Designing of class i and class ii/ oral surgery courses

DESIGNING CLASS IDESIGNING CLASS I
AND CLASS IIAND CLASS II
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing Dental EducationLeader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

CONTENTSCONTENTS
 INTRODUCTIONINTRODUCTION
 PRINCIPLES OF DESIGNINGPRINCIPLES OF DESIGNING
 PHILOSOPHIES OF DESIGNINGPHILOSOPHIES OF DESIGNING
 BIOMECHANICAL CONSIDERATIONBIOMECHANICAL CONSIDERATION
 ESSENTIALS OF PARTIAL DENTUREESSENTIALS OF PARTIAL DENTURE
DESIGNDESIGN
 DESIGNING OF CLASS IDESIGNING OF CLASS I
 DESIGNING OF CLASS IIDESIGNING OF CLASS II
 CONCLUSIONCONCLUSION
 BIBLIOGRAPHYBIBLIOGRAPHY

INTRODUCTIONINTRODUCTION
 The design process is a series of steps that leadThe design process is a series of steps that lead
toward a solution of the problem and includes;toward a solution of the problem and includes;
identifying a need, definition of the problem, settingidentifying a need, definition of the problem, setting
design objectives, searching for backgrounddesign objectives, searching for background
information and data, developing a design rationale,information and data, developing a design rationale,
devising and evaluating alternative solutions, anddevising and evaluating alternative solutions, and
providing the solution.providing the solution.

 Design of the partial denture framework shouldDesign of the partial denture framework should
systematically developed and outlined on an accuratesystematically developed and outlined on an accurate
diagnostic cast .diagnostic cast .
 The completed design will serve as a blueprint forThe completed design will serve as a blueprint for
removable partial denture construction.removable partial denture construction.
 Designing is done with great care considering theDesigning is done with great care considering the
mechanical characteristics of the removable partialmechanical characteristics of the removable partial
denture.denture.
 Components must be neatly drawn and accuratelyComponents must be neatly drawn and accurately
positioned and the design must convey essentialpositioned and the design must convey essential
information to the laboratory personnel responsibleinformation to the laboratory personnel responsible
for prosthesis construction.for prosthesis construction.

Principles by A.H. SchmidtPrinciples by A.H. Schmidt
(1956).(1956).
1.1. The dentist must have a thorough knowledge ofThe dentist must have a thorough knowledge of
both the mechanical and biologic factors involvedboth the mechanical and biologic factors involved
in removable partial denture design.in removable partial denture design.
2.2. The treatment plan must be based on a completeThe treatment plan must be based on a complete
examination and diagnosis of the individualexamination and diagnosis of the individual
patient.patient.

3.3. The dentist must correlate the pertinent factorsThe dentist must correlate the pertinent factors
and determine a proper plan of treatment.and determine a proper plan of treatment.
4.4. A removable partial denture should restore formA removable partial denture should restore form
and function without injury to the remaining oraland function without injury to the remaining oral
structure.structure.
5.5. A removable partial denture is a form ofA removable partial denture is a form of
treatment and not a cure.treatment and not a cure.

PHILOSOPHIES OF DESIGNINGPHILOSOPHIES OF DESIGNING
Stress EqualizationStress Equalization
Physiologic BasingPhysiologic Basing
Broad Stress DistributionBroad Stress Distribution

Stress EqualizationStress Equalization
The rigid connection between the denture bases andThe rigid connection between the denture bases and
the direct retainer on the abutment teeth is damagingthe direct retainer on the abutment teeth is damaging
and that some type of stress director or stressand that some type of stress director or stress
equalizer is essential to protect the vulnerableequalizer is essential to protect the vulnerable
abutment teeth.abutment teeth.
Stress EqualizerStress Equalizer-:-: According to GPT 8According to GPT 8
A device which relieves the abutment teeth of all orA device which relieves the abutment teeth of all or
part of occlusal forces.part of occlusal forces.

Types of StressTypes of Stress
EqualizersEqualizers
Type I:Type I:
Hinges, sleeves andHinges, sleeves and
cylinders, and ball –and-cylinders, and ball –and-
socket devices.socket devices.

Type II:Type II:
Designs having flexibleDesigns having flexible
connection whichconnection which
include the use ofinclude the use of
wrought wirewrought wire
connection, dividedconnection, divided
major connectors ormajor connectors or
other flexible devicesother flexible devices
for movement of distalfor movement of distal
extension.extension.

AdvantagesAdvantages
Forces are distributed equally on abutment and theForces are distributed equally on abutment and the
soft tissue.soft tissue.
Minimize the tipping forces on abutment tooth,Minimize the tipping forces on abutment tooth,
thereby limiting bone resorption.thereby limiting bone resorption.
Minimal direct retention because the denture basesMinimal direct retention because the denture bases
operate more independently.operate more independently.

DisadvantagesDisadvantages
Fragile,complex and costly.Fragile,complex and costly.
Requires constant maintenance.Requires constant maintenance.
Difficult to repair.Difficult to repair.
Bulky and annoying to patient.Bulky and annoying to patient.

Physiologic BasingPhysiologic Basing
The equalization of stress can be best and mostThe equalization of stress can be best and most
simply be accomplished by some form ofsimply be accomplished by some form of
physiologic basing, or lining, of the denture base.physiologic basing, or lining, of the denture base.
Mucosa is recorded in its functioning form.Mucosa is recorded in its functioning form.
Soft tissue offer more resistance to furtherSoft tissue offer more resistance to further
compression.This increases resistance provided bycompression.This increases resistance provided by
mucosa equates to that of periodontal ligament ofmucosa equates to that of periodontal ligament of
abutment tooth.abutment tooth.
Artificial teeth will be above occlusal plane in restArtificial teeth will be above occlusal plane in rest
position.position.

Stimulating effect on underlying tissueStimulating effect on underlying tissue
Reduced necessity of reliningReduced necessity of relining
Simplicity in design and constructionSimplicity in design and construction
Lightweight prostheses requiring minimalLightweight prostheses requiring minimal
maintenance and repair.maintenance and repair.
Reduced stresses on abutment tooth, hence retainedReduced stresses on abutment tooth, hence retained
for longer period.for longer period.

Premature contacts.Premature contacts.
Decreased effect of indirect retention.Decreased effect of indirect retention.
Not well stabilized against lateral forces.Not well stabilized against lateral forces.

Broad Stress DistributionBroad Stress Distribution
Advocates believe that excessive trauma to
remaining teeth and the residual ridge can be
prevented by distributing occlusal forces over as
much the available area of teeth and soft tissue as
possible.

Broad stress distribution.Broad stress distribution.
Excellent horizontal stabilization.Excellent horizontal stabilization.
Removable splinting.Removable splinting.
Easier and less expensive to construct.Easier and less expensive to construct.
Less danger of distortion and breakage of denture.Less danger of distortion and breakage of denture.
Decreased chances of relining.Decreased chances of relining.www.indiandentalacademy.comwww.indiandentalacademy.com

Less comfortable.Less comfortable.
Requires good maintenance of oral hygiene.Requires good maintenance of oral hygiene.

Biomechanical considerations.Biomechanical considerations.
 A better understanding of the methods of controllingA better understanding of the methods of controlling
forces on RPD may be achieved by a brief review offorces on RPD may be achieved by a brief review of
the development of forces. This considers thethe development of forces. This considers the
application of mathematical formulas.application of mathematical formulas.
 As Tylman states, “ great caution and reserve areAs Tylman states, “ great caution and reserve are
essential whenever an attempt is made to interpretessential whenever an attempt is made to interpret
biological phenomenon entirely by mathematicalbiological phenomenon entirely by mathematical
computation.”computation.”

RPD as a simple machineRPD as a simple machine
 LeverLever
 WedgeWedge
 Inclined planeInclined plane
 ScrewScrew
 Wheel and axleWheel and axle
 pulleypulley

LeverLever
 In its simplest form, a lever is a rigid bar supportedIn its simplest form, a lever is a rigid bar supported
somewhere along its length. It may rest on thesomewhere along its length. It may rest on the
support or may be supported from above.support or may be supported from above.
 There are three types of levers;There are three types of levers;

Class IClass I
 AA class-1class-1 leverlever has itshas its
fulcrum locatedfulcrum located
somewhere between thesomewhere between the
effort and the resistanceeffort and the resistance
 E.g. Distal extensionE.g. Distal extension
removable partialremovable partial
denturedenture

Class IIClass II
 With aWith a class-2 leverclass-2 lever, the, the
fulcrum is at one end,fulcrum is at one end,
the effort is at the otherthe effort is at the other
end and the resistance isend and the resistance is
in the middlein the middle
 Seen as indirectSeen as indirect
retention in removableretention in removable
partial denturepartial denture

Class IIIClass III
 In aIn a class-3 leverclass-3 lever, the, the
fulcrum is at one endfulcrum is at one end
and the effort is appliedand the effort is applied
between the fulcrumbetween the fulcrum
and the resistance.and the resistance.
 Not encountered inNot encountered in
partial denturespartial dentures
 TMJ muscles and teethTMJ muscles and teeth
act as a class III leveract as a class III lever

Inclined PlaneInclined Plane
 Forces against theForces against the
inclined plane mayinclined plane may
result in deflection ofresult in deflection of
that which is applyingthat which is applying
the force or may resultthe force or may result
in the movement of thein the movement of the
inclined plane .inclined plane .
 Neither of these resultsNeither of these results
are desirableare desirable

WedgeWedge
 A wedge by definition is a solid object with a broadA wedge by definition is a solid object with a broad
base and its two sides arising to intersect each otherbase and its two sides arising to intersect each other
forming an acute angle opposite the base.forming an acute angle opposite the base.

Forces acting on theForces acting on the
partial denture.partial denture.

 Forces acting on a distalForces acting on a distal
extension partial denture are aextension partial denture are a
result of a composite of forcesresult of a composite of forces
arising from the threearising from the three
principal fulcrums.principal fulcrums.
1) Fulcrum on the horizontal1) Fulcrum on the horizontal
plane.plane.
2) Fulcrum on the sagittal plane.2) Fulcrum on the sagittal plane.
3) Fulcrum on the vertical plane.3) Fulcrum on the vertical plane.

 Fulcrum on the sagittal planeFulcrum on the sagittal plane

 Fulcrum on the frontal PlaneFulcrum on the frontal Plane

 Fulcrum on the horizontal planeFulcrum on the horizontal plane

Essentials of partialEssentials of partial
denture design.denture design.

Essentials of partial dentureEssentials of partial denture
design.design.
 It should be systemically developed andIt should be systemically developed and
outlined on an accurate diagnostic casts.outlined on an accurate diagnostic casts.

First stepFirst step
 Decide how the partial denture has to beDecide how the partial denture has to be
supported.supported.
 If Tooth supported.If Tooth supported.
 EvaluateEvaluate
1.1. Periodontal healthPeriodontal health
2.2. Crown and root morphologiesCrown and root morphologies
3.3. Crown to root ratio.Crown to root ratio.
4.4. Bone index area.Bone index area.
5.5. Location of tooth in arch.Location of tooth in arch.
6.6. Length of edentulous span.Length of edentulous span.
7.7. Opposing dentition.Opposing dentition.

 If tooth and tissue supported.If tooth and tissue supported.

Also ConsiderAlso Consider
1.1. Quality and contour of supporting bone andQuality and contour of supporting bone and
mucosamucosa
2.2. Extent to planned coverage of ridge.Extent to planned coverage of ridge.
3.3. Type and accuracy of impression registration.Type and accuracy of impression registration.
4.4. Accuracy of denture base.Accuracy of denture base.
5.5. Design characteristics of the component partsDesign characteristics of the component parts
of framework.of framework.
6.6. Anticipated occlusal load.Anticipated occlusal load.

Second stepSecond step
 Connect the tooth and tissue support units.Connect the tooth and tissue support units.
 These connection is facilitated by designingThese connection is facilitated by designing
and locating major and minor connectors inand locating major and minor connectors in
compliance with the basic principles andcompliance with the basic principles and
concepts.concepts.

Third step.Third step.
 Determine how the partial denture is to beDetermine how the partial denture is to be
retained.retained.
 Select clasp design that willSelect clasp design that will
1.1. Avoid direct transmission of tipping for torquingAvoid direct transmission of tipping for torquing
forces to the abutmentforces to the abutment
2.2. Accommodate the basic principles of clasp design byAccommodate the basic principles of clasp design by
definitive location of components parts correctlydefinitive location of components parts correctly
positioned on abutment tooth surfaces.positioned on abutment tooth surfaces.
3.3. Provide retention against reasonable dislodgingProvide retention against reasonable dislodging
forces.forces.
4.4. Be compatible with undercut locations,tissueBe compatible with undercut locations,tissue
contour,and esthetic desires of the patient.contour,and esthetic desires of the patient.

Fourth step.Fourth step.
 Connect the retention units to the support unitsConnect the retention units to the support units

Fifth step.Fifth step.
 Outline and join the edentulous area to theOutline and join the edentulous area to the
already established design components.already established design components.

Class I and class II designClass I and class II design

 1. Direct retention1. Direct retention
The main objective should be restoration ofThe main objective should be restoration of
the function and appearance and the maintenancethe function and appearance and the maintenance
of comfort, with great emphasis on preservationof comfort, with great emphasis on preservation
of the health and integrity of the remaining oralof the health and integrity of the remaining oral
structures.structures.

PRIMARY RETENTIONPRIMARY RETENTION
SECONDARY RETENTIONSECONDARY RETENTION

 2. clasps2. clasps
a. simplest type of clasp should be useda. simplest type of clasp should be used
b. clasp should have a good stabilizing quality,b. clasp should have a good stabilizing quality,
remain passive until activated by functional stress.remain passive until activated by functional stress.

Clasps in class I prosthesisClasps in class I prosthesis
 Requires only two retentiveRequires only two retentive
clasps, one on each side.clasps, one on each side.
 If a distobuccal undercutIf a distobuccal undercut
is present, the verticalis present, the vertical
projection retentive claspprojection retentive clasp
is preferred.is preferred.

 If mesiobuccalIf mesiobuccal
undercut is present,undercut is present,
wrought wire clasp iswrought wire clasp is
indicated. A castindicated. A cast
circumferential claspcircumferential clasp
should not be used.should not be used.
 The reciprocal orThe reciprocal or
bracing arm must bebracing arm must be
rigidrigid..
 Bilateral configuration.Bilateral configuration.

Clasps in class II prosthesisClasps in class II prosthesis
 Usually there are threeUsually there are three
retentive claspsretentive clasps
 The distal extension sideThe distal extension side
should be designed withshould be designed with
the same considerationsthe same considerations
as for a class Ias for a class I
prosthesis.prosthesis.
 The opposite side shouldThe opposite side should
have two retentivehave two retentive
clasps, one as forclasps, one as for
posterior and one as farposterior and one as far
anterior.anterior.

 If a modification space isIf a modification space is
present, clasp the teethpresent, clasp the teeth
adjacent to theadjacent to the
edentulous space.edentulous space.
 Tripod configuration.Tripod configuration.

 3. rests3. rests
a. rests seats should bea. rests seats should be
prepared so that stressprepared so that stress
will be directed alongwill be directed along
the long axis of the teeththe long axis of the teeth
b. rests should be placedb. rests should be placed
next to the edentulousnext to the edentulous
space.space.

 4. indirect retention4. indirect retention
a. should be located asa. should be located as
far anterior to thefar anterior to the
fulcrum line as possiblefulcrum line as possible
b. two indirect retainersb. two indirect retainers
should be used for classshould be used for class
I prosthesis.I prosthesis.

one indirect retainer canone indirect retainer can
be used on the sidebe used on the side
opposite the edentulousopposite the edentulous
space in a class IIspace in a class II
designdesign

should be placed inshould be placed in
properly prepared restproperly prepared rest
seats so that forces willseats so that forces will
be directed along thebe directed along the
long axis of the teethlong axis of the teeth
 Lingual plating can alsoLingual plating can also
be used as an effectbe used as an effect
indirect retainer.indirect retainer.

 Major connectorMajor connector
 Should be rigidShould be rigid
 Not impinge on theNot impinge on the
gingival tissuesgingival tissues
 Support from the hardSupport from the hard
palate should be used inpalate should be used in
design of the maxillarydesign of the maxillary
major connectormajor connector

 Can be extended ontoCan be extended onto
the lingual surfaces ofthe lingual surfaces of
the tooth to increasethe tooth to increase
rigidity, distributerigidity, distribute
lateral forces, improvelateral forces, improve
indirect retention, andindirect retention, and
eliminate foodeliminate food
impactionimpaction

 MINOR CONNECTORSMINOR CONNECTORS
- rigidrigid
- it’s position should enhance comfort,- it’s position should enhance comfort,
cleanliness and to place teeth.cleanliness and to place teeth.

 OcclusionOcclusion
- centric relation should coincide with centric- centric relation should coincide with centric
occlusionocclusion
- harmonious occlusion- harmonious occlusion
- prosthetic teeth should minimize the stresses;- prosthetic teeth should minimize the stresses;
a. fewer teeth, narrow buccolingually.a. fewer teeth, narrow buccolingually.
b. placed over the crest of the ridge.b. placed over the crest of the ridge.
c. should display sharp cutting edges and amplec. should display sharp cutting edges and ample
escapeways.escapeways.

 Denture basesDenture bases
- broader coverage to distribute forces without- broader coverage to distribute forces without
interfering with functional movement ofinterfering with functional movement of
tissues.tissues.
- selective pressure impressions for distal- selective pressure impressions for distal
extension.extension.

Conclusion:Conclusion:
Adequate time must be spent in properly diagnosingAdequate time must be spent in properly diagnosing
the particular case and devising a workablethe particular case and devising a workable
treatment plan. Once this is done the mechanicaltreatment plan. Once this is done the mechanical
task of laying out the “nuts and bolts” of removabletask of laying out the “nuts and bolts” of removable
partial denture design can be carried out to ensurepartial denture design can be carried out to ensure
that our patients receive full benefits of ourthat our patients receive full benefits of our
knowledge and skillsknowledge and skills..

REFERENCESREFERENCES
 Removable partial prosthodontics- McRemovable partial prosthodontics- Mc
Crackens 11Crackens 11thth
eded
 Clinical removable partial prosthodontics-Clinical removable partial prosthodontics-
Stewart 2Stewart 2ndnd
eded
 Partial dentures- John Osborne 4Partial dentures- John Osborne 4thth
eded
 Textbook of removable partial dentures-Textbook of removable partial dentures-
KratochvilKratochvil
 Removable partial prosthodontics- Grosso-Removable partial prosthodontics- Grosso-
Miller 3Miller 3rdrd
eded
 Evolution of removable partial denture designEvolution of removable partial denture design
– journal of prosthodontics, vol 3, no 3,– journal of prosthodontics, vol 3, no 3,
September 1994 pg 155-166.September 1994 pg 155-166.www.indiandentalacademy.comwww.indiandentalacademy.com

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