Toothpaste makers are pitching enamel-strengthening toothpastes that they say harden the tooth's protective layer, making it more resistant to attacks from acids found in food and beverages such as soda, orange juice and even pickles. Scientists say the toothpastes do make enamel more acid-resistant—but not enough to protect you if you guzzle soda all day.

Enamel is a thin covering over teeth made from an organic matrix and minerals, largely crystals of calcium phosphate, says scientist George Stookey, chief executive of Therametric...