The document discusses the philosophy of designing removable partial dentures (RPDs). There are several key principles that must be considered in RPD design:
1. Stress distribution - Forces acting on RPDs should be distributed broadly across remaining teeth and soft tissues to minimize damage.
2. Physiologic basing - Recording the soft tissue ridge under functional pressure better supports the denture base and stimulates tissue health.
3. Broad coverage - Using multiple clasps and ensuring broad denture base coverage distributes forces over more surfaces.
Proper consideration of stress distribution, tissue support, and force dispersion are fundamental to preserving remaining oral structures with an RPD.
2. ● Introduction
● Rationale
● Indications
● Stress considerations
● Forces acting on partial dentures
● Lever principle
● Principles of design
● Philosophy of design
● Fundamental design principles
● Conclusion
● References
CONTENTS
3. REMOVABLE PARTIAL DENTURE
A removabledenturethatreplacessometeethin a partiallyedentulousarch;the
removable partialdenturecanbereadilyinserted andremoved fromthemouthby
the patient.
● Anyconsiderationofthe logical design ofapartialdenturemust establishthebasic
requirementsof sucha restoration.ie retention,stability,support,functionand
esthetics.
INTRODUCTION
4. ● In partialdenturedesign, themain concernis forprostheses
thatarepartiallysupportedbyteeth andpartiallysupportedby
softtissues.
Prosthesesthatareentirely supportedbyteeth
○ Straightforward
○ Derive allof theirsupportfromthe remaining teeth
○ A single impression maybe usedtorecordtheteeth andsofttissues.
○ Indirect retentionor flexibledirectretentionis notrequired.
○ Retentiveclasping is basedonconvenience
5. ● Removablepartialdenturesshouldenhancethehealthof remaining dentitionand
surroundingoraltissues.
● It is importantto understandthe movements takingplaceon thecomponentsand
logically design them in ordertocontrolthe movements takingplacein them.
6. ● Dr M. M.Devan, the primarypurpose of removable partial denturetherapymust always be“the
preservation of that which remains, and not the meticulous replacement of that which has been
lost”.
● Maintaining orimproving phonetics, establishing or increasing masticatory efficiency, stabilizing dental
relationships, and developing the required esthetics.
RATIONALE FOR REMOVABLE
PARTIAL DENTURE THERAPY
7. ● Long-spanedentulous area
● Noabutmenttoothposteriortothe edentulousspace
● Reducedperiodontalsupportforremaining teeth
● Need forcross-archstabilization
● Immediate need toreplaceextractedteeth
INDICATIONS
13. ● It is atwisting rotationaltypeofforce
● Combinationofbothvertical andhorizontalforce
TORSIONAL STRESS
14. ● The abilityof living tissuestotolerateforcesis largely dependentupon
■ The magnitudeandintensity
■ The duration
■ The direction
■ The frequency
FORCES ACTING ON PARTIAL
DENTURES
17. ● Lever- Itis arigid barsupportedsomewherealongits length
● It mayreston supportor maybesupportedfromabove.
● The supportpointis fulcrumandthelever can movearoundthe fulcrum
FIRST CLASS LEVER THIRD CLASS LEVER
SECOND CLASS LEVER
The distalextensionpartialdenturepresentsthe greatestpotentialfordamagingloadsbecauseit
rotatesaboutthreefulcrums.
18. ● One fulcrumis on thehorizontalplanethatextendsthroughtwo
principalabutments,one oneach sideofthe dentalarch,and
generally istermed theprincipal fulcrumline.
● This fulcrumcontrolsthe rotationalmovement ofthe denturein the
sagittalplane.
● Rotationalmovement aroundthis fulcrumline is thegreatestin
magnitude,butis notnecessarily themost damaging.
● Therefore,horizontalorlateralforcesof muchless magnitudecanbe
moredestructiveto thehardandsofttissuesofthe periodontium.
19. ● A secondfulcrum line lies in the sagittalplane andextendsthrough
the occlusalrest onthe terminalabutmentandalongthe crestof the
residualridge onone sideofthe arch.
● This fulcrumline controlsthe rotationalmovements ofthe denturein
the frontalplane
● Theresultantforcesaremorenearlyhorizontalandarenotwell
resisted bytheoralstructures.Therefore,theseforcescanbe
moderatelydamaging.
20. ● Thethird fulcrumis locatedin thevicinity ofthemidline, just
lingual tothe anteriorteeth
● This fulcrumline isoriented verticallyandcontrolsrotational
movement in thehorizontalplane
● Consequently,theseforcescanbeextremelydamaging and
shouldreceive significantattentionduring thedesign process.
21. A.H.Schmidtin1953
● The dentistmusthaveathoroughknowledgeofboththe mechanicalandbiological factors
involved in removable partialdenturedesign.
● The treatmentplanmustbebasedon acompleteexaminationanddiagnosisofthe individual
patient.
● Thedentistmustcorrelatethe pertinentfactorsanddetermine aproperplanoftreatment.
● A removablepartialdentureshouldrestoreformandfunctionwithoutinjury totheremaining
oralstructures.
PRINCIPLES OF DESIGN
22. ● In restoringocclusion, theprosthesisshouldalso restoreanormalordesirablefacialcontourand
notimpedethe normalmovement ofthe tongueandothertissues.
● A removable partialdentureis a formoftreatmentandnotacure.
● Oraltissuesneverremain static,butareconstantlyundergoing change, reflecting the general
healthandageofthe patient.The patientshouldberecalled periodicallyto preventany
deleterious changesfromtakingplace.
29. ● TYPE1: Thesetypeshaveamovable joint betweenthe direct retainerandthe denture
baseandpermit vertical movement andhingeactionofthe distalextensiondenture
base.
○ Hinge
○ Sleeve
○ Cylinder
○ Ball andsocket
● TYPE2: flexibleconnectionbetween direct retaineranddenturebase.
○ Wroughtwiresoldered tomajorconnector
○ Splitmajorconnectors
○ Claspshaving stressbreakingeffect
○ Disjunctpartialdentures
30. ● The mostcommonlyusedstressdirectorsaresimple hinges interposedbetween thedenturebases
andtheadjacentclasping assemblies.Thesehinges aredesigned to permitvertical movement of
the denturebaseswithoutcausing undueloading oftheabutments.
31. ● Lengthof edentulous span
● Qualityof ridge support
○ Large,well-formedridges arecapableofwithstandinggreaterloadsthanare
small, thin,orknife-edgedridges.
○ Broadridges with parallelsides permit theuseof denturebaseswithlonger
vertical surfaces.Providesstability.
● Claspflexibility
○ The moreflexible theretentivearm oftheclasp,theless loadis transferredto
the abutment.
FACTORS INFLUENCING STRESSES
TRANSMITTED TO ABUTMENT TEETH
32. ● Claspdesign
○ claspthatis designed tobepassivewhen it is completely seatedonthe abutmenttoothwill exert
less loadon thetooththanwill onethatis notpassive.
○ A claspshouldbedesigned sothatduringinsertionor removal oftheprosthesis,the reciprocal
armcontactsthe toothbeforethe retentivetippasses overthegreatestbulge ofthe abutment.
This will stabilizeorneutralizethe loadtowhich theabutmentis subjectedas theretentive tip
passesover thegreatestbulge ofthetooth.
● Lengthof clasp
Flexibility canbeincreased bylengthening theclasp.
33. ● Materialusedinclaspconstruction
A claspconstructedof achromium-basedalloywill normallyexerta greaterloadonthe abutmentthan
will a gold-basedalloy
● Surfacecharacteristics of theabutment
Thesurfaceof acastgold restorationoffersmorefrictionalresistanceto clasparmmovement thandoes
the enamel surfaceofatooth.
● Occlusalharmony
Ideally, theocclusal loadshouldbeappliedin the centerof thedenture-bearingarea,bothantero-
posteriorlyandfacio-lingually.
34. ADVANTAGES
○ Minimal direct retention
○ Used in conjunctionwith intracoronalattachments.
○ Theoretically,stressdirectorsminimizethe tippingforceson abutmentteeth,therebylimiting
boneresorption.
38. ADVANTAGES
● The minimal retention requirements associated with
physiologic basing result in lightweight prostheses requiring
minimal maintenance and repair.
● The forgiving nature of retentive produces a significant
reduction in the forces transmitted to the abutment teeth. As a
result, advocates of this theory believe that abutments are
retained for longer periods.
42. ● The resultantprosthesesareeasierandless expensive toconstruct.
● Therigid componentsminimizerotationalmovements andprovideexcellent horizontal
stabilization
DISADVANTAGES
● The increasedcoverage providedbysuch prosthesesmaynotbeacceptedbysomepatients.
● Complicatesoralhygiene.
43. ● Support for removable partial dentures may be derived from the
remaining teeth, the hard and soft tissues of the residual ridge, or
both.
● Teeth are connected to the surrounding bone via thin periodontal
ligaments.
● Under function, healthy teeth may be displaced as much as 0.2 mm.
In contrast, soft tissues overlying residual bone generally may be
displaced 1.0 mm or more.
● As a result, there may be a significant difference in the support
provided by the teeth and the tissues of the residual ridge.
FUNDAMENTAL DESIGN
CONSIDERATIONS
44. CLASS I REMOVABLE PARTIAL
DENTURES
CLASSI
Bilateraledentulousareaslocatedposteriortothe remaining naturalteeth
45. ● Derive supportfromthe remaining teethandresidual ridges
● Topreservetheremaining teeth andresidualridges,removable partialdenturesmust
provideanequitable distribution of forces
53. ● Clasp assemblies are largelyresponsible for direct retention,
● Proper extension and adaptation of one or moredenture bases also contributeto
retention of a removable partial denture.
● A class I prosthesis usually requires only two clasp assemblies
● If a distobuccal undercut is present, an infrabulge clasp (tor 1/2 t) is preferred
● If a mesiobuccal undercut is present, a wrought-wire clasp is preferred
● Thereciprocal elements must be rigid. Thesecomponents may be inthe form of
bracing arms or lingual plating
SUMMARY
54. ● Two indirect retainers should generallybeused ina Class I design.
● Lingual plating may beused to augment indirect retention.
● Themajor connector must berigid and must not impinge ongingival tissues.
○ Inthe maxillaryarch,a broad major connector maybe used to derive additional support from thehard
palate.
● Minor connectors must be rigid and should bepositioned to enhancecomfort, cleanliness, and theplacement
of artificial teeth.
● Occlusion -maximum intercuspation should coincide with centricrelation.
● Denture bases should bedesigned to provide broad coverage.
Selective pressure impressions are recommended
56. ● ClassIII removablepartialdenturesaresupportedbyteethor dentalimplantsatbothends ofan
edentulousspace, denturebasesgenerally donotrotateorlift awayfromtheunderlying tissues.
Therefore,compensationforrotationalforcesis notneeded.
● Supportshouldbeprovided entirelybythe abutmentteeth.
● Due tothefavorabledistributionofabutments,classIII removable partialdenturesoftenfunction
like fixedprostheses.
● Residualridges shouldbeusedforsupportonly whenedentulousspansarelong or abutments
displaydecreasedperiodontalsupport.
57. ● ClassIII removable partialdenturesdo nottendtomove in function.Directretentionis needed
onlytoprevent dislodgement ofthe prosthesis.
● Indirect retentiongenerally is notnecessary.
58. ● Directretention -Because these prostheses areentirelytooth borne, the trasmission of harmfulforces to the
abutment teeth and residual ridges can be minimized.
● Clasps -Quadrilateral positioning of direct retainersis considered ideal (simple circlet clasps)
Reciprocal elements must be rigid.
● Rests- When possible, rests and/or rest seats
should bepositioned adjacent to the edentulous spaces.
Rests should be usedto support major connectors
and lingual plating.
SUMMARY
59. ● Indirect retention isusuallynotrequired
● Major and minor connectorsmust berigid
● Occlusion- sameas forkennedy’sclassI andclassII arches.
● Denture bases
○ Functionalimpressionsarenotrequired.
○ Coverageofthe residualridge areasshould bedeterminedbyappearance,
comfort,andthe avoidanceoffoodimpaction.
61. ● The unilateraldistalextensionside mustbedesigned asaClassI removable partialdenture,
whereasthe tooth-supportedside mustbedesigned asaClass III removablepartialdenture.
● The prosthesismust include awell-adapteddenturebase,properlydesigned direct retention,and
appropriatelypositionedindirect retention.
62. ● A kennedyclass IIremovable partial dentureshould have three clasp
assemblies.
●
● For a kennedyclass ii application with nomodifications, clasp assemblies should
bepositioned as far posterior as is practical and as far anterior as esthetics will
permit.
● Theprimaryaxis of rotation passes throughthe most posterior abutment on each
side of the dental arch.An indirect retainer should be placed opposite the distal
extension base and as far from the rotational axis as practical.
● One indirect retainer is generally adequate. It should be
located on the side opposite the distal extension base
SUMMARY
64. • A classIV design shouldberegardedasaclassI removable partialdenturein reverse,
particularlyif the edentulousspanis lengthy.
• The prosthesismust include awell-adapteddenturebase,properlydesigned direct
retention,andappropriatelypositionedindirectretention.
65. ● Every effort should bemade to preserve the hardand soft tissue
components of the anterior edentulous ridge.
● A quadrilateral configuration of direct retainers is considered ideal.
● Themajor connector should berigid, and broad palatal coverage should
beused in the maxillaryarch.
● Indirect retention should belocated as far posterior to the fulcrumline as
possible.
● Functional impression may beindicated if the edentulous area is
extensive.
SUMMARY