Tooth-supported and distal extension partial dentures
• Excessive soft tissue undercut
• This concept was proposed by Kroll in 1980.
• It consists of mesio-occlusal rest, proximal plate and Akers’ clasp (Fig. 16-
• The retentive component of circumferential clasp arises from the
proximal plate adjacent to the edentulous area.
• The retentive arm approaches above the height of contour and the
retentive terminal engages into the undercut which is located away
from the edentulous space on the facial surface.
• Here, the reciprocal arm contacts the lingual surface.
FIGURE 16-26 RPA concept (mesio-occlusal rest, proximal
• Retentive undercut is located away from the edentulous space
• Where aesthetics is the prime concern.
Commonly used direct retainers for distal extension RPDs:
1. Kratochvil design (1963): It uses mesial rest or cingulum rest, distal
guide plate and I bar clasp with 0.01 inch undercut located
2. Roach design (1934): This design uses distal or cingulum rest, distal
guide plate, T bar with 0.01 inch retentive undercut located
distofacially and lingual reciprocation.
3. Applegate design (1955): This design uses distal or cingulum rest,
distal guide plate, wrought wire or platinum gold–palladium clasp
with 0.02 inch retentive undercut located mesiofacially and lingual
Indirect retainers and their importance
Indirect retainers are defined as ‘the component of a removable dental
prosthesis that assist the direct retainers in preventing displacement of the
distal extension denture base by functioning through lever action on the
opposite side of the fulcrum line when the denture base moves away from the
tissues in pure rotation around the fulcrum line’. (GPT 8th Ed)
Indirect retention is defined as ‘the ef ect achieved by one or more
indirect retainers of a partial removable denture prosthesis that reduces the
tendency for a denture base to move in an occlusal direction or rotate about
the fulcrum line’. (GPT 8th Ed)
Fulcrum line is defined as ‘an imaginary line, connecting occlusal rests,
around which a partial removable dental prosthesis tends to rotate under
masticatory forces. The determinants for the fulcrum line are usually the
cross-arch occlusal rests located adjacent to the tissue-borne components’.
Retentive fulcrum line is ‘an imaginary line, connecting the retentive
points of the clasp arms, around which the removable dental prosthesis tends
to rotate when subjected to dislodging forces’. (GPT 8th Ed)
In distal extension cases (unilateral or bilateral), there is a tendency for
the prosthesis to rotate around the fulcrum line in function. Therefore,
there is a need to resist the rotational forces by providing indirect
retention through indirect retainer.
Functions of indirect retainers
• It resists rotation of the prosthesis around fulcrum line under
• It aids in additional support and stability to the prosthesis.
• It helps in accurate repositioning of the prosthesis during relining or
rebasing procedure, as it acts as a third point of tooth contact.
• Major connectors such as lingual plate supported on both the ends
with rests can provide effective indirect retention.
• Contact of its minor connector with the axial tooth surface helps in
providing stabilization against horizontal movement of the
Indirect retainers in distal extension cases
• In Kennedy class I arch, the fulcrum line passes through the most
posterior abutments, provided some of the rigid components of the
framework are located occlusal to the abutments’ height of contour.
• In Kennedy class II arch, the fulcrum line is diagonal, passing through
abutment on the distal extension side and the most posterior
abutment on the opposite side.
Factors influencing the effectiveness of the
Distance between the fulcrum line and indirect retainer: Greater the
distance between the fulcrum line and the indirect retainer, greater
and more effective will be the indirect retainer (Fig. 16-27).
• Indirect retainer should always be placed perpendicular to the
• It should be located as far away from the fulcrum line as possible.
• Indirect retainers are not capable of resisting displacement of the
Rigidity: The indirect retainers should be rigid.
Lingual plate can effectively provide indirect retention, if it is
supported with rests on both the ends.
Location of the fulcrum line influences the effectiveness of the indirect
Ef ectiveness of the supporting tooth surface: The indirect retainers should
be placed in definite rest seats that transmit forces along the long
FIGURE 16-27 Effectiveness of indirect retainer depends on
distance between the fulcrum line and the indirect retainer.
1. Occlusal rest: This is most commonly used.
• Definite occlusal rest seat should be prepared on the
occlusal surface so that the forces are transmitted
along the long axis of the tooth.
• It is most commonly placed on the mesial marginal
ridge of the first premolar in Kennedy’s class I
• In class II situation, it is commonly placed on the
first premolar on the opposite side.
2. Canine rest: Given in case the first premolar is closer to the fulcrum
• It is placed on the cingulum of the canine.
• Canine rest is always preferred to the incisal rest
because of its mechanical advantages.
• This type of rest becomes more effective, if the
minor connector is placed in the embrasure space
anterior to the canine and arcs backward into the
3. Canine extension from the occlusal rest: A finger extension from a
premolar occlusal rest is placed on the lingual slope of the canine.
• This extension helps in providing indirect retention.
• This type of extension is used in cases where the
first premolar serves as the primary abutment.
4. Lingual plate: When the lingual plate is supported with the rests on
both the ends, it provides effective indirect retention.
5. Modification area: In cases of class II modification I, the secondary
abutment can serve as an indirect retainer.
6. Rugae area: The rugae area of the maxillary arch, if covered in the
partial denture, can serve as effective indirect retainer as in horseshoe
design where posterior retention is not sufficient.
• Tissue support provided by the rugae region is less
effective than the tooth-supported indirect retainer.
Denture base and functions of distal
extension partial denture base
Denture base is defined as ‘the part of the denture that rests on the
foundation tissues and to which teeth are attached’. (GPT 8th Ed)
• It provides attachment to the artificial teeth.
• It helps in distributing the forces to the supporting oral tissues.
• With characterization of the denture base, it can satisfy the aesthetic
• It helps in stimulation of the underlying supporting tissues.
Requirements of ideal denture base
• It should have adequate strength to resist fracture or distortion.
• It should accurately adapt to the tissues with minimal volume
• It should be aesthetically acceptable.
• It should be dense and easy to finish.
• It should be capable of relining.
• It should be cost-effective.
• It should have low-specific gravity.
Functions of distal extension partial denture
• In distal extension cases, the denture bases provide support to the
prosthesis, although the primary support is provided by the
• As the distance from the abutment tooth increases, the contribution
of support by denture base becomes more significant.
• Maximum support is provided by broad and accurate denture
• Consideration of quality of ridge is important in assessing the
amount of support which will be provided by the denture base.
• Denture bases also provide secondary retention to the prosthesis;
the primary retention is provided by the direct retainers.
• Physical factors of retention are the same as in complete denture.
Some of the factors are adhesion, cohesion, surface tension, effect of
gravity, atmospheric pressure and physical moulding of tissues
around the prosthesis. However, the role of atmospheric pressure in
retention of RPD is questionable.
Metal base is defined as ‘the metallic portion of a denture base forming a
part or the entire basal surface of the denture. It serves as a base for the
attachment of the resin portion of the denture base and the teeth’. (GPT 8th
Metal denture bases are usually indicated in tooth-supported partial
• Metal denture bases are more accurate and maintain the accuracy of
form without alteration in the mouth.
• Accurate castings are not subjected to distortion by the release of
internal strains as observed in acrylic resins.
• These are easy to clean and contribute to more healthy oral tissues
• Thinner section of metal can provide adequate strength and rigidity
• Temperature changes in the oral cavity are transmitted by the metal
denture bases and contribute in better patient acceptance of the
prosthesis and maintenance of healthy tissues.
• Better tissue response as the metal denture bases have greater
density and bacteriostatic activity provided by the ionization and
• These are difficult to repair and reline.
• These are difficult to adjust.
• These have poor aesthetic outcomes.
• Overextension and underextension of the prosthesis are difficult to
correct and contribute to injury of the tissues.
Usually anterior teeth replacements are best treated by fixed
restorations. However, there are instances where the RPD is logical
Methods of Replacing Anterior Teeth with RPD (Table 16-1):
(v) Reinforced acrylic pontics (RAPs)
VARIOUS METHODS OF REPLACING ANTERIOR TEETH
Methods of replacing posterior teeth with RPD are described in the
• The wear of acrylic resin is clinically significant when opposing
natural teeth or porcelain teeth.
• These can lead to gradual decrease in vertical dimension.
• Unlike porcelain teeth, they do not chip and have softer impact
• They can be easily adjusted and grinded in close interridge spaces.
• These require recall visit for repair or replacement.
• These can be easily arranged over the ridge in natural position.
• They have poor wear resistance and cause minimal wear of the
• They are capable of bonding with denture base material.
• Posterior teeth are retained in acrylic denture base by diatoric holes.
• These should be used when opposing teeth are artificial and not
• These have excellent aesthetics.
• Wear resistance and abrasion resistance are good.
• These have poor fracture resistance.
• Strength is compromised in thin sections.
• There are high chances of abrading the opposing teeth.
• Metal tooth or pontic is indicated where the interarch space is
highly limited or restricted and strength is required.
• A facial veneer can be processed on the metal surface to improve
• Gold is ideally used for occlusal surface of the replacement tooth.
• These have excellent strength.
• These have good wear resistance.
• These can be used in limited space.
• These may add to the bulk of the prosthesis.
Metal pontic with acrylic windows
• When aesthetics is required and the available space is limited, the
facial surface of the pontic is removed and acrylic resin is processed
• Aesthetics is inferior to porcelain or acrylic teeth.
FIGURE 16-28 Metal pontic with acrylic window.
• These can be used to replace one or two posterior teeth in mostly
tooth-supported partial denture cases.
• These are best used for the replacement of maxillary first premolars.
• These are not indicated for distal extension cases.
• These should be placed on well-healed ridges.
• Fulcrum line is an imaginary line which joins the occlusal rests
around which the prosthesis tends to rotate in function.
• Continuous gum denture is an artificial denture consisting of
porcelain teeth and tinted porcelain denture base material fused to a
• Fulcrum line is an imaginary line, connecting occlusal rests, around
which a partial denture tends to rotate under functional stresses.
• The maxillary palatal strap should be minimum 8 mm in width.
• Quasicingulum rest is given in mandibular first premolar which
• The rest seat in mesially inclined molar is prepared with the floor
perpendicular to the long axis of the teeth.
• Rest seat should always be prepared in sound enamel whenever
• Push type of retention is given by bar clasps.
• Pull type of retention is given by the reciprocal clasp.
• The clasp terminal should be placed below the height of contour of
the tooth to act as a primary retainer.
• The amount of undercut required by the wrought clasp is 0.020 inch.
• Terminal third of the retention arm is the component of direct
retainer which lies below the height of contour and provides
• Indirect retainer should be placed as far anterior or far from the
saddle as possible to get best mechanical advantage.
• Porcelain teeth are mechanically retained in an acrylic base through
Objectives and Principles of Surveying, 274
Methods of Stress Control in RPD, 284
Reducing Load on Abutment and the
Distribution of Load between the Teeth and the
Shortened Dental Arch Concept, 287
It is essential to understand various principles in designing of
removable partial dentures (RPDs). Success in RPD depends not only
on understanding these principles but also on applying them in
relevant clinical situation. Broadly, RPDs can be tooth and tissue
supported or completely tooth supported. According to the situation,
Dental surveyor is defined as ‘a paralleling instrument used in
construction of a dental prosthesis to locate and delineate the contours and
relative positions of abutment teeth and associated structures’. (GPT 8th Ed)
Surveying is defined as ‘an analysis and comparison of the prominence
of intraoral contours associated with the fabrication of the dental prosthesis’.
• A surveyor is essentially a parallelometer, which is used to
determine the relative parallelism of the surfaces of teeth or other
• Dr A.J. Fortunati introduced dental surveyor in 1918.
• Ney’s surveyor was first commercially used dental surveyor in
1923. It is one of the most widely used surveyors.
• To design a removable prosthesis
• To determine suitable path of insertion
• To locate and measure the retentive undercut
• To trim or eliminate blockout material parallel to the path of
• To determine any soft tissue or hard tissue interference
Two surveyors are commonly used in dentistry:
(ii) Wills surveyor by Jalenko: It is similar to Ney’s surveyor, except
for the following differences:
• The surveying arm is spring loaded and when not
in use it is held at its most vertical position by
• The horizontal arm is capable of revolving
horizontally around vertical column, whereas
horizontal arm in Ney’s surveyor is fixed.
Other commercially available surveyors are:
Parts of Ney’s surveyor (fig. 17-1)
• Surveying platform: Flat metal base which is parallel to the floor or
bench top on which the surveying table or the cast holder can move
• Vertical column: Vertical arm arising from the base of the surveying
platform. It supports the horizontal arm and the surveying arm.
• Horizontal arm: It arises from the vertical column at right angle and
at the other end extends a surveying arm. In the Ney’s surveyor, it
is fixed, whereas in the Wills surveyor, it can revolve horizontally
• Surveying arm: It extends from the horizontal arm vertically
downwards. It is capable of moving in the vertical direction. At its
lower end, mandrel is attached, where the surveying tools are
• Surveying table or cast holder: On this table, the cast to be studied is
locked-in position by means of a clamp. The base of the surveying
table is mounted over the ball and socket joint, which is capable of
tilting the cast in various horizontal planes. At the desired tilt, the
cast can be locked by means of locking device.
• Surveying tools: These tools are attached to the mandrel of the
surveying arm. Different types of surveying tools are:
• Analysing rod or the paralleling tool: It is a cylindrical
metal rod which is used to determine the relative
parallelism between the tooth surfaces. It contacts
the convex surface of the object to be surveyed
much in the same way as the tangent contacts the
• Undercut gauges: These are used to determine the
specific amount and location of the retentive
undercut on the surface of the abutment.
• Carbon marker: It is used to scribe the height of
contour or the survey line of the object which is
surveyed. It is also useful in delineating an
undercut area of the soft tissue or the residual
• Wax knife: It is used to eliminate or block out
undercut during wax-up of the cast before
FIGURE 17-1 Ney’s dental surveyor.
Survey line is defined as ‘a line produced on a cast by a surveyor marking
the greatest prominence of contour in relation to the planned path of
placement of a restoration’. (GPT 8th Ed)
Survey lines are scribed by the carbon marker on abutment tooth
during surveying. It denotes the height of contour on the abutment
tooth. The significance of survey line is that all rigid components of
the removable prosthesis are kept occlusal to it. Only the retentive
terminal is kept gingival to the survey line. It helps in identifying
undesirable undercut that is avoided or eliminated by contouring or
placing restorations on the teeth.
The height of contour is defined as ‘a line encircling a tooth and
designating its greatest circumference at a selected axial position determined
by a dental surveyor; a line encircling a body designating its greatest
circumference in a specified plane’. (GPT 8th Ed)
• This survey line lies closer to the occlusal third of the abutment
• Usually, there will be deep undercut and wrought clasp will be
• It is seen in inclined teeth or teeth with broader occlusal diameter
• It lies between the occlusal third and the middle third of the
• Circumferential clasp is usually preferred.
• It lies closer to the cervical third of the abutment tooth.
• A modified ‘T’ clasp is usually preferred in low survey line.
• It lies between the occlusal third of the near zone and cervical third
• It is commonly seen on the premolars and canines.
• Reverse circlet clasp is commonly used.
• Ring type Akers’ clasp or T-type bar clasp can be used.
The concept of near zone and far zone was given by L.A. Blatterfien.
He divided the buccal and lingual surfaces of the tooth adjacent to the
edentulous space into two halves by an imaginary line passing
vertically through the long axis of the tooth.
The half of the tooth closer to the edentulous space is called the near
zone and the half of the tooth away from the edentulous space is
called the far zone. This concept can also be applied similarly to the
proximal surface. Proximal surface closer to the edentulous space is
the near zone and the proximal surface away from the edentulous
• To survey the diagnostic cast:
• Diagnostic cast is always surveyed before
formulating the treatment plan.
• Relative parallelism is studied on the cast which
helps in designing the framework.
• Soft tissue and hard tissue undercuts are
determined and evaluated for any correction
during mouth preparation procedure.
• The tilt of the cast can be altered to best suit the
conditions of the mouth without much alteration.
• At the final tilt, the survey lines can be scribed on
• Cast should be tripoded in the position of the final
• Three widely separated marks are scribed on the
cast with analysing rod at the same vertical height.
• To transfer the tripod marks to another cast:
• The second cast can be positioned at the same tilt as
• Analysing rod is positioned at the selected three
points on the diagnostic cast at same vertical height.
• The second cast is positioned at the survey table
and the cast is tilted till three widely separated
points are located at the fixed vertical height.
• Three additional reference points can be scribed on
the diagnostic cast to ensure that the second cast is
mounted at the same vertical height and tilt.
The additional reference points are:
(i) Distal marginal ridge of the right first premolar
(ii) Incisal edge of the lateral incisor
(iii) Lingual cusp tip of the left first premolar
• The tilt of both the casts should be exactly same at
• To contour crowns and cast restorations:
• It is important to contour the final restoration as
• For this, the restoration with the die is placed on the
survey table at the original tilt.
• Handpiece attached to the vertical column of the
surveyor and the restoration is refined with the
• Analysing rod is finally used to verify the contours
• The wax patterns of the cast restoration are
contoured on the surveyor at the final tilt selected
• The survey line can be adjusted to place the
retention and reciprocal arm at the most desired
• Master cast is made after mouth preparation is
• Master cast is surveyed on the surveyor to verify
whether the alteration sought in the mouth during
mouth preparation are successfully accomplished
• If the mouth preparation did not give satisfactory
result, the mouth preparation procedure is repeated
• To place internal attachment and rests in intracoronal retainers:
• Surveyor is very useful to place the intracoronal
attachments during the wax pattern stage on the
• This requires utmost precision as absolute
• Internal rests or occlusal rests can be prepared in
the wax pattern of the restorations using the
• Mock preparation on the diagnostic cast:
• Mock preparation can be done on the cast before
mouth preparation to determine the outcome of the
• To survey the ceramic veneers before final glazing:
• Contour of the ceramic crown is determined on the
surveyor before the final glazing procedure.
• The height of contour is modified and verified on
Objectives and principles of surveying
• To locate and evaluate tooth and soft tissue undercuts on the cast
• To identify the height of contour
• To identify the proximal tooth surface to prepare the guide planes
• To determine the most favourable path of placement which has least
interference and provides best aesthetics
• To identify the most favourable cast tilt and preserve it for future
• The cast is positioned on the surveying table at
• At the zero tilt, the occlusal surfaces of the teeth are
at or nearly parallel to the horizontal plane.
• The four basic tilts from the horizontal or reference
position are anterior tilt, posterior tilt, right lateral
• The cast can be tilted in any of the above-mentioned
positions until the most effective use of the
available undercut is achieved. It should be
remembered that the established tilt should not be
more than 10º otherwise extensive mouth
preparation will be required to design a prosthesis.
2. To survey the abutment teeth
• To determine the height of contour: Once the tilt is
determined, the height of contour is scribed on the
cast by carbon marker. Rigid components of the
direct retainers should lie above the height of
contour and the flexible component should lie
• To locate and determine the depth of the undercut:
It is done by using the undercut gauges. Greater the
depth of undercut, greater will be the flexibility of
the retention arm required to achieve proper
retention. Undesirable undercut should be blocked
• To determine guide planes: In order to achieve
parallelism between the abutment teeth, guide
planes are prepared. Parallelism is necessary for
easy path of placement and removal of the
• To determine the path of insertion: The tilt of the
cast determines the path of insertion and removal
of the prosthesis. Single or multiple path of
insertion depends on the type of the RPD design,
i.e. whether totally tooth supported or tooth-tissue
3. To survey the soft tissue contours on the cast
• Soft tissue undercuts should be determined during
• Any unfavourable soft tissue undercut may require
preprosthetic surgery to eliminate it.
FIGURE 17-2 Guide plane should be parallel to each other
Tripoding is defined as ‘those marks or lines drawn on a cast in a single
plane perpendicular to the survey rod to assist with repositioning the cast on
a dental surveyor in a previously defined orientation’. (GPT 8th Ed)
Basically, tripoding is a procedure of indexing the cast in a
horizontal plane after the final tilt of the cast is determined on the
surveyor. This procedure helps in repositioning the cast accurately in
the same horizontal plane in which it was surveyed.
• Three widely separated and easily identifiable
marks are placed on the tissue portion of the cast
after the final tilt of the cast is determined (Fig. 17-
• These marks are placed in the same horizontal
• This permits the cast to be repositioned accurately
by realigning the cast in the same horizontal
• Carbon marker, trimmed at 45°
• Tripoding procedure is done once the tilt of the cast
• At this tilt, the cast is positioned on the surveying
• Three widely separated points on the anatomical
portion of the cast are touched at the same vertical
• Analysing rod is used to scratch the cast at these
• The analysing rod can be substituted with a carbon
• A small line of 3 mm length is made at these three
• A mark is made across this line and is circled to
identify the area of tripoding.
• It is accomplished by using an analysing rod, which
is held against the art portion of the cast at a
• Three lines are drawn with the lead marker, one on
the anterior aspect and one each on the posterior
aspect of the art portion of the cast.
• Disadvantage of this method is that there are
chances of smudging of the lines during handling
FIGURE 17-3 Tissue surface tripoding.
• It preserves the tilt of the cast.
• It permits the cast to be removed and repositioned accurately
• It helps in recording the spatial orientation of the cast in a particular
Path of insertion is defined as ‘the specific direction in which prosthesis is
placed on the abutment teeth or dental implant(s)’. (GPT 8th Ed)
The tilt of the cast on the surveyor determines the angle at which
the partial denture will seat over the remaining teeth. The path of
insertion is always parallel to the vertical arm of the surveyor and is
determined by the final tilt of the cast. The type of partial denture
design determines the number of paths of insertion of the dentures.
• In Kennedy class I situation, there can be multiple paths of
insertion. Since the distal extension bases are controlled by two
terminal abutment teeth, additional guide planes are created on the
lingual surface to limit the path of insertion.
• In Kennedy class II cases with a modification space, the path of
insertion is determined by the modification space. This results in a
single path of insertion and removal.
• Usually, the tooth-bounded spaces (Kennedy class III) with guiding
planes created on the proximal surface of all the teeth will have
• In Kennedy class IV situation, there will be usually single path of
• Minor connectors are usually the components of the partial denture
which contacts the guiding planes and, therefore, govern the path of
• If the guiding planes are created on the lingual surface of the teeth,
the reciprocal arm or the lingual plate can definitely influence the
Factors influencing the path of insertion
• One of the basic requirements in designing partial
denture is that there should be a retentive undercut
on the abutment tooth in horizontal tilt.
• Tilt of the cast may be varied to alter the position of
the survey line so that the clasp may be placed
• The retentive undercut is measured by the undercut
gauge. The shank of the gauge contacts the height
of contour of the tooth and the undercut gauge
contacts the surface of the tooth in the undercut.
• The amount of the retentive undercut required if
cast chrome alloy is used is 0.010 inch undercut and
if wrought wire combination clasp is used, it is
• There are certain regions in the patient’s mouth
which can interfere with the path of insertion of the
• These areas can be identified and treated either by
surgical removal or by altering the tilt of the cast on
Interferences in the mandible:
• Lingual inclination of the remaining teeth
• Bony exostosis or bony undercuts
• This factor can influence the path of insertion of the
• Optimum aesthetics can be obtained by placing the
artificial teeth in the natural position and by placing
the metal clasps more gingivally. Bar clasps are far
superior to the circumferential clasp.
• Mesially tilted abutment will create large
unaesthetic undercut. This undercut can be
eliminated by tilting the cast or by selectively
grinding the teeth to establish proper guide planes.
• These are formed by the proximal or the axial
surfaces of the teeth which contact the minor
connectors during insertion or removal of the
• Guiding planes protect the periodontally
compromised teeth from harmful lateral forces.
• These provide stabilization and retention to the
The principles of RPD designing were first given by A.H. Schmidt in
1956. According to him, the principles were:
• The clinician should have thorough knowledge of the biological and
the mechanical factors involved in RPD design.
• The treatment plan is based on thorough examination and diagnosis
• The clinician should correlate the pertinent factors and determine
• An RPD should restore form and function without injury to the
• An RPD is a form of treatment and not a cure.
There are three basic concepts of designing an RPD. These concepts
are based on distributing the forces acting on the partial denture
between the soft tissue and the teeth.
(iii) Broad stress distribution
Based on the concept that the resiliency of the periodontal ligament is
smaller in comparison to the resiliency of the mucosa covering the
edentulous ridge, a nonrigid connection is required to distribute the
stresses over the abutment and the edentulous ridge. This nonrigid
connection is called stress equalizer or stress director (Fig. 17-4).
FIGURE 17-4 Split lingual bar used to equalize forces
transmitted by the partial dentures.
Its purpose is to equalize the forces transmitted by the RPD.
• Useful in distal extension cases
• Stimulating effect on the supporting tissues during function
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