4. RPI

Question 1

What aspects of denture support/retention/stabilization are demonstrated in each aspect of the teeth

• Occlusal third
• Middle third
• Gingival third

Answer 1

• Occlusal third= support (rests)
• Middle third = Stabilization (reciprocation arms, and plates)
• Gingival third= retention

Question 2

Indications for infrabuldge clasps

Answer 2

• Esthetics
• Distal extension
• Decreased caries incidence

Question 3

What is the clasp that is suprabuldge and stress releasing

Answer 3

combination clasp

Question 4

List all the infrabuldge clasps

Answer 4

• RPI (I-bar)
• T-bar (or clasp)
• 1/2 T-bar or modified T-clasp

Question 5

Describe the movement of the distal extension partial and abutment during occlusal loading with a suprabuldge clasp

Answer 5

Fulcrum= distal occlusal rest

• Distal extension moves down and mesial toward the ridge
• Clasp moves up engaging the undercut
• Forces move the abutment tooth distally

Question 6

Describe the movement of the distal extension partial and abutment during occlusal loading with an RPI clasp

Answer 6

Fulcrum is at the mesial occlusal rest

• rotation occurs at the mesial occlusal rest (ball-and-sock like)
• Downward movement of the distal extension –> downward and mesial movement of the clasp –> disengagement of the undercut on the abutment tooth
• No torquing forces on the tooth

Question 7

Describe the movement of the distal extension partial and abutment during occlusal loading with a wrought wire clasp

Answer 7

Flucrum is at the distal occlusal of the abutment tooth
-Wrought-wire clasp is flexible and is capable of bending in many different directions (compared to half-round clasp arm)

Question 8

What are the two forms of reciprocation on a combination clasp

Answer 8

• Reciprocal arm

- Plate

Question 9

What are the two ways to incorporate a WW clasp into a partial

Answer 9

• Solder it to the framework

- Incorporation into the acrylic

Question 10

What are the three components of the RPI accemblt

Answer 10

• I- bar
• Proximal plate
• Mesial rest

Question 11

Describe the design and mechanics of the mesial rest

Answer 11

• Ball and socket rest design*
• Allows for true rotation through the rest when toward the distal extension
• Moves the rotational axis anteriorly

Question 12

Describe where the proximal plate extends occlusally and lingually

Answer 12

Occlusally= Extends ~1mm occlusal to the gingival portion of the guide plane

Lingually= Extends to the DL line angle of the tooth

Question 13

Why does relief wax need to be placed gingival to the inferior portion of the guide plane

Answer 13

When the distal extension moves toward the tissue the framework will release into the area of gingival relief

Question 14

The guide plane is prepped from _ to _

Answer 14

marginal ridge to the junction of the middle and gingival thirds

Question 15

Decreasing the amount of surface area of contact between the proximal plate and the guide plane results in

Answer 15

more even distribution of functional force between the abutment and ridge

Question 16

The GP is prepped to what width

Answer 16

2/3 the width of the cusps

Question 17

For the I-bar the lowest point of contact is… the highest point of contact is…

Answer 17

Lowest= undercut
Highest= HOC

Question 18

The I bar is placed where relative to the HOC

Answer 18

Mesial or mid buccal

Question 19

The I bar is placed (mesial/distal) to the rotational axis

Answer 19

distal (because remember the fulcrum in an I bar is a MESIAL occlusal rest!)

Question 20

The I bar moves in what two directions upon loading of the distal extension

Answer 20

gingivally and mesially

Question 21

What serves as reciprocation for an I-bar

Answer 21

• remember there is no reciprocation arm*
• Minor connector of the mesial rest
• Procimal plate (wraps to the dl line angle)

Question 22

What the the three points of contact that provide encirclement for an I-bar

Answer 22

• I-bar (buccal)
• Proximal plate (distal)
• Minor connector of mesial rest

Question 23

To obtain encirclement the clasps must surround the abutment teeth a minimum of _ degrees

Answer 23

190

Question 24

Advantages of RPI assembly

Answer 24

• Stress release (doesn’t put stress on abutment during chewing)
• Mesial rest placement (places all forces along the long axis of tooth and toward the mesial where there is an adjacent tooth)
• Minimizes gingigval trauma
• Direction of forces (toward the mesial)
• Prevents posterior movement of framework (due to mesial rest)
• Decreased caries risk
• Esthetics

Question 25

What happens when the distal extension is loaded with an RPI… where are the forces directed to

Answer 25

• Clasp rotates through mesial rest
• Proximal plate moves into the gingival relief areaa
• I-bar moves gingivally and mesially

Forces are directed

• Along the long axis of the abutment
• Posterior residual ridge

Question 26

What happens when you increase the height of the PP occlusally

Answer 26

• Transfers more stress to the tooth (less on the ridge)

- Fulcrum shifts from the mesial rest to the PP (assembly no longer rotates as planned)

Question 27

Advantages of the mesial rest are

Answer 27

• Allows for rotation (resulting in movement of the claps gingivally and mesially thus less torquing forces on the tooth)
• Directs the forces along the long axis of the tooth
• Drives abutment mesially into the adjacent tooth

Question 28

What would happen if an I-bar was paired with a distal rest

Answer 28

• I-bar would engage the undercut upon distal extension loading
• Forces on abutment would cause movement distally

Question 29

With a RPI the support of the denture relies more on (abutment teeth/ridge)

Answer 29

ridge

Question 30

Explain how RPI reduces gingival trauma

Answer 30

• Relief space prevents compression of distal gingiva by the proximal plate
• Less horizontal components allow more normal stimulation

Question 31

Posterior (Distal) movement of the framework is prevented by what two areas

Answer 31

• I-bar mesial to the mid-buccal HOC

- Minor connector contacting at the MO embrassure

Question 32

Why does RPI –> decreased caries susceptibility

Answer 32

-Less tooth coverage

Question 33

_% of people can’t see the gingival third of a maxillary and mandibular cuspid

Answer 33

Maxillary= 44%
Mandibular= 93%

Question 34

What are the disadvantages of RPI design

Answer 34

• Increased force on the ridge
• Increased gingival coverage
• Decreased stability (due to less horizontal components)
• Need to control tooth contours is exacting
• May need to crown abutments

Question 35

Contraindications for RPI

Answer 35

• Insufficient undercut (lingually tipped tooth or no MB undercut)
• Revere rotation of abutment (prevents correct placement of mesial rest and negates proper placement of rotational axis)
• Severe mesial inclination of abutment (prevents creation of guide plane)
• Height of FOM <8 mm requiring a lingual plate

Question 36

What would requiring a lingual plate rather than a lingual bar contraindicate the use of an RPI complex

Answer 36

because the lingual plate negates the principle stress release as the rotational axis moves from the rest to the area of plate contact
-Thus the plate becomes the area of reciprocation not the pp.

Question 37

What is a condition where a lingual plate and RPI may be used

Answer 37

When the I bar is used for esthetics

Question 38

Contraindications for all infrabuldge clasps

Answer 38

• Insufficient attached gingiva

- Inadequate vestibular depth (severe soft tissue undercuts or buccal tilt of abutment tooth)