拔牙 is a separable verb (离合词) meaning 'to pull out a tooth' or 'to have a tooth extracted.' The two characters split when you add a measure word (颗), a duration, or a complement between them — for example, 拔了一颗牙 ('pulled out one tooth') or 拔过牙 ('have had teeth extracted'). You cannot put an object after 拔牙; instead, say 去拔牙 or 医生给我拔牙.