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.
Aside from Tianjin, Beijing is bordered on all other sides by Hebei Province, including a piece wedged between Beijing and Tianjin. Due it its strategic location, Beijing is an important international trading center. Beijing city covers a total area of 16,807.8 sq. km.