OCHWA Crown Reduction Guidelines
Quick-reference tooth-reduction depths for full-coverage crowns at the UWA Oral Health Centre, by material, arch and surface. Transcribed from the OCHWA reduction table taught in DENT4216 (Source: Operative Crown Tips And Reduction Guidelines — “OCHWA Reduction Guidelines”). For the full appointment-by-appointment workflow these figures sit inside, see Clinical Sequence for Crowns.
How to read these
All figures are millimetres of tooth reduction. Prepare to the depth for the crown material you have chosen. 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
Which cusp takes the deeper reduction
- Functional (supporting) cusps — maxillary lingual, mandibular buccal. They maintain vertical dimension and contact opposing fossae/marginal ridges in centric occlusion, so they bear the most occlusal force and take the deeper reduction.
- Non-functional (guiding) cusps — maxillary buccal, mandibular lingual. They guide mandibular movement and protect soft tissues but do not bear heavy occlusal load.
Notes and caveats
- All-ceramic is a single category here. The table groups lithium disilicate and zirconia together, and no DENT4216 lecture gives a zirconia-specific figure. Monolithic zirconia tolerates thinner sections than layered ceramic in manufacturers’ own guidance — confirm with the lab before reducing a zirconia case to these layered-ceramic figures.
- Margin design follows the material. The all-ceramic 1 mm margin is prepared as a shoulder / modified shoulder; a ceramic shoulder needs at least 1.5 mm of reduction where porcelain bulk is required and cannot be cut as a chamfer or feather edge (Source: M2 PFM Prep — “Margin design”). The metal-crown 0.5–1 mm margin is a chamfer.
- Partial-coverage PFM is not in this table. For a PFM with partial ceramic coverage the figures differ (functional 1.5–2.0 mm, non-functional 1.0 mm, axial 1.0 mm metal / 1.5 mm metal-ceramic) (Source: M2 PFM Prep — “PFM: Partial coverage with ceramic”).
- Gold conserves wall height. Gold needs only 1.0–1.5 mm occlusal vs ~2.0 mm for ceramics, “crucial for achieving adequate retention and resistance form on teeth that are already clinically short” (Source: F1 FullMetalCrowns — “Advantages”).
- Keep occlusal contacts at least 1.5 mm away from the metal-ceramic junction on a PFM (Source: M2 PFM Prep — “Fabrication principles”).