Dental decay, also known as dental caries, begins first inside the tooth. A white spot appears on the enamel where the tooth has started to weaken inside. At this stage, the tooth can repair the weakened area with the help of fluoride and minerals in saliva.
Beijing, also Peking, is the capital of the People's Republic of China and one of the most populous cities in the world. Its population in 2013 was 21,150,000. The city proper is the 3rd largest in the world.
The Evolving Urban Form: Beijing. China's capital, Beijing, has long been one of the world's largest urban areas. Some reports placed its population at over 1 million in 1800, which would have made Beijing the largest urban area in the world at that time.