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BDS2 RPD > Pros rpd design features > Flashcards

Pros rpd design features Flashcards

1
Q

flange

A

the replacement tissue extending into the vestibular sulcus from the alveolar area

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2
Q

tooth support

A

directs the masticatory occlusal load through the periodontal ligaments of adjacent teeth
- more natural as it directs the load down the natural central axis which feels better for patients

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3
Q

mucosal support

A

requires a large surface area to prevent sinking into the mucosa
- can accelerate resorption of underlying tissue if not placed correctly

  • spreads the load through the mucosa onto the bone
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4
Q

tooth borne support

A 
craddock class 1 
- directs load down the central axis of teeth
  • protects the soft tissue from trauma
  • more comfortable for the patient as it feels more natural
  • directs the load of spaces into the PDL of abutment teeth
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5
Q

mucosal borne support

A 
craddock class 2
- abutment teeth not involved
  • load is directed through the residual ridge below the saddles
  • large palate to maximise distribution
  • reduces the occlusal table
  • allows the denture base to move slightly which could cause damage to adjacent teeth
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6
Q

tooth and mucosa support

A

combination when there are still teeth available for support but not enough to completely support the load or in larger saddle areas
- MUST be used in free end saddle areas

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7
Q

order of teeth in load bearing

A
  1. molars
  2. canines
  3. premolars
  4. anteriors
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8
Q

the best teeth for providing tooth support are those with the largest…

A

root area

- depending on the health of the PD attachment

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9
Q

a tooth can bear

A

its own occlusal load plus one half of the load of similar teeth

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10
Q

what ratio should be considered when deciding if a tooth is suitable for support

A

the crown to root ratio

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11
Q

types of rests

A
  1. occlusal
  2. cingulum
  3. incisal (rarely used)
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12
Q

cutting tooth rests

A

may need to cut into a healthy tooth tissue to provide area for a rest seat without interfering with the occlusion
- not ideal

  • try and seat rests in existing areas
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13
Q

axial tork

A

tilting and rotation of the tooth if the load is not directed down the central axis of the tooth
- minimised by placing the rest as close to the central axis of the tooth as possible

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14
Q

cingulum rests

A

placed on prominent cingulums

- can remove tooth tissue or add composite to produce a vertical stop for which the rest can sit on

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15
Q

functions of rests

A
  1. prevents RPD moving to soft tissues
  2. assists in distribution of occlusal load
  3. prevents over eruption of opposing teeth
  4. provides bracing to anterior teeth
  5. determines the acid of rotation on the free end saddles of RPDs
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16
Q

when is crown to root ratio unacceptable for using a tooth for support

A

all teeth used for support have their ratios added to give a total root area
- this is multiplied by 1.5

  • if this exceeds the total of the ratios of the missing teeth then there is insufficient tooth support and mucosal support must be considered
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17
Q

in a bounded saddle, occlusal rests are placed

A

on either side of the saddle (one mesial one distal)

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18
Q

in a free end saddle, the occlusal rest is placed on the

A

other side of the tooth to the saddle (mesial side)

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19
Q

centric stop

A

the point where opposing teeth touch in centric occlusion

- should not place rest seats here as this can interfere with the occlusion and feel unnatural to patients

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20
Q

primary mucosal support comes from

A
  1. the hard palate (maxillary)
  2. the buccal shelf/sulcus and pear shaped pad (mandibular)
  3. the residual ridges
  4. the maxillary tuberosity
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21
Q

how far fro the gingival margi should a base place be placed

A

3mm to prevent bone resorption, pressure causing recession and to allow clearing and flow of saliva (no food traps)

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22
Q

paeriodontium can be displaced by

A

0.1mm

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23
Q

mucoperiosteum can be compressed by

A

2mm

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24
Q

if there is no hard tissue support to the mesial of the abutment tooth on a free end saddle, this could result in

A

DISTAL AXIAL TORQUE

- the denture sinks into the compressible mucoperiosteum over time

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25
Q

retention

A

the resistance of a denture to lifting away from the tissues

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26
Q

means of achieving retention

A

mechanical, frictional, muscular or physical means

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27
Q

denture features which aid retention

A
  1. altering the path of insertion
  2. clasps
  3. frictional contacts (guide planes)
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28
Q

achieving mechanical retention

A
  1. from a clasp

2. the clasp engages the undercut of the tooth under the maximum bulbosity

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29
Q

muscular faces in retention

A

comes through time once the patient is used to the denture

- over time the orofacial muscles will have strengthened around the denture to hold it in place

30
Q

frictional forces in retention

A

the use of parallel guide planes helps to retain the base of the denture between two frictional contacts

31
Q

physical forces in denture retention

A

adhesion and cohesion
- adhesion from the surface forces between the saliva and mucosa

  • cohesion from the forces with the saliva and its viscosity
32
Q

negative pressure

A

pressure used to retain the entire base from the saliva suction and peripheral seal in the maxilla
- better in dentures with larger base and made acrylic

33
Q

ring clasp

A

most common type
- starts at the occlusal and goes around the tooth

  • terminates in the undercut it engages
  • self reciprocating as it goes all the way around the tooth
34
Q

direct retention

A

resistance to vertical displacement of the denture

- clasps and oromusculature

35
Q

indirect retention

A

resistance to the rotational displacement of the denture

36
Q

clasps should be

A

as close to the denture base as possible

37
Q

guide planes are parallel to

A

the path of insertion and removal

38
Q

gingival approaching clasps approach the undercut from

A

the gingival margin

39
Q

occlusally approaching clasps approach the undercut from

A

the occlusal surface

40
Q

occlusal approaching clasps

A

15mm or greater in length
- 2.5mm undercut necessary for CoCr

  • begin not he occlusal surface and terminate in the undercut
41
Q

gingival approaching clasp

A

usually on canines and premolars
- below the lipline so more subtle

  • crosses the gingival margin which can be an issue
    1. gum stripping
    2. plaque retentive factor
42
Q

clasp elements affecting retention

A
  1. flexibility
    - depends on material and thickness
  2. placement of the retentive arm
    - should be placed to 15mm and engage an undercut but this is not always possible
  3. depth of the undercut
    - needs to be sufficient to seat a clasp
43
Q

reciprocation component

A

a retentive arm which deflects over the bulbosity of the crown to counteract the forces of the retentive component by using an equal and opposite force

44
Q

purpose of reciprocation

A
  1. stops the tooth from moving when the clasp is engaged

2. prevents pressure from the clasp acting on or damaging the tooth

45
Q

how much of the clasp sits below the survey line to engage the undercut

A

01-Mar

46
Q

how much of the clasp sits above the survey line

A

02-Mar

47
Q

once the 1/3 of the clasp is activated, what should happen

A

it should be passive and no longer exert forces on the tooth

48
Q

benefits of altering the path of insertion

A
  1. more frictional retention
  2. better aesthetic result
  3. prevents gaps forming
49
Q

pattern of retention

A

needs to be as large a triangle as possible

50
Q

when can using 2 clasps for the pattern of retention be allowed

A

when there is bilateral free end saddles

51
Q

3 parts to the RPI clasp

A
  1. rest
  2. proximal plate
  3. I-bar clasp
52
Q

the only part of the RPI clasp which applies pressure to the tooth is the

A

occlusal rest

53
Q

the occlusal rest in RPI

A

must be on the mesial side of the tooth
- rounded to impression on the surface

  • the only part of the clasp which put pressure on the tooth
54
Q

the proximal plate of the RIP system

A

adjacent to the saddle
- sits in the undercut

  • on the proximal surface
  • provides bracing and stability of the denture during function and helps to guide during insertion
  • slips into the undercut and disengages during function
55
Q

I-Bar clasp of the RPI system

A

gingivally approaching
- greatest prominence of the tooth contour is where it site

  • when there is loading it moves down and forward away from the tooth
56
Q

why are RPI systems only used in the lower arch

A

the upper arch has a plate which restricts movement more than the lower

57
Q

where is the reciprocation on the RPI system

A

there is minor connectors on both the mesial and distal of the engaged tooth
- the gap before the tooth to here is narrower to prevent the denture moving lingually

58
Q

why is the rest to the mesial of a free end saddle

A

it puts the fulcrum further away from the clasp to allow it to resist the rotational movement

59
Q

connector

A

a rigid part of the denture which unites components

60
Q

minor connectors

A

join the smaller individual parts of the denture to the major connector
- transfers the function stresses to and from the abutment teeth

61
Q

ideal characteristics of a minor connector;

A
  1. rigid
  2. finished above the survey lie on the teeth (toward occlusal)
  3. cross the gingival margins at 90 degrees
    • maintains an area of self cleaning
  5. cross the gingival tissues as little as possible
62
Q

major connector

A

the part of the denture than connects components other side of the arch to the other

63
Q

plates

A
  1. horshoe
  2. ring (anterior/posterior bar)
  3. full plate with gingival clearance
  4. lingual plate
64
Q

bars

A
  1. dental bar
  2. lingual bar
  3. sublingual bar
65
Q

dental bar

A

sits on the cingulum of the teeth to avoid the mucosa

- has to be quite bulky to be rigid enough

66
Q

thickness of plates

A
  1. can be made thinner and still maintain rigidity
  2. thickness however depends on the shape of the mucosal areas and the amount of coverage
  3. can be 0.45-0.5mm thin
67
Q

bars thickness

A

less mucosal coverage so needs to be ticker

- shoud be 2mm thick

68
Q

how far must the plate or bar be from the gingival margin

A

3mm

69
Q

what amount of space is required for a mandibular plate and why

A

8mm
- 2mm from gingival margin

  • 4mm height of the bar
  • 1mm for clearance
70
Q

every design

A

open connector design to prevent an of the gingiva being irritated

BDS2 RPD (13 decks)

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