direct retainer (dr vikas ppt.ppt
-
Upload
vikas-aggarwal -
Category
Documents
-
view
224 -
download
0
Transcript of direct retainer (dr vikas ppt.ppt
-
7/22/2019 direct retainer (dr vikas ppt.ppt
1/128
DR VIKAS AGGARWAL
-
7/22/2019 direct retainer (dr vikas ppt.ppt
2/128
COMPONENTS OF REMOVABLE PARTIAL DENTURE
MAJOR CONNECTOR-the part of a partialremovable dental prosthesis that joins the componentson one side of the arch to those on the opposite side
(GPT 8TH
)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
3/128
MINOR CONNECTORthe connecting link between
the major connector or base of a partial removabledental prosthesis and the other units of theprosthesis, such as the clasp assembly, indirectretainers, occlusal rests, or cingulum rests (GPT 8TH)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
4/128
DIRECT RETAINER- that component of a partial
removable dental prosthesis used to retain and preventdislodgment, consisting of a clasp assembly orprecision attachment (GPT 8TH)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
5/128
INDIRECT RETAINER- the component of a partialremovable dental prosthesis that assists the direct
retainer(s) in preventing displacement of the distalextension denture base by functioning through leveraction on the opposite side of the fulcrum line whenthe denture base moves away from the tissues in pure
rotation around the fulcrum line (GPT 8TH)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
6/128
GUIDING PLANE- vertically parallel surfaces onabutment teeth or/and dental implant abutments
oriented so as to contribute to the direction of thepath of placement and removal of a removabledental prosthesis (GPT 8TH)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
7/128
6) REST- unit of a partial denture that is placed on anabutment tooth , ideally in a prepared rest seat, so that it
limits movement of denture in a gingival direction andtransmits functional forces to the tooth. They aredesignated by the surface of the tooth prepared to receivethem: Occlusal rest- placed on the occlusal surface of a posterior tooth
Lingual rest- placed on the lingual surface of an anterior tooth, Incisal rest- placed on the incisal edge of an anterior tooth.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
8/128
Denture base part of a denture (made of metal or resin)that rests on a residual bone covered by soft tissue , to
which teeth are attached and which effects the transfer of
occlusal forces to supporting oral structures. Tooth replacements-refers to artificial teeth placed in
denture. They can be acrylic, resin metal or porcelain
-
7/22/2019 direct retainer (dr vikas ppt.ppt
9/128
-
7/22/2019 direct retainer (dr vikas ppt.ppt
10/128
Retention is that quality inherent in theremovable partial denture that resists the vertical
forces of dislodgement for e.g., the force ofgravity, the adhesiveness of foods or the forcesassociated with the opening of the jaws
Adirect retainer is that component of aremovable partial denture used to retain andprevent dislodgement, consisting of a claspassembly or precision attachment (GPT 8TH )
-
7/22/2019 direct retainer (dr vikas ppt.ppt
11/128
DIRECTRETAINER
EXTRACORONAL
RETENTIVECLASP
ASSEMBLY
SUPRABULDGE INFRABULDGE
ATTACHMENTS
INTRACORONAL
PRECISIONATTACHMENT
SEMIPRECISIONATTACHMENT
-
7/22/2019 direct retainer (dr vikas ppt.ppt
12/128
EXTRACORONAL ATTACHMENTS
1900- introduced by Henry. R .Boos
1908- modified by F.Ewing.Roach
located outside the normal clinical
contours of abutment crowns derive their retention from closely
fitting components termedmatrices and patrices.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
13/128
The male unit is soldered to the surface of the
abutment crowns, forming a projection to which
the female element, buried within the denture,
can be joined. The male portion projects as an L
shaped bar with a ball joint on the lower extremely
The female section fits over the bar and engages
the sides of the ball connection of the male.
Advantages
They provide excellent resistance to toothdistal and lateral displacing forces.
Stress breaking effect.
They require no buccal retainers or lingual bracing
arms.
esthetics
They do not interfere with the contour of the
abutment crown.
Disadvantages
Difficulty in maintaining plaque free environment
Dalbo attachment
-
7/22/2019 direct retainer (dr vikas ppt.ppt
14/128
EXTRACORONAL DIRECT RETAINER/COMPONENTS
Retentive clasp assembly
m/c method of extracoronal retention
first appeared in the dental literature with Dr W. G. A.Bonwill's description in 1899
In1916 Prothero advanced cone theory as the basis forclasp retention. He described the shape of crowns ofpremolar and molar teeth as that of two cones sharing acommon base.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
15/128
The line at which the two converging cones meet is
called the height of contour, a term first used byKennedy .
De Van : SUPRABULGE and INFRABULGE
Cummer called it GUIDELINE How clasp helps in retention??
If the clasp terminal is placed cervical to this line, it
has to deform in order to escape from undercut area. Indoing so, it generates resistance called retention.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
16/128
Rest : It is the part of theclasp that lies on theocclusal, lingual orincisal surface of a toothand resist tissue ward
movement of the clasp.
Body of the clasp : It isthe part of the clasp that
connects the rest andshoulder of the clasp tothe minor connector.
Basic parts of a clasp assembly :
-
7/22/2019 direct retainer (dr vikas ppt.ppt
17/128
Shoulder : It is the part of the clasp
that connects the body to theclasp 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.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
18/128
Retentive arm : It is the part of theclasp comprising the shoulder
which is not flexible and islocated above the height of thecontour.
Retentive terminal : It is the terminalend of the retentive clasp arm. Itis the only component of theremovable partial denture thatlies on the tooth surface cervicalto the height of the contour. Itpossesses a certain degree of
flexibility and offers the propertyof direct retention.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
19/128
Extracoronal circumferential direct retainer
-
7/22/2019 direct retainer (dr vikas ppt.ppt
20/128
Approach arm It is a component of the bar clasp. It isa minor connector that projects from the framework,runs along the mucosa and turns to cross the gingivalmargin of the abutment tooth to approach theundercut from a gingival direction.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
21/128
PRINCIPLES OF CLASP DESIGN
1) Encirclement basic principle ,more than 180 degree in the greatestcircumference of the tooth
can be continuous contact, such as in a circumferential clasp,
or discontinuous contact, such as in the use of a bar clasp.
The clasp should make contact with three areas 1) occlusal rest andbody area 2) the reciprocal terminal area 3) the retentive terminal area.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
22/128
2) The occlusal rest should be located in prepared
recess on the occlusal surface so all forces aretransmitted along the long axis of the abutment
3) Each retentive terminal should be opposed by areciprocal component capable of resisting any
pressure exerted by retentive arm during removalor insertion
4) Clasp retainers on abutment teeth adjacent to
distal extension bases should be designed so thatthey will avoid direct transmission of tipping androtational forces to the abutment
-
7/22/2019 direct retainer (dr vikas ppt.ppt
23/128
5) Unless guiding planes will
positively control the path ofremoval and stabilizeabutments against rotationalmovements, retentive clasps
should be bilaterally opposed,i. e., buccal retention on oneside of the arch should beopposed by buccal retention
on the other, or lingual on oneside opposed by lingual on theother
-
7/22/2019 direct retainer (dr vikas ppt.ppt
24/128
6) To resist dislodgment path of escapementfor retentive clasp terminal must be otherthan parallel to the path of removal ofprosthesis
7)The amount ofretention should always bethe minimum necessary to resist reasonable
dislodging forces. 8) Reciprocal elements of the clasp assembly
should be located at the junction of thegingival and middle thirds of the crowns of
abutment teeth. The terminal end of theretentive arm is optimally placed in thegingival third of the crown. These locationspermit better resistance to horizontal and
torqueing forces.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
25/128
All clasps must be designed so that they satisfythe following six basic requirements:
1.Retention2.Support
3.Stability
4.Reciprocation5.Encirclement
6.Passivity
-
7/22/2019 direct retainer (dr vikas ppt.ppt
26/128
1) RETENTION
Retention is provided mainly by the retentive arm but also by the effectivedesign and adequate construction ofother parts
The retention must be very definitely limited and minimal .
The retention should be balanced
the path of escapement of a retentive terminal must not be parallel to
path of appliance removal
-
7/22/2019 direct retainer (dr vikas ppt.ppt
27/128
Guiding planes control the path of
placement and removal; they can alsoprovide additional retention for the partialdenture by limiting the possibilities thatexist for its dislodgment. The more vertical
walls (guiding planes) that are preparedparallel, the fewer the possibilities that existfor dislodgment
Therefore without guiding planes, claspretention will either be detrimental orpractically non-existent. If clasp retention isonly frictional because of an activerelationship of the clasp to the teeth, thenorthodontic movement or damage toperiodontal tissue, or both, will result.Instead a clasp should bear a passiverelationship to the teeth except when a
dislodging force is applied
-
7/22/2019 direct retainer (dr vikas ppt.ppt
28/128
Factors affecting retention
Size and the distance into the angle of cervicalconvergence
To be retentive a tooth must have
an angle of convergence cervical
to the height of contour.
The location and depth of a tooth
undercut available for retention are
relative to the path of placement
and removal of the partial denture. Greater the degree of gingival
convergence, the greater will be
the retention of the clasp, provided
all other factors are equal
-
7/22/2019 direct retainer (dr vikas ppt.ppt
29/128
When the angle of convergencebetween two abutments differsuniformity of retention can beobtained by placing the clasparms into the same degree ofundercut (i.e. both .02"). Aguiding principle of partialdenture design is that retentionshould be uniform in magnitudeand bilaterally opposed amongstabutments.
The tool used to identify the proper position for each clasp terminus is
called an undercut gauge. Undercut gauges are available in 0.010-,
0.020-, and 0.030- inch configurations
-
7/22/2019 direct retainer (dr vikas ppt.ppt
30/128
Degree of undercut
When all other clasp factors
remain constant, positioning
the retentive clasp terminus
at a greater horizontal
undercut will result in
increased retentive force.Therefore, a retentive clasp
terminus positioned in a
0.020-inch horizontal
undercut (B) will provide
greater retentive force thanwill a clasp positioned in a
0.010-inch undercut (A).
-
7/22/2019 direct retainer (dr vikas ppt.ppt
31/128
FLEXIBILITY OF CLASP ARMLENGHT OF CLASP ARM
Flexibility
LENGTH (POWER OF 3)
The retentive circumferential clasp armshould be tapered uniformly from its pointof origin through the full length of theclasp arm.
For the same length, the bar clasp arm isless f lexible than a circumferential clasparm because of its half round cross section
which lies in several planes and prevents
total flexibility. In practice however, the gingivally
approaching clasp is longer and moreflexible, with less retentiveness thanocclusally approaching clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
32/128
DIAMETER OF
CLASP ARM FLEXIBILITY
1/(DIAMETER)3 The greater the average
diameter of a clasp armthe less flexible it willbe.
A clasp should be half as
thick at the tip than atthe origin.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
33/128
CROSS-SECTIONAL FORM
Round form is used in distal extension cases where as half
round is used in tooth supported partial dentures
-
7/22/2019 direct retainer (dr vikas ppt.ppt
34/128
Material used for clasp arm : Two types of materials areused : Type IV gold alloys and cobalt-chrome alloys whichhave different modulus of elasticity.
The modulus of elasticity of cobalt-chrome alloys is greaterthan that of casting gold. Therefore a clasp of the samecross-section is stiffer in cobalt-chrome than in cast gold.
This can be overcome by using longer clasps of thinnersection.
The retentive terminal has to be flexible and therefore havelow modulus of elasticity. The reciprocal elements have to be
stiff and unyielding and have high modulus of elasticity.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
35/128
Structure of the alloy: The alloy may be cast or wrought
in nature. Wrought wires have greater flexibility than a caststructure due to its grain structure being fibrous.
The tensile strength of a wrought structure is at least 25%greater than that of the cast alloy from which it was made.
Wrought forms can be used in smaller diameters toenhance the flexibility. They offer minimum friction andcan have a stress breaking effect.
Disadvantage of wrought alloy is recrystallization can lead
to fracture
-
7/22/2019 direct retainer (dr vikas ppt.ppt
36/128
2.SUPPORT Property that resist displacement of clasp in
gingival direction.
Support in a clasp is generally provided by the rest.Thus while chewing food the rest prevents tissue
ward movement of the clasp assembly, plus directsthe force along the long axis of the tooth, thusreduces periodontal tissue damage.
Secondary support is obtained by the rigidcomponents i.e. body and shoulder of the clasp
which are placed above the greatest diameter of thetooth.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
37/128
3. STABILITY
Resistance to horizontal displacement of a prosthesis.
All clasp component except retentive terminal providestability
Greatest contribution to the stability is offered byreciprocal element, shoulder and vertically orientedminor connector.
The components of the cast circumferential clasp offerbetter stabilization than either the bar clasp or thewrought wire clasp, because of greater amount ofrigidity of the clasp material.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
38/128
4. RECIPROCATION
Reciprocation is the quality of clasp assemblythat counteracts lateral displacement of anabutment when the retentive clasp terminuspasses over the height of contour.
Ideally, reciprocal elements of the clasp
assembly should be located at the junction ofthe gingival and middle thirds of the crownsof abutment teeth. The terminal end of theretentive arm is optimally placed in thegingival third of the crown. These locations
will permit the abutment teeth to better resisthorizontal and torqueing forces.
Reciprocal arm is not tapered like retentivearm.
It is tapered in one dimension(OG)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
39/128
During insertion of the prosthesis, the reciprocal elementshould contact the abutment slightly before the retentivearm contacts the abutment. Contact of the reciprocal
element should be maintained while the retentive terminuspasses over the height of contour and into the prescribedundercut.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
40/128
If the retentive terminus contacts the abutment before the reciprocal element
contacts the abutment damaging non-axial forces may be applied to the
abutment. For this reason, the abutment surface that will be contacted by
the reciprocal element should be parallel to the removable partial denture'spath of insertion and removal.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
41/128
5.ENCIRCLEMENT
The clasp must be designed
to encircle more than 180 degrees.
Encirclement may be:
Continous contact (circumferential) Broken contact (bar)
In bar, clasp contact at 3 diff. tooth areas:
Occlusal rest, retentive terminal, reciprocal terminal
-
7/22/2019 direct retainer (dr vikas ppt.ppt
42/128
6. PASSIVITY The retentive clasp arm should be passive (no active
force) until a dislodging force is applied.
The retentive arm should be activated only whendislodging forces are applied to the removable partial
denture
-
7/22/2019 direct retainer (dr vikas ppt.ppt
43/128
Classification of extra-coronal retainers:1.Supra bulge clasps (occlusally approaching,
circumferential or encircling clasps).The retentive arm approaches the undercut area from
the suprabulge direction.
2.Infrabulge clasps (gingivally approaching, projection orbar clasps)
The retentive arm approaches the undercut from theinfrabulge direction ,e.g. Bar clasp arm (I-Bar etc.)
Circumferential Clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
44/128
Circumferential Clasp
Introduced by Dr N. B. Nesbitt in 1916
Easiest to design and construct. Also it is easy to repair.
The most logical clasp to use with all tooth-supported partialdentures because of its retentive and stabilizing ability
Design Rules for use
Retentive clasp arm occlusal and Retentive terminal gingival to height of contour
Terminal toward occlusal surface, never towards thegingiva.
Retentive tip terminate at mesial and distal line angle andnever in the centre of facial or lingual surface.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
45/128
DISADVANTAGES:
increased risk fordecalcification
covers large area
width of occlusal table is
increased More metal is visible
ADVANTAGES:
Good support ,bracing and
retentive properties
displays close adaptation to theabutment and therefore
minimizes the entrapment of
food and debris Easy to make and repair
-
7/22/2019 direct retainer (dr vikas ppt.ppt
46/128
Types of circumferential clasps
Simple Circlet clasp.
Reverse approach circlet.
Multiple circlet
Embrasure clasp Ring clasp.
Back action clasp.
Reverse action / hair pin clasp.
Half-and-half clasp.
Combination clasp.
Onlay clasp.
Extended clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
47/128
Simple Circlet clasp
Disadvantages
Because of half round cross-
section geometry adjustment
of clasp arm is difficult.
increase the occlusal table
Increased calcification and
compromised esthetics
Cannot be used in distal
extension cases
Advantages
Easy to construct, repair.
It provides better support, stability,
reciprocity, encirclement, and passivity
Approaches the undercut
on abutment from the
edentulous area.
Engage the undercut
remote from edentulous
space
Most widely used least complex in
design
Clasp of choice for
tooth supported
RPD
-
7/22/2019 direct retainer (dr vikas ppt.ppt
48/128
Reverse-action clasp
Features Retentive undercut adjacent to
edentulous space.
m/c DB under undercut
Used when bar clasp cannot be
used due to soft/hard tissue
undercut
Advantages
In distal extension partial dentures, asdenture base is depressed under
function, retentive clasp tip rotate
gingivally to enter greater amount of
undercut and reduce torsional stresses
transmitted to abutment.
Disadvantages
As the shoulder of the clasp extendsover the abutments mesial marginal
ridge, it may be difficult to provide
adequate clearance without removing
significant tooth structure
The gingival mucosa may not be well
protected because of the mesial
occlusal rest resulting in food traps
between proximal plate and surface of
abutment.
It may be esthetically compromised as
it has a mesial approach.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
49/128
Multiple circlet clasp.
Indication:
When additional retention is needed.
Tooth borne partial denture Multiple clasping required, when the
partial denture replaces an entire half of
the dental arch.
Used in the form of splinting tooth.
Disadvantage
Two embrasure approaches arenecessary rather than a single
common embrasure for both clasps
Features The multiple clasp is simply two
opposing circumferential claspsjoined at the terminal end of thetwo reciprocal arms.
Upon emerging through occlusalembrasure retentive arm engagesopposite line angle
.
Embrasure clasp/ modified crib clasps/ Bonwill
-
7/22/2019 direct retainer (dr vikas ppt.ppt
50/128
p/ p /clasp
Features
Two simple circlet clasp
joined at the body. Used on the side where
no edentulous space
Occlusal rest preparation on
both teeth.
Upon emerging through
occlusal embrasureretentive arm engages
opposite line angle
Disadvantages
Sufficient space must be provided
between the abutment teeth in theirocclusal third to make room for the
common body of the clasp. This
involves more of tooth reduction,
which increases caries susceptibility,
and risk of encroachment of the pulp.
Advantages
The double occlusal rests prevent
interproximal wedging by the
prosthesis, which could causeseparation of the abutment tooth
and result in food impaction and
clasp displacement.
In addition to providing support,
occlusal rests also serve to shunt
food away from the contact area.
Ri l
-
7/22/2019 direct retainer (dr vikas ppt.ppt
51/128
Ring claspFeatures
It is that form of a circumferential claspthat encircles nearly the entire tooth
from its point of origin. It is usually used
when a proximal undercut cannot be
approached by any other means
Mandibular molars tend to drift
mesiolingually and maxillary molarsmesiobuccally
Retentive undercut on mesiolingual line
angle of mandibular molar and
mesiobuccal line angle of maxillary
molars
The undercut is on the same side as therest seat (i.e. adjacent to edentulous
span)
The lower bracing arm should be at
least 1 mm from the free gingival margin
and relieved to prevent impingement of
the gingival tissues
Should always be used with a
supporting strut on the non-
retentive side with an auxiliary
occlusal rest on the opposite side Omission of the supporting strut will
allow the clasp arm to open and
close with minimum or no
reciprocation.
Ad t
-
7/22/2019 direct retainer (dr vikas ppt.ppt
52/128
Advantages
Provides adequate encirclement of
more than 180 degrees.
excellent retention with adequate
flexibility due to increased length of
clasp arm.
restores the occlusal surface by its
anatomy and thereby uprights the tooth
decreasing unfavourable stress to the
abutment.
provides vertical support andprevents tissueward movement.
The auxiliary distal rest prevent
further mesial drift of the tooth.
Indication
It is used mainly when the proximal
undercut cannot be approached directly
from the occlusal rest area, and / or
tissue undercuts prevent a gingivalapproach of the clasp
Disadvantages:a. Covers a large area requiring
meticulous hygiene
b. Very difficult to adjust
Contra indication Limited vestibular depth
contraindicated when the
bracing arm must cross the soft
tissue undercut.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
53/128
Back action clasp
This clasp is a modification of the ring
clasp with no apparent advantages.
It lacks a guide plane and the occlusal
rest does not have a rigid support.
Here minor connector is connected to
end of clasp arm and occlusal rest is
left unsupported. Hence it is a
biologically and mechanically unsound
design.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
54/128
FISH HOOK/HAIRPIN/ C CLASP
FEATURES Simple circlet clasp with retentive
arm after crossing the facial surface,
loops back in a hairpin to engage
the undercut below its point of
origin.
Upper part is rigid considered asminor connector and lower part is
flexible.
Crown must have sufficient
occlusogingival height.
The bend that connects the upper
and lower parts of the arm shouldbe rounded to prevent strain
accumulation and fracture of the
arm at the bend
-
7/22/2019 direct retainer (dr vikas ppt.ppt
55/128
Indication:
Distal extension partial denture.
Mesially inclined posterior teeth.
If proximal undercut must be used
on a posterior abutment and when
the tissue undercut, tilted teeth or
high tissue attachment prevent theuse of bar clasp arm ( although ring
clasp can be placed but lingual
undercut may prevent the
placement of supporting strut
without tongue interference
Indicated when reverse circlet clasp
cannot used because of lack of occ.
space
Contra Indication:
Tight occlusal contact, increase
posterior overbite and short
crown.
The clasp covers considerable tooth
surface and may trap debris..
It has limited flexibility and is
unesthetic for use on an anterior
abutment
Disadvantages Inadequate flexibility
Difficult to fabricate
Accumulation of food and debris
Esthetically unacceptable
Half and half clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
56/128
Half and half clasp It consists of a circumferential retentive
arm arising from one direction and areciprocal arm arising from another.
The second arm must arise from asecond minor connector, this arm isused with or without an auxiliaryocclusal rest.
Reciprocation is achieved with a shortbar or with an auxiliary occlusal rest.
The principle of half and-half clasp isused only for unilateral partial denturedesign.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
57/128
ONLAY CLASP
Is extended occlusal rest with buccaland lingual clasp arm.
The clasp may originate from anypoint on the onlay that will not createocclusal interferences.
Therefore, this type of clasp is usedwhen the occlusal surface of theabutment tooth is below the occlusalplane. The onlay can be used torestore the lost vertical dimension.
Indicated in caries resistant mouth
Extended clasp arm
-
7/22/2019 direct retainer (dr vikas ppt.ppt
58/128
Extended clasp armAdvantages:
It has splinting andstabilization action.
Distribution of lateral loads
over two teeth.
Disadvantages:
More tooth structure
covered, easily distorts and
breakage of the arm.
Features
similar to the
circumferential arm but it
covers two teeth.
It remains above the survey
line of the 1st tooth; crosses
the undercut of the
adjacent tooth..
Indications:
Tooth supported RPD.
tooth next to edentulous space that
has no buccal and lingual undercut.
Contra Indication:
Distal extension dentures
because functional forces will
cause rotation around the rest
and upward movement of
clasp tip.
COMBINATION CLASP
-
7/22/2019 direct retainer (dr vikas ppt.ppt
59/128
COMBINATION CLASP
In 1965, Dr O. C. Applegate
introduced a modified wrought-wire clasp assembly known asthe "combination clasp
The combination clasp consistsof a wrought-wire retentiveclasp arm and a cast reciprocalclasp arm. .
Indicated on abutment adj. todistal extension space, when theundercut is on mesiobuccalsurface.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
60/128
The wrought-wire component is circular in cross
section, thereby permitting flexure in all
directions.
This omnidirectional flexure allows the clasp to
flex in all planes and can minimize the transfer
of potentially harmful forces to the abutment
b) In addition to advantages of
flexibility, adjustability, and
appearance, wrought-wire
retentive arm makes only line
contact with abutment tooth,
rather than broader contact ofcast clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
61/128
Uses
Kennedy Class I or Class II posterior edentulous area
when the usable undercut is located at the mesiofacialline angle of the most posterior abutment
It is used on abutment tooth adjacent to a distalextension base where where a large tissue undercut
contraindicates a bar type retainer.
ADVANTAGES
-
7/22/2019 direct retainer (dr vikas ppt.ppt
62/128
ADVANTAGES Not only the flexibility is maximal, but it is effective
in any direction.Greater flexibility of wrought wire actas stress equalizer, prevent undesirable forces.
Can be placed in deeper undercut or in gingival third ofclinical crown so more esthetic appearance. So often usedon maxillary canines and premolars.
Round wrought wire makes only a line contact, can beused in caries prone mouth.
readily adjustable to more retentive position. better esthetics (due to its round form and smaller
diameter - 18 gauge)
can be placed in 0.02" undercut due to its flexibility
(allows lower placement for better esthetics)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
63/128
Disadvantages More prone to breakage or damage.
Need extra lab procedures Easily distorted by careless handling by patient during
removal, who tend to remove it by lifting retentiveportion of wrought wire clasp.
Retentive arm not possess bracing or stabilizing qualitydue to its increased flexibility.
There are four laboratory approaches to construct
-
7/22/2019 direct retainer (dr vikas ppt.ppt
64/128
There are four laboratory approaches to constructwrought wire clasp arm (JPD 1973)
1. Cast to.
2. Soldered to the minor connector.
3. Soldered to the base retentive mesh area.
4. Attached only in the resin of the denture base.This is most commonly used in the repair of brokenclasp components.
Wire components which have been incorporated
into the casting are 42 per cent less flexible thanwire components soldered to the base retentivemesh or unsoldered and buried in resin.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
65/128
Clasp that allow functional movement
Clasp assemblies that accommodate functional prosthesismovement are designed to address the concern of a Class Ilever.
The concern is that the distal extension acts as a long "effortarm" across the distal rest "fulcrum" to cause the clasp tip"resistance arm" to engage the tooth undercut.
This results in a harmful tipping or torquing of the tooth andis greater with stiff clasps and more denture base movement.
Two strategies are adopted to either change the fulcrumlocation and subsequently the "resistance arm" engagingeffect (mesial rest concept clasp assemblies), or to minimizethe effect of the lever by use of a flexible arm (wrought-wireretentive arm)
Gingivally approaching clasps/infra bulge/push clasp/roach
-
7/22/2019 direct retainer (dr vikas ppt.ppt
66/128
clasp
Clasp is termed by Dr. F. Ewing
Roach in 1930 Approaches the retentive undercut
from a gingival direction.
Push type of retention, which isbetter than pull type retention of
roach clasp. The bar clasp is classified by shape
of the retentive terminal T, modifiedT, I, Y forms, all of which originatefrom the denture base frame work
and approaches the undercut fromgingival direction
It is easier to seat but difficut toremove
Ad t
-
7/22/2019 direct retainer (dr vikas ppt.ppt
67/128
Advantages
Minimal tooth contact and minimal distortion ofnormal tooth contours leading to improved tissuestimulation, oral hygiene, caries and periodontalproblems.
Improved esthetics if the approach portion of the armis not visible as it crosses the gingiva.
Increased retention because of tripping action.
Decreased torqueing forces applied to terminalabutments in distal extension RPD.
Large undercut can be engaged.
Di d t
-
7/22/2019 direct retainer (dr vikas ppt.ppt
68/128
Disadvantages
Cannot be used in the presence of soft tissueundercuts, shallow vestibule and high frenumattachments.
Bracing action provided by bar clasp is considerable
less than that provided by cast circumferential clasps. Food entrapment.
Difficult to fabricate and adjust.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
69/128
a) horizontal projection portion of the
approach arm (A),
b) vertical projection aspect of the
approach arm (B),
c) location where the approach arm
crosses perpendicular to the free
gingival margin (C),
d) point of first tooth contact at or
occlusal to the height of abutment
contour (D),
e) terminus of the retentive clasp
contacting the abutment apical to
the height of contour(E),
f) encirclement portion of the clasp
contacting the abutment occlusal to
the height of contour (F).
Design rules
-
7/22/2019 direct retainer (dr vikas ppt.ppt
70/128
Design rules
The approach arm must not impinge on the soft tissues adjacent to
the abutment The approach arm should cross perpendicular to the free gingival
margin.
The approach arm should never be designed to "bridge" an area ofsoft tissue undercut since this will produce an increased risk of food
entrapment and may result in irritation of the soft tissue To optimize flexibility, the approach arm should be uniformly
tapered from its origin to the clasp terminus.
The clasp terminus should be positioned a far apically on the abutmentas is practical. Proper placement of the clasp terminus yields a decrease
in leverage-induced stresses resulting from movement of theprosthesis.
The minor connector that attaches the occlusal rest to the frameworkshould be rigid and should contribute to the overall bracing andstabilization characteristics of the prosthesis.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
71/128
Approach arm must not bridge area of soft issue undercut can lead to food entrapment
and soft tissue irritation
-
7/22/2019 direct retainer (dr vikas ppt.ppt
72/128
Upon loading of the extension base, the distal rest serves as a centre of
rotation. The tip of the retentive clasp moves apically and mesially. This
minimizes potentially harmful torqueing forces while transmitting a relatively
small, mesially directed force to the abutment. The mesially directed force is
well tolerated as a result of sound contact with the adjacent natural tooth.
Types of bar clasps
-
7/22/2019 direct retainer (dr vikas ppt.ppt
73/128
Types of bar clasps
T- barModified T-barY- barI- bar
-
7/22/2019 direct retainer (dr vikas ppt.ppt
74/128
T CLASP Retentive terminal and itsopposing encircling fingerproject laterally from the
approach to form T. Both projections should point toward the occlusal surface. The retentive terminal must cross under the height of
contour to engage the retentive undercut.
Used in distal extension base situations, on distobuccalundercut. Dont use it on mesiobuccal undercut.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
75/128
It shouldnot be used if approach arm bridge a softtissue undercut.
If T clasp used on tooth where height of contour isclose to occlusal surface then a large surface is
covered b/w approach arm and tooth leads to foodaccumulation.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
76/128
MODIFIED T CLASP
it is a T clasp with non
retentive finger of the
crossbar of T terminal is
omitted. It is used on canines and premolars for esthetic reasons.
Potential danger the encirclement of 180 degrees issacrificed for esthetics.
.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
77/128
Y CLASP
Basically it has T- barconfiguration , usedwhen height of contour
on the facial surface ofthe abutment tooth ishigh on the mesial anddistal line angles but lowat the center of the facialsurface
I CLASP/ 1 BAR
-
7/22/2019 direct retainer (dr vikas ppt.ppt
78/128
I CLASP/ 1 BAR
Derives its name from its shape The clasp arm contacts the
abutment surface over an area thatextends from the measuredundercut to the height of contour
Typically, the contact areabetween the clasp and theabutment is 2.0 to 3.0 mm inheight and 1.5 to 2.0 mm in width.
The approach arm has a half round,cross-sectional geometry and ischaracterized by a gradual anduniform taper throughout its length.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
79/128
Often, the I-clasp design is used in conjunction with a
mesial rest preserving the abutment from torqueingforces
This design is commonly used in the treatment ofKennedy Class I and Class II partially edentulous
arches it may occasionally be used on the distobuccal surface
of maxillary canines for esthetic reasons.
Disadvantage:
Encirclement horizontal stabilization may becompromised.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
80/128
I-clasp Is An Integral Retentive Component In TwoDistinct Design Philosophies:
The Mesial Rest/I-bar Concept And
The RPI Concept.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
81/128
I BAR CONCEPTIt is modified type roach clasp designed by Kratochvil in 1963, which consisted of
three separate units connected to each other only through the framework. They
were the mesial occlusal rest, a distal guide plate and an I-bar retainer.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
82/128
DESIGN Mesial rest
The mesioocclusal rest with the minorconnector is placed into themesiolingual embrasure, but notcontacting the adjacent tooth.
Rest are extensively prepared as in
premolars it involves marginal andtriangular ridges where as in molar itextends into central fossa.
Due to this occlusal forces are directedvertically thus eliminating harmful
lateral stresses. It shifts the fulcrum line more anteriorly
-
7/22/2019 direct retainer (dr vikas ppt.ppt
83/128
Proximal plates
A distal guiding plane is prepared to receive a proximal
plate. Usually guiding plane is 2-5 mm but in this case it is
very long as it extends onto attached gingiva for 2 mm
The buccolingual width of the guiding plane isdetermined by the proximal contour of the tooth.
The proximal plate in conjunction with the mesialocclusal rest and minor connector provides thestabilizing and reciprocal aspects of the clasp assembly.This configuration permits improved stabilization ofthe prosthesis
Long guide plane provides increased horizontal
stability reduces food impaction between the tooth and the
proximal plate
Provides reciprocation during insertion and removal ofthe prosthesis
Distributes occlusal forces throughout the arch
-
7/22/2019 direct retainer (dr vikas ppt.ppt
84/128
I bar retainer
Arm of I bar is long
tapering with half roundcross section
Retentive I bar is placed on
buccal surface ofabutment mesial to mesiodistal height of contour
The I bar should extend
about 2 mm above toothtissue junction
Reciprocation here ismesiodistally
-
7/22/2019 direct retainer (dr vikas ppt.ppt
85/128
Advantages
1. Food accumulation is minimized because tooth
contours are not significantly altered.
2. The clasp terminus disengages from the tooth whenan occlusal load is applied to the adjacent distalextension base.
3. Because the approach arm does not contact theabutment, lateral forces are minimized.
Disadvantages
1. Less horizontal stability than other types of claspassemblies
2. Less retention
RPI CONCEPT
-
7/22/2019 direct retainer (dr vikas ppt.ppt
86/128
RPI CONCEPT
RPI concept was given by KROLL 1973
RPI means mesial rest, proximal plate and I bar.
The principle was stress control with minimal
tooth and gingival coverage. Normally retentive and reciprocal units act
bucco-lingually but here they act in mesio-distaldirection.
He modified I bar clasp concept to meet minimalcoverage criteria
Mesial rest modification
-
7/22/2019 direct retainer (dr vikas ppt.ppt
87/128
Mesial rest extends only in triangular fossa even in molarpreparation. It doesnt cover entire marginal ridge.
Proximal plate modification
The prepared guiding plane is 2 to 3 mm highocclusogingivally, and the proximal plate contacts onlythe apical 1 mm of the guiding plane.
Relief is provided at the tooth-tissue junction to allowthe proximal plate to disengage when loaded.
The stated purpose for reducing the proximal plate is toimprove gingival health
I bar modification
Modifications in 1-bar configuration and placement areneeded to compensate for reduced tooth contact by the
proximal plate. The 1-bar terminus is pod shaped to allow additional
tooth contact, and the vertical portion of the clasp armassumes a more mesial position to achieve efficientreciprocation from the smaller proximal plate.
RPI CONCEPT
-
7/22/2019 direct retainer (dr vikas ppt.ppt
88/128
RPI CONCEPT
-
7/22/2019 direct retainer (dr vikas ppt.ppt
89/128
ADVANTAGES More esthetic due to minimal tooth contact
Good for caries prone patients
Adequate encirclement by engaging more than
180 degree. Encirclement provided by mesial rest and
proximal plate
Under vertical masticatory forces, both the plate
and I bar disengage the abutment.
Relative merits and demerits of occlusally and gingivally approaching clasps
-
7/22/2019 direct retainer (dr vikas ppt.ppt
90/128
Retention-The bar clasp is easier to seat on the toothand more difficult to remove than the circumferentialclasp. If all factors i.e. length of clasp arm, depth ofundercut, flexibility of the arm etc are equal, the barclasp is more retentive than the circumferential claspdue to tripping action.
In practice however, the gingivally approaching clasp islonger and more flexible, with less retentiveness thanocclusally approaching clasp
) B i Th i f i l l i i id i h
-
7/22/2019 direct retainer (dr vikas ppt.ppt
91/128
2) Bracing: The circumferential clasp is rigid in theupper 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 tostability.
3) Stress breaking effect: The gingivally approachingclasp allows a certain degree of functional movementof the distal extension base which helps to dissipatethe stresses and lessen the load on the abutment.
Occlusally approaching clasps have the potential totorque abutment teeth in distal extension basedpartial denture situations.
4) Tooth contact:
The gingivally approaching clasp contacts minimum tooth structure and
-
7/22/2019 direct retainer (dr vikas ppt.ppt
92/128
The gingivally approaching clasp contacts minimum tooth structure andhas a minimum interference with natural tooth contour permittingmaximum natural cleansing action,
whereas the occlusally approaching clasps covers more of toothstructure. This occlusal approach may increase the width of the occlusaltable.
5) Oral health: The gingivally approaching clasp has a likely potential tocreate gingival pathology. The area of food stagnation is at the neck of
the tooth and the cementum in this area is more likely to be affected bycaries than enamel. Trauma to the gingiva can also occur with bar clapsunless sufficiently relieved. Mishandling of the clasps by the patientsduring removal of the prosthesis can result in deformation of the claspand damage to soft tissues.
Decalcification of tooth is more in occlusally approaching clasp due tomore tooth contact.
6) Esthetics: Gingivally approaching clasps are more esthetic thanocclusally approaching clasps except in instances where large amounts ofgingivae are visible on smiling.
RPA CLASP
-
7/22/2019 direct retainer (dr vikas ppt.ppt
93/128
The rest, proximal plate, Akers
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 superiorportion of the proximal plate
and extends around the tooth to
engage the mesial undercut.
It is indicated when bar-type
clasp is contraindicated anddesirable undercut is located in
gingival third of tooth away from
extension base area
-
7/22/2019 direct retainer (dr vikas ppt.ppt
94/128
RPL CLASP
Ben-Urin 1988 described the rationale for using an L shaped bar
clasp direct retainer for distal extension removable partial dentures.The L shaped bar crosses the gingival margin of the abutment
tooth in the shortest possible line, ascends to the survey line, and
engages the distobuccal undercut.
VRHR CLASP
-
7/22/2019 direct retainer (dr vikas ppt.ppt
95/128
VRHR CLASP developed by Grasso in 1980
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 denturebase.
Advantages
Minimum tooth contact
No guide planespreparation required
Used in high survey lines
Esthetically acceptable
Cingulum clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
96/128
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 theabutment 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 ofthe rigid metal framework.
Advantages
-
7/22/2019 direct retainer (dr vikas ppt.ppt
97/128
Advantages Esthetic A tooth of short clinical crown can be used. The young pulp is not imperiled by close
proximity to metal which shows thermalconduction.
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 areesthetically unacceptable
Choice of clasp
-
7/22/2019 direct retainer (dr vikas ppt.ppt
98/128
Choice of clasp
It depends upon1. Position of tooth undercuts, restorations, occlusion,classification of edentulous arch, tooth type
2. Nature of the bony and soft tissue support. Is there an
unfavourable:
a) bony undercut
b) frenal attachment
c) vestibular depth
3. Esthetics
Kenned I & II (Tooth & Tiss e Borne)
-
7/22/2019 direct retainer (dr vikas ppt.ppt
99/128
Tooth supported partial
dentures Clasp of choice: cast
circumferential
if abutment is severely
tilted use (depending onlocation of undercut):
Cast circumferentialclasp with lingual
retention Ring claspwith support
strut
Kennedy I & II (Tooth & Tissue Borne)
For posterior abutments, or any tooth
needing stress release:
Clasp of choice: RPI (mesial rest, distal
proximal plate and I-bar)
If cant use an I-bar in vestibule, because
of
frenumshallow vestibule
deep soft tissue undercut
then use an RPA retainer (mesial rest,
distal proximal plate and wrought wire
clasp)
If cant use a mesial rest because of:rotation
heavy centric contact on mesial
large amalgam restoration on mesial
then use Combination Clasp
INTRACORONAL RETAINERS
-
7/22/2019 direct retainer (dr vikas ppt.ppt
100/128
INTRACORONAL RETAINERS
AND ATTACHMENTS The first intracoronal direct retainer was introduced byHerman E. S.
Chayes in 1906.
As its name implies, an intracoronal direct retainer resides within thenormal contours of an abutment and functions to retain and stabilize a
removable partial denture The Glossary of Prosthodontic Terms defines a precision attachment
as a retainer consisting of a metal receptacle (matrix) and aclosely fitting part (patrix); the matrix is usually containedwithin the normal or expanded contours of the crown on the
abutment tooth and the patrix is attached to a pontic or theremovable partial denture framework. The receptacle is alsoknown as female/ keyway. The closely fitting part is also knownas male/key.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
101/128
Intracoronal direct retainers may be subdivided intotwo categories based on their method of fabricationand the tolerance of fit between components
A) PRECISION ATTACHMENTS
B SEMIPRECISION ATTACHMENTS Frequently used synonyms of precision attachments
are internal attachment, frictional attachment, slottedattachment and parallel attachment
-
7/22/2019 direct retainer (dr vikas ppt.ppt
102/128
MECHANISM OF ACTION When the removable partial denture is
placed in the patient's mouth, the twocomponents interlock in a sliding jointconfiguration. This sliding joint resideswithin the normal clinical contours of anabutment and functions to retain,support, and stabilize the removablepartial denture.
Parallelism of multiple attachments mustbe carefully considered when designing aremovable partial denture.
The paths of engagement for the
attachments ie, the long axes of theattachments must be parallel to each otherand parallel to path of insertion.
When parallelism is achieved, friction andbinding between components occurs asforces act to dislodge the prosthesis.
ADVANTAGES
-
7/22/2019 direct retainer (dr vikas ppt.ppt
103/128
ADVANTAGES
Elimination of a visible retentive component thereby contributing toesthetics.
Better vertical support through a rest seat located more favourably inrelation to the horizontal axis of the abutment tooth.
Compared to conventional occlusal rests, the apical extension of an
intracoronal attachment reduces non-axial loading and diminishesrotational movement of the abutment
It provides horizontal rest and prevents lateral stresses to theperiodontium of the abutment teethwhen inserting or removing theprosthesis.
Cross arch stabilization is improved Broad stress distribution
Applies broken stress philosophythus reduces damaging forcesapplied to abutment
DISADVANTAGES
-
7/22/2019 direct retainer (dr vikas ppt.ppt
104/128
DISADVANTAGES The teeth have to be extensively prepared to provide the required space
for the key resulting in encroachment and danger to the health of thepulp tissues and a need for prepared abutments and castings.
Adequate crown length is required to generate the required frictionalresistance.
They require complicated clinical and laboratory procedures.
They eventuallywear with progressive loss of frictional resistance todenture removal.
Difficulty in maintaining hygiene beneath the attachment.
They are difficult to repair and replace.
They are expensive.
It requires the services of a skilled technician.
This form of treatment is not justified in a poorly motivated anddisinterested patient.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
105/128
Preisikel 1979 has classified precision attachments into
-
7/22/2019 direct retainer (dr vikas ppt.ppt
106/128
Preisikel 1979 has classified precision attachments into
1. Internal attachments ( Chayes attachment, McCollum
attachment, Crismani 699)2. External attachments ( Dalbo attachment)
3. Stud (Dalla Bona, Gerber )
Gerardo Becerra et al in 1987 classified precision attachments
as :jpd 1987 58 322 327
-
7/22/2019 direct retainer (dr vikas ppt.ppt
107/128
as :jpd 1987 58 322-327
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
-
7/22/2019 direct retainer (dr vikas ppt.ppt
108/128
2) Extra coronal attachments
a. Cantilever attachments
- rigid attachments
- movable attachments
b. Bar attachments
-
7/22/2019 direct retainer (dr vikas ppt.ppt
109/128
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.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
110/128
McCOLLUM ATTACHMENTS
Adjustable Metal Plates
-
7/22/2019 direct retainer (dr vikas ppt.ppt
111/128
Adjustable Metal Plates
Similar to block and box variety .
Provided with a narrow slit in the metal block or maleportion of the attachment to increase the friction.
Provides a simple and effective form of directretention.
Atleast 2.5 mm of tooth height is required. E.g.: Crismani attachment.
Mc Collum attachment.
Stern attachment
Chayes or Rley attachment.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
112/128
CHAYESATTACHMENT
CRISMANI
ATTACHMENT
S i
-
7/22/2019 direct retainer (dr vikas ppt.ppt
113/128
Springs
Incorporated in the male part to control the friction.
Approximately 4 5 mm of vertical height is required.
E.g.: Schatzmann attachment.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
114/128
SCHATZMANN ATTACHMENT
St d
-
7/22/2019 direct retainer (dr vikas ppt.ppt
115/128
Studs
A metallic stud can be soldered to post and core andcemented 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
-
7/22/2019 direct retainer (dr vikas ppt.ppt
116/128
Ceka attachment
-
7/22/2019 direct retainer (dr vikas ppt.ppt
117/128
-
7/22/2019 direct retainer (dr vikas ppt.ppt
118/128
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
-
7/22/2019 direct retainer (dr vikas ppt.ppt
119/128
Rigid attachments
They are pin and tube joints that use a slit in thepin or multiple pin tubes and slots to enhance
retentive friction between the parts with the
natural teeth on the either side of the edentulousspace.
These attachments offer excellent stability and
retention in tooth supported partial dentures.
e.g.: Scott attachment
Thompson dowel rest system
Movable attachments.
Th ll th th i t t t d
-
7/22/2019 direct retainer (dr vikas ppt.ppt
120/128
These allow the prosthesis to rotate around ahorizontal axis and transmit occlusal forces to the
residual alveolar ridge . E.g.: Dolbo attachments
B h
-
7/22/2019 direct retainer (dr vikas ppt.ppt
121/128
Bar attachments
These can be connectedto the cast metal crownsor copings .
Custom made bars can becast with a flat uppersurface to support theprosthesis and parallel
sides that help to stabilizeit.
E.g.: Dolder bar.
Esthetic metal free clasps
-
7/22/2019 direct retainer (dr vikas ppt.ppt
122/128
1) Natural Flex clasps: Based on acetyl resin technology
high elastic memory and remarkable
dimensional stability
biocompatible, non-allergenic andmonomer-free
20 times harder than acrylic
-
7/22/2019 direct retainer (dr vikas ppt.ppt
123/128
Opti-flex clasps: Is a acetyl resin homopolymer.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
124/128
Properties: 20 times stronger than acrylic
High density, hardness,tensile strength compared toother homopolymers
Better wear strength Resistance to staining & water sorption.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
125/128
Proflex clear wire clasp:
-
7/22/2019 direct retainer (dr vikas ppt.ppt
126/128
ValplastValplast is a flexible denture base resin that is ideal for
partial dentures and unilateral restorations. The resinis a biocompatible nylon thermoplastic .
Cu-Sil
-
7/22/2019 direct retainer (dr vikas ppt.ppt
127/128
Cu Sil
Cu-Sil is a patented tissue-bearing appliance
featuring a soft elastomeric gasket which clasps the
neck of each natural tooth, sealing out food and
fluids, cushioning and splinting each natural tooth
from the hard denture base.
-
7/22/2019 direct retainer (dr vikas ppt.ppt
128/128
Thank you