Why the edge of a crown can look grey

The grey line you're noticing around the edge of an older dental crown is likely due to the metal base of a porcelain-fused-to-metal (PFM) crown becoming exposed. PFM crowns consist of a metal substructure covered by a layer of porcelain. The grey line typically becomes visible over time for a few reasons:

1. Gum Recession:

- As you age, your gums may naturally recede, exposing more of the tooth and the crown. When gums recede around a PFM crown, the metal base that was initially hidden under the gumline may become visible, appearing as a grey line, especially if the tooth is root treated.

2. Wear and Tear:

- The porcelain layer of the crown may wear down or chip at the margins over time, especially if it's in an area of heavy biting pressure. This wear can reveal the underlying metal.

3. Crown Fabrication:

- Sometimes, the grey line can be due to the way the crown was originally made. If the porcelain does not fully cover the metal base at the crown's edges, or if the metal is too close to the surface, a grey line can be visible from the start.

4. Porcelain Thickness:

- The thickness of the porcelain can also play a role. In some cases, the porcelain may be thin around the edges of the crown, allowing the darker shade of the metal to show through.

This grey line is more of a cosmetic issue and typically does not indicate a problem with the function or fit of the crown. However, if the grey line is accompanied by symptoms like pain, swelling, or a bad taste, it could suggest other issues, such as crown loosening, decay under the crown, or gum disease, and you should consult a dentist.

For aesthetic reasons, some people opt to replace older PFM crowns with all-ceramic or all-porcelain crowns, which don't have a metal base and therefore don't show a grey line. However, this decision should be made in consultation with a dental professional, considering the health and function of the crown, as well as aesthetic preferences.