There are artifacts, named items, "books" and copies of "books".
- Artifacts are almost indestructible and what's created by moods and world gen events.
- Named items are regular items that's been used by militia members enough to get them to grow attached to them (they are not better stat wise). As far as I think I've seen, that's only happened to hand held items, i.e. weapons and shields, not clothing/armor. I can not say for certain, but I suspect they accumulate wear. At the very least they can have wear, although it might have been accumulated before they were named. Also note that militia gear belongs to the squad, not the members, and I don't know if named items get removed from squad ownership when named. Also, I don't know if there's any adventurer mode mechanism corresponding to fortress item naming, although I believe killing named creatures with items may result in the items acquiring a name (if so, probably in both modes).
- "Book", i.e. the various forms of written works, are artifacts when they are originals, i.e. near indestructible (can be doused after being on fire for extended lengths of time with no damage, etc).
- Copies of "books" aren't real artifacts, but I haven't seen whether they are consumed by fire and similar abuse or not.
It's possible to turn off wear of clothing, although I'm unsure whether it's a DF or DFHack thing (I've never done it).
The best way to ensure someone will continue to wear something is probably to ensure they won't find something better. Given that companies may provide gear to their members (in the next release), someone who joins them may well upgrade. Villains and other artifact seekers may well rob/kill for artifacts as well.
Strange moods are exclusive to dwarves and can happen only once in a dwarf's lifetime. I haven't checked if the data structures would allow for multiple moods (the field(s) involved in the mood would have to be vectors rather than single entries).