What are the principles of tooth preparation?
- Preserve tooth structure
- Retention and resistance
- Structural durability
- Marginal integrity
- Preservation of periodontium
- Aesthetics considerations
What will under preparation result in?
- Over built crown with periodontal and occlusal consequences
- Poor aesthetics
What will over preparation result in?
Pulp and tooth strength compromised
Define retention
Prevention of removal of rest along path of insertion or long axis of tooth prep
Define resistance
- Prevention of dislodging of rest in apical/ oblique direction
- Prevention of any movement under occlusal forces
How is retention and resistance increased?
- Taper of opposing walls (ideally 6 deg)
- Length of walls (longer = more resistance)
- Extra means of retention (slots, grooves)
- Path of insertion (limit)
How is structural durability of the restoration achieved?
Adequate preparation of
- Occlusal reduction
- Fuctional cusp bevel
- Axial reduction
What are the type of finish line configurations?
- Knife edge
- Bevel
- Champfer
- Shoulder
- Bevel shoulder
How is the periodontium persevered?
- Preparations of margins;
- -> smooth
- -> placed where pt can readily clean
- -> at gingival margin whenever possible
What are the preparation dimensions for a metal crown (incl gold)?
Axial reduction = 0.5mm
Occlusal reduction
- Functional cusp = 1.5mm
- Non-functional cusp = 0.5mm
Finish line = Chamfer (0.5mm)
What are the preparation dimensions for a traditional ceramic crown?
Axial reduction = 1mm
Occlusal reduction
- Functional cusp = 1.5mm
- Non-functional cusp = 1mm
Finish line = Shoulder (1mm)
What are the preparation dimensions for a MCC (metal ceramic crown)?
Axial reduction = 1.3mm
Occlusal reduction
- Functional cusp = 1.8mm
- Non-functional cusp = 1.3mm
Finish line
a. Chamfer (0.5mm); where metal required
b. Shoulder (1.3mm); 0.4mm for metal and 0.9mm for porcelain
What are the preparation dimensions for a all ceramic crown (alumina/ zirconia reinforced framework)?
Axial reduction = 1.5mm
Occlusal reduction
- Functional cusp = 2mm
- Non-functional cusp = 1.5mm
Finish line = Chamfer (1-1.5mm)
What are the stages of preparation?
- Occlusal reduction
- Separation (axial reduction)
- Buccal reduction
- Palatal/lingual reduciton
- Finish line
- Check occlusal surface and clearance
