Retainers in fpd/dental courses

INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

Introduction:Introduction:
General considerations:General considerations:
The preparation design of any cast restoration must includeThe preparation design of any cast restoration must include
the following principles:the following principles:
Preservation of tooth structurePreservation of tooth structure
Retention and resistance formRetention and resistance form
Structural durabilityStructural durability
Marginal integrityMarginal integrity
Preservation of the periodontiumPreservation of the periodontium

Retention :Retention : quality that prevents removal ofquality that prevents removal of
restoration along the path of insertion or longrestoration along the path of insertion or long
axis of the tooth preparationaxis of the tooth preparation
Resistance :Resistance : quality that prevents dislodgementquality that prevents dislodgement
due to apically or obliquely directed forcesdue to apically or obliquely directed forces
Retention and resistance form are closelyRetention and resistance form are closely
interrelatedinterrelated
Retention – function of height , diameter andRetention – function of height , diameter and
convergence of the preparationconvergence of the preparation
When convergence changes from 1-5 degrees –When convergence changes from 1-5 degrees –
40% of the retention of the opposing walls is lost40% of the retention of the opposing walls is lost
… Kaufman,Coelho and Colin 1961… Kaufman,Coelho and Colin 1961

Grooves Box forms and pins Accessory groove
Retention and resistance increased by addition of grooves,Retention and resistance increased by addition of grooves,
pins and box formspins and box forms

Marginal integrity:Marginal integrity:
Cavosurface bevels should be used as this allows closer marginalCavosurface bevels should be used as this allows closer marginal
adaptationadaptation
chamfer gingival margin-metal restorationschamfer gingival margin-metal restorations
shoulder margin – ceramometal and porcelainshoulder margin – ceramometal and porcelain
restorationsrestorations
shoulder with bevel –ceramometal restorationshoulder with bevel –ceramometal restoration
Shoulder with bevel is best for ceramometal restorations since bevelShoulder with bevel is best for ceramometal restorations since bevel
can produce closest fitting margincan produce closest fitting margin
If esthetic demands are high sloping shoulder is the desired marginalIf esthetic demands are high sloping shoulder is the desired marginal
designdesign

Classification of restorations by preparationClassification of restorations by preparation
design:design:
Inlays and onlaysInlays and onlays
Partial veneer crownsPartial veneer crowns
Full veneer crownsFull veneer crowns
Cosmetic restorationsCosmetic restorations
CopingsCopings

InlaysInlays
Inlays are generally considered to be individual restorations forInlays are generally considered to be individual restorations for
reestablishing coronal integrityreestablishing coronal integrity
Inlays generally are not acceptable retainers for FPDInlays generally are not acceptable retainers for FPD
They exhibit phenomenon of deflectionThey exhibit phenomenon of deflection
When deflection occurs the occlusal portion will tend to lift up andWhen deflection occurs the occlusal portion will tend to lift up and
proximal flanges will tend to flareproximal flanges will tend to flare

InlaysInlays
Inlays without cuspal coverage is restricted to anterior or minor retainerInlays without cuspal coverage is restricted to anterior or minor retainer
of a fixed movable bridgeof a fixed movable bridge
Inlays without cuspal coverage as retainer in a fixed fixed bridge mayInlays without cuspal coverage as retainer in a fixed fixed bridge may
fail at cement sealfail at cement seal
OnlayOnlay
Is a modification of the MOD inlay which covers the entire occlusalIs a modification of the MOD inlay which covers the entire occlusal
surface and provides protection and reinforcement of the cuspssurface and provides protection and reinforcement of the cusps
Onlay indications:Onlay indications:
Broken down teeth with buccal and lingual cusps still intactBroken down teeth with buccal and lingual cusps still intact
In endodontically treated posterior teeth with sound buccolingualIn endodontically treated posterior teeth with sound buccolingual
tooth structuretooth structure
When half or more of the buccolingual dimension of a crown isWhen half or more of the buccolingual dimension of a crown is
involved in the isthmus of an MOD restorationinvolved in the isthmus of an MOD restoration

OnlayOnlay
They are occasionally used as retainer in short span FPDThey are occasionally used as retainer in short span FPD
The onlay must be carefully prepared to establish retention andThe onlay must be carefully prepared to establish retention and
resistance formresistance form
Buccal and lingual cusps covered to for protection and preventionBuccal and lingual cusps covered to for protection and prevention
of fractureof fracture
Onlays prepared with proximal boxes as well as an occlusal boxOnlays prepared with proximal boxes as well as an occlusal box
formform

Partial veneer crowns or three – quarter crowns used primarily asPartial veneer crowns or three – quarter crowns used primarily as
FPD retainers but occasionally indicated as single restorationFPD retainers but occasionally indicated as single restoration
Usually covers – proximal , lingual and occlusal surfacesUsually covers – proximal , lingual and occlusal surfaces
Contraindication:Contraindication: Short teeth,grossly carious teethShort teeth,grossly carious teeth
Upper canines that have long cusps , contact areasUpper canines that have long cusps , contact areas
at gingival margin and very short mesial and distalat gingival margin and very short mesial and distal
surfacessurfaces www.indiandentalacademy.comwww.indiandentalacademy.com

Contraindication:Contraindication: teeth that are too small or thin for proper grooveteeth that are too small or thin for proper groove
placementplacement
teeth with extensive cervical cariesteeth with extensive cervical caries
pt’s with high caries indexpt’s with high caries index
Design:Design:
Because one surface is left uncovered a groove must be placed toBecause one surface is left uncovered a groove must be placed to
compensate for retention and resistence lostcompensate for retention and resistence lost
Groove must have a definite lingual wallGroove must have a definite lingual wall

They are indicated for maximum retention or for esthetic considerations
Design features:
Sufficient axial reduction to establish retention, resistance and proper
axial contour
Adequate occlusal reduction to provide thickness and rigidity to
casting
A light smooth symmetrical chamfer margin should be developed

A secondary bevel in the occlusal third of the buccal and lingual
surfaces allows proper contour of axial surfaces
Buccal and lingual grooves can be added to improve retention and
resistance form of preparation - indicated in long span bridges and on
short teeth
All sharp angles should be rounded

Metal ceramic restorationsMetal ceramic restorations

Cosmetic restorationsCosmetic restorations
Cosmetic restorations include ceramometal restorations andCosmetic restorations include ceramometal restorations and
porcelain jacket crownporcelain jacket crown
Porcelain jacket crown does not have a cast metal substructure
Preparation design:
Overshortened preparation results in stress concentration in the
labiogingival area – classic half moon fracture
So left as long as possible to provide maximum support for porcelain
A shoulder of uniform thickness is used to provide a flat gingival seat
Incisal edge is flat and placed at slight lingual inclination
All sharp edges must be rounded to prevent stress concentrations

CopingsCopings
Indications :Indications :
Rebuilding grossly defective vital teethRebuilding grossly defective vital teeth
In combination with dowels to provide firm, stable restorationIn combination with dowels to provide firm, stable restoration
foundationsfoundations
In extensive treatment cases with multiple abutments and inIn extensive treatment cases with multiple abutments and in
splintingsplinting
To support removable superstructuresTo support removable superstructures

Telescopic crownsTelescopic crowns
The retainer is constructed in two parts: inner open topped sleeveThe retainer is constructed in two parts: inner open topped sleeve
made of hard gold and an outer full crownmade of hard gold and an outer full crown
Indication :Indication : to overcome differences in the inclination of abutmentto overcome differences in the inclination of abutment
teeth which can not be resolved by retainer preparationsteeth which can not be resolved by retainer preparations

Special considerationsSpecial considerations
Crown contours are essential to tissue health and ultimate success ofCrown contours are essential to tissue health and ultimate success of
restorationrestoration
Contours also play an important role in estheticsContours also play an important role in esthetics
Facial contoursFacial contours
Facial surfaces should have long flat convex contours with no bulges orFacial surfaces should have long flat convex contours with no bulges or
marked convexities in the gingival thirdmarked convexities in the gingival third
Gingival third of tooth should be a straight line continuance of facialGingival third of tooth should be a straight line continuance of facial
root surfaceroot surface

Facial contoursFacial contours
SteinStein – termed this contour the “emergence profile’’– termed this contour the “emergence profile’’
Overcontouring of restoration predisposes to periodontal diseaseOvercontouring of restoration predisposes to periodontal disease
Contour of labial surface is essential for estheticsContour of labial surface is essential for esthetics
Lingual surfacesLingual surfaces
In posterior teeth they should be flatly convex and no markedIn posterior teeth they should be flatly convex and no marked
bulgesbulges
They should represent a linear extension of the lingual root surface ofThey should represent a linear extension of the lingual root surface of
the tooththe tooth

Interproximal surfacesInterproximal surfaces
The most neglected in the fabrication of restorations
Natural tendency is to construct crowns with convex proximal surfaces
Proximal surfaces are convex through the contact area but they become
concave occlusogingivally from below the contact to gingival margin
This area is occupied by interdental papilla
If space is not provided in our restorations tissue will be constricted
Contours important in providing both esthetics and tissue health

Teeth must be prepared in distinct two planes

Retainers in fpd/dental courses

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