Tooth Preparation

Question 1

TOC

Answer 1

ideally 5 degrees, but difficult to achieve in practice

10-20 degrees

Goodacre

Question 2

occlusocervical prep dimension (axial height)

Answer 2

incisors and premolars: 3mm
molars: 4mm

Question 3

height:base crown prep ratio

Answer 3

0.4 or higher

(i.e. if the base is 10mm, the height should be at least 4mm)

Question 4

circumferential prep morphology

Answer 4

preserve axial corners
(rectangular mand molars, rhomboidal max molars, oval premolars/anteriors)

if unable to preserve, use boxes/grooves

Question 5

benefits of supragingival finish line

Answer 5

• preserves tooth structure
• enhances periodontal health

Question 6

reasons for subgingival finish line

Answer 6

• retention/resistance form (axial height)
• extension beyond caries/fractures/defects
• esthetics

Question 7

finish line form and depth for zirconia

Answer 7

rounded shoulder or chamfer, 0.5mm

Bruxzir says chamfer, and knife-edge is ok

Question 8

axial and incisal reduction depths

Answer 8

axial: 0.5mm
occlusal: 1mm for FPDs, 0.5mm for single units

Question 9

benefits of rounded line angles

Answer 9

• reduce stress concentrations
• facilitate milling
• facilitate impression-pouring

Question 10

benefits and disadvantages of smooth preps

Answer 10

benefits:
- machinability
- fit
- distribution of forces

disadvantages:
- decreased retention (debatable)

Question 11

benefits of immediate dentin sealing

Answer 11

• improved bond strength - allows dentin-resin hybrid layer to develop in a stress-free environment, protected from contamination and collapse
• allows for application of light-activated bonding agent vs. solely dual-cure
• may decrease post-op sensitivity (rdxn of fluid and bacterial penetration - ltd evidence)

TKTK

Magne (via Japan)

Question 12

disadvantages of immediate dentin sealing

Answer 12

• technique sensitive (isolation, matrix placement, dentin identification, control of materials)