Divya dant munjun, Ayurvedic powder is excellent. There are some Indian stores that may carry this. Also found this website that carries it.......http://www.swamibabaramdevmedicines.com/divya-dant-manjan/
You can small amount in your left Palm, wet your brush, dab it the powder and brush as you would with tooth paste. I wen you it is a bit spicy, but very effective and no chemicals.
You can use it with Mercury filings, but I would plan on removing those as soon as possible. Ask your dentist to use white filling.