The Taʼamei HaMinhagim (pg. 203, He'aros) brings a segulah from the Radziner Rebbe: If one wishes to be protected from toothache, then during Kiddush Levanah, after reciting כך לא יוכלו כל אויבי לנגוע בי לרעה three times, he should add each time the words:ולא יהיה לי באב שיניים “I should not have a toothache.”
The Sefer Otzar Pelois HaTorah (Bo, pg. 253) brings that R' Chaim Kanievsky zt”l told him that he heard such a segulah from the Ya'ares Devash.
R' Chaim further related, that his mother once told him that once she had a toothache, and she told her husband the Steipler, and reminded him to daven for her teeth during Kiddush Levanah. Immediately after Kiddush Levanah, the pain left.