Quick: What’s the most common infectious disease in children? Hint: it’s entirely preventable, yet about 20% of children have potentially disfiguring complications from this that are going untreated.For the first time in 40 years, dental caries, or “cavities”, are on the rise again. Once thought to be an inevitable part of childhood in the developed world, cavities became relatively scarce with the advent of routine dental care, improved nutrition, and the widespread use of fluoride in toothpaste and water. But we may have let our guard down—our modern lifestyle might be handing the fight right back to the cavities again.Cavities and other forms of tooth decay are caused by bacteria, including Streptococcus mutans, that live in the mouth. Under certain conditions these bacteria make excessive acid that contributes to the loss of the hard mineral coat that covers the tooth. In time, the decay leads to a hole into the living material inside of the tooth, causing pain and sometimes the spread of infection and more tissue destruction.The keys to preventing cavities are to suppress the bacteria and their acid and to encourage a healthy tooth environment where the mineral coating can remain strong.Start a brushing habit early, by the time your child is one year old. Use a tiny dab of fluoride-containing toothpaste—not enough to swallow. Help your child brush, but always keep in mind that brushing should be a pleasant experience. You want to create a lifetime habit. If brushing is traumatic, painful, or a big fight, you know your child is unlikely to keep brushing well. A good tooth-brushing takes 2 minutes. Use a timer! We’re not sure if electric toothbrushes really do a better job than manual, so use whichever kind you and your children prefer.Sugary, sticky foods encourage bacterial growth and acid. Don’t allow your child to walk around sipping juice or milk—those contain plenty of sugar, just like soft drinks and soda. If your child wants sips between meals, water is the best choice.Fluoride suppresses bacterial growth and stabilizes the minerals that keep teeth strong. The addition of fluoride to water and toothpaste, in addition to fluoride treatments at dentists’ offices, has contributed to a huge drop in dental decay and cavities. However, there can be too much of a good thing—in some communities with water that was already high in fluoride, the addition of extra fluoride has led to too much mineralization of teeth. Though in almost all cases this causes unnoticeable or barely noticeable changes in the teeth themselves, in rare extreme cases it can cause noticeable pitting and weakening of the teeth. The US government adjusted fluoride guidelines for tap water in 2010 to address the potential for too much fluoride in municipal water supplies. Though there are some groups who feel fluoridation is bad, there’s overwhelming evidence for the safety and effectiveness of routine fluoridation of water.Cavities do seem to be becoming more common again—but there are simple things parents can do to help protect their children’s teeth. Good dental care and food and drink choices can go a long way towards keeping those smiles bright!