rpd design

Partial denture design

Objectives

To understand:Decision making process for RPDsThe stages of PD design

Communicate:Design instructions to the lab

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Saddles (yellow)

Rests on and covers alveolar ridge and includes artificial teeth and gum work.

Saddles

Pt naturally regards it as the most important component because it imparts both appearance and function to the denture.

Our main concerns are:1. Design of occlusal surface

2. Base extension

3. Polished surface

4. Material for fitting surface

5. Saddle/ abutment tooth junction

• area of occlusal table of posterior teeth esp if distal extension saddle present

• Use narrow posterior teeth or by reducing length by omitting teeth = force to underlying tissues during mastication

• bucco-lingual width of teeth - space for tongue (? Spread laterally)

All help in the success of a mdr RPD!

‘on the ridge’ – hard to adjust the metal.‘off the ridge retention of acrylic base.

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Support (red)

Resistance to vertical force directed towards the teeth and mucosa.

Vertical force may be resisted by:1. Mucosa

2. Tooth

3. Both

Type of support available may vary and assessment of its quality is made during design procedures:1. Root area of the abutment teeth

2. Extent of the saddles

3. Expected force on the saddles

Quality of support

Tooth support:Rest designTooth preparation

Mucosa support:Saddle extensionQuality of support

Tooth-mucosa support:Free-end saddleDifficult to Rx (when missing posterior teeth)

? Shortened dental arch

Concept accepted by a great majorly of dentists but not widely practiced.

Should be included in all Rx planning for partially edentulous pts.

Pt’s don’t lose tooth surface by just eating. They are more likely to lose them by erosion/ bruxism.

Free end saddle• Distal rest placement

causes tilting

• Mesial rest placement prevents tilting

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Types of retention (green)

1.Clasps

2.Neuromuscular forces

3.Physical forces

4.Guide surfaces

5.Other devices

Clasp

Metal arm which retains, or stabilises, a denture by contacting a tooth

Factors affecting clasp choice

Position of undercut

Periodontal status

Sulcus shape (deep undercuts)

Clasp length

Appearance

Occlusally approaching

Gingivally approaching

Flexibility of clasp

Influenced by:MaterialLength Cross section

In a premolar use a wrought clasp – malleable

In molar you may use wrought/ cast clasp

Clasps

Clasps may be round

Half round:? More directional, accurate and stable

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Reciprocation/ bracing (blue)

Prevents tooth movement escape

Reciprocation

1. As clasp being pulled up it goes over the bulbosity of the tooth2. As clasp is going up, the other clasp on the other side is stopping it from going up thus stopping the tooth moving

Bracing

Force resisted by the other side of the denture

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Upper jaw design

Full coverage

Ring connector

Bar connectors:1.Anterior2.Posterior3.mid-palatal

Lower jaw design

1. Lingual bar

2. Sublingual bar: least well tolerated

3. Lingual plate

4. Continuous or dental bar

5. Labial bar

Design Stages (after surveying mounted and articulated

casts)

1. Saddles

2. Support

3. Retention

4. Reciprocation and Bracing

5. Connection

6. Indirect Retention

Indirect retention

The clasp is always nearer to the indirect retainer (fulcrum) than is the displacing

force. The clasp is therefore working at a mechanical disadvantage relative to the

displacing force.

The RPD design should strive to reduce the mechanical advantage of the displacing force by placing the clasp axis as close as possible to the saddle and by

placing the indirect retainers as far as possible from the saddle.

Support for indirect retainer

1. Tooth support

2. Mucosa support

F (indirect retainer)

R (clasp)

E (displacing force)

Test

1. What Kennedy classification is this?2. Where can we put the saddles and what colour do we

use?3. What rests can you identify and what colour do we use?4. How can we achieve retention, what types of clasps

should we use and colour?5. Where may we obtain bracing/ reciprocation from and

what colour do we use?6. What coverage can we consider for this case?7. What other considerations do we need to have when

designing a denture?

Answers

1. Class II mod II

2. .

3. .

4. .

5. .

6. Wide palatal coverage by the connector. However, it is possible to keep the anterior border of the palatal plate away from the anterior teeth and from the sensitive area around the incisive papilla to promote hygiene and tolerance to the framework.

7. OHI compliance, tolerance, comfort, ? Addition, material selection, aesthetics, pt expectations

References

1. A clinical guide to removable partial denture design. Davenport et al 2000.

2. Factors to consider in panning a removable partial denture. Dent update. 2002. 29 (8): 375

3. Impression making for partial dentures. Dent update. 2002. 29 (9): 422-7

4. Principles of design for removable partial dentures. Dent update. 2002. 29 (8): 474-81

5. Technological considerations when designing removable partial dentures. Dent update. 2003. 30 (1): 7-9

6. Diagnosis and treatment of removable denture problems. Dent update. 2003. 30 (2): 88-94, 96-7