RPD Basics and Design Theories Flashcards
What are some indications for RPD’s?
- Long edentulous span
- Resorbed ridge
- Reduced periodontal support
- Cross-arch stabilization
- No posterior abutment
- Physical or emotional problems
- Multiple edentulous spaces
- Esthetics
- Patient desires
- Financial Implications
Where does stability come from for RPD’s?
- Guide planes
- Reciprocation
- Lingual Plating
- Rests
- Denture Base
What are the advantages of FDP’s Supported Prostheses vs. RPD?
- Not “removable”
- Excellent anteroposterior stabilization
- Small size
- Less requirements for adjustment/repairs
- Support at both ends
When you have a tooth or implant borne RPD, where are the functional forces applied?
Remaining Teeth or Implant
If you have a mucosa borne RPD, where are the forces distributed?
They transmit equitably to mucosa AND remaining teeth
Describe the 3 fulcrum lever systems…
First Class: Like a teeter-totter
Second Class: Like a wheel-barrow
Third Class: Man fishing on dock
What is the most efficient type of fulcrum (lever class)?
1st Class Lever…
Tissue compression up to 2 mm
Example: Distal Extension RPD on Mandible
What is an example of a 2nd Class Lever?
Maxillary Distal Extension RPD
What is an example of a 3rd class lever?
Tooth borne RPD, with sticky foods lifting the RPD opposite from the ridge…
Define Kennedy Class I and II…
- Kennedy Class I: bilateral edentulous areas located posterior to the remaining natural teeth
- Kennedy Class II: unilateral edentulous area located posterior to the remaining natural teeth
Describe Kennedy Class III & IV…
- Kennedy Class III: edentulous areas with natural teeth located both anterior and posterior to it
- Kennedy Class IV: a single edentulous area located anterior to the remaining natural teeth
Of the wonderful 8 rules of Applegate…what are the first two?
- Classification should follow rather than precede extractions that might alter the original classification
- If a third molar is missing and not to be replaced it is not considered in the classification
Of the 8 wonderful rules of Applegate…what are rules 3 and 4?
- If a third molar IS present and is to be used as an abutment, it IS considered in the classification
- If a second molar IS MISSING and is not to be replaced, IT IS NOT considered in the classification
What are rules 5 and 6 of Applegate?
- The most posterior edentulous area or areas always determines the classification
- Edentulous areas other than those determining the classification are referred to as MODIFICATION spaces and are designated by their number
Finally, of Appliegate’s 8 rules…what are rules 7 and 8?
- The extent of the modification is not considered, only the number of additional edentulous areas
- There can be no modification areas in Class IV arches. Any edentulous area lying posterior to the single bilateral area determines the classification
What must a Kenedy Class I prosthesis provide for?
- Adequate support for the distal extension denture base
- Flexible direct retention
- Indirect retention
For a Kennedy Class II Prosthesis, what design perameters should you consider?
- Has Features of both Class I and III designs
- The dentulous side (if modification space is present) must be designed as a Class III RPD
- The distal extension side must be designed as a Class I RPD
- Indirect retentative retainer: flexible
What design perameters should you consider when treatment planning a Kennedy Class III Prosthesis?
Tooth (&impl) supported:
- Supported at both ends
- Does not move during function
- Indirect retention may be needed if direct retention is not obtained on one or more teeth
- Rest seat preferably adjacent to edentulous areas
What design perameters should you consider when treatment planning a Kennedy Class IV Prosthesis?
Must be regarded as a Class I denture in reverse (especially if long edentulous span)
- Forces of rotation aroudn ANTERIOR abutment teeth
- Indirect retention must be obtained POSTERIOR to the fulcrum line
What are the 4 RPD Components?
- Major Connector
- Minor Connector
- Rest
- Clasp Assembly
Define Major Connector…
“The part of a removable partial denture that joins the components on one side of the arch to those on the opposite side”
What are 4 Major Connector Requirements?
- RIGIDITY
- Avoid impingement of the free gingival margin
- Avoid creating food traps
- Patient comfort
Can you name 6 Maxillary Major Connectors?
- Posterior palatal bar
- Anteroposterior palatal bar
- Palatal strap
- Anteroposterior palatal strap
- Horseshoe
- Complete palate: metal/acrylic resin
What 4 things should you keep in mind when Beading the Maxillary Framework?
- Beading depth and width of 0.5 - 1.0 mm
- Fades out 6 mm from free gingival margin
- Prevents collection of food under major connector
- Allows thinning of metal at borders
Can you name 4 Mandibular Major Connectors?
- Lingual Plate
- Double Lingual Bar
- Labial Bar
- Lingual Bar
What are 4 reasons to use a Lingual Plate?
- Inadequate space for bar
- Can splint/brace periodontally compromised teeth
- May add to if anticipate tooth loss later
- More comfortable than lingual bar
What is the minimum space required for a lingual bar?
- 8 (7) mm from the gingival margin to the floor of the mouth
- 3 mm from free gingival margin to superior border of the bar
- The bar should be at least 5 (4) mm in height
Define Minor Connector…
“The connecting link between the major connector or base of a RPD and the other units of the prosthesis, such as the clasp assembly, inddirect retainers, occlusal rests, or cingulum rests.”
What are 2 aspects or characteristics of a Minor Connector?
- Must be rigid
- Transfer functional stress to teeth and ridge
Can you name 4 types of Rest Seats?
- Occlusal Rest - proximal, channel
- Cingulum Rest
- Incisal Rest
- Lingual Rest - resin bonded, “Ivanhoe”, dimple
Can you name 5 function of a rest?
- Directs forces (vertical and lateral) along long axis of tooth (support)
- Vertical stop
- Can function as an indirect retainer in distal extension areas
- Prevents tooth extrusion, food impaction
- Correction of occlusal plane (occlusal onlay rest)
What are 5 design characteristics to keep in mind when prepping an Occlusal Rest?
- Triangular and concave shaped
- Rounded apex
- Should follow the fossa outline
- Inclined towards the center of the tooth
- Should allow for minimum 1.0 mm metal thickness
What design parameters should you keep in mind when prepping a Cingulum Rest?
- Chevron (“V”) shaped
- Must be gingival to occlusal contacts
- ONLY indicated on maxillary cuspids
- Bonded rests
What is an Incisal Rest?
Rounded “V” shaped notch, extends onto facial surface of the tooth
What design parameters should you keep in mind for Incisal Rests?
- Place 1.5 to 2.0 mm from the proximal - incisal angle
- Place at mesial cusp ridge for bar clasps
- Distal cusp ridge for circumferential clasps
Define Direct Retainer…
“That component of a RPD used to retain and prevent dislodgement, consisting of a clasp assembly or precision attachment”
What 2 types of Direct Retainers are there?
- Extracoronal
- Intracoronal
What are the different parts of a clasp?
- Rest
- Body
- Shoulder (above contour line)
- Reciprocal arm (above)
- Retentive arm (above)
- Retentive terminal (below)
- Minor connector
- Approach arm
For clasp design, what must it provide?
- Vertical Support
- Stability (bracing)
- ENCIRCLEMENT
- Retention
- Reciprocation
- Passivity
Define Reciprocation…
“The mechanism by which lateral forces generated by a retentive clasp passing over a heigh of contour are counterbalanced by a reciprocal clasp passing along a reciprocal guiding plane.”
What is the Flexibility of Clasps affected by?
- Length
- Taper
- Diameter
- Cross-sectional form
- Material
What are the undercut measurements for Chromium Allow, Titanium, Gold, and Wrought Wire?
- Chromium Alloy - 0.010”
- Titanium - 0.010”
- Gold - 0.015”
- Wrought Wire - 0.020
What are the 4 types of Clasp Designs?
- Circumferential Clasp
- Bar Clasp
- Suprabulge
- Infrabulge
What are some different clasp designs of Circumferential Clasps (Aker’s Clasp)?
- Simple Circlet (reverse and multiple circlet)
- Combination Clasp
- Embrasure Clasp
- Ring Clasp
- Hairpin Clasp
- Onlay Clasp
What are some Circumferential Clasp Design Features?
- Clasp should originate from framework above the height of contour
- Retentive tip directed OCCLUSALLY ideally at junction middl and gingival 1/3
- Terminate at line angles
- Retentive arm positioned as far apical as possible
Can you name the 4 different Bar Clasps?
- T-Bar Clasp
- Modified T-Bar Clasp
- I-Bar Clasp
- Y Clasp
Describe 5 characteristics of an I-Bar…
- Exact placement of retention contact
- Minimal interference with natural tooth contour
- Maximum natural cleansing action
- Passive functional movement of an extension prosthesis
- Reduced metal display, better esthetics
What are 5 design characteristics of an I-Bar?
- Bar must cross the tooth-tissue junction at right angles, parallel to long axis of tooth
- Retention in 0.01 inches, oval-shaped contact
- Tip of I-Bar kept below the survey line
- Origin of approach arm located between the denture teeth
- “Push” type of retention
What are 4 key Bar Clasp Design Features?
- No impingement on tissues
- Approach arm pass perpendicular to gingival margin
- Approach arm should be uniformly tapered
- Clasp terminus should be positioned as far apically as possible
Define Indirect Retainer…
“The component of an RPD that assists the direct retainer(s) in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of hte fulcrum line WHEN THE DENTURE BASE MOVES AWAY from the tissues in pure rotation around the fulcrum line.”
Define Indirect Retention…
“The effect achieved by one or more indirect retainers of a RPD that reduces the tendency for a denture base to move in an occlusal direction or rotate around the fulcrum line.”
What are 4 functions of Indirect Retainers?
- Counteract lifting forces
- Increase stability and support
- Prevent mucosa impingement by lingual bar
- Stabilize the framework during relining
What 3 factors contribute to Effectiveness of Indirect Retainers?
- Needs definitive rest seat
- Distance from fulcrum line
- Major and minor connector rigidity
What are some uses of a Surveyor?
- Survey of diagnostic and master casts - locate and measure undercuts for fixed and removable prostheses
- Create measurable contours in wax patterns for fixed prostheses
- Aid in placement of precision attachments for fixed and removable prostheses
- Standard of Care
What is the Path of Insertion?
The direction in which the prosthesis is inserted and removed from the abutment teeth
- Governed by the minor connector
- Most prostheses have two or more insertion paths
- Too much tilt creates ineffective tooth contours
- Design for disloding forces
What are Guidling Planes?
- Flat surface
- 2-4 mm in occlusogingival heigh - dependent on Clasp Assembly
- Curved buccolingually
- Parallel tot he path of placement
Define Heigh of Contour…
“A line encircling a tooth and designating its greatest circumference at a selected axial position determined by a dental surveyor”
This contour will change position as the cast is tilted on the surveying table
Where to infrabulge and suprabulge undercuts fit relative to the height of contour?
- Infrabulge - portion of the crown apical to the survey line
- Suprabulge - portion of crown that converges toward the occlusal surface
What are some ideals for Height of Contour?
- Retentive tip junction of middle and cervial 1/3
- Reciprocation in Middle 1/3
- Ideal H/C placement guides toth reduction
What are 4 aspects of Retentive Undercuts?
- Depth for clasp alloy
- Deeper undercut allowed for large teeth and certain metals (gold alloy, wrought wires)
- Recontour/restore teeth if undercuts are not present
- Must be present on the tooth at the horitzontal tilt
What 3 dimensions are there for the Retentive Undercut?
- Occlusogingival
- Mesiodistal
- Buccolingual
What are 3 Philosophies of RPD Construction?
- Equalized Support (stress-breakers)
- Physiologic (functional) basing
- Broad stress distribution
How do you prevent excessive trauma to the remaining teeth and residual ridge?
Broad Stress Distribution!
Prevented by distributing the forces of occluusion to as many teeth and as much of the available soft tissue as possible
Accomplished by…the use of additional rests, indirect retainers, clasps, and broad coverage denture bases
What are some advantages of Broad Stress Distribution?
- Functional stresses are limited and distributed; over-stimulation is prevented
- The teeth and base area aid each other by bearing their proportianate share of stress
- Good indirect retention and stability for lateral forces
What are some Disadvantages of Broad Stress Distribution?
- Additional supports and contacts on teeth may cause irritation
- Because of multiple contacts, the prosthesis may be more conducive to caries
What are some Biomechanical Considerations for RPD Design Philosophies?
- Location of rest
- Rotation in rest seat
- Arc of rotation
- Placement of retentive tip
- Freedom for guiding plane
- Clasp assembly requirements
Define Combination Clasp…
“A circumferential retainer for a RPD that has a cast reciprocal arm and a WROUGHT WIRE retentive clasp.”
An example of a Combination Clasp…
- Distal Rest
- WW Clasp to MF - 0.010 to 0.020 undercut*
What are some characteristics of Wrought Wire?
- Omnidirectional flexing
- Easily adjusted and repaired
- Smaller surface contact with tooth
- Flexibility of 18 ga. WW = 19 ga. cast round*
- Clasp can be easily distorted
How does Wrought Wire attach to framework?
- Solder/Laser weld the wire to the metal framework
- Solder remote from retentive arm
What gauge of Wrough Wire do you use for molar, short cuspid, premolars, small teeth, and short clasp arm?
- 18 ga. - molars
- 19 ga. - short cuspid, premolars
- 20 ga. - small teeth, short clasp arm
Describe a Bar, Distal Rest (BDR)…
- Bar (T-bar in 0.01 inch distal undercut)
- Distal Rest (with distal guiding plane)
- Rotation around distal rest*
- During function, retentive clasp moves interiorly and mesially
Describe a Modified T-Bar (Mesial Rest)…
- 1/2 T-bar placed into a distofacial undercut
- Mesial rest
- Distal proximal plate
- Retentive clasp moves inferiorly and mesially under function
What is a Kratochvil: I-Bar?
- Mesial rest, distal rest in adjacent tooth
- I-bar placed at greatest prominence of facial surface of abutment tooth
- Guide plane: line angle to line angle reciprocation
- Proximal plate on long distal guidling plane, from marginal ridge to the tooth-tissue junction and 2 mm onto attached tissue
- MUST PHYSIOLOGICALLY ADJUST metal-tissue contact area with chloroform/rouge
Describe an RPI (Kroll)…
- Mesial Rest
- Short Proximal Plate
- I-bar direct retainer (Mid F to MF)
What are 3 RPI Mechanics?
- Rotation occurs in area of mesial rest
- I-bar and proximal plate diengage from the tooth during function
- Mesial torquing and axial forces directed through mesial rest; abutment tooth is braced by the mesially adjacent tooth
What 3 factors contribute to an RPI Guide Plane?
- Distal guiding plane is 2-3 mm occlusogingivally, in the occlusal one third and 3-4 mm faciolingually
- The superior edge of the proximal plate contacts 1 mm of the inferior portion of the guiding plane (junction of occlusal and middle 1/3)
- Gingival portion of proximal plate is relieved with 30 ga. wax
For RIP, where is the I-bar placed relative to the greatest prominence of the abutment tooth?
Mesially
This enhances the reciprocation from the proximal plate and increases the gingival exposure between the approach arm and the denture base
What are 3 advantages of RPI?
- Minimal tooth coverage
- Minimal gingival coverage
- Good stress control
What are some RPI contraindications?
- Insufficient vestibular depth to place I-bar 3 mm from gingival margin
- Teeth with severe lingual tilt, no fcial undercut
- Soft tissue undercut below the abutment tooth
- Teeth with severe facial tilt
- Mouth with high lingual fllor in which linguoplating is indicated
What is RPA (RPTC) - Eliason?
Rest, Proximal Plate, Akers (Circumferential)
- Rest (mesial)
- Proximal plate (distal guide plate)
- Aker’s type clasp (circumferential clasp)
What is RPA (RPC)?
- Proximal plate and circumferential clasp move in a mesiogingival direction, disengaging from the tooth
- Placement of clasp arm OVER survey line is CRITICAL for proper function
What are 2 advanced concepts for RPD?
- Rotational Path (dual path, anterior to posterior, posterior to anterior)
- Twin Flex
What are some characteristics of Twin-Flex?
- 19 gauge Ticonium wire
- 0.010 inch undercut on the mesial or distal undercut of the abutment tooth
- Need 180 degrees of encirclement
