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fixed pros i > Margin Design > Flashcards

Margin Design Flashcards

1
Q

a full coverage restoration can survive in the biologic environment of the oral cavity only if:

A

the margins are closely adapted to the surface finish line of the prep

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2
Q

what are the types of finish lines

A

-knife edge
- chamfer- heavy and light
- shoulder
- beveled shoulder

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3
Q

when is the knife edge used and what burs are used

A
  • full metal crowns only
  • gold crowns
  • most conservative prep
  • use flame or needle shaped bur
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4
Q

what are the disadvantages to knife edge

A
  • difficult to see finish line in an impression or scan
  • metal can be thin and is suscpetible to distortion under heavy occlusal load
  • often leads to an over bulking of crown material to compensate for thinness along margin
  • easy to miss creating distinct end of finish line and instead axial wall never terminates
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5
Q

when is knife edge indicated

A
  • tipped molar to be conservative in abnormal area
  • young patients
    -metal restoration
  • MOD onlay
  • inaccessible areas
  • when finish line extends to cementum
  • lingual surface of mandibular posterior teeth
  • pin ledge 3/4 crown
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6
Q

when is light chamfer used

A
  • metal crowns
  • zirconia crowns
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7
Q

when is heavy chamfer used

A
  • ceramic crowns
  • zirconia crowns
  • metal ceramic crowns
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8
Q

what bur do you use to make chamfer

A

round ended diamond

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9
Q

what are advantages to chamfer

A
  • well suited to full metal crowns and zirconia crowns
  • ease of seating crown and placing crown
  • ease of detecting margin on impression or scan
  • if full metal, chamfer is easy to wax and cast
  • provides adequate thickness of restoration material at margin
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10
Q

describe light chamfer

A
  • 0.3-0.5mm deep into axial wall
  • produces 30-45 degree margin with rounded internal angle
  • chamfer combines knife edge burnish-ability with bulk of material for all metal crowns
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11
Q

describe the heavy chamfer

A
  • provides room for thicker ceramic margin
  • internal rounded angle decreases material stresses in this area
  • 1-1.2mm deep
  • use large round ended diamond bur
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12
Q

what margins can work with any crown

A

heavy chamfer or shoulder

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13
Q

describe a shoulder and what burs used

A
  • close to a 90 degree angle
  • flat end diamond burs
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14
Q

what does a modified shoulder have

A

a rounded angle

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15
Q

when is shoulder used

A

metal ceramic (PFM or PFZ) and all ceramic crowns

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16
Q

what does the 90 degree angle at the axial wall and finish line of the shoulder do

A

decrease stress on restoration material

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17
Q

describe shoulder with bevel and when it is used

A
  • finish lines can have bevel at a 30-45 degree angle
  • often used for inlays and onlays
  • can be used for metal ceramic crowns where there is a metal collar
  • bevel allows for adaptability of metal to ensure marginal fit
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18
Q

significant roughness of preparation finish line can prevent :

A

close adaptation of crown marginug

19
Q

rough margin = ______ = ______

A

plaque accumulation; recurrent decay

20
Q

what does the finish line design vary based on

A

restoration material, location in the mouth and desired results

21
Q

what are advantages to knife edge

A

-conservative
- ideal for marginal adaptatoin
- useful in metal and gold crowns
- considered an ideal finish line

22
Q

what are advantages and disadvantages to shoulder

A
  • A: less distortion of crown margins, provides adequate bulk, good crown contours, can attain good esthetics
  • D: marginal adaptation can be affected, more tooth structure needs to be removed
23
Q

when is beveled shoulder indicated

A

gingival finish line on the proximal box of inlays and onlays, occlusal shoulder of onlays and mandibular 3/4 crowns, the finish line for extremely short walls, the facial margin of posterior metal ceramic crowns with a supragingival margin

24
Q

are are advantages and disadvantages to shoulder with bevel

A
  • A: to get proper marginal adaptation, the bulk of the material in border
    -D: more tooth structure is removed, less conservative approach, prep should be extended apically
25
Q

describe the chamfer

A

a finish line design for a tooth prep in which the gingival aspect meets the external axial surface at an obtuse angle

26
Q

when is a chamfer indicated

A

cast metal restorations or lingual margin of metal ceramic restorations

27
Q

what are advantages and disadvantages of chamfer

A
  • A: conservative, good marginal adaptation, provides bulk to the restoration
  • D: technique sensitive and any defect in fabrication can lead to unsupported tip of the crown
28
Q

describe the heavy chamfer

A

similar to chamfer finish line but comes with a 90 degree cavosurface angle with a large radius rounded internal angle, in metal restorations a bevel is added to the finish line

29
Q

what are advantages and disadvantages to a heavy chamfer

A

-advantages: best finish line for a ceramic crown
- disadvantages: technique sensitive, the little discrepancy can lead to the formation of a lip or unsupported fragile enamel

30
Q

what do you use for caries removal

A
  • slow speed with 2,4,6 round bur
  • spoon excavators
31
Q

how do diamond burs remove enamel and dentin

A

grinding

32
Q

how do carbide burs remove tooth

A

shearing

33
Q

how much faster are diamond burs than carbide burs

A

2-3 times

34
Q

what are the advantages of full metal crowns

A

gold and many metal crowns are soft metals
- gentle to opposing teeth
- metal is strong so material can be thin
- allows for very conservative preps
- metals have some antibacterial properties making recurrent decay less likely
- most gold and full metal crowns are much more gentle on gingiva
- metal crowns are durable even if worn through or with endo access
- if contact is missing you can add it on

35
Q

what are disadvantages to full fetal crowns

A

esthetics

36
Q

what is the margin design for full metal crown

A
  • light chamfer 0.3-0.5mm
    -can use knife edge
  • reduce until half bur is in the axial wall then follow around the contours of the tooth to create chamfer
37
Q

describe the axial reduction on full metal crown

A
  • reduced to create taper between 6-10 degrees but can have TOC up to 20 degrees
  • axial walls can be reduced as little as 0.5mm
38
Q

describe occlusal reduction on full metal crown

A
  • uniform occlusal reduction depth of 1.0-1.5mm following depths and pathways of developmental grooves
39
Q

describe zirconia

A
  • tooth colored ceramic like material
  • considered metal free
  • has propertieis similar to metal
  • can be very hard and tought
  • is less translucent than natural teeth
  • allow for conservative preps bc of strength
  • they wear opposing teeth less
40
Q

describe the reduction in the zirconia esthetic crowns

A
  • 1.25mm ideal reduction
  • chamfer or modified shoulder
41
Q

describe the reduction in the zirconia full strength

A
  • 1.0mm ideal reduction
  • chamfer or shoulder margin preffered, knife edge is ok
42
Q

the more esthetic your zirconia is, the ____ reduction you will need

A

more

43
Q
A

fixed pros i (13 decks)

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