crown prep Flashcards
Principles of crown prep
Preservation of tooth structure
Retention and resistance form
Marginal integrity
Structural durability
Preservation of the periodontium
Aesthetic considerations
Preservation of tooth structure
Under prep - poor aesthetics, insufficient thickness, over build with occlusal and periodontal consequences
Over prep - pulp and tooth strength compromised
Retention
Prevents removal of restoration along path of insertion or long axis of tooth prep
Resistance
Prevents dislodgement of the restoration by forces directed in apical or oblique direction
Prevents any movement of restoration under occlusal forces
How to provide retention and resistance
Taper - 6-10º
Length of walls
Path of insertion
Grooves and slots
Structural durability
Can withstand forces of occlusion
Achieved through:
- occlusal reduction
- functional cusp bevel
- axial reduction
Marginal integrity
Through finish ling configurations
Knife edge
Bevel
Chamfer
Shoulder
Bevelled shoulder
Preservation of periodontium
Margins of restoration should be:
- smooth and fully exposed to cleansing action
- placed where dentist can finish them and patient can clean them
- super-gingivally or at gingival margin whenever possible
What is the biological width?
Connective tissue above alveolar bone to and the junctional epithelium
Metal crown prep
Axial - 0.5mm
Occlusal:
- functional cusp - 1.5mm
- non-functional cusps - 0.5mm
Finish - chamfer
Porcelain crown prep
Axial - 1mm
Occlusal:
- functional cusp - 1.5mm
- non-functional cusp - 1mm
Finish - shoulder
MCC crown prep
Axial - 1.3mm
Occlusal reduction:
- functional cusp - 1.8mm
- non-functional cusp - 1.3mm
Finish:
- chamfer - 0.5mm where only metal required
- shoulder - 1.3mm, 0.4mm for metal, 0.9mm for porcelain
All ceramic crown prep
Axial - 1.5mm
Occlusal:
- functional cusp - 2mm
- non-functional cusps - 1.5mm
Finish - chamfer
