Breaking the milk-to-sleep association is the most effective long-term solution. Try to finish the final milk feed 30 minutes before bedtime so you can complete your routine, including brushing, while the baby is awake. If they are already exhausted, you can use a damp muslin cloth wrapped around your finger to gently wipe their gums and teeth; this is often less disruptive than a toothbrush and can be done quickly and quietly.