Removeable partial denture design - PowerPoint Presentation

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Removeable partial denture design

Arabella

Yelland

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Damage that may result from poor design

Plaque accumulation (decalcification, periodontal issues)

Direct trauma from components (abrasion/fracture of teeth/restorations; inflammation of gingival tissues)

Transmission of excessive

occlusal

forces (tooth mobility/aggravation of existing periodontal disease)

Occlusal

error (tooth mobility/aggravation of existing periodontal disease)

And inflammation to edentulous areas/

resorption

of bone

Slide3

Assessment of existing teeth

Recent

periapical

view to assess bone levels and

periapical

status

Are teeth

restoreable

?

Patient medical history

Likelihood of losing more teeth

Periodontal condition

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Kennedy classification

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Modification of teeth?

Rest seats

Undercuts

Guide surfaces

Milled parallel surfaces

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Rest seats

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Guide surfaces

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“Six core elements”

1. teeth to be replaced

2. support

3 rigid major connector

4. retention

5. anti-rotation/indirect retention

6. reciprocation/bracing

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Teeth to be replaced

Do all missing teeth need to be replaced?

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Support

From teeth

From soft tissues

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Rigid major Connector

May also provide support

Must not flex

Incorporate hygienic design

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Retention

Direct – usually clasps

Indirect – opposing rotation is obtained anterior to the rotational axis

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Indirect retention

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Davenport’s rules for clasps

A clasp should always be supported by a rest.

A molar ring clasp should have occlusal rests mesially and distally.

A molar ring clasp, which engages lingual undercut, should have a buccal strengthening arm.

Retentive clasps can be used to provide indirect support for a distal extension saddle by being placed on the opposite side of the support axis from the saddle.

A wrought wire clasp should be attached to a saddle, not to exposed parts of the metal framework.

An occlusally-approaching clasp should not approach closer than 1 mm to the gingival margin.

A retentive occlusally-approaching clasp should run from the side of the tooth with the least undercut to the side with the greatest undercut.

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Occlusally-approaching retentive clasps should have the terminal third of the retentive arm entering the undercut.

A retentive clasp should engage 0.25 mm of undercut if it is constructed in cast cobalt-chromium alloy.

If an undercut on a tooth that needs to be clasped for retention is less than 0.25 mm, then composite resin should be added to the tooth to create at least this amount of undercut.

A retentive clasp should be at least 15 mm in length if it is constructed in cast cobalt-chromium alloy.

Occlusally-approaching retentive clasps should be restricted to molar teeth if constructed in cast cobalt chromium alloy.

A retentive clasp should engage 0.5 mm of undercut if it is constructed in wrought wire.

A retentive clasp should be at least 7 mm in length if it is constructed in wrought wire.

If an occlusally-approaching retentive clasp is used on a premolar or canine it should be constructed in wrought wire.

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Retentive clasps should usually be placed buccally on upper teeth.

Retentive clasps should usually be placed lingually on lower molars.

Retentive clasps should usually be placed buccally on lower premolar or canine teeth.

Where there are clasps on opposite sides of the arch, the retentive arms are best placed on opposing tooth surfaces ie buccal/buccal or lingual/lingual.

Retentive and bracing/reciprocating elements of a clasp should encircle the tooth by more than 180 degrees.

Reciprocation should be provided on a clasped tooth diametrically opposite the retentive clasp tip.

If a reciprocating clasp, rather than a plate, is used it should be placed at the gingival end of a guide surface on the clasped tooth.

Where a plate connector is used, reciprocation can be obtained by a guide plate on the connector.

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Gingivally-approaching clasps are contra-indicated if the buccal sulcus is less than 4 mm in depth.

Gingivally-approaching clasps are contra-indicated if there is a tissue undercut buccally on the alveolus more than 1mm in depth and within 3 mm of the gingival margin.

A gingivally-approaching clasp should be used if a retentive cast cobalt chromium clasp is required on a premolar or canine tooth, assuming that sulcus anatomy is favourable.

The RPI system (rest, plate, I-bar clasp) should be used on premolar abutment teeth for mandibular distal extension saddles if the tooth and buccal sulcus anatomy is favourable.

The RPI system (rest, plate, I-bar clasp) should be used on premolar abutment teeth for maxillary distal extension saddles if the tooth and buccal sulcus anatomy is favourable.

A distal extension saddle should have a retentive I-bar clasp whose tip contacts the most prominent part of the buccal surface of the abutment tooth mesio-distally.

If the retentive clasp for a distal extension saddle is on a premolar or canine abutment, it should be either a cast gingivally-approaching I-bar or a wrought wire occlusally-approaching clasp.

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RPI system

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A distal extension saddle should have a retentive clasp on the abutment tooth.

A unilateral distal extension saddle denture (Kennedy II) should have one clasp as close to the saddle as possible and the other as far posteriorly as possible on the other side of the arch.

Bounded saddles should have a clasp at least at one end.

A Kennedy III modification 1 denture should have 2 retentive clasps forming a diagonal clasp axis which bisects the denture.

A Kennedy IV denture should have retentive clasps on the first molars if there is suitable undercut present.

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Reciprocation

Prevents tooth movement when clasps is activated

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Bracing

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Connectors

Plate

Horseshoe/anterior bar

Ring

Mid palatal bar

(posterior bar)

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Lower connectors

Lingual bar – requires >7mm between

gingival margin

and functional

sulcus

depth

Sublingual bar

Plate

Dental bar/

kennedy

bar/continuous clasp (need crowns at least 12mm in height)

(labial bar)

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References

BDJ JC Davenport series 2000-2001 (also available as BDJ Clinical Guide

to Removable

Partial

Denture Design)

Revisiting the principles of partial denture design, C. Stilwell, Dental Update 2010, 682-690

Successful removable partial dentures, C. Lynch, Dental Update 2012, 118-126