Before Midterm: Biomechanics of Partial Denture Design Flashcards
Which type of partial will move?
tooth supported
Tooth-tissue supported partials:
Class I, II, and IV
Residual ridge provides only ___% of the support compared to the PDL.
0.4
Soft tissues are ____ times more displaceable than the adjacent teeth
250
Thickness of periodontal membrane:
0.25mm
In Class I and II, occlusal loads caues;
displacement of distal extension
Force exerted on a Class ! or 2 tooth-tissue supported partial may cause:
distal tipping of abutment
Force exerted on a Class 4 tooth-tissue supported partial may cause:
displacement of anterior extension, mesial tipping of abutment
WHat do differences in tooth and soft tissue support result in?
nono-axial loading, damaging to abutments, moust be controlled
Non-axial loading can result in:
mobility and restoration failure
What does the force on abutment teeth depend on ?
ratio of tooth vs tissue support
Order of how effective the different class of levers are:
1st through 3rd
What class lever system can do greatest amt for work with least amt of effort
Class 1
Where is the object to be moved in relation to the fulcrum and force for a Class 1, most efficient, fulcrum?
opposite the force w the fulcrum in the center
This lever system represents the wheel barrel:
2nd class
This lever system represents a man fishing:
Class 3
What type of lever system is created with loading of distal extension base?
1st class lever
Where does rotation occur around a 1st class clever system?
around distal abutment
What does the framework rotation have a direct impact on?
clasp assembly
Consequence of poor clasp selection
overlioading abutment
Occlusal loading of the distal extension w a circumferential clasp causes:
rotation around fulcrum, retentive clasp to move superiorly, engaging the UC, causing the abutment to move distally (why distal?)
These forces are created when there is rotation about the fulcrum:
off axis forces
What can off axis forces lead to?
partial denture to start pulling abutment tooth posteriorly
TF? Circumferential clasps are recommended w a distal extension base
F. use stress releasing clasps (all infrabulge except for wrought wire clasp which is considered stress releasing)
TF? All stress releasing clasps are infrabulge clasps.
F. wrought wire is not infrabulge
Where does the framework fulcrum with occlusal loading of the distal extension for T clasp?
at the rest
Direction of forces w occ loading of distal extension with a T clasp:
M and apical, abutment moves M (down and forward)
What resists M movement of teh abutment with a T clasp distal extension?
mesial contact
Aspect of the T clasp assembly that decreases forces on the abutment tooth:
When retentive feature moves down it disengages form the UC
Location of the retentive feature of clasp:
right below rest
Occlusal loading of the distal extension w an I bar causes:
retentive clasp moves M and A, disengaging from UC
Where does the framework fulcrum with occlusal loading of the distal extension for I bar?
mesial rest
I bar is similar to which Class lever system?
Class II
Most favorable clasp for distal extension:
I bar (check)
Is the fulcrum anterior or posterior to the resistance in I bar clasp?
anterior
All distal extensions req one of these clasp types:
I bar, T clasp or circumferential
Types of rests we could use for the abutment for the distal extension:
D or M-O (any others?)
The longer the extension base, the greater the potential for:
damaging loads generated on the abutments
Is the p[otential for damaging loads greater or less the further away from the abutment the forces are applied?
greater (check)
Occlusal forces are (normally?) centered over these teeth:
2nd premolar and 1st molar
These resist forces acting to dislodge prosthesis:
indirect retainers
These resist rotational displacement of an extension bae away from the supporting tissues
idirect retainers
Is it prefered to rotate about the fulcrum or the rest?
rest, down forces on real teeth, up force on fake teeth
The additional of this to a framework will prevent rotation of the distal extension:
vertical stop (indirect retainer)
Use these to counteract rotational forces:
indirect retainers
Kennedy Classes that require indirect retention:
1, 2, 4
Define fulcrum line:
runs thru the rest of the most distal abutment
Where to place indirect retainer on the framework:
side opposite distal extension, perpendicular to fulcrum as far anterior as possible (meaning not perpendicular in some cases? ask) check), in a dfinitie rest seat
Don’t place indirect retainer on these teeth
incisors
Ideal teeth or indirect retainer placement:
canines, premolars (I would assume molars, too)
Class II mod I with 3rd molar behind modification space, do you want the clasp on the molar to be retentive or non-retentive?
non-retentive
Does a lingual plate provide indirect retention?
no
Why doesn’t a lingual plate provide indirect retention?
bc the contact bw the lingula plate and the teeth occurs on inclined planes
Indirect retention will never work if the contacting surfaces are on this type of plane:
inclined
Clasp configuration of Class III arch:
Quadrilateral configuration, A and P to each edentulous span
Clasp configuration of Class II arch:
Tripodal Configuration
Clasp location for Class II arch with edentulous span on opposite side of arch:
adjacent to distal extension, A and P to edentulous span
Clasp location for Class II arch wo edentulous span on opposite side of arch:
adjacent to distal extension, separate clasp assemblies on the intact side of arch
Clasp configuration of Class I arch:
Bilateral
Clasp configuration of Class I arch:
most posterior teeth + indirect, bilateral retainers
Factors influencing stresses transmitted to abutment teeth:
length of edentulous span, quality of ridge support, claps design, occlusal factors, clasp flexibility
Factors affecting clasp flexibility:
clasp length, diameter, taper and material used
The more flexible the retentive arm of the clasp, the less/more load is transferred to the abutment
less
Disadv of a flexible clasp:
less resistance to horizontal displacement, increasing non-axial loads to the edentulous ridge and other abutments
Clasp recommended on abutments opposite fulcrum line:
wrought wire
Flexibility of clasp is directly proportional to:
the cube of its length
How to increase clasp length
by using a curved (instead of straight) path on a tooth (I don’t understand. check)
This type of clasp is tapered from its origin to its tip:
retentive cast clasp
Dimension of tip in relation to origin for retentive clasp:
about 1/2 it’s origin
How many times more flexible are tapered clasps than non?
2X
A clasp constructed of a _____ alloy places a greater load on an abutment than a alloy
chromium-based, gold-based
A clasp constructed of a _____ alloy places a greater load on an abutment than a alloy
chromium-based, gold-based
How do the diameters of the clasp arms compare bw chromium based and gold-based?
similar diamters
How to increase the retentive force of a retentive clasp:
have it engage a greater angle of cervical convergence (theta)
Any of these partials require indirect retainers:
tissue supported
Where is the fulcrum placed for distal retainers?
around the distal rest
Direction of movement of any portion of framework anterior to the fulcrum (rest) for the distal extension:
apically toward tissue
TF? Tooth-tissue supported should have indirect retainer.
T
Reasons to choose a non-retentive clasp vs. retentive for an edentulous span with teeth on either side:
Might be no UC’s, mobility, compromised tooth
(2nd molar with mobility - better to create parial including it in? Can we simply cut that clasp off when the tooth comes out? check ask)
These provide indirect retention for Class IV partial:
rest seats
TF? The lingual plate is a vertical stop.
F, no indirect retention
To where does the lingual plate extend?
all the way through the posterior
TF? Use quadrilateral configuration for Class II arch.
F. tripod
How to increase horizontal stability of the partial:
Make clasp less flexible (shorter is the most common way to modify)
Most common way to modify clasp flexibility:
clasp length
What type of alloy is wrought wire?
chrome based
More flexible, gold or base metal?
gold
Material no longer used for framework anymore:
cast gold
Greater flexure over a shorter amt of time requires more/less force to dislodge
less
