Brushing Your Teeth On Shabbos

Rabbi Gil Student writes: "This past Shabbos my eight-year-old son had a friend sleeping over. At night, I told my son to go brush his teeth with toothpaste and I told his friend not to brush his teeth. My son quickly went for the issue dearest to his heart, "That’s not fair." Then he went for the piety argument, "It’s assur." I quickly explained to him that we follow Rav Soloveitchik (and Rav Ovadiah Yosef and Rav Chaim Regensburg) who allowed it while his friend probably follows Rav Moshe Feinstein who did not allow it."