Can Siri log tooth brushing?

Yes, through Apple's Shortcuts app. There is no Siri sentence for it: iOS lets an app have 10, and Veilleuse uses all 10.

1. Open the Shortcuts app and tap the Add button.
2. Tap New Shortcut, tap Rename, and type a name such as "Teeth brushed".
3. Tap Add Action, search for Veilleuse, then tap "Log tooth brushing". Tap Done.

Then say "Hey Siri, teeth brushed". Siri answers Tooth brushing logged.