RPD Flashcards
Components of an RPD
Each component has a name that is descriptive of its function:
major connector, minor connector, rests, direct retainers/clasps, indirect retainers, guide planes, base supporting replacement teeth
RPD must have
1) support derived from the abutment teeth through the use of rests
2) from the residual ridge through well fitting bases
3) stabilized against horizontal movement through the use of rigid connectors, indirect retainers
4) sufficient retention to resist reasonable dislodging forces
RPD Max & Mand Frameworks
Properties of the major connector
rigidity
not impinge on soft tissue
not placed on movable tissue
cross arch stability
connects all components
resists flexure
provide a means for placement of one or more denture bases
makes sure that parts are unified and effective
Mandibular MC: Lingual bar, lingual plate
Sublingual bar, lingual bar with cingulum bar, cingular bar
labial bar
Lingual Bar
above the movable tissue in the floor of the mouth
below the gingival margin
half pear shaped: superior margin is tapered and the inferior is rounded 4mm below
Mandibular Connector
height of the floor of the mouth measurement:
tongue lightly touching vermillion border of the upper lip - raises the floow of the mouth
measurement can be transferred to the case - indicates location of the inferior border of major connector - 8 mm from free gingival margin to the elevated floor of the mouth
Lingual plate
lingual frenum is too high
space for the lingual bar is limited - the superior border of the bar would be too close to the gingival tissue
plate permits the inferior border to be placed superiorly - avoiding tongue or gingival irritation
half-pear shape as w/ the bar & thin as technically possible incisally & follow the contour of the teeth and embrasures
bracing & stabilizing effect for periodontally challenged mandibular anterior teeth
Lingual Bar vs. Lingual Plate
Bar: superior border of the bar 4 mm below gingival margin of anterior teeth.
Inferior border of bar should not impinge on the movable tissue of the floor of the mouth
Plate: if inferior border of the bar is impinging on the tissue fo the floor of the mouth
if mandible tori is present
Maxillary Major Connector
In contrast to the mandible, the maxilla has no movable tissue as in the floor of the mouth
tissue covering the palate has firm submucosal connective tissue and good blood supply
Variety of maxillary major connectors:
single palatal bar
single palaral strap
U-shaped
anterior-posterior bar
anterior-posterior strap
full palatal
Location of the Major Connector
Maxillary: superior border located at least 6mm below free gingival margin
8mm in width
Single palatal strap:
Kennedy Class III
short edentulous areas
needs additional bulk in thickness
interfere with speech 8 mm in width
Anterior-posterior strap
any kennedy class
flat min of 8mm in width
max torus interferes in placement
weak perio support
flexure is non-existent
anterior strap can be extended to support an anterior edentulous area
Palatal Plate
Kennedy Class I
anterior edentulous area
can be uniformly thin
reproduced the anatomic contour
more acceptable to the tongue
U-shaped
used in particular in case of torus palatinus
patient that has had u-shaped before
interferes with speech
less rigid therefore made thicker
Single Palatal Bar
less than 8 mm in width
made thicker for rigidity
poor patient acceptance
Anterior-posterior bars
not used frequently
requires bulk for strength - interferes w/ speech
Indications for Max MC
weak perio support of the remaining teeth-more of the palate uncovered: A-P strap
long span distal extension, need more rigidity: A-P strap
anterior teeth to be replaced: A-P strap, u-shaped, or complete palate
torus present: u-shaped
modifying factors: number & location remaining teeth, perio support, type of opposing occlution
Minor connectors
primary function: connecting link between the major connector and the other components of the prosthesis (RPD)
distributes forces to the teeth and ridge tissues
rigid, at same time min bulk, conform to the interdental embrasure
Types of minor connectors
clasps assemblies
indirect retainers & auxiliary rests
denture bases
bar-type clasps
Rests
forces that are applied to an RPD must be transferred to the supporting teeth and tissue
rests are the components of an RPD that transfer the forces down the long axis of the abutment teeth
the prepared areas of the abutment teeth in which the rest fits is called the rest seat
Primary function of the Rests
maintains components in planned position
maintains established occlusal relationships prevents settling of the RPD
prevents impingement of soft tissue
directs and distributes occlusal (vertical) loads to long axis of abutment teeth
Types of Rests
occlusal rests - occlusal surfaces of posterior teeth
lingual or cingulum - lingual surfaces of anterior teeth
incisal - incisal edges of anterior teeth
Occlusal Rests
rounded triangular form w/ apex toward center of occlusal surface
should be as long as wide
marginal ridge is lowered for strength & rigidity at the rest-minor connector
floor of rest at the most internal is slightly deeper than the marginal ridge
angle formed between the rest & the vertical minor connector: <90 degrees
angle greater than 90 degrees - forces not transmitted down long axis
Lingual/Cingulum Rests
lingual rest is preferred to an incisal rest
closer to horizontal axis thus less tendency to tip
more esthetic
slightly rounded V
apex of the V is incisal
placed at the junction between the gingival & middle 1/3
Incisal Rests
placed at the incisal angles of anterior teeth
used indirect retainers
little less tooth structure removed
provide stabilization perio compromised tooth
floor inclination to long axis of abutment
least esthetic
select clinical situations
Direct Retainers/clasps
direct retainer: a component of the RPD that prevents/resists the displacement of the prosthesis during function
unit of the RPD that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from seat tissues (abutment teeth & soft tissue)
retention: quality inherent in a prostehsis acting to resist the forces of dislodgement along the path of placement
resists forces that want to dislodge a prosthesis during function
Direct retainer - extracoronal
uses mechanical resistance to displacement through components placed on or attached to the external surfaces of an abutment tooth -> clasp/direct retainer
most common method of extracoronal direct retention
clasp assembly of which the retentive element is the metal clasp arm with limited flexibility
requirement of the clasp assembly
retention: resists forces acting to dislodge RPD away from the supporting tissues
support: resists displacement of teh RPD apically
stability: resists displacement in a horizontal direction
reciprocation: counter acts lateral displacement of an abutment when the retentive arm passes over the hieght of contour
encirclement: prevents movement of the abutment away from the assembly
passivitiy: retentive arm is passive until a dislodging force is applied
clasp assembly
part of teh RPD that acts as a direct retainer and/or stabilizer for a prosthesis by partially encompassing an abutment tooth
components are: retentive arm, reciprocating arm, minor connector, rest
all components of the assembly should be passive
retentive part of the retentive arm is only activated in the presence of dislogement
clasp arm assembly
clasp assembly
components are:
retentive arm: B
reciprocating arm: C
minor connector: D
rest: A
demonstrates the location of the clasp components in relation to the crown or abutment thirds
buccal - retentive arm
lingual - reciprocating arm
encirclement
more than 180 degrees in the greatest circumference of the abutment must be engaged by the clasp assembly
reciprocating arm - functions and requirements
intended to resist tooth movement in response to the deformation of the retentive arm as engages the height of contour
must be rigid
must contact the abutment tooth at or occlusal to the height of contour
when RPD is fully seated - reciprocating arm is passive
height of contour
greatest convexity
guideline: used as a guide in the placement of retentive arms and reciprocating arms
area of cervical convergence: below the height of contour - retentive clasp components
area of occlusal convergence above the height of contour - reciprocating components
types of clasp assemblies
suprabulge: retentive clasp that approaches the undercut from the occlusal or incisal
infrabulge: retentive clasp that approaches the undercut from the apical direction
Three distinct segments of a suprabulge clasp
s: shoulder - originates from the minor connector
m: midsection - relatively flexible and approches the height of contour
t: terminus - crosses the height of contour and engages the undercut
suprabulge
cast circumferential/Akers:
simplicity in design
disadv. - large amt of tooth structure covered
rules: originates from above the height of contour
retentive terminus should be directed occlusally
terminate at the distal or mesial line angle
combination clasp
less stress on the abutment
wrought wire: soldered to the RPD versus cast as part of RPD
wrought wire: round
soldered to RPD framework
factors influencing clasp retention
based on retention to deformation (must be in an undercut where the clasp is forced to deform on placement and removal)
retention is produced by:
tooth factors - undercut and how far clasp is placed into undercut
prosthesis factors - flexibility of the clasp arm, material of clasp arm
Flexibility of the Clasp
the length-longer, the more flexible
the diameter-greater diameter, less flexible
cross-section - can limit flexibility e.g. half round one dimensional flexure v. round can flex in all directions
all cast metals have flexibility proportional to the bulk of metal and type of metal
wrought wire - flexes in all directions & greater flexibility w/out fracture due to tensile strength that is greater than cast clasp - increase flexure w/ less bulk
wrought wire vs. cast clasp
RPD Clasp - RPI
R - rest, P - proximal plate, I - “I” bar clasp (infrabulge)
used in a Kennedy Class I, II
case: moves fulcrum to mesial
less tipping force when denture base is in function
used also in other classifications
RPI Clasps
Fulcrum: axis about which the denture will rotate when the denture base moves away from the residual ridge
RPI: the mesial rest of the clasp moves the fulcrum mesially
Indirect Retainers
resists rotational displacement of the denture base away from the supporting tissues
*a Kennedy Class III - tooth supported/borne RPD has adequate support and retention to resist functional displacement - no indirect retainers needed
fulcrum: axis about which the denture will rotate when the denture base moves away from the residual ridge
Axis: passes through the most posterior rests on each side of the arch
Levers
all levers consist of a rigid bar, fulcrum, an object to be moved, and an applied force
efficiency of the lever system depends on the arrangement of the fulcrum, object, and the force in relation to the bar
Indirect retainer effectiveness
activated during rotation
distance from the fulcrum: the farther the indirect retainer is from the fulcrumm, the more efficient
rigidity
placed in a definite rest seat
guide planes
2 or more parallel vertical surfaces of abutment teeth
these parallel surfaces direct the prostesis during removal insertion
gives positive direction during placement and removal
contribute to the retention of the prosthesis when the dislodging forces are other than parallel
eliminates gross food traps between abutment teeth and components of the RPD
denture base
primary function:
supports the artificial teeth
receives the functional forces
transfers the forces to the supporting structures
the transfer of forces is most important for the distal extension prosthesis
denture base 1
primary function is related to masticatory function
cosmetic effect of the replacement particularly in the anterior area - natural effect as to contour & shade
stimulation of the underlying tissues - tissues under functional stress w/in their physiologic limits maintain their form and tone better
denture base 2
primary retention of an RPD is mechanical by direct and indirect retainers
secondary retention is by intimate contact w/the underlying tissues by adhesion and cohesion
adhesion: attraction of saliva to the denture and to underlying tissue
cohesion: attraction of the saliva molecules to each other
Finishing lines
junction - between the major connector and the minor connector
90 degree butt type joint
forms interface between major connector & denture base material
tissue stops
master cast with relief wax and tissue stop drawn on cast
refractory cast with tissue stop drawn on cast
RPD wax pattern on refractory cast w/ tissue stop waxed in as it was drawn prior
tissue stop in contact with the ridge and a space under framework where relief wax had been
dental surveyor
to locate the most desirable path of placement & remove removal of an RPD
path of placement: direction in which the RPD moves from point of initial point of contact to terminal resting position with rest seats seated and denture base in contact w/ the supporting tissues
to locate path of removal: the reverse of placement
to identify tooth surfaces to act as guide planes
dental surveyor
to locate and measure undercut areas of abutments to be used for the retentive arm of a clasp assembly
to determine whether teeth and/or soft tissue areas that could be an interference that need alteration or removal
to determine path of placement that will allow esthetic clasp placement
determine heights of contour
determine cast position for future references
locate soft tissue undercut areas
determine relative parallelism of proximal surfaces of all of the potential abutment teeth
dental surveyor
Dental surveyor
dental surveyor components
surveyor steps for design
RPD support: tooth or tooth-tissue
abutment teeth
potential guide planes
undercuts
heights of contour
tripoding
rests and potential clasps
indirect retainer
major connector
minor connectors
surveying steps: additional considerations
occlusal plane approx. parallel to base of surveyor platform
retentive tooth areas - try for uniformity/balance
determine interferences - bone undercuts, malpositions teeth, etc…
will path in insertion satisfy esthetics?
surveyor: analyzing
analyzing rod attachment for the surveyor spindle
analyzing rod in place to initiate evaluation of the cast
*analyzing rod perpendicular to the occlusal plane
surveyor - analyzing rod
analyzing rod initial position perpendicular to the occlusal plane
visible black dot on ball joint indicates that analyzing rod is perpendicular to the occl. plane
analyzing for parallelism
5 distal proximal
abutments #21, 28, & 31
potential path of placement
locating proximal surfaces of relative parallelism of and potential guide planes (proximal surfaces of abutment teeth adjacent to an edentulous area)
potential guide planes
locating proximal surfaces of relative parallelism of proximal tooth surfaces and potential guide planes
proximal surfaces of abutment teeth adjacent to an edentulous area
abutment teeth
max #5, 12, & 15
mand #21, 28, 31
Tooth undercut
view of an undercut using an analyzing rod
triangle formed:
abutment tooth
surveyor rod
gingival tissue
undercuts gauges
2 sizes:
.25 mm (.010 in.)
.50 mm (.020 in.)
undercits marked in red
measuring undercut
12 undercut guage .25mm - mesial buccal
undercut present when:
shank of undercut gauge contacts height of contour
simultaneous contact of the lip of the undercut guage in the infrabulge area indicates definite degree of undercut and location
soft tissue/ridge analysis
analyzing rod evaluating edentulous ridge for undercuts and possible interferences with the denture base placements
tripoding
three lines on the lingual surface of the cast made w/ survey leadwith vertical arm in a locked position
relates cast to surveyor
lines should be in divergent areas
denture base
tooth-tissue supported:
as the distance from the abutments increases, the ridge support increases in importance
knowledge of the limiting factors e.g. frenum & mylohyoid muscle
Good Basic Drawing Example
AP strap, guide planes, RPIs, Occlusal rests, cingulum rests, finish lines, tissue stops
drawing
remember - retentive forces need to be balanced. “retention must include one buccal retentive area on the right. Can not have L retention on one side and B on the other
dr geaman’s drawing example
Lingual plate & guide planes
drawing - lingual bar
lingual bar (lingual plate option), retention wedding, tissue stops, cingulum, rests - indirect retainers, tripod marks
RPD drawing
maxilary minor connector, occlusal rest & tissue stop
survey lines, cingulum rest, occlusal rests, reciprocating arms, finish lines, retention wedding, tripod maring
guide plane
Tip should end slightly above undercut. I bar has retentive and stabilizing features
Akers Clasp (type of circumferential clasp): not position relative to survey line
Lingual retentive arm - buccal reciprocation is above survey
