar bone constituting the denture-bearing area: Cortical
bone with adequate thickness provides best support for the denture.
Design of the partial denture: It is important to reduce the amount of
stress on the edentulous ridge in distal extension cases. This is made
possible by the following ways:
• Placing indirect retainers anterior to the fulcrum
line in order to resist the rotational movement of
• Additional components such as minor connectors
are used to contact the proximal guide plane to
resist the rotation of the denture around the
Magnitude of occlusal force: Amount of force per unit of the denture
base is reduced to enhance the longevity of the prosthesis. It is done
• Broad coverage of the edentulous ridge.
• Narrowing of the occlusal table.
• Increasing efficiency of the occlusal table by
providing sluiceways to improve the mastication.
Amount of tissue covering the denture base: Broader the coverage of
the edentulous ridge, greater will be the distribution of the stresses.
ridges to provide maximum support.
• In the maxillary arch, buccal slopes of the ridge are
capable of resisting the lateral forces and the bony
palate is capable of resisting the vertical forces.
• In the mandibular arch, buccal shelf region is an
excellent primary stress-bearing area.
Fit of the denture base: Accurate fit of the denture is important in
transmitting forces to the primary stress-bearing area.
Impression methods used for distal extension
The dual impression technique is often indicated for distal extension
RPD. There are basically two types of dual impression techniques:
(i) The physiological or functional impression techniques
(ii) The selected pressure impression technique
Functional impression techniques used in distal
The functional impression technique records the edentulous ridge by
placing occlusal load on the impression tray during impression
making. By doing this, the underlying tissues are displaced under
Types of functional impression techniques:
(i) McLean and Hindel’s physiological method
(ii) The functional relining method
Mclean–Hindel’s physiological method
• The physiological impression technique was first advocated by
• According to the proponents of this technique, the tissues of the
residual ridge of distal extension cases are recorded in functional
form and then a second impression is made over it.
• A custom impression tray is fabricated over the primary cast of the
• Occlusal rim is made on the custom tray.
• The custom tray is loaded with the impression paste and the tray is
• The patient is asked to bite over the occlusal rim as the impression
• With the biting, the underlying tissues are compressed and the
tissues are recorded in functional state.
• Without removing the custom tray, a second impression is made
with alginate using a stock tray.
• While making the second impression, the finger pressure is applied
until the alginate impression material sets.
FIGURE 19-1 The patient is instructed to bite on a loaded
• Finger pressure is not equal to the biting pressure applied during
• The small amount of alginate material present between the occlusal
rim and the stock tray acts as buffer and restricts transfer of entire
load (finger pressure) to the custom tray.
• According to G.W. Hindel, the first impression which is made of the
edentulous ridge should be an anatomic impression, i.e. the
impression is made with impression paste without applying any
• Hindel developed a stock tray for the second impression which was
provided with holes so that the finger pressure could be applied
• While making the second impression, a finger pressure is applied
through the holes provided in the stock tray (Fig. 19-2).
• The finger pressure is maintained until the alginate sets.
• This pressure simulates the condition as if the masticatory force was
• The primary aim of this technique was to record the edentulous
ridge in the form of functional loading.
FIGURE 19-2 Impression making with Hindel’s modified
• In a denture made with this technique, if the clasp assembly is
effective, it will allow the denture base to displace the soft tissue in
functional form. This will lead to adverse tissue reaction and
• If the clasp assembly is not effective, it will maintain the denture
base slightly occlusal in rest position. When the patient occludes,
the artificial teeth come in contact before the natural teeth which is
• Here, a physiological impression is obtained to support a distal
extension denture base (after the completion of partial denture).
• It consists of adding a new surface to the tissue surface before the
insertion of the denture or at a later stage.
Steps in functional relining technique
• First an anatomic impression is obtained using irreversible
• The impression is poured to get the master cast.
• The master cast is duplicated to obtain a duplicating cast.
• Over the duplicating cast, a soft metal spacer is provided to ensure
uniform space for the impression material between the denture base
• The cast framework is then fabricated.
• After processing, the metal spacer is removed and an even space is
created between the denture base and the ridge.
• A low-fusing modelling plastic is flown over the tissue surface of the
denture base, tempered in water bath and seated in the patient’s
• This procedure is repeated until an accurate impression of the ridge
• Border moulding is accomplished by proper manipulation of the
• After completion of this procedure, a final impression is made by
uniform scrapping of modelling plastic to a depth of 1 mm to
provide adequate space for the impression material.
• The final impression is made with free flowing zinc oxide eugenol
paste. In case of undercuts, light-bodied polysulphide or addition
• During this technique, the patient is instructed to maintain the
mouth in partially open position.
• This is done in order to best control the movement of cheeks and the
tongue and observe the relationship between the framework and
• Fit of the denture base on the edentulous ridge is superior.
• The amount of soft tissue displacement can be controlled by the
amount of relief given. Greater the relief provided to the modelling
plastic before the final impression, lesser will be the tissue
• As this is an open mouth impression technique, it is difficult to
maintain a correct relationship between the framework and the
abutment teeth during impression making.
• It is difficult to maintain correct occlusal contact following relining.
• This technique is used to reline the existing partial denture
• This technique is used to correct the distal extension edentulous
ridge portion of the original master cast.
• To obtain the maximum possible extension of the peripheral borders
of the denture base without interfering with the function of the
• To record the stress-bearing areas in the functional form
• To record the non-stress-bearing areas in the anatomic form
• This is an open mouth technique.
• Fluid wax consists of special waxes which are rigid at room
temperature and it has the ability to flow at mouth temperature
(e.g. Iowa wax developed by Dr Smith and the Korrecta wax
developed by Dr O.C. Applegate and Dr S.G. Applegate).
• Approximately, 1–2 mm relief space is desired between the
impression tray and the edentulous ridge.
• Once the loaded tray is seated in the patient’s mouth, it should be
left undisturbed for 5–7 min in order to allow the wax to flow
sufficiently without pressure build up.
• For the clinical technique, a water bath is maintained at a
temperature of 51–54°C into which the wax container is placed.
• The fluid wax is painted on the tissue surface of the impression tray.
• Borders of the impression tray should be short by 2 mm of all
• It is important to note that the fluid wax lacks sufficient strength to
support itself, if the border is made short by more than 2 mm.
• The loaded tray is positioned in the patient’s mouth for at least 5
min before making another addition.
• Before every addition, the impression tray is inspected for proper
• If tissue contact is there, the wax will appear glossy; it will be dull, if
• The peripheral extensions are recorded by proper tissue movements
• These movements are repeated a number of times until a positive
• Once complete tissue contact with anatomy of the limiting border
tissue is evident, the impression tray is again placed in the mouth
for the final time for about 12 min to ensure complete flow of the
• The finished final impression is poured as soon as possible, as the
fluid wax is subjected to distortion, if not handled carefully.
• This technique can produce an accurate impression, if the steps are
• The procedure is time consuming and technique sensitive.
• Proper time period during impression procedure should be
followed; otherwise, an impression with excessive tissue
• This technique is based on the concept of loading the stress-bearing areas
and adequately relieving the non-stress-bearing areas.
• The custom tray is selectively relieved by trimming with acrylic bur.
• The primary stress-bearing areas are minimally relieved and the
non-stress-bearing areas are sufficiently relieved.
• Greater the relief, lesser will be the tissue displacement and vice
• In the lower arch, the buccal shelf area is the primary stress-bearing
area and should be slightly relieved.
• The lingual slope of the residual ridge that resists the horizontal or
the rotational forces should also be relieved minimally.
• In patients with easily displaceable tissues covering the ridge, more
relief can be obtained by making holes in the impression tray so as
to avoid excessive pressure of the impression material.
• This technique provides a closely fitting denture base.
• The tissues are selectively loaded depending on the stress-bearing
• It is difficult to accurately demarcate and relieve the stress-bearing
Altered cast technique or corrected cast
• In both the fluid wax impression technique and the selective
pressure impression technique, an impression of the edentulous
ridge is made by the impression tray attached to the metal
• The master cast is then altered to accommodate new ridge
• This technique is called the altered cast or the corrected cast technique.
Altered cast partial denture impression is defined as ‘a negative
likeness of a portion or portions of the edentulous denture bearing areas made
independent of and after the initial impression of the natural teeth. This
technique employs an impression tray(s) attached to the removable dental
prosthesis framework or its likeness’. (GPT 8th Ed)
Altered cast is defined as ‘a final cast that is revised in part before
processing a denture base also called corrected cast or modified cast’. (GPT
The altered cast method is composed of the following three main
Step 1: Individual acrylic resin impression base is added to the lattice
• Holes are placed along the alveolar groove for the
excess impression material to escape.
• Framework with the attached trays is adjusted in
• Borders of the tray are trimmed 2–3 mm short of all
the reflections but should cover the retromolar pad.
• Low-fusing modelling plastic is used for border
• Completed border moulded tray is inspected for fit
Step 2: Final impression is made with zinc oxide eugenol paste, fluid
wax or rubber base impression materials.
• Framework should be completely seated and
maintained in position during the setting of the
Step 3: Altering the master cast.
• The master cast is altered to accommodate the
• The edentulous ridge area of the master cast, originally recorded in
anatomic form, is removed with the help of saw in two planes (Fig.
• One cut is made perpendicular to the longitudinal axis of the ridge,
1 mm distal to the abutment tooth.
• The second cut is made just lingual and parallel to the lingual
sulcus, as recorded in original impression.
• The cut surface of the cast is grooved for additional retention of the
stone poured to get the altered cast.
• Completed final impression is seated on this cut cast and secured in
position with the help of sticky wax (Fig. 19-4).
• The assembly with new impression and cast is reversed.
• The peripheral borders of the impression are protected with the
utility wax and the entire assembly is wrapped with boxing wax.
• Before pouring stone, the original cast is saturated with 12 mm of
• The ridge areas are then poured with stones of different colours to
differentiate the new impression from the rest of the cast.
• After final set of stone, the boxing wax is removed and the cast is
• This corrected cast or the altered cast is used to complete the partial
FIGURE 19-3 Sectioned master cast.
FIGURE 19-4 Framework with final impression seated on a
FIGURE 19-5 An altered master cast.
• Dual impression technique is usually indicated in distal extension
• Fluid waxes have ability to flow at mouth temperature and be firm
• Iowa wax was developed by Dr E.S. Smith.
• Zinc oxide eugenol paste is the material of choice for recording
edentulous ridge, which is without gross undercut.
Laboratory procedures, occlusal
relationship and postinsertion of
Steps Involved in the Fabrication of Cast Partial Denture, 304
Relief in Relation to Fabrication of Cast Partial
Waxing of the Cast Partial Framework, 306
Spruing in Relation to Cast Partial Denture
Procedure of Burnout, Casting and Finishing
and Polishing of the Cast Framework, 308
Methods of Establishing Occlusal Relationship for Partial
Articulator or Static Technique, 309
Aesthetic Try-In in Removable Partial Dentures, 310
This chapter includes various laboratory steps involved in the
fabrication of cast partial dentures. It is essential to have the
knowledge of principles and techniques involved in the fabrication of
removable partial denture (RPD) for better understanding and success
Steps involved in the fabrication of cast
The steps involved in the fabrication of cast partial framework are as
(i) Fabrication of the master cast
(ii) Surveying of the master cast
(iii) Block out and relief of master cast
(v) Refractory cast fabrication
(vii) Waxing of the partial denture framework
(viii) Spruing of the waxed framework
(ix) Investing of the waxed framework
Fabrication and surveying of the master cast have already been
described in Chapters 17 and 19.
Block out is defined as ‘the process of applying wax or another similar
temporary substance to undercut portions of a cast so as to leave only those
undercuts essential to the planned construction of the prosthesis’. (GPT 8th
Objective of block out is to eliminate undercut areas on the master cast
that will be crossed by the rigid parts of the partial denture.
• Before the block out procedure, maxillary cast will require beading.
• Beading is not done on the mandibular cast because the major
connector lies on thin, attached mucosa, which will not tolerate the
• Mater cast should be sprayed with a sealer to protect the design
through the block out and duplication procedures.
• Block out wax should always be placed below the height of contour
• Any wax placed above the height of contour and not removed will
result in cast framework which will not contact the tooth on the
• Cast scrapping during wax removal will result in oversized casting
which will require adjustment during framework fitting.
• The shaping of the wax should take place when excess of block out
wax is placed in all the undercut areas.
• In this type of block out, all the undercuts below the height of
• It is done once the master cast is surveyed and the desired path of
• Block out wax is used to fill all the undercuts below the survey line
and parallel to the determined path of insertion.
• Excess wax is trimmed by the parallel wax carving blade-like device
• Parallel block out is usually accomplished in all tooth-borne partial
• This is indicated just below the retentive tip of the clasp arm on the
• Block out wax is shaped to provide a slight ledge just apical to the
• This ledge helps in guiding the placement of the wax or plastic
pattern for the clasp arm so that it lies at the desired position in the
• This is indicated in all the areas not involved in the framework
design in order to minimize distortion during duplication.
This block out is also indicated in the following areas:
• All areas of gross soft tissue undercuts
• Tissue undercuts distal to the cast framework
• Labial and buccal tooth and tissue undercuts not involved in
Relief in relation to fabrication of cast partial
During the fabrication of the partial denture, certain areas require
relief. The common areas which require relief are:
• Below the lingual bar connectors or bar portion of the linguo-plates
• Maxillary or the mandibular tori
• Below the framework, over the edentulous ridge for attachment of
The purpose of relief is to create a space between the framework and
the cast. To provide relief, a sheet of wax is adapted over the ridge
area of the cast. The amount of space provided for the acrylic resin is
determined by the thickness of the relief wax. It is important to have
at least 1 mm of thickness of the acrylic resin. Thinner resin is often
Relief is also required to obtain sharp and definite internal finish line.
This ensures the metal resin junction to be at right angles. A small
square of wax of dimension 2 mm is cut in the relief wax to form the
FIGURE 20-1 Diagram showing relief wax and tissue stops.
Waxing of the cast partial framework
The waxing procedure of the cast partial denture framework is started
after the design is transferred from the master cast to the refractory
cast. Boley gauze is used for the accurate transfer of the design to the
refractory cast. A sharp lead pencil is useful in copying the outline of
the framework on the refractory cast. The position of the clasp tip is
the most critical part during design transfer.
Commercially available plastic patterns are commonly used during
• The plastic patterns are adhered to the refractory cast using an
• The shape of the clasp greatly affects its flexibility.
• The clasp pattern is cut greater than that required.
• Once the plastic patterns are placed on the cast they are adapted to
• Care is taken so that the pattern is not stretched.
• Plastic pattern once contoured is joined together with wax similar in
composition to the blue inlay wax.
• This wax is used to seal the margin of the major connectors. This is
also used in freehand waxing of minor connectors and rests.
• Soft blue casting wax is used to reinforce the wax joints, occlusal rest
seat and for build-up of the periphery of the pattern.
• Waxed-up framework is then finished and polished with precise
FIGURE 20-2 Complete wax-up maxillary framework.
Refractory cast is defined as ‘a cast made of a material that will withstand
high temperatures without disintegrating also called investment cast’. (GPT
Duplication of the master cast is important in fabrication of the cast
partial denture. The duplication of the master cast results in the
formation of the refractory cast. Duplication begins after the block out
and relief of the master cast are completed. The material and the type
of technique used for duplication depend on the type of alloy used for
fabrication of cast partial denture.
The investment material or the refractory is chosen depending on
the alloy selected for fabrication. Low heat investment such as the
gypsum-bonded investment material is used for casting type IV gold
alloy and ticonium. This refractory material can be burned out at 704°C
without causing breakdown of the investment. High heat investment
material such as the phosphate-bonded investment material is used
for casting cobalt–chrome alloy. The burnout temperature of this
The investment material is mixed following the manufacturer’s
instructions and is poured over the colloid mould. Once the
investment material is completely set, the refractory cast is carefully
removed and placed in the drying oven at 93°C. The dry refractory
cast is soaked in hot beeswax dip to ensure smooth and dense surface.
The heated cast is dipped in beeswax at 138–149°C for 15 s.
Spruing in relation to cast partial denture
Sprue is defined as ‘the channel or hole through which plastic or metal is
poured or cast into a gate or reservoir and then into a mold’. (GPT 8th Ed)
• It acts as a reservoir of the molten metal.
• It leads the molten metal from the crucible into the mould cavity.
• Sprues should be large enough to feed the molten metal into the
• It should consist of 8–12 gauze round wax.
• Channel should lead into the cavity as directly as possible for
• The primary sprue should be attached to the most bulky portion of
• Secondary or accessory sprues should be attached to the thinner
section to complete the casting.
• All the sprue channels should originate from a common point in the
• The point of attachment of the sprue to the wax pattern should be
flared rather than at right angle.
Single: It consists of using a single sprue such as with casting ticonium
Multiple: It consists of using multiple sprues such as with casting gold
alloys and high heat chrome–cobalt alloy.
Based on the location of the main sprue
Direct or top spruing: This is done for mostly spruing the maxillary wax
framework. It consists of sprue originating from the top of the wax
pattern from the crucible former.
Indirect or bottom spruing: This is usually done for the mandibular
partial dentures. The spruing is done from the centre of the
refractory cast. It consists of a 7-mm wide and 10-mm long central
sprue coming out from the central hole. The auxiliary sprues are
attached to the central sprue about 7 mm below the tip of the central
Rear spruing: This consists of a single large sprue attached to the rear
of the maxillary complete palatal major connector.
Procedure of burnout, casting and finishing and
polishing of the cast framework
• To drive off moisture in the mould
• To completely eliminate the plastic and wax pattern
• To expand the mould in order to compensate for the shrinkage of
• To completely remove the carbon residue from the investment
The investment ring is placed in the burnout furnace. At the start of
the burnout cycle, the investment should be moist.
1st hour: Temperature is maintained at 100°C; water is driven out
2nd hour: Temperature is increased to 238°C.
• Temperature equalization between the mould and
• Wax vaporization takes place and there is complete
removal of water during this phase.
3rd hour: Temperature is raised to 675–710°C for 1.5–2 h.
• This is called the soaking period.
• There is complete removal of carbon residues, wax
pattern and moisture from the interstices of the
Purpose of casting is to quickly inject the molten metal into the
• Induction casting: It is the most common method used for modern
casting. It is based on the alternating electric current by the
induction of the magnetic field.
It is done by the optical sensor which is located above the crucible.
Some of the sensors may be activated by the infrared wavelengths
emitted by the metal and are called optical pyrometers.
• Casting machine is set according to the manufacturer’s instruction.
• Metal of required quantity is placed in the uncontaminated crucible.
• Metal is melted by activating the alternating current.
• Meanwhile, the mould is removed from the furnace and placed in
• Once the desired temperature is achieved, the lever is released.
• Molten metal is released from the crucible and enters the empty
• The casted framework is retrieved after removing the investment
• First the sprues are cut using high abrasive discs.
• Coarse finishing of the framework is done using abrasive stones or
• Fine stones are used to finish the critical areas such as the retentive
• Fitting of the framework is checked on the master cast using sprays,
• Seating and grinding continues until the framework completely fits
Final finishing of the framework
• The framework is finally given a satin finish using the rubber
• The framework is placed in ultrasonic cleanser to remove debris
collected during the polishing procedure.
Methods of establishing occlusal
relationship for partial dentures
There are two methods of establishing occlusal relationship:
(i) Functionally generated path technique (refer Chapter 28)
(ii) Articulator or static technique
Articulator or static technique
This technique includes the following.
Direct apposition of the casts or hand articulation: This technique is
used when only a few teeth are missing and need to be replaced, as
sufficient number of opposing teeth are present to establish a
• Occluded casts are secured together with a sticky
wax and mounted arbitrarily on the hinge
Using interocclusal record: It is used when adequate number of teeth
is present but the relation of the opposing natural occlusion does
• Metal-reinforced wax such as the Aluwax is used
for interocclusal record in centric occlusion or
• If wax record is used, it should be corrected by
flowing rigid zinc oxide eugenol paste.
Jaw relation record entirely made on occlusion rims: This method is
used when there are no posterior natural teeth. For example, when
maxillary complete denture opposes the mandibular class I
situation or when both the maxillary and mandibular arches are
• Vertical dimension is established in such cases as in
conventional complete dentures.
Occlusal relation using bite rims on the denture bases: This method
can be used with distal extension cases or in totally tooth-supported
cases with large edentulous spaces.
• Accurately fitting record bases are fabricated on the
• Bite rims are fabricated over the record bases to
establish the jaw relationship.
• Bite registration paste or the impression plaster is
used to make interocclusal record at the established
Aesthetic try-in in removable partial
Aesthetic try-in of the denture is an essential step before the insertion
of the final prosthesis. This step is indicated when all the posterior
teeth are missing in both the arches or distal extension RPD is
opposed with complete denture.
• Any correction in tooth size, shape, position or shade can be easily
accomplished during this stage.
• Jaw relation can be verified.
• To give the psychological satisfaction to the patient.
• The patient is seated comfortably on the chair and is instructed not
• The waxed partial dentures are completely seated in the patient’s
mouth and he/she closes the mouth lightly.
• First the gross error, if any, is corrected.
• The anteroposterior positioning of the anterior teeth is examined.
• The anterior teeth should provide adequate support to the lip and
should aid in natural appearance of the profile.
• Tooth length in relation to the lip length and length of the remaining
teeth are carefully evaluated.
• In patients with average lip length, the incisal edge of the anterior
teeth is slightly visible when the lips are relaxed.
• In the smiling position, gingival portion of the denture base is just
• Proper overjet and overbite are evaluated.
• The midline of the denture should be in harmony with the midline
• The shade of the selected teeth should be verified in natural light.
• The final satisfaction and appearance of the denture should be left to
• Aerosol spray is useful in fitting the framework on the master cast.
• Functionally generated pathway technique eliminates the need for
• Gypsum-bonded investment is used for casting type IV gold alloys
Insertion, relining and rebasing
Troubleshooting during Metal Try-In and Fitting of the Framework in
Troubleshooting during Metal Try-In of the
Troubleshooting during Fitting of the Framework
Postinsertion Instructions to the Partial Denture Patient, 312
Insertion and Postinsertion Problems and Their Management in
Problems Encountered during Insertion, 312
Problems during Postinsertion, 313
Special Removable Partial Dentures, 315
Guide Plane Removable Partial Denture, 315
Computer-Aided RPD Designing, 317
The insertion of new removable partial dentures in patient’s mouth is
an important step in denture fabrication, as the patient appreciates the
final outcome of his/her treatment. The clinician ensures that the
dentures have a good fit, retention, aesthetics and comfort. The
removable partial dentures require far greater level of maintenance
than the fixed partial dentures because the edentulous ridges resorb
and the soft tissue support gets loose with time. The procedures of
relining and rebasing are indicated to maintain the fit and accuracy of
the removable partial dentures.
Troubleshooting during metal try-in
and fitting of the framework in patient’s
Troubleshooting during metal try-in of the
• First, the metal framework should be examined on the master cast
for its fit. The framework should not fit too tightly on the cast.
• Any undercut should be relieved on the cast so as to avoid excessive
flexing of the retentive clasp arm.
• The tissue side of the framework is then carefully examined for any
blebs or metal artefacts which interfere during insertion. Any such
interference is removed with the help of suitable abrasive stone.
Troubleshooting during fitting of the framework in
• The framework is tried in the patient’s mouth for complete seating.
• Any interference during seating of the framework is disclosed using
disclosing white paste or wax.
• Any interference is eliminated by using an appropriate abrasive.
• Framework is aligned along the path of insertion and with light
finger pressure is seated on to the abutment teeth to the final
• Excessive force during seating should be avoided.
• The framework in the areas of occlusal rest and the clasp assembly
is checked thoroughly for any interference in occlusion.
• Any interference is checked by articulating paper and corrected with
• The aim of this procedure is to adjust the occlusion in all functional
Postinsertion instructions to the partial
After the insertion of the cast partial denture, the patient is given
instructions regarding its usage and maintenance. The written
instructions should preferably be given to the patient.
• The patient is advised for possibility of minor discomfort with the
• The patient can have difficulty with speech and during eating.
• The patient is advised to maintain proper hygiene.
• After every meal, the dentures should be cleaned with a small stiff
• The patient is advised to soak the dentures in cleansing solution for
• The patient should always remove the denture at night and place it
• The patient should follow strict follow-up regime.
• There may be a possibility of gagging with the new prosthesis.
• The patient should be taught the insertion and removal of the
prosthesis in determined path of placement.
• The patient should never bite on the prosthesis to seat it.
Insertion and postinsertion problems
and their management in relation to
The primary objectives of the insertion of the removable partial
• To accurately fit the denture base to the edentulous ridge
• To adjust the retentive clasps and correct occlusal discrepancies, if
• To instruct the patient on the maintenance of the prosthesis
Problems encountered during insertion
Problems regarding correct fit of the denture base
• Cast metal denture base should not be corrected during insertion
because any correction or adjustment is done during framework
• If the denture base is made of acrylic resin, it may require correction
due to polymerization shrinkage during processing.
• Pressure-indicating paste is used to identify any overextensions or
• Denture base is altered or adjusted accordingly.
• During insertion, occlusal discrepancy can occur between the
artificial teeth in one arch and the natural teeth or artificial teeth in
• Any discrepancy or interference is identified and then corrected
• Occlusal correction can also be corrected by laboratory remount
• The completed partial denture is remounted on the articulator and
any occlusal discrepancy is identified and corrected. This procedure
saves the chairside time during insertion.
Problems with the retention of the prosthesis
If retention of the prosthesis is poor, the clasp arms are carefully
adjusted by applying a controlled force using pliers.
Caution: Overadjustment of the clasp may lead to breakage of the
The dentures are evaluated 24 h after the insertion. Postinsertion
problems can be due to the following reasons:
• Irritation of the soft tissues
• Irritation of the hard tissues
Irritation of the soft tissues
This can be due to some reasons which are as follows:
Overextended denture base: Overextended denture base can result in
soreness or ulceration of the soft tissues.
• Overextensions are checked using pressureindicating paste.
• Any overextension is trimmed using an acrylic
• After correction, the denture base is smoothened
• Topical anaesthetic gel is prescribed for local
Tissue side of the denture base is rough: Rough tissue surface of the
denture can cause redness and soreness.
• The rough tissue surface is identified using
• Any rough surface is identified and smoothened
Occlusal prematurities or discrepancies: This can result in pain.
• Occlusal discrepancies are checked using
• Occlusal prematurities are checked in both the
centric and the eccentric positions.
• Occlusal adjustment is done using appropriate
Irritation of the hard tissues
• Once the causes of soft tissue irritation are identified and treated,
the abutment teeth and the remaining teeth should be carefully
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