After a root canal, how do you decide between a filling, onlay, and crown?

I’m trying to understand what determines the final restoration after a root canal. It seems like the safest choice may depend less on the root canal itself and more on how much tooth remains.

For example, would the decision usually change based on whether it’s a molar, premolar, or front tooth, and whether one or more cusps are missing or unsupported? I’m also unclear when a bonded filling or onlay is reasonable instead of covering the whole tooth with a crown.

How long is it generally safe to leave a temporary filling in place, especially if the final restoration has to wait? I’d want to know whether the tooth is protected adequately during that period and whether chewing on that side should be limited.

For anyone who was offered more than one option, what did your dentist say about:

- the amount of remaining tooth structure and cusp support
- biting or grinding forces
- the proposed temporary filling, bonded filling, onlay, or crown
- how long the interim restoration would remain
- what signs would mean it needed attention sooner

I’m mainly trying to work out what questions to ask before accepting an immediate crown, without assuming that every root-treated tooth needs the same treatment.