Principles Of Crown Prep Flashcards
How can retention and resistance be improved in crown preps?
Grooves and mini-inlays
Taper / paralleling preps - 6 degree ideal
Having sufficient length of walls to prevent tipping displacement
POI - limit number of paths of insertion
What are the 6 principles of tooth prep?
1- preserve tooth structure as much as possible
2- retention and resistance
3- structural durability
4- marginal integrity
5- preservation of periodotnium
6- aesthetics
Risk of under prepping tooth for a crown/onlay etc?
Poor aesthetics
Fracture of thin restoration
Overbuilt crown resulting in heavy occlusal contacts
How is structural durability maintained in crown preps?
Sufficient occlusal reduction - reduce .5mm more on functional cusp
Functional cusp bevel - palatal upper and buccal lower (PUBL)
Axial reduction
How is the periodontium preserved in crown preps?
Margins should be
- smooth and fully cleanseable
- placed where dentist can finish them and patient clean them
- placed at gingival margin where possible
Give the axial reduction, occlusal reduction and finish line for a:
Full metal crown
Axial - 0.5mm
Occlusal
- Functional cusps - 1.5mm
- Non functional cusps - 0.5mm
Finish line
- 0.5mm chamfer
Give the axial reduction, occlusal reduction and finish line for a:
Ceramic crown - full porcelain
Axial - 1mm
Occlusal
- functional cusp = 1.5mm
- non functional cusps = 1mm
Finish line
- 1mm shoulder
Give the axial reduction, occlusal reduction and finish line for a:
MCC
Axial - 1.5mm
Occlusal
- Functional cusp = 2mm
- non functional cusps = 1.5mm
Finish line
- where only metal needed e.g. palatal = 0.5mm CHAMFER
- where both metal and ceramic needed = 1.5mm (1mm for porcelain and 0.5mm for metal) SHOULDER
Give the axial reduction, occlusal reduction and finish line for an:
All ceramic crown e.g. porcelain with alumina or zirconia
Axial - 1.5mm
Occlusal
- functional cusps - 2mm
- non functional cusps - 1.5mm
Chamfer
- 1.5mm
