teeth-grinding.

There’s no hypen in TEETH GRINDING unless it’s used as an adjective.

Igor, “TOOTH grinding” would apply more to a dentist grinding down one tooth. However, to grind your teeth at night, you need at least two TEETH)))

GNASHING OF TEETH is a strictly biblical term, literally used to describe the torments of hell.

Yet, GNASHING OF TEETH is used sometimes humorously.

Uly, I have investigated the case of tooth-grinding and found several dictionaries to be blamed of. They are:
* Dictionary.com Unabridged, 2015: Red-Eye abruptly ceased his breast-beating and tooth-grinding, and ran across the timber-jam to the shore. (Jack London, Before Adam)
* Vocabulary.com: Acid erosion, brushing too hard, dry mouth and tooth grinding can all wear away at the enamel of your teeth and cause pain. (Washington Post, 2011)
+
Like tension headaches or nocturnal tooth grinding, the pain appears to be a response to stress. (New York Times, 2013)
* Oxford English Dictionary 2: thegosis - Tooth-grinding in animals as a means of sharpening the teeth.
* Everest Medical: Treatment depends on the cause and severity of the problem, and can range from a mouth guard or medication to prevent nighttime tooth-grinding, to surgery.

* Wikipedia: While it had larger front teeth compared to the back, the emphasis was on back tooth grinding. (Australopithecus africanus)
+
Four popular E-R dics use only "tooth-grinding" for "скрежетание зубами".

Why "teeth-gnashing" (CALD), but "teeth grinding" (w/o a hyphen)? That's not politically correct! ))

There’s no hypen in... (Uly)

A lot of hype (хайп) may happen if you write "hypen"! )))

So, Uly... Will you allow us to write "tooth-grinding"? Ple-e-ase...

Igor, you may write whatever you like))) I only give my insights as a professional editor and leave you to your own devices. In proper modern English, nouns are no longer hyphenated (with rare exceptions), only adjectives. English has changed considerably since Jack London. When there’s a discrepancy, many editors and translators turn to Wikipedia for the going term - in this case they concur with TEETH GRINDING: https://en.wikipedia.org/wiki/Bruxism

Igor, you may write whatever you like)))

So do I! I usually write according to "my own devices" (in order to give you a job and some work to do).)))

I only give my insights as a professional editor ...

So, in addition to all that, you work as a professional editor. Wow!

and leave you to your own devices.

It's not fair to leave me alone as a babe in the woods with my devices that often go down.

In proper modern English, nouns are no longer hyphenated (with rare exceptions), only adjectives. English has changed considerably since Jack London.

In Russia, it will be great if you write like Alex Pushkin!

When there’s a discrepancy, many editors and translators turn to Wikipedia ...

In Russia, we'd better not mention (Russian) Wikipedia in our (various) disputes.