6. RPD Retainers Flashcards
What is an RPD retainer?
- Any type of device used for stabilization or retnetion of a prosthesis
- Keep the RPD in place at rest and during fucntion
Primary retention is provided by?
direct retainers
Secondary retention is prvided by? What is secondary retention?
- Provided by major connectors and bases
- Adhesion
- Cohesion
- Border seal
Objective of retainers? (4)
- Retention
- Horizontal Stabilization
- Support
- Reciprocation
Retainers: Where is horizontal stabilization? (2)
antero-posteriorly: proximal plates
laterally: reciprocal arm
Retainers: How do we achieve support?
Occlusal rest
Retainers: what is reciprocation and how is it achieved? (2)
- Counterbalance of lateral forces during insertion
- Reciprocal arm
What are the different types of retainers? (2)
- Direct
- Indirect
Characteristics of direct retainers? (2)
- Retain at the very place where they are
- Oppose to all movements
What are the types of retention mechanism for direct retainers? (2)
- Clasp
- Frictional
Characteristics of indirect retainers? (3)
- Passive
- Oppose to rotation around fulcrum line
- At a distance where they are
What do circumferential retainers consist of? (2)
- Minor connector (rigid)
- Retentive system
- Body of the retainer
What does the retentive system of the circumferential retainer consist of? (4)
- Occlusal rest
- Body
- Reciprocal arm
- Retentive arm
Circumferential retainers: Body of the retainer ?
Body of retainer joins many elements
Circumferential retainers: Body of the retainer functions? (3)
- Stabilization
- Connection
- Guide the path of insertion
Circumferential retainers: Body of the retainer connection function? (2)
- Arms (clasps) and occlusal rest
- Extension of the minor connector
Bar/contact point retainers: What does the proximal plate act as?
Acts as the reciprocal arm and body of the retainer at the same time
Bar/contact point retainers: What does the proximal plate do? (5)
- Limits and guides the insertion and removal path of the denture
- improves stability
- friction retention
- reciprocation
- reduces embrasures
Where is the occlusal rest placed?
- At occlusal surface of the tooth
- Over marginal ridges and fossae
Where is the occlusal rest put when they limit bounded edentulous space?
Occlusal rest must be near the space
Where is the occlusal rest put when they limit free-ended edentulous areas?
Occlusal rest must be far from the space
Occlusal rest must be _____ to comply with its functions
Rigid
Functions of the occlusal rest? (3)
- Support
- Prevention of tooth movements
- Help keep VD and occlusion
How does the occlusal rest help with support?
Prevents denture from embedding into the soft tissues
What movements does the occlusal rest help to prevent? (3)
- Rotations
- Migrations
- Inclinations
What should be the shape of the occlusal rest? (2)
- Rounded and slightly triangular
- Spoon shape
- Same width and length
Describe the thickness of the occlusal rest
Adequate thickness: importance of the articulator
What should the width of the occlusal rest be?
of 1/2 to 1/3 of the distance between cusps
Angle between body-minor connector and occlusal rest must be… (2)
Less than 90 degrees
coaxility of forces
If the occlusal rest is made at the anterior teeth then… (2)
- Its better to have it at the canines than at the incisors
- Better if they rest over the cingulum than the incisal edge
Circumferential retainers provide? (3)
- Retention
- Reciprocation
- Stabilization
Circumferential retainers clasp arms? (2)
- Retentive clasp arm
- Reciprocal clasp arm
Retentive clasp arms: What determines the amount of retention? (3)
- Cervical convergence angle
- How deep the retentive arm goes below the undercut area
- Flexibility of the retentive arm
Retentive clasp arms: Cervical convergence angle? (3)
- Path in insertion
- Shape of the tooth
- Survey line
How deep the retentive clasp arms goes below the undercut area: undercut gauges? (3)
- Measure the horizontal depth of the undercut
- Rest over the survey line and at a point below it
- Gauges of 0.25, 0.5 and 0.75
Retentive clasp arms: how deep the retentive arm goes below the undercut area is influenced by?
The cervical convergence angle
What does length of the retentive clasp arms do to flexibility?
Length of arm increases flexibility
What does the diameter of the retentive clasp arms do to flexibility?
Smaller diameter = more flexibility
What does shape of the section of the retentive clasp arms do to flexibility?
Circular section = more flexibility
What does the manufacturing technique of the retentive clasp arms do to flexibility? (2)
- Wrought wire = more flexibility
- Cast
Where are the reciprocal clasp arms located?
Over the survey line
The reciprocal arms counterbalance…
forces made by retentive arms when crossing the survey line
Reciprocal arms require a flat surface parallel to…
the path of insertion
Design principle of circumferential retainers: encirclement?
- more than 180 degrees
- ideally 3/4 = 270 degrees
First 4 design principles of circumferential retainers?
- encirclement
- occlusal rest for support
- rigid reciprocal arm over survey line
- same amount of retention for all abutment teeth
5-8th design principles of circumferential retainers?
- minimum efficient possibile retention: 0.25mm
- all the retentive arms through lingual or buccal surfaces
- Passivity
- Tapered retentive arm
Circumferential retainers: Why are the retentive arms through lingual or buccal surfaces?
To prevent torsion
How does a circumferential retainer display passivity?
Retentive portion of retentive arm must be inactive after placement
How is the circumferential retainer arm tapered?
Only last third is under the survey line
9 th and 10th design principles for circumferential retainers?
- Tip ends at line angles not at the center of the surface
10. At a minimum of 2mm of the gingival margin
Another name for Akers clasp? (2)
- E clasp
- Ney’s n.1 clasp
Akers clasp arms?
- Come up from the body of the retainer
- final 1/3 of the arm is more flexible
Akers clasp has a ________ section
half-pipe
Main indication of akers clasp?
Bounded edentulous areas
Ackers clasp advantages? (4)
- Embrace whole perimeter of tooth
- Stability
- Force spread
- Reciprocation
Ackers clasp disadvantages? (2)
- Inability to avoid deep undercuts
- not aesthetic at anterior teeth
Why can’t an ackers clasp avoid deep undercuts?
Because its only flexible at the final 1/3 of the retentive arm
What is another names for the reverse ackers clasp?
Reverse E clasp
Whats the difference between an akers clasp and reverse akers clasp?
Same retainer as an akers but it faces the edentulous area
What is another name for a bonwill clasp? (2)
- Double akers clasp
- Embrasure clasp
When do we use a buch and carmona clasp? (2)
- Reduces food retention
- Used over a modified crown
What is another name for a C clasp? (2)
- Hair pin clasp
- Reverse action clasp
When do we use a C clasp? (2)
when an undercut area is next to:
- The minor connector
- The occlusal rest
What do we use a single continuous arm clasp for?
Dont know
When do we use the nally-martinet clasp?
in free ended edentulous areas
What do we use the back action clasp for?
For posterior isolated teeth
What do we use a ring clasp for?
For posterior isolated teeth
What do we use multiple clasp for?
Dont know
What are the types of bar clasa?
- Roach clasps
- RPI
- RPA
What are the types of roach clasps? (4)
- I-bar
- Y-bar
- T-bar
- Modified T-bar
What do roach clasps have? (3)
- Occlusal rests
- Reciprocal arms
- just like circumferential retainers
What are bar clasps called?
Infrabulge clasps
Why are bar clasps called infrabulge clasps?
Because their retentive arm comes up from below height of contour (survey line)
Indications for bar clasps?
Adjacent to edentulous area
How do roach clasps achieve their great flexibility? (2)
- Circular section
- Long retentive arm
Roach clasps in comparison to circumferential clasps? (3)
- Less support
- Less stability
- Less encirclement
Roach clasps and undercut areas?
They can reach deeply undercut areas
Roach clasps and forces?
transmit milder forces due to the flexibility
Where does the I-bar clasp contact the tooth?
Contacts tooth at only one single point
Difference with all the bar clasps?
Ask
What does RPI stand for?
- Rest
- Proximal plate
- I-bar clasp
How far away should the RPI from the soft tissues?
3-6mm
What is the advantage of the RPI? (2)
- More esthetic
- Minimum tooth and gingival contact
What is the disadvantage of an RPI?
Less encirclement
What are the contraindications of the RPI? (4)
- Shallow vestibule
- Frenulum
- Tooth greatly inclined buccaly
- Tissue undercuts
What does RPA stand for?
- Rest
- Proximal plate
- Akers clasp
When do we use an RPA? (5)
when the RPI is contraindicated:
- Shallow vestibule
- Frenulum
- Tooth greatly inclined buccaly
- Tissue undercuts
Where is the fulcrum line in free-ended biomechanics?
At the most posterior occlusal rests
What happens with everything behind the fulcrum line?
Will move towards the tissues
What happens with everything in front of the fulcrum line?
will tend to separate from teeth
What is a wrought wire clasp? (4)
- Not cast retainers
- Prefabricated
- great elasticity
- Acceptable retention and reciprocation
Wrought wire clasp indication? (2)
- Tissue supported RPD
- Bad periodontal support of remaining teeth
What is a frictional retainer?
- The closely fitting fiting part (female matrix) is usually within the normal or expanded contours of the crown of the abutment tooth
- Metal receptacle (male PATRIX) is attached to a pontic or denture framework
What are frictional retainers more commonly known as?
Attachments
Frictional retainers are used for…? (3)
Combined prostheses:
- Fixed partial denture
- RPD
What is an indirect retainer?
Assists the direct retainer in preventing displacement of the distal extension denture base by functioning through level action on the opposite side of the fulcurm line when the denture base moves away from the tissues in pure rotation around the fulcrum line
What does an indirect retainer do in free-ended RPDs?
Prevents rotation around fulcrum line
An indirect retainer is more effective…
Farther away from fulcrum line
What type of RPD do we use an indirect retainer for?
Tooth-tissue supported
Where is the best place to put an indirect retainer?
- Better at a premolar than at a canine
- Better at a canine than at an incisor
How are indirect retainers classified? (2)
- Rests
- Major connector
How are indirect retainers classified by rests? (2)
- Occlusal rests
- Incisal rests
How are indirect retainers classified by major connector?
- Any maxillary MC forward of fulcrum line
- Lingual plates and double lingual bars
If an indirect retainer has to be located at an incisor… (3)
- Better over the cingulum
- Rests over incisal edges are unaesthetic
- Better over several incisors
If a major connector is located infront of the fulcrum line…
They act as an indirect retainer
If there is an upper diastema the major connector ends at…
the palatal rugae
Along with lower major connectors, these also operate as indirect retainers…
What do they need? (3)
- Lingual plate
- Double lingual bar
*Need cingular rest seats
Indirect retainer effectiveness? (2)
- Good seats - axial forces
- Maximum distance from fulcrum line
Indirect retainers function? (3)
- Prevent movements of free-ended bases
- Reduce oblique forces over abutment teeth
- Should be passive at rest and active at function
