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Copyright 2008, Jeffrey Shotwell

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Class I RPD

DesignConsiderations

CLASS I - DESIGN

• Premolar abutments– mandible– maxilla

• Canine abutments– mandible– maxilla

• Premolar, canine and lateral abutments

FULCRUM LINES

• Page 96 of your text (you need to knowthis material, all three columns, especiallyfulcrum and retentive fulcrum line axes.)

• FULCRUM LINE AXIS – Tissue directedmovement of the base under loading – goesthrough the most distal occlusal rests.

• RETENTIVE FULCRUM LINE AXIS –Movement of the base AWAY from theridge – goes through retentive clasp tips.

INDIRECT RETENTION

• The component of an RPD that assists thedirect retainers (clasps) in preventingdisplacement of a distal extension base byfunctioning through lever action on theopposite side of the fulcrum line when thedenture base rotates away from thetissues around the fulcrum line. (from theprevious slide, which fulcrum line would thisbe?)

Class I – Premolar abutments -Mandible

Primary fulcrumline

Primaryrests

IndirectRetainer

rests

Clasparm

Majorconnector

Primary rests

19ga wroughtwire clasps

Indirectretainer rests

Lingual barwith 30ga

relief

Think about the pros and cons of placing rest seats on the mesial ordistal surface of abutment teeth in such a case as this.

Class I – Premolar abutments - Maxilla

Think about clasp selection (design and material) – when and why?

Primaryfulcrum lineMajor

connector

Primaryrests

Indirectretainer

rests

Clasparm

T bar castclasp

Primaryrests

Indirectretainers

Anterior border ofpalatal plate endingin valley of rugae

Class I – Premolar abutments – Combinationcase

Balancing Working

Gold occlusals allow formore accuracy in theocclusion – they also ‘hold’the vertical dimensionbetter because they resistwear more than acrylicdoes. This patient was abruxer….

PFM abutments

Primary occlusalrests

Cingulum ballindirectretainers

A combination caseshould have

bilaterally balancedocclusion with

maximum contacts incentric, balancing

and working.

Class I – Canine abutments - Mandible

Primaryfulcrum line

Indirect retentionprovided by mesial

portion of longrest

PFM crowns withraised cingulum

rests

A lingual platecovers the rests

A Class I-A case

Select appropriate clasparms

Primary restsprovided by firstportion of long

rest

Class I – Canine abutment - Mandible

Rotated caninesmake incisal

notch the restseat of choice

Lingual plate majorconnector with incisal

notch restsCombination case.

Class I – Canine abutments - Maxilla

Primaryfulcrum

line

Primaryrests

Palatal platemajor

connector

Claspsappropriatefor tooth

Indirect retentionprovided by proximalplates which bind

against guide planeswhen rotation awayfrom tissues occurs

Class I – Canine, lateral and premolarabutments – maxilla and mandible

Ibar

round castclasp

Modified Tclasp

Class I-A – Premolar abutments -maxilla

Primary rests

Secondary rests on laterals tosupport base in modificationspace and provide indirect

retention

Primaryfulcrum line

Customizeyour choice of

clasp arm

Separate restto provideindirect

retention isNOT needed

Class II RPD

DesignConsiderations

Class II

Class II:

• Mandibular

• Maxillary

Class II - Mandibular

Indirectretainer

Primaryfulcrum line

Clasps asappropriate forthe abutment

#21 – MO and DOrests, lingual guideplane, mid-buccal

undercut

#28 – MOrest forindirectretainer

#30 – full goldcrown with DO rest,

lingual guideplaneand MB undercut

How do the clasps differ?

Class II - Maxillary

IndirectRetainer

Clasp arms asappropriate

Primaryfulcrum line

Majorconnector –

anteroposterior palaltal strap

ML cingulum ballrest as part of

PRI system

Indirectretainer

roundcast clasp

T-bar castclasp

Class II-P – Mandibular

Indirect retainers:plate and rests

Primary fulcrumline

Different claspdesigns for lonestanding molar

- rd CC clasp engaging 0.01inMB undercut.-MO and DO rest seats.-Lingual BAR (above)-OR lingual PLATE (below) majorconnector on lingual of molar.

(note how clasps on anteriorabutment are optional)

Class II-P - Mandibular

teeth #18, #20, & #28 abutments#28 - pfm cr. with DO rest#20-#22 pfm fpd with raised cingulumrest on #22 and DO rest on #20#18 - natural tooth with MO & DO rests

Class II - A-P - Mandibular

Indirect retention providedby teeth in modification space

and rests

Cast claspWroughtwire clasp

#20 - PFM crown, DO rest#21 – PFM crown, MO rest#27 – PFM crown, raisedcingulum #30 - Gold crown,MO & DO rests

Class II – AP - Mandibular

#22, #23, #24 – PFM crowns; raisedcingulums#29 – Full gold crown, MO rest#30 – Full gold crown, MO and DO rests

Lingual plate,indirect retainerrest #24

1/2 rd. castclasp on

#22

Class II-P - Maxillary

secondary rest seat tosupport modification

base is also the indirectretainer rest

#5 – PFM crown, MO rest#11 - ML ball rest#15 – Gold crown with MO and DO rests

I-bar castclasp - #5 &#111/2 rd. castclasp - #15

left lateral view of workingocclusion showing canine guidance

Class III RPD

DesignConsiderations

Class 3-P – Mandibular (bilateral)

Mesial and distalrest seats on lone-

standing molarspreferred to mesial

rest alone

Molars: gold crowns, MO & DOrests, buccal guide planes, andML retention

#20 - DO rest, lingual guideplane, & MB retention

#27 - raised cingulum compositerest, lingual guide plane, & MBretention

Metal bases;re-line notlikely to benecessary

C-clasp on molar and 18 ga. rd.clasp on canine.

C-clasp on molar and 18 ga.rd. clasp on premolar

secondary restseat to support the

major connector

#27 – raisedcomposite cingulum -

lingualplate majorconnector is

fabricated aroundthe new lingual cusp.

Metal base withretention beads

Class 3-P – Mandibular (bilateral)

Clasps: cast vs. wrought wire –wire thought to be more stress-broken and therefore gentler on

weaker teeth

Clasp on #20 OR #27can be eliminatedwithout reducing

retention

Class 3 – Mandibular (Unilateral)

This framework rests on a gold copingcemented onto the molar. This is an

alternative to placing a post and core,and crown on the tooth.

Class 3-A - Mandibular

An additionalrest seat onthe distal ofthe molar isdesirable.

Class 3 - Maxillary

For patient comfort, a fullpalatal plate major

connector, as shown in thediagram on the right, alongwith a secondary rest onthe premolar, is more

desirable than the designshown below.

Class 3-P – Maxillary (bilateral)

Compositereplacing an

amalgam – why?

Palatal strap majorconnector and metal

bases – why notacrylic?

1/2 rd. cast claspson molars and 18

ga. rd. cast claspson the canines

Class 3-P – Maxillary and Mandibular

#18,#31 - full goldcrowns#22,#27 - 3/4 goldcrowns

#18,#31 - 1/2 rd. castclasps #22,#27 - 18 ga.rd. cast clasps

Class 3-A - Maxillary

Modified T-bar clasp – remember that the clasp arm must have adequatelength for flexibility – too short an arm = rigidity.

In the images below, the I-bars on the bicuspids approach from the interproximalspace one-tooth removed – why?

(A good guess would be that the prognosis for #4 is guarded or finances precludecrowning the tooth – and #13 may lack the necessary height of contour.)

Class 3-A-P - Maxillary

Anterior PalatalStrap or Open

Horseshoe majorconnector to

circumvent thepalatal torus

Class 3-P-2A - Maxillary

An adaptationof a modifiedT-bar clasp

Class IV RPD

DesignConsiderations

Class 4 - Mandibular

Rest seat location - try to place arest seat on the two teeth

adjacent to the edentulous areaand also the most posterior teethremaining on each side; preferablymolars and on the distal surface

as shown on right image

- Embrasure clasps on #20,21 &#28,29-Lingual plate major connector-Molars tipped too far lingually touse as direct retainers.

Ledge type cingulum restseats on #22 & 27 to support

anterior base.

Class 4 – Mandibular

lingual inclination of all molarspreculdes using a conventional

major connector

Lingual plate imparts rigidity andbracing (reciprocation) for I-bar

clasps on the premolars

-Labial bar major connector-#18,32: i/2 rd. cast clasps to ML retention-Bracing/reciprocation: #18: horizontal arm, #32: buccal plate

-Labial bar-#21,28: I-bar castclasps

Class 4 - MaxillaRest seat location - try toplace a rest seat on the

two teeth adjacent to theedentulous area and alsothe most posterior teethremaining on each side;

preferably molars and onthe distal surface as

shown on the image atright.

major connector choicesare full palate

(preferred), closedhorseshoe (as shown) or

open horseshoe

T-bar cast clasps onboth molar abutmentshave retention on both

“wings” of the “T”

#2 & #15: DO rests#12: gold inlay

Major connector atleast 6mm from fgm.

I-bar clasps on thepremolars

Class 4 - Maxilla

Note the red,irritated palataltissue associatedwith the RPD base

and majorconnector causedby occlusal traumaand plaque on thetissue surface of

the rpd

Two more examples of Class 4RPD’s – on the right with a fullpalate major connector, and

below with a closed horseshoe(ant/post palatal strap)

QUESTIONS ???????