13 Rotational Path

Question 1

Can a true rotational path partial denture be seated along a straight path?

Answer 1

No, it cannot. One portion of the RPD must be seated first, followed by rotation of the retainer of the RPD to its final.

Question 2

Conventional clasps are replaced by the use of _ _ _ in combination of specially designed __.

Answer 2

1. Rigid retentive units

2. Rests (if no proper form of rest, rotational path is contraindicated)

Question 3

Three types of rotational paths

Answer 3

1. A-P
2. P-A
3. Lateral

Question 4

Cat I
Rotational centers located where?
Rotational centers on each side of the arch determine what?

Answer 4

1. Termini of the extended rests of the rigid retainers

2. Rotational centers determine the axis of rotation for placement of the RPD

Question 5

Cat I - Maxilla is typically A-P or P-A? What about mandible?

Answer 5

Maxilla - AP

Mandible - PA

Question 6

Cat II - Rotational centers are located where?

Rotational centers on each side of the arch determine what?

Answer 6

1. Gingival extension of rigid retainers

2. Determine axis of rotation for final placement of RPD

Question 7

Depth for extended occlusal rest seat prep?

How should floor of rest be angled?

How should facial walls be angled?

How about rest-seat prep M-D?

Symmetric or asymmetrical design? This is equivalent to what property of a clasp?

Do you need intimate contact of rest and minor connector with tooth?

Answer 7

A. 1.5 to 2 mm
B. Floor of rest should be perpendicular to long axis of tooth
C. Facial walls should be bilaterally parallel or slightly divergent
D. Rest seat prep should extend more than 1/2 M-D dimension
E. Asymmetrical (equivalent to encirclement)
F. Yes. If removed, retainer is ineffective

Question 8

Cingulum rest - Depth?

- What should the rest shape be?

Answer 8

A. 1.5 mm

2. U or V

Question 9

Advantage of RP RPD (5)

Answer 9

1. Minimizes # of clasps/tooth coverage - may reduce plaque
2. Anterior clasps removed for improved esthetics
3. Min. tooth prep (vs FPD or attachments)
4. Distortion of rigid retentive component is unlikely
5. May prevent further tipping of abutment

Question 10

Disadvantage of RP RPD (4)

Answer 10

1. Adjustment of rigid retentive component is difficult
2. Less tolerance of error
3. Requires well prepared rest seats
4. If anterior flange needed, cannot use with rotational path RPD

Question 11

What additional instrument do you need to evaluate casts for a RP RPD?

Answer 11

A divider

Question 12

Cat I Procedure - AP (posterior teeth)

0. Surveying is done with what degree tilt for undercut determination?
   1a. Where do you place the points of dividers to evaluate the retentive clasp undercut?
   1b. Which points do you rotate and what does this confirm?
   2a. Where do you place the points of dividers to evaluate rigid retainer undercut?
   2b. Which points do you rotate?
   3a. Divider evaluates what? This determines what?

Answer 12

0. 0 degree
   1a. One point at proposed undercut and one at the cervical area to be engaged by the rigid retainer
   1b. Rotate the rigid to make sure it stays engaged in the undercut
   2a. One point on axis where framework will rotate and the other at the most cervical portion of the tooth where the rigid retainer will be
   2b. Must rotate out of the undercut
1. Blockout needed - Divider points placed on axis around framework rotation and other in contact with height of contour of mesial surface of posterior abutment

Question 13

When is Cat I - PA rotational path typically indicated (when replacing posterior teeth)?

Answer 13

1. Used mainly for medially tipped when clasping would be difficult

Question 14

Cat II - AP Procedure (replace anterior)

• Survey cast at __ degrees
• Anterior undercut at least?
• Posterior undercut determined by?
• (Make tripod marks)
• Tilt cast upward anteriorly to do what?
• Use analyzing rod for what?
• If interference, what is needed?
• (Makes second set of tripod marks in another color)
• Now identify all necessary what?
• Make master cast impression and __
• Place dual __ marks
• How can you improve resistance to vertical displacement?

Answer 14

1. 0 degrees
2. 0.20’’
3. Determined by clasp type
4. Until the undercuts on mesial surfaces of anterior abutments disappear
5. Rod determines if access still exists for rest seat
6. If interference, more tooth reduction needed
7. All necessary reductions
8. re-survey
9. Dual survey
10. Use a proximal plate on distal surface of the molar

Question 15

RP RPD w/ multiple edentulous areas

• Closer the minor connector is to the axis of rotation, the lesser or greater the curvature of the arc
• This requires more or less blockout?

Answer 15

1. Closer, the greater the curvature

2. More blockout

Question 16

Cat 1 - Square arch

• Describe the radii
• What is an example of square arch?

Answer 16

1. Parallel, bilaterally passing through all abutments perpendicularly from rotational axis
2. PA

Question 17

Cat I - Tapering Arch

• Describe radii
• How about blockout?

Answer 17

1. Radii shorter if extended perpendicularly from axis of rotation to a point on the proximal surface of the tooth
2. Shorter radii require more blockout

Question 18

Cat II - Arch shape effect

• Distance between fulcrum line and incisal edges influences what on the molar abutments?
• Distance may also affect what for molar clasp?
• The more posteriorly the retentive undercut is located, the more favorable what is?

Answer 18

1. Amount of retention necessary
2. Affect amount of undercut on for molar clasps
3. Favorable leverage factor

Question 19

A-P vertical relation

• As curve of spee increases, retentive point on conventional clasp is lower/higher
• Will this increase or decrease effectiveness of proximal plate undercut?

Answer 19

1. Higher

2. Decrease effectiveness

Question 20

RP RPD - Problems

• Lingually tilted teeth issue?
• Not recommended for what Kennedy classifications?

Answer 20

1. Can prevent rotation of framework from seating

2. Not recommended in distal extensions (Class I/II)