retainers for fixed partial denture dentistry .

Retainers
in
fixed partial denture

 Contents
 Introduction
 Definitions
 Factors influencing design
 Factors preventing restoration dislodgement
 Selection of retainers
 Basic designs of bridges
 Classification

 Complete veneer crown
- full metal
- metal ceramic
- all ceramic
 Partial veneer crown
 Pinledge restorations
 Resin bonded bridges
 Fiber reinforced composite bridges
 Conclusion
 References.

INTRODUCTION
 Fixed prosthodontic treatment involves the replacement
of teeth by artificial substitutes.
 Function, esthetics and comfort.
 Satisfactory dental treatment.
 Diagnosis and treatment planning.

Definitions
 Fixed prosthodontics,
The branch of prosthodontics concerned with the
replacement and /or restoration of teeth by artificial
substitutes that are not readily removed from the mouth.
 Fixed dental prosthesis,
Any dental prostheses that is luted, screwed, or
mechanically attached or otherwise securely retained to
natural teeth, tooth roots, and/or dental implant abutments
that furnish the primary support for the dental prostheses.

 Retainer
Any type of device used for the stabilization
or retention of a prostheses.
 Fixed dental prosthesis retainer,
The part of a fixed dental prosthesis that
unites the abutment(s) to the remainder of the
restoration.
Framework
An interior or imbedded, open-wok or structural
frame used to support some other object or
objects.
The skeleton portion of prosthesis around which
and to which are attached the remaining portions of
the prostheses.

 Pontic
An artificial tooth on a fixed dental prosthesis
that replaces a missing natural tooth, restores its
function, and usually fills the space previously
occupied by the clinical crown.
 Abutment
That part of a structure that directly receives
thrust or pressure.
A tooth, a portion of a tooth, or that portion
of a dental implant that serves to support and/or
retain a prosthesis.

Factors influencing design
 Crown length
teeth must have adequate occluso-cervical crown length.
 Crown form
 Degree of mutilation
size, number and location of carious lesions.
 Root length and form
Roots with parallel sides and developmental depressions are
better able to resist additional occlusl forces than are smooth
sided conical roots.
multirooted teeth – greater stability.

 Crown root ratio
a comparison of the tooth length projecting out of
the alveolar bone and the length embedded in the
bone.
higher the ratio, the less likely the tooth will be
able to withstand additional occlusal forces.
 Antes law
combined periodontal ligament area of the
abutment teeth should equal or exceed that of the
tooth or teeth to be replaced.

 Periodontal health
The selection of retainers and pontics must be planned to
promote effective oral hygiene and must not become a
hindrance.
 Mobility
Teeth with grade 1 mobility are frequently capable of being
used as abutments for a fixed prosthesis and should not
automatically be considered unsuitable. The magnitude of the
mobility and the cause must be evaluated.
If the mobility is related to deflective occlusal contacts that
can be eliminated and if a short span prosthesis is involved, the
tooth is likely to be a suitable abutment.

 Span length
 Axial alignment
The crowns of proposed abutment teeth must be
sufficiently well aligned that retentive preparations
can be developed.
Minor alterations in axial alignment like tipped or
rotated teeth often necessitate the use of full –
coverage retainers either to achieve adequate
retention or to obtain acceptable esthetic results.

 Arch form
A curvature in the arches often places pontics facially
to a straight line (the fulcrum line) drawn between
the teeth immediately adjacent to the edentulous
area.
This relationship creates a lever arm, which can exert
excessive forces on the abutment teeth when
occlusion occurs on the pontic.
The forces can exceed the capacity of these teeth to
resist tipping, depending on the length. Retention
must be provided to offset the lever arm length.

Retention on additional teeth ideally should
extend at least as far behind the fulcrum line
as the pontics are located ahead of the
fulcrum line.

 Long term abutment prognosis
When there is some question of the ability
of the remaining supporting structures to
accept additional occlusal forces, the
bilateral bracing afforded by a removable
prosthesis may be advantageous.
Also, a tooth with sufficient loss of
periodontal support and questionable long
term prognosis may best be treated with a
removable prosthesis.
•Esthetics
•Psychological factors.

 Types of occlusal forces
 Tipping forces
 Twisting forces/rotational forces
 Path of insertion forces.

Factors affecting dislodgement of
retainers/ prosthesis
 Axial wall height
 Taper of the preparation
 Ratio of preparation diameter to axial wall height
 Circumferential irregularity
 Occlusal irregularity
 Rigidity
 Adaptation
 Surface area.

 Axial Wall Height
An abutment tooth must be prepared so the retainer
covers an adequate amount of occlusocervical crown
dimension (axial wall height).
The minimal acceptable height is that which allows tooth
structure to interfere with the arc of rotation as
tipping forces attempt to cause rotation around a
fulcrum located at the finish line on the opposite side
of the tooth.

 Taper of the preparation
 Opposing walls must converge occlusally
 Increased taper reduces the ability of a restoration
to resist occlusally directed dislodging forces and
also lessens its ability to interfere with the arc of
rotation as tipping forces act to unseat the
restoration.
 A total convergence of 3-5 degrees

 When the unprepared tooth possesses
excessive crown taper, additional length must
be achieved to help compensate for this
defect. Conversely, short teeth must be
prepared with a minimal amount of taper.

 Ratio of preparation diameter to axial
wall height
If the axial wall height and taper are the same for both
small and large diameter teeth, the smaller diameter
tooth interferes more effectively with the arc of
rotation because the smaller radius of curvature
allows the preparation to better resist dislodgement.

Rigidity
 The ability of a prosthesis to resist flexure and
loosening is related to its thickness.
 Occlusal surfaces must be reduced a minimum of 1 to
1.5mm to provide sufficient rigidity.
 Axial reduction of 0.3 – 0.5 mm cervically, increasing
to 1 mm toward the occlusal surface allows sufficint
thickness peripherally.

 Adaptation
A small amount of space is required between a
restoration and the prepared tooth to allow complete
seating during cementation.
 Surface area,
In general, when preparations of teeth are compared,
those with greater coronal surface area provide more
resistance to dislodgement.
Increased surface area is most significant when the
additional area results in greater axial wall length.

 Deciding factors for Selection of
retainers
 Age
 DMF rate
 Edentulous space
 Periodontal support
 Arch position of the teeth
 Interocclusal and intraocclusal conditions, such as
crown length
 Oral hygiene of the patient
 Vitality of the abutment

Additional retention
 Method of increasing resistance and retention without
lengthening axial surfaces is with grooves or boxes.
 Pins are also used to increase retention.
 Theoretically, pins improve retention by increasing surface area.
 Two types of pins are commonly used,
- tapered pins
- parallel walled pins
 the tapered pin provide a strong form of additional retention.

 Five ways to resist displacing forces
 Maintaining 4 to 10 degrees axial taper
 Preparing suitable gingival finish line
 Contouring and placing suitable contact area
 Incorporating occlusal locks, i.e., dovetail, boxes, and
grooves
 Adding tapered or parallel pins.

 Basic designs of bridges
 Fixed – fixed bridge
 Fixed – movable bridge
 Cantilever bridge
 Spring cantilever bridge

 Fixed – fixed bridge
 Rigid connectors at both ends of the pontic
 The retainers should have approximately the same
retention as each other to reduce the risk that
forces applied to the bridge will dislodge one retainer
from its abutment, leaving the bridge suspended from
the other abutment.
 To minimize this risk it is also important for the
entire occluding surface of all the abutment teeth to
be covered by the retainers.

 Fixed – movable bridge
 It has a rigid connector, usually at the distal end of
the pontic and a movable connector that allows some
vertical movement of the mesial abutment tooth.
 The movable connector should resist both separation
of the pontic from the retainer and lateral movement
of the pontic.
 The retainer with the movable connector is smaller
and less visible.
 Mesial drift tends to unseat distal movable
connector, but is resisted by mesial ones.

 The moveable connector can be separated before the
bridge is cemented and so the parts of the bridge can
be cemented separately.
 The abutment do not therefore have to be prepared
parallel to each other and the retention for the minor
retainer does not need to be as extensive as for the
major retainer.
 No need for full occlusal protection.

 Cantilever bridge
 It provides support for the pontic at only one end.
 The pontic may be attached to a single retainer or to
two or more retainers splinted together, but has no
connection at the other end of the pontic.
 Abutment tooth/teeth may be either mesial or distal
to the span but for small bridges are usually distal.

 Spring cantilever bridge
 Restricted to the replacement of upper incisor teeth.
 Only one pontic can be supported
 Pontic is attached to the end of a long metal arm
running high into the palate and then sweeping down
to a rigid connector on the palatal side of a single
retainer or a pair of splinted retainers.
 Forces applied to the pontic are absorbed by the
springiness of the arm and by displacement of the
soft tissues of the palate so that excessive leverage
forces do not disturb the abutment teeth.

 The arm is made long and fairly thin so that it
is springy, but not so thin that it will deform
permanently with normal occlusal forces.
 The abutments are usually the two premolar
teeth splinted together, or a single premolar
or molar tooth.

 Extracoronal retainers
 complete metal crown
 Metal – ceramic crown
 Partial veneer crown
- three quarter crowns
- seven eighth crowns
- pin modified three quarter crown
 All ceramic crown
 Intracoronal retainers
 Inlays
 Onlays.

 The complete cast crown
 Has the best longevity of all fixed restorations
 Advantages
1) Greater retention
2) Greater resistance form
3) Strength

 Disadvantages
1) Extensive removal of tooth structure
2) Adverse effects on soft tissue
3) Vitality tests not feasible
4) Display of metal

 Indications
1) Extensive coronal destruction by caries or
trauma
2) Endodontically treated teeth
3) More conservative treatment non feasible
4) To provide support to a removable partial
denture
5) Correction of occlusal plane

 Contraindications
1) When conservative treatment can be
carried out
2) If intact buccal or lingual wall exists
3) If less than maximum retention and
resistance are needed
4) High esthetic needs

 The metal ceramic crown
 Indications
 Teeth that require complete coverage with significant
esthetic demands.
 Retainer for fixed partial denture.
 To accommodate a rest for a removable prosthesis.
 Extensive tooth destruction as a result of caries.
 Existing previous restorations that precludes the use
of a more conservative restoration.
 Need for superior retention and strength.
 Endodontically treated tooth.
 Need to recontour axial surfaces or correct minor
mal-inclinations.

 Contraindications
 Patients with active caries or untreated periodontal
diseases.
 Young patients with large pulp chambers.
 High risk of pulp exposure.
 Should not be considered when more conservative
retainer is feasible, unless maximum retention is
needed.
 If the facial wall is intact, the practitioner should
decide whether it is truly necessary to involve all
axial surfaces of the tooth in the proposed
restoration.

 Advantages
 The metal ceramic restoration combines, to a large
degree, the strength of cast metal with the esthetics
of an all ceramic crown.
 Natural appearance can be closely matched by good
technique and if desired through characterization of
the restoration with internally or externally applied
stains.
 Excellent retentive qualities as all axial walls are
included in the preparation.

 Disadvantages
 Significant tooth reduction to provide sufficient
space for the restorative materials.
 To achieve better esthetics, the facial margin of
an anterior restoration is often placed
subgingivally, which increases the potential
periodontal disease.
 Slightly inferior esthetics compared to all-
ceramic.

 Because of the glasslike nature of the veneering
material, a metal-ceramic crown is subject to
brittle fracture.
 Difficulty of accurate shade selection.
 High laboratory costs, more expensive.

retainers for fixed partial denture dentistry .

 Partial veneer crowns
 An extracoronal metal restoration that covers only part
of the clinical crown.
 Buccolingual displacement of the restoration is
prevented by internal features (proximal box, grooves).
 Can be used as a single tooth restoration, or it may serve
as a retainer for a fixed partial denture.

 For posterior teeth,
- three quarter crown,
- modified three-quarter,
- seven-eigth crowns.
 For anterior teeth,
- three quarter crown,
- pinledges.

 Indications
 To support posterior teeth that have lost
moderate amounts of tooth structure, provided
the buccal wall is intact and well supported by
sound tooth structure.
 Retainers for a fixed partial denture.
 Anterior partial veneers can be used as
retainers, to reestablish anterior guidance, and
to splint teeth.
 Suitable for teeth with sufficient bulk.

 On short clinical crowns
 As retainers for long span FPDs
 Rarely suitable for endodontically treated teeth
 Active caries or periodontal diseases.
 Poorly aligned teeth
 Should not be placed on teeth that are proximally
bulbous. (unsupported enamel).
 Difficult to prepare adequate grooves on thin
teeth of restricted faciolingual dimension.

 Advantages
 Conservation of tooth structure.
 Reduced pulpal and periodontal insult during
tooth preparation.
 Access to supragingival margin is easy.
 Allows the operator to perform selected
finishing procedures that are more difficult
with complete coverage restorations.
 Better access for oral hygiene maintainance.

 During cementation, the luting agent can escape
more easily, which produces relative good
seating of the restoration.
 Because of Direct visibility, verification of
seating and cement removal are simple.
 Permits electric vitality testing.

 Disadvantages
 Less retention and resistance
 Preparation is difficult, primarily because only
limited adjustments can be made in the path
of withdrawal
 Placement of grooves, boxes and pinholes
requires dexterity from the operator.
 Display of metal

 Pinledge restorations
•Has the greatest potential for optimal esthetics
•preservation of facial enamel
•retention comes from three or more pins
•resistance form is provided by indentations and
ledges
•involves less than 50% of the coronal area of the
tooth.
•pin ledge must be cast from a type IV gold alloy

 Indications
 Undamaged anterior teeth in dentitions with a
low caries experience.
 High esthetic requirement
 On bulbous teeth that are unsuitable for
three quarter crowns
 The lingual concavity of a maxillary anterior
tooth can be modified successfully with a
pinledge restoration to establish the desired
anterior guidance.

 Poor oral hygiene or high caries index
 Young patients with large pulp chambers
 Teeth that are thin labiolingually
 When the alignment of the abutment will
conflict with the proposed path of withdrawal
 When optimum retention is required.

 Advantages
 Minimal tooth structure
 Supragingival finish margins
 Highly esthetic restorations
 Plaque control after treatment is easier
because of short margin length and largely
supragingival margin location
 On bulbous tooth that are unsuitable for
three quarter crowns

 Disadvantages
 Pinledges are not as retentive as their less
conservative counterpart.
 Though a simple design, should be executed
with greater than average skill and care.
 Can not be used when optimum retention is
required.

 Intracoronal restorations
 Intracoronal inlay is the simplest of the cast
restorations and has been used for the
restoration of occlusal, gingival, and proximal
lesions.
 They utilize wedge retention, which exerts
some outward pressure on tooth.
 Inlay simply replaces missing tooth structure.
 Recommended isthmus width is one fourth the
intercuspal distance.

 Indications
 Almost same as for amalgam restorations.
 Should be considered in the restoration of a
severely worn dentition when the teeth are
otherwise minimally damaged.
 Replacement of an MOD amalgam restoration
when sufficient tooth structure remains for
retention and resistance form.

 Contraindicated unless there is sufficient
bulk to provide resistance and retention form.
 MOD inlays may increase the risk of cusp
fracture and are generally not recommended.
 Extensive onlays, required where caries or
existing restorations extend beyond the
facial or lingual line angles, are
contraindicated unless pins are used to
supplement retention and resistance.

 Advantages
 Least complicated cast restorations to make and
can be very durable when it is carefully done.
 An onlay allows the damaged occlusal surface to
be restored with a casting in the more
conservative manner.
 Extremely long lived restoration because of the
excellent mechanical properties of the gold alloy.

 Low creep and corrosion mean that if inlay or
onlay margins are accurately cast and
finished, they will not deteriorate.
 Lack of corrosion may be an esthetic
advantage.
 No tooth discoloration.
 Onlay can support cusps, reducing the risk of
tooth fracture.

 Disadvantages
 In the restoration of a small carious lesion, an
inlay is not conservative of tooth structure.
 Additional tooth removal is necessary after
minimal proximal extension.
 This extension may lead to additional display of
metal and gingival encroachment.
 Inlays relay on the bulk of the buccal and lingual
cusps for resistance and retention form.
 High occlusal force will lesd to cusp fracture due
to wedging of the inlay.

 All ceramic restorations
 Most esthetically pleasing restorations.
 Indications
 Areas with high esthetic requirement where a
more conservative restoration would be
inadequate.
 tooth should be relatively intact with sufficient
coronal structure to support.
 Occlusal load should be favorably distributed.

 When a more conservative restoration can be
used.
 Usually they are not recommended for posterior
teeth.
 Unfavorable occlusal loading.
 If it is not possible to produce adequate support
or an even shoulder width of at least 1mm
circumferentially.
 Para functional habits.

 Advantages
 Superior esthetics.
 Excellent translucency.
 Generally good tissue response.
 More conservative reduction of the facial
surface.
 Appearance of the completed restoration can
be influenced and modified by selecting
different colors of luting agent.

 Disadvantages
 Reduced strength of the restoration.
 Significant tooth reduction on proximal and
lingual sides. (shoulder margin)
 Difficulties may be associated with obtaining
a well fitting margin.
 Inadequate tooth preparation- fracture.
 Proper preparation design is critical to
ensuring mechanical success.
 Severely damaged tooth can not be restored.

 Not effective as retainers for FPDs.
 Requires connectors of large cross sectional
dimension which may impinge on the
interdental papilla.
 Wear has been observed on the functional
surfaces of natural teeth that oppose
porcelain restoration.

 Resin retained fixed partial dentures
•A fixed dental prosthesis that is luted to
tooth structures, primarily enamel, which
has been etched to provide mechanical
retention for the resin cement (GPT-9)
• Rochette in 1973
•Primary goal of resin retained FPD is the
replacement of missing teeth and maximum
conservation of tooth structure.

 Indications
 Replacement of missing anterior teeth in
children and adolescents.
 Short span.
 Unrestored abutments.
 Single posterior teeth.
 Significant crown length.
 Excellent moisture control.

 Parafunctional habits.
 Long edentulous span.
 Restored or damaged abutments.
 Compromised abutments.
 Significant pontic width discrepancy.
 Deep vertical overlap.
 Nickel allergy.

 Advantages
 Minimal removal of tooth structure.
 Minimal potential for pulp trauma.
 Anesthesia not usually required.
 Supragingival preparation.
 Easy impression making.
 Provisional not usually required.
 Reduced chair time.
 Reduced patient expense.
 Rebond possible.

 Disadvantages
 Reduced restoration longevity
 Enamel modifications are required.
 Space correction is difficult.
 Good alignment of abutment teeth is required.
 Esthetics is compromised in posterior teeth.

 Types
 Cast perforated resin retained FPDs.
(mechanical retention).
 Etched cast Resin-retained FPDs.
(Micromechanical retention- “MARYLAND
BRIDGE”).
 Macroscopic Mechanical retention resin retained
FPDs (“Virginia bridge”).
 Chemical bonding resin retained FPDs (Adhesion
bridges).

 Cast perforated resin retained FPDs
 Introduced by Rochette in 1973.
 Replacement of posterior teeth by Livaditis.
 Perforated retainers were used to increase resistance
and retention.

 Limitations
 Weakening of the metal retainer by the
perforations.
 Exposure to wear of the resins at the
perforations.
 Limitation adhesion of the metal provided by the
perforations.

 Etched cast resin retained FPDs
 Thompson and Livaditis at the at the university
of Maryland.
 Developed a technique for the electrolytic
etching of Ni-Cr and Cr-Co alloys.

 Advantages
 Retention improved because the resin-to-etched
metal bond can be substantially stronger than
the resin-to-etched enamel. The retainer can be
thinner and still resist flexing.
 The oral surface of the cast retainers is highly
polished and resists plaque accumulation.

 Macroscopic Mechanical Retention Resin
Retained FPDs
 Developed at the Virginia Commonwealth University
School of Dentistry.
 Involves a “lost salt crystal” technique.
 An alternative technique for the macroscopic retention is
the use of a cast mesh pattern on the internal surface of
the retainers.

 Fiber-Reinforced Composite Fixed
Prostheses
 The restoration consists of a fiber reinforced
composite (FRC) substructure veneered with a
particulate composite material.

 Indications
 Optimal esthetic result.
 Need to decrease wear of the opposite
dentition.
 Conservative abutment preparation.
 Desire for a metal free, nonporcelain
prostheses.
 Potential for bonding the prosthesis retainer
to the abutment teeth.

 Inability to maintain good fluid control.
 Long span.
 Parafunctional habits.
 Patients with unglazed opposing porcelain.
 Patients who abuse alcoholic substances.

Conclusion
The basis of logical treatment planning consists
of identifying the patients needs, eliciting
his/her expectations and wishes, and
comparing these with the available corrective
materials and techniques. It also involves
evaluating whether a technique has a good
prognosis.
preparation and design should follow
general principles suitably adapted to the
particular case. Retention still depends on
conventional methods. The criteria for
selecting retainers depend on the condition of
the abutment teeth, appearance, cost, and
conservation of the tooth structure.

References
 Contemporary fixed prosthodontics-
Stephen F. Rosensteil.
 Fundamentals of fixed
prosthodontics- Herbert T.
Shillingburg.

retainers for fixed partial denture dentistry .

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