Hi OP, can you specify a time(ish) and place? At present, the scope is every culture that exited prior to "modern medicine", which falls afoul of our "example-seeking" rule. Do you mean, for example, in Western Europe in, say 19th c? Thanks!

I have not come across any treatment for this disease. I mostly see doctors discussing bruxism as a symptom of something greater in the 19th century (like gout, the flu, migraines, etc.). An article from the BMJ describes that:

In a large proportion of the cases, the teeth were found flattened on their edges, as the result of "tooth-grinding"; the teeth mostly ground were the incisors and canines, but the special teeth flattened depended upon their arrangement in the jaws.

Source: Letters, Notes, And Answers To Correspondents, The British Medical Journal, Vol. 1, No. 1788 (Apr. 6, 1895), pp. 795-796

Additionally there is a description of 8 children, two parents and two grandparents living in a house that: grind their teeth almost incessantly at nights, and have done so all their lives. I am told by the mother that the conjoint noise made by several sleeping in one room is painfully audible outside the door.

Source: Horatio Donkin, The British Medical Journal, Vol. 1, No. 999 (Feb. 21, 1880), p. 279

So without speculating too much, I'd say that not much was done about tooth grinding at all. This answer may vary based on class and I'd be incredibly interested to hear what someone else might say about this.