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Design considerations for a distal extension rpd/prosthodontic courses
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Design considerations for a distal extension rpd/prosthodontic courses
Design considerations for aDesign considerations for a
distal extension RPDdistal extension RPD
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
• ““Plans may be useless but planning isPlans may be useless but planning is
• RPDs are intended to be placed in theRPDs are intended to be placed in the
mouth and removed. Hence, they cannotmouth and removed. Hence, they cannot
be rigidly connected to the teeth orbe rigidly connected to the teeth or
tissue. This makes them subject totissue. This makes them subject to
movement within the oral cavity.movement within the oral cavity.
• Movements induce stress.Movements induce stress.
• It is important for the clinicians toIt is important for the clinicians to
understand the possible movements andunderstand the possible movements and
be able to logically design thebe able to logically design the
component parts of the RPD to helpcomponent parts of the RPD to help
control these movements.control these movements.
CLASSIFICATIONCLASSIFICATION: by: by
Beckett(1953), Craddock(1956)Beckett(1953), Craddock(1956)
and Osborne and Lammie (1974)and Osborne and Lammie (1974)
• Class I – denture supported by mucosaClass I – denture supported by mucosa
and underlying boneand underlying bone
• Class II – denture supported by teeth.Class II – denture supported by teeth.
• Class III- denture supported by aClass III- denture supported by a
combination of mucosa and tooth bornecombination of mucosa and tooth borne
• Class IV- denture supported by implants.Class IV- denture supported by implants.
Differentiation between the twoDifferentiation between the two
main types of removable partialmain types of removable partial
• Manner of supportManner of support
• Method of impression registrationMethod of impression registration
• Need for some kind of indirect retentionNeed for some kind of indirect retention
• Denture base materialDenture base material
• Differences in clasp design.Differences in clasp design.
Biomechanical considerations.Biomechanical considerations.
• A better understanding of the methods ofA better understanding of the methods of
controlling forces on RPD may be achieved by acontrolling forces on RPD may be achieved by a
brief review of the development of forces. Thisbrief review of the development of forces. This
considers the application of mathematicalconsiders the application of mathematical
• As Tylman states, “ great caution and reserveAs Tylman states, “ great caution and reserve
are essential whenever an attempt is made toare essential whenever an attempt is made to
interpret biological phenomenon entirely byinterpret biological phenomenon entirely by
mathematical computation.”mathematical computation.”
RPD as a simple machineRPD as a simple machine
• Inclined planeInclined plane
• Wheel and axleWheel and axle
• In its simplest form, a lever is a rigid barIn its simplest form, a lever is a rigid bar
supported somewhere along its length. Itsupported somewhere along its length. It
may rest on the support or may bemay rest on the support or may be
supported from above.supported from above.
• There are three types of levers;There are three types of levers;
First class leverFirst class lever
Second class leverSecond class lever
Third class leverThird class lever
Inclined planeInclined plane
• The inclined plane is a plane surface setThe inclined plane is a plane surface set
at an angle, other than a right angle,at an angle, other than a right angle,
against a horizontal surface . The inclinedagainst a horizontal surface . The inclined
plane permits one to overcome a largeplane permits one to overcome a large
resistance by applying a relatively smallresistance by applying a relatively small
force through a longer distance than theforce through a longer distance than the
load is to be raised.load is to be raised.
• A wedge by definition is a solid object withA wedge by definition is a solid object with
a broad base and its two sides arising toa broad base and its two sides arising to
intersect each other forming an acuteintersect each other forming an acute
angle opposite the base.angle opposite the base.
Movement of the denture aroundMovement of the denture around
an axisan axis
• The imaginary line passing through the teethThe imaginary line passing through the teeth
and direct retainers, around which the dentureand direct retainers, around which the denture
rotates slightly when subjected to various forcesrotates slightly when subjected to various forces
directed toward or away from the residual ridgedirected toward or away from the residual ridge
is called a fulcrum line.is called a fulcrum line.
• There can be three fulcrums around which aThere can be three fulcrums around which a
RPD may rotate. Most of these movementsRPD may rotate. Most of these movements
occur simultaneously.occur simultaneously.
Denture rotation along the fulcrum lineswww.indiandentalacademy.comwww.indiandentalacademy.com
One fulcrum ( the most commonlyOne fulcrum ( the most commonly
Second fulcrum lineSecond fulcrum line
Third fulcrum lineThird fulcrum line
The second and third fulcrums induce horizontalThe second and third fulcrums induce horizontal
stresses. These stresses are better toleratedstresses. These stresses are better tolerated
when they occur close to the horizontal axis ofwhen they occur close to the horizontal axis of
rotation of the toothrotation of the tooth..
Factors influencing magnitude ofFactors influencing magnitude of
stresses transmitted to thestresses transmitted to the
abutment teeth.abutment teeth.
• 1.Length of the span.1.Length of the span.
• The potential of theThe potential of the
lever system tolever system to
relatively magnify arelatively magnify a
force is illustrated as-force is illustrated as-
advantage= effortadvantage= effort
arm/ resistance armarm/ resistance arm
• 2. Quality of support2. Quality of support
of ridgeof ridge
• 3.Qualities of the3.Qualities of the
• Clasp designClasp design
• Length of theLength of the
• Material used inMaterial used in
clasp constructionclasp construction
• 4. Abutment tooth surface4. Abutment tooth surface
• The surface of a gold crown or restorationThe surface of a gold crown or restoration
offers more frictional resistance to claspoffers more frictional resistance to clasp
arm movement than does the enamelarm movement than does the enamel
surface of tooth. Therefore, greater stresssurface of tooth. Therefore, greater stress
is exerted on a tooth restored with goldis exerted on a tooth restored with gold
than on tooth with intact enamel.than on tooth with intact enamel.
• 5. Occlusal harmony5. Occlusal harmony
• Occlusion with deflective occlusal contactsOcclusion with deflective occlusal contacts
between opposing teeth generatesbetween opposing teeth generates
horizontal forces which magnify by thehorizontal forces which magnify by the
factor of leverage and transmit destructivefactor of leverage and transmit destructive
forces to the abutment teeth and residualforces to the abutment teeth and residual
• Opposing occlusion influences stress.Opposing occlusion influences stress.
• Area of the denture base against whichArea of the denture base against which
the force is applied.the force is applied.
• Artificial teeth should be arranged so thatArtificial teeth should be arranged so that
the bulk of the masticating force is appliedthe bulk of the masticating force is applied
to the center of the denture bearing area,to the center of the denture bearing area,
both anteroposteriorly and buccolingually.both anteroposteriorly and buccolingually.
Amount of stress transferred toAmount of stress transferred to
ridges and abutment teeth-ridges and abutment teeth-
• The direction and magnitude of forceThe direction and magnitude of force
• The length of the lever armsThe length of the lever arms
• The quality of resistance ( support fromThe quality of resistance ( support from
the edentulous ridges and remainingthe edentulous ridges and remaining
natural teeth).natural teeth).
• The design characteristics of the partialThe design characteristics of the partial
CONTROLLING STRESS BYCONTROLLING STRESS BY
DESIGN CONSIDERATIONSDESIGN CONSIDERATIONS
DIRECT RETENTION;DIRECT RETENTION;
• Retentive clasp armRetentive clasp arm
• Forces of adhesion and cohesionForces of adhesion and cohesion
• Frictional controlFrictional control
• Neuromuscular controlNeuromuscular control
• Clasp positionClasp position
• Clasp design –Clasp design –
• 1. reverse circumferential cast clasp1. reverse circumferential cast clasp
• 2. bar clasp2. bar clasp
• 3.Combination clasp3.Combination clasp
• Splinting of abutment teethSplinting of abutment teeth
INDIRECT RETENTIONINDIRECT RETENTION
• It assists in direct retention.It assists in direct retention.
• Moves the fulcrum away from the force.Moves the fulcrum away from the force.
• The necessity and design of the indirect retainerThe necessity and design of the indirect retainer
varies with each type of prosthesis.varies with each type of prosthesis.
• As the rotation axis is moved anteriorly or awayAs the rotation axis is moved anteriorly or away
from the edentulous area, the arc of rotationfrom the edentulous area, the arc of rotation
becomes greater and more of the denture basebecomes greater and more of the denture base
force is delivered in a vertical direction.force is delivered in a vertical direction.
Increases the length of the resistance arm
• The occlusion provided should beThe occlusion provided should be
harmonious with movements of the TMJharmonious with movements of the TMJ
and the neuromusculature.and the neuromusculature.
• Natural teeth should guide theNatural teeth should guide the
• The number and buccolingual width ofThe number and buccolingual width of
teeth may be reducedteeth may be reduced
• Steep cuspal inclines should be avoidedSteep cuspal inclines should be avoided..
DENTURE BASE:DENTURE BASE:
• Should cover as much of the areaShould cover as much of the area
possible within physiologic limitspossible within physiologic limits
• Flanges for horizontal stabilizationFlanges for horizontal stabilization
• Accurate adaptation and relineableAccurate adaptation and relineable
• Retromolar pad and TuberositiesRetromolar pad and Tuberosities
coverage in addition to providing supportcoverage in addition to providing support
can contribute to indirect retention.can contribute to indirect retention.
• Polished surface should assist retention.Polished surface should assist retention.
MAJOR CONNECTOR.MAJOR CONNECTOR.
• Should contribute to load distributionShould contribute to load distribution
whenever called for.whenever called for.
• A lingual plate major connector supportedA lingual plate major connector supported
by rests is the one preferred in theby rests is the one preferred in the
mandibular arch and the full palatal platemandibular arch and the full palatal plate
major connector for the maxillary arch.major connector for the maxillary arch.
• Basic principles for design is valid.Basic principles for design is valid.
MINOR CONNECTORSMINOR CONNECTORS
• With guiding planes offers horizontalWith guiding planes offers horizontal
stability to the partial denture.stability to the partial denture.
• The abutment tooth receives stabilizationThe abutment tooth receives stabilization
against lateral stresses.against lateral stresses.
• When the number of teeth contactedWhen the number of teeth contacted
increases, the force resisted by each toothincreases, the force resisted by each tooth
is minimized.is minimized.
• Should direct forces along the long axis of theShould direct forces along the long axis of the
• Should not act as an inclined plane or wedgeShould not act as an inclined plane or wedge
• Should provide free ball and socket movement.Should provide free ball and socket movement.
• Moving the rest position from a distal to a mesialMoving the rest position from a distal to a mesial
location on one tooth can change the direction oflocation on one tooth can change the direction of
movement of the retainer 180 degrees.movement of the retainer 180 degrees.
• Retainer position must always beRetainer position must always be
coordinated with the rest position so thatcoordinated with the rest position so that
the retainer disengages from tooth contactthe retainer disengages from tooth contact
during movement of the prosthesis.during movement of the prosthesis.www.indiandentalacademy.comwww.indiandentalacademy.com
STRESS BREAKERS( STRESSSTRESS BREAKERS( STRESS
• It separates the action of the retaining elementsIt separates the action of the retaining elements
from the movement of the denture base byfrom the movement of the denture base by
allowing independent movement of the dentureallowing independent movement of the denture
• They effectively dissipate vertical stresses but atThey effectively dissipate vertical stresses but at
the cost of horizontal stability.the cost of horizontal stability.
• 1. excessive ridge resorption1. excessive ridge resorption
• 2. tissue impingement2. tissue impingement
• 3. inefficient mastication3. inefficient mastication
• Split bar major connector, TiconiumSplit bar major connector, Ticonium
Hidden- lock RPD, hinge type of stressHidden- lock RPD, hinge type of stress
breaker, Dalbo extra coronal retainer.breaker, Dalbo extra coronal retainer.
OTHER DESIGNOTHER DESIGN
• OVERLAY ABUTMENT: salvaging of anOVERLAY ABUTMENT: salvaging of an
existant tooth using endodontic,existant tooth using endodontic,
periodontal or a combination of treatmentsperiodontal or a combination of treatments
should be considered. The tooth shapedshould be considered. The tooth shaped
into a dome can provide better supportinto a dome can provide better support
and decrease resorption of the ridges.and decrease resorption of the ridges.
Essentials of partial dentureEssentials of partial denture
First step- determine supportFirst step- determine support
for the partial denturefor the partial denture
• ABUTMENT TOOTHABUTMENT TOOTH
• periodontal healthperiodontal health
• crown and root morphologiescrown and root morphologies
• crown to root ratioscrown to root ratios
• bone index areasbone index areas
• location of the tooth in the archlocation of the tooth in the arch
• relationship to other support unitsrelationship to other support units
• the opposing dentitionthe opposing dentition
• RESIDUAL RIDGESRESIDUAL RIDGES
• quality of the residual ridgequality of the residual ridge
• Extent of residual ridge coverage by the dentureExtent of residual ridge coverage by the denture
• Type of impression registrationType of impression registration
• Accuracy of the denture baseAccuracy of the denture base
• Design of the partial denture frameworkDesign of the partial denture framework
• Total occlusal load applied.Total occlusal load applied.
Second step- to connect the toothSecond step- to connect the tooth
and tissue support unitsand tissue support units
• Involves the designing of major and minorInvolves the designing of major and minor
connectors in compliance with basicconnectors in compliance with basic
principles and conceptsprinciples and concepts
Third step- to determine how theThird step- to determine how the
partial denture is to be retainedpartial denture is to be retained
• DIRECT RETENTION:The key toDIRECT RETENTION:The key to
selecting a successful clasp design is toselecting a successful clasp design is to
choose a clasp that will-choose a clasp that will-
• 1. avoid direct transmission of tipping or1. avoid direct transmission of tipping or
torquing forces to the abutment.torquing forces to the abutment.
• 2. accommodate the basic principles of2. accommodate the basic principles of
clasp designclasp design
• 3. provide retention against reasonable3. provide retention against reasonable
dislodging forcesdislodging forces
• 4. be compatible with undercut location,4. be compatible with undercut location,
tissue contour and esthetic desires of thetissue contour and esthetic desires of the
INDIRECT RETENTIONINDIRECT RETENTION
• To counteract any lifting of the distalTo counteract any lifting of the distal
extension base away from the supportingextension base away from the supporting
• Resistance to anteroposteriorResistance to anteroposterior
displacement by-displacement by-
• 1. clasps encircling M-D convexity1. clasps encircling M-D convexity
• 2. continuous clasps2. continuous clasps
• 3. onlays3. onlays
• 4. embrasure hooks4. embrasure hookswww.indiandentalacademy.comwww.indiandentalacademy.com
FOURTH STEP- to connect theFOURTH STEP- to connect the
retention units to the support unitsretention units to the support units
• The direct and indirect retainers are rigidlyThe direct and indirect retainers are rigidly
attached to the major connector.attached to the major connector.
• The components designed to contact theThe components designed to contact the
tooth surfaces may be prepared to act astooth surfaces may be prepared to act as
guide planes.guide planes.
FIFTH STEP- to outline and join theFIFTH STEP- to outline and join the
edentulous area to the alreadyedentulous area to the already
established design componentsestablished design components
• Support is the primary concern in selectingSupport is the primary concern in selecting
designing and fabricating a distaldesigning and fabricating a distal
extension denture base.extension denture base.
• Of secondary importance are- esthetics,Of secondary importance are- esthetics,
stimulation of the underlying tissues andstimulation of the underlying tissues and
oral cleanliness.oral cleanliness.
Adequate time must be spent in properlyAdequate time must be spent in properly
diagnosing the particular case and devising adiagnosing the particular case and devising a
workable treatment plan. Once this is doneworkable treatment plan. Once this is done
the mechanical task of laying out the “nutsthe mechanical task of laying out the “nuts
and bolts” of removable partial dentureand bolts” of removable partial denture
design can be carried out to ensure that ourdesign can be carried out to ensure that our
patients receive full benefits of our knowledgepatients receive full benefits of our knowledge
and skillsand skills..
Any plan conceived in moderation mustAny plan conceived in moderation must
fail when the circumstnaces are set infail when the circumstnaces are set in
• Removable partial prosthodontics- McRemovable partial prosthodontics- Mc
Crackens 11Crackens 11thth
• Clinical removable partial prosthodontics-Clinical removable partial prosthodontics-
Stewart 2Stewart 2ndnd
• Partial dentures- John Osborne 4Partial dentures- John Osborne 4thth
• Textbook of removable partial dentures-Textbook of removable partial dentures-
• Removable partial prosthodontics-Removable partial prosthodontics-
Grosso- Miller 3Grosso- Miller 3rdrd
• Combinations in fixed- removableCombinations in fixed- removable
prostheses- JPD1971,26prostheses- JPD1971,26www.indiandentalacademy.comwww.indiandentalacademy.com