There is no harm in using the siwāk or a toothbrush during the day in Ramadan, as the Prophet ﷺ used to use the siwāk while fasting without distinguishing between morning and afternoon. However, care must be taken with toothpaste because of its strong flavour, which may reach the throat unintentionally. The safer practice is to brush the teeth before fajr or after iftar, and if one needs to clean during the day, to use a siwāk or a toothbrush without paste. If toothpaste is used and a small amount is accidentally swallowed despite reasonable care, the fast remains valid.