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Impressions in removable
partial dentures
DR. HEMANT SHARMA
Impression : a negative likeness or copy
in reverse of the surface of an object; an
imprint of the teeth and adjacent
structures for use in dentistry
Diagnostic impressions
Permit analysis of contour of hard and soft tissues
Types of restorations on abutment teeth
Determination of need for surgical correction of exostosis, frena, tuberosities and undercuts
Serve as blueprint for placement of restorations, recontouring of teeth and rest seat preparation
Permit analysis of patients occlusion
Adequacy of interarch space
Presence of overerupted, malposed teeth
and tuberosity interference.
Material of choice for diagnostic
impression
Irreversible hydrocolloid (alginate)
Technique for Making
Diagnostic Impressions
1)Position of patient and Dentist
2)Impression Trays
a) selection
b) Checking trays for Correct size
c) Extending impression trays
3)Control of Gagging
4)Control of saliva
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Technique for Making
Diagnostic Impressions
Contd)Manipulation of the impression material
6)Making the Impressions
7)Removal of Impression from the mouth
8)Inspecting the Impression
9)Cleaning the impression
10)Disinfecting the impression
11)Poring the cast
Tray Selection for Diagnostic
Impressions
➢Tray of choice - Rim lock tray because it is rigid- it confines the impression material, helping toforce it into all the areas to be included in theimpression.
➢Perforated trays are rigid, but do not confine thematerial as well as the rim lock tray .
➢Disposable plastic trays - too flexible to ensurethe accuracy of impression and cast that isneeded for removable partial dentures
Extending an Impression Tray
➢ The modeling plastic is softened in a 60° C (140° water bath, kneaded, and adapted to the tray partially removed several times to prevent the locking of the tray into the undercuts.
➢ Frequently an impression tray that has a correct width is too short to cover the entire desired impression area. The impression tray can be lengthened by the use of modeling plastic .
➢ After the modeling plastic has been chilled, it is relieved to provide approximately 5 to 7 mm of clearance & then coated with alginate adhesive
Extending an Impression Tray
Extending an
Impression Tray
Working properties of Alginate
Easy to use and inexpensive
Available as bulk and preweighted quantity
Deteriorates rapidly at high temperature
and humidity
Is contaminated by gypsum
Accuracy not affected by changes in water
to powder ratio
Cont.
Ideal temp of water 22degreeC
Cooler water will provide more working
time
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Storage of impression
Measurable distortion if not poured within
12 minutes
Technique of making alginate
impressions
Position of patient and dentist
Dentist position-standing
Patient position-upright
Occlusal plane parallel to floor
Patients mouth is at same level as dentists
elbow
Stand behind the patient for maxillary
impression
Checking tray
Clearance of 5-7mm between tray and the
ridge
Tray should cover all anatomic landmarks
or can be modified
Gagging
Methods to prevent gagging
Seating patient in upright position
Correcting palatal area with modelling plastic
Not overfilling the tray with alginate
Seating the posterior part first
Patient to keep eyes open during procedure
Use of astringent mothwash and cold water
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Control of saliva
Use of gauze packs
Saliva ejection
15mg propantheline bromide 30min before
procedure
Mixing impression material
Hand spatulation
Mechanical spatulation
Mechanical spatulation under vacuum
Inspecting the impression
Alginate sticking to teeth
Alginate pulling away from tray
Voids
Layered impression
Granular impression
Inadquate extension
Contact between teeth and tray
Problems
Error. Using irreversible hydrocolloid that has beenfrozen, even when it is stored in its original,sealedcontainer.
Problem: Freezing may alter the setting time of thematerial drastically.
Solution: In the winter, when temperatures in some partsof the country are considerably below freezing,irreversible hydrocolloid should be tested before use.
. Error: Using irreversible hydrocolloid that has beenstored in defective packaging or in an unsealedcontainer after being opened for first use.
Problem: Moisture contamination due to water uptakefrom the atmosphere can accelerate or retard the settingtime and cause rapid deterioration of physical andchemical properties of the irreversible hydrocolloid.4
Solution: Test the irreversible hydrocolloid before using it
Solution: Use prepackaged irreversiblehydrocolloid to eliminate this error, even thoughit is more costly than a can of irreversiblehydrocolloid or bulk irreversible hydrocolloid. Ifbulk irreversible hydrocolloid is used, separateand weigh amounts for individual use; then sealeach portion in an airtight container such as aspecimen containers. In addition, use adedicated mixing bowl and spatula only formixing irreversible hydrocolloid. When in doubtabout the deterioration of the irreversiblehydrocolloid, test it before use
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Error: Using a mix of irreversible hydrocolloidthat is too thick.
Problem: A thick mix of irreversible hydrocolloidmay set before it is fully seated in the mouth.When this happens, the irreversible hydrocolloidwill set under pressure. When irreversiblehydrocolloid sets as pressure is applied, it isalways distorted.6
The irreversible hydrocolloid may not flow into theinterproximal spaces between the teeth or pick up theanatomy of the soft tissues. This error may also result inthe creation of drag marks in the impression and on thecast during seating of the impression. The marks will notfill in because the material is too stiff to flow after it isseated.
Solution: Follow the manufacturer's instructions forwater/powder proportions by weight rather than byvolume.
Error: Attempting to control the setting time ofirreversible hydrocolloid by altering thewater/powder ratio.5'6
Problem: If the mixture is thin one time and thickanother time, a standardized procedure cannotbe established for seating the impression tray.The resulting inconsistency can cause unreliableresults, in addition to other problems (see errors9 and 10).
Solution: Control the water temperature to vary the setting time of irreversible hydrocolloid mixes. Always use the manufacturer's recommended water-to-powder ratio. Use water heated to more than room temperature to make the irreversible hydrocolloid set faster; use water chilled to lower than room temperature to increase the working time.7 A 10°F increase or decrease in the water temperature will increase or decrease the working time by approximately 40 seconds.
Error: Failing to adequately mix the irreversiblehydrocolloid.
Problem: If irreversible hydrocolloid is not mixed long orthoroughly enough to completely saturate all of thepowder with water, pockets of dry or partially wetirreversible hydrocolloid can cause distortions.
Solution: Hand mix the irreversible hvdrocoll-oidthoroughly for 60 seconds. Alternately, vacuum mix theirreversible hydrocolloid for 15 seconds with at least 25inches of vacuum
Error: Allowing partially mixed irreversible hydrocolloidfrom around the top of the mixing bowl to beincorporated into the mix as the tray is loaded.
Problem: Dry irreversible hydrocolloid particles absorbwater when the impression is washed. The dry particlesexpand as they get wet and set. If a pocket of dry orpartially wet irreversible hydrocolloid is in contact with atooth or other critical area when the impression is made,dry material will expand after impression is removedfrom mouth and washed, resulting in inaccuracies.5'6
Solution: Make certain that partially mixed or dryirreversible hydrocolloid powder is not incorporated intothe mix for the impression.
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Dr. HEMANT
SHARMA
Introduction
◼ Retention is that quality inherent in the
removable partial denture that resists the vertical
forces of dislodgement for e.g., the force of
gravity, the adhesiveness of foods, or the forces
associated with the opening of the jaws.
◼ A retainer is defined as any type of clasp,
attachment, device etc. used for the fixation,
stabilization or retention of a prosthesis.
◼ Direct retention is the retention obtained in a
removable partial denture by the use of
attachments or direct retainers (clasps) resist the
displacement or removal of the partial denture
from the abutment teeth in a direction opposite
to that of their insertion.
◼ Direct retainer is any unit of removable partial
denture that engages an abutment tooth in such
a manner as to resist displacement of the
prosthesis away from basal seat tissues by
1. Functional means by engaging a tooth
undercut lying cervically to the height of the
contour.
2. Wedge principle.
3. Mechanical means
DEFINITION
According to the Glossary of Prosthodontic Terms, a direct
retainer is that component of a removable partial denture
used to retain and prevent dislodgement, consisting of a
clasp assembly or precision attachment.
Factors affecting the retention in Removable
Partial Dentures:
I. Primary retention : This is mechanical in action.
II. Secondary Retention: Achieved by intimate relationship
of the denture base and the rigid major connector to
the underlying soft tissues.
a. Adhesion
b. Cohesion
c. Atmosphere pressure
d. Molding of tissues
e. Effect of gravity
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1. Clasps which engage undercuts.
2. Acting through the polished surfaces.
3. Coverage of mucosa by the denture.
Classification of direct retainers
◼ Direct Retainers are of two types:
◼ Extra Coronal
◼ Intra Coronal
Extra Coronal Direct Retainers:
Mechanical resistance to displacement.
There are of three types:
a. Manufactured attachment.
Eg. Dalbo, Spring loaded plungers.
b. Flexible clips/Rings.
c. Clasp type retainer.
The flexible area engages a prepared depression are
an undercut area cervical to the area of greatest
convexity of the tooth.
◼ Intra Coronal Retainer:
Regarded as an internal/precision attachment.
◼ Formulated by Dr.Herman.E.S. Chayes in 1906.
◼ Cast/Attached within the tooth structure
◼ Prefabricated
◼ Frictional resistance.
EXTRACORONAL DIRECT RETAINERS
◼ Occlusally approaching / Suprabulge / Ney Type I clasp / Circumferential
◼ Gingivally approaching / Infrabulge/ Bar/ Roach / Ney Type II Clasp
The basic parts of a clasp assembly :
◼ Rest : It is the part of the clasp that lies on the occlusal, lingual or incisal surface of a tooth and resist tissue ward movement of the clasp.
◼ Body of the clasp : It is the part of the clasp that connects the rest and shoulder of the clasp to the minor connector.
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◼ Shoulder : It is the part of
the clasp that connects the
body to the clasp terminals.
It must lie above the height
of contour and provide
some stabilization against
horizontal displacement of
the prosthesis.
◼ Reciprocal arm : A rigid
clasp arm placed above the
height of contour on the side
of the tooth, opposing the
retentive clasp arm.
◼ Retentive arm : It is the
part of the clasp comprising
the shoulder which is not
flexible and is located
above the height of the
contour.
◼ Retentive terminal : It is
the terminal end of the
retentive clasp arm. It is the
only component of the
removable partial denture
that lies on the tooth
surface cervical to the
height of the contour. It
possesses a certain degree
of flexibility and offers the
property of direct retention.
◼ Minor connector : It is
the part of the clasp that
joins the body of the clasp
to the remainder of the
framework and must be
rigid.
◼ Approach arm : It is a
component of the bar
clasp. It is a minor
connector that projects
from the framework, runs
along the mucosa and
turns to cross the gingival
margin of the abutment
tooth to approach the
undercut from a gingival
direction.
PRINCIPLES OF CLASP DESIGN
◼ Encirclement:
More than 1800 of greatest circumference of the
tooth must be included passing from diverging axial
surface to converging axial surface.
This may be in the form of continuous contact when
circumferential clasp arms are used.
Bar clasps are used, at least 3 areas of tooth contact
must be embracing more than ½ the tooth
circumference. These are occlusal rest area, the
retentive terminal area and reciprocal terminal area.
The surveyed cast clasp embraces about 270° of the
abutment tooth. Its parts are : Bracing arm (blue).
Retentive arm (red).
Shoulder and rest (yellow).
Minor connector (green).
◼ Support:
Property of the clasp that resist the displacement of
the clasp in gingival direction.
Primary support units of a clasp are occlusal, lingual
or incisal rest.
The occlusal rest must be designed so that cervical
movement of the clasp arm is prevented.
The rest should provide only vertical support.
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◼ Reciprocation:
◼ Each retentive terminal should be opposed by a
reciprocal arm or element capable of resisting
any orthodontic pressures exerted by the
retentive arm. Reciprocal and stabilizing
elements must be rigidly connected bilaterally.
◼ This arm is positioned on the opposite side of
the tooth from the retentive arm.
◼ In addition to reciprocating stress generated
against the tooth by the retentive clasp, it also
play an important role in stabilizing the denture
against horizontal movement.
◼ Some cases, additional rest is positioned on the
opposite side of the tooth and minor connector
will provide reciprocation.
◼ Reciprocal clasp must be rigid, it is not tapered as
the retentive clasp. Reciprocal arm should be
positioned on the surface of a tooth is reasonally
parallel to the denture’s path of insertion and
removal.
◼ If it is placed on the surface that is tapered
occlusally, a slight movement of denture will cause
the clasp to loose contact with the tooth and
reciprocation and retention is lost.
◼ It must be positioned above the height of contour at
the junction of the gingival and middle 3rd.
◼ To reciprocate the forms properly, it should contact
the tooth at the same time or before the retentive
arm does.
◼ Retention:
The path of escapement of each retentive clasp terminal should be other than
parallel to the path of removal of the prosthesis.
The amount of retention always should be the minimum necessary to resist
reasonable dislodging forces.
Only the terminal third of an
occlusally approaching
clasp (stippled section)
should engage the undercut.
A gingivally approaching claspcontacts the tooth surface only at
its tip.
The retentive clasp is divided into 3 parts; each with its
arm functional requirement. The terminal third is flexible
and engages the undercut.
The middle third has a limit degree of flexibility and
may engage a minimal amount of undercut.
Proximal third, or shoulder, is rigid, and must be
positioned above the height of contour.
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◼ Stability / Bracing:
All 3 clasp have reciprocal or bracing arm, which provides
equal amount of stability.
Stability is the resistance to horizontal displacement of a
prosthesis.
All clasp terminal except the retentive clasp terminals
contribute to this property in varying degree.
Eg: Cast circumferential clasp great amount of stability,
because its shoulder is rigid and it aids in stabilization.
The wrought wire clasp has flexible shoulder
Bar clasp does not have a shoulder so both provide less
stability.
◼ Passivity:
A clasp in place should be completely passive the
retentive function is activated only when dislodging
forces are applied to the partial denture.
◼ Bilateral Opposition:
Unless guide planes will positively control the path
of removal, retentive clasp should be bilateral
opposed. i.e., buccal retention on the other or
lingual on one side opposed by lingual on the other.
In class II situation, the 3rd abutment may have
either buccal or lingual retention.
In class III retention may be either bilaterally or
dimeterically opposed.
◼ Stress Breaking:
Clasp retainers on abutment teeth adjacent to distal
extension bases should be designed so that they will
avoid direct transmission of tipping and rotational
forces on abutments. In effect they must act as
stress breakers either by their design or by their
construction. This is accomplished by proper
location of the retentive terminal or by use of a
more flexible arm is relation to rotation of the
denture under varying direct forces.
◼ Location of components:
The reciprocal element of the clasp assembly should
be located at the junction of the gingival and middle
3rd of the crowns of an abutment teeth. The terminal
end of the retentive arm is placed in the gingival 3rd of
the crown.
Criteria for Clasp Selection
1. Surveyline location and degree of undercut.
2. Requirement of retention and stability depending on
whether upper or lower arch and configuration of
edentulous area or areas; axis of rotation and selection
of retainers.
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SURVEY LINE
◼ Blatterfein in 1951 put forth a simple
and comprehensive classification of
surveyline with suggestion on clasp
selection.
◼ He divided the buccal and lingual
tooth surface into two halves using a
vertical imaginary line through the
long axis of the tooth. These halves
were described as the nearzone and
farzone depending on its closeness to
the edentulous space.
◼ He described four kinds of surveyline:
1. Typical surveyline or medium
2. Atypical A or Diagonal
3. Atypical B or High
4. Atypical C or Low
Typical or medium:
Extends from the occlusogingival midpoint in the
near zone to the junction between the occlusal two
third and cervical one third in the far zone.
Clasps suggested for use where such a survey line
exists include the occlusally approaching and
gingivally approaching clasps.
◼ Atypical A or diagonal:
This runs diagonally across the tooth surface from
a high position in the nearzone to a low position in
the farzone.
- A reverse action or hairpin clasp is
recommended.
- Gingivally approaching clasp may also be used.
◼ Atypical B or High Surveyline:
This type of surveyline is parallel to the occlusal surface and lies
close to it.
A wrought occlusally approaching clasp arm may be used.
If accompanied by a low surveyline on the opposite side of the
tooth, a ring, back action or reverse back action have been
recommended.
◼ Atypical C or Low Surveyline:
The low surveyline is parallel to occlusal surface but has just above
the level of the gingival margin.
This type of surveyline contraindicate the placement of a retentive
clasp arm on the tooth surface concerned, as the arm would need to
be placed too close to the gingival margin for safe application.
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When all the usable surface of a tooth present the
surveylines of this type, retention may be obtained by
1. Placement of a crown on the tooth to artificially
develop undercuts.
2. Placement of a class IV gold inlay – a dimple is in
the inlay and a ball head on a gingivally approach
arm is positioned to engage the dimple.
3. An extended clasp may be used where the tooth
offers favourable conditions for retention.
4. Undercut may be developed by recontouring the
tooth.
◼ Ney: 3 basic surveyline with an appropriate clasp
form.
◼ Class I :
Surveyline runs diagonally across the tooth surface
from a low position on the side of the rest to a
high position on the other proximal side.
A cast occlusally approaching arm or its variants,
back action, reverse back action and ring clasps are
recommended called as Ney class I clasps.
◼ Class II:
Similar to Blatterfein atypical A or Diagonal
surveyline. Here gingivally approaching is
recommended and termed as Ney class II clasp.
◼ Class III:
It is the same as the Blatterfein Atypical B or High
surveyline. The wrought wire arm is used and termed
as the Ney class III clasp.
Selection of clasp based on requirement of
retention & stability
◼ A large number of edentulous area, bilaterally placed would
mean more number of clasps and guide planes, thus the
entire prosthesis has greater retention and stability.
◼ Cast circumferential clasp properly designed shows greater
retentive and bracing properties than a bar clasp used in a
similar situation.
◼ Ideal amount of retention is that which will retain the
removable partial denture against reasonable dislodging
forces without placing the undue strain on the abutment
teeth. Thus minimum retention and maximum stability is the
ideal.
◼ Support:
Selection based on nature of support
whether tooth / tissue or tooth and tissue
borne and length of the edentulous span.
In case of long span – class I situation
preservation of abutment teeth is important,
where a RPI, RPL clasp is used to prevent
torque on the abutment.
◼ Root size and form of the tooth:
Clinical conditions of supporting structures is
alveolar bone and periodontal ligament should be
considered abutment teeth with short, conical roots,
bone loss, and periodontal ligament, mild
periodontal problem may not be able to withstand
lateral forces that would be within physiologic limits
of a healthy sound tooth. Such tooth must be
preserved.
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◼ Oral hygiene and caries:
1. Maintaining oral hygiene is pre requisite to
treatment with cast partial denture.
2. High caries index. Contraindicate the use of clasp
with an unprotected tooth surface as with a ring
clasp.
3. Bar clasp has minimum tooth structure contact
and less interference with natural cleansing action.
Patient education is essential to maintenance of
oral hygiene, proper use of prostheses, its
placement and removal.
◼ Esthetics:
Gingivally approaching claps are generally
preferred for esthetics reason but may be more
unestheics than occlusally approaching clasp if the
patient has a high lip line and exposes the excessive
gingiva.
◼ Presence of excessive tissue undercut:
Gingivally approaching clasp is contraindicate in
the presence of excessive tissue undercut.
Factors affecting retention of a clasp
Size of the angle of cervical convergence
◼ When the surveyor blade contacts a tooth on the
cast at its greatest convexity, a triangle is formed, the
apex of which is at the point of contact of the
surveyor blade with the tooth, and the base is the
area of the cast representing the gingival tissues. The
apical angle is called the angle of cervicalconvergence.
◼ To be retentive a tooth must have an angle ofconvergence cervical to the height of contour.
◼ Guiding planes determine the path of placement andremoval of a partial denture. Therefore without the use ofguide planes, clasp retention will either be determined orpractically non existent.
◼ The guide plane moves down the proximal surface which is
prepared on the distal aspect of the tooth. When thedenture
is fully seated, the plane contacts the lower parts of that
surface.
DEGREE OF UNDERCUT
◼ Relative uniformity of retention will depend on the
location of the retentive part of the clasp arm, which is not
in relation to the height of contour, but in relation to the
angle of cervical convergence.
◼ Retentive clasp arms must be located so that they lie in the
same approximate degree of undercut on each abutment
tooth, despite the variation in the distance below the
height of contour.
◼ The measurement of the degree of undercut by mechanical
means is achieved by the help of an undercut gauge
attached to a dental surveyor.
The retentive force is dictated by tooth shape and by clasp design.
Though clasps 1 and 2 are in an undercut of 0.25mm, 1 offers
more retention than 2.
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Flexibility of clasp arms
Length of the clasp arm : The longer
the clasp arm, the more flexible it is,
all other factors being equal. The
length of a clasp arm is measured from
the point at which a uniform taper
begins.
A Co-Cr clasp arm engaging
the same degree of undercut will have
different flexibility and resistance to
distortion on the molar and the
premolar because of the difference in
length.
Circumferential Bar type
Length
(inches)
Flexibility
(inches)
Length
(inches)
Flexibility
(inches)
0-0.3 0.004 0-0.7 0.004
0.3-0.6 0.008 0.7-0.9 0.008
0.6-0.8 0.012 0.9-1.0 0.012
Diameter of clasp arm
◼ The diameter of a clasp arm is inversely
proportional to its flexibility, all other factors
being equal.
◼ The average diameter to be considered is at a
point midway between its origin and its terminal
end.
◼ The thickness of the clasp arm in the
buccolingual direction is to be considered rather
than the width in the occluso-gingival direction.
Cross-sectional form
◼ Round cross-sectional form enables the clasp to be
flexible in all directions whereas the half-round form
limits the flexibility to only one direction.
◼ Cast clasps are half round in form and they flex away
from the tooth, but edgewise flexing is limited.
◼ If the cross-sectional area of clasp is doubled,
the stiffness will be increased 4 times and the
flexibility reduced 4 times.
Material used for clasp arm :
▪ Type IV gold alloys and cobalt-chrome alloys
which have different modulus of elasticity.
▪ The modulus of elasticity of cobalt-chrome
alloys is greater than that of cast golds, which
have a higher modulus than wrought gold
wires.
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▪ The retentive terminal has to be flexible and therefore have
low modulus of elasticity. The reciprocal elements have to
be stiff and unyielding and have high modulus of elasticity.
▪ Therefore a clasp of the same cross-section is stiffer in
cobalt-chrome than in cast gold. This can be overcome by
using longer clasps of thinner section, and by doing
contour modification so as to reduce the degree of undercut.
Structure of the alloy
◼ The alloy may be cast or wrought in nature. Wrought
wires have greater flexibility than a cast structure due to
its grain structure being fibrous.
◼ The tensile strength of a wrought structure is at least
29% greater than that of the cast alloy from which it was
made.
◼ Wrought forms can be used in smaller diameters to
enhance the flexibility and they offer minimum friction
and can have a stress breaking effect.
Support
◼ Support is the property of the clasp which
enables it to resist displacement in a gingival
direction.
◼ Primary support is obtained by the occlusal or
incisal rest.
◼ Secondary support is obtained by the rigid
components i.e. body and shoulder of the clasp
which are placed above the greatest diameter of
the tooth.
Stabilization or Bracing:
◼ It is the resistance which the clasp contributes to
displacement of the prosthesis in a horizontal plane.
◼ All of the clasp components, with the exception of the
retentive terminal, contribute this property in varying
degrees.
◼ Bracing elements, united by rigid major connector, are
capable of distributing horizontal forces throughout the
partially edentulous arch.
◼ The components of the cast circumferential clasp offer
better stabilization than either the bar clasp or the
wrought wire clasp, because of greater amount of rigidity
of the clasp material.
Reciprocation
◼ Reciprocation may be defined as “the means
by which one part of the appliance is made to
counter the effect created by another part”.
◼ For effective reciprocation clasps should be
planned and designed so that the two arms of
the clasps are in balanced.
RECIPROCATION
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Indirect Retention
◼ The reciprocal arm may behave as an indirect
retainer when it rests occlusal to the height of
contour on the abutment tooth, lying anterior
to the fulcrum line.
◼ Lifting of a distal extension base away from
the tissues is resisted by a rigid arm, which is
not displaced cervically
TYPES OF CLASP RETAINERS
◼ Circumferential clasps/ Occlusally approaching
• Circumferential clasp
• Embrasure clasp.
• Ring clasp.
• Back action clasp.
• Reverse action / hair pin clasp.
• Multiple clasps.
• Half-and-half clasp.
• Combination clasp.
• Onlay clasp.
Bar/Roach clasps / Gingivally
approaching clasps.
◼ T-clasp
◼ Modified T-clasp
◼ Y-clasp
◼ I-clasp
◼ RPI concept.
Other clasp designs
▪ RPA clasp.
▪ VRHR clasp.
▪ Clasps utilizing proximal undercuts
-Mesiodistal clasp
-Devan clasp.
▪ Movable arm clasp.
▪ Cingulum clasp
CIRCUMFERENTIAL CLASP
◼ Although a thorough knowledge of the principles of clasp
design lead to the logical application of those principles. It is
better to understand some of the more common clasp
design individually.
◼ The clasp is usually the most logical drip to use with all
tooth borne partial denture. Beam of its retentive and
stabilizing ability.
◼ Basic forces of the clasp is a buccal and lingual arm
originating from a common body.Circumferential clasp on a molar
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Advantages:
1) The clasp fulfills the requirement of support,
stability reciprocation, encirclement & passivity
better than any other type of clasp.
2) It is easy to construct.
3) It is simple to repair.
Disadvantages:
1. It tends to increase the circumference of the crown.
2. In is not acceptable in the anterior region.
3. It covers more tooth surface then the bar clasp and prone to
caries.
4. Retentive undercuts on some teeth are difficult to reach with
retentive terminal of the clasp
EMBRASSURE CLASP
◼ Bonwill clasp
◼ Rib clasp
◼ Double a
◼ Back to back clasp
◼ This clasp is essentially two single circlet clasps
joined at the body.
Embrasure clasp on a maxillary premolar and
molar
▪ Kennedy class II, III, IV cases where no
edentulous space on opposite side of the arch
sufficient space must be provided between the
abutment teeth in their occlusal third to make
room for the body of embrasure clasp.
▪ Contact area should not be eliminated
completely.
◼ Abutment tooth should be protected with crowns or inlays
if necessary. This depends upon the age of the patient caries
index and oral hygiene.
◼ This clasp should be used with double occlusal rest.
◼ Proximal shoulder be established. To avoid interproximal
wedging by the prosthesis.
◼ This clasp should have two retentive clasp arms and two
reciprocal arms either bilaterally or diagonally opposed.
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◼ An auxillary rest or a bar clasp arm can be
substituted for a circumferential reciprocal arm as
long as definite reciprocation and stabilization is
achieved.
Contra indication:
1. Short and bulboss crown.
2. Not preferred in teeth with more undercuts.
Disadvantages:
◼ Needs adequate cleaness in occlusal surface.
◼ Breakage of inadequate preparation and clearance
◼ Wedging action.
RING CLASP
◼ Indication:
1. In tilted molar :
2. Single standing tooth
Unsupported mandibular molar tend to drift and tip in a
mesiolingual direction.
Maxillary molar tip is a mesio buccal direction. So qvileble
retentive undercut will be located on the mesiolingual line
angles of a mandibular molar and the mesiobuccal line angle
of maxillary molar.
◼ This ring clasp permits engagement of this undercut by
encircling almost the entire tooth from its point of origin.
◼ Mandibular molar, clasp encircles the tooth beginning on
the mesiobuccal surface and terminating in an infra bulge
area on the mesiolingual surface.
◼ Because of the length of the clasp, it must be designed with
additional support, usually in the form of an auxillary bracing
arm.
In mandible, bracing arm usually extends from the acrylic
resin retention metal, run across the mucosa and turns
upward to engage the buccal arm of the ring clasp near the
center of the buccal surface.
◼ This can provide reciprocation and some amount of
stability for the denture.
◼ The entire clasp except the retentive terminal shall be
placed above the height of the contour.
◼ An additional occlusal rest can be placed may provide
additional support and prevent mesial migration of tooth.
◼ Contra indication:
1. In mandibular molar, where the attachment of
buccinator muscle is so close to the tooth, that
the auxillary bracing arm encroaches on it.
2. When the bracing arm must cross the soft
tissue undercut.
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14
◼ Advantages:
1. Excellent bracing
2. Decreased leverage
3. Less stress to abutment teeth.
◼ Disadvantages:
1. Needs long crown and enough occlusal clearance.
2. Difficult to repair.
REVERSE ACTION CLASP OR HAIR PIN
◼ This clasp is essentially a simple circlet clasp in which the
retentive arm after crossing the facial surface of the tooth
from its point of origin. Loops back in a hairpin turn to
engage a proximal undercut below its point of origin.
◼ The upper part of the retentive arm must be considered to
be minor connector and should be rigid.
◼ The lower part of the clasp arm should be tapered. It is the
only flexible part of the clasp arm.
◼ The crown of the abutment tooth must have
sufficient occlusogingival height to accommodate
this double width of the clasp arm.
◼ The upper and lower arms of the retentive clasp
must also be shaped in such a way that food debris
will not be retained between them.
◼ And there must be enough space between the arms
so that the metal may be adequately finished and
polished.
◼ Indication:
1. Distal extension partial denture.
2. Mesially inclined posterior.
3. Undercut addition to the edentulous area.
4. If proximal undercut must be used on a posterior
abutment and when the tissue undercut or high tissue
attachment prevent the use of bar clasp arm, the reverse
action clasp may be preferable.
5. If lingual undercut in present which prevent the
placement of a supporting strut without tongue
interference hairpin clasp is indicated.
◼ Contra Indication:
1. Tight occlusal contact, increase posterior overbite short
crown,
2. Clasp cover considerable tooth surface and may trap
debris.
◼ Advantages:
◼ Easier to construct
◼ Adjust
◼ Disadvantages:
◼ Food trapment
◼ Esthetics
◼ Caries
◼ Multiple clasp is two opposing simple circlet clasp joined
at the terminal end of the two reciprocal arms.
MULTIPLE CLASP
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15
MULTIPLE CLASP
Indication:
1. When additional retention is needed.
2. Tooth borne partial denture
3. Multiple clasping required, when the partial
denture replaces an entire half of the dental arch.
4. When the principal abutment tooth it periodontal
support can be used in the form of splinting
tooth.
◼ Advantages:
1. Less metal display
2. Less tooth coverage
3. Leaves room for the mesial portion of the denture base
to a larger extent than it would be otherwise.
4. It braces the abutment on the mesial even if the tooth is
tipped distally.
5. Marginal gingiva can be left uncovered of the abutment
teeth for better partial denture health.
◼ Advantages:
1. It provides additional support for the weakened
premolar.
2. Use of adjacent retentive arm on approximately teeth.
Half-and-half clasp
◼ This clasp consists of a circumferential retention arm
arising from one direction and a reciprocal arm arising
from another minor connector.
◼ This design provides retention , a principle that
should be applied only to a unilateral denture design.
◼ The buccal arm provides for bracing only.
◼ The lingual arm utilizes an undercut adjacent to the
edentulous space for retention.
◼ Indication:
• Lingually inclined premolars where lingual undercut are
close to the edentulous space.
◼ Contra indication:
• Buccal inclined premolars –
If it is used for distal extension RPD a distal rest
should be placed. Mesial rest also can be used in
conjunction with the distal rest.
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16
BACK ACTION CLASP
◼ It is a modification of the ring clasp.
◼ It has a rest which is connected to a rigid minor connector.
Indication:
For unilateral and bilateral distal extension partial denture.
Combination clasp
• This type of clasp consists of a wrought wire retentive clasp
arm and a cast reciprocal clasp arm.
• The retentive arm is usually occlusally approaching, but it may
also be used from a gingivally approaching direction.
Uses:
◼ It is used on abutment tooth adjacent to a distal
extension base where only a mesiogingival undercut
exists on the abutment or where a large tissue
undercut contraindicates a bar type retainer.
◼ The tapered wrought wire retentive arm offers
greater flexibility than does the cast clasp arm and
therefore better dissipates functional stresses.
Advantages
◼ Flexibility on account of fibrous grain structure of the
wrought wire retentive arm.
◼ Adjustability : It can be adjusted later to increase or decrease
the retention without danger of breakage.
◼ Esthetic appearance since it is used in smaller diameters of
round cross-section.
▪ A minimum of tooth surface is covered because of its line
contact with the tooth, rather than a surface contact of a
cast clasp arm.
▪ Fatigue failures in service are less likely to occur with the
tapered wrought wire retentive arm.
Disadvantages
◼ It involves extra steps in fabrication, particularly
when high fusing chromium alloys are used.
◼ It may be distorted by careless handling on the part
of the patient.
◼ Since it is bent by hand, it may be less accurately
adapted and therefore provide less stabilization
above the height of contour.
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17
EXTENDED CLASP ARM
◼ It is similar to the circumferential arm but it covers two
teeth. It remains above the surveyline of the 1st tooth;
crosses the undercut of the adjacent tooth. It is rarely
used direct retainer.
Indications:
• Tooth supported RPD.
• Tooth next to edentulous space has no buccal and lingual
undercut.
• The occlusion in the embrasure area will not allow passage
of the clasp arm to an undercut on the second tooth from
the edentulous space.
• The second tooth from edentulous space has a buccal
undercut available.
◼ Contra Indication:
1. Distal extension dentures because the retentive
lies forward of the axis rotation. Functional
forces will cause rotation around the rest and
upward movement of clasp tip.
◼ Advantages:
1. It has splinting and stabilization action.
2. Distribution of lateral loads over two teeth.
◼ Disadvantages:
1. Tooth structure covered.
2. Easily distorts.
3. Breakage of the arm.
4. If made in gold limited o 2 premolar
in Cr. Ch – longer arm can be used.
- 2 molars can be clasped.
MESIODISTAL CLASP
◼ Used to clasp canine and central only if little undercut on
buccal surface.
Disadvantage:
◼ Metal displaces alloy made of gold.
If diastema between the lateral incisor and canine, then
the space provides a accommodation for the mesial part
of the clasp otherwise space reaction with safe side disc,
contact point with L.I. is returned when clasp an
position. It is similar to inlay.
ONLAY CLASP
1. Extends from an occlusal onlay into an undercut
located mesio distally.
2. This clasp is an extended occlusal rest with buccal and
lingual clasp arms.
3. This clasp may originate from any point on the onlay
that will not create any occlusal interference.
4. If the onlay is prepared with chrome cobalt alloy, and
is opposed by natural teeth, the occlusal surface should
be constructed of acrylic resin or gold, if you use
chrome alloy, because of its extreme hardness will
cause rapid wear of enamel
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18
Indications:
1. When the occlusal surface of the abutment tooth is the
occlusal plane mesially tilted rotated tooth molar.
2. Only in caries resistant mouth unless it is covered by
gold crown.
◼ Advantages:
1. Mesially tilted molars to be used to provide retention.
2. 3rd molar occlusion may be improved.
◼ Disadvantages:
1. Difficult to fir clasp to tooth.
2. Increased contact area, accurate impression and the
resultant cast is difficult to achieve.
DEVAN CLASP
◼ Uses proximal undercut and has a small head that bears
on tooth entirely below survey line.
◼ Clasp arises and lies closely against at the periphery of
the denture base.
◼ Denture base is under extended to provide room for
the approaching arm.
◼ It is reciprocated with lingual and palatal strut.
◼ It gives little bracing effect.
Devan clasp
◼ Advantages:
1. Esthetically acceptable, became of interproximal
location, or it is hidden behind the buccal concavity.
2. The distribution of stress during insertion and
removal is minimal.
3. Increased retention without tipping action on the
abutment.
4. Less chance of accidental deformation because it
doesn’t project very far away from the denture base.
GINGIVALLY APPROACHING CLASPS
◼ Infra Bulge
◼ Push Clasp
◼ Roach Clasp
◼ This bar clasp approaches the retentive undercut in a
gingival direction resulting in a push type of retention.
This push type of retention is more effective than pull
type retention characteristic of circumferential clasp.-
tripping action.
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19
◼ This clasp is termed by F.E.
Roach in 1930 and hence
the name Roach clasp.
◼ The bar clasp is classified by
shape of the retentive
terminal T, modified T, I, Y
forms, all of which originate
from the denture base frame
work and approaches the
undercut from gingival
direction.
◼ Advantages:
1. Minimal tooth contact and minimal distortion of
normal tooth contours, leading to improved tissue
stimulation and oral hygiene and caries and
periodontal problems.
2. Improved esthetics if the approach portion of the arm
is not visible as it crosses the gingiva.
3. Increased retention became of tripping action.
4. Decreased torquing forces applied to terminal
abutments in extension RPDs.
5. Large undercut can be engaged.
◼ Disadvantages:
1. Cannot be used in the presence of soft tissue undercuts
shallow vestibule. And high frenum attachments.
2. Bracing action provided by bar clasp is considerable less
than that provided by cast circumferential clasps.
3. The bar clasp will not totally disengage in certain distal
extension cases.
4. Appearance may be adversely affected if he smile line high
enough to expose the approach arm as it crosses the
gingiva
5. Food trapment.
6. Difficult to fabricate and adjust.
◼ Indication:
1. Class I and Class II distal extension partial dentures to
engage the distobuccal undercut on abutment, It can be
employed on canines and sometimes even on molars.
2. Where the anterior retention is needed: It is often used
on distobuccal surface of maxillary canines and
mandibular premolar as the retentive arm can be hidden
from the vision.Esthetically this clasp is superior to
circumferential clasp it is inferior in providing stability
because of greater flexibility of the retentive arm.
◼ Guidelines for use:
1. The approach arm of the bar clasp must not impinge on
the soft tissue. It is not desirable to provide an area of
relief under the arm.s But the tissue side of the approach
arm should be smoothed and polished.
2. Minor connector that attaches the occlusal rest to the
frame work should be strong and rigid. To provide some
bracing.
3. The approach arm must always be tapered uniformily
from its attachment at the framework to the clasp
terminal.
4. The approach arm positioned over a soft tissue
undercut will collect food and irritates lips or cheeks.
5. The approach arm should cross the gingival margin
at a 90 degree angle.
6. The bar retentive clasp is used only when the
retentive undercut is adjacent to the edentulous
from which the approach arm originate.
The approach arm must extend on the abutment
tooth to the height of contour.
The retentive terminal leaves the approach at that
point and extends into the undercut area.
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20
◼ The other terminal which is away from edentulous area
is positioned above the height of contour.
◼ The retentive terminal tip must point towards the
occlusal surface never towards the gingiva.
◼ The bar clasp should be placed as low as on the tooth
as possible while engaging the height of contour to
reduce the leverage induced stress to the abutment
tooth.
TYPES OF BAR CLASP
◼ T Clasp
◼ Modified T Clasp
◼ Y clasp
◼ I clasp
T-Clasp:
• Used in combination with cast circumferential reciprocal arm.
• The retentive terminal and its opposing encircling finger
projects laterally from the approach arm to form T.
• The retentive terminal must cross under the height of contour
to engage the retentive undercut, while the other finger of the
T stays on the suprabulge of the tooth.
• The approach arm should taper gradually and uniformly
from its origin to the retentive terminal.
• The approach arm contacts the tooth only at the height
of contour.
◼ Indication:
- Most frequently used is distal extension ridge where the
usable undercuts is on the distobuccal surface of the
terminal abutment tooth.
- It can also be used for tooth supported partial denture
when the retentive undercut is located on the abutment
tooth adjacent to the edentulous space.
◼ Contra Indication:
- Should not be used on a terminal abutment adjacent to a
distal extension base if the usable undercut is located on
the side of the tooth away from the edentulous space.
- The T clasp can never be used if the approach arm is in
the soft tissue undercut.
- This clasp cannot be used when the height contour is a
large space will be created between the approach arm of
the clasp and the tooth, which would result in irritation of
the lips or cheeks and in trapping food debris.
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21
MODIFIED T-CLASP
◼ It is a T clasp with the non retentive (mesial) finger of
the cross bar of the T terminal is omitted.
◼ Indication:
- Used on canines or premolar for esthetic reasons.
- When we use this type of a clasp the encirclement of
the abutment tooth is sacrificed.
Y-CLASP
◼ It is basically a T-clasp, its configuration occurs when the
height of contour on the facial surface of the abutment
tooth is high on mesial and distal line angles but low on
the center of the facial surface.
I-CLASP
◼ Used on distobuccal surface of maxillary canine for
esthetic reason.
◼ Disadvantage:
- The contact of the retentive clasp with the abutment tooth
is the tip of the clasp an area of 2-3 mm. Encirclement
horizontal stabilization may be compromised.
RPI System (Rest, Proximal plate, I-bar)
Kratochvil in 1963 developed the early clasp assembly which
consisted of three separate units connected to each other
only through the framework. They were the mesial occlusal
rest, a distal guide plane and an I-bar retainer. He preferred a
full length guide plane that is subsequently relieved in the
mouth to prevent torque or binding.
◼ His purposes were:
◼ Elimination of the V-shaped food trap distal to
the tooth.
◼ A highly polished metal contact with the marginal
gingiva, rather than resin .
◼ Intimate metal-to-tooth contact to minimize
food impaction
◼ This design had certain basic disadvantages:
◼ Physiologic relief was required to prevent
impingement of gingival tissues during function.
◼ Since the proximal plate covers a greater surface
area of the tooth, the functional forces are
directed in the horizontal direction, thus the tooth
is located more than the edentulous ridge.
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22
◼ Krol in 1973 made certain modifications in the design of
the proximal plate and named it the RPI bar clasp
design.
◼ He had a 2-3mm of contact of the tooth with the guide
plane, the section below this point being relieved and he
felt that the V shaped space that is left underneath was
not as detrimental as the possible restriction of rotation.
◼ This design however, leaves a region occlusal to the
proximal plate where contact between the abutment and
denture must be made by the replacement tooth.
BASIC PRINCIPLES OF RPI CONCEPT
◼ The mesiobuccal rest with the minor connector is placed
into the mesiolingual embrasure, but not contacting the
adjacent tooth.
◼ A distal guiding plane, extending from the marginal ridge
to the junction of the middle and gingival thirds of the
abutment tooth, is prepared to receive a proximal plate.
▪ The buccolingual width of the guiding plane is
determined by
the proximal contour of the tooth.
▪ The proximal plate in conjunction with the mesial
occlusal
rest and minor connector provides the stabilizing and
reciprocal aspects of the clasp assembly.
◼ The I-bar contributes to the retentive aspect and
should be located in the gingival third of the buccal
or labial surface of the abutment in 0.01 inch
undercut.
◼ The whole arm of the I-bar should be tapered to its
terminus, with no more than 2mm of its tip
contacting the abutment.
◼ The approach arm must be located at least 4mm from
the gingival margin and even more if possible.
OTHER CLASP DESIGNS
RPA clasps
◼ The rest-proximal plate-Aker’s clasp was
developed and described by Eliason in 1983. It
consists of a mesial occlusal rest, proximal plate
and a circumferential clasp arm, which arises
from the superior portion of the proximal plate
and extends around the tooth to engage the
mesial undercut.
VRHR Clasp
◼ The vertical reciprocal horizontal retentive arm concept
was developed by Grasso in 1980 and is characterized by:
◼ A distal occlusal rest supported by a minor connector.
◼ A lingual vertical reciprocal component originating
from the major connector.
◼ A horizontal retentive arm attached to either the
major connector or the retention latticework for the
denture base.
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23
Cingulum clasp
◼ Miller in 1972 designed a clasp to satisfy both the
mechanical and esthetic requirements without the
shortcomings of the internal attachment.
◼ The cingulum clasp has 2 lingual clasp arms. The use
of this clasp requires that the lingual surface of the
abutment tooth be covered with a gold casting.
◼ A guiding plane is incorporated into the distal surface
of the crown and the clasp is designed as an integral
part of the rigid metal framework.
Advantages◼ Esthetic
◼ A tooth of short clinical crown can be used.
◼ The young pulp is not imperiled by close proximity to metal which shows thermal conduction.
◼ Less expensive.
Disadvantages▪ The clasp arms are vulnerable to breakage.
Use▪ The cingulum clasp can be used as a retainer on cuspid
teeth when other extracoronal retainers are esthetically unacceptable
Occlusally and gingivally approaching clasps:
Relative merits and demerits
Retention : The bar clasp approaches the undercut
from below the height of contour and to resist
dislodgement, the clasp pushes towards the occlusal
surface of the abutment tooth. The circumferential
clasp engages the retentive undercut from above the
height of contour and pulls towards the occlusal
surface from the undercut to resist dislodgement.
◼ Bracing : The circumferential clasp is rigid in the
upper two-thirds of the retentive arm and offers
some bracing or stabilization against lateral stresses.
On the other hand, the bar clasp is flexible
throughout its length and does not contribute to
stability.
◼ Stress breaking effect : The gingivally approaching
clasp allows a certain degree of functional movement
of the distal extension base which helps to dissipate
the stresses and lessen the load on the abutment.
Occlusally approaching clasps have the potential to
torque abutment teeth in distal extension based partial
denture situations.
◼ Contact with tooth structure : The gingivally
approaching clasp contacts minimum tooth structure
and has a minimum interference with natural tooth
contour permitting maximum natural cleansing action,
whereas the occlusally approaching clasps covers more
of tooth structure. This occlusal approach may increase
the width of the occlusal table.
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24
◼ Damage to oral tissues : The area of food
lodgement is at the neck of the tooth, with the cementum
in this area being more likely to be affected by caries than
enamel. Trauma to the gingiva can also occur with bar
claps unless sufficiently relieved. Mishandling of the
clasps by the patients during removal of the prosthesis
can result in deformation of the clasp and damage to soft
tissues.
◼ Esthetics : Gingivally approaching clasps are more
esthetic than occlusally approaching clasps except in
instances where large amounts of gingiva is visible
on smiling.
Relative merits & demerits of
cast and wrought wire clasps
◼ Flexibility : The wrought wire clasp has a high degree of
flexibility which helps to better dissipate functional stress
and give a stress breaking effect.
◼ Adjustability : The wrought clasp is adjustable to the
required retention.
◼ Toughness and resiliency : The fabricating process
imparts to the wrought wire a fibrous structure which
accounts for its toughness and resiliency.
◼ Stabilization : The cast clasp on account of
rigid crystalline structure offers better stability.
◼ Cost : Cast clasp requires less cost as soldering
is not required
◼ Fit : The adaptation of a cast clasp to the
abutment tooth is accurate and not subject to
variation by the clinician’s adjustment as with
wrought wire clasps.
◼ Strength and durability : A solder joint near
the origin of a wrought wire clasp reduces its
flexibility and increases the likelihood of
breakage.
◼ Apart from these, cast clasps can be formed to
act as a bracing element, can easily include an
occlusal rest and be cast as an integral part of
gold alloy or a cobalt-chrome denture base.
INTRACORONAL RETAINERS
◼ The intracoronal retainer is usually regarded as an internal
attachment or precision attachment.
◼ The Glossary of Prosthodontic Terms defines precision
attachment as:
“A retainer consisting of a metal receptacle
(matrix) and a closely fitting part (patrix); the matrix is
usually contained within the normal or expanded
contours of the crown on the abutment tooth and the
patrix is attached to a pontic or the removable partial
denture framework.”
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25
As a direct retainer it must provide :
▪ Support
▪ Retention
▪ Reciprocation
▪ Stabilization
▪ Fixation
The precision attachment is the only type of intracoronal
attachment that provides for all three functions of a
removable partial denture system.
▪ Lateral force transmission or bracing from the parallel
proximal walls of the rest against the rest seat.
▪ Occlusal force transmission or support from the flat
gingival floor of the result on the rest seat.
▪ Primary retention from the frictional fit between the rest
and rest seat.
Advantages of intra coronal retainers:
1. Esthetically acceptable, because not much of metal display
like extracoronal retainers.
2. It is preferred in many of the situation because of its
vertical support through a rest seat located more
favourable to the horizontal axis of the abutment tooth.
3. Horizontal stabilization to some extent. Similar
to internal rest, but extracoronal stabilization is
needed.
4. Stimulation to the underlying tissues greater
when internal attachment are used because of
the intermittent vertical massage.
Disadvantages of intra coronal retainers:
1. They require preparation of abutment tooth and
casting.
2. Difficult clinical and laboratory procedure.
3. They eventually wear, result in loss of frictional
resistance to denture removal.
4. Difficult to repair and replace.
5. They are effective in longer teeth and least
effective in shorter teeth.
6. Difficult to place completely in the abutment
teeth.
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26
Limitations of intra coronal retainers:
1. Large pulp size which is usually related to the age of
patient.
2. Length of the clinical crown, not used in short or abraded
teeth.
3. Expensive
4. Distal extension denture bases.
Classification
Classification by Good Kind and Baker in 1976 :
1)Intra coronal
a. resilient
b. non resilient
2) Extra coronal
a. resilient
b. non resilient
Gerardo Becerra et al in 1987 classified precision attachments
as :
1) Intra coronal attachments
a. Frictional
- tapered and parallel walled boxes and tubes
- adjustable metal plates
- springs
- studs
- locks
b. Magnets
2) Extra coronal attachments
a. Cantilever attachments
- rigid attachments
- movable attachments
b. Bar attachments
Tapered And Parallel Walled Boxes And Tubes
◼ Designed to be used in FPD.
◼ Plastic pre fabricated patterns.
◼ Provides vertical support and lateral stabilization.
◼ Simple pin and tube or rectangular block and boxes.
E.g. : Mc Collum attachments.
McCOLLUM ATTACHMENTS
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27
Adjustable Metal Plates
◼ Similar to block and box variety .
◼ Provided with a narrow slit in the metal block or male portion of
the attachment to increase the friction.
◼ Provides a simple and effective form of direct retention.
◼ Atleast 2.5 mm of tooth height is required.
◼ E.g.: Crismani attachment.
Mc Collum attachment.
Stern attachment
Chayes or Rley attachment.
CHEYES
ATTACHMENT
CRISMANI
ATTACHMENT
Springs
◼ Incorporated in the male part to control the friction.
◼ Spring activates a plunger rod which protrudes from
male part to engage a depression in the female part.
◼ Approximately 4 – 5 mm of vertical height is required.
◼ E.g.: Schatzmann attachment.
SCHATZMANN ATTACHMENT
Studs
◼ A metallic stud can be soldered to post and core and
cemented into an abutment.
◼ Direct retention can be obtained by using a stud which
clips into an flexible ring.
◼ Sufficient clearance is required to arrange the artificial
teeth.
◼ E.g.: Ceka attachment
Rotherman attachment
Ceka attachment
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28
Locks
◼ These lock rigidly into the attachments .
◼ The vertical height required for this attachment is
atleast 6 mm.
◼ Retained with pins or incorporated in post and core .
◼ E.g.: T - block attachment
T-ATTACHMENT
Magnets
◼ Small metal keeper is attached to the tooth surface,
usually into the root canal and magnet is incorporated
into the resin.
◼ Alloy in the magnet produces a magnetic force that is
strong .
◼ Magnets are brittle and corrode unless protected in a
stainless steel shelf.
Cantilever attachments
◼ Rigid attachments
They are pin and tube joints that use a slit in the pin or
multiple pin tubes and slots to enhance retentive
friction between the parts with the natural teeth on the
either side of the edentulous space.
These attachments offer excellent stability and
retention in tooth supported partial dentures.
e.g.: Scott attachment
Thompson dowel rest system.
◼ Movable attachments.
◼ These allow the prosthesis to rotate around a horizontal
axis and transmit occlusal forces to the residual alveolar
ridge .
◼ E.g.: Dolbo attachments
Bar attachments
◼ These can be connected to
the cast metal crowns or
copings .
◼ Custom made bars can be
cast with a flat upper surface
to support the prosthesis
and parallel sides that help to
stabilize it.
E.g.: Dolder bar.
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29
Precision attachment selection
◼ Kennedy’s class III partially edentulous arch.
• Rigid internal attachments are recommended .
• Provides good retention, support and brazing because of
its rigid interlocking components.
• If the posterior abutment prognosis is questionable then a
resilient type of attachments are recommended with
anterior abutment.
Kennedy’s class I and class II partially
edentulous arches
◼ The most difficult type of treatment plan.
◼ Some practitioners advocate non rigid and
resilient attachments and some advocate resilient
attachment in distal extension to minimize
rotation and torquing of the abutment tooth,
when the components of an attachment are
rigidly connected.
◼ Another philosophy , known as the stable base
precison attachment RPD concept or floating
denture base concept recommends
incorporation of rigid internal attachments and a
cast metal base made from mucostatic
impression of the residual ridge. The male
portion of the attachment is connected to the
denture base , allowing the complete seating
within the abutment.
◼ The hinged or directionally oriented attachment such as
the Dolbo attachments are recommended to provide
additional bearing or resistance to lateral movement
when the residual ridge is severely resorbed.
◼ The Ceka attachments can be used successfully where
the ridges are not parallel to one another .
Kennedy’s class IV partially edentulous arch
◼ The ideal RPD design for such situation involves the
use of a tissue bar placed close to the edentulous ridge
and connected as a fixed unit to the abutment teeth on
either side of the space using crowns.
SUMMARY & CONCLUSIONS
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30
BIBLIOGRAPHY
◼ Applegate O.C. : Text book of Removable Partial
Prosthodontics, St. Louis, CV Mosby Co.
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