I have yellowish teeth due to 8 years of smoking and not taking care of my teeth. I no longer smoke and wanted to whiten my teeth at home and tried brushing with baking soda. I brushed for about one minute, adding more baking soda about half way through. I only brushed the teeth you see when I smile. I do not see any real difference in the shade of my teeth. Do I need to brush daily with baking soda (once a day) or is that too much? Will it damage my enamel?