Margin Design

Question 1

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

Answer 1

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

Question 2

what are the types of finish lines

Answer 2

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

Question 3

when is the knife edge used and what burs are used

Answer 3

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

Question 4

what are the disadvantages to knife edge

Answer 4

• 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

Question 5

when is knife edge indicated

Answer 5

• 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

Question 6

when is light chamfer used

Answer 6

• metal crowns
• zirconia crowns

Question 7

when is heavy chamfer used

Answer 7

• ceramic crowns
• zirconia crowns
• metal ceramic crowns

Question 8

what bur do you use to make chamfer

Answer 8

round ended diamond

Question 9

what are advantages to chamfer

Answer 9

• 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

Question 10

describe light chamfer

Answer 10

• 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

Question 11

describe the heavy chamfer

Answer 11

• 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

Question 12

what margins can work with any crown

Answer 12

heavy chamfer or shoulder

Question 13

describe a shoulder and what burs used

Answer 13

• close to a 90 degree angle
• flat end diamond burs

Question 14

what does a modified shoulder have

Answer 14

a rounded angle

Question 15

when is shoulder used

Answer 15

metal ceramic (PFM or PFZ) and all ceramic crowns

Question 16

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

Answer 16

decrease stress on restoration material

Question 17

describe shoulder with bevel and when it is used

Answer 17

• 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

Question 18

significant roughness of preparation finish line can prevent :

Answer 18

close adaptation of crown marginug

Question 19

rough margin = ______ = ______

Answer 19

plaque accumulation; recurrent decay

Question 20

what does the finish line design vary based on

Answer 20

restoration material, location in the mouth and desired results

Question 21

what are advantages to knife edge

Answer 21

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

Question 22

what are advantages and disadvantages to shoulder

Answer 22

• 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

Question 23

when is beveled shoulder indicated

Answer 23

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

Question 24

are are advantages and disadvantages to shoulder with bevel

Answer 24

• 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

Question 25

describe the chamfer

Answer 25

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

Question 26

when is a chamfer indicated

Answer 26

cast metal restorations or lingual margin of metal ceramic restorations

Question 27

what are advantages and disadvantages of chamfer

Answer 27

- 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

Question 28

describe the heavy chamfer

Answer 28

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

Question 29

what are advantages and disadvantages to a heavy chamfer

Answer 29

-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

Question 30

what do you use for caries removal

Answer 30

- slow speed with 2,4,6 round bur - spoon excavators

Question 31

how do diamond burs remove enamel and dentin

Answer 31

grinding

Question 32

how do carbide burs remove tooth

Answer 32

shearing

Question 33

how much faster are diamond burs than carbide burs

Answer 33

2-3 times

Question 34

what are the advantages of full metal crowns

Answer 34

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

Question 35

what are disadvantages to full fetal crowns

Answer 35

esthetics

Question 36

what is the margin design for full metal crown

Answer 36

- 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

Question 37

describe the axial reduction on full metal crown

Answer 37

- 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

Question 38

describe occlusal reduction on full metal crown

Answer 38

- uniform occlusal reduction depth of 1.0-1.5mm following depths and pathways of developmental grooves

Question 39

describe zirconia

Answer 39

- 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

Question 40

describe the reduction in the zirconia esthetic crowns

Answer 40

- 1.25mm ideal reduction - chamfer or modified shoulder

Question 41

describe the reduction in the zirconia full strength

Answer 41

- 1.0mm ideal reduction - chamfer or shoulder margin preffered, knife edge is ok

Question 42

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

Answer 42

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