 From VOA Learning English, this is the Health Report. Nearly four billion people around the world have serious, untreated problems with their teeth. That is what a recent report from the World Health Organization says. Both officials say failure to repair cavities can even lead to social and emotional problems. Wagner Marcenes is with the Institute of Dentistry at Queen Mary University of London. He led a team of researchers as part of the Global Burden of Disease 2010 study. They used the information to estimate rates of infection. The report says untreated tooth decay is the most common of all 291 major diseases and injuries. Professor Marcenes says increases in tooth decay are affecting sub-Saharan Africa and probably other areas on the continent. He says this increase in tooth decay could be a result of changes in diet as developing countries adopt Western-style diets. Many Western diets are rich in sugar, a leading cause of health problems in the mouth. But in Western countries, water supplies are often treated with the chemical fluoride. Adding fluoride to the water makes teeth resistant to the bacteria that can cause tooth decay. Wagner Marcenes says oral health problems can have a major effect on a person's quality of life. Cavities make eating difficult. As a result, people may eat softer foods that are easier to chew. However, softer foods are often higher in fat. Professor Marcenes is calling for an urgent, organized social response to oral health problems. He believes in fighting tooth decay through a healthier diet. He is also calling for the development of new and less costly dental materials and treatments. For VOA Learning English, I'm Mario Ritter.