REMOVABLE PARTIAL
DENTURE (RPD)
Introduction to removable Partial Denture
Removable Partial Dentures (RPDs) stand as a cornerstone in prosthodontics, focusing on the replacement of missing teeth and contiguous tissues with prostheses designed to be removable by the wearer. This discipline encompasses two primary categories: removable complete denture prosthodontics and removable partial denture prosthodontics.
In the realm of dentistry, the art of restoring smiles and functionality to individuals with missing teeth is a paramount endeavor. One such solution that stands out is the Removable Partial Denture (RPD). In this comprehensive guide, we delve into the intricacies of RPDs, exploring their types, indications, objectives, hazards of improper design, advantages over fixed partial dentures, classifications of partially edentulous arches, and more.
WHAT IS A PARITAL DENTURE?
A partial denture is a dental
prosthesis. It can be described as a fixed
partial denture or removable
partial denture based on the patient’s
capability to remove or not remove
the prosthesis.
Kennedy’s Classification OF REMOVABLE PARTIAL DENTURE (RPD)
Class l. Bilateral free end saddles.
Class ll. Unilateral free end saddle
Class lll. Unilateral bounded saddle, which has not
crossed the mid line.
Class lV. A single bounded saddle, which has crossed
the midline.
Modification: Additional
edentulous area for classes (l-lll) only and designated as 1,2,3,etc.
However, amendments to Kennedy’s
classification were made by Applegate because of its over simplicity.
Kennedy Class I
Bilateral free-end saddles
Unilateral free-end saddle
Class III Modification IV
Class I Modification I
Class II Modification II
Applegate's Classification OF REMOVABLE PARTIAL DENTURE (RPD)
Rule 1: Classification should
follow rather than precede extraction that might alter the original
classification.
Rule 2: If the 3rd
molar is missing and not to be replaced, it is not considered in the
classification
Rule 3: If a 3rd molar
is present and is to be used as an abutment, it is considered in the
classification.
Rule 4: If the 2nd molar is missing and it is not to be replaced it is not considered in the classification.
Rule 5: The most posterior
edentulous area or areas always determines the classification.
Rule 6: Edentulous areas other
than those which determine the classification are referred to as modification
spaces and are designated by their number.
Rule 7: The extent of
modifications is not considered, only the number of additional edentulous areas
i.e. the number of teeth missing in the modification spaces is not considered
only the number of additional edentulous spaces are considered.
Rule 8: There can be no
modification areas in class IV because any additional edentulous space will
definitely be posterior to it and will determine the classification
PARTS OF REMOVABLE PARTIAL DENTURE
Saddle
Definition:The saddle
is the part of RPD that replaces lost alveolar tissue and carries artificial teeth.
Types:The saddle
covers the edentulous area and may be classified based on material, support
and design.
The saddle may be constructed of metal e.g Cobalt-chromium alloy, gold
alloy, and stainless steel alloy or
acrylic resin or a combination of metal and acrylic resin.
.
Support: Tooth support, mucosa or tooth-mucosa support.
Saddle especially in free end saddle are usually made in acrylic resin.
This is because saddle made in arylic are easy to reline or rebase and
this is often necessary in free end saddle.
The saddle should cover a maximum area of the edentulous ridge in mucosa
borne denture.
Metal base can transmit the sensation of heat and cold to the underlying
tissue. This simulate natural condition in the mouth than acrylic resin ; so it
may be compactible with oral mucosa than acrylic resin.
Disadvantages of metallic saddle
Fabrication of metal base is more
expensive.
The contour of the lip and cheeks cannot be restored with metal base as with
acrylic.
Metal base cannot be easily relined or rebased.
Proper extension of the border cannot be achieved.
Types of saddle based on design
- Lattice pattern: It consists of two long struts of metal placed on the buccal and lingual slopes of the ridge with small struts running over the crest connecting the long struts
- Meshwork:It consist of a sheet of metal placed over the crest of the ridge with small holes for retention of acrylic denture base/artificial teeth.
- Plate with beads or nail heads: It consists of metal plate with projection of metal on the superior surface as beads or nail neads for retention of artificial teeth to the saddle
Functions of saddle OF REMOVABLE PARTIAL DENTURE (RPD)
It carries artificial
teeth
Replaces lost alveolar tissue
It support the lip and cheeks
it gives support to the denture
5.Enhance bracing when extended buccaly and lingually
It provides retention.
Rests (Occlusal,cingulum, And Incisal Rest )
Definition: A rest is
a component of a RPD that extend over a prepared tooth surface to provide support to the denture.
A rest may be placed upon the occlusal surface of molar or premolar - Occlusal rest
Cingulum of anterior teeth -
cingulum rest
Incisal edge of anterior teeth - incisal rest
When the area of the rest is extended to a large proportion of occlusal
surface - Onlay
Precision manufactured attachments
placed within a crown or retainer- Intracoronal (Precision) Rest
Occlusal rest
This is a cast metal projection attached to a partial denture extending
on to the prepared occlusal surface of a standing tooth. It may be part
of the clasp arms or may
be a seperate component not related to the
clasp.
Requirement of ideal Occlusal Rest
It must fit the tooth accurately with bevealed margin to prevent food
stagnation.
It may rest on a natural depression on the occlusal surface or occupy a
prepared surface on the tooth or on an inlay restoration.
It should cover one-third of the marginal ridge and extend to
1/3 to 1/2 the
mesio-distal surface of the tooth.
4.It must be at right angle or less to the long axis of the tooth..
Requirement of ideal occlusal rest (cont)
The internal angle of the seat should be rounded to prevent fracture
It should be made in cast metal
It must not gag the occlusion
It must have sufficient bulk / of adequate thickness to prevent
deformation. This depends on i)the alloy
used ii)the heaviness of the bite/occlusion iii) wether the the rest is opposed
by natural or artificial teeth.
Functions of rest OF REMOVABLE PARTIAL DENTURE (RPD)
1.It transmits vertical load to the abutment teeth thereby supporting the
saddle .
2. It helps in transmission of lateral load
3. It deflects food.
4.Maintains the arm of the clasp in the right vertical relation on the abutment tooth thus preventing the clasp arm from moving towards the tissue. This prevents damage to the tissue and preserve the retentive effort of the clasp. (i.e. maintain a clasp -tooth relationship)
5.May improve occlusion.
May correct occlusion
May act as indirect retainer
It prevent super-eruption of tooth on which it is placed where no opposing
tooth is present to perform this function.
Provide reference for relines or
impressions in free end saddle dentures
Preparation of Rest Seats
No anesthesia
High-speed hand piece
Light pressure
+/- Water spray
Minimal heat is generated
Keep in enamel
Occlusal Rest Seats with:
-Diamonds
-Medium round carbide burs
Rest seat form
No sharp line angles
Rounded triangular shape
Base of triangle should be 1/3
bucco-lingual width
Marginal ridge must be lowered and
rounded (1-1.5mm)
Floor inclined towards the center
Angle formed by rest and minor
connector should be less than 900
Floor should be concave or spoon
shaped or saucer shaped (Prevents horizontal stresses & torque)
Others: Box shape,
Flat shape
Occlusal Rest seat form
Cingulum Rest
Cingulum rest is used on
the palatal or lingual surface of anterior
teeth especially the upper canine.
When the cingulum is well developed other teeth that are favourable
for the use of cingulum rest are upper central incisors, and lower
canine. The use of cingulum rest is
usually unsatisfactory because of
the slope of the palatal surface of maxillary anterior which are not
suitable to carry the the rest when the enamel is prepared. In such
situation, an inlay cavity is cut on the tooth and the rest is placed on
the inlay.
Cingulum rest presents
esthetic advantages in that it does not show metal. However, it may require extensive tooth preparaton
which may result in caries, hypersensitivity.
Other problem that may be encountered is the bulging on the tooth surface in an area of high
tongue activity and so may give rise to tongue irritation.
Cingulum rest seat preparation
No anaesthesia
Fast hand piece
Place in sound tooth structure or
restorations
Not on amalgam restorations
Preparation of Cingulum Rest Seats
Long, medium diameter cylindrical
bur or diamond
Cingulum rest seat form
- Inverted “V”
- < 900
Incisal Rest
Incisal rest are placed on anterior teeth and they present esthetic
problem. They are therefore used on anterior teeth where cingulum
rest cannot be used.
Generally they present as an extension of
metal on the lingual or
palatal surface of anterior teeth and terminate on the prepared
surface on the incisal edge. It is required that the antero-posterior
thickness of the tooth is adequate to receive the rest
Major connectors OF REMOVABLE PARTIAL DENTURE (RPD)
It is the part of RPD that
connects the components on one side to
the components on the other side of the arch.
Qualities
Rigid but not interfere with
movable tissues
Conform to anatomical shape
No food trapping/hygiene.
Relief where there are small
prominences
Functional and acceptable
Classification of major connectors OF REMOVABLE PARTIAL DENTURE (RPD)
Mandibular major connector:
They include:
- Lingual plate,
- Lingual bar,
- Sublingual bar,
- labial bar,
- continuos clasp/ bar, Kennedy (combination) connectors
Maxillary major connector OF REMOVABLE PARTIAL DENTURE (RPD)
This includes
- Palatal plates,
- palatal bar,
- palatal strap,
- Horse shoe connector,
- closed horse shoe connector,
- Ring Connector
Lingual Plate
It is a mandibular major connector that covers most of the lingual
aspects of the teeth, the gingival margins, and the lingual aspect of the
ridge. The plate terminates inferiorly at the functional depth of the sulcus.
It may be made of acrylic or metal alloy.
Cast alloy plate are mostly
employed and are very satisfactory provided adequate gingival relief is given.
Uses: It acts as
indirect retainers and provides bracing against lateral load.
It can be used in those cases where there is insufficient space between the gingival margin and the floor of the mouth for a lingual bar to be inserted
Disadvantages: If not well
fabricated, it tends to encourage food
packing around the gingival margins causing damage
to the gingivae.
This may also result in cervical caries.
A lingual plate may create dead-end tunnels between the teeth.
When used in patient
with spaced anterior
teeth, it produce
unsatisfactory
appearance.
Lingual Bar
Lingual bar is mandibular major connector that is placed mid-way
between the gingival margins of the teeth and the floor of the mouth.
At least 8mm depth
of alveolar ridge is required for a lingual bar.
Lingual bars can be cast in gold or cobalt chromium alloys. An oval
section may be used but a half-pear shaped is more ideal and is less
irritating to the tongue.
Advantages of lingual bar:
It leaves gingival
crevice uncovered by the denture
Patients are less aware of bars than lingual plates.
Contra-indication
Lack of space.
Lingually inclined teeth.
Marked anteriorly
inclined alveolar process .
Sublingual Bar
The sublingual bar is an improvement on the lingual bar. It is less obtrusive to the patient because it lies in the anterior lingual sulcus, but it is more difficult to make.
Its fabrication
requires an impression
technique that accurately records the functional depth and width of the lingual
sulcus.
The sublingual bar is kidney-shaped or rounded triangular in
cross-section. The increased width compared to lingual bar confers satisfactory
property of rigidity.
Labial bar
This bar is situated in the labial or buccal sulcus and lies in relation
to alveolus. These are always
made of cast alloy.
They may be used when lingual connectors are impracticable due to
lingual inclination of the standing teeth, the presence of excessive
lingual undercuts or problems such as a torus mandibularis.
They are not used very often as they tend to be uncomfortable to
patient’s lips.
Labial or buccal bar
Kennedy Bar
This is a combination of lingual bar with continuous clasp. The continuous bar runs on the lingual surface of the anterior teeth, incisal to the cingulae.
It was designed by Kennedy to obtain the benefit of the depth of a plate without the coverage of
gingival margin.
The advantages include increased rigidity and the additional clasp acts
as indirect retainer.
This system is generally poorly tolerated by patients because the tongue seeks out the spaced between the
two connectors.
Maxillary major connector
Palatal plate.
It is a maxillary major connector that covers wide area of the palate.
It can be extended to the cingulum of the anterior teeth. It may be made entirely of metal or all acrylic or may be
partly metal and partly acrylic. The combination
allows for relining/ rebasing over the residual ridge and post insertion
readjustment of post dam area.
The metal plate should be kept as thin as possible .The palatal plate
should be along the free anterior and
posterior border so that:
the tongue may pass from mucosa to denture without encountering an edge.
fine particle may not collect readily underneath the denture.
Advantages of palatal plate
They are wider and therefore can be made thinner in section than bar.
They can transfer some of the occlusal load to the plate.
They can be constructed in non metallic denture base materials.
They do not disturb the
tongue as much as thicker palatal bar.
Palatal bars
They are always made of alloys and must fit the palatal tissue accurately
otherwise the patient will always be conscious of a space between the bar and
the tissue and of food packing in the space.
The position of the bar vary according to the position of the saddle area
to be connected.
When it is located just
anterior to the junction of hard and soft palate it is called posterior
palatal bar, middle palatal bar when on the middle third and anterior
palatal bar when it is located on the anterior third of the patate.
Posterior palatal barIt It is located in an area not frequently associated with bony prominence. Advantages:
1). It act as posterior indirect retainer
2).It is well tolerated by the tongue.
A maximum lenght of the bar lies in contact with the lateral walls of
the hard palate, thus resisting lateral load.
Disadvantages:
Denture
shows anterior posterior rocking because it located in area with compressible
tissue.
The middle palatal bar.
It is usually employed in bounded saddle.It is not encroaching upon the
sloping rugae area and therefore is well tolerated.
Denture with middle palatal rarely shows the anterior posterior
rocking
occasionally found with posterior palatal bar.
The anterior palatal bar
It may be used as an anterior indirect retainer especially when the anterior
occlusion contraindicate the use of continuous clasp. It can act as a link to anterior saddle from posterior saddle. It
can be combined with posterior palatal bar in long saddle cases to form a ring
connector. This gives adequate rigidity to the denture.
Disadvantage:
The major disadvantage of the anterior palatal bar is that it covers the
rugae area where tongue activity is marked. As a result, it is poorly toleranced by the tongue and
often associated with phonetic problems.
Palatal Strap
A palatal strap is a major connector used primarily in tooth suported RPD.
The minimum width of the strap should be about 8-10mm. The support
provided by a strap is minimal. The borders of the srap should be beaded.
Anterior-posterior palatal strap May be used for Kennedy class I, II, III,
or IV partially edentulous arches. The anterior and posterior strap should be 6
to 8 mm wide and the palatal opening should be about 15mm or more in anterior
posterior dimension. It is the major connector of choice in the presence of an
inoperable torus that end posteriorly 6 to 8 mm short of the junction of soft and
hard palate. The anterior palatal strap part is located on the valley of the
rugae, the posterior just anterior to the junction of hard and soft palate.
Ring connector
It is indicated in cases where there are multiple saddles
widely distributed round the arch and where tooth support can be obtained. It
is also indicated where a prominent torus contraindicate the use of mid-palatal plate or strap.
Advantage: rigidity
Disadvantage: Poor tolerance
U shaped (Horse shoe ) palatal connector
The U shape connector often lack rigidity particularly at the open end.
Indications:
When a large in-operable torus extend posteriorly within 6 to 8mm or less of the junction of the soft
and hard palate
when the patient cannot tolerate posterior palatal bar or strap (wretching)
reaction.
It is also indicated when several anterior teeth are to be replaced.
Minor Connector
Minor connectors are rigid elements that connect rests, direct and indirect
retainers, and denture base to the major connector.
Functions:
connects minor elements to major connector
They contribute to broad stress distribution. When forces are applied to
the artificial teeth the forces are transfered to the abutment teeth by the major
and minor connectors.
The major and minor connector are also instumental in transfering the
effect of retainer, indirect retaine and
rests around the arch.
Minor connector cont
They should be positioned in interproximal space. They must be rigid and strong.
Must not interfere with opposing occlusion and should not trap food.
Convex surface should be avoided whenever possible.
Major and minor connector should join at a right angle.
Direct Retainer
It is a clasp or attachment
applied to an abutment tooth for the purpose of holding RPD in position.
Classification:
Extracoronal direct retainer) casted clasp, wrought wire clasp).
a) Occlusally approaching
clasp (circumferential) .
b)
Gingivally approaching clasps (Bar clasps)
Intracoronal direct retainer(
attachments):
Internal attachment.
External attachment.
Special attachment.
Direct retainer cont.
All clasps are part of a larger
units called clasp assemblies.
The components of clasp assemblies
-one or two rests
-a retentive arm
-a reciprocating /bracing
element.
-one or more minor connectors.
Ideal clasp assemblies should possess the following qualities.
Support
Bracing action
Reciprocation
Retention
Greater than 1800
encirclement.
Two types of clasp retainers
- Suprabulge retainers/occlusally approaching clasps.
- Infrabulge retainers/ gingivally approaching clasps.
Suprabulge clasp
Originates from a point at or
above the height of contour-usually from
a minor connector or guide plate-
and angle downwards across the
clinical crown where the tip is
located in a prescribed undercut.
Infrabulge
Infrabulge retainers emanates from the denture base or denture
base retentive network and approaches the undercut from a gingival direction.
Types of infrabulge
The most common types are I,T and
Y.
The Y and T forms usually have one
tip in undercut the second tip produces minimal bracing.
Because the second arm has no
specific function it is usually omitted creating a modified T and Y forms
Infrabulge Clasp
Advantages of infrabulge clasp.
Minimal tooth contact and minimal
distortion of normal tooth contours. Hence improved tissue stimulation and oral
hygiene hence decrease caries and periodontal problems.
Improved esthetics
Increased retention because of the
tripping action.
Decreased torquing forces on
terminal abutments
Improved adjustability
Disadvantages of infrabulge
Cannot be used where there is soft
tissue undercut, a shallow vestibule or high frenal attachments.
Bracing action provided by bar
clasps is considerably less than that provided by cast circumferential clasp.
Appearance may not be too pleasing
in high smile line patients
May not be retentive unless rigid
elements determine the path of insertion and withdrawal.
Indirect Retainers
Required in Class l & ll RPD
and possibly long span Kennedy class IV.
Located on the opposite side of
the fulcrum line from the denture base,
Placed 90 degrees as far from the
primary fulcrum line as possible,
Normally not required for
tooth-borne RPD’s (Class lll & IV).
Canine usually the most anterior
tooth used not lateral or central incisors (speech).
Denture Base
Denture base is defined as that
part of a denture which rests on the oral mucosa and to which teeth are
attached.
Ideal requirements OF Denture Base:
Accurate tissue adaptation with
minimal change in volume.
Thermal conductivity.
Sufficient strength to resist
fracture or distortion under function.
Cleansability.
Ability to be relined if
necessary.
6 Cost effective.
Low specific gravity.
Ability to achieve a good finish.
Types of denture base:
- Acrylic
- Metal.
- Combination.
Acrylic Resin denture base; mainly
used for distal extension PD- attached to the frame work by minor
connector-with 1.5mm thick to have a adequate strength.
Advantages of acrylic denture base
Anterior teeth can be replaced at
their original position (aesthetic level).
Restore the contour of the
edentulous ridge.
Brings out the normal contour of
the lip and cheeks.
Can be relined.
Disadvantages of acrylic denture base
May break on usage.
Tend to accumulate mucous deposits
and food debris.
Soft tissue irritation.
Allergy.
Metal denture base
Mainly used for tooth supported
PD.
Advantages:
Accurate tissue adaptation( better
retention).
Easy to clean.
Strong even in thin section.
Heat conductivity( physiologic
tissue stimulation).
Disadvantages of metal denture base
Difficult to trim and adjust.
Over extension can injure the soft
tissue.
Poor aesthetic.
Difficult to reline and rebase.
COCLUSION
Removable partial dentures play a pivotal role in prosthetic dentistry, catering to individuals with missing teeth and contiguous oral structures. They are meticulously designed to restore oral function, comfort, appearance, and overall health. At the heart of prosthodontics, RPDs offer a versatile solution for patients seeking tooth replacement options.
REFERENCES
1. oceanbreezeprosthodontics.com - Removable
Partial Dentures: Everything You Need to Know
2. sciencedirect.com - Removable Partial Denture
- an overview
3. dentureliving.com - What Are the Different
Types of Partial Dentures?
4. braintreefamilydental.com - Removable Partial
Dentures - Dr. Mytrei Chaturvedula
5. nature.com - Unilateral removable partial dentures | British
Dental Journal
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