Your child by now is already accustomed to teeth falling and new teeth emerging. At this age the lower 4 incisors would be emerging.
What you need to know
In some children there might be 2 lines of teeth; this could happen because the baby teeth have not yet fallen but the permanent teeth have erupted, usually along the inside layer of the gums. It is better to visit a dentist and get his opinion.
If the baby teeth have strong roots and do not seem to fall on their own within a week or two after the new teeth have erupted, the dentist may suggest removing the baby teeth. This is done in order to make room for the permanent teeth so that the teeth line does not get crooked.
What you need to do
Allow the loosened tooth to fall out by itself rather than pulling it out manually. By this age, your child would have mastered brushing teeth on their own, but you should still monitor how they brush once in a while and look for cavities, which should be treated immediately. Teeth grinding (Bruxism) can be observed at this age also, as new teeth are growing.
Relieve your child of any anxieties, stress and worms in stomach as these might be one of the reasons for the grinding. Also visit the dentist to check if there is any wear or tear of the enamel.