# Teeth are not Treatment Areas

A Treatment Area is a `CatalogCategory` snapshotted onto a case, which made "one category per tooth"
look like a free way to get dental charting. It was rejected: FDI tooth numbering is a universal fact,
not a per-clinic taxonomy, so it would duplicate 32 to 52 identical rows into every clinic's service
tree, surfaces would need a further level below that, and the persistent condition of a tooth — missing,
crowned, implanted years before the patient ever arrived — has nowhere to live on a settings row.
A tooth is instead an FDI `smallint` on the record that targets it, and tooth condition is its own
snapshot table in the Dental context.

## Consequences

Tooth condition must be updated after each visit, and that projection lives in exactly one class rather
than being spread across controllers. In exchange, rendering a chart is one query and never a replay of
history.