Can you use cornstarch to whiten teeth instead of baking soda?

Won't work. It's proper brushing and flossing, not necessarily the toothpaste, that is the most important.
You can use. cornstarch or over the counter tooth paste or crest 3D whitening strips or pens. However, they are not so effective and/or stable. OTC bleach and whitening tooth paste could be used as a supplement only. A professional teeth whitening without laser, followed by home whitening system with custom trays for the long term effect. You will be very happy with the results.
Tooth whitening. Tooth whitening with abrasives, including whitening toothpaste, will gradually do damage to tooth enamel. Start with professional cleaning, then follow Dentist's/Hygienist's advice for a whitening program. Save cornstarch and baking soda for the kitchen... to particularly effective in the bathroom.
No. And baking soda really doesn't whiten your teeth, it just removes surface stains. Overuse of the abrasive baking soda will wear away your enamel, making your teeth look more yellow.
No. No. Cornstarch and baking soda do not whiten teeth. Baking soda can be used to clean your teeth. If you want whiter teeth, see your dentist to have them professionally whitened.
Sort of. To clarify, 'whitening' is not the same as 'bleaching'. Toothpaste, cornstarch, baking powder will scrub superficial stains off your teeth->whitening. Only chemicals like 'carbamide peroxide' or 'hydrogen peroxide' will penetrate discolored teeth to lighten them->bleaching.