Removable Partial Denture: Direct Retainers

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Questions and Answers

What design principle dictates that the flexible lingual retentive arm of a circumferential clasp should be thinner than the rigid buccal bracing arm?

Reciprocity

In an Akers clasp, what specific feature primarily provides direct retention?

The terminal end of retentive arm located in the undercut

Why is it essential to have adequate interproximal space when considering the use of an embrasure clasp?

To accommodate the bulk of the clasp without causing excessive occlusal interference or impinging on soft tissues.

In a 'back-to-back' embrasure clasp design, where are the buccal and lingual components typically located?

<p>The buccal component is on the buccal surface, and the lingual component is on the lingual surface, both adjacent to the embrasure.</p> Signup and view all the answers

When is a multiple clasp indicated?

<p>When there are multiple missing teeth.</p> Signup and view all the answers

What is the primary advantage of using a back-action clasp (hairpin clasp) in distal extension partial dentures?

<p>It allows for retention from an undercut on the opposite side of the tooth when the abutment is close to the edentulous area.</p> Signup and view all the answers

What mechanical principle does a 'half-and-half' clasp utilize to minimize stress on the abutment tooth?

<p>Stress-breaking or Leverage reduction.</p> Signup and view all the answers

What is one of the main indications of a ring clasp?

<p>When there is a long clinical crown with significant undercut around the entire circumference of the tooth.</p> Signup and view all the answers

In a ring clasp, what is the purpose of an occlusal rest?

<p>To provide vertical support and prevent the clasp from migrating gingivally.</p> Signup and view all the answers

In what clinical situation would a reverse-action or hairpin clasp be best suited?

<p>When the undercut is located on the side of the abutment tooth away from the edentulous space.</p> Signup and view all the answers

What is a key biomechanical advantage of using an I-bar clasp compared to a traditional circumferential clasp?

<p>Reduced tooth encirclement and improved esthetics.</p> Signup and view all the answers

Why is it important for an I-bar clasp to approach the undercut from below the height of contour?

<p>To avoid interference with the lips and cheeks during function.</p> Signup and view all the answers

Name one situation where the approach of the I-bar clasp from the gingival is contraindicated.

<p>High frenal attachment, shallow vestibule, or significant soft tissue undercut.</p> Signup and view all the answers

What is the primary benefit of a Y-bar clasp design in terms of stress distribution on the abutment tooth?

<p>Distribution of forces over a wider area of the tooth surface.</p> Signup and view all the answers

In an RPI clasp system, what specific function does the rest play?

<p>To provide vertical support, prevent settling of the denture, and direct forces along the long axis of the abutment tooth.</p> Signup and view all the answers

Describe the function of the I-bar in the RPI system.

<p>The I-bar provides retention.</p> Signup and view all the answers

In the RPI system, what is the purpose of the guiding plate?

<p>To provide a reciprocal arm, bracing and stability, and to guide the denture during insertion and removal.</p> Signup and view all the answers

What does RPA stand for in the context of clasp designs, relating it to partial dentures?

<p>Rest, Proximal Plate, Akers Clasp</p> Signup and view all the answers

What materials are typically used for a combination clasp, and why are these materials chosen?

<p>Cast metal (chromium alloy) and wrought wire because cast metal is rigid and provides support/stability and wrought wire flexibility provides retention with less stress on the abutment.</p> Signup and view all the answers

What are the three components of the RPI clasp system?

<p>Rest, Proximal Plate, I-bar</p> Signup and view all the answers

What is the primary purpose of the proximal plate in the RPI clasp system, and how does it contribute to the overall function of the partial denture?

<p>It provides bracing, reciprocation, and close apposition to a guiding plane.</p> Signup and view all the answers

What specific characteristic of wrought wire makes it suitable for the retentive arm in a combination clasp?

<p>Flexibility</p> Signup and view all the answers

What is a direct retainer?

<p>A component of a removable partial denture that engages an abutment tooth to resist dislodgment of the prosthesis.</p> Signup and view all the answers

What is the function of the circumferential clasp?

<p>A clasp that originates above the height of contour of the abutment tooth and encircles more than half of the tooth's circumference.</p> Signup and view all the answers

In what situation should an embrasure clasp be used?

<p>When restoring adjacent teeth without sufficient interdental space for two separate clasps.</p> Signup and view all the answers

What benefit is provided by a multiple clasp?

<p>Enhanced retention and stability for extensive partial dentures.</p> Signup and view all the answers

What is a 'back action' clasp?

<p>A clasp that originates from the denture base and reaches around the abutment tooth to engage an undercut on the opposite side.</p> Signup and view all the answers

Describe the design of a 'half-and-half clasp'.

<p>A clasp design that combines features of both circumferential and bar clasps, with one arm approaching from the occlusal and the other from the gingival.</p> Signup and view all the answers

What is the primary advantage of using an I-bar clasp over a traditional circumferential clasp in terms of aesthetics?

<p>reduced tooth encirclement and improved esthetics.</p> Signup and view all the answers

In RPD design, how might a Y-bar clasp be beneficial in preserving the health of the periodontium?

<p>By approaching the tooth from the gingival, reducing plaque accumulation and improving tissue access.</p> Signup and view all the answers

When designing an RPI clasp system how does the rest provide support?

<p>Preventing vertical settling of the denture base.</p> Signup and view all the answers

What advantage does the RPA clasp system provide in function?

<p>Predictable retention and stability.</p> Signup and view all the answers

How does the combination clasp leverage its two part construction to maximize retention and function?

<p>Rigid cast metal framework creates support and stability, while the flexible wrought wire provides retention.</p> Signup and view all the answers

What is the primary function of the metal framework in a removable partial denture (RPD)?

<p>To provide rigidity, support, and connection for the denture components.</p> Signup and view all the answers

What is the primary function of a direct retainer in a removable partial denture (RPD)?

<p>To provide retention which resists dislodgment during function.</p> Signup and view all the answers

Flashcards

Direct Retainer

A component of a removable partial denture that engages abutment teeth to resist dislodging forces.

Circumferential Clasp

A clasp that approaches the undercut area from an occlusal direction.

Akers Clasp

A common type of circumferential clasp, also known as a simple circlet clasp.

Embrasure Clasp

A clasp that spans the embrasure between two adjacent teeth to engage undercuts.

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Multiple Clasp

Two Akers clasps joined together, can be back to back.

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Back Action Clasp

A clasp design where the retentive arm originates from the denture base and extends toward the occlusal surface.

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Half and Half Clasp

A clasp with one circumferential arm and one bar arm.

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Ring Clasp

A clasp that encircles nearly the entire circumference of a tooth.

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I-Bar Clasp

A type of clasp that originates from the denture base and approaches the undercut from a gingival direction.

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Y-Bar Clasp

A bar clasp that approaches the retentive undercut from a gingival direction, resembling a 'Y' shape.

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RPI System

A clasp system utilizing a mesial rest, proximal plate, and I-bar clasp.

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RPA system

Clasp system using a rest, proximal plate, and Akers clasp

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Combination Clasp

A clasp that combines cast and wrought wire elements for flexibility and strength.

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Study Notes

  • Direct retainers are components of removable partial dentures to provide retention.

Circumferential Clasp

  • A clasp that approaches the undercut area from an occlusal direction.
  • The most common type is the circlet clasp on a mandibular molar.
  • A flexible lingual retentive arm is thinner than the rigid buccal bracing arm.

Circumferential (Akers) Clasp

  • Also known as Akers clasp.

Embrasure Clasp

  • Designed for maxillary molars, the embrasure clasp is also referred to as a "back-to-back" clasp.
  • Requires sufficient space between adjacent teeth, especially on the buccal and lingual sides.

Multiple Clasp

Back Action Clasp

Half and Half Clasp

  • From an occlusal view, it can be seen that the clasp engages both the buccal and lingual surfaces of the abutment tooth.

Ring Clasp

  • A type of direct retainer that encircles nearly the entire circumference of a tooth.
  • Often used on molars, particularly when other retention options are limited.
  • Can be implemented on a mandibular molar.

Reverse - Action Clasp (Hairpin)

  • Also referred to as a hairpin clasp.

I-Bar Clasp

  • On mandibular partial dentures with an acrylic resin base, the "I" bar crosses the gingival margin at a 90-degree angle, maintaining at least 5mm distance from the denture base border.
  • Correctly positioned to the gingival tissues for promoting gingival tissue exposure.

Modified T-Bar

Y-Bar Clasp

  • Features support in the occlusal third, stabilization in the middle third, and retention in the gingival third of the tooth.
  • Positioned on the buccal aspect of the tooth.

RPI System

  • The RPI (Rest, Proximal Plate, I-bar) clasp on a mandibular first premolar minimizes tooth movement out of the clasp due to limited space.

RPA System

  • Features a facial view of the "RPC"(Rest, Proximal Plate, Clasp) clasp.

Combination Clasp

  • Consists of a wrought wire.

Combination Wrought Wire

  • Typically made from an 18-gauge round wrought wire.

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