Fundamentals for Digital Preparation

by Stephen T. True D.D.S.

Design and engineering win out over chemistry. A well-designed preparation will outlast a poorly designed one that depends on adhesion from cement.

1

Start with a well-designed preparation
- Parallel walls
  - The goal is to have nearly parallel walls; be careful of undercuts!
  - Taper the walls between 4° and 8°.
- Additional retention when needed
  - Well-placed grooves and box forms increase retention, especially on short preps.
- Round edges
  - Round edges are necessary. Sharp edges on the preparation create design challenges and compromise material strength.
- Reduction
  - Taper the occlusal surface - a flat surface requires a thin restoration in the primary grooves. Proper reduction helps maintain adequate thickness, which strengthens the integrity of the restoration.
2

Prepare for scanning
- Make sure the prep is CDC:
            Clean (no debris)
            Dry, dry, dry!
            Clean (margins)
- Remember that tissue and tooth structure look the same to a scanner.
- Double pack the cord and remove the top one before taking the scan.
- Clean the margins with a micro brush.
- Beware of double margins! Double-check before scanning.
3

Evaluate the scan for margin clarity