CLASP DESIGNING PRINCIPLES (SUMMARY)

Where should the retentive arm be placed?

Below the survey line, only on the desirable undercut.

How much of the clasp arm should engage the undercut?

1/3 of the clasp arm.

How should a circumferential clasp arm taper?

From the body to the tip.

Why should a circumferential clasp arm taper from body to tip?

To have a flexible arm at the terminal end of the clasp.

How much of the circumference of the abutment should the clasp arms engage?

More than 180 degrees or 2/3 of the circumference.

How many opposing undercuts should a clasp engage to be retentive?

2 opposing undercuts.

What should be the amount of retention?

Minimum necessary to resist reasonable dislodging forces.

Why should the occlusal rest be thick enough?

To resist vertical forces, provide adequate support, and avoid distortion and breakage.

What should the vertical projection arm avoid?

It should not impinge the gingiva.

Where does the vertical projection arm pass?

It passes the attached gingiva and goes vertically upward to reach the desirable undercut of the tooth.

What should the arms and rest NOT interfere with?

Occlusion or mastication.

What should the arms and rest avoid being too close to?

The gingiva, to avoid causing injury.

Where should a rest NOT be placed without a rest seat preparation?

On inclined surfaces, such as the lingual surface of anterior teeth.

What are partners in rest design?

The rest and rest seat.

What is essential for both circumferential and bar clasps?

Uniform taper in thickness and width.

How should a clasp arm cross a groove on a tooth?

It should follow the groove contour.

Why should a clasp arm follow the groove contour?

To maintain a uniform thickness.

What must be present and properly designed to prevent cervical movement of the clasp arm?

The occlusal rest.

What should oppose each retentive terminal?

A reciprocal arm or element capable of resisting orthodontic pressures exerted by the retentive arm.

How must the reciprocal and stabilizing elements be connected for reciprocation?

Rigidly connected bilaterally.

What must the path of escapement of each retentive clasp terminal be relative to the path of removal?

Other than parallel to the path of removal of the prosthesis.

How should clasp retainers adjacent to distal extension bases be designed?

To avoid direct transmission of tipping and rotational forces to the abutment teeth.

What type of clasp arm should be used to reduce stress?

A more flexible clasp arm.

What stress breaker should be used?

Always a mesial rest.

What system can be used for stress release?

RPI System.

What is important regarding the retentive terminal clasp?

Proper location of the retentive terminal clasp.

What clasp is used for Kennedy Class III and IV?

Circumferential / Akers clasp.

What can be used if the abutment is severely tilted?

Ring clasp with support strut or Akers with occlusal rest, depending on the location of the undercut, vestibular depth, and soft tissue undercut.

What is the clasp of choice for posterior abutments or any tooth needing stress release in Class I and II?

RPI.

What are the components of the RPI system?

Mesial rest, distal proximal plate, and I-bar.

What does RPI stand for based on its components?

Rest, Proximal plate, and I-bar.

Where does the retentive arm come from in the RPI system?

The proximal plate.

When is an RPA retainer used?

When an I-bar cannot be used in the vestibule because of a frenum, shallow vestibule, or deep soft tissue undercut.

What are the components of an RPA retainer?

Mesial rest, distal proximal plate, and wrought wire clasp.

When can a mesial rest NOT be used?

Because of rotation, heavy centric contact on the mesial, or a large amalgam restoration on the mesial.

What can be used when a mesial rest cannot be used?

Combination clasp or a correctly designed Distal Rest Concept.

What are the components of a combination clasp?

Distal rest, buccal wrought wire retention, and lingual bracing.

How many direct retainers are used in Kennedy Class I?

2 abutments, one on each side.

How many direct retainers are used in Kennedy Class II?

3 abutments, 1 on the distal extension side and 2 on the opposing side.

What is the maximum number of direct retainers for Kennedy Class III and IV?

Maximum is 4

What is the maximum distribution of direct retainers on one side for Class III and IV?

Maximum of 2 on its side.

How do you know if a tooth can be used as an abutment?

If you can place a survey line.