What is the best way to resecure a temporary crown that has fallen out, drugstore temporary cement is practically useless?

Yes, it's useless: Unfortunately, drugstore cement isn't helpful. You're cementing a tooth that hasn't been cleaned and is wet, so you won't get much retention. Additionally, when you place the cement, it extrudes to areas under your gum line, and if this is not cleaned appropriately, you can develop a severe irritation. It's just not a good idea; drop by your dentist and they can cement it back.

Denture Adhesive: In somes cases, a denture adhesive may be useful. However, if the missing temporary crown does not cause pain, and there is no cosmetic problem, it is better to leave the temporary crown out and and call your dentist immediately.

Dentist visit: If temporary cement is useless you have no choice but to return to your dentist.

Try denture adhesive: If you have already tried drugstore temp cement you will need to clean it out of the temporary crown before trying the denture adhesive. See your dentist as soon as possible since this is only a temporary solution.

No easy way: Just go back to your dentist have him used stronger material otc do not work as well.

Dentist: Best way is to return to your Dentist to have temporary crown cleaned an recemented. Really isn't a DIY project.