4. RPI Flashcards
(38 cards)
What aspects of denture support/retention/stabilization are demonstrated in each aspect of the teeth
- Occlusal third
- Middle third
- Gingival third
- Occlusal third= support (rests)
- Middle third = Stabilization (reciprocation arms, and plates)
- Gingival third= retention
Indications for infrabuldge clasps
- Esthetics
- Distal extension
- Decreased caries incidence
What is the clasp that is suprabuldge and stress releasing
combination clasp
List all the infrabuldge clasps
- RPI (I-bar)
- T-bar (or clasp)
- 1/2 T-bar or modified T-clasp
Describe the movement of the distal extension partial and abutment during occlusal loading with a suprabuldge clasp
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
Describe the movement of the distal extension partial and abutment during occlusal loading with an RPI clasp
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
Describe the movement of the distal extension partial and abutment during occlusal loading with a wrought wire clasp
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)
What are the two forms of reciprocation on a combination clasp
- Reciprocal arm
- Plate
What are the two ways to incorporate a WW clasp into a partial
- Solder it to the framework
- Incorporation into the acrylic
What are the three components of the RPI accemblt
- I- bar
- Proximal plate
- Mesial rest
Describe the design and mechanics of the mesial rest
- Ball and socket rest design*
- Allows for true rotation through the rest when toward the distal extension
- Moves the rotational axis anteriorly
Describe where the proximal plate extends occlusally and lingually
Occlusally= Extends ~1mm occlusal to the gingival portion of the guide plane
Lingually= Extends to the DL line angle of the tooth
Why does relief wax need to be placed gingival to the inferior portion of the guide plane
When the distal extension moves toward the tissue the framework will release into the area of gingival relief
The guide plane is prepped from _ to _
marginal ridge to the junction of the middle and gingival thirds
Decreasing the amount of surface area of contact between the proximal plate and the guide plane results in
more even distribution of functional force between the abutment and ridge
The GP is prepped to what width
2/3 the width of the cusps
For the I-bar the lowest point of contact is… the highest point of contact is…
Lowest= undercut Highest= HOC
The I bar is placed where relative to the HOC
Mesial or mid buccal
The I bar is placed (mesial/distal) to the rotational axis
distal (because remember the fulcrum in an I bar is a MESIAL occlusal rest!)
The I bar moves in what two directions upon loading of the distal extension
gingivally and mesially
What serves as reciprocation for an I-bar
- remember there is no reciprocation arm*
- Minor connector of the mesial rest
- Procimal plate (wraps to the dl line angle)
What the the three points of contact that provide encirclement for an I-bar
- I-bar (buccal)
- Proximal plate (distal)
- Minor connector of mesial rest
To obtain encirclement the clasps must surround the abutment teeth a minimum of _ degrees
190
Advantages of RPI assembly
- 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
