Is it required to have dental insurance in order to work in Switzerland? Or is that included in Swiss health insurance? If I am opting out of Swiss insurance (which is possible because of the temporary nature of my stay and because it is for training purposes) do I have to get some kind of dental insurance which will be valid internationally?

In a word ...no. It's just an additional option.

You will also be subject to an exam before being accepted for insurance and I believe that the insurance will not pay for work on any teeth that have already been worked on. It's worth looking into what exactly is covered before opting for it.

Oh yes, they do pay for work on teeth previously worked on. Why not? But they do not pay for work that is deemed necessary according to the result of that initial assessment, which, of course, makes sense. That's what's called a preexisting condition. Otherwise everybody could totally neglect their teeth and then have them fixed by signing an insurance contract.

Anyway, good nutrition plus decent oral hygiene are much cheaper and way more efficient than any insurance. By the way, dental / oral accidents are insured by your accident insurance.

What about wisdom teeth? Is that a dental accident? Wishful thinking, perhaps.

I am afraid not... wisdom teeth are usually not covered by basic health or accident insurance.