Before Midterm: Kennedy Classification/ Principles of Design I - Rest and Direct Retainers Flashcards
Kennedy Class, bilateral edentulous posterior to natural teeth:
Class 1
Type of denture to make for Class 1 and Class 2:
tissue supported
Kennedy Class, unilateral edentulous, posterior to natural teeth:
Class 2
Unilateral edentulous w natural teeth both anterior and posterior:
Class 3
Type of denture to make for Kennedy Class 3:
tooth supported partial
Kennedy Class, single bilateral edentulous crossing midline, anterior to natural teeth:
Class 4
Classification, before or after extractions?
after
If 3rd molar missing and not to be replaced is it considered in classification?
no
If 3rd molar is present and to be used as abutment is it considered in classification?
Yes
If 2nd molar missing & not to be replaced is it considered in classification
No
What determines classification?
Most posterior edentulous area(s)
How to name edentulous areas other than those determining classification:
modification spaces, designated by their #
When to replace 3rd molar via removable?
never
Options if 3rd is not in periodontally sound condition or if it s restoratively compromised.
May opt to place a rest on the tooth wo clasping it if you don’t want to use it as an abutment.
TF? Class IV will never have modification spaces.
T
prepared surface of the abutment into which a rest fits.
rest seat
What is the rest:
component of RPD that transfers forces down long axis of abutment, fits into rest seats of teeth
5 fxns of rest:
vertical support, maintain position, maintain occlusal relationships by preventing settling of partial, prevent impinging on soft tissue, direct and distribute occlusal loads to abutment teeth
Rests transmit forces here:
PDL instead of soft tissue
How do rests prevent soft tiussue injury:
by minimizing vertical displacement
Is the retentive clasp above or below HOC?
below
Wo the non-retentiv clasp or rests what would happen?
partial would be forced down and impinge upon soft tissue
What state does a partial assume when a partial is seated properly?
passive state
When seated properly the retentive clasp is actively engaging the tooth.
F. not engaging
When does the retentive clasp engage the tooth?
only when unseating forces are exerted
List 4 types of rests:
occlusal, interproximal, lingual, incisal
Interproximal rest is aka:
embrasure rest
3 types of lingual rests:
cingulum rest, inverted V rest, anterior lingual rest
Cingulum rest is aka:
ledge rest
anterior lingual rest is aka:
spoon rest
2 ways to change HOC:
change path of insertion OR grind tooth
Occlusal rests:
Triangular or bell shape, angle of floor of rest and guide plane < 90°, rounded at marginal ridge (to prevent fracture?)
Fxn of angle of floor of rest and guide plane < 90°:
better mechanical locking
Where is force directed on an occlusal rest?
perpendicular to the direction of force: off tooth for the rest, into tooth for tooth
Depth of occlusal ridge at marginal ridge:
1-1.5mm
Thickness of occlusal rest at thinnest point:
0.5mm
Follow this when making rest seat:
natural anatomy, mesial pit is lower than MMR, most central portion of seat will be thinnest
B-L dimension of occlusal rest for premolars and molars:
2.5mm or 1/2 distance bw summit of cusps
M-D dimension of occlusal rest for premolars and molars:
premolars: 1/ M-D length, molars: 1/4 M-D length
Marginal ridge and B/L embrasure reduction for interproximal rests;
1.5mm
Beware of this when making interproximal embrasure:
don’t break contact
What would happen if contact is broken while making interproximal rests:
teeth drift
Where are interproximal rests typically found?
side of arch that is not edentulous, like two occlusal rests side by side
Shape of occlusal portion of interproximal rest when viewed from B:
semicircle
lingual/ cingulum/ ledge rest for MaxC:
1mm L-L, 1,5mm I-A, 2.5-3mm M-D following cingulum
When does the vertical dimension becomes relevant?
Only if rest were providing reciprocation and you had a clasp on the facial aspect
This type of rest typically is not used on mandibular canines:
Lingual/ cingulum, ledge rest
Why aren’t Lingual/ cingulum, ledge rests typically used on mandibular canines?
enamel thickness not enough
Type of rest to use for mandibular canines;
spoon rest
What to do if If dentin is exposed on mandibular canine
Place restoration to protect, sensitivity to pt and caries risk.
Shape of lingual/ cingulum rest in X-section:
V-shaped
Fxn of V-shaped lingual/ cingulum rest in X-section:
prevents migration of abutment away from framework
TF? If it is not possible to make floor of cingulum rest less than 90’ it is ok to make the floor flat.
T
Inverted V rest dimensions:
1mm L-L, 1.5mm I-A, 2.5-3mm M-D following congulum
When are inverted V rests most commonly done?
survey crowns
Why are inverted V rests less frequently done?
req more skil
Dimensions of Incisal rest, mandibular canine:
1/3 M-D width, 1.5mm I-A, wider L than B, gingival wall less that 90’ to POT, axial wall parallel to POT, internal line angles rounded
Can we have incisal rests on maxillary canines?
yes, more often mandibular though
Negative aspect of incisal rest, mandibular canine:
aggressive, unesthetic
Beware of this common mistake when making incisal rest on man canine:
creating UC’s
Teeth for lingual spoon rests:
Max and Man anteriors, sometimes used on canines
Beware of this common mistake when making ilingual spoon rests:
creating dimple that is UC that would not provide POI
Type of edge created by lingual spoon rest:
feather edge
Lingual spoon rest is this shape in appearance:
ovoid
DImensions of lingual spoon rest:
2mm wide, 1mm deep
Verify this when prepping a rest seat:
adequate interocclusal clearance
What does the depth of prep for rest seat depend upon?
Amount of space you have bw seat and opposing cusp
If the DMR is the only POC, when the partial is not in the mouth, the tooth will be prone to:
shifting and super-eruption, leading to issues with the partial seating properly
When to prepare away the only occlusal contact of a tooth?
Never
TF? The reciprocal clasp is always occlusal to the retentive clasp.
T
Portion attached to clasps and rest that is parallel to long axis of tooth:
proximal plate
Fxn of direct retainer:
engages abutment to resist displacement of prosthesis away from basal seat
1’ retention:
direct retainers on abutment teeeth
2’ retentions:
minor/ major connectors, GP’s + denture base w underlying tissue in relation to each other
When to use major connectors for mandibular partials.
Never
The 3 sizes of UC measurements we have in our surveyor:
0.010’’, 0.020’’, 0.030’’
Clasp assemblies should meet these req’s:
retention, passivity, reciprocation, encirclement, support, stability (Retention PRESS)
Clasps should encircle a tooth by ___ degress
180’, only M or D surface not covered by clasp
Portion of retentive clasp tha engages UC:
terminus
This clasp assembly req ensures the clasp in maintained in ideal location
support
This clasp assembly requ ensure resistance to horizontal forces:
stability
Where does stability of partial come from?
reciprocal component, shoulders of cast circumferential retentive clasp, vertically oriented minor connectors (all resist hor forces)
Give 1 example of a vertically oriented minor connector:
proximal plate
Portion of clasp that is flexible:
terminus
Parts of a clasp:
shoulder, middle terminus
Minor connector connects to:
clasp body
Clasp shoulders connect to:
Clasp body
Clasp body connects to:
clasp shoulders, rest, and minor connector
Quality of clasp that counteracts lateral displacement of abutment when retentive clasp terminus passes over HOC
reciprocation
Location of reciprocal element of clasp:
At or above HOC
Result of not having a reciprocal clasp at all:
PDL trauma
Reciprocal clasp is used to:
stabilize and brace tooth
When should reciprocal clasp contact the tooth during removal?
same time as retentive clasp
Support via the reciprocal clasp are most necessary when:
retentive clasp engages HOC
Contact of both reciprocal and retentive clasps must be maintained until:
prosthesis is fully seated, to protect abutment from lateral forces
Reciprocal surface should be:
parallel to POI
This type of surface is better for reciprocal surface to increase efficiency:
Flat (check)
4 things that can make the reciprocal element:
cast claps, lingual plate, combo of M & D minor connectors, rests (in the sense of a lingual ledge rest)
Is a lingual plate a type fo proximal plate?
check
prevents movement of an abutment away from clasp assembly:
encirclement
When will a retentive clasp be more noticeable to pts tongue?
clasp terminates in a line angle
Prevents transmission of adverse forces to abutment when prosthesis is completely seated:
passivity
In which direction are forces being exerted when a retentive clasp is engaged?
L on more coronal portion of tooth, B on more apical portion
2 major types of clasps:
infra / supra bulge
3 types of suprabulge clasps:
circumferential, embrasure, combo
3 types of infrabulge clasps:
T-clasp, Modified T-clasp, I-bar
Modified T-clasp is aka:
1/2 T-clasp
Where are circumferential clasps typically used?
tooth-suppported partials, class 3
For what Class denture are circumferential clasps typically used?
Class III, natural teeth both A and P, some Class I
Required UC for circumferential clasp and where:
0.010’’ UC on surface farthest from edentulous area (M or D UC?)
Adv of circumferential clasps:
simple, effective design, close adaptation, min food entrapment
Disadv to circumferential clasps:
Lots of tooth covered, pot metal display for distal facing clasp
TF? Mesial facing circumferential clasps have a larger potential for display than distal.
F. distal
Effect of a large amt of tooth surface covered by circumferential clasps:
enamel, inc risk for decalcification and caries
Design rules for circumferential clasps:
originates above HOC, extends in a gently arcing mahner, terminal 3rd passes over HOC and extends into UC, clasp arm should end at M or D line angle (not mid-facial or mid-lingual)
This provides flexibility to clasps
tapering effect
Didn’t we say that pts tongue is more likely to notice the clasp if if ends at the line angle?
check?
To where should the terminus of a circumferential clasp extend?
to M or D line angle
Embrasure clasps originate:
above HOC
UC for embrasure clasp:
0.01’’
Where are embrasure clasps mostly used?
side of arch where there is no edentulous space
Embrasure clasps:
originate above HOC, extend in a gently arcing manner, terminal 3rd passes over HOC and extends into UC (0.01”), mostly used on side of arch where there is not edentulous space
Sometimes this allows for reciprocation in an embrasure clasp:
proximal plate (?)
Parts of combination clasp:
occlusal rest, reciprocal clasp, wrought-wire retentive clasp
How is wrought wire formed?
Wire formed by drawing a cast structure through a die into a desired shape and size
Wrought wire is used for:
PFD clasps and ortho appliances
Portion of combo clasp that is formed from a different type of metal:
Retentive clasp and lingul surface of distal extension
Adv of wrought wire:
minimizes force on tooth, less lateral force, round in X section (not half round like cast claps) can flex in different dimensions, half round: flex in 1 plane
Wrought-wire clasps allow flexure in this/ these directions:
all directions
Wrought-wire in __ -in X-section:
circular
These are stress releasing clasps:
wrought-wire and infrabulge
Type of clasp commonly used w distal extension partials, Class I or II
combo clasp
TF? Combo clasps can be used in deeper UC, up to 0-.020”.
T, bc they are more flexible
Combo clasps are indicated on:
abutment adjacent to distal extension, Class 1 or 2
Where should the UC be located for combo clasp:
MB line angle
How is the retentive clasp added on in combo claps?
soldering
Disadv of combo clasps:
additional steps (soldering), susceptible to distortion (more flexible), less bracing/ stabilization than circumferential
Adv of combo clasp:
can adjust multiple times since it is soldered on, cast clasp can only be adjusted a couple times before it distort/ breaks
TF? Pts w combo clasps will return for adjustments less freq than those with cast claps.
F. more freq
Advantages of infrabulge clasps:
stress-releasing, esthetics, no clasp shoulder
Why do infrabulge clasps have better esthetics?
no clasp shoulder
Portion of suprabulge clasps that can lead to poor esthetics:
clasp shoulder
Disadv of infrabulge clasps:
greater flexibility of approach arm dec bracing ability, can’t be used w excessive soft-stissue UC
Indicatons for T clasp:
abutment adjacent to distal extension Class I or 2 arch)
UC for T clasp should be here:
DBline angle (MB for combo)
How deep should the UC be for T clasp?
0.01”
The T clasp should cross this at a 90’ angle:
free gingival margin
Contraindication for T clasp:
approach arm crosses severe soft tissue UC (bc this would lead to food impaction? check?)
If approach arm is more than __mm away from soft tissue UC it will be too far away from skin and will bother pt.
1mm
What are the main causes of severe soft tissue UC?
check
When to use modified T clasp:
only if esthetics are an issue
Modified T clasps lack:
M clasp projection
Adv of modified T clasp:
cleanable bc less coverage of abutment, esthetics
Disavd to Modified T clasp:
less bracing/ stability
Why can’t a modified T clasp be done on the distal?
bc this would not create encirclement of the tooth (?check?)
Indications for modified T clasp:
abutment adjacent to distal extension (class 1 or 2) in esthetic region
Location of UC for Modified T clasp:
DB line angle, same as regular T clasp
Size of DB line angle UC for modified T clasp:
0.01”
Modified T clasp approach arm should cross the free gingival margin at ___ degree angle.
90’
Indications for I bar:
abutment adjacent to distal extension (Class 1 or 2)
Location of UC for I bar:
mid-B or MB line angle
UC size for I bar:
0.01”
TF? The approach arm for I bar should cross free gingival margin at 90’ angle.
T
I bar should contact tooth from here to here:
0.01” UC to HOC
Location of UC for both T or Modified T:
DB
Width of clasp at tip:
1mm
Amt of UC for retentive clasp:
0.01” cast clasp, 0.02” -18 gauge wrought-wire (good for most situations)
Which is larger, 18 gauge or 19 gauge?
18
TF? The taper of clasp should be uniform.
T
Retentive clasp location:
gingival 3rd, 1.5-2mm from gingival margin
Relationship of terminal 3rd of clasp to POI:
perpendicular
Reciprocal clasp location:
junction of middle and gingival 3rd, at or above HOC
Type of clasp to use if If you have a deeper UC on the abutment tooth to the posterior extension
combination clasp rather than compromising healthy tooth structure to make one of the other designs work
