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PRDP, Final > 10. Loads and Levers > Flashcards

10. Loads and Levers Flashcards

1
Q

Overview
 Partial dentures subject to many forces
 ____-vertical, lateral
 ____ foods- lifting
 Actions of tongue, lips & cheeks
 Need to review basic elementary school physics of loads and levers
 If you understand how a PRDP works you know how to approach each design challenge.

A

chewing

sticky

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2
Q 
Loads
 \_\_\_\_ support
 Directly to \_\_\_\_ crown 
 Between two supports
fixed bridge or tooth supported PRDP
A

tooth

single

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3
Q 
Loads
 How is the load applied? 
 \_\_\_\_ vs unequal
 \_\_\_\_ bridge
 PRDP with only \_\_\_\_
A

equal
fixed
rests

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4
Q

Loads
 Tissue support
 Prosthesis must be designed so that supporting tissues withstand the ____
 ____ PRDP need support from teeth and tissues
 Tissues are ____
 Load is ____ the support (free end saddle) must understand lever system to minimize torsional stresses

A

loads
large
compressible
outside

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5
Q

Levers
 Class I
 Load (L) weight or force to be acted upon
 Effort (E) weight or force required to cause action
 Fulcrum (F) pivot point

 Perfect system is static:
E x distance to F = L x distance to F
no ____ advantage

L nearer F & L greater E
mechanical ____

 L further F & E greater L
mechanical ____

A

mecahnical
advantage
advantage

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6
Q

Levers

 The greater distance of the effort from the fulcrum the ____ the mechanical advantage

A

bigger

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7
Q

Levers
 Class II
 Load ____ the fulcrum and the effort
 Mechanical advantage as load always ____ fulcrum

A

between

nearer

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8
Q

Levers
 Class III
 Effort lies ____ the fulcrum and load
 Mechanical disadvantage as the effort is always ____ to the fulcrum

A

between

nearer

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9
Q

Loads and Levers
 Applied load is the ____ force on the denture teeth in the case of support or the displacing force on the denture teeth on opening when chewing sticky food
 Fulcrum is the point about which the denture tries to ____
 Effort is the restraining component usually the ____

A

biting
rotate
clasps

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10
Q

Support
 Healthy tooth can withstand its own occlusal loading plus ____ of a similar tooth
 Soft tissue support should cover the greatest possible ____
 ____ of occlusal area will reduce the load required to penetrate a bolus of food

A

1.5
area
reduction

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11
Q 
Tooth supported prosthesis
 \_\_\_\_ supply the support 
 Scenario 1
 Short saddle even load
on \_\_\_\_ and molars
A

rests

premolars

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12
Q 
Tooth supported prosthesis
 Scenario 2
 Move \_\_\_\_ support further away from the load 
 Prevent \_\_\_\_ of the
premolar
A

anterior

overload

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13
Q

Tooth supported prosthesis
 Scenario 3
 Anterior support moved even further from the ____,
molar load ____

A

load

increases

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14
Q

Tooth supported prosthesis
 Scenario 4
 Multiple ____, load shared by the ____ and premolar

A

support

canine

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15
Q

Tooth supported prosthesis
 Scenario 5
 Moving the molar rest to the ____ will result in the ____ and canine sharing the load equally

A

distal

molar

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16
Q

Tooth &Tissue Supported Prosthesis

 Under masticatory load tooth may be intruded ____ mm whereas the mucosa can be compressed up to ____ mm
 In Kennedy Class I and II situations the tooth and tissue support is partly unyielding and yielding which can lead to prosthesis ____
 Mixing the two forms
of support is not easy,
rocking will occur about the ____ of the most ____ substance

A 
0.1
2
rocking
edge
unyielding
17
Q

Tooth &Tissue Supported Prosthesis
 The prosthesis will rock about the occlusal rest nearest the ____ part of the prosthesis when the tissue supported part is ____

The second premolar takes too much load
and torque, mechanically and clinically bad

A

tissue

loaded

18
Q

Tooth & Tissue Supported Prosthesis

 Move the occlusal rest further from the ____
 Better, less load & torque to the first premolar, more
compressive support from the soft tissue
 Common practice to place rest on ____ side of premolar adjacent to the saddle

A

saddle

mesial

19
Q

Tissue & Tooth Supported Prosthesis

 Are more rests mechanically useful?
 ____, adding an additional ____ rest moves the fulcrum to that rest making any rest anterior useless for support

A

no

distal

20
Q

Reciprocal Action(reciprocation)
 Reciprocal arm lies on the ____ but not in the undercut area.
 Prevents ____ of a tooth by a direct retainer
 A lone clasp arm without reciprocation will place unacceptable lateral ____ during insertion, removal & function creating and intermittent orthodontic appliance

A

survey line
displacement
stresses

21
Q

Bracing
 Counteract ____ displacing forces applied to the PRDP
 Resistance to ____ components of force applied to the prosthesis as a whole
 The ____ arm or denture base provides bracing action

A

lateral
horizontal
reciprocal

22
Q

Indirect Retention
 Prevents the ____ of a saddle which is cantilevered out from a direct retainer, such as free- end saddle or curved anterior saddle.
 Indirect retention is always a Class ____ lever system with ____ mechanical advantage

A

displacement
III
no

23
Q

Where would you put the nail (E)?

As a Class III system the ____ E is to the lifting load L the better.

A

nearer

24
Q

Fulcrum cannot move must be on ____

Effort is where the ____ (retentive tips) resist ____ movement

A

teeth

upward

25
Q 
Indirect Retention
 Class \_\_\_\_ lever system
 Fulcrum axis cannot \_\_\_\_
(on teeth F-F)
 Effort (E-E) where clasps
(retentive tips) resist \_\_\_\_
movement
 Load is force trying to displace \_\_\_\_
 Posterior part of denture is retained by the \_\_\_\_ lever system
A 
III
move
upward
saddles
indirect
26
Q

Indirect Retention
Indirect retention of a saddle cannot be achieved by ____ or rests acting on their own. Indirect retention can only be achieved through a ____ of clasps and rests to form a lever system to retain the free part of the denture.

A

clasps

combination

27
Q

Indirect Retention
Changing the lengths of the ____ alters the efficiency of the system and the degree of indirect retention possible.

The ____ the distance between the rests and the tips of this clasps the better, as it ____ the retaining lever.

A

lever arms
greater
lengthens

28
Q

Indirect Retention

The retaining lever is so short that it would be useless against the leverage of the displacing force unless the clasp was so strong that
it would apply an ____ force on the tooth with relatively little ____ force applied to the saddle

A

extracting

displacing

29
Q

Indirect Retention

The retaining lever must be a ____ as possible
Fulcrum to Effort

A

long

30
Q

Indirect Retention
 Indirect retainer for a saddle is a ____ element the other side of a ____ joining the tips of the direct retaining elements.

A

supporting

line

31
Q

Indirect retention

  • ____ arms
    (cingulum rests)
  • ____ extension of the denture base
A

cummer

backward

32
Q

Indirect Retention
 Indirect retention is never a Class ____ or Class ____ lever system, which presupposes that the clasp(s) is the fulcrum
 The fulcrum is on the ____ (which do not move) and the effort is the tip of the ____ (which can move)
 The displacing load (sticky food) is applied to, for example, a ____ saddle as the mouth opens
 The prosthesis will try to displace by ____ about the fulcrum created by the most ____ supporting component of the denture, perhaps a cingulum rest
 Resistance to movement, the effort , will be provided by the ____(s) placed as far ____ from the fulcrum as possible

A 
I
II
teeth
clasps
free-end
rotation
distant
clasp
away
33
Q

Indirect or Cantilevered Support
 Indirect support provides support for a saddle which is ____ out beyond the area of available tooth support.

 The action is one of a Class ____ lever system and can therefore be very effective or very poor, depending on how the load, effort and fulcrum are distributed.

A

cantilevered

I

34
Q

Indirect or Cantilevered Support
 In a Class I lever system it is obvious to the user that the greater distance the ____ is from the fulcrum the better (less effort needed to lever up the lid of a tin by using a long screwdriver). Likewise the nearer the ____ to the Load the greater the load that can be moved or balanced (same reasoning).

A

effort

fulcrum

35
Q

Indirect or Cantilevered Support
 Do not confuse support with ____.
 All stages of design are interrelated, whenever you work with rests and clasps you must think of the effect of the lever systems you are creating.

A

retention

36
Q

Is this a good design?

No, as the saddle sinks the denture will ____ around the fulcrum and the clasp on the canine will be displaced ____. Too much retention on the canine would cause extracting leverage and mobility.

This is a better design, by moving the rests ____ the rock is reduced and tooth damage is avoided.

A

rotate
upward
forward

37
Q

RPI Clasp
The anterior of a free end saddle must be ____ supported otherwise functional load will displace (compress) tissues causing damage.

An occlusal or cingulum ____ is required and should be placed ____ to avoid tilting forces.

A

tooth
required
rest
mesially

38
Q

RPI Clasp

 ____ Rest, ____ Plate, ____ Bar

A

mesial
distal
I

39
Q

RPI Clasp
• The denture is going to rotate about the ____ edge of the mesial occlusal rest.
• The I bar is placed on that axis and the active tip will show ____ movement (further into the undercut).
• The distal plate will only touch the ____ survey line so rotational movement will be into ____ of the distal surface without applying torque to the ____.

A 
distal
minimal
vertical
undercut
tooth

PRDP, Final (21 decks)

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