Another thing you could try is magnesium oil. Many have used it orally for rinsing/brushing and even as an OP agent, and have reported great results. I'm using it myself and feel it's helping. I dilute it 50/50 with water. My mouth sure feels good and tingly from it, teeth feel stronger and are whiter. I also use Coral White toothpaste for more whitening power, it's great!