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.
According to our just released Demographia World Urban Areas, Tokyo-Yokohama, the worldâs largest city, has 30 times the population of Beijing in 1800. And, Beijing itself has reached 21 million. Beijing remains one of the ten largest cities, but London with a population of 10 million ranks 32nd.