I no longer drink real cola or other soft drinks because of the calories, but I have been told that diet versions of carbonated beverages can nevertheless be harmful to the tooth enamel because they are very acidic. When and how often can one drink acidic beverages to protect one's teeth? And what about acidic solid foods? - B.K., Nahariya Judy Siegel-Itzkovich replies: The February issue of the Mayo Clinic Health Letter discusses this topic. It notes that sugar isn't the only enemy of teeth. Acids found in diet and regular soft drinks, energy drinks, juice and wine can erode the surface of the teeth, leading to decay. It recommends limiting consumption of all of these, along with tart candies, citrus fruits and foods containing vinegar. Eating acidic foods as part of a meal helps neutralize and eliminate acids. Before bedtime is the worst time to consume acidic foods, because the production of saliva - which helps neutralize and dilute acids - decreases during sleep. Using a straw for consuming acidic beverages helps minimize contact with the teeth. Drinking quickly - not sipping over long periods - also helps. After consuming acidic food or drink, eating cheese or swishing with water or a fluoride rinse helps neutralize the acid. Brushing teeth with fluoride toothpaste 30 minutes before consuming acidic foods or drink is beneficial, but brushing immediately afterward should be avoided. However, chewing sugar-free gum can help stimulate saliva flow, which neutralizes and dilutes acid. Do decaffeinated green, black and white teas have the same antioxidant effect as regular caffeinated green, black and white teas? Does red wine from which the alcohol has been boiled away (for someone who is not allowed alcohol for health reasons) have the same health benefits as drinking a glass of red wine? - S.W., Elazar Dr. Shela Gorinstein of the Hebrew University's School of Pharmacy, who has for decades conducted research on the health benefits of various beverages and fruits, replies to both queries: As to your first question, the answer is no. Regular caffeinated green, black and white teas will have a stronger antioxidant effect than the decaffeinated ones. As for your second question, red wine without alcohol has fewer health benefits but there is not a great difference, because the antioxidant activity of red wine depends mostly on the polyphenols, not on alcohol. The alcohol has just a minor influence. I'm a healthy 32-year-old woman who is in the process of trying to conceive. Is it okay for me to visit the dentist and have x-rays done, even though I don't know yet if I'm pregnant? - T.N., Chicago Dr. Steve Sattler, a veteran Jerusalem dentist, comments: I recommend that you avoid x-rays for the first three months of any pregnancy, especially because you are over the age of 30, and even when you are not yet pregnant. In any such situation, it is best to do just a simple examination, a filling if indicated and simple cleaning, and avoid any larger treatments. In my estimation, lead aprons placed over the chest and abdomen of patients before x-rays offer only partial protection (about 90 percent) against the rays, even though the companies that make them claim they offer 100% protection. It is hard to know how much radiation will "sneak down" the neck past the top of the lead apron into the body of the patient. So it is best to postpone x-rays in pregnant women unless there is no choice. Rx for Readers welcomes queries from readers about medical problems. Experts will answer those we find most interesting. Write Rx for Readers, The Jerusalem Post, POB 81, Jerusalem 91000, fax your question to Judy Siegel-Itzkovich at (02) 538-9527, or e-mail it to email@example.com, giving your initials, age and residence.