tooth decay is usually down to acids produced by bacteria in the mouth. As bicarbonate neutralizes acids, it would seem a good thing, though thorough brushing would be better.
Bicarb should make your teeth bright and shiny but brushing too harshly & often with it could wear the enamel away as it is rather abrasive.
Is it the same bicarb crystals which is used in stain removal from clothes? The instructions on the container also said that it could be used as a moss killer in the patio/pathway so i sprinkled it on the patio.
NO! Don't go brushing your teeth with Soda Crystals. Baking soda is sodium bicarbonate (as used in cooking and toothpaste,) Soda Crystals are sodium carbonate decahydrate for clothes and cleaning.