Prelim-Principles of tooth prep

Question 1

mechanical tx of dental disease or injury to hard tissues that restores th to original form, reduction of th is preceded by mental image of design of artificial crown and anticipated occlusion

Answer 1

tooth prep

Question 2

Biologic consideration

Answer 2

• prevention of damage during th prep

- adj th -soft tissues -pulp

Question 3

5 basic principals of th prep

Answer 3

1. preservation of th structure
2. Retention and Resistance
3. structural durability
4. marginal integrity
5. preservation of periodontium

Question 4

• use partial than complete coverage restoration
• minimal angle of convergence (taper)
• occlusal reduction following anatomic planes
• selection of conservative margin
• avoid unnecessary apical extension
• uniform axial surfaces prep

Answer 4

preservation of th structure

Question 5

ability of prep to prevent displacement of the resto in a direction opposite the path of insertion

Answer 5

retention

Question 6

restoration must have sufficient strength to prevent permanent deformation during function

Answer 6

deformation

Question 7

factors that affect retention form

Answer 7

• magnitude of dislodging force
• geometry of th prep
• roughness of fitting surface of resto
• material being cemented
• type of luting agent
• film thickness of luting agent

Question 8

greater retention

Answer 8

• taper parallel
• SA large
• type of prep molar complete
• surface texture: rough
• film thickness: uncertain
• luting agent: adhesive resin

Question 9

factors affect resistance form

Answer 9

• magnitude and direction of dislodging force
• geometry of th prep
• physical property of luting agent (based on compressive strength)

Question 10

higher resistance

Answer 10

• dislodging force: habits
• taper: minimum
• diameter: small (pm)
• height: long
• type of prep: complete coverage
• luting agent: silicophosphate

Question 11

-degree of __ proportional to retention form
-0__: most retentive but difficult to obtain
-

Answer 11

taper

Question 12

sum of degree of taper

• for optimum
• Md pm

Answer 12

degree of convergence

• 4-10 deg
• lingually tilted by 9 deg

Question 13

• limit from torqueing and twisting forces
• single path of insertion
• overtapered prep produces multiple path of insertion
• proximal box w/ walls prepared at right angles to pulpal wall prevent rotation

Answer 13

Freedom of displacement

Question 14

• greater height, greater retention
• increased height increases area of cementation
• smaller diameter th resist pivoting movements better than prep of equal length with larger diameter
• resistance of short prep can be improved by adding grooves

Answer 14

length

Question 15

• prox grooves, boxes, pinholes
  1. overtapered prep
  2. partial veneer crowns
  3. absence of 2 opposing walls

Answer 15

addition of internal features to improve retention

Question 16

an imaginary line along w/c the resto will be placed onto or removed from the prep
-mesiodistal inclination of prep’d th be parallel to prox inclination of adjacent ts

Answer 16

path of insertion

Question 17

• ability of resto to w/stand destruction due to external forces
• ___comes w/ thickness of resto
• adequate reduction during preparation (depend on type of resto)

Answer 17

structural durability

Question 18

• marginal adaptation and seating of resto
• poor adaptation: percolation of oral fluids (marginal leakage) and secondary caries
• casting shrinkage = marginal discrepancy
• acceptable discrepancy = around 10 microns; compensated by luting cement

Answer 18

marginal integrity

Question 19

types of margin (according to location)

Answer 19

1. supragingiva
2. equigingiva
3. subgingiva

Question 20

easily finished, to maintain, to identify and reproduce in impression, to examine during future visits

Answer 20

supragingiva

Question 21

• for ts w/ short clinical crowns
• ts affected w/ subging caries or cervical erosion
• if contact area is at or below gingival crest
• where esthetics is of concern (gummy smile)
• for cases of unmanageable root sensitivity
• when axial contours need to be modified
• when additional retention is required
• to conceal the metal-ceramic margins

Answer 21

subgingiva

Question 22

characteristics of finish lines

Answer 22

• bevels parallel to cavosurface margins should be avoided
• bevel should not produce a very acute margin
• when using torpedo bur, don’t reduce more than 1/2 of the size of bur using

Question 23

• curve slope from axial wall til margin
• use torpedo shaped bur
• for 1. cast metal 2. lingual margins of metal-ceramic resto
• not indicated where finish line will be obvious
• th conservation

Answer 23

chamfer

Question 24

gingival wall perpendicular to axial surfaces of ts

• for 1. all ceramic resto 2. facial margin of metal-ceramic resto wher sufficient thickness is required (for structural durability)
• good where esthetics is concern
• more th reduction

Answer 24

shoulder

Question 25

• on gingival margin
• used on gingival finish line on prox box of inlays and onlays
• if theres existing resto or cervical erosion
• minimal marginal discrepancy

Answer 25

shoulder w/ bevel

Question 26

• extremely thin finish lines
• difficult to wax up and cast
• difficult to produce smooth margins
• susceptible to distortion
• prone to overcontoured resto
• for ling surface of mandi post surface

Answer 26

knife edge

Question 27

the more accurately the resto is adapted to th, the less chance for recurrent C

Answer 27

margin adaptation

Question 28

casted crowns:

Answer 28

10 microns

Question 29

porcelain:

Answer 29

50 microns

Question 30

• margin should be at least 3mm from crest to alveolar bone
• care not to damage gums/adj th during th prep
• don’t violate biologic width

Answer 30

shoulder w/ bevel