Operative Crown Tips and Reduction Guidelines
Class tips and the OCHWA tooth-reduction table for full-coverage crowns. The reduction table is also kept as a standalone clinic protocol at OCHWA Crown Reduction Guidelines; the appointment-by-appointment workflow it belongs to is in Clinical Sequence for Crowns.
Tips
- The crown is prepared in relation to the long axis of the occlusal surface — confusing, because it usually looks as if it should be relative to the long axis of the tooth.
- It’s okay to have an undercut at first — preparation is about fixing things as you go.
- For the occlusal reduction, reduce through the peak height at the cusps; don’t worry about the grooves too much.
OCHWA Reduction Guidelines
How to read these
All figures are millimetres of tooth reduction, by material, arch and surface. Where a functional/non-functional split is given, the functional (supporting) cusp takes the deeper figure.
Metal-ceramic / PFM
| Reduction (mm) | Anterior | Posterior |
|---|---|---|
| Incisal / occlusal | 2 | 2 functional cusp · 1.5 non-functional cusp |
| Axial | 1.5 | 1.5 |
| Margin | 1.5 | 1.5 |
All-ceramic / full-ceramic
| Reduction (mm) | Anterior | Posterior |
|---|---|---|
| Incisal / occlusal | 1.5 | 2 functional cusp · 1.5 non-functional cusp |
| Axial | 1 | 1 |
| Margin | 1 | 1 |
Metal crown (posterior)
| Reduction (mm) | Posterior |
|---|---|
| Occlusal | 1.5 functional cusp · 1 non-functional cusp |
| Axial | 1 |
| Margin | 0.5–1 |
Functional vs non-functional cusps
- Functional cusps (supporting cusps): maxillary lingual, mandibular buccal. They maintain vertical dimension and contact opposing fossae/marginal ridges in centric occlusion.
- Non-functional cusps (guiding cusps): maxillary buccal, mandibular lingual. They guide mandibular movement and protect soft tissues but do not bear heavy occlusal load.