A'uudhu Billaahi minash-shaytaanir Rajeem
Bismillaahir Rahmaanir Raheem
As salaamu'alaikum waRahmatullah waBarakaatuhu!!
"Allah's Messenger (sal Allahu alaihi wa sallam) drank milk and then rinsed his mouth and said, 'It contains fat.'" [Sahih Bukhari]
This hadith informs us that it is a Sunnah to rinse our mouths after drinking milk. In fact, we should rinse our mouths after consuming any drink that has a fat content. Following the Sunnah of His beloved Prophet (Sal Lallaahu 'Alaihi wa sallam) will bring us Allah's Pleasure and will also result in better oral hygiene for us.
As salaamu'alaikum waRahmatullah waBarakaatuhu:-)